Structure of the PTEN-like region of auxilin, a detector of clathrin-coated vesicle budding

PubMed Central

Guan, Rong; Han, Dai; Harrison, Stephen C.; Kirchhausen, Tomas

2010-01-01

Auxilin, a J-domain containing protein, recruits the Hsc70 uncoating ATPase to newly budded clathrin-coated vesicles. The timing of auxilin arrival determines that uncoating will commence only after the clathrin lattice has fully assembled and after membrane fission is complete. Auxilin has a region resembling PTEN, a PI3P phosphatase. We have determined the crystal structure of this region of bovine auxilin 1; it indeed resembles PTEN closely. A change in the structure of the P-loop accounts for the lack of phosphatase activity. Inclusion of phosphatidylinositol phosphates substantially enhances liposome binding by wild-type auxilin, but not by various mutants bearing changes in loops of the C2 domain. Nearly all these mutations also prevent recruitment of auxilin to newly budded coated vesicles. We propose a specific geometry for auxilin association with a membrane bilayer and discuss implications of this model for the mechanism by which auxilin detects separation of a vesicle from its parent membrane. PMID:20826345

[Modification of retinal photoreceptor membranes and Ca ion binding].

PubMed

Korchagin, V P; Berman, A L; Shukoliukov, S A; Rychkova, M P; Etingof, R N

1978-10-01

Calcium binding by modified photoreceptor membranes of cattle retina has been studied. Ca2+-binding the membranes significantly changes after C-phospholipase treatment, displaying the initial growth (less than 65% of lipid phosphorus removed) with subsequent decrease (more than 65% of phosphorus removed). Liposomes of the photoreceptor membranes lipids were found to bind more calcium than do the native photoreceptor membranes. Proteolytic enzymes (papaine, pronase) splitting some rhodopsin fragments do not affect the ability of the membrane to bind Ca2+. The increase of light-induced Ca-binding is observed only after the outer segments preincubation under conditions providing for rhodopsin phosphorylation. This effect was observed also after the splitting of the rhodopsin fragment by papaine. It is concluded that calcium binding in the photoreceptor membranes is mainly due to the phosphate groups of phospholipids.

Cholesterol is necessary both for the toxic effect of Abeta peptides on vascular smooth muscle cells and for Abeta binding to vascular smooth muscle cell membranes.

PubMed

Subasinghe, Supundi; Unabia, Sharon; Barrow, Colin J; Mok, Su San; Aguilar, Marie-Isabel; Small, David H

2003-02-01

Accumulation of beta amyloid (Abeta) in the brain is central to the pathogenesis of Alzheimer's disease. Abeta can bind to membrane lipids and this binding may have detrimental effects on cell function. In this study, surface plasmon resonance technology was used to study Abeta binding to membranes. Abeta peptides bound to synthetic lipid mixtures and to an intact plasma membrane preparation isolated from vascular smooth muscle cells. Abeta peptides were also toxic to vascular smooth muscle cells. There was a good correlation between the toxic effect of Abeta peptides and their membrane binding. 'Ageing' the Abeta peptides by incubation for 5 days increased the proportion of oligomeric species, and also increased toxicity and the amount of binding to lipids. The toxicities of various Abeta analogs correlated with their lipid binding. Significantly, binding was influenced by the concentration of cholesterol in the lipid mixture. Reduction of cholesterol in vascular smooth muscle cells not only reduced the binding of Abeta to purified plasma membrane preparations but also reduced Abeta toxicity. The results support the view that Abeta toxicity is a direct consequence of binding to lipids in the membrane. Reduction of membrane cholesterol using cholesterol-lowering drugs may be of therapeutic benefit because it reduces Abeta-membrane binding.

Occurrence and removal of microbial indicators from municipal wastewaters by nine different MBR systems.

PubMed

Hirani, Zakir M; Decarolis, James F; Lehman, Geno; Adham, Samer S; Jacangelo, Joseph G

2012-01-01

Nine different membrane bioreactor (MBR) systems with different process configurations (submerged and external), membrane geometries (hollow-fiber, flat-sheet, and tubular), membrane materials (polyethersulfone (PES), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE)) and membrane nominal pore sizes (0.03-0.2 μm) were evaluated to assess the impact of influent microbial concentration, membrane pore size and membrane material and geometries on removal of microbial indicators by MBR technology. The log removal values (LRVs) for microbial indicators increased as the influent concentrations increased. Among the wide range of MBR systems evaluated, the total and fecal coliform bacteria and indigenous MS-2 coliphage were detected in 32, 9 and 15% of the samples, respectively; the 50th percentile LRVs were measured at 6.6, 5.9 and 4.5 logs, respectively. The nominal pore sizes of the membranes, membrane materials and geometries did not show a strong correlation with the LRVs.

Tropomodulin1 is required for membrane skeleton organization and hexagonal geometry of fiber cells in the mouse lens

PubMed Central

Nowak, Roberta B.; Fischer, Robert S.; Zoltoski, Rebecca K.; Kuszak, Jerome R.

2009-01-01

Hexagonal packing geometry is a hallmark of close-packed epithelial cells in metazoans. Here, we used fiber cells of the vertebrate eye lens as a model system to determine how the membrane skeleton controls hexagonal packing of post-mitotic cells. The membrane skeleton consists of spectrin tetramers linked to actin filaments (F-actin), which are capped by tropomodulin1 (Tmod1) and stabilized by tropomyosin (TM). In mouse lenses lacking Tmod1, initial fiber cell morphogenesis is normal, but fiber cell hexagonal shapes and packing geometry are not maintained as fiber cells mature. Absence of Tmod1 leads to decreased γTM levels, loss of F-actin from membranes, and disrupted distribution of β2-spectrin along fiber cell membranes. Regular interlocking membrane protrusions on fiber cells are replaced by irregularly spaced and misshapen protrusions. We conclude that Tmod1 and γTM regulation of F-actin stability on fiber cell membranes is critical for the long-range connectivity of the spectrin–actin network, which functions to maintain regular fiber cell hexagonal morphology and packing geometry. PMID:19752024

Analysis of the diffusion of Ras2 in Saccharomyces cerevisiae using fluorescence recovery after photobleaching

NASA Astrophysics Data System (ADS)

Vinnakota, Kalyan C.; Mitchell, David A.; Deschenes, Robert J.; Wakatsuki, Tetsuro; Beard, Daniel A.

2010-06-01

Binding, lateral diffusion and exchange are fundamental dynamic processes involved in protein association with cellular membranes. In this study, we developed numerical simulations of lateral diffusion and exchange of fluorophores in membranes with arbitrary bleach geometry and exchange of the membrane-localized fluorophore with the cytosol during fluorescence recovery after photobleaching (FRAP) experiments. The model simulations were used to design FRAP experiments with varying bleach region sizes on plasma membrane-localized wild-type GFP-Ras2 with a dual lipid anchor and mutant GFP-Ras2C318S with a single lipid anchor in live yeast cells to investigate diffusional mobility and the presence of any exchange processes operating in the time scale of our experiments. Model parameters estimated using data from FRAP experiments with a 1 µm × 1 µm bleach region-of-interest (ROI) and a 0.5 µm × 0.5 µm bleach ROI showed that GFP-Ras2, single or dual lipid modified, diffuses as single species with no evidence of exchange with a cytoplasmic pool. This is the first report of Ras2 mobility in the yeast plasma membrane. The methods developed in this study are generally applicable for studying diffusion and exchange of membrane-associated fluorophores using FRAP on commercial confocal laser scanning microscopes.

Reconstitution of high affinity. cap alpha. /sub 2/ adrenergic agonist binding by fusion with a pertussis toxin substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, M.H.; Neubig, R.R.

1986-03-05

High affinity ..cap alpha../sub 2/ adrenergic agonist binding is thought to occur via a coupling of the ..cap alpha../sub 2/ receptor with N/sub i/, the inhibitory guanyl nucleotide binding protein. Human platelet membranes pretreated at pH 11.5 exhibit a selective inactivation of agonist binding and N/sub i/. To further study the mechanism of agonist binding, alkali treated membranes (ATM) were mixed with membranes pretreated with 10 ..mu..M phenoxybenzamine to block ..cap alpha../sub 2/ receptors (POB-M). The combined membrane pellet was incubated in 50% polyethylene glycol (PEG) to promote membrane-membrane fusion and assayed for binding to the ..cap alpha../sub 2/ agonistmore » (/sup 3/H)UK 14,304 (UK) and the antagonist (/sup 3/H) yohimbine. PEG treatment resulted in a 2-4 fold enhancement of UK binding whereas yohimbine binding was unchanged. No enhancement of UK binding was observed in the absence of PEG treatment. The reconstitution was dependent on the addition of POB-M. They found that a 1:1 ratio of POB-M:ATM was optimal. Reconstituted binding was inhibited by GppNHp. Fusion of rat C6 glioma cell membranes, which do not contain ..cap alpha../sub 2/ receptors, also enhanced agonist binding to ATM. Fusion of C6 membranes from cells treated with pertussis toxin did not enhance (/sup 3/H) UK binding. These data show that a pertussis toxin sensitive membrane component, possibly N/sub i/, can reconstitute high affinity ..cap alpha../sub 2/ agonist binding.« less

Sensing Membrane Stresses by Protein Insertions

PubMed Central

Campelo, Felix; Kozlov, Michael M.

2014-01-01

Protein domains shallowly inserting into the membrane matrix are ubiquitous in peripheral membrane proteins involved in various processes of intracellular membrane shaping and remodeling. It has been suggested that these domains sense membrane curvature through their preferable binding to strongly curved membranes, the binding mechanism being mediated by lipid packing defects. Here we make an alternative statement that shallow protein insertions are universal sensors of the intra-membrane stresses existing in the region of the insertion embedding rather than sensors of the curvature per se. We substantiate this proposal computationally by considering different independent ways of the membrane stress generation among which some include changes of the membrane curvature whereas others do not alter the membrane shape. Our computations show that the membrane-binding coefficient of shallow protein insertions is determined by the resultant stress independently of the way this stress has been produced. By contrast, consideration of the correlation between the insertion binding and the membrane curvature demonstrates that the binding coefficient either increases or decreases with curvature depending on the factors leading to the curvature generation. To validate our computational model, we treat quantitatively the experimental results on membrane binding by ALPS1 and ALPS2 motifs of ArfGAP1. PMID:24722359

Mutagenesis of the C2 domain of protein kinase C-alpha. Differential roles of Ca2+ ligands and membrane binding residues.

PubMed

Medkova, M; Cho, W

1998-07-10

The C2 domains of conventional protein kinase C (PKC) have been implicated in their Ca2+-dependent membrane binding. The C2 domain of PKC-alpha contains several Ca2+ ligands that bind multiple Ca2+ ions and other putative membrane binding residues. To understand the roles of individual Ca2+ ligands and protein-bound Ca2+ ions in the membrane binding and activation of PKC-alpha, we mutated five putative Ca2+ ligands (D187N, D193N, D246N, D248N, and D254N) and measured the effects of mutations on vesicle binding, enzyme activity, and monolayer penetration of PKC-alpha. Altered properties of these mutants indicate that individual Ca2+ ions and their ligands have different roles in the membrane binding and activation of PKC-alpha. The binding of Ca2+ to Asp187, Asp193, and Asp246 of PKC-alpha is important for the initial binding of protein to membrane surfaces. On the other hand, the binding of another Ca2+ to Asp187, Asp246, Asp248, and Asp254 induces the conformational change of PKC-alpha, which in turn triggers its membrane penetration and activation. Among these Ca2+ ligands, Asp246 was shown to be most essential for both membrane binding and activation of PKC-alpha, presumably due to its coordination to multiple Ca2+ ions. Furthermore, to identify the residues in the C2 domain that are involved in membrane binding of PKC-alpha, we mutated four putative membrane binding residues (Trp245, Trp247, Arg249, and Arg252). Membrane binding and enzymatic properties of two double-site mutants (W245A/W247A and R249A/R252A) indicate that Arg249 and Arg252 are involved in electrostatic interactions of PKC-alpha with anionic membranes, whereas Trp245 and Trp247 participate in its penetration into membranes and resulting hydrophobic interactions. Taken together, these studies provide the first experimental evidence for the role of C2 domain of conventional PKC as a membrane docking unit as well as a module that triggers conformational changes to activate the protein.

Characterization of Rose Bengal binding to sinusoidal and bile canalicular plasma membrane from rat liver.

PubMed

Yachi, K; Sugiyama, Y; Sawada, Y; Iga, T; Ikeda, Y; Toda, G; Hanano, M

1989-01-16

The binding of Rose bengal, a model organic anion, to sinusoidal and bile canalicular membrane fractions isolated from rat liver was compared. The fluorescence change of Rose bengal after being bound to liver plasma membranes was utilized for measuring the binding. The dissociation constants (Kd = 0.1-0.12 microM) and the binding capacities (n = 11-15 nmol/mg protein) for Rose bengal are comparable between the two membrane fractions, although the n value for sinusoidal membrane is somewhat larger than that for bile canalicular membrane. The Rose bengal binding to both membrane fractions was inhibited by various organic anions at relatively low concentrations, i.e., the half-inhibition concentrations (IC50) for Indocyanine green, sulfobromophthalein, Bromophenol blue and 1-anilino-8-naphthalene sulfonate were 0.1, 100, 1.5-2.5 and 100 microM, respectively, while taurocholate did not inhibit the Rose bengal binding to either membrane fraction at these low concentration ranges. The type of inhibition of sulfobromophthalein and Indocyanine green for Rose bengal binding is different between the two membrane domains. That is, in sinusoidal and bile canalicular membrane fractions, these organic anions exhibit mixed-type and competitive-type inhibition, respectively. It was suggested that the fluorescence method using Rose bengal may provide a simple method for detecting the specific organic anion binding protein(s) in the liver plasma membrane.

Hydrodynamic optimization of membrane bioreactor by horizontal geometry modification using computational fluid dynamics.

PubMed

Yan, Xiaoxu; Wu, Qing; Sun, Jianyu; Liang, Peng; Zhang, Xiaoyuan; Xiao, Kang; Huang, Xia

2016-01-01

Geometry property would affect the hydrodynamics of membrane bioreactor (MBR), which was directly related to membrane fouling rate. The simulation of a bench-scale MBR by computational fluid dynamics (CFD) showed that the shear stress on membrane surface could be elevated by 74% if the membrane was sandwiched between two baffles (baffled MBR), compared with that without baffles (unbaffled MBR). The effects of horizontal geometry characteristics of a bench-scale membrane tank were discussed (riser length index Lr, downcomer length index Ld, tank width index Wt). Simulation results indicated that the average cross flow of the riser was negatively correlated to the ratio of riser and downcomer cross-sectional area. A relatively small tank width would also be preferable in promoting shear stress on membrane surface. The optimized MBR had a shear elevation of 21.3-91.4% compared with unbaffled MBR under same aeration intensity. Copyright © 2015 Elsevier Ltd. All rights reserved.

Lipid-regulated sterol transfer between closely apposed membranes by oxysterol-binding protein homologues.

PubMed

Schulz, Timothy A; Choi, Mal-Gi; Raychaudhuri, Sumana; Mears, Jason A; Ghirlando, Rodolfo; Hinshaw, Jenny E; Prinz, William A

2009-12-14

Sterols are transferred between cellular membranes by vesicular and poorly understood nonvesicular pathways. Oxysterol-binding protein-related proteins (ORPs) have been implicated in sterol sensing and nonvesicular transport. In this study, we show that yeast ORPs use a novel mechanism that allows regulated sterol transfer between closely apposed membranes, such as organelle contact sites. We find that the core lipid-binding domain found in all ORPs can simultaneously bind two membranes. Using Osh4p/Kes1p as a representative ORP, we show that ORPs have at least two membrane-binding surfaces; one near the mouth of the sterol-binding pocket and a distal site that can bind a second membrane. The distal site is required for the protein to function in cells and, remarkably, regulates the rate at which Osh4p extracts and delivers sterols in a phosphoinositide-dependent manner. Together, these findings suggest a new model of how ORPs could sense and regulate the lipid composition of adjacent membranes.

2,2'-Bis(monoacylglycero) PO4 (BMP), but Not 3,1'-BMP, increases membrane curvature stress to enhance α-tocopherol transfer protein binding to membranes.

PubMed

Baptist, Matilda; Panagabko, Candace; Nickels, Jonathan D; Katsaras, John; Atkinson, Jeffrey

2015-03-01

Previous work revealed that α-tocopherol transfer protein (α-TTP) co-localizes with bis(monoacylglycero)phosphate (BMP) in late endosomes. BMP is a lipid unique to late endosomes and is believed to induce membrane curvature and support the multivesicular nature of this organelle. We examined the effect of BMP on α-TTP binding to membranes using dual polarization interferometry and vesicle-binding assay. α-TTP binding to membranes is increased by the curvature-inducing lipid BMP. α-TTP binds to membranes with greater affinity when they contain the 2,2'-BMP versus 3,1'-BMP isomers.

2,2'-Bis(monoacylglycero) PO 4 (BMP), but Not 3,1'-BMP, Increases Membrane Curvature Stress to Enhance α-Tocopherol Transfer Protein Binding to Membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baptist, Matilda; Panagabko, Candace; Nickels, Jonathan D.

2015-01-21

Previous work revealed that α-tocopherol transfer protein (α-TTP) co-localizes with bis(monoacylglycero)phosphate (BMP) in late endosomes. BMP is a lipid unique to late endosomes and is believed to induce membrane curvature and support the multivesicular nature of this organelle. In this paper, we examined the effect of BMP on α-TTP binding to membranes using dual polarization interferometry and vesicle-binding assay. α-TTP binding to membranes is increased by the curvature-inducing lipid BMP. Finally, α-TTP binds to membranes with greater affinity when they contain the 2,2'-BMP versus 3,1'-BMP isomers.

Interplay of electrostatics and lipid packing determines the binding of charged polymer coated nanoparticles to model membranes.

PubMed

Biswas, Nupur; Bhattacharya, Rupak; Saha, Arindam; Jana, Nikhil R; Basu, Jaydeep K

2015-10-07

Understanding of nanoparticle-membrane interactions is useful for various applications of nanoparticles like drug delivery and imaging. Here we report on the studies of interaction between hydrophilic charged polymer coated semiconductor quantum dot nanoparticles with model lipid membranes. Atomic force microscopy and X-ray reflectivity measurements suggest that cationic nanoparticles bind and penetrate bilayers of zwitterionic lipids. Penetration and binding depend on the extent of lipid packing and result in the disruption of the lipid bilayer accompanied by enhanced lipid diffusion. On the other hand, anionic nanoparticles show minimal membrane binding although, curiously, their interaction leads to reduction in lipid diffusivity. It is suggested that the enhanced binding of cationic QDs at higher lipid packing can be understood in terms of the effective surface potential of the bilayers which is tunable through membrane lipid packing. Our results bring forth the subtle interplay of membrane lipid packing and electrostatics which determine nanoparticle binding and penetration of model membranes with further implications for real cell membranes.

Refined structure of dimeric diphtheria toxin at 2.0 A resolution.

PubMed Central

Bennett, M. J.; Choe, S.; Eisenberg, D.

1994-01-01

The refined structure of dimeric diphtheria toxin (DT) at 2.0 A resolution, based on 37,727 unique reflections (F > 1 sigma (F)), yields a final R factor of 19.5% with a model obeying standard geometry. The refined model consists of 523 amino acid residues, 1 molecule of the bound dinucleotide inhibitor adenylyl 3'-5' uridine 3' monophosphate (ApUp), and 405 well-ordered water molecules. The 2.0-A refined model reveals that the binding motif for ApUp includes residues in the catalytic and receptor-binding domains and is different from the Rossmann dinucleotide-binding fold. ApUp is bound in part by a long loop (residues 34-52) that crosses the active site. Several residues in the active site were previously identified as NAD-binding residues. Glu 148, previously identified as playing a catalytic role in ADP-ribosylation of elongation factor 2 by DT, is about 5 A from uracil in ApUp. The trigger for insertion of the transmembrane domain of DT into the endosomal membrane at low pH may involve 3 intradomain and 4 interdomain salt bridges that will be weakened at low pH by protonation of their acidic residues. The refined model also reveals that each molecule in dimeric DT has an "open" structure unlike most globular proteins, which we call an open monomer. Two open monomers interact by "domain swapping" to form a compact, globular dimeric DT structure. The possibility that the open monomer resembles a membrane insertion intermediate is discussed. PMID:7833807

Specificity and kinetics of alpha-synuclein binding to model membranes determined with fluorescent excited state intramolecular proton transfer (ESIPT) probe.

PubMed

Shvadchak, Volodymyr V; Falomir-Lockhart, Lisandro J; Yushchenko, Dmytro A; Jovin, Thomas M

2011-04-15

Parkinson disease is characterized cytopathologically by the deposition in the midbrain of aggregates composed primarily of the presynaptic neuronal protein α-synuclein (AS). Neurotoxicity is currently attributed to oligomeric microaggregates subjected to oxidative modification and promoting mitochondrial and proteasomal dysfunction. Unphysiological binding to membranes of these and other organelles is presumably involved. In this study, we performed a systematic determination of the influence of charge, phase, curvature, defects, and lipid unsaturation on AS binding to model membranes using a new sensitive solvatochromic fluorescent probe. The interaction of AS with vesicular membranes is fast and reversible. The protein dissociates from neutral membranes upon thermal transition to the liquid disordered phase and transfers to vesicles with higher affinity. The binding of AS to neutral and negatively charged membranes occurs by apparently different mechanisms. Interaction with neutral bilayers requires the presence of membrane defects; binding increases with membrane curvature and rigidity and decreases in the presence of cholesterol. The association with negatively charged membranes is much stronger and much less sensitive to membrane curvature, phase, and cholesterol content. The presence of unsaturated lipids increases binding in all cases. These findings provide insight into the relation between membrane physical properties and AS binding affinity and dynamics that presumably define protein localization in vivo and, thereby, the role of AS in the physiopathology of Parkinson disease.

Anisotropic biodegradable lipid coated particles for spatially dynamic protein presentation.

PubMed

Meyer, Randall A; Mathew, Mohit P; Ben-Akiva, Elana; Sunshine, Joel C; Shmueli, Ron B; Ren, Qiuyin; Yarema, Kevin J; Green, Jordan J

2018-05-01

There has been growing interest in the use of particles coated with lipids for applications ranging from drug delivery, gene delivery, and diagnostic imaging to immunoengineering. To date, almost all particles with lipid coatings have been spherical despite emerging evidence that non-spherical shapes can provide important advantages including reduced non-specific elimination and increased target-specific binding. We combine control of core particle geometry with control of particle surface functionality by developing anisotropic, biodegradable ellipsoidal particles with lipid coatings. We demonstrate that these lipid coated ellipsoidal particles maintain advantageous properties of lipid polymer hybrid particles, such as the ability for modular protein conjugation to the particle surface using versatile bioorthogonal ligation reactions. In addition, they exhibit biomimetic membrane fluidity and demonstrate lateral diffusive properties characteristic of natural membrane proteins. These ellipsoidal particles simultaneously provide benefits of non-spherical particles in terms of stability and resistance to non-specific phagocytosis by macrophages as well as enhanced targeted binding. These biomaterials provide a novel and flexible platform for numerous biomedical applications. The research reported here documents the ability of non-spherical polymeric particles to be coated with lipids to form anisotropic biomimetic particles. In addition, we demonstrate that these lipid-coated biodegradable polymeric particles can be conjugated to a wide variety of biological molecules in a "click-like" fashion. This is of interest due to the multiple types of cellular mimicry enabled by this biomaterial based technology. These features include mimicry of the highly anisotropic shape exhibited by cells, surface presentation of membrane bound protein mimetics, and lateral diffusivity of membrane bound substrates comparable to that of a plasma membrane. This platform is demonstrated to facilitate targeted cell binding while being resistant to non-specific cellular uptake. Such a platform could allow for investigations into how physical parameters of a particle and its surface affect the interface between biomaterials and cells, as well as provide biomimetic technology platforms for drug delivery and cellular engineering. Copyright © 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Reversible binding kinetics of a cytoskeletal protein at the erythrocyte submembrane.

PubMed Central

Stout, A. L.; Axelrod, D.

1994-01-01

Reversible binding among components of the cellular submembrane cytoskeleton and reversible binding of some of these components with the plasma membrane likely play a role in nonelastic morphological changes and mechanoplastic properties of cells. However, relatively few studies have been devoted to investigating directly the kinetic aspects of the interactions of individual components of the membrane skeleton with the membrane. The experiments described here investigated whether one component of the erythrocyte membrane cytoskeleton, protein 4.1, binds to its sites on the membrane reversibly and if so, whether the different 4.1-binding sites display distinct kinetic behavior. Protein 4.1 is known to stabilize the membrane and to mediate the attachment of spectrin filaments to the membrane. Protein 4.1 previously has been shown to bind to integral membrane proteins band 3, glycophorin C, and to negatively charged phospholipids. To examine the kinetic rates of dissociation of carboxymethyl fluorescein-labeled 4.1 (CF-4.1) to the cytofacial surface of erythrocyte membrane, a special preparation of hemolyzed erythrocyte ghosts was used, in which the ghosts became flattened on a glass surface and exposed their cytofacial surfaces to the solution through a membrane rip in a distinctive characteristic pattern. This preparation was examined by the microscopy technique of total internal reflection/fluorescence recovery after photobleaching (TIR/FRAP). Four different treatments were employed to help identify which membrane binding sites gave rise to the multiplicity of observed kinetic rates. The first treatment, the control, stripped off the native spectrin, actin, 4.1, and ankyrin. About 60% of the CF-4.1 bound to this control binded irreversibly (dissociation time > 20 min), but the remaining approximately 40% binded reversibly with a range of residency times averaging approximately 3 s. The second treatment subjected these stripped membranes to trypsin, which presumably removed most of the band 3. CF-4.1 binded significantly less to these trypsinized membranes and most of the decrease was a loss of the irreversibly binding sites. The third treatment simply preserved the native 4.1 and ankyrin. CF-4.1 binded less to this sample too, and the loss involved both the irreversible and reversible sites. The fourth treatment blocked the gycophorin C sites on the native 4.1-stripped membranes with an antibody. CF-4.1 again binded less to this sample than to a nonimmune serum control, and almost all of the decrease is a loss of irreversible sites. These rest suggest that 1) protein 4.1 binds to membrane or submembrane sites at least in part reversibly ; 2) the most reversible sites are probably not proteinaceous and not glycophorin C, but possibly are phospholipids (especially phosphatidylserine); and 3) TIWRFRAP can successfully examine the fast reversible dynamics of cytoskeletal components binding to biological membranes. Images FIGURE 2 FIGURE 3 FIGURE 4 PMID:7811947

Extending rule-based methods to model molecular geometry and 3D model resolution.

PubMed

Hoard, Brittany; Jacobson, Bruna; Manavi, Kasra; Tapia, Lydia

2016-08-01

Computational modeling is an important tool for the study of complex biochemical processes associated with cell signaling networks. However, it is challenging to simulate processes that involve hundreds of large molecules due to the high computational cost of such simulations. Rule-based modeling is a method that can be used to simulate these processes with reasonably low computational cost, but traditional rule-based modeling approaches do not include details of molecular geometry. The incorporation of geometry into biochemical models can more accurately capture details of these processes, and may lead to insights into how geometry affects the products that form. Furthermore, geometric rule-based modeling can be used to complement other computational methods that explicitly represent molecular geometry in order to quantify binding site accessibility and steric effects. We propose a novel implementation of rule-based modeling that encodes details of molecular geometry into the rules and binding rates. We demonstrate how rules are constructed according to the molecular curvature. We then perform a study of antigen-antibody aggregation using our proposed method. We simulate the binding of antibody complexes to binding regions of the shrimp allergen Pen a 1 using a previously developed 3D rigid-body Monte Carlo simulation, and we analyze the aggregate sizes. Then, using our novel approach, we optimize a rule-based model according to the geometry of the Pen a 1 molecule and the data from the Monte Carlo simulation. We use the distances between the binding regions of Pen a 1 to optimize the rules and binding rates. We perform this procedure for multiple conformations of Pen a 1 and analyze the impact of conformation and resolution on the optimal rule-based model. We find that the optimized rule-based models provide information about the average steric hindrance between binding regions and the probability that antibodies will bind to these regions. These optimized models quantify the variation in aggregate size that results from differences in molecular geometry and from model resolution.

Size-dependent protein segregation at membrane interfaces

NASA Astrophysics Data System (ADS)

Schmid, Eva M.; Bakalar, Matthew H.; Choudhuri, Kaushik; Weichsel, Julian; Ann, Hyoung Sook; Geissler, Phillip L.; Dustin, Michael L.; Fletcher, Daniel A.

2016-07-01

Membrane interfaces formed at cell-cell junctions are associated with characteristic patterns of membrane proteins whose organization is critical for intracellular signalling. To isolate the role of membrane protein size in pattern formation, we reconstituted model membrane interfaces in vitro using giant unilamellar vesicles decorated with synthetic binding and non-binding proteins. We show that size differences between membrane proteins can drastically alter their organization at membrane interfaces, with as little as a ~5 nm increase in non-binding protein size driving its exclusion from the interface. Combining in vitro measurements with Monte Carlo simulations, we find that non-binding protein exclusion is also influenced by lateral crowding, binding protein affinity, and thermally driven membrane height fluctuations that transiently limit access to the interface. This sensitive and highly effective means of physically segregating proteins has implications for cell-cell contacts such as T-cell immunological synapses (for example, CD45 exclusion) and epithelial cell junctions (for example, E-cadherin enrichment), as well as for protein sorting at intracellular contact points between membrane-bound organelles.

Size-dependent protein segregation at membrane interfaces

PubMed Central

Schmid, Eva M; Bakalar, Matthew H; Choudhuri, Kaushik; Weichsel, Julian; Ann, HyoungSook; Geissler, Phillip L; Dustin, Michael L; Fletcher, Daniel A

2016-01-01

Membrane interfaces formed at cell-cell junctions are associated with characteristic patterns of membrane protein organization, such as E-cadherin enrichment in epithelial junctional complexes and CD45 exclusion from the signaling foci of immunological synapses. To isolate the role of protein size in these processes, we reconstituted membrane interfaces in vitro using giant unilamellar vesicles decorated with synthetic binding and non-binding proteins. We show that size differences between binding and non-binding proteins can dramatically alter their organization at membrane interfaces in the absence of active contributions from the cytoskeleton, with as little as a ~5 nm increase in non-binding protein size driving its exclusion from the interface. Combining in vitro measurements with Monte Carlo simulations, we find that non-binding protein exclusion is also influenced by lateral crowding, binding protein affinity, and thermally-driven membrane height fluctuations that transiently limit access to the interface. This simple, sensitive, and highly effective means of passively segregating proteins has implications for signaling at cell-cell junctions and protein sorting at intracellular contact points between membrane-bound organelles. PMID:27980602

How Does Mg2+ Modulate the RNA Folding Mechanism: A Case Study of the G:C W:W Trans Basepair.

PubMed

Halder, Antarip; Roy, Rohit; Bhattacharyya, Dhananjay; Mitra, Abhijit

2017-07-25

Reverse Watson-Crick G:C basepairs (G:C W:W Trans) occur frequently in different functional RNAs. This is one of the few basepairs whose gas-phase-optimized isolated geometry is inconsistent with the corresponding experimental geometry. Several earlier studies indicate that through post-transcriptional modification, direct protonation, or coordination with Mg 2+ , accumulation of positive charge near N7 of guanine can stabilize the experimental geometry. Interestingly, recent studies reveal significant variation in the position of putatively bound Mg 2+ . This, in conjunction with recently raised doubts regarding some of the Mg 2+ assignments near the imino nitrogen of guanine, is suggestive of the existence of multiple Mg 2+ binding modes for this basepair. Our detailed investigation of Mg 2+ -bound G:C W:W Trans pairs occurring in high-resolution RNA crystal structures shows that they are found in 14 different contexts, eight of which display Mg 2+ binding at the Hoogsteen edge of guanine. Further examination of occurrences in these eight contexts led to the characterization of three different Mg 2+ binding modes: 1) direct binding via N7 coordination, 2) direct binding via O6 coordination, and 3) binding via hydrogen-bonding interaction with the first-shell water molecules. In the crystal structures, the latter two modes are associated with a buckled and propeller-twisted geometry of the basepair. Interestingly, respective optimized geometries of these different Mg 2+ binding modes (optimized using six different DFT functionals) are consistent with their corresponding experimental geometries. Subsequent interaction energy calculations at the MP2 level, and decomposition of its components, suggest that for G:C W:W Trans , Mg 2+ binding can fine tune the basepair geometries without compromising with their stability. Our results, therefore, underline the importance of the mode of binding of Mg 2+ ions in shaping RNA structure, folding and function. Copyright © 2017. Published by Elsevier Inc.

α-Synuclein and huntingtin exon 1 amyloid fibrils bind laterally to the cellular membrane.

PubMed

Monsellier, Elodie; Bousset, Luc; Melki, Ronald

2016-01-13

Fibrillar aggregates involved in neurodegenerative diseases have the ability to spread from one cell to another in a prion-like manner. The underlying molecular mechanisms, in particular the binding mode of the fibrils to cell membranes, are poorly understood. In this work we decipher the modality by which aggregates bind to the cellular membrane, one of the obligatory steps of the propagation cycle. By characterizing the binding properties of aggregates made of α-synuclein or huntingtin exon 1 protein displaying similar composition and structure but different lengths to mammalian cells we demonstrate that in both cases aggregates bind laterally to the cellular membrane, with aggregates extremities displaying little or no role in membrane binding. Lateral binding to artificial liposomes was also observed by transmission electron microscopy. In addition we show that although α-synuclein and huntingtin exon 1 fibrils bind both laterally to the cellular membrane, their mechanisms of interaction differ. Our findings have important implications for the development of future therapeutic tools that aim to block protein aggregates propagation in the brain.

α-Synuclein and huntingtin exon 1 amyloid fibrils bind laterally to the cellular membrane

PubMed Central

Monsellier, Elodie; Bousset, Luc; Melki, Ronald

2016-01-01

Fibrillar aggregates involved in neurodegenerative diseases have the ability to spread from one cell to another in a prion-like manner. The underlying molecular mechanisms, in particular the binding mode of the fibrils to cell membranes, are poorly understood. In this work we decipher the modality by which aggregates bind to the cellular membrane, one of the obligatory steps of the propagation cycle. By characterizing the binding properties of aggregates made of α-synuclein or huntingtin exon 1 protein displaying similar composition and structure but different lengths to mammalian cells we demonstrate that in both cases aggregates bind laterally to the cellular membrane, with aggregates extremities displaying little or no role in membrane binding. Lateral binding to artificial liposomes was also observed by transmission electron microscopy. In addition we show that although α-synuclein and huntingtin exon 1 fibrils bind both laterally to the cellular membrane, their mechanisms of interaction differ. Our findings have important implications for the development of future therapeutic tools that aim to block protein aggregates propagation in the brain. PMID:26757959

Three-dimensional structure of the human immunodeficiency virus type 1 matrix protein.

PubMed

Massiah, M A; Starich, M R; Paschall, C; Summers, M F; Christensen, A M; Sundquist, W I

1994-11-25

The HIV-1 matrix protein forms an icosahedral shell associated with the inner membrane of the mature virus. Genetic analyses have indicated that the protein performs important functions throughout the viral life-cycle, including anchoring the transmembrane envelope protein on the surface of the virus, assisting in viral penetration, transporting the proviral integration complex across the nuclear envelope, and localizing the assembling virion to the cell membrane. We now report the three-dimensional structure of recombinant HIV-1 matrix protein, determined at high resolution by nuclear magnetic resonance (NMR) methods. The HIV-1 matrix protein is the first retroviral matrix protein to be characterized structurally and only the fourth HIV-1 protein of known structure. NMR signal assignments required recently developed triple-resonance (1H, 13C, 15N) NMR methodologies because signals for 91% of 132 assigned H alpha protons and 74% of the 129 assignable backbone amide protons resonate within chemical shift ranges of 0.8 p.p.m. and 1 p.p.m., respectively. A total of 636 nuclear Overhauser effect-derived distance restraints were employed for distance geometry-based structure calculations, affording an average of 13.0 NMR-derived distance restraints per residue for the experimentally constrained amino acids. An ensemble of 25 refined distance geometry structures with penalties (sum of the squares of the distance violations) of 0.32 A2 or less and individual distance violations under 0.06 A was generated; best-fit superposition of ordered backbone heavy atoms relative to mean atom positions afforded root-mean-square deviations of 0.50 (+/- 0.08) A. The folded HIV-1 matrix protein structure is composed of five alpha-helices, a short 3(10) helical stretch, and a three-strand mixed beta-sheet. Helices I to III and the 3(10) helix pack about a central helix (IV) to form a compact globular domain that is capped by the beta-sheet. The C-terminal helix (helix V) projects away from the beta-sheet to expose carboxyl-terminal residues essential for early steps in the HIV-1 infectious cycle. Basic residues implicated in membrane binding and nuclear localization functions cluster about an extruded cationic loop that connects beta-strands 1 and 2. The structure suggests that both membrane binding and nuclear localization may be mediated by complex tertiary structures rather than simple linear determinants.

Analysis of diffusion in curved surfaces and its application to tubular membranes

PubMed Central

Klaus, Colin James Stockdale; Raghunathan, Krishnan; DiBenedetto, Emmanuele; Kenworthy, Anne K.

2016-01-01

Diffusion of particles in curved surfaces is inherently complex compared with diffusion in a flat membrane, owing to the nonplanarity of the surface. The consequence of such nonplanar geometry on diffusion is poorly understood but is highly relevant in the case of cell membranes, which often adopt complex geometries. To address this question, we developed a new finite element approach to model diffusion on curved membrane surfaces based on solutions to Fick’s law of diffusion and used this to study the effects of geometry on the entry of surface-bound particles into tubules by diffusion. We show that variations in tubule radius and length can distinctly alter diffusion gradients in tubules over biologically relevant timescales. In addition, we show that tubular structures tend to retain concentration gradients for a longer time compared with a comparable flat surface. These findings indicate that sorting of particles along the surfaces of tubules can arise simply as a geometric consequence of the curvature without any specific contribution from the membrane environment. Our studies provide a framework for modeling diffusion in curved surfaces and suggest that biological regulation can emerge purely from membrane geometry. PMID:27733625

Binding of Signal Recognition Particle Gives Ribosome/Nascent Chain Complexes a Competitive Advantage in Endoplasmic Reticulum Membrane Interaction

PubMed Central

Neuhof, Andrea; Rolls, Melissa M.; Jungnickel, Berit; Kalies, Kai-Uwe; Rapoport, Tom A.

1998-01-01

Most secretory and membrane proteins are sorted by signal sequences to the endoplasmic reticulum (ER) membrane early during their synthesis. Targeting of the ribosome-nascent chain complex (RNC) involves the binding of the signal sequence to the signal recognition particle (SRP), followed by an interaction of ribosome-bound SRP with the SRP receptor. However, ribosomes can also independently bind to the ER translocation channel formed by the Sec61p complex. To explain the specificity of membrane targeting, it has therefore been proposed that nascent polypeptide-associated complex functions as a cytosolic inhibitor of signal sequence- and SRP-independent ribosome binding to the ER membrane. We report here that SRP-independent binding of RNCs to the ER membrane can occur in the presence of all cytosolic factors, including nascent polypeptide-associated complex. Nontranslating ribosomes competitively inhibit SRP-independent membrane binding of RNCs but have no effect when SRP is bound to the RNCs. The protective effect of SRP against ribosome competition depends on a functional signal sequence in the nascent chain and is also observed with reconstituted proteoliposomes containing only the Sec61p complex and the SRP receptor. We conclude that cytosolic factors do not prevent the membrane binding of ribosomes. Instead, specific ribosome targeting to the Sec61p complex is provided by the binding of SRP to RNCs, followed by an interaction with the SRP receptor, which gives RNC–SRP complexes a selective advantage in membrane targeting over nontranslating ribosomes. PMID:9436994

Binding equilibrium and kinetics of membrane-anchored receptors and ligands in cell adhesion: Insights from computational model systems and theory.

PubMed

Weikl, Thomas R; Hu, Jinglei; Xu, Guang-Kui; Lipowsky, Reinhard

2016-09-02

The adhesion of cell membranes is mediated by the binding of membrane-anchored receptor and ligand proteins. In this article, we review recent results from simulations and theory that lead to novel insights on how the binding equilibrium and kinetics of these proteins is affected by the membranes and by the membrane anchoring and molecular properties of the proteins. Simulations and theory both indicate that the binding equilibrium constant [Formula: see text] and the on- and off-rate constants of anchored receptors and ligands in their 2-dimensional (2D) membrane environment strongly depend on the membrane roughness from thermally excited shape fluctuations on nanoscales. Recent theory corroborated by simulations provides a general relation between [Formula: see text] and the binding constant [Formula: see text] of soluble variants of the receptors and ligands that lack the membrane anchors and are free to diffuse in 3 dimensions (3D).

Binding equilibrium and kinetics of membrane-anchored receptors and ligands in cell adhesion: Insights from computational model systems and theory

PubMed Central

Weikl, Thomas R.; Hu, Jinglei; Xu, Guang-Kui; Lipowsky, Reinhard

2016-01-01

ABSTRACT The adhesion of cell membranes is mediated by the binding of membrane-anchored receptor and ligand proteins. In this article, we review recent results from simulations and theory that lead to novel insights on how the binding equilibrium and kinetics of these proteins is affected by the membranes and by the membrane anchoring and molecular properties of the proteins. Simulations and theory both indicate that the binding equilibrium constant K2D and the on- and off-rate constants of anchored receptors and ligands in their 2-dimensional (2D) membrane environment strongly depend on the membrane roughness from thermally excited shape fluctuations on nanoscales. Recent theory corroborated by simulations provides a general relation between K2D and the binding constant K3D of soluble variants of the receptors and ligands that lack the membrane anchors and are free to diffuse in 3 dimensions (3D). PMID:27294442

Binding of (/sup 3/H)forskolin to solubilized preparations of adenylate cyclase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nelson, C.A.; Seamon, K.B.

1988-01-01

The binding of (/sup 3/H)forskolin to proteins solubilized from bovine brain membranes was studied by precipitating proteins with polyethylene glycol and separating (/sup 3/H)forskolin bound to protein from free (/sup 3/H)forskolin by rapid filtration. The K/sub d/ for (/sup 3/H)forskolin binding to solubilized proteins was 14 nM which was similar to that for (/sup 3/H)forskolin binding sites in membranes from rat brain and human platelets. Forskolin analogs competed for (/sup 3/H)forskolin binding sites with the same rank potency in both brain membranes and in proteins solubilized from brain membranes. (/sup 3/H)forskolin bound to proteins solubilized from membranes with a Bmaxmore » of 38 fmolmg protein which increased to 94 fmolmg protein when GppNHp was included in the binding assay. In contrast, GppNHp had no effect on (/sup 3/H)forskolin binding to proteins solubilized from membranes preactivated with GppNHp. Solubilized adenylate cyclase from non-preactivated membranes had a basal activity of 130 pmolmgmin which was increased 7-fold by GppNHp. In contrast, adenylate cyclase from preactivated membranes had a basal activity of 850 pmolmgmin which was not stimulated by GppNHp or forskolin« less

Deconstructing the DGAT1 enzyme: membrane interactions at substrate binding sites.

PubMed

Lopes, Jose L S; Beltramini, Leila M; Wallace, Bonnie A; Araujo, Ana P U

2015-01-01

Diacylglycerol acyltransferase 1 (DGAT1) is a key enzyme in the triacylglyceride synthesis pathway. Bovine DGAT1 is an endoplasmic reticulum membrane-bound protein associated with the regulation of fat content in milk and meat. The aim of this study was to evaluate the interaction of DGAT1 peptides corresponding to putative substrate binding sites with different types of model membranes. Whilst these peptides are predicted to be located in an extramembranous loop of the membrane-bound protein, their hydrophobic substrates are membrane-bound molecules. In this study, peptides corresponding to the binding sites of the two substrates involved in the reaction were examined in the presence of model membranes in order to probe potential interactions between them that might influence the subsequent binding of the substrates. Whilst the conformation of one of the peptides changed upon binding several types of micelles regardless of their surface charge, suggesting binding to hydrophobic domains, the other peptide bound strongly to negatively-charged model membranes. This binding was accompanied by a change in conformation, and produced leakage of the liposome-entrapped dye calcein. The different hydrophobic and electrostatic interactions observed suggest the peptides may be involved in the interactions of the enzyme with membrane surfaces, facilitating access of the catalytic histidine to the triacylglycerol substrates.

Large Deformation and Adhesive Contact Studies of Axisymmetric Membranes

PubMed Central

Laprade, Evan J.; Long, Rong; Pham, Jonathan; Lawrence, Jimmy; Emrick, Todd; Crosby, Alfred; Hui, Chung-Yuen; Shull, Kenneth R.

2013-01-01

A model membrane contact system consisting of an acrylic copolymer membrane and polydimethyl-siloxane substrate was utilized to evaluate a recently developed nonlinear large-deformation adhesive contact analysis. Direct measurements of the local membrane apex strain during non-contact inflation indicated that the neo-Hookean model provides an accurate measure of membrane strain and supports its use as the strain energy function for the analysis. A time dependent modulus emerges from the analysis, with principal tensions obtained from a comparison of predicted and experimental membrane profiles. A displacement controlled geometry was more easily modeled than the pressure controlled geometry, the applicability of the analysis was limited by wrinkling instabilities. The substantial viscoelastic behavior of these membranes made it difficult to describe the entire membrane with a single modulus, given the nonuniform deformation history of the membranes. Given the difficulty in determining membrane tension from the measured pressure and profile fits using the model, the peel energy was used as a simpler measure of adhesion. Using an analytical balance in the displacement controlled geometry, the membrane tension at the contact line was directly measured. Coupled with contact angle imaging, the peel energy was determined. For the model membranes studied, this peel energy described the membrane/substrate adhesive interactions quite well, giving well-defined peel energies that were independent of the detailed strain state of the membrane. PMID:23289644

Cell-geometry-dependent changes in plasma membrane order direct stem cell signalling and fate

NASA Astrophysics Data System (ADS)

von Erlach, Thomas C.; Bertazzo, Sergio; Wozniak, Michele A.; Horejs, Christine-Maria; Maynard, Stephanie A.; Attwood, Simon; Robinson, Benjamin K.; Autefage, Hélène; Kallepitis, Charalambos; del Río Hernández, Armando; Chen, Christopher S.; Goldoni, Silvia; Stevens, Molly M.

2018-03-01

Cell size and shape affect cellular processes such as cell survival, growth and differentiation1-4, thus establishing cell geometry as a fundamental regulator of cell physiology. The contributions of the cytoskeleton, specifically actomyosin tension, to these effects have been described, but the exact biophysical mechanisms that translate changes in cell geometry to changes in cell behaviour remain mostly unresolved. Using a variety of innovative materials techniques, we demonstrate that the nanostructure and lipid assembly within the cell plasma membrane are regulated by cell geometry in a ligand-independent manner. These biophysical changes trigger signalling events involving the serine/threonine kinase Akt/protein kinase B (PKB) that direct cell-geometry-dependent mesenchymal stem cell differentiation. Our study defines a central regulatory role by plasma membrane ordered lipid raft microdomains in modulating stem cell differentiation with potential translational applications.

The specificity of binding of growth hormone and prolactin to purified plasma membranes from pregnant-rabbit liver.

PubMed Central

Webb, C F; Cadman, H F; Wallis, M

1986-01-01

The binding of 125I-labelled human growth hormone (hGH) to a purified plasma membrane preparation from the liver of pregnant rabbit, and to receptors solubilized from this fraction with Triton X-100, was dependent on time, temperature, the cations used and the receptor concentration. Solubilization did not affect the binding properties of the receptors at low concentrations of Triton X-100. Some somatogenic hormones, such as bovine GH, and some lactogenic hormones, such as ovine prolactin, displaced 125I-labelled hGH from purified plasma membranes and solubilized receptor preparations, but GHs and prolactins from various other species were rather ineffective. The results indicate that although there are binding sites for hGH in these pregnant rabbit liver membranes, few of these are specifically somatogenic or lactogenic. The binding properties of the purified plasma membranes are similar to those of a microsomal preparation studied previously, suggesting that the complex nature of the binding of hGH is not due to the heterogeneity of cellular membranes used to study binding, but is a property of the receptors associated with plasma membranes. PMID:3790086

Time scale of diffusion in molecular and cellular biology

NASA Astrophysics Data System (ADS)

Holcman, D.; Schuss, Z.

2014-05-01

Diffusion is the driver of critical biological processes in cellular and molecular biology. The diverse temporal scales of cellular function are determined by vastly diverse spatial scales in most biophysical processes. The latter are due, among others, to small binding sites inside or on the cell membrane or to narrow passages between large cellular compartments. The great disparity in scales is at the root of the difficulty in quantifying cell function from molecular dynamics and from simulations. The coarse-grained time scale of cellular function is determined from molecular diffusion by the mean first passage time of molecular Brownian motion to a small targets or through narrow passages. The narrow escape theory (NET) concerns this issue. The NET is ubiquitous in molecular and cellular biology and is manifested, among others, in chemical reactions, in the calculation of the effective diffusion coefficient of receptors diffusing on a neuronal cell membrane strewn with obstacles, in the quantification of the early steps of viral trafficking, in the regulation of diffusion between the mother and daughter cells during cell division, and many other cases. Brownian trajectories can represent the motion of a molecule, a protein, an ion in solution, a receptor in a cell or on its membrane, and many other biochemical processes. The small target can represent a binding site or an ionic channel, a hidden active site embedded in a complex protein structure, a receptor for a neurotransmitter on the membrane of a neuron, and so on. The mean time to attach to a receptor or activator determines diffusion fluxes that are key regulators of cell function. This review describes physical models of various subcellular microdomains, in which the NET coarse-grains the molecular scale to a higher cellular-level, thus clarifying the role of cell geometry in determining subcellular function.

C2 Domain of Protein Kinase Cα: Elucidation of the Membrane Docking Surface by Site-Directed Fluorescence and Spin Labeling†

PubMed Central

Kohout, Susy C.; Corbalán-García, Senena; Gómez-Fernández, Juan C.; Falke, Joseph J.

2013-01-01

The C2 domain is a conserved signaling motif that triggers membrane docking in a Ca2+-dependent manner, but the membrane docking surfaces of many C2 domains have not yet been identified. Two extreme models can be proposed for the docking of the protein kinase Cα (PKCα) C2 domain to membranes. In the parallel model, the membrane-docking surface includes the Ca2+ binding loops and an anion binding site on β-strands 3–4, such that the β-strands are oriented parallel to the membrane. In the perpendicular model, the docking surface is localized to the Ca2+ binding loops and the β-strands are oriented perpendicular to the membrane surface. The present study utilizes site-directed fluorescence and spin-labeling to map out the membrane docking surface of the PKCα C2 domain. Single cysteine residues were engineered into 18 locations scattered over all regions of the protein surface, and were used as attachment sites for spectroscopic probes. The environmentally sensitive fluorescein probe identified positions where Ca2+ activation or membrane docking trigger measurable fluorescence changes. Ca2+ binding was found to initiate a global conformational change, while membrane docking triggered the largest fluorescein environmental changes at labeling positions on the three Ca2+ binding loops (CBL), thereby localizing these loops to the membrane docking surface. Complementary EPR power saturation measurements were carried out using a nitroxide spin probe to determine a membrane depth parameter, Φ, for each spin-labeled mutant. Positive membrane depth parameters indicative of membrane insertion were found for three positions, all located on the Ca2+ binding loops: N189 on CBL 1, and both R249 and R252 on CBL 3. In addition, EPR power saturation revealed that five positions near the anion binding site are partially protected from collisions with an aqueous paramagnetic probe, indicating that the anion binding site lies at or near the surface of the headgroup layer. Together, the fluorescence and EPR results indicate that the Ca2+ first and third Ca2+ binding loops insert directly into the lipid headgroup region of the membrane, and that the anion binding site on β-strands 3–4 lies near the headgroups. The data support a model in which the β-strands are tilted toward the parallel orientation relative to the membrane surface. PMID:12564928

Insights into the complex association of bovine factor Va with acidic-lipid-containing synthetic membranes.

PubMed Central

Cutsforth, G A; Koppaka, V; Krishnaswamy, S; Wu, J R; Mann, K G; Lentz, B R

1996-01-01

The mechanism of binding of blood coagulation cofactor factor Va to acidic-lipid-containing membranes has been addressed. Binding isotherms were generated at room temperature using the change in fluorescence anisotropy of pyrene-labeled bovine factor Va to detect binding to sonicated membrane vesicles containing either bovine brain phosphatidylserine (PS) or 1,2-dioleoyl-3-sn-phosphatidylglycerol (DOPG) in combination with 1-palmitoyl-2-oleoyl-3-sn-phosphatidylcholine (POPC). The composition of the membranes was varied from 0 to 40 mol% for PS/POPC and from 0 to 65 mol % for DOPG/POPC membranes. Fitting the data to a classical Langmuir adsorption model yielded estimates of the dissociation constant (Kd) and the stoichiometry of binding. The values of Kd defined in this way displayed a maximum at low acidic lipid content but were nearly constant at intermediate to high fractions of acidic lipid. Fitting the binding isotherms to a two-process binding model (nonspecific adsorption in addition to binding of acidic lipids to sites on the protein) suggested a significant acidic-lipid-independent binding affinity in addition to occupancy of three protein sites that bind PS in preference to DOPG. Both analyses indicated that interaction of factor Va with an acidic-lipid-containing membrane is much more complex than those of factor Xa or prothrombin. Furthermore, a change in the conformation of bound pyrene-labeled factor Va with surface concentration of acidic lipid was implied by variation of both the saturating fluorescence anisotropy and the binding parameters with the acidic lipid content of the membrane. Finally, the results cannot support the contention that binding occurs through nonspecific adsorption to a patch or domain of acidic lipids in the membrane. Factor Va is suggested to associate with membranes by a complex process that includes both acidic-lipid-specific and acidic-lipid-independent sites and a protein structure change induced by occupancy of acidic-lipid-specific sites on the factor Va molecule. Images FIGURE 5 PMID:8744332

Cyclotides Insert into Lipid Bilayers to Form Membrane Pores and Destabilize the Membrane through Hydrophobic and Phosphoethanolamine-specific Interactions*

PubMed Central

Wang, Conan K.; Wacklin, Hanna P.; Craik, David J.

2012-01-01

Cyclotides are a family of plant-derived circular proteins with potential therapeutic applications arising from their remarkable stability, broad sequence diversity, and range of bioactivities. Their membrane-binding activity is believed to be a critical component of their mechanism of action. Using isothermal titration calorimetry, we studied the binding of the prototypical cyclotides kalata B1 and kalata B2 (and various mutants) to dodecylphosphocholine micelles and phosphoethanolamine-containing lipid bilayers. Although binding is predominantly an entropy-driven process, suggesting that hydrophobic forces contribute significantly to cyclotide-lipid complex formation, specific binding to the phosphoethanolamine-lipid headgroup is also required, which is evident from the enthalpic changes in the free energy of binding. In addition, using a combination of dissipative quartz crystal microbalance measurements and neutron reflectometry, we elucidated the process by which cyclotides interact with bilayer membranes. Initially, a small number of cyclotides bind to the membrane surface and then insert first into the outer membrane leaflet followed by penetration through the membrane and pore formation. At higher concentrations of cyclotides, destabilization of membranes occurs. Our results provide significant mechanistic insight into how cyclotides exert their bioactivities. PMID:23129773

Analysis of Perforin Assembly by Quartz Crystal Microbalance Reveals a Role for Cholesterol and Calcium-independent Membrane Binding.

PubMed

Stewart, Sarah E; Bird, Catherina H; Tabor, Rico F; D'Angelo, Michael E; Piantavigna, Stefania; Whisstock, James C; Trapani, Joseph A; Martin, Lisandra L; Bird, Phillip I

2015-12-25

Perforin is an essential component in the cytotoxic lymphocyte-mediated cell death pathway. The traditional view holds that perforin monomers assemble into pores in the target cell membrane via a calcium-dependent process and facilitate translocation of cytotoxic proteases into the cytoplasm to induce apoptosis. Although many studies have examined the structure and role of perforin, the mechanics of pore assembly and granzyme delivery remain unclear. Here we have employed quartz crystal microbalance with dissipation monitoring (QCM-D) to investigate binding and assembly of perforin on lipid membranes, and show that perforin monomers bind to the membrane in a cooperative manner. We also found that cholesterol influences perforin binding and activity on intact cells and model membranes. Finally, contrary to current thinking, perforin efficiently binds membranes in the absence of calcium. When calcium is added to perforin already on the membrane, the QCM-D response changes significantly, indicating that perforin becomes membranolytic only after calcium binding. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

[Molecular organization of glutamate-sensitive chemoexcitatory membranes of nerve cells. Binding of L-[3H]glutamate to synaptic membranes of the rat cerebral cortex].

PubMed

Dambinova, S A; Gorodinskiĭ, A I

1984-01-01

The binding of L-[3H]glutamate to rat cerebral cortex synaptic membranes was investigated. Two types of binding sites, a Na+-independent (Kd = 140-160 nm; Bmax = 3.8-4.5 pmol-mg of protein) and a Na+-dependent (Kd = 2.0 microM; Bmax = 45-50 pmol/mg of protein) ones, were detected. The dependence of Na+-insensitive binding on time and temperature and membrane content in a sample was determined. Mono- and divalent cations (5-10 mM) potentiated specific binding by 2.1-3.3 times. The Na+-dependent binding is associated with active transport systems, while the Na+-independent one-with true receptor binding. The relationship between CNS glutamate receptors and Na+-independent binding sites is discussed.

Interactions between peroxiredoxin 2, hemichrome and the erythrocyte membrane.

PubMed

Bayer, Simone B; Low, Felicia M; Hampton, Mark B; Winterbourn, Christine C

2016-12-01

Peroxiredoxin 2 (Prx2) is an abundant antioxidant protein in erythrocytes that protects against hemolytic anemia resulting from hemoglobin oxidation and Heinz body formation. A small fraction of Prx2 is bound to the cell membrane, but the mechanism and relevance of binding are not clear. We have investigated Prx2 interactions with the erythrocyte membrane and oxidized hemoglobin and whether these interactions are dependent on Prx2 redox state. Membrane binding of Prx2 in erythrocytes decreased when the cells were treated with H 2 O 2 , but studies with purified Prx2 and isolated ghosts showed that the interaction was independent of Prx2 redox state. Hemoglobin oxidation leads to the formation of hemichrome, a denatured form of the protein that binds to Band3 protein in the cell membrane as part of the senescence process and is a precursor of Heinz bodies. Hemichrome competed with Prx2 and decreased Prx2 binding to the membrane, potentially explaining the decreased binding in oxidant-exposed cells. The increased membrane binding of Prx2 seen with increasing intracellular calcium was less sensitive to H 2 O 2 or hemichrome, suggesting an alternative mode of binding. Prx2 was also shown to exhibit chaperone-like activity by retarding the precipitation of pre-formed hemichrome. Our results suggest that Prx2, by restricting membrane binding of hemichrome, could impede Band3 clustering and exposure of senescence antigens. This mechanism, plus the observed chaperone activity for oxidized hemoglobin, may help protect against hemolytic anemia.

Determining Membrane Protein-Lipid Binding Thermodynamics Using Native Mass Spectrometry.

PubMed

Cong, Xiao; Liu, Yang; Liu, Wen; Liang, Xiaowen; Russell, David H; Laganowsky, Arthur

2016-04-06

Membrane proteins are embedded in the biological membrane where the chemically diverse lipid environment can modulate their structure and function. However, the thermodynamics governing the molecular recognition and interaction of lipids with membrane proteins is poorly understood. Here, we report a method using native mass spectrometry (MS), to determine thermodynamics of individual ligand binding events to proteins. Unlike conventional methods, native MS can resolve individual ligand binding events and, coupled with an apparatus to control the temperature, determine binding thermodynamic parameters, such as for protein-lipid interactions. We validated our approach using three soluble protein-ligand systems (maltose binding protein, lysozyme, and nitrogen regulatory protein) and obtained similar results to those using isothermal titration calorimetry and surface plasmon resonance. We also determined for the first time the thermodynamics of individual lipid binding to the ammonia channel (AmtB), an integral membrane protein from Escherichia coli. Remarkably, we observed distinct thermodynamic signatures for the binding of different lipids and entropy-enthalpy compensation for binding lipids of variable chain length. Additionally, using a mutant form of AmtB that abolishes a specific phosphatidylglycerol (PG) binding site, we observed distinct changes in the thermodynamic signatures for binding PG, implying these signatures can identify key residues involved in specific lipid binding and potentially differentiate between specific lipid binding sites.

LHRH-pituitary plasma membrane binding: the presence of specific binding sites in other tissues.

PubMed

Marshall, J C; Shakespear, R A; Odell, W D

1976-11-01

Two specific binding sites for LHRH are present on plasma membranes prepared from rat and bovine anterior pituitary glands. One site is of high affinity (K = 2X108 1/MOL) and the second is of lower affinity (8-5X105 1/mol) and much greater capacity. Studies on membrane fractions prepared from other tissues showed the presence of a single specific site for LHRH. The kinetics and specificity of this site were similar to those of the lower affinity pituitary receptor. These results indicate that only pituitary membranes possess the higher affinity binding site and suggest that the low affinity site is not of physiological importance in the regulation of gonadotrophin secretion. After dissociation from membranes of non-pituitary tissues 125I-LHRH rebound to pituitary membrane preparations. Thus receptor binding per se does not result in degradation of LHRH and the function of these peripheral receptors remains obscure.

G protein-membrane interactions II: Effect of G protein-linked lipids on membrane structure and G protein-membrane interactions.

PubMed

Casas, Jesús; Ibarguren, Maitane; Álvarez, Rafael; Terés, Silvia; Lladó, Victoria; Piotto, Stefano P; Concilio, Simona; Busquets, Xavier; López, David J; Escribá, Pablo V

2017-09-01

G proteins often bear myristoyl, palmitoyl and isoprenyl moieties, which favor their association with the membrane and their accumulation in G Protein Coupled Receptor-rich microdomains. These lipids influence the biophysical properties of membranes and thereby modulate G protein binding to bilayers. In this context, we showed here that geranylgeraniol, but neither myristate nor palmitate, increased the inverted hexagonal (H II ) phase propensity of phosphatidylethanolamine-containing membranes. While myristate and palmitate preferentially associated with phosphatidylcholine membranes, geranylgeraniol favored nonlamellar-prone membranes. In addition, Gαi 1 monomers had a higher affinity for lamellar phases, while Gβγ and Gαβγ showed a marked preference for nonlamellar prone membranes. Moreover, geranylgeraniol enhanced the binding of G protein dimers and trimers to phosphatidylethanolamine-containing membranes, yet it decreased that of monomers. By contrast, both myristate and palmitate increased the Gαi 1 preference for lamellar membranes. Palmitoylation reinforced the binding of the monomer to PC membranes and myristoylation decreased its binding to PE-enriched bilayer. Finally, binding of dimers and trimers to lamellar-prone membranes was decreased by palmitate and myristate, but it was increased in nonlamellar-prone bilayers. These results demonstrate that co/post-translational G protein lipid modifications regulate the membrane lipid structure and that they influence the physico-chemical properties of membranes, which in part explains why G protein subunits sort to different plasma membrane domains. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá. Copyright © 2017 Elsevier B.V. All rights reserved.

The Receptor Binding Domain of Botulinum Neurotoxin Stereotype C Binds Phosphoinositides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yanfeng; Varnum, Susan M.

2012-03-01

Botulinum neurotoxins (BoNTs) are the most toxic proteins known for humans and animals with an extremely low LD50 of {approx} 1 ng/kg. BoNTs generally require a protein and a ganglioside on the cell membrane surface for binding, which is known as a 'dual receptor' mechanism for host intoxication. Recent studies have suggested that in addition to gangliosides, other membrane lipids such as phosphoinositides may be involved in the interactions with the receptor binding domain (HCR) of BoNTs for better membrane penetration. Here, using two independent lipid-binding assays, we tested the interactions of BoNT/C-HCR with lipids in vitro. BoNT/C-HCR was foundmore » to bind negatively charged phospholipids, preferentially phosphoinositides. Additional interactions to phosphoinositides may help BoNT/C bind membrane more tightly and transduct signals for subsequent steps of intoxication. Our results provide new insights into the mechanisms of host cell membrane recognition by BoNTs.« less

Tc-99m galactosyl-neoglycoalbumin: in vitro characterization of receptor-mediated binding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vera, D.R.; Krohn, K.A.; Stadalnik, R.C.

1984-07-01

Hepatic binding protein (HBP) is a membrane receptor that binds and transports plasma glycoproteins from hepatic blood to hepatocellular lysosomes. A characterization is made of the in vitro binding of Tc-99m galactosyl-neoglycoalbumin (Tc-NGA), a synthetic HBP ligand, to liver membrane. Structural modifications of NGA resulted in the alteration of the equilibrium constant, KA, and the forward-binding rate constant, kb. Binding was second-order; the relative amount of membrane-bound NGA depended on the initial concentrations of ligand and membrane. Membrane displacement studies, using carrier ligands in contrast to previously bound Tc-NGA or I-NGA, correlated with the binding characteristics of a native HBPmore » ligand, asialo-orosomucoid. Computer simulation was used to study the detectability of the changes in HBP concentration at different values of kb. The simulations indicated that radiopharmacokinetic sensitivity to alterations in (HBP) should be possible using a neoglycoalbumin preparation with a carbohydrate density within the range of 15 to 25 galactose units per albumin molecule.« less

Isothermal titration calorimetric studies on the interaction of the major bovine seminal plasma protein, PDC-109 with phospholipid membranes.

PubMed

Anbazhagan, V; Sankhala, Rajeshwer S; Singh, Bhanu Pratap; Swamy, Musti J

2011-01-01

The interaction of the major bovine seminal plasma protein, PDC-109 with lipid membranes was investigated by isothermal titration calorimetry. Binding of the protein to model membranes made up of diacyl phospholipids was found to be endothermic, with positive values of binding enthalpy and entropy, and could be analyzed in terms of a single type of binding sites on the protein. Enthalpies and entropies for binding to diacylphosphatidylcholine membranes increased with increase in temperature, although a clear-cut linear dependence was not observed. The entropically driven binding process indicates that hydrophobic interactions play a major role in the overall binding process. Binding of PDC-109 with dimyristoylphosphatidylcholine membranes containing 25 mol% cholesterol showed an initial increase in the association constant as well as enthalpy and entropy of binding with increase in temperature, whereas the values decreased with further increase in temperature. The affinity of PDC-109 for phosphatidylcholine increased at higher pH, which is physiologically relevant in view of the basic nature of the seminal plasma. Binding of PDC-109 to Lyso-PC could be best analysed in terms of two types of binding interactions, a high affinity interaction with Lyso-PC micelles and a low-affinity interaction with the monomeric lipid. Enthalpy-entropy compensation was observed for the interaction of PDC-109 with phospholipid membranes, suggesting that water structure plays an important role in the binding process.

Isothermal Titration Calorimetric Studies on the Interaction of the Major Bovine Seminal Plasma Protein, PDC-109 with Phospholipid Membranes

PubMed Central

Anbazhagan, V.; Sankhala, Rajeshwer S.; Singh, Bhanu Pratap; Swamy, Musti J.

2011-01-01

The interaction of the major bovine seminal plasma protein, PDC-109 with lipid membranes was investigated by isothermal titration calorimetry. Binding of the protein to model membranes made up of diacyl phospholipids was found to be endothermic, with positive values of binding enthalpy and entropy, and could be analyzed in terms of a single type of binding sites on the protein. Enthalpies and entropies for binding to diacylphosphatidylcholine membranes increased with increase in temperature, although a clear-cut linear dependence was not observed. The entropically driven binding process indicates that hydrophobic interactions play a major role in the overall binding process. Binding of PDC-109 with dimyristoylphosphatidylcholine membranes containing 25 mol% cholesterol showed an initial increase in the association constant as well as enthalpy and entropy of binding with increase in temperature, whereas the values decreased with further increase in temperature. The affinity of PDC-109 for phosphatidylcholine increased at higher pH, which is physiologically relevant in view of the basic nature of the seminal plasma. Binding of PDC-109 to Lyso-PC could be best analysed in terms of two types of binding interactions, a high affinity interaction with Lyso-PC micelles and a low-affinity interaction with the monomeric lipid. Enthalpy-entropy compensation was observed for the interaction of PDC-109 with phospholipid membranes, suggesting that water structure plays an important role in the binding process. PMID:22022488

Specific interaction of postsynaptic densities with membrane rafts isolated from synaptic plasma membranes.

PubMed

Liu, Qian; Yao, Wei-Dong; Suzuki, Tatsuo

2013-06-01

Postsynaptic membrane rafts are believed to play important roles in synaptic signaling, plasticity, and maintenance. We recently demonstrated the presence, at the electron microscopic level, of complexes consisting of membrane rafts and postsynaptic densities (PSDs) in detergent-resistant membranes (DRMs) prepared from synaptic plasma membranes (SPMs) ( Suzuki et al., 2011 , J Neurochem, 119, 64-77). To further explore these complexes, here we investigated the nature of the binding between purified SPM-DRMs and PSDs in vitro. In binding experiments, we used SPM-DRMs prepared after treating SPMs with n-octyl-β-d-glucoside, because at concentrations of 1.0% or higher it completely separates SPM-DRMs and PSDs, providing substantially PSD-free unique SPM-DRMs as well as DRM-free PSDs. PSD binding to PSD-free DRMs was identified by mass spectrometry, Western blotting, and electron microscopy. PSD proteins were not incorporated into SPMs, and significantly less PSD proteins were incorporated into DRMs prepared from liver membranes, providing in vitro evidence that binding of PSDs to DRMs is specific and suggestion of the presence of specific interacting molecules. These specific interactions may have important roles in synaptic development, function, and plasticity in vivo. In addition, the binding system we developed may be a good tool to search for binding molecules and binding mechanisms between PSDs and rafts.

Non-Native Metal Ion Reveals the Role of Electrostatics in Synaptotagmin 1-Membrane Interactions.

PubMed

Katti, Sachin; Nyenhuis, Sarah B; Her, Bin; Srivastava, Atul K; Taylor, Alexander B; Hart, P John; Cafiso, David S; Igumenova, Tatyana I

2017-06-27

C2 domains are independently folded modules that often target their host proteins to anionic membranes in a Ca 2+ -dependent manner. In these cases, membrane association is triggered by Ca 2+ binding to the negatively charged loop region of the C2 domain. Here, we used a non-native metal ion, Cd 2+ , in lieu of Ca 2+ to gain insight into the contributions made by long-range Coulombic interactions and direct metal ion-lipid bridging to membrane binding. Using X-ray crystallography, NMR, Förster resonance energy transfer, and vesicle cosedimentation assays, we demonstrate that, although Cd 2+ binds to the loop region of C2A/B domains of synaptotagmin 1 with high affinity, long-range Coulombic interactions are too weak to support membrane binding of individual domains. We attribute this behavior to two factors: the stoichiometry of Cd 2+ binding to the loop regions of the C2A and C2B domains and the impaired ability of Cd 2+ to directly coordinate the lipids. In contrast, electron paramagnetic resonance experiments revealed that Cd 2+ does support membrane binding of the C2 domains in full-length synaptotagmin 1, where the high local lipid concentrations that result from membrane tethering can partially compensate for lack of a full complement of divalent metal ions and specific lipid coordination in Cd 2+ -complexed C2A/B domains. Our data suggest that long-range Coulombic interactions alone can drive the initial association of C2A/B with anionic membranes and that Ca 2+ further augments membrane binding by the formation of metal ion-lipid coordination bonds and additional Ca 2+ ion binding to the C2 domain loop regions.

Synthesis and Properties of Dodecyl Trehaloside Detergents for Membrane Protein Studies

PubMed Central

Tao, Houchao; Fu, Yu; Thompson, Aaron; Lee, Sung Chang; Mahoney, Nicholas; Stevens, Raymond C.; Zhang, Qinghai

2012-01-01

Sugar-based detergents, mostly derived from maltose or glucose, prevail in the extraction, solubilization, stabilization and crystallization of membrane proteins. Inspired by the broad use of trehalose for protecting biological macromolecules and lipid bilayer structures, we synthesized new trehaloside detergents for potential applications in membrane protein research. We devised an efficient synthesis of four dodecyl trehalosides, each with the 12-carboned alkyl chain attached to different hydroxyl groups of trehalose, thus presenting a structurally diverse but related family of detergents. The detergent physical properties, including solubility, hydrophobicity, critical micelle concentration (CMC) and size of micelles, were evaluated and compared with the most popular maltoside analog, β- D-dodecylmaltoside (DDM), which varied from each other due to distinct molecular geometries and possible polar group interactions in resulting micelles. Crystals of 2-dodecyl trehaloside (2-DDTre) were also obtained in methanol, and the crystal packing revealed multiple H-bonded interactions among adjacent trehalose groups. The few trehaloside detergents were tested for the solubilization and stabilization of the nociceptin/orphanin FQ peptide receptor (ORL1) and MsbA, which belong to the G-protein coupled receptor (GPCR) and ATP-binding cassette transporter families, respectively. Our results demonstrated the utility of trehaloside detergents as membrane protein solubilization reagents with the optimal detergents being protein dependent. Continuing development and investigations of trehaloside detergents are attractive given their interesting and unique chemical-physical properties and potential interactions with membrane lipids. PMID:22780816

Multiscale modeling of a Chemofilter device for filtering chemotherapy toxins from blood

NASA Astrophysics Data System (ADS)

Maani, Nazanin; Beyhaghi, Saman; Yee, Daryl; Nosonovsky, Micheal; Greer, Julia; Hetts, Steven; Rayz, Vitaliy

2016-11-01

Purpose: Chemotherapy drugs injected intra-arterially to treat cancer can cause systemic toxic effects. A catheter-based Chemofilter device, temporarily deployed in a vein during the procedure can filter excessive drug from the blood thus reducing chemotherapy side-effects. CFD modeling is used to design the membrane of the Chemofilter in order to optimize its hemodynamic performance. Methods: Multiscale approach is used to model blood flow through the Chemofilter. The toxins bind to the Chemofilter's membrane formed by a lattice of numerous micro cells deployed in a blood vessel of much larger size. A detailed model of the flow through a 2x2 microcell matrix with periodic boundary conditions is used to determine the permeability of the membrane. The results are used to simulate the flow through the whole device modeled as a uniform porous membrane. The finite-volume solver Fluent is used to obtain the numerical solution. Results: The micro cell matrix has a porosity of 0.92. The pressure drop across the resolved microcells was found to be 630 Pa, resulting in the permeability of 6.21 x10-11 m2 in the normal direction. These values were used to optimize the device geometry in order to increase the contact area of the membrane, while minimizing its obstruction to the flow. NIH NCI R01CA194533.

Interaction of Clostridium perfringens delta toxin with erythrocyte and liposome membranes and relation with the specific binding to the ganglioside GM2.

PubMed

Jolivet-Reynaud, C; Hauttecoeur, B; Alouf, J E

1989-01-01

The specific interaction of the cytolytic Clostridium perfringens delta toxin with membrane GM2 was indicated by: (i) characterization of this glycolipid in the membrane of sheep and goat erythrocytes, which are lysed by the toxin, whereas GM2 was undetectable in insensitive rabbit erythrocytes, (ii) demonstration of 125I-toxin binding to GM2, by autoradiography, following incubation with thin-layer chromatograms containing separated neuroblastoma gangliosides, and (iii) toxin fixation by phospholipid-cholesterol unilamellar vesicles containing either sheep gangliosides or GM2. In order to investigate the intramembrane events leading to membrane disruption following toxin binding, the photoreactive probe 12(4-azido-2-nitrophenoxy)stearoyl 1-14C glucosamine, which inserts into the outer layer and labels integral membrane proteins, was used to establish whether delta toxin penetrates into target cell membrane. No toxin labeling was found, suggesting that toxin action takes place at the membrane surface. This contention is supported by the observation that despite toxin binding, GM2 liposomes did not release entrapped 14C-glucose. Treatment of toxin with carboxypeptidases, but not aminopeptidases, abolished both toxin binding capacity onto erythrocytes and its combination with antitoxin neutralizing antibodies, suggesting that the carboxy terminal end of the toxin is critical for binding to cell membrane.

Regulation of Hippocampal Glutamate Receptors: Evidence for the Involvement of a Calcium-Activated Protease

NASA Astrophysics Data System (ADS)

Baudry, Michel; Lynch, Gary

1980-04-01

Specific [3H]glutamate binding to rat hippocampal membranes and the calcium-induced increase in this binding are markedly temperature-sensitive and are inhibited by alkylating or reducing agents as well as by various protease inhibitors. N-Ethylmaleimide, chloromethyl ketone derivatives of lysine and phenylalanine, and tosylarginine methyl ester decrease the maximum number of [3H]glutamate binding sites without changing their affinity for glutamate. Preincubation of the membranes with glutamate does not protect the glutamate ``receptors'' from the suppressive effects of these agents. The proteases trypsin and α -chymotrypsin increase the maximum number of [3H]glutamate binding sites. The effects of calcium on glutamate binding are different across brain regions. Cerebellar membranes are almost insensitive whereas hippocampal and striatal membranes exhibit a strong increase in the number of binding sites after exposure to even low concentrations of calcium. These results suggest that an endogenous membrane-associated thiol protease regulates the number of [3H]glutamate binding sites in hippocampal membranes and that this is the mechanism by which calcium stimulates glutamate binding. The possibility is discussed that the postulated mechanisms participate in synaptic physiology and in particular may be related to the long-term potentiation of transmission found in hippocampus under certain conditions.

Membrane-Mediated Cooperativity of Proteins

NASA Astrophysics Data System (ADS)

Weikl, Thomas R.

2018-04-01

Besides direct protein-protein interactions, indirect interactions mediated by membranes play an important role for the assembly and cooperative function of proteins in membrane shaping and adhesion. The intricate shapes of biological membranes are generated by proteins that locally induce membrane curvature. Indirect curvature-mediated interactions between these proteins arise because the proteins jointly affect the bending energy of the membranes. These curvature-mediated interactions are attractive for crescent-shaped proteins and are a driving force in the assembly of the proteins during membrane tubulation. Membrane adhesion results from the binding of receptor and ligand proteins that are anchored in the apposing membranes. The binding of these proteins strongly depends on nanoscale shape fluctuations of the membranes, leading to a fluctuation-mediated binding cooperativity. A length mismatch between receptor-ligand complexes in membrane adhesion zones causes repulsive curvature-mediated interactions that are a driving force for the length-based segregation of proteins during membrane adhesion.

Direct membrane binding by bacterial actin MreB.

PubMed

Salje, Jeanne; van den Ent, Fusinita; de Boer, Piet; Löwe, Jan

2011-08-05

Bacterial actin MreB is one of the key components of the bacterial cytoskeleton. It assembles into short filaments that lie just underneath the membrane and organize the cell wall synthesis machinery. Here we show that MreB from both T. maritima and E. coli binds directly to cell membranes. This function is essential for cell shape determination in E. coli and is proposed to be a general property of many, if not all, MreBs. We demonstrate that membrane binding is mediated by a membrane insertion loop in TmMreB and by an N-terminal amphipathic helix in EcMreB and show that purified TmMreB assembles into double filaments on a membrane surface that can induce curvature. This, the first example of a membrane-binding actin filament, prompts a fundamental rethink of the structure and dynamics of MreB filaments within cells. Copyright © 2011 Elsevier Inc. All rights reserved.

[3H]aniracetam binds to specific recognition sites in brain membranes.

PubMed

Fallarino, F; Genazzani, A A; Silla, S; L'Episcopo, M R; Camici, O; Corazzi, L; Nicoletti, F; Fioretti, M C

1995-08-01

[3H]Aniracetam bound to specific and saturable recognition sites in membranes prepared from discrete regions of rat brain. In crude membrane preparation from rat cerebral cortex, specific binding was Na+ independent, was still largely detectable at low temperature (4 degrees C), and underwent rapid dissociation. Scatchard analysis of [3H]aniracetam binding revealed a single population of sites with an apparent KD value of approximately 70 nM and a maximal density of 3.5 pmol/mg of protein. Specifically bound [3H]aniracetam was not displaced by various metabolites of aniracetam, nor by other pyrrolidinone-containing nootropic drugs such as piracetam or oxiracetam. Subcellular distribution studies showed that a high percentage of specific [3H]aniracetam binding was present in purified synaptosomes or mitochondria, whereas specific binding was low in the myelin fraction. The possibility that at least some [3H]aniracetam binding sites are associated with glutamate receptors is supported by the evidence that specific binding was abolished when membranes were preincubated at 37 degrees C under fast shaking (a procedure that substantially reduced the amount of glutamate trapped in the membranes) and could be restored after addition of either glutamate or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) but not kainate. The action of AMPA was antagonized by DNQX, which also reduced specific [3H]aniracetam binding in unwashed membranes. High levels of [3H]aniracetam binding were detected in hippocampal, cortical, or cerebellar membranes, which contain a high density of excitatory amino acid receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Surface plasmon resonance spectroscopy for characterisation of membrane protein-ligand interactions and its potential for drug discovery.

PubMed

Patching, Simon G

2014-01-01

Surface plasmon resonance (SPR) spectroscopy is a rapidly developing technique for the study of ligand binding interactions with membrane proteins, which are the major molecular targets for validated drugs and for current and foreseeable drug discovery. SPR is label-free and capable of measuring real-time quantitative binding affinities and kinetics for membrane proteins interacting with ligand molecules using relatively small quantities of materials and has potential to be medium-throughput. The conventional SPR technique requires one binding component to be immobilised on a sensor chip whilst the other binding component in solution is flowed over the sensor surface; a binding interaction is detected using an optical method that measures small changes in refractive index at the sensor surface. This review first describes the basic SPR experiment and the challenges that have to be considered for performing SPR experiments that measure membrane protein-ligand binding interactions, most importantly having the membrane protein in a lipid or detergent environment that retains its native structure and activity. It then describes a wide-range of membrane protein systems for which ligand binding interactions have been characterised using SPR, including the major drug targets G protein-coupled receptors, and how challenges have been overcome for achieving this. Finally it describes some recent advances in SPR-based technology and future potential of the technique to screen ligand binding in the discovery of drugs. This article is part of a Special Issue entitled: Structural and biophysical characterisation of membrane protein-ligand binding. Copyright © 2013 Elsevier B.V. All rights reserved.

Repair of Nerve Cell Membrance Damage by Calcium-Dependent, Membrane-Binding Proteins

DTIC Science & Technology

2013-09-01

In acute spinal cord injury the plasma membranes of spinal neurons are torn allowing high concentrations of calcium to enter the cytoplasm, activating...repairing the cell membrane as soon as the increase in intracellular calcium is sensed by calcium -binding proteins. If these repair mechanisms can be...testing the hypothesis that the action of copine, a human calcium -dependent-membrane-binding protein, in model systems can promote a stable repair of

Inhibition of vincristine binding to plasma membrane vesicles from daunorubicin-resistant Ehrlich ascites cells by multidrug resistance modulators.

PubMed Central

Sehested, M.; Jensen, P. B.; Skovsgaard, T.; Bindslev, N.; Demant, E. J.; Friche, E.; Vindeløv, L.

1989-01-01

The multidrug resistance (MDR) phenotype is presumed to be mostly dependent on changes in the resistant cell plasma membrane, notably the emergence of a 170 kDa glycoprotein called P-glycoprotein, which facilitate increased drug efflux. We have previously demonstrated that ATP-enhanced binding of vincristine (VCR) to plasma membrane vesicles is much greater in MDR than in wild type cells. The present study has shown that VCR binding to MDR Ehrlich ascites tumour cell plasma membrane vesicles is inhibited 50% most efficiently by quinidine (0.5 microM) followed by verapamil (4.1 microM) and trifluoperazine (23.2 microM). This is the reverse order of the effect on whole cells where a ranking of efficiency in terms of enhancement of VCR accumulation, inhibition of VCR efflux, DNA perturbation and modulation of resistance in a clonogenic assay, was trifluoperazine greater than or equal to verapamil much greater than quinidine. The detergent Tween 80 inhibited VCR binding to plasma membrane vesicles at 0.001% v/v which agreed with the level which modulated resistance and increased VCR accumulation in whole cells. No effect was observed on daunorubicin binding to MDR plasma membrane vesicles after incubation with either Tween 80 (up to 0.1% v/v) or verapamil (up to 25 microM). We conclude that the effect of a modulating drug in reversing resistance to VCR correlates with its ability to raise intracellular VCR levels but not with its capability to inhibit VCR binding to the plasma membrane. Thus, enhancement of VCR accumulation in MDR cells is hardly solely due to competition for a drug binding site on P-glycoprotein. Furthermore, the lack of a demonstrable effect on daunorubicin binding to the plasma membrane by modulators points to transport mechanisms which do not utilise specific drug binding to the plasma membrane. PMID:2605092

Spacer geometry and particle deposition in spiral wound membrane feed channels.

PubMed

Radu, A I; van Steen, M S H; Vrouwenvelder, J S; van Loosdrecht, M C M; Picioreanu, C

2014-11-01

Deposition of microspheres mimicking bacterial cells was studied experimentally and with a numerical model in feed spacer membrane channels, as used in spiral wound nanofiltration (NF) and reverse osmosis (RO) membrane systems. In-situ microscopic observations in membrane fouling simulators revealed formation of specific particle deposition patterns for different diamond and ladder feed spacer orientations. A three-dimensional numerical model combining fluid flow with a Lagrangian approach for particle trajectory calculations could describe very well the in-situ observations on particle deposition in flow cells. Feed spacer geometry, positioning and cross-flow velocity sensitively influenced the particle transport and deposition patterns. The deposition patterns were not influenced by permeate production. This combined experimental-modeling approach could be used for feed spacer geometry optimization studies for reduced (bio)fouling. Copyright © 2014 Elsevier Ltd. All rights reserved.

Membrane-Protein Binding Measured with Solution-Phase Plasmonic Nanocube Sensors

PubMed Central

Wu, Hung-Jen; Henzie, Joel; Lin, Wan-Chen; Rhodes, Christopher; Li, Zhu; Sartorel, Elodie; Thorner, Jeremy; Yang, Peidong; Groves, Jay. T.

2013-01-01

We describe a solution-phase sensor of lipid-protein binding based on localized surface plasmon resonance (LSPR) of silver nanocubes. When silica-coated nanocubes are mixed into a suspension of lipid vesicles, supported membranes spontaneously assemble on their surfaces. Using a standard laboratory spectrophotometer, we calibrate the LSPR peak shift due to protein binding to the membrane surface and then characterize the lipid-binding specificity of a pleckstrin-homology domain protein. PMID:23085614

Differences in Organizational Structure of Insulin Receptor on Rat Adipocyte and Liver Plasma Membranes: Role of Disulfide Bonds

NASA Astrophysics Data System (ADS)

Schweitzer, John B.; Smith, Robert M.; Jarett, Leonard

1980-08-01

Binding of 125I-labeled insulin to rat liver and adipocyte plasma membranes has been investigated after treatment of the membranes with agents that modify disulfide bonds or sulfhydryl groups. Dithiothreitol, a disulfide-reducing agent, produced a bimodal response in adipocyte plasma membranes with dose-dependent increases in binding occurring over the range of 0-1 mM dithiothreitol; 5 mM dithiothreitol produced decreased binding. Insulin binding reached its maximal increase at 1 mM and was 3 times control values. Scatchard analysis of the 1 mM dithiothreitol effect revealed a straight line plot indicative of one class of sites with a Ka of 1.0× 108 M-1 which is intermediate between the two Kas obtained from the curvilinear Scatchard plot of control membranes. There was a 20-fold increase in the number of intermediate-affinity receptors compared to high-affinity receptors. The increased 125I-labeled insulin binding after dithiothreitol treatment was reversed by oxidized glutathione in a dose-dependent manner. Interposition of treatment with N-ethylmaleimide, an alkylating agent, prevented oxidized glutathione from reversing the dithiothreitol effect. Reduced glutathione produced the same effect as dithiothreitol. Liver plasma membranes treated with up to 1 mM dithiothreitol exhibited a maximum increase in insulin binding of 20% compared to control. Dithiothreitol at 5 mM decreased insulin binding below that of control membranes. The results indicate that the dithiothreitol effect on insulin binding to adipocyte plasma membranes is due to disruption of disulfide bonds, and that the structural organization of the insulin receptor on the plasma membranes is different for liver and for adipose tissue. The data imply that the insulin receptors on the plasma membrane of adipocytes possess at least two functionally distinct subclasses of disulfide bond but liver insulin receptors do not.

Phosphatidic acid binding proteins display differential binding as a function of membrane curvature stress and chemical properties.

PubMed

Putta, Priya; Rankenberg, Johanna; Korver, Ruud A; van Wijk, Ringo; Munnik, Teun; Testerink, Christa; Kooijman, Edgar E

2016-11-01

Phosphatidic acid (PA) is a crucial membrane phospholipid involved in de novo lipid synthesis and numerous intracellular signaling cascades. The signaling function of PA is mediated by peripheral membrane proteins that specifically recognize PA. While numerous PA-binding proteins are known, much less is known about what drives specificity of PA-protein binding. Previously, we have described the ionization properties of PA, summarized in the electrostatic-hydrogen bond switch, as one aspect that drives the specific binding of PA by PA-binding proteins. Here we focus on membrane curvature stress induced by phosphatidylethanolamine and show that many PA-binding proteins display enhanced binding as a function of negative curvature stress. This result is corroborated by the observation that positive curvature stress, induced by lyso phosphatidylcholine, abolishes PA binding of target proteins. We show, for the first time, that a novel plant PA-binding protein, Arabidopsis Epsin-like Clathrin Adaptor 1 (ECA1) displays curvature-dependence in its binding to PA. Other established PA targets examined in this study include, the plant proteins TGD2, and PDK1, the yeast proteins Opi1 and Spo20, and, the mammalian protein Raf-1 kinase and the C2 domain of the mammalian phosphatidylserine binding protein Lact as control. Based on our observations, we propose that liposome binding assays are the preferred method to investigate lipid binding compared to the popular lipid overlay assays where membrane environment is lost. The use of complex lipid mixtures is important to elucidate further aspects of PA binding proteins. Copyright © 2016. Published by Elsevier B.V.

Autoinhibition of ankyrin-B/G membrane target bindings by intrinsically disordered segments from the tail regions

PubMed Central

Wang, Chao; Wei, Zhiyi

2017-01-01

Ankyrins together with their spectrin partners are the master organizers of micron-scale membrane domains in diverse tissues. The 24 ankyrin (ANK) repeats of ankyrins bind to numerous membrane proteins, linking them to spectrin-based cytoskeletons at specific membrane microdomains. The accessibility of the target binding groove of ANK repeats must be regulated to achieve spatially defined functions of ankyrins/target complexes in different tissues, though little is known in this regard. Here we systemically investigated the autoinhibition mechanism of ankyrin-B/G by combined biochemical, biophysical and structural biology approaches. We discovered that the entire ANK repeats are inhibited by combinatorial and quasi-independent bindings of multiple disordered segments located in the ankyrin-B/G linkers and tails, suggesting a mechanistic basis for differential regulations of membrane target bindings by ankyrins. In addition to elucidating the autoinhibition mechanisms of ankyrins, our study may also shed light on regulations on target bindings by other long repeat-containing proteins. PMID:28841137

NMR studies reveal the role of biomembranes in modulating ligand binding and release by intracellular bile acid binding proteins.

PubMed

Pedò, Massimo; Löhr, Frank; D'Onofrio, Mariapina; Assfalg, Michael; Dötsch, Volker; Molinari, Henriette

2009-12-18

Bile acid molecules are transferred vectorially between basolateral and apical membranes of hepatocytes and enterocytes in the context of the enterohepatic circulation, a process regulating whole body lipid homeostasis. This work addresses the role of the cytosolic lipid binding proteins in the intracellular transfer of bile acids between different membrane compartments. We present nuclear magnetic resonance (NMR) data describing the ternary system composed of the bile acid binding protein, bile acids, and membrane mimetic systems, such as anionic liposomes. This work provides evidence that the investigated liver bile acid binding protein undergoes association with the anionic membrane and binding-induced partial unfolding. The addition of the physiological ligand to the protein-liposome mixture is capable of modulating this interaction, shifting the equilibrium towards the free folded holo protein. An ensemble of NMR titration experiments, based on nitrogen-15 protein and ligand observation, confirm that the membrane and the ligand establish competing binding equilibria, modulating the cytoplasmic permeability of bile acids. These results support a mechanism of ligand binding and release controlled by the onset of a bile salt concentration gradient within the polarized cell. The location of a specific protein region interacting with liposomes is highlighted.

Identification of the components of a glycolytic enzyme metabolon on the human red blood cell membrane.

PubMed

Puchulu-Campanella, Estela; Chu, Haiyan; Anstee, David J; Galan, Jacob A; Tao, W Andy; Low, Philip S

2013-01-11

Glycolytic enzymes (GEs) have been shown to exist in multienzyme complexes on the inner surface of the human erythrocyte membrane. Because no protein other than band 3 has been found to interact with GEs, and because several GEs do not bind band 3, we decided to identify the additional membrane proteins that serve as docking sites for GE on the membrane. For this purpose, a method known as "label transfer" that employs a photoactivatable trifunctional cross-linking reagent to deliver a biotin from a derivatized GE to its binding partner on the membrane was used. Mass spectrometry analysis of membrane proteins that were biotinylated following rebinding and photoactivation of labeled GAPDH, aldolase, lactate dehydrogenase, and pyruvate kinase revealed not only the anticipated binding partner, band 3, but also the association of GEs with specific peptides in α- and β-spectrin, ankyrin, actin, p55, and protein 4.2. More importantly, the labeled GEs were also found to transfer biotin to other GEs in the complex, demonstrating for the first time that GEs also associate with each other in their membrane complexes. Surprisingly, a new GE binding site was repeatedly identified near the junction of the membrane-spanning and cytoplasmic domains of band 3, and this binding site was confirmed by direct binding studies. These results not only identify new components of the membrane-associated GE complexes but also provide molecular details on the specific peptides that form the interfacial contacts within each interaction.

Identification of the Components of a Glycolytic Enzyme Metabolon on the Human Red Blood Cell Membrane*

PubMed Central

Puchulu-Campanella, Estela; Chu, Haiyan; Anstee, David J.; Galan, Jacob A.; Tao, W. Andy; Low, Philip S.

2013-01-01

Glycolytic enzymes (GEs) have been shown to exist in multienzyme complexes on the inner surface of the human erythrocyte membrane. Because no protein other than band 3 has been found to interact with GEs, and because several GEs do not bind band 3, we decided to identify the additional membrane proteins that serve as docking sites for GE on the membrane. For this purpose, a method known as “label transfer” that employs a photoactivatable trifunctional cross-linking reagent to deliver a biotin from a derivatized GE to its binding partner on the membrane was used. Mass spectrometry analysis of membrane proteins that were biotinylated following rebinding and photoactivation of labeled GAPDH, aldolase, lactate dehydrogenase, and pyruvate kinase revealed not only the anticipated binding partner, band 3, but also the association of GEs with specific peptides in α- and β-spectrin, ankyrin, actin, p55, and protein 4.2. More importantly, the labeled GEs were also found to transfer biotin to other GEs in the complex, demonstrating for the first time that GEs also associate with each other in their membrane complexes. Surprisingly, a new GE binding site was repeatedly identified near the junction of the membrane-spanning and cytoplasmic domains of band 3, and this binding site was confirmed by direct binding studies. These results not only identify new components of the membrane-associated GE complexes but also provide molecular details on the specific peptides that form the interfacial contacts within each interaction. PMID:23150667

Tunable Membrane Binding of the Intrinsically Disordered Dehydrin Lti30, a Cold-Induced Plant Stress Protein[W

PubMed Central

Eriksson, Sylvia K.; Kutzer, Michael; Procek, Jan; Gröbner, Gerhard; Harryson, Pia

2011-01-01

Dehydrins are intrinsically disordered plant proteins whose expression is upregulated under conditions of desiccation and cold stress. Their molecular function in ensuring plant survival is not yet known, but several studies suggest their involvement in membrane stabilization. The dehydrins are characterized by a broad repertoire of conserved and repetitive sequences, out of which the archetypical K-segment has been implicated in membrane binding. To elucidate the molecular mechanism of these K-segments, we examined the interaction between lipid membranes and a dehydrin with a basic functional sequence composition: Lti30, comprising only K-segments. Our results show that Lti30 interacts electrostatically with vesicles of both zwitterionic (phosphatidyl choline) and negatively charged phospholipids (phosphatidyl glycerol, phosphatidyl serine, and phosphatidic acid) with a stronger binding to membranes with high negative surface potential. The membrane interaction lowers the temperature of the main lipid phase transition, consistent with Lti30’s proposed role in cold tolerance. Moreover, the membrane binding promotes the assembly of lipid vesicles into large and easily distinguishable aggregates. Using these aggregates as binding markers, we identify three factors that regulate the lipid interaction of Lti30 in vitro: (1) a pH dependent His on/off switch, (2) phosphorylation by protein kinase C, and (3) reversal of membrane binding by proteolytic digest. PMID:21665998

Luteinizing hormone-releasing hormone inactivation by purified pituitary plasma membranes: effects of receptor-binding studies.

PubMed

Clayton, R N; Shakespear, R A; Duncan, J A; Marshall, J C

1979-05-01

Inactivation of LHRH by purified bovine pituitary plasma membranes was studied in vitro. After incubation of [125I]iodo-LHRH with plasma membranes, the amount of tracer bound to the pellet was measured, and the integrity of the unbound tracer in the supernatant was assessed. Reduction in ability to bind to anti-LHRH serum and to rebind to plasma membranes together with altered electrophoretic mobility on polyacrylamide gels showed that the unbound [125I]iodo-LHRH was inactivated. LHRH inactivation occurred rapidly and was dependent upon membrane concentration and incubation temperature. These results indicate that hormone inactivation must be taken into account in the interpretation of LHRH-receptor interactions. During 37 C incubations, the apparent absence of specific LHRH binding can be explained by inactivation of tracer hormone. Significant LHRH inactivation also occurred at 0 C, which in part explains the insensitivity of LHRH receptor assays. Assessment of LHRH inactivation by different particulate subcellular fractions of pituitary tissue showed that the inactivating enzyme was associated with the plasma membranes; other organelles did not alter LHRH. The enzyme appeared to be an integral part of the plasma membrane structure, since enzymic activity could not be removed by washing without reducing specific LHRH binding. Additionally, reduction of LHRH inactivation by the inhibitors Bacitracin and Trasylol and by magnesium was also accompanied by reduced LHRH binding. Previous studies have shown that the majority of LHRH binding to pituitary plasma membranes is to the low affinity site (approximately 10(-6) M), but the significance of this binding has been uncertain. Our findings indicate that low affinity binding probably represents binding of LHRH to the inactivating enzyme. The LHRH analog, D-Ser6(TBu), des Gly10, ethylamide, has greater biological activity than LHRH and is not inactivated to a significant extent by pituitary plasma membranes. The enhanced biological activity of the analog, therefore, may be due to its resistance to inactivation by enzymes on the pituitary cell surface. The membrane-associated inactivating enzyme could play an important role in vivo in determining the concentration of intact LHRH available at the receptor site which initiates gonadotropin release.

Membrane Modulates Affinity for Calcium Ion to Create an Apparent Cooperative Binding Response by Annexin a5

PubMed Central

Gauer, Jacob W.; Knutson, Kristofer J.; Jaworski, Samantha R.; Rice, Anne M.; Rannikko, Anika M.; Lentz, Barry R.; Hinderliter, Anne

2013-01-01

Isothermal titration calorimetry was used to characterize the binding of calcium ion (Ca2+) and phospholipid to the peripheral membrane-binding protein annexin a5. The phospholipid was a binary mixture of a neutral and an acidic phospholipid, specifically phosphatidylcholine and phosphatidylserine in the form of large unilamellar vesicles. To stringently define the mode of binding, a global fit of data collected in the presence and absence of membrane concentrations exceeding protein saturation was performed. A partition function defined the contribution of all heat-evolving or heat-absorbing binding states. We find that annexin a5 binds Ca2+ in solution according to a simple independent-site model (solution-state affinity). In the presence of phosphatidylserine-containing liposomes, binding of Ca2+ differentiates into two classes of sites, both of which have higher affinity compared with the solution-state affinity. As in the solution-state scenario, the sites within each class were described with an independent-site model. Transitioning from a solution state with lower Ca2+ affinity to a membrane-associated, higher Ca2+ affinity state, results in cooperative binding. We discuss how weak membrane association of annexin a5 prior to Ca2+ influx is the basis for the cooperative response of annexin a5 toward Ca2+, and the role of membrane organization in this response. PMID:23746516

Membrane Stored Curvature Elastic Stress Modulates Recruitment of Maintenance Proteins PspA and Vipp1.

PubMed

McDonald, Christopher; Jovanovic, Goran; Ces, Oscar; Buck, Martin

2015-09-01

Phage shock protein A (PspA), which is responsible for maintaining inner membrane integrity under stress in enterobacteria, and vesicle-inducting protein in plastids 1 (Vipp1), which functions for membrane maintenance and thylakoid biogenesis in cyanobacteria and plants, are similar peripheral membrane-binding proteins. Their homologous N-terminal amphipathic helices are required for membrane binding; however, the membrane features recognized and required for expressing their functionalities have remained largely uncharacterized. Rigorously controlled, in vitro methodologies with lipid vesicles and purified proteins were used in this study and provided the first biochemical and biophysical characterizations of membrane binding by PspA and Vipp1. Both proteins are found to sense stored curvature elastic (SCE) stress and anionic lipids within the membrane. PspA has an enhanced sensitivity for SCE stress and a higher affinity for the membrane than Vipp1. These variations in binding may be crucial for some of the proteins' differing roles in vivo. Assays probing the transcriptional regulatory function of PspA in the presence of vesicles showed that a relief of transcription inhibition occurs in an SCE stress-specific manner. This in vitro recapitulation of membrane stress-dependent transcription control suggests that the Psp response may be mounted in vivo when a cell's inner membrane experiences increased SCE stress. All cell types maintain the integrity of their membrane systems. One widely distributed membrane stress response system in bacteria is the phage shock protein (Psp) system. The central component, peripheral membrane protein PspA, which mitigates inner membrane stress in bacteria, has a counterpart, Vipp1, which functions for membrane maintenance and thylakoid biogenesis in plants and photosynthetic bacteria. Membrane association of both these proteins is accepted as playing a pivotal role in their functions. Here we show that direct membrane binding by PspA and Vipp1 is driven by two physio-chemical signals, one of which is membrane stress specific. Our work points to alleviation of membrane stored curvature elastic stress by amphipathic helix insertions as an attractive mechanism for membrane maintenance by PspA and Vipp1. Furthermore, the identification of a physical, stress-related membrane signal suggests a unilateral mechanism that promotes both binding of PspA and induction of the Psp response. Copyright © 2015 McDonald et al.

Membrane Association of the PTEN Tumor Suppressor: Electrostatic Interaction with Phos-phatidylserine-Containing Bilayers and Regulatory Role of the C-Terminal Tail

PubMed Central

Shenoy, Siddharth S.; Nanda, Hirsh; Lösche, Mathias

2012-01-01

The phosphatidylinositolphosphate phosphatase PTEN is the second most frequently mutated protein in human tumors. Its membrane association, allosteric activation and membrane dissociation are poorly understood. We recently reported PTEN binding affinities to membranes of different compositions and a preliminary investigation of the protein-membrane complex with neutron reflectometry (NR). Here we use NR to validate molecular dynamics (MD) simulations of the protein and study conformational differences of the protein in solution and on anionic membranes. NR shows that full-length PTEN binds to such membranes roughly in the conformation and orientation suggested by the crystal structure of a truncated PTEN protein, in contrast with a recently presented model which suggested that membrane binding depends critically on the SUMOylation of the CBR3 loop of PTEN’s C2 domain. Our MD simulations confirm that PTEN is peripherally bound to the bilayer surface and show slight differences of the protein structure in solution and in the membrane-bound state, where the protein body flattens against the bilayer surface. PTEN’s C2 domain binds phosphatidylserine (PS) tightly through its CBR3 loop, and its phosphatase domain also forms electrostatic interactions with PS. NR and MD results show consistently that PTEN’s unstructured, anionic C-terminal tail is repelled from the bilayer surface. In contrast, this tail is tightly tugged against the C2 domain in solution, partially obstructing the membrane-binding interface of the protein. Arresting the C-terminal tail in this conformation by phosphorylation may provide a control mechanism for PTEN’s membrane binding and activity. PMID:23073177

Membrane association of the PTEN tumor suppressor: electrostatic interaction with phosphatidylserine-containing bilayers and regulatory role of the C-terminal tail.

PubMed

Shenoy, Siddharth S; Nanda, Hirsh; Lösche, Mathias

2012-12-01

The phosphatidylinositolphosphate phosphatase PTEN is the second most frequently mutated protein in human tumors. Its membrane association, allosteric activation and membrane dissociation are poorly understood. We recently reported PTEN binding affinities to membranes of different compositions (Shenoy et al., 2012, PLoS ONE 7, e32591) and a preliminary investigation of the protein-membrane complex with neutron reflectometry (NR). Here we use NR to validate molecular dynamics (MD) simulations of the protein and study conformational differences of the protein in solution and on anionic membranes. NR shows that full-length PTEN binds to such membranes roughly in the conformation and orientation suggested by the crystal structure of a truncated PTEN protein, in contrast with a recently presented model which suggested that membrane binding depends critically on the SUMOylation of the CBR3 loop of PTEN's C2 domain. Our MD simulations confirm that PTEN is peripherally bound to the bilayer surface and show slight differences of the protein structure in solution and in the membrane-bound state, where the protein body flattens against the bilayer surface. PTEN's C2 domain binds phosphatidylserine (PS) tightly through its CBR3 loop, and its phosphatase domain also forms electrostatic interactions with PS. NR and MD results show consistently that PTEN's unstructured, anionic C-terminal tail is repelled from the bilayer surface. In contrast, this tail is tightly tugged against the C2 domain in solution, partially obstructing the membrane-binding interface of the protein. Arresting the C-terminal tail in this conformation by phosphorylation may provide a control mechanism for PTEN's membrane binding and activity. Copyright © 2012 Elsevier Inc. All rights reserved.

Structural insights into the methyl donor recognition model of a novel membrane-binding protein UbiG.

PubMed

Zhu, Yuwei; Jiang, Xuguang; Wang, Chongyuan; Liu, Yang; Fan, Xiaojiao; Zhang, Linjuan; Niu, Liwen; Teng, Maikun; Li, Xu

2016-03-15

UbiG is a SAM-dependent O-methyltransferase, catalyzing two O-methyl transfer steps for ubiquinone biosynthesis in Escherichia coli. UbiG possesses a unique sequence insertion between β4 and α10, which is used for membrane lipid interaction. Interestingly, this sequence insertion also covers the methyl donor binding pocket. Thus, the relationship between membrane binding and entrance of the methyl donor of UbiG during the O-methyl transfer process is a question that deserves further exploration. In this study, we reveal that the membrane-binding region of UbiG gates the entrance of methyl donor. When bound with liposome, UbiG displays an enhanced binding ability toward the methyl donor product S-adenosylhomocysteine. We further employ protein engineering strategies to design UbiG mutants by truncating the membrane interacting region or making it more flexible. The ITC results show that the binding affinity of these mutants to SAH increases significantly compared with that of the wild-type UbiG. Moreover, we determine the structure of UbiG∆(165-187) in complex with SAH. Collectively, our results provide a new angle to cognize the relationship between membrane binding and entrance of the methyl donor of UbiG, which is of benefit for better understanding the O-methyl transfer process for ubiquinone biosynthesis.

Selective effect of cell membrane on synaptic neurotransmission

NASA Astrophysics Data System (ADS)

Postila, Pekka A.; Vattulainen, Ilpo; Róg, Tomasz

2016-01-01

Atomistic molecular dynamics simulations were performed with 13 non-peptidic neurotransmitters (NTs) in three different membrane environments. The results provide compelling evidence that NTs are divided into membrane-binding and membrane-nonbinding molecules. NTs adhere to the postsynaptic membrane surface whenever the ligand-binding sites of their synaptic receptors are buried in the lipid bilayer. In contrast, NTs that have extracellular ligand-binding sites do not have a similar tendency to adhere to the membrane surface. This finding is a seemingly simple yet important addition to the paradigm of neurotransmission, essentially dividing it into membrane-independent and membrane-dependent mechanisms. Moreover, the simulations also indicate that the lipid composition especially in terms of charged lipids can affect the membrane partitioning of NTs. The revised paradigm, highlighting the importance of cell membrane and specific lipids for neurotransmission, should to be of interest to neuroscientists, drug industry and the general public alike.

Annexin-A6 presents two modes of association with phospholipid membranes. A combined QCM-D, AFM and cryo-TEM study.

PubMed

Buzhynskyy, Nikolay; Golczak, Marcin; Lai-Kee-Him, Joséphine; Lambert, Olivier; Tessier, Béatrice; Gounou, Céline; Bérat, Rémi; Simon, Anne; Granier, Thierry; Chevalier, Jean-Marc; Mazères, Serge; Bandorowicz-Pikula, Joanna; Pikula, Slawomir; Brisson, Alain R

2009-10-01

Annexins are soluble proteins that bind to biological membranes in a Ca(2+)-dependent manner. Annexin-A6 (AnxA6) is unique in the annexin family as it consists of the repeat of two annexin core modules, while all other annexins consist of a single module. AnxA6 has been proposed to participate in various membrane-related processes, including endocytosis and exocytosis, yet the molecular mechanism of association of AnxA6 with biological membranes, especially its ability to aggregate membranes, is still unclear. To address this question, we studied the association of AnxA6 with model phospholipid membranes by combining the techniques of quartz crystal microbalance with dissipation monitoring (QCM-D), (cryo-) transmission electron microscopy (TEM) and atomic force microscopy (AFM). The properties of membrane binding and membrane aggregation of AnxA6 were compared to two reference systems, annexin A5 (AnxA5), which is the annexin prototype, and a chimerical AnxA5-dimer molecule, which is able to aggregate two membranes in a symmetrical manner. We show that AnxA6 presents two modes of association with lipid membranes depending on Ca(2+)-concentration. At low Ca(2+)-concentration ( approximately 60-150microM), AnxA6 binds to membranes via its two coplanar annexin modules and is not able to associate two separate membranes. At high Ca(2+)-concentration ( approximately 2mM), AnxA6 molecules are able to bind two adjacent phospholipid membranes and present a conformation similar to the AnxA6 3D crystallographic structure. Possible biological implications of these novel membrane-binding properties of AnxA6 are discussed.

[3H]-nitrendipine binding in membranes obtained from hypoxic and reoxygenated heart.

PubMed

Matucci, R; Bennardini, F; Sciammarella, M L; Baccaro, C; Stendardi, I; Franconi, F; Giotti, A

1987-04-01

We compared the binding properties of [3H]-nitrendipine in heart membranes from normal guinea-pig heart and from hypoxic or hypoxic and reoxygenated heart. The [3H]-nitrendipine binds a single class of high capacity (Bmax 667.2 +/- 105.2) with high affinity (KD 0.14 +/- 0.02) binding sites. By contrast, in membranes of hypoxic and reoxygenated heart the Bmax decreases significantly while it remains unaffected during hypoxia. Xanthinoxidase activity is increased in hypoxic-reoxygenated hearts.

Early stages of clathrin aggregation at a membrane in coarse-grained simulations

NASA Astrophysics Data System (ADS)

Giani, M.; den Otter, W. K.; Briels, W. J.

2017-04-01

The self-assembly process of clathrin coated pits during endocytosis has been simulated by combining and extending coarse grained models of the clathrin triskelion, the adaptor protein AP2, and a flexible network membrane. The AP2's core, upon binding to membrane and cargo, releases a motif that can bind clathrin. In conditions where the core-membrane-cargo binding is weak, the binding of this motif to clathrin can result in a stable complex. We characterize the conditions and mechanisms resulting in the formation of clathrin lattices that curve the membrane, i.e., clathrin coated pits. The mechanical properties of the AP2 β linker appear crucial to the orientation of the curved clathrin lattice relative to the membrane, with wild-type short linkers giving rise to the inward curving buds enabling endocytosis while long linkers produce upside-down cages and outward curving bulges.

Quantitation of Membrane-Ligand Interactions Using Backscattering Interferometry

PubMed Central

Baksh, Michael M.; Kussrow, Amanda K.; Mileni, Mauro; Finn, M.G.; Bornhop, Darryl J.

2011-01-01

Though membrane-associated proteins are ubiquitous within all living organisms and represent the majority of drug targets, a general method for direct, label-free measurement of ligand binding to native membranes has not been reported. Here we show backscattering interferometry (BSI) to be a viable technique for quantifying ligand-receptor binding affinities in a variety of membrane environments. By detecting minute changes in the refractive index of a solution, BSI allows binding interactions of proteins with their ligands to be measured at picomolar concentrations. Equilibrium binding constants in the micromolar to picomolar range were obtained for small- and large-molecule interactions in both synthetic- and cell-derived membranes without the use of labels or supporting substrates. The simple and low-cost hardware, high sensitivity, and label-free nature of BSI should make it readily applicable to the study of many membrane-associated proteins of biochemical and pharmacological interest. PMID:21399645

Deacetylation of forskolin catalyzed by bovine brain membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Selfe, S.; Storm, D.R.

1985-11-27

Radiolabeled forskolin, 7-(/sup 3/H-acetyl)-forskolin, was synthesized to explore interactions between forskolin and bovine brain membrane preparations. The radiolabeled derivative was chemically characterized, and found to be indistinquishable from unlabeled forskolin in its ability to stimulate bovine brain adenylate cyclase. Preliminary binding data demonstrated that binding of 7-(/sup 3/H-acetyl)-forskolin to membranes was concentration dependent. However, competition binding studies using a constant concentration of 7-(/sup 3/H-acetyl)-forskolin with increasing levels of unlabeled forskolin showed enhanced binding of the labeled derivative. This suggested that 7-(/sup 3/H-acetyl)-forskolin was degraded by membranes and protected by native forskolin. Incubation of forskolin with membranes and analysis of themore » products by thin layer chromatography and mass spectroscopy showed the formation of 7-desacetylforskolin. The deacetylation of forskolin was monitored by quantitating the release of (/sup 3/H)acetate from 7-(/sup 3/H-acetyl)-forskolin. The reaction was linear with time and protein concentration. These data illustrate that forskolin can be degraded by membranes and indicate that ligand binding studies using labeled forskolin and membrane preparations should be cautiously interpreted.« less

The action of stress hormones on the structure and function of erythrocyte membrane.

PubMed

Mokrushnikov, Pavel V; Panin, Lev E; Zaitsev, Boris N

2015-07-01

The action of a mixture of hormones (cortisol and adrenaline) on erythrocyte membrane during their binding was investigated. Changes in the membrane structure were elucidated by atomic force microscopy; microviscosity of the lipid bilayer and changes in the activity of Na(+),K(+)-ATPase at different concentrations of the hormones in erythrocyte suspension were estimated by the fluorescence method. Cortisol and adrenaline were shown to compete for the binding sites. A hormone that managed to bind nonspecifically to the membrane hindered the binding of another hormone. In a mixture of these hormones, cortisol won a competition for the binding sites; therewith, microviscosity of the membranes increased by 25%, which corresponds to a change in microviscosity produced by the action of cortisol alone. The competitive relationships affected also the Na(+),K(+)-ATPase activity, which was indicated by appearance of the second maximum of enzyme activity. It is assumed that an increase in microviscosity of erythrocyte membrane first raises the Na(+),K(+)-ATPase activity due to a growth of the maximum energy of membrane phonons, and then decreases the activity due to hindering of conformational transitions in the enzyme molecule.

LH-RH binding to purified pituitary plasma membranes: absence of adenylate cyclase activation.

PubMed

Clayton, R N; Shakespear, R A; Marshall, J C

1978-06-01

Purified bovine pituitary plasma membranes possess two specific LH-RH binding sites. The high affinity site (2.5 X 10(9) l/mol) has low capacity (9 X 10(-15) mol/mg membrane protein) while the low affinity site 6.1 X 10(5) l/mol) has a much higher capacity (1.1 X 10(-10) mol/mg). Specific LH-RH binding to plasma membranes is increased 8.5-fold during purification from homogenate whilst adenylate cyclase activity is enriched 7--8-fold. Distribution of specific LH-RH binding to sucrose density gradient interface fractions parallels that of adenylate cyclase activity. Mg2+ and Ca2+ inhibit specific [125I]LH-RH binding at micromolar concentrations. Synthetic LH-RH, up to 250 microgram/ml, failed to stimulate adenylase cyclase activity of the purified bovine membranes. Using a crude 10,800 g rat pituitary membrane preparation, LH-RH similarly failed to activate adenylate cyclase even in the presence of guanyl nucleotides. These data confirm the presence of LH-RH receptor sites on pituitary plasma membranes and suggest that LH-RH-induced gonadotrophin release may be mediated by mechanisms other than activation of adenylate cyclase.

PtdInsP2 and PtdSer cooperate to trap synaptotagmin-1 to the plasma membrane in the presence of calcium

PubMed Central

Pérez-Lara, Ángel; Thapa, Anusa; Nyenhuis, Sarah B; Nyenhuis, David A; Halder, Partho; Tietzel, Michael; Tittmann, Kai; Cafiso, David S; Jahn, Reinhard

2016-01-01

The Ca2+-sensor synaptotagmin-1 that triggers neuronal exocytosis binds to negatively charged membrane lipids (mainly phosphatidylserine (PtdSer) and phosphoinositides (PtdIns)) but the molecular details of this process are not fully understood. Using quantitative thermodynamic, kinetic and structural methods, we show that synaptotagmin-1 (from Rattus norvegicus and expressed in Escherichia coli) binds to PtdIns(4,5)P2 via a polybasic lysine patch in the C2B domain, which may promote the priming or docking of synaptic vesicles. Ca2+ neutralizes the negative charges of the Ca2+-binding sites, resulting in the penetration of synaptotagmin-1 into the membrane, via binding of PtdSer, and an increase in the affinity of the polybasic lysine patch to phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2). These Ca2+-induced events decrease the dissociation rate of synaptotagmin-1 membrane binding while the association rate remains unchanged. We conclude that both membrane penetration and the increased residence time of synaptotagmin-1 at the plasma membrane are crucial for triggering exocytotic membrane fusion. DOI: http://dx.doi.org/10.7554/eLife.15886.001 PMID:27791979

Pressure reversal of the action of octanol on postsynaptic membranes from Torpedo.

PubMed Central

Braswell, L. M.; Miller, K. W.; Sauter, J. F.

1984-01-01

Octanol increases the binding of [3H]-acetylcholine to the desensitized state of the nicotinic receptor in postsynaptic membranes prepared from Torpedo californica. This increase in binding results from an increase in the affinity of [3H]-acetylcholine for its receptor without any change in the number of sites or the shape of the acetylcholine binding curve. High pressures of helium (300 atm) decrease [3H]-acetylcholine binding by a mechanism that changes only the affinity of acetylcholine binding. Helium pressure reverses the effect of octanol on the affinity of [3H]-acetylcholine for its receptor. This pressure reversal of the action of octanol at a postsynaptic membrane is consistent either with pressure counteracting an octanol-induced membrane expansion or with independent mechanisms for the actions of octanol and pressure. The data do not conform with a mechanism in which pressure displaces octanol from a binding site on the receptor protein. PMID:6487895

Spontaneous adsorption of coiled-coil model peptides K and E to a mixed lipid bilayer.

PubMed

Pluhackova, Kristyna; Wassenaar, Tsjerk A; Kirsch, Sonja; Böckmann, Rainer A

2015-03-26

A molecular description of the lipid-protein interactions underlying the adsorption of proteins to membranes is crucial for understanding, for example, the specificity of adsorption or the binding strength of a protein to a bilayer, or for characterizing protein-induced changes of membrane properties. In this paper, we extend an automated in silico assay (DAFT) for binding studies and apply it to characterize the adsorption of the model fusion peptides E and K to a mixed phospholipid/cholesterol membrane using coarse-grained molecular dynamics simulations. In addition, we couple the coarse-grained protocol to reverse transformation to atomistic resolution, thereby allowing to study molecular interactions with high detail. The experimentally observed differential binding of the peptides E and K to membranes, as well as the increased binding affinity of helical over unstructered peptides, could be well reproduced using the polarizable Martini coarse-grained (CG) force field. Binding to neutral membranes is shown to be dominated by initial binding of the positively charged N-terminus to the phospholipid headgroup region, followed by membrane surface-aligned insertion of the peptide at the interface between the hydrophobic core of the membrane and its polar headgroup region. Both coarse-grained and atomistic simulations confirm a before hypothesized snorkeling of lysine side chains for the membrane-bound state of the peptide K. Cholesterol was found to be enriched in peptide vicinity, which is probably of importance for the mechanism of membrane fusion. The applied sequential multiscale method, using coarse-grained simulations for the slow adsorption process of peptides to membranes followed by backward transformation to atomistic detail and subsequent atomistic simulations of the preformed peptide-lipid complexes, is shown to be a versatile approach to study the interactions of peptides or proteins with biomembranes.

Binding and Fusion of Extracellular Vesicles to the Plasma Membrane of Their Cell Targets.

PubMed

Prada, Ilaria; Meldolesi, Jacopo

2016-08-09

Exosomes and ectosomes, extracellular vesicles of two types generated by all cells at multivesicular bodies and the plasma membrane, respectively, play critical roles in physiology and pathology. A key mechanism of their function, analogous for both types of vesicles, is the fusion of their membrane to the plasma membrane of specific target cells, followed by discharge to the cytoplasm of their luminal cargo containing proteins, RNAs, and DNA. Here we summarize the present knowledge about the interactions, binding and fusions of vesicles with the cell plasma membrane. The sequence initiates with dynamic interactions, during which vesicles roll over the plasma membrane, followed by the binding of specific membrane proteins to their cell receptors. Membrane binding is then converted rapidly into fusion by mechanisms analogous to those of retroviruses. Specifically, proteins of the extracellular vesicle membranes are structurally rearranged, and their hydrophobic sequences insert into the target cell plasma membrane which undergoes lipid reorganization, protein restructuring and membrane dimpling. Single fusions are not the only process of vesicle/cell interactions. Upon intracellular reassembly of their luminal cargoes, vesicles can be regenerated, released and fused horizontally to other target cells. Fusions of extracellular vesicles are relevant also for specific therapy processes, now intensely investigated.

Simple method provides resolution of albumin, lipoprotein, free fraction, and chylomicron to enhance the utility of protein binding assays.

PubMed

Brockman, Adam H; Oller, Haley R; Moreau, Benoît; Kriksciukaite, Kristina; Bilodeau, Mark T

2015-02-12

Medicinal chemists have been encouraged in recent years to embrace high speed protein binding assays. These methods employ dialysis membranes in 96-well format or spin filters. Membrane-based methods do not separate lipoprotein binding from albumin binding and introduce interference despite membrane binding controls. Ultracentrifugation methods, in contrast, do not introduce interference if density gradients can be avoided and they resolve lipoprotein from albumin. A new generation of compact, fast ultracentrifuges facilitates the rapid and fully informative separation of plasma into albumin, albumin/fatty acid complex, lipoprotein, protein-free, and chylomicron fractions with no need of salt or sugar density gradients. We present a simple and fast ultracentrifuge method here for two platinum compounds and a taxane that otherwise bound irreversibly to dialysis membranes and which exhibited distinctive lipoprotein binding behaviors. This new generation of ultracentrifugation methods underscores a need to further discuss protein binding assessments as they relate to medicinal chemistry efforts.

Mixed bilayer containing dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylserine: lipid complexation, ion binding, and electrostatics.

PubMed

Pandit, Sagar A; Bostick, David; Berkowitz, Max L

2003-11-01

Two mixed bilayers containing dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylserine at a ratio of 5:1 are simulated in NaCl electrolyte solutions of different concentration using the molecular dynamics technique. Direct NH.O and CH.O hydrogen bonding between lipids was observed to serve as the basis of interlipid complexation. It is deduced from our results and previous studies that dipalmitoylphosphatidylcholine alone is less likely to form interlipid complexes than in the presence of bound ions or other bilayer "impurities" such as dipalmitoylphosphatidylserine. The binding of counterions is observed and quantitated. Based upon the calculated ion binding constants, the Gouy-Chapman surface potential (theta) is calculated. In addition we calculated the electrostatic potential profile (Phi) by twice integrating the system charge distribution. A large discrepancy between and the value of Phi at the membrane surface is observed. However, at "larger" distance from the bilayer surface, a qualitative similarity in the z-profiles of Phi and psi(GC) is seen. The discrepancy between the two potential profiles near the bilayer surface is attributed to the discrete and nonbulk-like nature of water in the interfacial region and to the complex geometry of this region.

Affinity-purified tetanus neurotoxin interaction with synaptic membranes: properties of a protease-sensitive receptor component

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lazarovici, P.; Yavin, E.

1986-11-04

The pharmacokinetic interaction of an affinity-purified /sup 125/I-labeled tetanotoxin fraction with guinea pig brain synaptosomal preparations was investigated. Binding of tetanotoxin was time- and temperature-dependent, was proportional to protein concentration, and was saturable at about 8 x 10/sup -9/ M as estimated by a solid-surface binding assay. Binding was optimal at pH 6.5 under low ionic strength buffer and was almost entirely blocked by gangliosides or antitoxin. In analogy to intact nerve cells, binding of toxin to membranes resulted in a tight association operationally defined as sequestration. Binding and sequestration were abolished after membrane pretreatment with sialidase. The enzyme couldmore » not dissociate the membrane-bound toxin formed at 4 or 37/sup 0/C under low ionic strength conditions, which is in part compatible with internalization as defined in nerve cell cultures. In the latter system the toxin could be removed at 4/sup 0/C but not at 37/sup 0/C. Binding was significantly reduced upon pretreatment of guinea pig brain membranes by a variety of hydrolytic enzymes. It is proposed that, in addition to a ganglioside, interaction of tetanotoxin with synaptic membranes is facilitated by a protein and may also require an appropriate lipid environment. These latter membrane constituents may play a pivotal role in the sequestration of the toxin.« less

Analysis of diffusion in curved surfaces and its application to tubular membranes.

PubMed

Klaus, Colin James Stockdale; Raghunathan, Krishnan; DiBenedetto, Emmanuele; Kenworthy, Anne K

2016-12-01

Diffusion of particles in curved surfaces is inherently complex compared with diffusion in a flat membrane, owing to the nonplanarity of the surface. The consequence of such nonplanar geometry on diffusion is poorly understood but is highly relevant in the case of cell membranes, which often adopt complex geometries. To address this question, we developed a new finite element approach to model diffusion on curved membrane surfaces based on solutions to Fick's law of diffusion and used this to study the effects of geometry on the entry of surface-bound particles into tubules by diffusion. We show that variations in tubule radius and length can distinctly alter diffusion gradients in tubules over biologically relevant timescales. In addition, we show that tubular structures tend to retain concentration gradients for a longer time compared with a comparable flat surface. These findings indicate that sorting of particles along the surfaces of tubules can arise simply as a geometric consequence of the curvature without any specific contribution from the membrane environment. Our studies provide a framework for modeling diffusion in curved surfaces and suggest that biological regulation can emerge purely from membrane geometry. © 2016 Klaus, Raghunathan, et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).

Binding of /sup 18/F by cell membranes and cell walls of Streptococcus mutans

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yotis, W.W.; Zeb, M.; McNulty, J.

1983-07-01

The binding of /sup 18/F to isolated cell membranes and cell walls of Streptococcus mutans GS-5 or other bacteria was assayed. The attachment of /sup 18/F to these cell envelopes proceeded slowly and reached equilibrium within 60 min. /sup 18/F binding was stimulated by Ca/sup 2 +/ (1 mM). The binding of /sup 18/F to cellular components was dependent upon the pH, as well as the amount of /sup 18/F and dose of the binder employed. The binding of /sup 18/F by cell walls prepared from fluoride-sensitive and fluoride-resistant cells of S. salivarius and S. mutans did not differ significantly.more » The pretreatment of cell walls or cell membranes for 60 min at 30 degrees C with 1 mg of RNase, DNase, or trypsin per ml did not influence the binding of /sup 18/F by the walls and membranes of S. mutans GS-5. However, prior exposure of cell membranes to sodium dodecyl sulfate caused a significant reduction in the number of /sup 18/F atoms bound by the membranes. In saturated assay systems, cell membranes of S. mutans GS-5 bound 10(15) to 10(16) atoms of /sup 18/F per mg (dry weight), whereas cell walls from S. mutans GS-5, FA-1, and HS-6 or Actinomyces viscosus T14V and T14AV bound 10(12) to 10(13) atoms of /sup 18/F per mg (dry weight). /sup 18/F in this quantity (10(12) to 10(13) atoms) cannot be detected with the fluoride electrode. The data provide, for the first time, a demonstration of /sup 18/F binding by cell membranes and walls of oral flora.« less

Allostery in a disordered protein: Oxidative modifications to α-Synuclein act distally to regulate membrane binding

PubMed Central

Sevcsik, Eva; Trexler, Adam J.; Dunn, Joanna M.; Rhoades, Elizabeth

2011-01-01

Both oxidative stress and aggregation of the protein α-synuclein (aS) have been implicated as key factors in the etiology of Parkinson’s disease. Specifically, oxidative modifications to aS disrupt its binding to lipid membranes, an interaction considered critical to its native function. Here we seek to provide a mechanistic explanation for this phenomenon by investigating the effects of oxidative nitration of tyrosine residues on the structure of aS and its interaction with lipid membranes. Membrane binding is mediated by the first ~95 residues of aS. We find that nitration of the single tyrosine (Y39) in this domain disrupts binding due to electrostatic repulsion. Moreover, we observe that nitration of the three tyrosines (Y125/133/136) in the C-terminal domain is equally effective in perturbing binding, an intriguing result given that the C-terminus is not thought to interact directly with membranes. Our investigations show that tyrosine nitration results in a change of the conformational states populated by aS in solution, with the most prominent changes occurring in the C-terminal region. These results lead us to suggest that nitration of Y125/133/136 reduces the membrane binding affinity of aS through allosteric coupling by altering the ensemble of conformational states and depopulating those capable of membrane binding. While allostery is a well-established concept for structured proteins, it has only recently been discussed in the context of disordered proteins. We propose that allosteric regulation through modification of specific residues in, or ligand binding to, the C-terminus may even be a general mechanism for modulating aS function. PMID:21491910

The Tip of the Four N-Terminal α-Helices of Clostridium sordellii Lethal Toxin Contains the Interaction Site with Membrane Phosphatidylserine Facilitating Small GTPases Glucosylation

PubMed Central

Varela Chavez, Carolina; Haustant, Georges Michel; Baron, Bruno; England, Patrick; Chenal, Alexandre; Pauillac, Serge; Blondel, Arnaud; Popoff, Michel-Robert

2016-01-01

Clostridium sordellii lethal toxin (TcsL) is a powerful virulence factor responsible for severe toxic shock in man and animals. TcsL belongs to the large clostridial glucosylating toxin (LCGT) family which inactivates small GTPases by glucosylation with uridine-diphosphate (UDP)-glucose as a cofactor. Notably, TcsL modifies Rac and Ras GTPases, leading to drastic alteration of the actin cytoskeleton and cell viability. TcsL enters cells via receptor-mediated endocytosis and delivers the N-terminal glucosylating domain (TcsL-cat) into the cytosol. TcsL-cat was found to preferentially bind to phosphatidylserine (PS)-containing membranes and to increase the glucosylation of Rac anchored to the lipid membrane. We have previously reported that the N-terminal four helical bundle structure (1–93 domain) recognizes a broad range of lipids, but that TcsL-cat specifically binds to PS and phosphatidic acid. Here, we show using mutagenesis that the PS binding site is localized on the tip of the four-helix bundle which is rich in positively-charged amino acids. Residues Y14, V15, F17, and R18 on loop 1, between helices 1 and 2, in coordination with R68 from loop 3, between helices 3 and 4, form a pocket which accommodates L-serine. The functional PS-binding site is required for TcsL-cat binding to the plasma membrane and subsequent cytotoxicity. TcsL-cat binding to PS facilitates a high enzymatic activity towards membrane-anchored Ras by about three orders of magnitude as compared to Ras in solution. The PS-binding site is conserved in LCGTs, which likely retain a common mechanism of binding to the membrane for their full activity towards membrane-bound GTPases. PMID:27023605

Membrane interaction of the N-terminal domain of chemokine receptor CXCR1.

PubMed

Haldar, Sourav; Raghuraman, H; Namani, Trishool; Rajarathnam, Krishna; Chattopadhyay, Amitabha

2010-06-01

The N-terminal domain of chemokine receptors constitutes one of the two critical ligand binding sites, and plays important roles by mediating binding affinity, receptor selectivity, and regulating function. In this work, we monitored the organization and dynamics of a 34-mer peptide of the CXC chemokine receptor 1 (CXCR1) N-terminal domain and its interaction with membranes by utilizing a combination of fluorescence-based approaches and surface pressure measurements. Our results show that the CXCR1 N-domain 34-mer peptide binds vesicles of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and upon binding, the tryptophan residues of the peptide experience motional restriction and exhibit red edge excitation shift (REES) of 19nm. These results are further supported by increase in fluorescence anisotropy and mean fluorescence lifetime upon membrane binding. These results constitute one of the first reports demonstrating membrane interaction of the N-terminal domain of CXCR1 and gain relevance in the context of the emerging role of cellular membranes in chemokine signaling.

MFP1 is a thylakoid-associated, nucleoid-binding protein with a coiled-coil structure

PubMed Central

Jeong, Sun Yong; Rose, Annkatrin; Meier, Iris

2003-01-01

Plastid DNA, like bacterial and mitochondrial DNA, is organized into protein–DNA complexes called nucleoids. Plastid nucleoids are believed to be associated with the inner envelope in developing plastids and the thylakoid membranes in mature chloroplasts, but the mechanism for this re-localization is unknown. Here, we present the further characterization of the coiled-coil DNA-binding protein MFP1 as a protein associated with nucleoids and with the thylakoid membranes in mature chloroplasts. MFP1 is located in plastids in both suspension culture cells and leaves and is attached to the thylakoid membranes with its C-terminal DNA-binding domain oriented towards the stroma. It has a major DNA-binding activity in mature Arabidopsis chloroplasts and binds to all tested chloroplast DNA fragments without detectable sequence specificity. Its expression is tightly correlated with the accumulation of thylakoid membranes. Importantly, it is associated in vivo with nucleoids, suggesting a function for MFP1 at the interface between chloroplast nucleoids and the developing thylakoid membrane system. PMID:12930969

Membrane tension controls the assembly of curvature-generating proteins

PubMed Central

Simunovic, Mijo; Voth, Gregory A.

2015-01-01

Proteins containing a Bin/Amphiphysin/Rvs (BAR) domain regulate membrane curvature in the cell. Recent simulations have revealed that BAR proteins assemble into linear aggregates, strongly affecting membrane curvature and its in-plane stress profile. Here, we explore the opposite question: do mechanical properties of the membrane impact protein association? By using coarse-grained molecular dynamics simulations, we show that increased surface tension significantly impacts the dynamics of protein assembly. While tensionless membranes promote a rapid formation of long-living linear aggregates of N-BAR proteins, increase in tension alters the geometry of protein association. At high tension, protein interactions are strongly inhibited. Increasing surface density of proteins leads to a wider range of protein association geometries, promoting the formation of meshes, which can be broken apart with membrane tension. Our work indicates that surface tension may play a key role in recruiting proteins to membrane-remodelling sites in the cell. PMID:26008710

Synthesis of an un-supported, high-flow ZSM-22 zeolite membrane

DOEpatents

Thoma, Steven G [Albuquerque, NM; Nenoff, Tina M [Albuquerque, NM

2006-10-10

Novel methods for synthesizing wholly un-supported, high-flow catalytic membranes consisting of 100% crystalline ZSM-22 crystals with no binder phase, having sufficient porosity to allow high Weight Hourly Space Velocities of feedstock to pass through without generating back pressure. The ZSM-22 membranes perform favorably to existing bulk ZSM-22 catalysts (e.g., via 1-butene conversion and selectivity). The method of membrane synthesis, based on Vapor Phase Transport, allows free-standing, binder-less membranes to be fabricated in varied geometries and sizes so that membranes can be tailor-made for particular geometries applications. The ZSM-22 precursor gel may be consolidated into a semi-cohesive body prior to vapor phase crystallization, for example, by uniaxial pressing. These crystalline membranes may be modified by ion exchange, pore ion exchange, framework exchange, synthesis modification techniques to incorporate other elements into the framework, such as K, H, Mg, Zn, V, Ga, and Pt.

Anchoring antibodies to membranes using a diphtheria toxin T domain-ZZ fusion protein as a pH sensitive membrane anchor.

PubMed

Nizard, P; Liger, D; Gaillard, C; Gillet, D

1998-08-14

We have constructed a fusion protein, T-ZZ, in which the IgG-Fc binding protein ZZ was fused to the C-terminus of the diphtheria toxin transmembrane domain (T domain). While soluble at neutral pH, T-ZZ retained the capacity of the T domain to bind to phospholipid membranes at acidic pH. Once anchored to the membrane, the ZZ part of the protein was capable of binding mouse monoclonal or rabbit polyclonal IgG. Our results show that the T-ZZ protein can function as a pH sensitive membrane anchor for the linkage of IgG to the membrane of lipid vesicles, adherent and non-adherent cells.

Membrane Binding of HIV-1 Matrix Protein: Dependence on Bilayer Composition and Protein Lipidation

PubMed Central

Barros, Marilia; Nanda, Hirsh

2016-01-01

ABSTRACT By assembling in a protein lattice on the host's plasma membrane, the retroviral Gag polyprotein triggers formation of the viral protein/membrane shell. The MA domain of Gag employs multiple signals—electrostatic, hydrophobic, and lipid-specific—to bring the protein to the plasma membrane, thereby complementing protein-protein interactions, located in full-length Gag, in lattice formation. We report the interaction of myristoylated and unmyristoylated HIV-1 Gag MA domains with bilayers composed of purified lipid components to dissect these complex membrane signals and quantify their contributions to the overall interaction. Surface plasmon resonance on well-defined planar membrane models is used to quantify binding affinities and amounts of protein and yields free binding energy contributions, ΔG, of the various signals. Charge-charge interactions in the absence of the phosphatidylinositide PI(4,5)P2 attract the protein to acidic membrane surfaces, and myristoylation increases the affinity by a factor of 10; thus, our data do not provide evidence for a PI(4,5)P2 trigger of myristate exposure. Lipid-specific interactions with PI(4,5)P2, the major signal lipid in the inner plasma membrane, increase membrane attraction at a level similar to that of protein lipidation. While cholesterol does not directly engage in interactions, it augments protein affinity strongly by facilitating efficient myristate insertion and PI(4,5)P2 binding. We thus observe that the isolated MA protein, in the absence of protein-protein interaction conferred by the full-length Gag, binds the membrane with submicromolar affinities. IMPORTANCE Like other retroviral species, the Gag polyprotein of HIV-1 contains three major domains: the N-terminal, myristoylated MA domain that targets the protein to the plasma membrane of the host; a central capsid-forming domain; and the C-terminal, genome-binding nucleocapsid domain. These domains act in concert to condense Gag into a membrane-bounded protein lattice that recruits genomic RNA into the virus and forms the shell of a budding immature viral capsid. In binding studies of HIV-1 Gag MA to model membranes with well-controlled lipid composition, we dissect the multiple interactions of the MA domain with its target membrane. This results in a detailed understanding of the thermodynamic aspects that determine membrane association, preferential lipid recruitment to the viral shell, and those aspects of Gag assembly into the membrane-bound protein lattice that are determined by MA. PMID:26912608

Analysis of Ethylene Receptors: Ethylene-Binding Assays.

PubMed

Binder, Brad M; Schaller, G Eric

2017-01-01

Plant ethylene receptors bind ethylene with high affinity. Most of the characterization of ethylene binding to the receptors has been carried out using a radioligand-binding assay on functional receptors expressed in yeast. In this chapter, we describe methods for expressing ethylene receptors in yeast and conducting ethylene-binding assays on intact yeast and yeast membranes. The ethylene-binding assays can be modified to analyze ethylene binding to intact plants and other organisms as well as membranes isolated from any biological source.

Topographical analysis of the plasma membrane-associated sucrose binding protein from soybean.

PubMed

Overvoorde, P J; Grimes, H D

1994-05-27

Plasma membranes of soybean cells actively engaged in sucrose transport have a sucrose binding protein (SBP) that does not appear to be an integral membrane protein. Experiments were undertaken to analyze the topographical association of this protein with the membrane. Treatment of purified plasma membrane vesicles with either 1 M KCl or KI released less than 35% of the sucrose binding protein from the membrane whereas treatment with either 4 M urea or 0.1 M Na2CO3, pH 11.5, disassociated between 50 and 70%, respectively, of this protein from the membrane. SDS, at either 0.5x, 1x, or 10x of its critical micelle concentration, effectively solubilized the sucrose binding protein. The nonionic detergents Triton X-100 and CHAPS, at either 0.5x, 1x, or 10x of their critical micelle concentration, solubilized between 65 and 75% of this protein. When either native plasma membrane-associated or in vitro-transcribed and -translated SBP were subjected to Triton X-114 phase separation, 80% partitioned into the detergent-poor aqueous phase. These results indicate that the SBP is a peripheral membrane protein but also suggest that there is a population of this protein that is tethered to the membrane.

Binding of anti-basement membrane antibody to alveolar basement membrane after intratracheal gasoline instillation in rabbits.

PubMed Central

Yamamoto, T.; Wilson, C. B.

1987-01-01

A possible causal relationship has been suggested between hydrocarbon (gasoline, solvents, etc.) exposure and development of anti-basement membrane antibody-associated Goodpasture's syndrome in man. The authors evaluated the effect of hydrocarbons on pulmonary capillary permeability and binding of heterologous anti-basement membrane antibodies in the lungs after intratracheal instillation of minute amounts of unleaded gasoline into rabbits. The anti-glomerular basement membrane (GBM) antibodies used reacted with the alveolar basement membrane (ABM) in vitro by indirect immunofluorescence. The gasoline treatment altered pulmonary capillary permeability, judging from the increased accumulation of systemically administered radioiodinated bovine serum albumin in the alveolar and extravascular spaces of lungs; it also induced focal macroscopic and microscopic pulmonary histologic lesions. The gasoline caused focal in vivo binding of the anti-GBM antibodies to the ABM detectable by immunofluorescence microscopy. No binding was observed in lungs from control rabbits given saline instillations when assayed by immunofluorescence. The paired label radioisotope technique confirmed the increased antibody binding to lungs injured with gasoline (1.08 +/- 0.03 micrograms) versus 0.37 +/- 0.07 microgram after saline (P less than 0.001). These results indicate that gasoline exposure damages a pulmonary barrier that normally prevents binding of anti-GBM/ABM antibody to ABM and suggest that hydrocarbon exposure may be one of perhaps several pneumotoxic events that contribute to the episodic pulmonary hemorrhage in Goodpasture's syndrome by temporarily allowing ABM binding of anti-basement membrane antibodies. Images Figure 1 Figure 2 Figure 3 Figure 4 PMID:3548409

Structural basis of RND-type multidrug exporters

PubMed Central

Yamaguchi, Akihito; Nakashima, Ryosuke; Sakurai, Keisuke

2015-01-01

Bacterial multidrug exporters are intrinsic membrane transporters that act as cellular self-defense mechanism. The most notable characteristics of multidrug exporters is that they export a wide range of drugs and toxic compounds. The overexpression of these exporters causes multidrug resistance. Multidrug-resistant pathogens have become a serious problem in modern chemotherapy. Over the past decade, investigations into the structure of bacterial multidrug exporters have revealed the multidrug recognition and export mechanisms. In this review, we primarily discuss RND-type multidrug exporters particularly AcrAB-TolC, major drug exporter in Gram-negative bacteria. RND-type drug exporters are tripartite complexes comprising a cell membrane transporter, an outer membrane channel and an adaptor protein. Cell membrane transporters and outer membrane channels are homo-trimers; however, there is no consensus on the number of adaptor proteins in these tripartite complexes. The three monomers of a cell membrane transporter have varying conformations (access, binding, and extrusion) during transport. Drugs are exported following an ordered conformational change in these three monomers, through a functional rotation mechanism coupled with the proton relay cycle in ion pairs, which is driven by proton translocation. Multidrug recognition is based on a multisite drug-binding mechanism, in which two voluminous multidrug-binding pockets in cell membrane exporters recognize a wide range of substrates as a result of permutations at numerous binding sites that are specific for the partial structures of substrate molecules. The voluminous multidrug-binding pocket may have numerous binding sites even for a single substrate, suggesting that substrates may move between binding sites during transport, an idea named as multisite-drug-oscillation hypothesis. This hypothesis is consistent with the apparently broad substrate specificity of cell membrane exporters and their highly efficient ejection of drugs from the cell. Substrates are transported through dual multidrug-binding pockets via the peristaltic motion of the substrate translocation channel. Although there are no clinically available inhibitors of bacterial multidrug exporters, efforts to develop inhibitors based on structural information are underway. PMID:25941524

Structural basis of RND-type multidrug exporters.

PubMed

Yamaguchi, Akihito; Nakashima, Ryosuke; Sakurai, Keisuke

2015-01-01

Bacterial multidrug exporters are intrinsic membrane transporters that act as cellular self-defense mechanism. The most notable characteristics of multidrug exporters is that they export a wide range of drugs and toxic compounds. The overexpression of these exporters causes multidrug resistance. Multidrug-resistant pathogens have become a serious problem in modern chemotherapy. Over the past decade, investigations into the structure of bacterial multidrug exporters have revealed the multidrug recognition and export mechanisms. In this review, we primarily discuss RND-type multidrug exporters particularly AcrAB-TolC, major drug exporter in Gram-negative bacteria. RND-type drug exporters are tripartite complexes comprising a cell membrane transporter, an outer membrane channel and an adaptor protein. Cell membrane transporters and outer membrane channels are homo-trimers; however, there is no consensus on the number of adaptor proteins in these tripartite complexes. The three monomers of a cell membrane transporter have varying conformations (access, binding, and extrusion) during transport. Drugs are exported following an ordered conformational change in these three monomers, through a functional rotation mechanism coupled with the proton relay cycle in ion pairs, which is driven by proton translocation. Multidrug recognition is based on a multisite drug-binding mechanism, in which two voluminous multidrug-binding pockets in cell membrane exporters recognize a wide range of substrates as a result of permutations at numerous binding sites that are specific for the partial structures of substrate molecules. The voluminous multidrug-binding pocket may have numerous binding sites even for a single substrate, suggesting that substrates may move between binding sites during transport, an idea named as multisite-drug-oscillation hypothesis. This hypothesis is consistent with the apparently broad substrate specificity of cell membrane exporters and their highly efficient ejection of drugs from the cell. Substrates are transported through dual multidrug-binding pockets via the peristaltic motion of the substrate translocation channel. Although there are no clinically available inhibitors of bacterial multidrug exporters, efforts to develop inhibitors based on structural information are underway.

Determination of the State of Strain of Large Floating Covers Using Unmanned Aerial Vehicle (UAV) Aided Photogrammetry

PubMed Central

Ong, Wern Hann; Chiu, Wing Kong; Kuen, Thomas; Kodikara, Jayantha

2017-01-01

Floating covers used in waste water treatment plants are one of the many structures formed with membrane materials. These structures are usually large and can spread over an area measuring 470 m × 170 m. The aim of this paper is to describe recent work to develop an innovative and effective approach for structural health monitoring (SHM) of such large membrane-like infrastructure. This paper will propose a potentially cost-effective non-contact approach for full-field strain and stress mapping using an unmanned aerial vehicle (UAV) mounted with a digital camera and a global positioning system (GPS) tracker. The aim is to use the images acquired by the UAV to define the geometry of the floating cover using photogrammetry. In this manner, any changes in the geometry of the floating cover due to forces acting beneath resulting from its deployment and usage can be determined. The time-scale for these changes is in terms of weeks and months. The change in the geometry can be implemented as input conditions to a finite element model (FEM) for stress prediction. This will facilitate the determination of the state of distress of the floating cover. This paper investigates the possibility of using data recorded from a UAV to predict the strain level and assess the health of such structures. An investigation was first conducted on a laboratory sized membrane structure instrumented with strain gauges for comparison against strains, which were computed from 3D scans of the membrane geometry. Upon validating the technique in the laboratory, it was applied to a more realistic scenario: an outdoor test membrane structure and capable UAV were constructed to see if the shape of the membrane could be computed. The membrane displacements were then used to calculate the membrane stress and strain, state demonstrating a new way to perform structural health monitoring on membrane structures. PMID:28788081

Determination of the State of Strain of Large Floating Covers Using Unmanned Aerial Vehicle (UAV) Aided Photogrammetry.

PubMed

Ong, Wern Hann; Chiu, Wing Kong; Kuen, Thomas; Kodikara, Jayantha

2017-07-28

Floating covers used in waste water treatment plants are one of the many structures formed with membrane materials. These structures are usually large and can spread over an area measuring 470 m × 170 m. The aim of this paper is to describe recent work to develop an innovative and effective approach for structural health monitoring (SHM) of such large membrane-like infrastructure. This paper will propose a potentially cost-effective non-contact approach for full-field strain and stress mapping using an unmanned aerial vehicle (UAV) mounted with a digital camera and a global positioning system (GPS) tracker. The aim is to use the images acquired by the UAV to define the geometry of the floating cover using photogrammetry. In this manner, any changes in the geometry of the floating cover due to forces acting beneath resulting from its deployment and usage can be determined. The time-scale for these changes is in terms of weeks and months. The change in the geometry can be implemented as input conditions to a finite element model (FEM) for stress prediction. This will facilitate the determination of the state of distress of the floating cover. This paper investigates the possibility of using data recorded from a UAV to predict the strain level and assess the health of such structures. An investigation was first conducted on a laboratory sized membrane structure instrumented with strain gauges for comparison against strains, which were computed from 3D scans of the membrane geometry. Upon validating the technique in the laboratory, it was applied to a more realistic scenario: an outdoor test membrane structure and capable UAV were constructed to see if the shape of the membrane could be computed. The membrane displacements were then used to calculate the membrane stress and strain, state demonstrating a new way to perform structural health monitoring on membrane structures.

The Adipophilin C Terminus Is a Self-folding Membrane-binding Domain That Is Important for Milk Lipid Secretion*

PubMed Central

Chong, Brandi M.; Russell, Tanya D.; Schaack, Jerome; Orlicky, David J.; Reigan, Philip; Ladinsky, Mark; McManaman, James L.

2011-01-01

Cytoplasmic lipid droplets (CLD) in mammary epithelial cells undergo secretion by a unique membrane envelopment process to produce milk lipids. Adipophilin (ADPH/Plin2), a member of the perilipin/PAT family of lipid droplet-associated proteins, is hypothesized to mediate CLD secretion through interactions with apical plasma membrane elements. We found that the secretion of CLD coated by truncated ADPH lacking the C-terminal region encoding a putative four-helix bundle structure was impaired relative to that of CLD coated by full-length ADPH. We used homology modeling and analyses of the solution and membrane binding properties of purified recombinant ADPH C terminus to understand how this region possibly mediates CLD secretion. Homology modeling supports the concept that the ADPH C terminus forms a four-helix bundle motif and suggests that this structure can form stable membrane bilayer interactions. Circular dichroism and protease mapping studies confirmed that the ADPH C terminus is an independently folding α-helical structure that is relatively resistant to urea denaturation. Liposome binding studies showed that the purified C terminus binds to phospholipid membranes through electrostatic dependent interactions, and cell culture studies documented that it localizes to the plasma membrane. Collectively, these data provide direct evidence that the ADPH C terminus forms a stable membrane binding helical structure that is important for CLD secretion. We speculate that interactions between the four-helix bundle of ADPH and membrane phospholipids may be an initial step in milk lipid secretion. PMID:21383012

Membrane proteins bind lipids selectively to modulate their structure and function.

PubMed

Laganowsky, Arthur; Reading, Eamonn; Allison, Timothy M; Ulmschneider, Martin B; Degiacomi, Matteo T; Baldwin, Andrew J; Robinson, Carol V

2014-06-05

Previous studies have established that the folding, structure and function of membrane proteins are influenced by their lipid environments and that lipids can bind to specific sites, for example, in potassium channels. Fundamental questions remain however regarding the extent of membrane protein selectivity towards lipids. Here we report a mass spectrometry approach designed to determine the selectivity of lipid binding to membrane protein complexes. We investigate the mechanosensitive channel of large conductance (MscL) from Mycobacterium tuberculosis and aquaporin Z (AqpZ) and the ammonia channel (AmtB) from Escherichia coli, using ion mobility mass spectrometry (IM-MS), which reports gas-phase collision cross-sections. We demonstrate that folded conformations of membrane protein complexes can exist in the gas phase. By resolving lipid-bound states, we then rank bound lipids on the basis of their ability to resist gas phase unfolding and thereby stabilize membrane protein structure. Lipids bind non-selectively and with high avidity to MscL, all imparting comparable stability; however, the highest-ranking lipid is phosphatidylinositol phosphate, in line with its proposed functional role in mechanosensation. AqpZ is also stabilized by many lipids, with cardiolipin imparting the most significant resistance to unfolding. Subsequently, through functional assays we show that cardiolipin modulates AqpZ function. Similar experiments identify AmtB as being highly selective for phosphatidylglycerol, prompting us to obtain an X-ray structure in this lipid membrane-like environment. The 2.3 Å resolution structure, when compared with others obtained without lipid bound, reveals distinct conformational changes that re-position AmtB residues to interact with the lipid bilayer. Our results demonstrate that resistance to unfolding correlates with specific lipid-binding events, enabling a distinction to be made between lipids that merely bind from those that modulate membrane protein structure and/or function. We anticipate that these findings will be important not only for defining the selectivity of membrane proteins towards lipids, but also for understanding the role of lipids in modulating protein function or drug binding.

STARD4 Membrane Interactions and Sterol Binding

PubMed Central

2016-01-01

The steroidogenic acute regulatory protein-related lipid transfer (START) domain family is defined by a conserved 210-amino acid sequence that folds into an α/β helix-grip structure. Members of this protein family bind a variety of ligands, including cholesterol, phospholipids, sphingolipids, and bile acids, with putative roles in nonvesicular lipid transport, metabolism, and cell signaling. Among the soluble START proteins, STARD4 is expressed in most tissues and has previously been shown to transfer sterol, but the molecular mechanisms of membrane interaction and sterol binding remain unclear. In this work, we use biochemical techniques to characterize regions of STARD4 and determine their role in membrane interaction and sterol binding. Our results show that STARD4 interacts with anionic membranes through a surface-exposed basic patch and that introducing a mutation (L124D) into the Omega-1 (Ω1) loop, which covers the sterol binding pocket, attenuates sterol transfer activity. To gain insight into the attenuating mechanism of the L124D mutation, we conducted structural and biophysical studies of wild-type and L124D STARD4. These studies show that the L124D mutation reduces the conformational flexibility of the protein, resulting in a diminished level of membrane interaction and sterol transfer. These studies also reveal that the C-terminal α-helix, and not the Ω1 loop, partitions into the membrane bilayer. On the basis of these observations, we propose a model of STARD4 membrane interaction and sterol binding and release that requires dynamic movement of both the Ω1 loop and membrane insertion of the C-terminal α-helix. PMID:26168008

3D hydrophobic moment vectors as a tool to characterize the surface polarity of amphiphilic peptides.

PubMed

Reißer, Sabine; Strandberg, Erik; Steinbrecher, Thomas; Ulrich, Anne S

2014-06-03

The interaction of membranes with peptides and proteins is largely determined by their amphiphilic character. Hydrophobic moments of helical segments are commonly derived from their two-dimensional helical wheel projections, and the same is true for β-sheets. However, to the best of our knowledge, there exists no method to describe structures in three dimensions or molecules with irregular shape. Here, we define the hydrophobic moment of a molecule as a vector in three dimensions by evaluating the surface distribution of all hydrophilic and lipophilic regions over any given shape. The electrostatic potential on the molecular surface is calculated based on the atomic point charges. The resulting hydrophobic moment vector is specific for the instantaneous conformation, and it takes into account all structural characteristics of the molecule, e.g., partial unfolding, bending, and side-chain torsion angles. Extended all-atom molecular dynamics simulations are then used to calculate the equilibrium hydrophobic moments for two antimicrobial peptides, gramicidin S and PGLa, under different conditions. We show that their effective hydrophobic moment vectors reflect the distribution of polar and nonpolar patches on the molecular surface and the calculated electrostatic surface potential. A comparison of simulations in solution and in lipid membranes shows how the peptides undergo internal conformational rearrangement upon binding to the bilayer surface. A good correlation with solid-state NMR data indicates that the hydrophobic moment vector can be used to predict the membrane binding geometry of peptides. This method is available as a web application on http://www.ibg.kit.edu/HM/. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Cooperative binding of Annexin A5 to phosphatidylserine on apoptotic cell membranes

NASA Astrophysics Data System (ADS)

Janko, Christina; Jeremic, Ivica; Biermann, Mona; Chaurio, Ricardo; Schorn, Christine; Muñoz, Luis E.; Herrmann, Martin

2013-12-01

Healthy cells exhibit an asymmetric plasma membrane with phosphatidylserine (PS) located on the cytoplasmic leaflet of the plasma membrane bilayer. Annexin A5-FITC, a PS binding protein, is commonly used to evaluate apoptosis in flow cytometry. PS exposed by apoptotic cells serves as a major ‘eat-me’ signal for phagocytes. Although exposition of PS has been observed after alternative stimuli, no clearance of viable, PS exposing cells has been detected. Thus, besides PS exposure, membranes of viable and apoptotic cells might exhibit specific characteristics. Here, we show that Annexin A5 binds in a cooperative manner to different types of dead cells. Shrunken apoptotic cells thereby showed the highest Hill coefficient values. Contrarily, parafomaldehyde fixation of apoptotic cells completely abrogates the cooperativity effect seen with dead and dying cells. We tend to speculate that the cooperative binding of Annexin A5 to the membranes of apoptotic cells reflects higher fluidity of the exposed membranes facilitating PS clustering.

Membrane Stored Curvature Elastic Stress Modulates Recruitment of Maintenance Proteins PspA and Vipp1

PubMed Central

McDonald, Christopher; Jovanovic, Goran; Ces, Oscar

2015-01-01

ABSTRACT Phage shock protein A (PspA), which is responsible for maintaining inner membrane integrity under stress in enterobacteria, and vesicle-inducting protein in plastids 1 (Vipp1), which functions for membrane maintenance and thylakoid biogenesis in cyanobacteria and plants, are similar peripheral membrane-binding proteins. Their homologous N-terminal amphipathic helices are required for membrane binding; however, the membrane features recognized and required for expressing their functionalities have remained largely uncharacterized. Rigorously controlled, in vitro methodologies with lipid vesicles and purified proteins were used in this study and provided the first biochemical and biophysical characterizations of membrane binding by PspA and Vipp1. Both proteins are found to sense stored curvature elastic (SCE) stress and anionic lipids within the membrane. PspA has an enhanced sensitivity for SCE stress and a higher affinity for the membrane than Vipp1. These variations in binding may be crucial for some of the proteins’ differing roles in vivo. Assays probing the transcriptional regulatory function of PspA in the presence of vesicles showed that a relief of transcription inhibition occurs in an SCE stress-specific manner. This in vitro recapitulation of membrane stress-dependent transcription control suggests that the Psp response may be mounted in vivo when a cell’s inner membrane experiences increased SCE stress. PMID:26330516

Binding of canonical Wnt ligands to their receptor complexes occurs in ordered plasma membrane environments.

PubMed

Sezgin, Erdinc; Azbazdar, Yagmur; Ng, Xue W; Teh, Cathleen; Simons, Kai; Weidinger, Gilbert; Wohland, Thorsten; Eggeling, Christian; Ozhan, Gunes

2017-08-01

While the cytosolic events of Wnt/β-catenin signaling (canonical Wnt signaling) pathway have been widely studied, only little is known about the molecular mechanisms involved in Wnt binding to its receptors at the plasma membrane. Here, we reveal the influence of the immediate plasma membrane environment on the canonical Wnt-receptor interaction. While the receptors are distributed both in ordered and disordered environments, Wnt binding to its receptors selectively occurs in more ordered membrane environments which appear to cointernalize with the Wnt-receptor complex. Moreover, Wnt/β-catenin signaling is significantly reduced when the membrane order is disturbed by specific inhibitors of certain lipids that prefer to localize at the ordered environments. Similarly, a reduction in Wnt signaling activity is observed in Niemann-Pick Type C disease cells where trafficking of ordered membrane lipid components to the plasma membrane is genetically impaired. We thus conclude that ordered plasma membrane environments are essential for binding of canonical Wnts to their receptor complexes and downstream signaling activity. © 2017 The Authors. The FEBS Journal published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.

Salt Bridge Formation between the I-BAR Domain and Lipids Increases Lipid Density and Membrane Curvature.

PubMed

Takemura, Kazuhiro; Hanawa-Suetsugu, Kyoko; Suetsugu, Shiro; Kitao, Akio

2017-07-28

The BAR domain superfamily proteins sense or induce curvature in membranes. The inverse-BAR domain (I-BAR) is a BAR domain that forms a straight "zeppelin-shaped" dimer. The mechanisms by which IRSp53 I-BAR binds to and deforms a lipid membrane are investigated here by all-atom molecular dynamics simulation (MD), binding energy analysis, and the effects of mutation experiments on filopodia on HeLa cells. I-BAR adopts a curved structure when crystallized, but adopts a flatter shape in MD. The binding of I-BAR to membrane was stabilized by ~30 salt bridges, consistent with experiments showing that point mutations of the interface residues have little effect on the binding affinity whereas multiple mutations have considerable effect. Salt bridge formation increases the local density of lipids and deforms the membrane into a concave shape. In addition, the point mutations that break key intra-molecular salt bridges within I-BAR reduce the binding affinity; this was confirmed by expressing these mutants in HeLa cells and observing their effects. The results indicate that the stiffness of I-BAR is important for membrane deformation, although I-BAR does not act as a completely rigid template.

Interaction between two adapter proteins, PAG and EBP50: a possible link between membrane rafts and actin cytoskeleton.

PubMed

Brdicková, N; Brdicka, T; Andera, L; Spicka, J; Angelisová, P; Milgram, S L; Horejsí, V

2001-10-26

Phosphoprotein associated with GEMs (PAG), also known as Csk-binding protein (Cbp), is a broadly expressed palmitoylated transmembrane adapter protein found in membrane rafts, also called GEMs (glycosphingolipid-enriched membrane microdomains). PAG is known to bind and activate the essential regulator of Src-family kinases, cytoplasmic protein tyrosine kinase Csk. In the present study we used the yeast 2-hybrid system to search for additional proteins which might bind to PAG. We have identified the abundant cytoplasmic adapter protein EBP50 (ezrin/radixin/moesin (ERM)-binding phosphoprotein of 50 kDa), also known as NHERF (Na(+)/H(+) exchanger regulatory factor), as a specific PAG-binding partner. The interaction involves the C-terminal sequence (TRL) of PAG and N-terminal PDZ domain(s) of EBP50. As EBP50 is known to interact via its C-terminal domain with the ERM-family proteins, which in turn bind to actin cytoskeleton, the PAG-EBP50 interaction may be important for connecting membrane rafts to the actin cytoskeleton.

cAMP regulates DEP domain-mediated binding of the guanine nucleotide exchange factor Epac1 to phosphatidic acid at the plasma membrane.

PubMed

Consonni, Sarah V; Gloerich, Martijn; Spanjaard, Emma; Bos, Johannes L

2012-03-06

Epac1 is a cAMP-regulated guanine nucleotide exchange factor for the small G protein Rap. Upon cAMP binding, Epac1 undergoes a conformational change that results in its release from autoinhibition. In addition, cAMP induces the translocation of Epac1 from the cytosol to the plasma membrane. This relocalization of Epac1 is required for efficient activation of plasma membrane-located Rap and for cAMP-induced cell adhesion. This translocation requires the Dishevelled, Egl-10, Pleckstrin (DEP) domain, but the molecular entity that serves as the plasma membrane anchor and the possible mechanism of regulated binding remains elusive. Here we show that Epac1 binds directly to phosphatidic acid. Similar to the cAMP-induced Epac1 translocation, this binding is regulated by cAMP and requires the DEP domain. Furthermore, depletion of phosphatidic acid by inhibition of phospholipase D1 prevents cAMP-induced translocation of Epac1 as well as the subsequent activation of Rap at the plasma membrane. Finally, mutation of a single basic residue within a polybasic stretch of the DEP domain, which abolishes translocation, also prevents binding to phosphatidic acid. From these results we conclude that cAMP induces a conformational change in Epac1 that enables DEP domain-mediated binding to phosphatidic acid, resulting in the tethering of Epac1 at the plasma membrane and subsequent activation of Rap.

Time-resolved multimodal analysis of Src Homology 2 (SH2) domain binding in signaling by receptor tyrosine kinases.

PubMed

Jadwin, Joshua A; Oh, Dongmyung; Curran, Timothy G; Ogiue-Ikeda, Mari; Jia, Lin; White, Forest M; Machida, Kazuya; Yu, Ji; Mayer, Bruce J

2016-04-12

While the affinities and specificities of SH2 domain-phosphotyrosine interactions have been well characterized, spatio-temporal changes in phosphosite availability in response to signals, and their impact on recruitment of SH2-containing proteins in vivo, are not well understood. To address this issue, we used three complementary experimental approaches to monitor phosphorylation and SH2 binding in human A431 cells stimulated with epidermal growth factor (EGF): 1) phospho-specific mass spectrometry; 2) far-Western blotting; and 3) live cell single-molecule imaging of SH2 membrane recruitment. Far-Western and MS analyses identified both well-established and previously undocumented EGF-dependent tyrosine phosphorylation and binding events, as well as dynamic changes in binding patterns over time. In comparing SH2 binding site phosphorylation with SH2 domain membrane recruitment in living cells, we found in vivo binding to be much slower. Delayed SH2 domain recruitment correlated with clustering of SH2 domain binding sites on the membrane, consistent with membrane retention via SH2 rebinding.

Cd-binding to model membranes

NASA Astrophysics Data System (ADS)

Geszner, R.; Saibene, S.; Butz, T.; Lerf, A.

1990-08-01

The binding of Cd2+ to the model membranes Di-myristoyl L-α-phosphatidic acid (DMPA) and Di-myristoyl L-α-phosphatidylcholine (DMPC) was studied by time differential perturbed angular correlation (TDPAC) on111mCd, via its nuclear quadrupole interaction. Whereas Cd2+ does not bind to the neutral DMPC, it binds to charged DMPA up to a 0.8∶1 Cd/lipid ratio.

Fungal toxins bind to the URF13 protein in maize mitochondria and Escherichia coli.

PubMed Central

Braun, C J; Siedow, J N; Levings, C S

1990-01-01

Expression of the maize mitochondrial T-urf13 gene results in a sensitivity to a family of fungal pathotoxins and to methomyl, a structurally unrelated systemic insecticide. Similar effects of pathotoxins and methomyl are observed when T-urf13 is cloned and expressed in Escherichia coli. An interaction between these compounds and the membrane-bound URF13 protein permeabilizes the inner mitochondrial and bacterial plasma membranes. To understand the toxin-URF13 effects, we have investigated whether toxin specifically binds to the URF13 protein. Our studies indicate that toxin binds to the URF13 protein in maize mitochondria and in E. coli expressing URF13. Binding analysis in E. coli reveals cooperative toxin binding. A low level of specific toxin binding is also demonstrated in cms-T and cms-T-restored mitochondria; however, binding does not appear to be cooperative in maize mitochondria. Competition and displacement studies in E. coli demonstrate that toxin binding is reversible and that the toxins and methomyl compete for the same, or for overlapping, binding sites. Two toxin-insensitive URF13 mutants display a diminished capability to bind toxin in E. coli, which identifies residues of URF13 important in toxin binding. A third toxin-insensitive URF13 mutant shows considerable toxin binding in E. coli, demonstrating that toxin binding can occur without causing membrane permeabilization. Our results indicate that toxin-mediated membrane permeabilization only occurs when toxin or methomyl is bound to URF13. PMID:2136632

Accurate determination of the binding energy of the formic acid dimer: The importance of geometry relaxation

NASA Astrophysics Data System (ADS)

Kalescky, Robert; Kraka, Elfi; Cremer, Dieter

2014-02-01

The formic acid dimer in its C2h-symmetrical cyclic form is stabilized by two equivalent H-bonds. The currently accepted interaction energy is 18.75 kcal/mol whereas the experimental binding energy D0 value is only 14.22 ±0.12 kcal/mol [F. Kollipost, R. W. Larsen, A. V. Domanskaya, M. Nörenberg, and M. A. Suhm, J. Chem. Phys. 136, 151101 (2012)]. Calculation of the binding energies De and D0 at the CCSD(T) (Coupled Cluster with Single and Double excitations and perturbative Triple excitations)/CBS (Complete Basis Set) level of theory, utilizing CCSD(T)/CBS geometries and the frequencies of the dimer and monomer, reveals that there is a 3.2 kcal/mol difference between interaction energy and binding energy De, which results from (i) not relaxing the geometry of the monomers upon dissociation of the dimer and (ii) approximating CCSD(T) correlation effects with MP2. The most accurate CCSD(T)/CBS values obtained in this work are De = 15.55 and D0 = 14.32 kcal/mol where the latter binding energy differs from the experimental value by 0.1 kcal/mol. The necessity of employing augmented VQZ and VPZ calculations and relaxing monomer geometries of H-bonded complexes upon dissociation to obtain reliable binding energies is emphasized.

Specific strychnine binding sites on acrosome-associated membranes of golden hamster spermatozoa.

PubMed

Llanos, Miguel N; Ronco, Ana M; Aguirre, María C

2003-06-27

This study demonstrates for the first time, that membrane vesicles originated from the hamster sperm head after the occurrence of the acrosome reaction, possess specific strychnine binding sites. [3H]Strychnine binding was saturable and reversible, being displaced by unlabeled strychnine (IC(50)=26.7+/-2.3 microM). Kinetic analysis revealed one binding site with K(d)=120nM and B(max)=142fmol/10(6) spermatozoa. Glycine receptor agonists beta-alanine and taurine inhibited strychnine binding by 20-30%. Surprisingly, glycine stimulated binding by about 40-50%. Results obtained in this study strongly suggest the presence of glycine receptors-with distinctive kinetic properties on the periacrosomal plasma membrane of hamster spermatozoa. Localization of this receptor fits well with its previously proposed role in acrosomal exocytosis during mammalian fertilization.

Freeze-fracture studies of photoreceptor membranes: new observations bearing upon the distribution of cholesterol

PubMed Central

1983-01-01

We performed electron microscopy of replicas from freeze-fractured retinas exposed during or after fixation to the cholesterol-binding antibiotic, filipin. We observed characteristic filipin-induced perturbations throughout the disk and plasma membranes of retinal rod outer segments of various species. It is evident that a prolonged exposure to filipin in fixative enhances rather than reduces presumptive cholesterol detection in the vertebrate photoreceptor cell. In agreement with the pattern seen in our previous study (Andrews, L.D., and A. I. Cohen, 1979, J. Cell Biol., 81:215-228), filipin- binding in membranes exhibiting particle-free patches seemed largely confined to these patches. Favorably fractured photoreceptors exhibited marked filipin-binding in apical inner segment plasma membrane topologically confluent with and proximate to the outer segment plasma membrane, which was comparatively free of filipin binding. A possible boundary between these differing membrane domains was suggested in a number of replicas exhibiting lower filipin binding to the apical plasma membrane of the inner segment in the area surrounding the cilium. This area contains a structure (Andrews, L. D., 1982, Freeze- fracture studies of vertebrate photoreceptors, In Structure of the Eye, J. G. Hollyfield and E. Acosta Vidrio, editors, Elsevier/North-Holland, New York, 11-23) that resembles the active zones of the nerve terminals for the frog neuromuscular junction. These observations lead us to hypothesize that these structures may function to direct vesicle fusion to occur near them, in a domain of membrane more closely resembling outer than inner segment plasma membrane. The above evidence supports the views that (a) all disk membranes contain cholesterol, but the particle-free patches present in some disks trap cholesterol from contiguous particulate membrane regions; (b) contiguous inner and outer segment membranes may greatly differ in cholesterol content; and (c) the suggested higher cholesterol in the inner segment than in the outer segment plasma membrane may help direct newly inserted photopigment molecules to the outer segment. PMID:6411740

Kinase Associated-1 Domains Drive MARK/PAR1 Kinases to Membrane Targets by Binding Acidic Phospholipids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moravcevic, Katarina; Mendrola, Jeannine M.; Schmitz, Karl R.

Phospholipid-binding modules such as PH, C1, and C2 domains play crucial roles in location-dependent regulation of many protein kinases. Here, we identify the KA1 domain (kinase associated-1 domain), found at the C terminus of yeast septin-associated kinases (Kcc4p, Gin4p, and Hsl1p) and human MARK/PAR1 kinases, as a membrane association domain that binds acidic phospholipids. Membrane localization of isolated KA1 domains depends on phosphatidylserine. Using X-ray crystallography, we identified a structurally conserved binding site for anionic phospholipids in KA1 domains from Kcc4p and MARK1. Mutating this site impairs membrane association of both KA1 domains and intact proteins and reveals the importancemore » of phosphatidylserine for bud neck localization of yeast Kcc4p. Our data suggest that KA1 domains contribute to coincidence detection, allowing kinases to bind other regulators (such as septins) only at the membrane surface. These findings have important implications for understanding MARK/PAR1 kinases, which are implicated in Alzheimer's disease, cancer, and autism.« less

Solubilization of phencyclidine receptors from rat cerebral cortex in an active ligand binding site

DOE Office of Scientific and Technical Information (OSTI.GOV)

McVittie, L.D.; Sibley, D.R.

1989-01-01

A phencyclidine (PCP) receptor binding site has been solubilized in an active ligand-binding state from rat cerebral cortical membranes with sodium deoxycholate. Optimal receptor solubilization occurs at a detergent/protein ratio of 0.5 (w/w); for 5 mg protein/ml solubilized with 0.25% sodium deoxycholate, about 60% of the protein and 25% of the receptor is solubilized. Specific binding of either (/sup 3/H)-N-(1-(2-thienyl)cyclohexyl)piperidine ((/sup 3/H)TCP) or (/sup 3/H)MK-801 is measurable by filtration through Sephadex G-50 columns or glass fiber filters; more than 60% of the binding activity is stable after 48 h at 4/degrees/C. In the presence of detergent, (/sup 3/H)TCP binding exhibitsmore » a K/sub d/ of 250 nM, a B/sub max/ of 0.56 pmol/mg protein, and a pharmacological profile consistent with that of the membrane-bound PCP receptor, although most drugs bind with affinities 2 to 8 fold lower than in membranes. Upon reduction of detergent concentration, binding parameters approximate those for the membrane-bound receptor (/sup 3/H)TCP binding: K/sub d/ = 48 nM, M/sub max/ = 1.13 pmol/mg protein.« less

Determination of structure of the MinD-ATP complex reveals the orientation of MinD on the membrane and the relative location of the binding sites for MinE and MinC

PubMed Central

Wu, Wei; Park, Kyung-Tae; Holyoak, Todd; Lutkenhaus, Joe

2011-01-01

Summary The three Min proteins spatially regulate Z ring positioning in E. coli and are dynamically associated with the membrane. MinD binds to vesicles in the presence of ATP and can recruit MinC or MinE. Biochemical and genetic evidence indicate the binding sites for these two proteins on MinD overlap. Here we solved the structure of a hydrolytic-deficient mutant of MinD truncated for the C-terminal amphipathic helix involved in binding to the membrane. The structure solved in the presence of ATP is a dimer and reveals the face of MinD abutting the membrane. Using a combination of random and extensive site-directed mutagenesis additional residues important for MinE and MinC binding were identified. The location of these residues on the MinD structure confirms that the binding sites overlap and reveals that the binding sites are at the dimer interface and exposed to the cytosol. The location of the binding sites at the dimer interface offers a simple explanation for the ATP-dependency of MinC and MinE binding to MinD. PMID:21231967

Modification of opiate agonist binding by pertussis toxin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abood, M.E.; Lee, N.M.; Loh, H.H.

1986-03-05

Opiate agonist binding is decreased by GTP, suggesting the possible involvement of GTP binding proteins in regulation of opiate receptor binding. This possibility was addressed by asking whether pertussis toxin treatment, which results in ADP-ribosylation and modification of G proteins, would alter opiate agonist binding. The striatum was chosen for the initial brain area to be studied, since regulation of opiate action in this area had been shown to be modified by pertussis toxin. Treatment of striatal membranes with pertussis toxin results in up to a 55% decrease in /sup 3/(H)-DADLE binding as compared with membranes treated identically without toxin.more » This corresponds to a near complete ADP-ribosylation of both G proteins in the striatal membrane. The decrease in agonist binding appears to be due to an altered affinity of the receptor for agonist as opposed to a decrease in the number of sites. This effect of pertussis toxin on opiate agonist binding demonstrates the actual involvement of G proteins in regulation of opiate receptor binding.« less

Glycoconjugate pattern of membranes in the acinar cell of the rat pancreas.

PubMed

Willemer, S; Köhler, H; Naumann, R; Kern, H F; Adler, G

1990-01-01

Lectin-binding studies were performed at the ultrastructural level to characterize glycoconjugate patterns on membrane systems in pancreatic acinar cells of the rat. Five lectins reacting with different sugar moieties were applied to ultrathin frozen sections: concanavalin A (ConA): glucose, mannose; wheat-germ agglutinin (WGA): N-acetylglucosamine, sialic acid; Ricinus communis agglutinin I (RCA I): galactose; Ulex europaeus agglutinin I (UEA I): L-fucose; soybean agglutinin (SBA): N-acetylgalactosamine). Binding sites of lectins were visualized either by direct conjugation to colloidal gold or by the use of a three-step procedure involving additional immune reactions. The rough endoplasmic reticulum and the nuclear envelope of acinar cells was selectively labelled for ConA. The membranes of the Golgi apparatus bound all lectins applied with an increasing intensity proceeding from the cis- to the trans-Golgi area for SBA, UEA I and WGA. In contrast RCA I selectively labelled the trans-Golgi cisternae. The membranes of condensing vacuoles and zymogen granules were labelled for all lectins used although the density of the label differed between the lectins. In contrast the content of zymogen granules failed to bind SBA and WGA. Lysosomal bodies (membranes and content) revealed binding sites for all lectins used. The plasma membranes were heavily labelled by all lectins except for SBA which showed only a weak binding to the lateral and the apical plasma membrane. These results are in accordance to current biochemical knowledge of the successive steps in the glycosylation of membrane proteins. It could be demonstrated, that the cryo-section technique is suitable for the fine structural localisation of surface glycoconjugates of plasma membranes and internal membranes in pancreatic acinar cells using plant lectins.

Spring-Loaded Model Revisited: Paramyxovirus Fusion Requires Engagement of a Receptor Binding Protein beyond Initial Triggering of the Fusion Protein▿

PubMed Central

Porotto, Matteo; DeVito, Ilaria; Palmer, Samantha G.; Jurgens, Eric M.; Yee, Jia L.; Yokoyama, Christine C.; Pessi, Antonello; Moscona, Anne

2011-01-01

During paramyxovirus entry into a host cell, receptor engagement by a specialized binding protein triggers conformational changes in the adjacent fusion protein (F), leading to fusion between the viral and cell membranes. According to the existing paradigm of paramyxovirus membrane fusion, the initial activation of F by the receptor binding protein sets off a spring-loaded mechanism whereby the F protein progresses independently through the subsequent steps in the fusion process, ending in membrane merger. For human parainfluenza virus type 3 (HPIV3), the receptor binding protein (hemagglutinin-neuraminidase [HN]) has three functions: receptor binding, receptor cleaving, and activating F. We report that continuous receptor engagement by HN activates F to advance through the series of structural rearrangements required for fusion. In contrast to the prevailing model, the role of HN-receptor engagement in the fusion process is required beyond an initiating step, i.e., it is still required even after the insertion of the fusion peptide into the target cell membrane, enabling F to mediate membrane merger. We also report that for Nipah virus, whose receptor binding protein has no receptor-cleaving activity, the continuous stimulation of the F protein by a receptor-engaged binding protein is key for fusion. We suggest a general model for paramyxovirus fusion activation in which receptor engagement plays an active role in F activation, and the continued engagement of the receptor binding protein is essential to F protein function until the onset of membrane merger. This model has broad implications for the mechanism of paramyxovirus fusion and for strategies to prevent viral entry. PMID:21976650

Spring-loaded model revisited: paramyxovirus fusion requires engagement of a receptor binding protein beyond initial triggering of the fusion protein.

PubMed

Porotto, Matteo; Devito, Ilaria; Palmer, Samantha G; Jurgens, Eric M; Yee, Jia L; Yokoyama, Christine C; Pessi, Antonello; Moscona, Anne

2011-12-01

During paramyxovirus entry into a host cell, receptor engagement by a specialized binding protein triggers conformational changes in the adjacent fusion protein (F), leading to fusion between the viral and cell membranes. According to the existing paradigm of paramyxovirus membrane fusion, the initial activation of F by the receptor binding protein sets off a spring-loaded mechanism whereby the F protein progresses independently through the subsequent steps in the fusion process, ending in membrane merger. For human parainfluenza virus type 3 (HPIV3), the receptor binding protein (hemagglutinin-neuraminidase [HN]) has three functions: receptor binding, receptor cleaving, and activating F. We report that continuous receptor engagement by HN activates F to advance through the series of structural rearrangements required for fusion. In contrast to the prevailing model, the role of HN-receptor engagement in the fusion process is required beyond an initiating step, i.e., it is still required even after the insertion of the fusion peptide into the target cell membrane, enabling F to mediate membrane merger. We also report that for Nipah virus, whose receptor binding protein has no receptor-cleaving activity, the continuous stimulation of the F protein by a receptor-engaged binding protein is key for fusion. We suggest a general model for paramyxovirus fusion activation in which receptor engagement plays an active role in F activation, and the continued engagement of the receptor binding protein is essential to F protein function until the onset of membrane merger. This model has broad implications for the mechanism of paramyxovirus fusion and for strategies to prevent viral entry.

Fluorescence studies on the interaction of choline-binding domain B of the major bovine seminal plasma protein, PDC-109 with phospholipid membranes.

PubMed

Damai, Rajani S; Anbazhagan, V; Rao, K Babu; Swamy, Musti J

2009-12-01

The microenvironment and accessibility of the tryptophan residues in domain B of PDC-109 (PDC-109/B) in the native state and upon ligand binding have been investigated by fluorescence quenching, time-resolved fluorescence and red-edge excitation shift (REES) studies. The increase in the intrinsic fluorescence emission intensity of PDC-109/B upon binding to lysophosphatidylcholine (Lyso-PC) micelles and dimyristoylphosphatidylcholine (DMPC) membranes was considerably less as compared to that observed with the whole PDC-109 protein. The degree of quenching achieved by different quenchers with PDC-109/B bound to Lyso-PC and DMPC membranes was significantly higher as compared to the full PDC-109 protein, indicating that membrane binding afforded considerably lesser protection to the tryptophan residues of domain B as compared to those in the full PDC-109 protein. Finally, changes in red-edge excitation shift (REES) seen with PDC-109/B upon binding to DMPC membranes and Lyso-PC micelles were smaller that the corresponding changes in the REES values observed for the full PDC-109. These results, taken together suggest that intact PDC-109 penetrates deeper into the hydrophobic parts of the membrane as compared to domain B alone, which could be the reason for the inability of PDC-109/B to induce cholesterol efflux, despite its ability to recognize choline phospholipids at the membrane surface.

Structural features and lipid binding domain of tubulin on biomimetic mitochondrial membranes

PubMed Central

Hoogerheide, David P.; Noskov, Sergei Y.; Jacobs, Daniel; Bergdoll, Lucie; Silin, Vitalii; Worcester, David L.; Abramson, Jeff; Nanda, Hirsh; Rostovtseva, Tatiana K.; Bezrukov, Sergey M.

2017-01-01

Dimeric tubulin, an abundant water-soluble cytosolic protein known primarily for its role in the cytoskeleton, is routinely found to be associated with mitochondrial outer membranes, although the structure and physiological role of mitochondria-bound tubulin are still unknown. There is also no consensus on whether tubulin is a peripheral membrane protein or is integrated into the outer mitochondrial membrane. Here the results of five independent techniques—surface plasmon resonance, electrochemical impedance spectroscopy, bilayer overtone analysis, neutron reflectometry, and molecular dynamics simulations—suggest that α-tubulin’s amphipathic helix H10 is responsible for peripheral binding of dimeric tubulin to biomimetic “mitochondrial” membranes in a manner that differentiates between the two primary lipid headgroups found in mitochondrial membranes, phosphatidylethanolamine and phosphatidylcholine. The identification of the tubulin dimer orientation and membrane-binding domain represents an essential step toward our understanding of the complex mechanisms by which tubulin interacts with integral proteins of the mitochondrial outer membrane and is important for the structure-inspired design of tubulin-targeting agents. PMID:28420794

Modulation of GABAergic receptor binding by activation of calcium and calmodulin-dependent kinase II membrane phosphorylation.

PubMed

Churn, S B; DeLorenzo, R J

1998-10-26

gamma-Aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system (CNS). Because of the important role that GABA plays in the CNS, alteration of GABAA receptor function would significantly affect neuronal excitability. Protein phosphorylation is a major mechanism for regulating receptor function in the brain and has been implicated in modulating GABAA receptor function. Therefore, this study was initiated to determine the role of calmodulin-dependent kinase II (CaM kinase II) membrane phosphorylation on GABAA receptor binding. Synaptosomal membrane fractions were tested for CaM kinase II activity towards endogenous substrates. In addition, muscimol binding was evaluated under equilibrium conditions in synaptosomal membrane fractions subjected to either basal (Mg2+ alone) or maximal CaM kinase II-dependent phosphorylation. Activation of endogenous CaM kinase II-dependent phosphorylation resulted in a significant enhancement of the apparent Bmax for muscimol binding without significantly altering the apparent binding affinity. The enhanced muscimol binding could be increased further by the addition of exogenous CaM kinase II to synaptosomal membrane fractions. Co-incubation with inhibitors of kinase activity during the phosphorylation reactions blocked the CaM kinase II-dependent increase in muscimol binding. The data support the hypothesis that activation of CaM kinase II-dependent phosphorylation caused an increased GABAA receptor binding and may play an important role in modulating the function of this inhibitory receptor/chloride ion channel complex. Copyright 1998 Elsevier Science B.V.

The hepta-beta-glucoside elicitor-binding proteins from legumes represent a putative receptor family.

PubMed

Mithöfer, A; Fliegmann, J; Neuhaus-Url, G; Schwarz, H; Ebel, J

2000-08-01

The ability of legumes to recognize and respond to beta-glucan elicitors by synthesizing phytoalexins is consistent with the existence of a membrane-bound beta-glucan-binding site. Related proteins of approximately 75 kDa and the corresponding mRNAs were detected in various species of legumes which respond to beta-glucans. The cDNAs for the beta-glucan-binding proteins of bean and soybean were cloned. The deduced 75-kDa proteins are predominantly hydrophilic and constitute a unique class of glucan-binding proteins with no currently recognizable functional domains. Heterologous expression of the soybean beta-glucan-binding protein in tomato cells resulted in the generation of a high-affinity binding site for the elicitor-active hepta-beta-glucoside conjugate (Kd = 4.5 nM). Ligand competition experiments with the recombinant binding sites demonstrated similar ligand specificities when compared with soybean. In both soybean and transgenic tomato, membrane-bound, active forms of the glucan-binding proteins coexist with immunologically detectable, soluble but inactive forms of the proteins. Reconstitution of a soluble protein fraction into lipid vesicles regained beta-glucoside-binding activity but with lower affinity (Kd = 130 nM). We conclude that the beta-glucan elicitor receptors of legumes are composed of the 75 kDa glucan-binding proteins as the critical components for ligand-recognition, and of an as yet unknown membrane anchor constituting the plasma membrane-associated receptor complex.

Precise identification and manipulation of adsorption geometry of donor-π-acceptor dye on nanocrystalline TiO₂ films for improved photovoltaics.

PubMed

Zhang, Fan; Ma, Wei; Jiao, Yang; Wang, Jingchuan; Shan, Xinyan; Li, Hui; Lu, Xinghua; Meng, Sheng

2014-12-24

Adsorption geometry of dye molecules on nanocrystalline TiO2 plays a central role in dye-sensitized solar cells, enabling effective sunlight absorption, fast electron injection, optimized interface band offsets, and stable photovoltaic performance. However, precise determination of dye binding geometry and proportion has been challenging due to complexity and sensitivity at interfaces. Here employing combined vibrational spectrometry and density functional calculations, we identify typical adsorption configurations of widely adopted cyanoacrylic donor-π bridge-acceptor dyes on nanocrystalline TiO2. Binding mode switching from bidentate bridging to hydrogen-bonded monodentate configuration with Ti-N bonding has been observed when dye-sensitizing solution becomes more basic. Raman and infrared spectroscopy measurements confirm this configuration switch and determine quantitatively the proportion of competing binding geometries, with vibration peaks assigned using density functional theory calculations. We further found that the proportion of dye-binding configurations can be manipulated by adjusting pH value of dye-sensitizing solutions. Controlling molecular adsorption density and configurations led to enhanced energy conversion efficiency from 2.4% to 6.1% for the fabricated dye-sensitized solar cells, providing a simple method to improve photovoltaic performance by suppressing unfavorable binding configurations in solar cell applications.

Clostridium Perfringens Epsilon Toxin Binds to Membrane Lipids and Its Cytotoxic Action Depends on Sulfatide.

PubMed

Gil, Carles; Dorca-Arévalo, Jonatan; Blasi, Juan

2015-01-01

Epsilon toxin (Etx) is one of the major lethal toxins produced by Clostridium perfringens types B and D, being the causal agent of fatal enterotoxemia in animals, mainly sheep and goats. Etx is synthesized as a non-active prototoxin form (proEtx) that becomes active upon proteolytic activation. Etx exhibits a cytotoxic effect through the formation of a pore in the plasma membrane of selected cell targets where Etx specifically binds due to the presence of specific receptors. However, the identity and nature of host receptors of Etx remain a matter of controversy. In the present study, the interactions between Etx and membrane lipids from the synaptosome-enriched fraction from rat brain (P2 fraction) and MDCK cell plasma membrane preparations were analyzed. Our findings show that both Etx and proEtx bind to lipids extracted from lipid rafts from the two different models as assessed by protein-lipid overlay assay. Lipid rafts are membrane microdomains enriched in cholesterol and sphingolipids. Binding of proEtx to sulfatide, phosphatidylserine, phosphatidylinositol (3)-phosphate and phosphatidylinositol (5)-phosphate was detected. Removal of the sulphate groups via sulfatase treatment led to a dramatic decrease in Etx-induced cytotoxicity, but not in proEtx-GFP binding to MDCK cells or a significant shift in oligomer formation, pointing to a role of sulfatide in pore formation in rafts but not in toxin binding to the target cell membrane. These results show for the first time the interaction between Etx and membrane lipids from host tissue and point to a major role for sulfatides in C. perfringens epsilon toxin pathophysiology.

Bacillus thuringiensis Cry1A toxin-binding glycoconjugates present on the brush border membrane and in the peritrophic membrane of the Douglas-fir tussock moth are peritrophins

Treesearch

Algimantas P. Valaitis; John D. Podgwaite

2013-01-01

Bacillus thuringiensis (Bt) Cry1A toxin-binding sites in the Douglas fir tussock moth (DFTM) larval gut were localized using immunofluorescence microscopy. Cry1Aa, Cry1Ab and Cry1Ac all bound strongly to the DFTM peritrophic membrane (PM); weaker binding of the Cry1A toxins was observed along the apical brush border of the midgut epithelium....

Analysis of the interaction between membrane proteins and soluble binding partners by surface plasmon resonance.

PubMed

Wu, Zht Cheng; de Keyzer, Jeanine; Kusters, Ilja; Driessen, Arnold J M

2013-01-01

The interaction between membrane proteins and their (protein) ligands is conventionally investigated by nonequilibrium methods such as co-sedimentation or pull-down assays. Surface Plasmon Resonance can be used to monitor such binding events in real-time using isolated membranes immobilized to a surface providing insights in the kinetics of binding under equilibrium conditions. This application provides a fast, automated way to detect interacting species and to determine the kinetics and affinity (Kd) of the interaction.

Part I: an x-ray scattering study of cholera toxin penetration and induced phase transformations in lipid membranes.

PubMed

Miller, C E; Majewski, J; Watkins, E B; Kuhl, T L

2008-07-01

Cholera toxin is a highly efficient biotoxin, which is frequently used as a tool to investigate protein-membrane interactions and as a reporter for membrane rafts. Cholera toxin binds selectively to gangliosides with highest affinity to GM(1). However, the mechanism by which cholera toxin crosses the membrane remains unresolved. Using x-ray reflectivity and grazing incidence diffraction, we have been able to monitor the binding and penetration of cholera toxin into a model lipid monolayer containing the receptor GM(1) at the air-water interface. Very high toxin coverage was obtained allowing precise measurements of how toxin binding alters lipid packing. Grazing incidence x-ray diffraction revealed the coexistence of two monolayer phases after toxin binding. The first was identical to the monolayer before toxin binding. In regions where toxin was bound, a second membrane phase exhibited a decrease in order as evidenced by a larger area per molecule and tilt angle with concomitant thinning of the monolayer. These results demonstrate that cholera toxin binding induces the formation of structurally distinct, less ordered domains in gel phases. Furthermore, the largest decrease in lateral order to the monolayer occurred at low pH, supporting a low endosomal pH in the infection pathway. Surprisingly, at pH = 8 toxin penetration by the binding portion of the toxin, the B(5) pentamer, was also observed.

Atomistic models for free energy evaluation of drug binding to membrane proteins.

PubMed

Durdagi, S; Zhao, C; Cuervo, J E; Noskov, S Y

2011-01-01

The binding of various molecules to integral membrane proteins with optimal affinity and specificity is central to normal function of cell. While membrane proteins represent about one third of the whole cell proteome, they are a majority of common drug targets. The quest for the development of computational models capable of accurate evaluation of binding affinities, decomposition of the binding into its principal components and thus mapping molecular mechanisms of binding remains one of the main goals of modern computational biophysics and related drug development. The primary scope of this review will be on the recent extension of computational methods for the study of drug binding to membrane proteins. Several examples of such applications will be provided ranging from secondary transporters to voltage gated channels. In this mini-review, we will provide a short summary on the breadth of different methods for binding affinity evaluation. These methods include molecular docking with docking scoring functions, molecular dynamics (MD) simulations combined with post-processing analysis using Molecular Mechanics/Poisson Boltzmann (Generalized Born) Surface Area (MM/PB(GB)SA), as well as direct evaluation of free energies from Free Energy Perturbation (FEP) with constraining schemes, and Potential of Mean Force (PMF) computations. We will compare advantages and shortcomings of popular techniques and provide discussion on the integrative strategies for drug development aimed at targeting membrane proteins.

Vitreoscilla hemoglobin. Intracellular localization and binding to membranes.

PubMed

Ramandeep; Hwang, K W; Raje, M; Kim, K J; Stark, B C; Dikshit, K L; Webster, D A

2001-07-06

The obligate aerobic bacterium, Vitreoscilla, synthesizes elevated quantities of a homodimeric hemoglobin (VHb) under hypoxic growth conditions. Expression of VHb in heterologous hosts often enhances growth and product formation. A role in facilitating oxygen transfer to the respiratory membranes is one explanation of its cellular function. Immunogold labeling of VHb in both Vitreoscilla and recombinant Escherichia coli bearing the VHb gene clearly indicated that VHb has a cytoplasmic (not periplasmic) localization and is concentrated near the periphery of the cytosolic face of the cell membrane. OmpA signal-peptide VHb fusions were transported into the periplasm in E. coli, but this did not confer any additional growth advantage. The interaction of VHb with respiratory membranes was also studied. The K(d) values for the binding of VHb to Vitreoscilla and E. coli cell membranes were approximately 5-6 microm, a 4-8-fold higher affinity than those of horse myoglobin and hemoglobin for these same membranes. VHb stimulated the ubiquinol-1 oxidase activity of inverted Vitreoscilla membranes by 68%. The inclusion of Vitreoscilla cytochrome bo in proteoliposomes led to 2.4- and 6-fold increases in VHb binding affinity and binding site number, respectively, relative to control liposomes, suggesting a direct interaction between VHb and cytochrome bo.

High-resolution Structures of Protein-Membrane Complexes by Neutron Reflection and MD Simulation: Membrane Association of the PTEN Tumor Suppressor

NASA Astrophysics Data System (ADS)

Lösche, Matthias

2012-02-01

The lipid matrix of biomembranes is an in-plane fluid, thermally and compositionally disordered leaflet of 5 nm thickness and notoriously difficult to characterize in structural terms. Yet, biomembranes are ubiquitous in the cell, and membrane-bound proteins are implicated in a variety of signaling pathways and intra-cellular transport. We developed methodology to study proteins associated with model membranes using neutron reflection measurements and showed recently that this approach can resolve the penetration depth and orientation of membrane proteins with ångstrom resolution if their crystal or NMR structure is known. Here we apply this technology to determine the membrane bindung and unravel functional details of the PTEN phosphatase, a key player in the PI3K apoptosis pathway. PTEN is an important regulatory protein and tumor suppressor that performs its phosphatase activity as an interfacial enzyme at the plasma membrane-cytoplasm boundary. Acting as an antagonist to phosphoinositide-3-kinase (PI3K) in cell signaling, it is deleted in many human cancers. Despite its importance in regulating the levels of the phosphoinositoltriphosphate PI(3,4,5)P3, there is little understanding of how PTEN binds to membranes, is activated and then acts as a phosphatase. We investigated the structure and function of PTEN by studying its membrane affinity and localization on in-plane fluid, thermally disordered synthetic membrane models. The membrane association of the protein depends strongly on membrane composition, where phosphatidylserine (PS) and phosphatidylinositol diphosphate (PI(4,5)P2) act synergetically in attracting the enzyme to the membrane surface. Membrane affinities depend strongly on membrane fluidity, which suggests multiple binding sites on the protein for PI(4,5)P2. Neutron reflection measurements show that the PTEN phosphatase ``scoots'' along the membrane surface (penetration < 5 å) but binds the membrane tightly with its two major domains, the C2 and phosphatase domains. In the bound state, PTEN's regulatory C-terminal tail is displaced from the membrane and organized on the far side of the protein, ˜ 60 å away from the bilayer surface, in a rather compact structure. The combination of binding studies and neutron reflection allows us to distinguish between PTEN mutant proteins and ultimately may identify the structural features required for membrane binding and activation of PTEN. Molecular dynamics simulations, currently in progress, refine this structural picture further.

Electrostatic interactions and binding orientation of HIV-1 matrix studied by neutron reflectivity.

PubMed

Nanda, Hirsh; Datta, Siddhartha A K; Heinrich, Frank; Lösche, Mathias; Rein, Alan; Krueger, Susan; Curtis, Joseph E

2010-10-20

The N-terminal matrix (MA) domain of the HIV-1 Gag protein is responsible for binding to the plasma membrane of host cells during viral assembly. The putative membrane-binding interface of MA was previously mapped by means of mutagenesis and analysis of its trimeric crystal structure. However, the orientation of MA on membranes has not been directly determined by experimental measurements. We present neutron reflectivity measurements that resolve the one-dimensional scattering length density profile of MA bound to a biomimetic of the native viral membrane. A molecular refinement procedure was developed using atomic structures of MA to determine the orientation of the protein on the membrane. The orientation defines a lipid-binding interface consistent with previous mutagenesis results. The MA protein maintains this orientation without the presence of a myristate group, driven only by electrostatic interactions. Furthermore, MA is found to penetrate the membrane headgroup region peripherally such that only the side chains of specific Lys and Arg residues interact with the surface. The results suggest that electrostatic interactions are sufficient to favorably orient MA on viral membrane mimics. The spatial determination of the membrane-bound protein demonstrates the ability of neutron reflectivity to discern orientation and penetration under physiologically relevant conditions. Copyright © 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Involvement of the N-terminal region in alpha-crystallin-lens membrane recognition

NASA Technical Reports Server (NTRS)

Ifeanyi, F.; Takemoto, L.; Spooner, B. S. (Principal Investigator)

1991-01-01

Previous studies have demonstrated that alpha-crystallin binds specifically, in a saturable manner, to lens membrane. To determine the region of the alpha-crystallin molecule that might be involved in this binding, native alpha-crystallin from the bovine lens has been treated by limited digestion with trypsin, to produce alpha-A molecules with an intact C-terminal region, and a nicked N-terminal region. Compared to intact alpha-crystallin, trypsin-treated alpha-crystallin binds less avidly to lens membrane, suggesting that the N-terminal region of the alpha-A molecule may play a key role in the recognition between lens membrane and crystallin.

External location of sites on pig erythrocyte membranes that bind nitrobenzylthioinosine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agbanyo, F.R.; Cass, C.E.; Paterson, A.R.

1988-03-01

Nucleoside transport in erythrocytes of various species is inhibited by the binding of nitrobenzylthioinosine (NBMPR) to high affinity sites associated with nucleoside transport elements of the plasma membrane. The present study examined binding of (/sup 3/H)NBMPR to unsealed ghosts and to sealed right-side-out vesicles (ROVs) and inside-out vesicles (IOVs) prepared from pig erythrocytes. Kd values for NBMPR dissociation from the ligand-site complex in unsealed ghosts, ROVs and IOVs were similar (1.6-2.4 nM), and Bmax values (mean +/- SD) were, respectively, 22.2 +/- 5.5, 25.8 +/- 6.4, and 37.3 +/- 4.0 molecules/fg of protein, reflecting differences in the protein content ofmore » the membrane preparations. When temperatures were decreased from 22 degrees to 4 degrees, NBMPR binding to erythrocyte membrane preparations was reduced in IOVs relative to that in unsealed ghosts and ROVs. At 22 degrees, the association of NBMPR molecules with IOVs was slower than with ROVs and unsealed ghosts, differences that were virtually eliminated by permeabilization of the membrane preparations with saponin. Thus, the binding sites were more accessible to external NBMPR in sealed ROVs and unsealed ghosts than in sealed IOVs, indicating that the NBMPR sites are located on the extracellular aspect of the membrane.« less

The HOPS/Class C Vps Complex Tethers High-Curvature Membranes via a Direct Protein-Membrane Interaction.

PubMed

Ho, Ruoya; Stroupe, Christopher

2016-10-01

Membrane tethering is a physical association of two membranes before their fusion. Many membrane tethering factors have been identified, but the interactions that mediate inter-membrane associations remain largely a matter of conjecture. Previously, we reported that the homotypic fusion and protein sorting/Class C vacuolar protein sorting (HOPS/Class C Vps) complex, which has two binding sites for the yeast vacuolar Rab GTPase Ypt7p, can tether two low-curvature liposomes when both membranes bear Ypt7p. Here, we show that HOPS tethers highly curved liposomes to Ypt7p-bearing low-curvature liposomes even when the high-curvature liposomes are protein-free. Phosphorylation of the curvature-sensing amphipathic lipid-packing sensor (ALPS) motif from the Vps41p HOPS subunit abrogates tethering of high-curvature liposomes. A HOPS complex without its Vps39p subunit, which contains one of the Ypt7p binding sites in HOPS, lacks tethering activity, though it binds high-curvature liposomes and Ypt7p-bearing low-curvature liposomes. Thus, HOPS tethers highly curved membranes via a direct protein-membrane interaction. Such high-curvature membranes are found at the sites of vacuole tethering and fusion. There, vacuole membranes bend sharply, generating large areas of vacuole-vacuole contact. We propose that HOPS localizes via the Vps41p ALPS motif to these high-curvature regions. There, HOPS binds via Vps39p to Ypt7p in an apposed vacuole membrane. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Competitive Binding Assay for the G-Protein-Coupled Receptor 30 (GPR30) or G-Protein-Coupled Estrogen Receptor (GPER).

PubMed

Thekkumkara, Thomas; Snyder, Russell; Karamyan, Vardan T

2016-01-01

The role of 2-methoxyestradiol is becoming a major area of investigation because of its therapeutic utility, though its mechanism is not fully explored. Recent studies have identified the G-protein-coupled receptor 30 (GPR30, GPER) as a high-affinity membrane receptor for 2-methoxyestradiol. However, studies aimed at establishing the binding affinities of steroid compounds for specific targets are difficult, as the tracers are highly lipophilic and often result in nonspecific binding in lipid-rich membrane preparations with low-level target receptor expression. 2-Methoxyestradiol binding studies are essential to elucidate the underlying effects of this novel estrogen metabolite and to validate its targets; therefore, this competitive receptor-binding assay protocol was developed in order to assess the membrane receptor binding and affinity of 2-methyoxyestradiol.

Membrane Curvature Sensing by Amphipathic Helices

PubMed Central

Jensen, Martin Borch; Bhatia, Vikram Kjøller; Jao, Christine C.; Rasmussen, Jakob Ewald; Pedersen, Søren L.; Jensen, Knud J.; Langen, Ralf; Stamou, Dimitrios

2011-01-01

Preferential binding of proteins on curved membranes (membrane curvature sensing) is increasingly emerging as a general mechanism whereby cells may effect protein localization and trafficking. Here we use a novel single liposome fluorescence microscopy assay to examine a common sensing motif, the amphipathic helix (AH), and provide quantitative measures describing and distinguishing membrane binding and sensing behavior. By studying two AH-containing proteins, α-synuclein and annexin B12, as well as a range of AH peptide mutants, we reveal that both the hydrophobic and hydrophilic faces of the helix greatly influence binding and sensing. Although increased hydrophobic and electrostatic interactions with the membrane both lead to greater densities of bound protein, the former yields membrane curvature-sensitive binding, whereas the latter is not curvature-dependent. However, the relative contributions of both components determine the sensing of AHs. In contrast, charge density in the lipid membrane seems important primarily in attracting AHs to the membrane but does not significantly influence sensing. These observations were made possible by the ability of our assay to distinguish within our samples liposomes with and without bound protein as well as the density of bound protein. Our findings suggest that the description of membrane curvature-sensing requires consideration of several factors such as short and long range electrostatic interactions, hydrogen bonding, and the volume and structure of inserted hydrophobic residues. PMID:21953452

Time-resolved multimodal analysis of Src Homology 2 (SH2) domain binding in signaling by receptor tyrosine kinases

PubMed Central

Jadwin, Joshua A; Oh, Dongmyung; Curran, Timothy G; Ogiue-Ikeda, Mari; Jia, Lin; White, Forest M; Machida, Kazuya; Yu, Ji; Mayer, Bruce J

2016-01-01

While the affinities and specificities of SH2 domain-phosphotyrosine interactions have been well characterized, spatio-temporal changes in phosphosite availability in response to signals, and their impact on recruitment of SH2-containing proteins in vivo, are not well understood. To address this issue, we used three complementary experimental approaches to monitor phosphorylation and SH2 binding in human A431 cells stimulated with epidermal growth factor (EGF): 1) phospho-specific mass spectrometry; 2) far-Western blotting; and 3) live cell single-molecule imaging of SH2 membrane recruitment. Far-Western and MS analyses identified both well-established and previously undocumented EGF-dependent tyrosine phosphorylation and binding events, as well as dynamic changes in binding patterns over time. In comparing SH2 binding site phosphorylation with SH2 domain membrane recruitment in living cells, we found in vivo binding to be much slower. Delayed SH2 domain recruitment correlated with clustering of SH2 domain binding sites on the membrane, consistent with membrane retention via SH2 rebinding. DOI: http://dx.doi.org/10.7554/eLife.11835.001 PMID:27071344

The Polar and Electrical Nature of Dye Binding Sites on Human Red Blood Cell Membranes.

DTIC Science & Technology

positive charges at the binding sites. By increasing the concentration of the anionic BPB (or by the addition of the anionic detergent sodium lauryl ... sulfate ) these positive charges appear to be successively titrated, rendering the membrane binding sites electrically neutral at this pH. The average

Ubiquitin Interacts with the Tollip C2 and CUE Domains and Inhibits Binding of Tollip to Phosphoinositides*

PubMed Central

Mitra, Sharmistha; Traughber, C. Alicia; Brannon, Mary K.; Gomez, Stephanie; Capelluto, Daniel G. S.

2013-01-01

A large number of cellular signaling processes are directed through internalization, via endocytosis, of polyubiquitinated cargo proteins. Tollip is an adaptor protein that facilitates endosomal cargo sorting for lysosomal degradation. Tollip preferentially binds phosphatidylinositol 3-phosphate (PtdIns(3)P) via its C2 domain, an association that may be required for endosomal membrane targeting. Here, we show that Tollip binds ubiquitin through its C2 and CUE domains and that its association with the C2 domain inhibits PtdIns(3)P binding. NMR analysis demonstrates that the C2 and CUE domains bind to overlapping sites on ubiquitin, suggesting that two ubiquitin molecules associate with Tollip simultaneously. Hydrodynamic studies reveal that ubiquitin forms heterodimers with the CUE domain, indicating that the association disrupts the dimeric state of the CUE domain. We propose that, in the absence of polyubiquitinated cargo, the dual binding of ubiquitin partitions Tollip into membrane-bound and membrane-free states, a function that contributes to the engagement of Tollip in both membrane trafficking and cytosolic pathways. PMID:23880770

Modeling FtsZ ring formation in the bacterial cell-anisotropic aggregation via mutual interactions of polymer rods.

PubMed

Fischer-Friedrich, Elisabeth; Gov, Nir

2011-04-01

The cytoskeletal protein FtsZ polymerizes to a ring structure (Z ring) at the inner cytoplasmic membrane that marks the future division site and scaffolds the division machinery in many bacterial species. FtsZ is known to polymerize in the presence of GTP into single-stranded protofilaments. In vivo, FtsZ polymers become associated with the cytoplasmic membrane via interaction with the membrane-binding proteins FtsA and ZipA. The FtsZ ring structure is highly dynamic and undergoes constantly polymerization and depolymerization processes and exchange with the cytoplasmic pool. In this theoretical study, we consider a scenario of Z ring self-organization via self-enhanced attachment of FtsZ polymers due to end-to-end interactions and lateral interactions of FtsZ polymers on the membrane. With the assumption of exclusively circumferential polymer orientations, we derive coarse-grained equations for the dynamics of the pool of cytoplasmic and membrane-bound FtsZ. To capture stochastic effects expected in the system due to low particle numbers, we simulate our computational model using a Gillespie-type algorithm. We obtain ring- and arc-shaped aggregations of FtsZ polymers on the membrane as a function of monomer numbers in the cell. In particular, our model predicts the number of FtsZ rings forming in the cell as a function of cell geometry and FtsZ concentration. We also calculate the time of FtsZ ring localization to the midplane in the presence of Min oscillations. Finally, we demonstrate that the assumptions and results of our model are confirmed by 3D reconstructions of fluorescently-labeled FtsZ structures in E. coli that we obtained.

Cooperative binding modes of Cu(II) in prion protein

NASA Astrophysics Data System (ADS)

Hodak, Miroslav; Chisnell, Robin; Lu, Wenchang; Bernholc, Jerry

2007-03-01

The misfolding of the prion protein, PrP, is responsible for a group of neurodegenerative diseases including mad cow disease and Creutzfeldt-Jakob disease. It is known that the PrP can efficiently bind copper ions; four high-affinity binding sites located in the octarepeat region of PrP are now well known. Recent experiments suggest that at low copper concentrations new binding modes, in which one copper ion is shared between two or more binding sites, are possible. Using our hybrid Thomas-Fermi/DFT computational scheme, which is well suited for simulations of biomolecules in solution, we investigate the geometries and energetics of two, three and four binding sites cooperatively binding one copper ion. These geometries are then used as inputs for classical molecular dynamics simulations. We find that copper binding affects the secondary structure of the PrP and that it stabilizes the unstructured (unfolded) part of the protein.

Addition of lysophospholipids with large head groups to cells inhibits Shiga toxin binding.

PubMed

Ailte, Ieva; Lingelem, Anne Berit Dyve; Kavaliauskiene, Simona; Bergan, Jonas; Kvalvaag, Audun Sverre; Myrann, Anne-Grethe; Skotland, Tore; Sandvig, Kirsten

2016-07-26

Shiga toxin (Stx), an AB5 toxin, binds specifically to the neutral glycosphingolipid Gb3 at the cell surface before being transported into cells. We here demonstrate that addition of conical lysophospholipids (LPLs) with large head groups inhibit Stx binding to cells whereas LPLs with small head groups do not. Lysophosphatidylinositol (LPI 18:0), the most efficient LPL with the largest head group, was selected for in-depth investigations to study how the binding of Stx is regulated. We show that the inhibition of Stx binding by LPI is reversible and possibly regulated by cholesterol since addition of methyl-β-cyclodextrin (mβCD) reversed the ability of LPI to inhibit binding. LPI-induced inhibition of Stx binding is independent of signalling and membrane turnover as it occurs in fixed cells as well as after depletion of cellular ATP. Furthermore, data obtained with fluorescent membrane dyes suggest that LPI treatment has a direct effect on plasma membrane lipid packing with shift towards a liquid disordered phase in the outer leaflet, while lysophosphoethanolamine (LPE), which has a small head group, does not. In conclusion, our data show that cellular treatment with conical LPLs with large head groups changes intrinsic properties of the plasma membrane and modulates Stx binding to Gb3.

Kappa-receptor selective binding of opioid ligands with a heterocyclic bicyclo[3.3.1]nonan-9-one structure.

PubMed

Benyhe, S; Márki, A; Nachtsheim, Corina; Holzgrabe, Ulrike; Borsodi, Anna

2003-01-01

Previous pharmacological results have suggested that members of the heterocyclic bicyclo[3.3.1]nonan-9-one-like compounds are potent kappa-opioid receptor specific agonists. One lead molecule of this series. called compound 1 (dimethyl 7-methyl-2,4-di-2-pyridyl-3.7-diazabicyclo[3.3.1]nonan-9-one-1,5-dicarboxylate) exhibited high affinity for [3H]ethylketocyclazocine and [3H]U-69.593 binding sites in guinea pig cerebellar membranes which known to be a good source for kappa1 receptors. It was shown by molecular modelling that heterocyclic bicyclo[3.3.1]nonan-9-ones fit very well with the structure of ketazocine, a prototypic kappa-selective benzomorphan compound; when compared to the arylacetamide structure of U-69.593, a specific kappa1-receptor agonist, a similar geometry was found with a slightly different distribution of the charges. It is postulated, that the essential structural skeleton involved in the opioid activity is an aryl-propyl-amine element distributed along the N7-C6-C5-C4-aryl bonds.

TopologyNet: Topology based deep convolutional and multi-task neural networks for biomolecular property predictions

PubMed Central

2017-01-01

Although deep learning approaches have had tremendous success in image, video and audio processing, computer vision, and speech recognition, their applications to three-dimensional (3D) biomolecular structural data sets have been hindered by the geometric and biological complexity. To address this problem we introduce the element-specific persistent homology (ESPH) method. ESPH represents 3D complex geometry by one-dimensional (1D) topological invariants and retains important biological information via a multichannel image-like representation. This representation reveals hidden structure-function relationships in biomolecules. We further integrate ESPH and deep convolutional neural networks to construct a multichannel topological neural network (TopologyNet) for the predictions of protein-ligand binding affinities and protein stability changes upon mutation. To overcome the deep learning limitations from small and noisy training sets, we propose a multi-task multichannel topological convolutional neural network (MM-TCNN). We demonstrate that TopologyNet outperforms the latest methods in the prediction of protein-ligand binding affinities, mutation induced globular protein folding free energy changes, and mutation induced membrane protein folding free energy changes. Availability: weilab.math.msu.edu/TDL/ PMID:28749969

The complex nature of calcium cation interactions with phospholipid bilayers

PubMed Central

Melcrová, Adéla; Pokorna, Sarka; Pullanchery, Saranya; Kohagen, Miriam; Jurkiewicz, Piotr; Hof, Martin; Jungwirth, Pavel; Cremer, Paul S.; Cwiklik, Lukasz

2016-01-01

Understanding interactions of calcium with lipid membranes at the molecular level is of great importance in light of their involvement in calcium signaling, association of proteins with cellular membranes, and membrane fusion. We quantify these interactions in detail by employing a combination of spectroscopic methods with atomistic molecular dynamics simulations. Namely, time-resolved fluorescent spectroscopy of lipid vesicles and vibrational sum frequency spectroscopy of lipid monolayers are used to characterize local binding sites of calcium in zwitterionic and anionic model lipid assemblies, while dynamic light scattering and zeta potential measurements are employed for macroscopic characterization of lipid vesicles in calcium-containing environments. To gain additional atomic-level information, the experiments are complemented by molecular simulations that utilize an accurate force field for calcium ions with scaled charges effectively accounting for electronic polarization effects. We demonstrate that lipid membranes have substantial calcium-binding capacity, with several types of binding sites present. Significantly, the binding mode depends on calcium concentration with important implications for calcium buffering, synaptic plasticity, and protein-membrane association. PMID:27905555

The complex nature of calcium cation interactions with phospholipid bilayers

NASA Astrophysics Data System (ADS)

Melcrová, Adéla; Pokorna, Sarka; Pullanchery, Saranya; Kohagen, Miriam; Jurkiewicz, Piotr; Hof, Martin; Jungwirth, Pavel; Cremer, Paul S.; Cwiklik, Lukasz

2016-12-01

Understanding interactions of calcium with lipid membranes at the molecular level is of great importance in light of their involvement in calcium signaling, association of proteins with cellular membranes, and membrane fusion. We quantify these interactions in detail by employing a combination of spectroscopic methods with atomistic molecular dynamics simulations. Namely, time-resolved fluorescent spectroscopy of lipid vesicles and vibrational sum frequency spectroscopy of lipid monolayers are used to characterize local binding sites of calcium in zwitterionic and anionic model lipid assemblies, while dynamic light scattering and zeta potential measurements are employed for macroscopic characterization of lipid vesicles in calcium-containing environments. To gain additional atomic-level information, the experiments are complemented by molecular simulations that utilize an accurate force field for calcium ions with scaled charges effectively accounting for electronic polarization effects. We demonstrate that lipid membranes have substantial calcium-binding capacity, with several types of binding sites present. Significantly, the binding mode depends on calcium concentration with important implications for calcium buffering, synaptic plasticity, and protein-membrane association.

Binding of (/sup 3/H)forskolin to platelet membranes and solubilized proteins from bovine brain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nelson, C.A.; Seamon, K.B.

1986-05-01

(/sup 3/H)Forskolin ((/sup 3/H)FSK) bound to platelet membranes with a Kd of 20 nM and a Bmax of 125 fmol/mg protein. The Bmax was increased to 400 fmol/mg protein in the presence of GppNHp (or NaF) and MgCl/sub 2/ with no change in Kd. PGE/sub 1/ decreased the EC50 of GppNHp to increase the Bmax for (/sup 3/H)FSK binding from 600 nM to 35 nM. In contrast, PGE/sub 1/ had no effect on the EC50 of NaF to increase (/sup 3/H)FSK binding. (/sup 3/H)FSK binding increased slowly over 60 min when forskolin and GppNHp were added to membranes simultaneously atmore » 20/sup 0/C. Preincubation of membranes with GppNHp at 20/sup 5/C also caused a linear increase in adenylate cyclase specific activity over 60 minutes. (/sup 3/H)FSK bound to solubilized protein from bovine brain membrane with a Kd of 22 nM. GppNHp increased the number of binding sites in solubilized proteins only if membranes were not preincubated with GppNHp prior to solubilization. In conclusion the number of binding sites for (/sup 3/H)FSK is increased by agents that activate adenylate cyclase through the Ns protein. These sites appear to be associated with an activated complex of the Ns protein and adenylate cyclase.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Band, L.; Xu, Heng; Bykov, V.

The present study demonstrates that pretreatment of rat brain membranes with (+)-cis-3-methylfentanyl ((+)-cis-MF), followed by extensive washing of the membranes, produces a wash-resistant decreasing in the binding of ({sup 3}H)-(D-ala{sup 2}, D-leu{sup 5})enkephalin to the d binding site of the opioid receptor complex ({delta}{sub cx} binding site). Intravenous administration of (+)-cis-MF (50 {mu}g/kg) to rats produced a pronounced catalepsy and also produced a wash-resistant masking of {delta}{sub cx} and {mu} binding sites in membranes prepared 120 min post-injection. Administration of 1 mg/kg i.v. of the opioid antagonist, 6-desoxy-6{beta}-fluoronaltrexone (cycloFOXY), 100 min after the injection of (+)-cis-MF (20 min prior tomore » the preparation of membranes) completely reversed the catatonia and restored masked {delta}{sub cx} binding sites to control levels. This was not observed with (+)-cycloFOXY. The implications of these and other findings for the mechanism of action of (+)-cis-MF and models of the opioid receptors are discussed.« less

Rearrangements under confinement lead to increased binding energy of Synaptotagmin-1 with anionic membranes in Mg2+ and Ca2.

PubMed

Gruget, Clémence; Coleman, Jeff; Bello, Oscar; Krishnakumar, Shyam S; Perez, Eric; Rothman, James E; Pincet, Frederic; Donaldson, Stephen H

2018-05-01

Synaptotagmin-1 (Syt1) is the primary calcium sensor (Ca 2+ ) that mediates neurotransmitter release at the synapse. The tandem C2 domains (C2A and C2B) of Syt1 exhibit functionally critical, Ca 2+ -dependent interactions with the plasma membrane. With the surface forces apparatus, we directly measure the binding energy of membrane-anchored Syt1 to an anionic membrane and find that Syt1 binds with ~6 k B T in EGTA, ~10 k B T in Mg 2+ and ~18 k B T in Ca 2+ . Molecular rearrangements measured during confinement are more prevalent in Ca 2+ and Mg 2+ and suggest that Syt1 initially binds through C2B, then reorients the C2 domains into the preferred binding configuration. These results provide energetic and mechanistic details of the Syt1 Ca 2+ -activation process in synaptic transmission. © 2018 Federation of European Biochemical Societies.

Multilayer affinity adsorption of albumin on polymer brushes modified membranes in a continuous-flow system.

PubMed

Hu, Meng-Xin; Li, Xiang; Li, Ji-Nian; Huang, Jing-Jing; Ren, Ge-Rui

2018-02-23

Polymer brushes modified surfaces have been widely used for protein immobilization and isolation. Modification of membranes with polymer brushes increases the surface concentration of affinity ligands used for protein binding. Albumin is one of the transporting proteins and shows a high affinity to bile acids. In this work, the modified membranes with cholic acid-containing polymer brushes can be facilely prepared by the immobilization of cholic acid on the poly(2-hydroxyethyl methacrylate) grafted microporous polypropylene membranes (MPPMs) for affinity adsorption of albumin. ATR/FT-IR and X-ray photoelectron spectroscopy were used to characterize the chemical composition of the modified membranes. Water contact angle measurements were used to analyze the hydrophilic/hydrophobic properties of the membrane surface. The modified MPPMs show a high affinity to albumin and have little non-specific adsorption of hemoglobin. The dynamic binding capacity of albumin in the continous-flow system increases with the cycle number and feed rate as the binding degree of cholic acid is moderate. The highest binding capacity of affinity membranes is about 52.49 g/m 2 membrane, which is about 24 times more than the monolayer binding capacity. These results reveal proteins could be captured in multilayers by the polymer brushes containing affinity ligands similar to the polymer brushes containing ion-exchange groups, which open up the potential of the polymer brushes containing affinity ligands in protein or another components separation. And the cholic acid containing polymer brushes modified membranes has the promising potential for albumin separation and purification rapidly from serum or fermented solution in medical diagnosis and bioseparation. Copyright © 2018 Elsevier B.V. All rights reserved.

Isolation, Characterization and Lipid-Binding Properties of the Recalcitrant FtsA Division Protein from Escherichia coli

PubMed Central

Zorrilla, Silvia; Reija, Belén; Alfonso, Carlos; Mingorance, Jesús; Rivas, Germán; Jiménez, Mercedes

2012-01-01

We have obtained milligram amounts of highly pure Escherichia coli division protein FtsA from inclusion bodies with an optimized purification method that, by overcoming the reluctance of FtsA to be purified, surmounts a bottleneck for the analysis of the molecular basis of FtsA function. Purified FtsA is folded, mostly monomeric and interacts with lipids. The apparent affinity of FtsA binding to the inner membrane is ten-fold higher than to phospholipids, suggesting that inner membrane proteins could modulate FtsA-membrane interactions. Binding of FtsA to lipids and membranes is insensitive to ionic strength, indicating that a net contribution of hydrophobic interactions is involved in the association of FtsA to lipid/membrane structures. PMID:22761913

The Effects of AR on Membrane Wing Performance in Low Re Flight

NASA Astrophysics Data System (ADS)

Jordan, Alex; Hubner, James

2011-11-01

There is increased interest in the design of micro air vehicles (MAVs) due to their military reconnaissance and surveying capabilities. Research has shown that the use of membrane wings in low Reynolds number flight results in performance characteristics that, when compared to rigid wing counterparts of similar geometry, are beneficial. An experimental study was performed to determine if the benefits of membrane wings change when AR is decreased. The membrane wings used silicon rubber affixed to aluminum frames of repeated cell geometry. The wings tested employed 1, 3, 5 and 9 cells and had ARs of 0.9, 2.6, 4.1, and 4.33 respectively. Measurements of lift and drag at a Reynolds number of 49,000 were acquired over a range of angles of attack. Vibration frequencies of the membranes were obtained via high-speed imagery. Comparisons of lift and drag data for the flat plates and membrane wings showed that the membrane wings with ARs of 0.9 and 2.6 did not show the same performance benefits as the higher AR membrane wings. Funded by NSF REU Site #1062611.

Food proteins and maturation of small intestinal microvillus membranes (MVM). I. Binding characteristics of cow's milk proteins and concanavalin A to MVM from newborn and adult rats.

PubMed

Stern, M; Gellermann, B

1988-01-01

To study maturational changes of food protein and lectin binding to rat small intestinal microvillus membranes (MVM), MVM were prepared from newborn and adult animals by a modified CaCl2 precipitation technique. Radiolabeled cow's milk proteins [alpha-lactalbumin, alpha-casein, beta-lactoglobulin, bovine serum albumin (BSA)] and the lectin concanavalin A (Con A) were used for incubations. Binding assays were done using miniature ultracentrifugation for separation of unbound material. Binding of Con A to MVM from newborn and adult rats was strong, specific, and saturable. Binding of Con A was inhibited by cold Con A and by the sugar ligand polymer mannan. Adult MVM bound more Con A than newborn preparations. Unlike Con A, binding of cow's milk proteins by MVM was weak, nonspecific, and noninhibitable. Newborn MVM bound more cow's milk proteins than adult controls. This was true for all the proteins tested (p less than 0.001). Binding rose with decreased molecular weight of cow's milk proteins, but molecular weight was not the only determining factor for binding. Trypsin treatment of MVM caused a marked increase of BSA binding in adult but not in newborn preparations. This finding indicated the importance of protein components of MVM for cow's milk protein binding. Maturational changes in protein-lipid interactions and membrane fluidity possibly influence nonspecific cow's milk protein binding to MVM. Differences in binding between newborns and adults were not directly related to maturational shifts in membrane glycosylation that are indicated by differential Con A binding. Increased cow's milk protein binding in newborn individuals might increase the potential risk to develop an adverse reaction to food proteins.

Interaction between phloretin and the red blood cell membrane

PubMed Central

1976-01-01

Phloretin binding to red blood cell components has been characterized at pH6, where binding and inhibitory potency are maximal. Binding to intact red cells and to purified hemoglobin are nonsaturated processes approximately equal in magnitude, which strongly suggests that most of the red cell binding may be ascribed to hemoglobin. This conclusion is supported by the fact that homoglobin-free red cell ghosts can bind only 10% as much phloretin as an equivalent number of red cells. The permeability of the red cell membrane to phloretin has been determined by a direct measurement at the time-course of the phloretin uptake. At a 2% hematocrit, the half time for phloretin uptake is 8.7s, corresponding to a permeability coefficient of 2 x 10(-4) cm/s. The concentration dependence of the binding to ghosts reveals two saturable components. Phloretin binds with high affinity (K diss = 1.5 muM) to about 2.5 x 10(6) sites per cell; it also binds with lower affinity (Kdiss = 54 muM) to a second (5.5 x 10(7) per cell) set of sites. In sonicated total lipid extracts of red cell ghosts, phloretin binding consists of a single, saturable component. Its affinity and total number of sites are not significantly different from those of the low affinity binding process in ghosts. No high affinity binding of phloretin is exhibited by the red cell lipid extracts. Therefore, the high affinity phloretin binding sites are related to membrane proteins, and the low affinity sites result from phloretin binding to lipid. The identification of these two types of binding sites allows phloretin effects on protein-mediated transport processes to be distinguished from effects on the lipid region of the membrane. PMID:5575

Effects of retinoids on differentiation, lipid metabolism, epidermal growth factor, and low-density lipoprotein binding in squamous carcinoma cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ponec, M.; Weerheim, A.; Havekes, L.

The relationship among keratinocyte differentiation capacity, lipid synthesis, low-density lipoprotein (LDL) metabolism, plasma membrane composition, and epidermal growth factor (EGF) binding has been studied in SCC-12F2 cells. The differentiation capacity of the cells, i.e., ionophore-induced cornified envelope formation, was inhibited by various retinoids and stimulated by hydrocortisone. Retinoids that caused a significant reduction of cornified envelope formation, i.e., retinoic acid and 13-cis-retinoic acid, caused only minor changes in lipid synthesis and plasma membrane composition. Arotinoid ethylsulfone, having a minor effect on cornified envelope formation, caused a drastic inhibition of cholesterol synthesis resulting in changes in the plasma membrane composition. Hydrocortisonemore » stimulated cornified envelope formation but had only minor effects on lipid synthesis and plasma membrane composition. Of all retinoids tested, only arotinoid ethylsulfone caused a drastic increase in EGF binding, while hydrocortisone had no effect. These results clearly demonstrate that the plasma membrane composition is not related to keratinocyte differentiation capacity, but most likely does determine EGF binding. Furthermore, EGF binding does not determine keratinocyte differentiation capacity.« less

Structural and mechanistic insights into phospholipid transfer by Ups1-Mdm35 in mitochondria

NASA Astrophysics Data System (ADS)

Watanabe, Yasunori; Tamura, Yasushi; Kawano, Shin; Endo, Toshiya

2015-08-01

Eukaryotic cells are compartmentalized into membrane-bounded organelles whose functions rely on lipid trafficking to achieve membrane-specific compositions of lipids. Here we focused on the Ups1-Mdm35 system, which mediates phosphatidic acid (PA) transfer between the outer and inner mitochondrial membranes, and determined the X-ray structures of Mdm35 and Ups1-Mdm35 with and without PA. The Ups1-Mdm35 complex constitutes a single domain that has a deep pocket and flexible Ω-loop lid. Structure-based mutational analyses revealed that a basic residue at the pocket bottom and the Ω-loop lid are important for PA extraction from the membrane following Ups1 binding. Ups1 binding to the membrane is enhanced by the dissociation of Mdm35. We also show that basic residues around the pocket entrance are important for Ups1 binding to the membrane and PA extraction. These results provide a structural basis for understanding the mechanism of PA transfer between mitochondrial membranes.

Hydrodynamic and Membrane Binding Properties of Purified Rous Sarcoma Virus Gag Protein

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dick, Robert A.; Datta, Siddhartha A. K.; Nanda, Hirsh

2016-05-06

Previously, no retroviral Gag protein has been highly purified in milligram quantities and in a biologically relevant and active form. We have purified Rous sarcoma virus (RSV) Gag protein and in parallel several truncation mutants of Gag and have studied their biophysical properties and membrane interactionsin vitro. RSV Gag is unusual in that it is not naturally myristoylated. From its ability to assemble into virus-like particlesin vitro, we infer that RSV Gag is biologically active. By size exclusion chromatography and small-angle X-ray scattering, Gag in solution appears extended and flexible, in contrast to previous reports on unmyristoylated HIV-1 Gag, whichmore » is compact. However, by neutron reflectometry measurements of RSV Gag bound to a supported bilayer, the protein appears to adopt a more compact, folded-over conformation. At physiological ionic strength, purified Gag binds strongly to liposomes containing acidic lipids. This interaction is stimulated by physiological levels of phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P2] and by cholesterol. However, unlike HIV-1 Gag, RSV Gag shows no sensitivity to acyl chain saturation. In contrast with full-length RSV Gag, the purified MA domain of Gag binds to liposomes only weakly. Similarly, both an N-terminally truncated version of Gag that is missing the MA domain and a C-terminally truncated version that is missing the NC domain bind only weakly. These results imply that NC contributes to membrane interactionin vitro, either by directly contacting acidic lipids or by promoting Gag multimerization. Retroviruses like HIV assemble at and bud from the plasma membrane of cells. Assembly requires the interaction between thousands of Gag molecules to form a lattice. Previous work indicated that lattice formation at the plasma membrane is influenced by the conformation of monomeric HIV. We have extended this work to the more tractable RSV Gag. Our results show that RSV Gag is highly flexible and can adopt a folded-over conformation on a lipid bilayer, implicating both the N and C termini in membrane binding. In addition, binding of Gag to membranes is diminished when either terminal domain is truncated. RSV Gag membrane association is significantly less sensitive than HIV Gag membrane association to lipid acyl chain saturation. These findings shed light on Gag assembly and membrane binding, critical steps in the viral life cycle and an untapped target for antiretroviral drugs.« less

The RNA-Binding Site of Poliovirus 3C Protein Doubles as a Phosphoinositide-Binding Domain.

PubMed

Shengjuler, Djoshkun; Chan, Yan Mei; Sun, Simou; Moustafa, Ibrahim M; Li, Zhen-Lu; Gohara, David W; Buck, Matthias; Cremer, Paul S; Boehr, David D; Cameron, Craig E

2017-12-05

Some viruses use phosphatidylinositol phosphate (PIP) to mark membranes used for genome replication or virion assembly. PIP-binding motifs of cellular proteins do not exist in viral proteins. Molecular-docking simulations revealed a putative site of PIP binding to poliovirus (PV) 3C protein that was validated using nuclear magnetic resonance spectroscopy. The PIP-binding site was located on a highly dynamic α helix, which also functions in RNA binding. Broad PIP-binding activity was observed in solution using a fluorescence polarization assay or in the context of a lipid bilayer using an on-chip, fluorescence assay. All-atom molecular dynamics simulations of the 3C protein-membrane interface revealed PIP clustering and perhaps PIP-dependent conformations. PIP clustering was mediated by interaction with residues that interact with the RNA phosphodiester backbone. We conclude that 3C binding to membranes will be determined by PIP abundance. We suggest that the duality of function observed for 3C may extend to RNA-binding proteins of other viruses. Copyright © 2017 Elsevier Ltd. All rights reserved.

Comparison of S. cerevisiae F-BAR domain structures reveals a conserved inositol phosphate binding site

PubMed Central

Moravcevic, Katarina; Alvarado, Diego; Schmitz, Karl R.; Kenniston, Jon A.; Mendrola, Jeannine M.; Ferguson, Kathryn M.; Lemmon, Mark A.

2015-01-01

SUMMARY F-BAR domains control membrane interactions in endocytosis, cytokinesis, and cell signaling. Although generally thought to bind curved membranes containing negatively charged phospholipids, numerous functional studies argue that differences in lipid-binding selectivities of F-BAR domains are functionally important. Here, we compare membrane-binding properties of the S. cerevisiae F-BAR domains in vitro and in vivo. Whereas some F-BAR domains (such as Bzz1p and Hof1p F-BARs) bind equally well to all phospholipids, the F-BAR domain from the RhoGAP Rgd1p preferentially binds phosphoinositides. We determined X-ray crystal structures of F-BAR domains from Hof1p and Rgd1p, the latter bound to an inositol phosphate. The structures explain phospholipid-binding selectivity differences, and reveal an F-BAR phosphoinositide binding site that is fully conserved in a mammalian RhoGAP called Gmip, and is partly retained in certain other F-BAR domains. Our findings reveal previously unappreciated determinants of F-BAR domain lipid-binding specificity, and provide a basis for its prediction from sequence. PMID:25620000

The mechanism of formation, structure and physiological relevance of covalent hemoglobin attachment to the erythrocyte membrane.

PubMed

Welbourn, Elizabeth M; Wilson, Michael T; Yusof, Ashril; Metodiev, Metodi V; Cooper, Chris E

2017-02-01

Covalent hemoglobin binding to membranes leads to band 3 (AE1) clustering and the removal of erythrocytes from the circulation; it is also implicated in blood storage lesions. Damaged hemoglobin, with the heme being in a redox and oxygen-binding inactive hemichrome form, has been implicated as the binding species. However, previous studies used strong non-physiological oxidants. In vivo hemoglobin is constantly being oxidised to methemoglobin (ferric), with around 1% of hemoglobin being in this form at any one time. In this study we tested the ability of the natural oxidised form of hemoglobin (methemoglobin) in the presence or absence of the physiological oxidant hydrogen peroxide to initiate membrane binding. The higher the oxidation state of hemoglobin (from Fe(III) to Fe(V)) the more binding was observed, with approximately 50% of this binding requiring reactive sulphydryl groups. The hemoglobin bound was in a high molecular weight complex containing spectrin, ankyrin and band 4.2, which are common to one of the cytoskeletal nodes. Unusually, we showed that hemoglobin bound in this way was redox active and capable of ligand binding. It can initiate lipid peroxidation showing the potential to cause cell damage. In vivo oxidative stress studies using extreme endurance exercise challenges showed an increase in hemoglobin membrane binding, especially in older cells with lower levels of antioxidant enzymes. These are then targeted for destruction. We propose a model where mild oxidative stress initiates the binding of redox active hemoglobin to the membrane. The maximum lifetime of the erythrocyte is thus governed by the redox activity of the cell; from the moment of its release into the circulation the timer is set. Copyright © 2016. Published by Elsevier Inc.

The interaction of substituted benzamides with brain benzodiazepine binding sites in vitro.

PubMed Central

Horton, R. W.; Lowther, S.; Chivers, J.; Jenner, P.; Marsden, C. D.; Testa, B.

1988-01-01

1. The interaction of substituted benzamides with brain benzodiazepine (BDZ) binding sites was examined by their ability to displace [3H]-flunitrazepam ([3H]-FNM) from specific binding sites in bovine cortical membranes in vitro. 2. Clebopride, Delagrange 2674, Delagrange 2335 and BRL 20627 displayed concentration-dependent displacement of [3H]-FNM with IC50 values of 73 nM, 132 nM, 7.7 microM and 5.9 microM, respectively. Other substituted benzamides including metoclopramide, sulpiride, tiapride, sultopride and cisapride were inactive at 10(-5) M. 3. Inhibition by clebopride and Delagrange 2674 of [3H]-FNM binding was apparently competitive and readily reversible. 4. In the presence of gamma-aminobutyric acid (GABA), the ability of diazepam and Delagrange 2674 to displace [3H]-Ro 15-1788 binding was increased 3.6 and 1.6 fold respectively, compared to the absence of GABA, while ethyl beta-carboline-3-carboxylate (beta CCE) and clebopride were less potent in the presence of GABA. 5. Diazepam was 30 fold less potent at displacing [3H]-Ro 15-1788 in membranes that had been photoaffinity labelled with FNM than in control membranes, whereas the potency of beta CCE did not differ. Clebopride and Delagrange 2674 showed a less than two fold loss of potency in photoaffinity labelled membranes. 6. The pattern of binding of clebopride and Delagrange 2674 in these in vitro tests is similar to that found previously with partial agonists or antagonists at BDZ binding sites. 7. Clebopride and Delagrange 2674 inhibited [3H]-FNM binding with similar potency in rat cerebellar and hippocampal membranes, suggesting they have no selectivity for BDZ1 and BDZ2 binding sites.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2850059

Studies on the uptake of fatty acids by brush border membranes of the rabbit intestine.

PubMed

Proulx, P; Aubry, H; Brglez, I; Williamson, D G

1985-04-01

Initial studies revealed that the uptake of palmitic acid and oleic acid into brush border membranes was similar when these were isolated from either whole small intestine, jejunum, or ileum. The uptake of these fatty acids was somewhat lower with membranes obtained from duodenum. Subsequent studies, all with membranes obtained from whole intestine, indicated an increase in binding with chain length of fatty acid of up to 16 carbons. Unsaturation decreased this uptake somewhat. Taurocholate and 1-palmitoyl lysolecithin had a moderate stimulatory effect on the binding of oleic acid and palmitic acid at concentrations of 10 and 0.5 mM, respectively, and inhibited at higher concentrations. Addition of 1.4 mM egg lecithin to the fatty acid - bile salt micelles, such that the lecithin - bile salt ratio was 0.2, decreased the uptake of fatty acids generally, but did not significantly affect the pattern of binding by membrane fractions isolated from different segments nor did it change the pattern of labelling when fatty acid chain length and unsaturation were varied. At lower concentrations, egg lecithin had little effect on the uptake of oleic acid, whereas dipalmitoyl phosphatidylcholine stimulated binding of both palmitic acid and oleic acid over the entire range of concentrations tested. Preincubation of the membranes with this saturated phospholipid stimulated the uptake of oleic acid, and addition of this choline lipid to the oleic acid - bile salt containing micelles did not substantially enhance fatty acid uptake in lipid-treated membranes. The binding of fatty acid was very rapid either in the presence or the absence of Ca2+, such that even in zero-time controls essentially equilibrium bindings were obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

The phosphatidylinositol transfer protein RdgBβ binds 14-3-3 via its unstructured C-terminus, whereas its lipid-binding domain interacts with the integral membrane protein ATRAP (angiotensin II type I receptor-associated protein).

PubMed

Garner, Kathryn; Li, Michelle; Ugwuanya, Natalie; Cockcroft, Shamshad

2011-10-01

PITPs [PI (phosphatidylinositol) transfer proteins] bind and transfer PI between intracellular membranes and participate in many cellular processes including signalling, lipid metabolism and membrane traffic. The largely uncharacterized PITP RdgBβ (PITPNC1; retinal degeneration type B β), contains a long C-terminal disordered region following its defining N-terminal PITP domain. In the present study we report that the C-terminus contains two tandem phosphorylated binding sites (Ser(274) and Ser(299)) for 14-3-3. The C-terminus also contains PEST sequences which are shielded by 14-3-3 binding. Like many proteins containing PEST sequences, the levels of RdgBβ are regulated by proteolysis. RdgBβ is degraded with a half-life of 4 h following ubiquitination via the proteasome. A mutant RdgBβ which is unable to bind 14-3-3 is degraded even faster with a half-life of 2 h. In vitro, RdgBβ is 100-fold less active than PITPα for PI transfer, and RdgBβ proteins (wild-type and a mutant that cannot bind 14-3-3) expressed in COS-7 cells or endogenous proteins from heart cytosol do not exhibit transfer activity. When cells are treated with PMA, the PITP domain of RdgBβ interacts with the integral membrane protein ATRAP (angiotensin II type I receptor-associated protein; also known as AGTRAP) causing membrane recruitment. We suggest that RdgBβ executes its function following recruitment to membranes via its PITP domain and the C-terminal end of the protein could regulate entry to the hydrophobic cavity.

Exceptionally tight membrane-binding may explain the key role of the synaptotagmin-7 C 2 A domain in asynchronous neurotransmitter release

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voleti, Rashmi; Tomchick, Diana R.; Südhof, Thomas C.

Synaptotagmins (Syts) act as Ca2+ sensors in neurotransmitter release by virtue of Ca2+-binding to their two C2 domains, but their mechanisms of action remain unclear. Puzzlingly, Ca2+-binding to the C2B domain appears to dominate Syt1 function in synchronous release, whereas Ca2+-binding to the C2A domain mediates Syt7 function in asynchronous release. Here we show that crystal structures of the Syt7 C2A domain and C2AB region, and analyses of intrinsic Ca2+-binding to the Syt7 C2 domains using isothermal titration calorimetry, did not reveal major differences that could explain functional differentiation between Syt7 and Syt1. However, using liposome titrations under Ca2+ saturatingmore » conditions, we show that the Syt7 C2A domain has a very high membrane affinity and dominates phospholipid binding to Syt7 in the presence or absence of L-α-phosphatidylinositol 4,5-diphosphate (PIP2). For Syt1, the two Ca2+-saturated C2 domains have similar affinities for membranes lacking PIP2, but the C2B domain dominates binding to PIP2-containing membranes. Mutagenesis revealed that the dramatic differences in membrane affinity between the Syt1 and Syt7 C2A domains arise in part from apparently conservative residue substitutions, showing how striking biochemical and functional differences can result from the cumulative effects of subtle residue substitutions. Viewed together, our results suggest that membrane affinity may be a key determinant of the functions of Syt C2 domains in neurotransmitter release.« less

Functional interaction between the two halves of the photoreceptor-specific ATP binding cassette protein ABCR (ABCA4). Evidence for a non-exchangeable ADP in the first nucleotide binding domain.

PubMed

Ahn, Jinhi; Beharry, Seelochan; Molday, Laurie L; Molday, Robert S

2003-10-10

ABCR, also known as ABCA4, is a member of the superfamily of ATP binding cassette transporters that is believed to transport retinal or retinylidene-phosphatidylethanolamine across photoreceptor disk membranes. Mutations in the ABCR gene are responsible for Stargardt macular dystrophy and related retinal dystrophies that cause severe loss in vision. ABCR consists of two tandemly arranged halves each containing a membrane spanning segment followed by a large extracellular/lumen domain, a multi-spanning membrane domain, and a nucleotide binding domain (NBD). To define the role of each NBD, we examined the nucleotide binding and ATPase activities of the N and C halves of ABCR individually and co-expressed in COS-1 cells and derived from trypsin-cleaved ABCR in disk membranes. When disk membranes or membranes from co-transfected cells were photoaffinity labeled with 8-azido-ATP and 8-azido-ADP, only the NBD2 in the C-half bound and trapped the nucleotide. Co-expressed half-molecules displayed basal and retinal-stimulated ATPase activity similar to full-length ABCR. The individually expressed N-half displayed weak 8-azido-ATP labeling and low basal ATPase activity that was not stimulated by retinal, whereas the C-half did not bind ATP and exhibited little if any ATPase activity. Purified ABCR contained one tightly bound ADP, presumably in NBD1. Our results indicate that only NBD2 of ABCR binds and hydrolyzes ATP in the presence or absence of retinal. NBD1, containing a bound ADP, associates with NBD2 to play a crucial, non-catalytic role in ABCR function.

Specific binding of 15 HETE to lymphocytes. Effects on the fluidity of plasmatic membranes.

PubMed

Mexmain, S; Gualde, N; Aldigier, J C; Motta, C; Chable-Rabinovitch, H; Rigaud, M

1984-01-01

Specific binding of mouse lymphocytes for 15 HETE was examined by incubating cells with [14C]-15 HETE, 1 X 10(-8) to 1 X 10(-10)M. It was observed that the specific binding of radiolabeled 15 HETE is a function of time, of temperature and is modified by Ca2+ and dithiothreitol. When a fluorescent probe was embedded in the phospholipid core of the lymphocyte membrane and its motion analysed by fluorescence polarization, it was observed that 15 HETE increases the viscosity of the plasmatic membrane.

Simulation of controllable permeation in PNIPAAm coated membranes

NASA Astrophysics Data System (ADS)

Ehrenhofer, Adrian; Wallmersperger, Thomas; Richter, Andreas

2016-04-01

Membranes separate fluid compartments and can comprise transport structures for selective permeation. In biology, channel proteins are specialized in their atomic structure to allow transport of specific compounds (selectivity). Conformational changes in protein structure allow the control of the permeation abilities by outer stimuli (gating). In polymeric membranes, the selectivity is due to electrostatic or size-exclusion. It can thus be controlled by size variation or electric charges. Controllable permeation can be useful to determine particle-size distributions in continuous flow, e.g. in microfluidics and biomedicine to gain cell diameter profiles in blood. The present approach uses patterned polyethylene terephthalate (PET) membranes with hydrogel surface coating for permeation control by size-exclusion. The thermosensitive hydrogel poly(N-isopropylacrylamide) (PNIPAAm) is structured with a cross-shaped pore geometry. A change in the temperature of the water flow through the membrane leads to a pore shape variation. The temperature dependent behavior of PNIPAAm can be numerically modeled with a temperature expansion model, where the swelling and deswelling is depicted by temperature dependent expansion coefficients. In the present study, the free swelling behavior was implemented to the Finite Element tool ABAQUS for the complex composite structure of the permeation control membrane. Experimental values of the geometry characteristics were derived from microscopy images with the tool Image J and compared to simulation results. Numerical simulations using the derived thermo-mechanical model for different pore geometries (circular, rectangle, cross and triangle) were performed. With this study, we show that the temperature expansion model with values from the free swelling behavior can be used to adequately predict the deformation behavior of the complex membrane system. The predictions can be used to optimize the behavior of the membrane pores and the overall performance of the smart membrane.

The membrane bound bacterial lipocalin Blc is a functional dimer with binding preference for lysophospholipids

PubMed Central

Campanacci, Valérie; Bishop, Russell E.; Blangy, Stéphanie; Tegoni, Mariella; Cambillau, Christian

2016-01-01

Lipocalins, a widespread multifunctional family of small proteins (15–25 kDa) have been first described in eukaryotes and more recently in Gram-negative bacteria. Bacterial lipocalins belonging to class I are outer membrane lipoproteins, among which Blc from E. coli is the better studied. Blc is expressed under conditions of starvation and high osmolarity, conditions known to exert stress on the cell envelope. The structure of Blc that we have previously solved (V. Campanacci, D. Nurizzo, S. Spinelli, C. Valencia, M. Tegoni, C. Cambillau, FEBS Lett. 562 (2004) 183–188.) suggested its possible role in binding fatty acids or phospholipids. Both physiological and structural data on Blc, therefore, point to a role in storage or transport of lipids necessary for membrane maintenance. In order to further document this hypothesis for Blc function, we have performed binding studies using fluorescence quenching experiments. Our results indicate that dimeric Blc binds fatty acids and phospholipids in a micromolar Kd range. The crystal structure of Blc with vaccenic acid, an unsaturated C18 fatty acid, reveals that the binding site spans across the Blc dimer, opposite to its membrane anchored face. An exposed unfilled pocket seemingly suited to bind a polar group attached to the fatty acid prompted us to investigate lyso-phospholipids, which were found to bind in a nanomolar Kd range. We discuss these findings in terms of a potential role for Blc in the metabolism of lysophospholipids generated in the bacterial outer membrane. PMID:16920109

Evidence for a G protein-coupled diadenosine-5',5'''-P1,P4-tetraphosphate (Ap4A) receptor binding site in lung membranes from rat.

PubMed

Laubinger, W; Reiser, G

1999-01-29

Nucleotide receptors are of considerable importance in the treatment of lung diseases, such as cystic fibrosis. Because diadenosine polyphosphates may also be of significance as signalling molecules in lung, as they are in a variety of tissues, in the present work we investigated the binding sites for [3H]diadenosine-5',5'''-P1,P4-tetraphosphate (Ap4A) in plasma membranes from rat lung and studied their possible coupling to G proteins. We present evidence for a single high-affinity binding site for [3H]Ap4A with similar affinity for other diadenosine polyphosphates ApnA (n = 2 to 6). Displacement studies with different nucleotides revealed that the [3H]Ap4A binding site was different from P2X and P2Y2 receptor binding sites. Pretreatment of lung membranes with GTPgammaS or GTP in the presence of Mg2+ increased the Ki for Ap4A from 91 nM to 5.1 microM, which is indicative of G protein coupling. The putative coupling to G proteins was further confirmed by the enhancement of [35S]GTPgammaS binding (to Galpha proteins) to lung membranes by Ap4A (63% increase over basal) in a concentration-dependent manner. Therefore, our data for the first time provide evidence of a G protein-coupled Ap4A binding site in lung membranes.

Interplay between membrane curvature and protein conformational equilibrium investigated by solid-state NMR.

PubMed

Liao, Shu Y; Lee, Myungwoon; Hong, Mei

2018-03-01

Many membrane proteins sense and induce membrane curvature for function, but structural information about how proteins modulate their structures to cause membrane curvature is sparse. We review our recent solid-state NMR studies of two virus membrane proteins whose conformational equilibrium is tightly coupled to membrane curvature. The influenza M2 proton channel has a drug-binding site in the transmembrane (TM) pore. Previous chemical shift data indicated that this pore-binding site is lost in an M2 construct that contains the TM domain and a curvature-inducing amphipathic helix. We have now obtained chemical shift perturbation, protein-drug proximity, and drug orientation data that indicate that the pore-binding site is restored when the full cytoplasmic domain is present. This finding indicates that the curvature-inducing amphipathic helix distorts the TM structure to interfere with drug binding, while the cytoplasmic tail attenuates this effect. In the second example, we review our studies of a parainfluenza virus fusion protein that merges the cell membrane and the virus envelope during virus entry. Chemical shifts of two hydrophobic domains of the protein indicate that both domains have membrane-dependent backbone conformations, with the β-strand structure dominating in negative-curvature phosphatidylethanolamine (PE) membranes. 31 P NMR spectra and 1 H- 31 P correlation spectra indicate that the β-strand-rich conformation induces saddle-splay curvature to PE membranes and dehydrates them, thus stabilizing the hemifusion state. These results highlight the indispensable role of solid-state NMR to simultaneously determine membrane protein structures and characterize the membrane curvature in which these protein structures exist. Copyright © 2018 Elsevier Inc. All rights reserved.

Avian pathogenic Escherichia coli bind fibronectin and laminin.

PubMed

Ramírez, Rosa María; Almanza, Yolanda; González, Rafael; García, Santos; Heredia, Norma

2009-04-01

Avian colisepticemia frequently occurs after respiratory tract damage, the primary site for infection allows bacteria to encounter an exposed basement membrane, where laminin and fibronectin are important components. We investigated the ability of an isolate of avian pathogenic Escherichia coli to bind fibronectin and laminin. Using Far-western dot blot analysis, we demonstrated the ability of this microorganism to bind basement membrane proteins fibronectin and laminin. Results from an ELISA-based approach indicate that the binding to these membrane proteins was bacterial-dose dependent. Furthermore, two specific E. coli polypeptides, of 32 kDa and 130 kDa, reacted with laminin and fibronectin, respectively. Further evaluation of these potential bacterial adhesins may provide insights into the pathogenesis of colibacillosis.

Membrane and Protein Interactions of the Pleckstrin Homology Domain Superfamily

PubMed Central

Lenoir, Marc; Kufareva, Irina; Abagyan, Ruben; Overduin, Michael

2015-01-01

The human genome encodes about 285 proteins that contain at least one annotated pleckstrin homology (PH) domain. As the first phosphoinositide binding module domain to be discovered, the PH domain recruits diverse protein architectures to cellular membranes. PH domains constitute one of the largest protein superfamilies, and have diverged to regulate many different signaling proteins and modules such as Dbl homology (DH) and Tec homology (TH) domains. The ligands of approximately 70 PH domains have been validated by binding assays and complexed structures, allowing meaningful extrapolation across the entire superfamily. Here the Membrane Optimal Docking Area (MODA) program is used at a genome-wide level to identify all membrane docking PH structures and map their lipid-binding determinants. In addition to the linear sequence motifs which are employed for phosphoinositide recognition, the three dimensional structural features that allow peripheral membrane domains to approach and insert into the bilayer are pinpointed and can be predicted ab initio. The analysis shows that conserved structural surfaces distinguish which PH domains associate with membrane from those that do not. Moreover, the results indicate that lipid-binding PH domains can be classified into different functional subgroups based on the type of membrane insertion elements they project towards the bilayer. PMID:26512702

The helical structure of DNA facilitates binding

NASA Astrophysics Data System (ADS)

Berg, Otto G.; Mahmutovic, Anel; Marklund, Emil; Elf, Johan

2016-09-01

The helical structure of DNA imposes constraints on the rate of diffusion-limited protein binding. Here we solve the reaction-diffusion equations for DNA-like geometries and extend with simulations when necessary. We find that the helical structure can make binding to the DNA more than twice as fast compared to a case where DNA would be reactive only along one side. We also find that this rate advantage remains when the contributions from steric constraints and rotational diffusion of the DNA-binding protein are included. Furthermore, we find that the association rate is insensitive to changes in the steric constraints on the DNA in the helix geometry, while it is much more dependent on the steric constraints on the DNA-binding protein. We conclude that the helical structure of DNA facilitates the nonspecific binding of transcription factors and structural DNA-binding proteins in general.

[Glutamate-binding membrane proteins from human platelets].

PubMed

Gurevich, V S; Popov, Iu G; Gorodinskiĭ, A I; Dambinova, S A

1991-09-01

Solubilization of the total membrane fraction of human platelets in a 2% solution of sodium deoxycholate and subsequent affinity chromatography on glutamate agarose resulted in two protein fractions possessing a glutamate-binding activity. As can be evidenced from radioligand binding data, the first fraction contains two types of binding sites (Kd1 = 1 microM, Bmax 1 = 100 pmol/mg of protein; Kd2 = 9.3 microMm Bmax2 = 395 pmol/mg of protein). The second fraction has only one type of binding sites (Kd = 1 microM, Bmax = = 110 pmol/mg of protein). SDS-PAAG electrophoresis revealed the presence in the first fraction of proteins with Mr of 14, 24, 56 and 155 kDa, whereas the second fraction was found to contain 14, 46, 71 and 155 kDa proteins. Solid phase immunoenzymatic analysis using poly- and monoclonal specific antibodies against mammalian brain glutamate-binding proteins revealed a marked immunochemical similarity of the isolated protein fractions with human brain synaptic membrane glutamate-binding proteins.

Highly potent antimicrobial peptides from N-terminal membrane-binding region of E. coli MreB.

PubMed

Saikia, Karabi; Sravani, Yalavarthi Durga; Ramakrishnan, Vibin; Chaudhary, Nitin

2017-02-23

Microbial pathogenesis is a serious health concern. The threat escalates as the existing conventional antimicrobials are losing their efficacy against the evolving pathogens. Peptides hold promise to be developed into next-generation antibiotics. Antimicrobial peptides adopt amphipathic structures that could selectively bind to and disrupt the microbial membranes. Interaction of proteins with membranes is central to all living systems and we reasoned that the membrane-binding domains in microbial proteins could be developed into efficient antimicrobials. This is an interesting approach as self-like sequences could elude the microbial strategies of degrading the antimicrobial peptides, one of the mechanisms of showing resistance to antimicrobials. We selected the 9-residue-long membrane-binding region of E. coli MreB protein. The 9-residue peptide (C-terminal amide) and its N-terminal acetylated analog displayed broad-spectrum activity, killing Gram-negative bacteria, Gram-positive bacteria, and fungi. Extension with a tryptophan residue at the N-terminus drastically improved the activity of the peptides with lethal concentrations ≤10 μM against all the organisms tested. The tryptophan-extended peptides caused complete killing of C. albicans as well as gentamicin and methicillin resistant S. aureus at 5 μM concentration. Lipid-binding studies and electron microscopic analyses of the peptide-treated microbes suggest membrane disruption as the mechanism of killing.

Fully Nonlinear Modeling and Analysis of Precision Membranes

NASA Technical Reports Server (NTRS)

Pai, P. Frank; Young, Leyland G.

2003-01-01

High precision membranes are used in many current space applications. This paper presents a fully nonlinear membrane theory with forward and inverse analyses of high precision membrane structures. The fully nonlinear membrane theory is derived from Jaumann strains and stresses, exact coordinate transformations, the concept of local relative displacements, and orthogonal virtual rotations. In this theory, energy and Newtonian formulations are fully correlated, and every structural term can be interpreted in terms of vectors. Fully nonlinear ordinary differential equations (ODES) governing the large static deformations of known axisymmetric membranes under known axisymmetric loading (i.e., forward problems) are presented as first-order ODES, and a method for obtaining numerically exact solutions using the multiple shooting procedure is shown. A method for obtaining the undeformed geometry of any axisymmetric membrane with a known inflated geometry and a known internal pressure (i.e., inverse problems) is also derived. Numerical results from forward analysis are verified using results in the literature, and results from inverse analysis are verified using known exact solutions and solutions from the forward analysis. Results show that the membrane theory and the proposed numerical methods for solving nonlinear forward and inverse membrane problems are accurate.

Thermodynamics of melittin binding to lipid bilayers. Aggregation and pore formation.

PubMed

Klocek, Gabriela; Schulthess, Therese; Shai, Yechiel; Seelig, Joachim

2009-03-31

Lipid membranes act as catalysts for protein folding. Both alpha-helical and beta-sheet structures can be induced by the interaction of peptides or proteins with lipid surfaces. Melittin, the main component of bee venom, is a particularly well-studied example for the membrane-induced random coil-to-alpha-helix transition. Melittin in water adopts essentially a random coil conformation. The cationic amphipathic molecule has a high affinity for neutral and anionic lipid membranes and exhibits approximately 50-65% alpha-helix conformation in the membrane-bound state. At higher melittin concentrations, the peptide forms aggregates or pores in the membrane. In spite of the long-standing interest in melittin-lipid interactions, no systematic thermodynamic study is available. This is probably caused by the complexity of the binding process. Melittin binding to lipid vesicles is fast and occurs within milliseconds, but the binding process involves at least four steps, namely, (i) the electrostatic attraction of the cationic peptide to an anionic membrane surface, (ii) the hydrophobic insertion into the lipid membrane, (iii) the conformational change from random coil to alpha-helix, and (iv) peptide aggregation in the lipid phase. We have combined microelectrophoresis (measurement of the zeta potential), isothermal titration calorimetry, and circular dichroism spectroscopy to provide a thermodynamic analysis of the individual binding steps. We have compared melittin with a synthetic analogue, [D]-V(5,8),I(17),K(21)-melittin, for which alpha-helix formation is suppressed and replaced by beta-structure formation. The comparison reveals that the thermodynamic parameters for the membrane-induced alpha-helix formation of melittin are identical to those observed earlier for other peptides with an enthalpy h(helix) of -0.7 kcal/mol and a free energy g(helix) of -0.2 kcal/mol per peptide residue. These thermodynamic parameters hence appear to be of general validity for lipid-induced membrane folding. As g(helix) is negative, it further follows that helix formation leads to an enhanced membrane binding for the peptides or proteins involved. In this study, melittin binds by approximately 2 orders of magnitude better to the lipid membrane than [D]-V(5,8),I(17),K(21)-melittin which cannot form an alpha-helix. We also found conditions under which the isothermal titration experiment reports only the aggregation process. Melittin aggregation is an entropy-driven process with an endothermic heat of reaction (DeltaH(agg)) of approximately 2 kcal/mol and an aggregation constant of 20-40 M(-1).

Membrane Curvature and Lipid Composition Synergize To Regulate N-Ras Anchor Recruitment.

PubMed

Larsen, Jannik B; Kennard, Celeste; Pedersen, Søren L; Jensen, Knud J; Uline, Mark J; Hatzakis, Nikos S; Stamou, Dimitrios

2017-09-19

Proteins anchored to membranes through covalently linked fatty acids and/or isoprenoid groups play crucial roles in all forms of life. Sorting and trafficking of lipidated proteins has traditionally been discussed in the context of partitioning to membrane domains of different lipid composition. We recently showed that membrane shape/curvature can in itself mediate the recruitment of lipidated proteins. However, exactly how membrane curvature and composition synergize remains largely unexplored. Here we investigated how three critical structural parameters of lipids, namely acyl chain saturation, headgroup size, and acyl chain length, modulate the capacity of membrane curvature to recruit lipidated proteins. As a model system we used the lipidated minimal membrane anchor of the GTPase, N-Ras (tN-Ras). Our data revealed complex synergistic effects, whereby tN-Ras binding was higher on planar DOPC than POPC membranes, but inversely higher on curved POPC than DOPC membranes. This variation in the binding to both planar and curved membranes leads to a net increase in the recruitment by membrane curvature of tN-Ras when reducing the acyl chain saturation state. Additionally, we found increased recruitment by membrane curvature of tN-Ras when substituting PC for PE, and when decreasing acyl chain length from 14 to 12 carbons (DMPC versus DLPC). However, these variations in recruitment ability had different origins, with the headgroup size primarily influencing tN-Ras binding to planar membranes whereas the change in acyl chain length primarily affected binding to curved membranes. Molecular field theory calculations recapitulated these findings and revealed lateral pressure as an underlying biophysical mechanism dictating how curvature and composition synergize to modulate recruitment of lipidated proteins. Our findings suggest that the different compositions of cellular compartments could modulate the potency of membrane curvature to recruit lipidated proteins and thereby synergistically regulate the trafficking and sorting of lipidated proteins. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Strychnine Binding Associated with Glycine Receptors of the Central Nervous System

PubMed Central

Young, Anne B.; Snyder, Solomon H.

1973-01-01

[3H]Strychnine binds to synaptic-membrane fractions of the spinal cord in a selective fashion, indicating an interaction with postsynaptic glycine receptors. Displacement of strychnine by glycine and other amino acids parallels their glycine-like neurophysiologic activity. The regional localization of strychnine binding in the central nervous system correlates closely with endogenous glycine concentrations. In subcellular fractionation experiments, strychnine binding is most enhanced in synaptic-membrane fractions. Strychnine binding is saturable, with affinity constants for glycine and strychnine of 10 and 0.03 μM, respectively. PMID:4200724

Molecular basis of endosomal-membrane association for the dengue virus envelope protein

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rogers, David M.; Kent, Michael S.; Rempe, Susan B.

Dengue virus is coated by an icosahedral shell of 90 envelope protein dimers that convert to trimers at low pH and promote fusion of its membrane with the membrane of the host endosome. We provide the first estimates for the free energy barrier and minimum for two key steps in this process: host membrane bending and protein–membrane binding. Both are studied using complementary membrane elastic, continuum electrostatics and all-atom molecular dynamics simulations. The predicted host membrane bending required to form an initial fusion stalk presents a 22–30 kcal/mol free energy barrier according to a constrained membrane elastic model. Combined continuummore » and molecular dynamics results predict a 15 kcal/mol free energy decrease on binding of each trimer of dengue envelope protein to a membrane with 30% anionic phosphatidylglycerol lipid. The bending cost depends on the preferred curvature of the lipids composing the host membrane leaflets, while the free energy gained for protein binding depends on the surface charge density of the host membrane. The fusion loop of the envelope protein inserts exactly at the level of the interface between the membrane's hydrophobic and head-group regions. As a result, the methods used in this work provide a means for further characterization of the structures and free energies of protein-assisted membrane fusion.« less

Molecular basis of endosomal-membrane association for the dengue virus envelope protein

DOE PAGES

Rogers, David M.; Kent, Michael S.; Rempe, Susan B.

2015-01-02

Dengue virus is coated by an icosahedral shell of 90 envelope protein dimers that convert to trimers at low pH and promote fusion of its membrane with the membrane of the host endosome. We provide the first estimates for the free energy barrier and minimum for two key steps in this process: host membrane bending and protein–membrane binding. Both are studied using complementary membrane elastic, continuum electrostatics and all-atom molecular dynamics simulations. The predicted host membrane bending required to form an initial fusion stalk presents a 22–30 kcal/mol free energy barrier according to a constrained membrane elastic model. Combined continuummore » and molecular dynamics results predict a 15 kcal/mol free energy decrease on binding of each trimer of dengue envelope protein to a membrane with 30% anionic phosphatidylglycerol lipid. The bending cost depends on the preferred curvature of the lipids composing the host membrane leaflets, while the free energy gained for protein binding depends on the surface charge density of the host membrane. The fusion loop of the envelope protein inserts exactly at the level of the interface between the membrane's hydrophobic and head-group regions. As a result, the methods used in this work provide a means for further characterization of the structures and free energies of protein-assisted membrane fusion.« less

Interaction of MreB-derived antimicrobial peptides with membranes.

PubMed

Saikia, Karabi; Chaudhary, Nitin

2018-03-25

Antimicrobial peptides are critical components of defense systems in living forms. The activity is conferred largely by the selective membrane-permeabilizing ability. In our earlier work, we derived potent antimicrobial peptides from the 9-residue long, N-terminal amphipathic helix of E. coli MreB protein. The peptides display broad-spectrum activity, killing not only Gram-positive and Gram-negative bacteria but opportunistic fungus, Candida albicans as well. These results proved that membrane-binding stretches of bacterial proteins could turn out to be self-harming when applied from outside. Here, we studied the membrane-binding and membrane-perturbing potential of these peptides. Steady-state tryptophan fluorescence studies with tryptophan extended peptides, WMreB 1-9 and its N-terminal acetylated analog, Ac-WMreB 1-9 show preferential binding to negatively-charged liposomes. Both the peptides cause permeabilization of E. coli inner and outer-membranes. Tryptophan-lacking peptides, though permeabilize the outer-membrane efficiently, little permeabilization of the inner-membrane is observed. These data attest membrane-destabilization as the mechanism of rapid bacterial killing. This study is expected to motivate the research in identifying microbes' self-sequences to combat them. Copyright © 2018 Elsevier Inc. All rights reserved.

Localization of Bacillus thuringiensis Cry1A toxin-binding molecules in gypsy moth larval gut sections using fluorescence microscopy

Treesearch

Algimantas P. Valaitis

2011-01-01

The microbial insecticide Bacillus thuringiensis (Bt) produces Cry toxins, proteins that bind to the brush border membranes of gut epithelial cells of insects that ingest it, disrupting the integrity of the membranes, and leading to cell lysis and insect death. In gypsy moth, Lymantria dispar, two toxin-binding molecules for the...

Lactose carrier protein of Escherichia coli. Transport and binding of 2'-(N-dansyl)aminoethyl beta-D-thiogalactopyranoside and p-nitrophenyl alpha-d-galactopyranoside.

PubMed

Overath, P; Teather, R M; Simoni, R D; Aichele, G; Wilhelm, U

1979-01-09

The elevated level of lactose carrier protein present in cytoplasmic membranes derived from Escherichia coli strain T31RT, which carries the Y gene of the lac operon on a plasmid vector (Teather, R. M., et al. (1978) Mol. Gen. Genet. 159, 239--248), has allowed the detection of a complex between the carrier and the fluorescent substrate 2'-(N-dansyl)-aminoethyl beta-D-thiogalactopyranoside (Dns2-S-Gal). Binding is accompanied by a 50-nm blue shift in the emission maximum of the dansyl residue. The complex (dissociation constant, KD = 30 micron) rapidly dissociates upon addition of competing substrates such as beta-D-galactopyranosyl 1-thio-beta-D-galactopyranoside or upon reaction with the thiol reagent p-chloromercuribenzenesulfonate. Binding of both Dns2-S-Gal and p-nitrophenyl alpha-D-galactopyranoside (alpha-NPG) occurs spontaneously in the absence of an electrochemical potential gradient across the membrane. Comparison of equilibrium binding experiments using Dns2-S-Gal or alpha-NPG and differential labeling of the carrier with radioactive amino acids shows that the carrier binds 1 mol of substrate per mol of polypeptide (molecular weight 30 000). In addition to specific binding to the lactose carrier, Dns2-S-gal binds unspecifically to lipid vesicles or membranes, as described by a partition coefficient, K = 60, resulting in a 25-nm blue shift in the emission maximum of the dansyl group. Both Dns2-S-Gal and alpha-NPG are not only bound by the lactose carrier but also transported across the membrane by this transport protein in cells and membrane vesicles. The fluorescence changes observed with dansylated galactosides in membrane vesicles in the presence of an electrochemical gradient (Schuldiner et al. (1975) J. Biol. Chem. 250, 1361--1370)) are interpreted as an increase in unspecific binding after translocation.

MinD-dependent conformational changes in MinE required for the Min oscillator to spatially regulate cytokinesis

PubMed Central

Park, Kyung-Tae; Wu, Wei; Battaile, Kevin P.; Lovell, Scott; Holyoak, Todd; Lutkenhaus, Joe

2011-01-01

Summary MinD recruits MinE to the membrane leading to a coupled oscillation required for spatial regulation of the cytokinetic Z ring in E. coli. How these proteins interact, however, is not clear since the MinD binding regions of MinE are sequestered within a 6-stranded β-sheet and masked by N-terminal helices. Here, minE mutations are isolated that restore interaction to some MinD and MinE mutants. These mutations alter the MinE structure releasing the MinD binding regions and N-terminal helices that bind MinD and the membrane, respectively. Crystallization of MinD-MinE complexes reveals a 4-stranded β-sheet MinE dimer with the released β strands (MinD binding regions) converted to α-helices bound to MinD dimers. These results suggest a 6 stranded, β-sheet dimer of MinE ‘senses’ MinD and switches to a 4-stranded β-sheet dimer that binds MinD and contributes to membrane binding. Also, the results indicate how MinE persists at the MinD-membrane surface. PMID:21816275

Heterotypic binding between neuronal membrane vesicles and glial cells is mediated by a specific cell adhesion molecule

PubMed Central

1984-01-01

By means of a multistage quantitative assay, we have identified a new kind of cell adhesion molecule (CAM) on neuronal cells of the chick embryo that is involved in their adhesion to glial cells. The assay used to identify the binding component (which we name neuron-glia CAM or Ng-CAM) was designed to distinguish between homotypic binding (e.g., neuron to neuron) and heterotypic binding (e.g., neuron to glia). This distinction was essential because a single neuron might simultaneously carry different CAMs separately mediating each of these interactions. The adhesion of neuronal cells to glial cells in vitro was previously found to be inhibited by Fab' fragments prepared from antisera against neuronal membranes but not by Fab' fragments against N-CAM, the neural cell adhesion molecule. This suggested that neuron-glia adhesion is mediated by specific cell surface molecules different from previously isolated CAMs . To verify that this was the case, neuronal membrane vesicles were labeled internally with 6-carboxyfluorescein and externally with 125I-labeled antibodies to N-CAM to block their homotypic binding. Labeled vesicles bound to glial cells but not to fibroblasts during a 30-min incubation period. The specific binding of the neuronal vesicles to glial cells was measured by fluorescence microscopy and gamma spectroscopy of the 125I label. Binding increased with increasing concentrations of both glial cells and neuronal vesicles. Fab' fragments prepared from anti-neuronal membrane sera that inhibited binding between neurons and glial cells were also found to inhibit neuronal vesicle binding to glial cells. The inhibitory activity of the Fab' fragments was depleted by preincubation with neuronal cells but not with glial cells. Trypsin treatment of neuronal membrane vesicles released material that neutralized Fab' fragment inhibition; after chromatography, neutralizing activity was enriched 50- fold. This fraction was injected into mice to produce monoclonal antibodies; an antibody was obtained that interacted with neurons, inhibited binding of neuronal membrane vesicles to glial cells, and recognized an Mr = 135,000 band in immunoblots of embryonic chick brain membranes. These results suggest that this molecule is present on the surfaces of neurons and that it directly or indirectly mediates adhesion between neurons and glial cells. Because the monoclonal antibody as well as the original polyspecific antibodies that were active in the assay did not bind to glial cells, we infer that neuron- glial interaction is heterophilic, i.e., it occurs between Ng-CAM on neurons and an as yet unidentified CAM present on glial cells. PMID:6725397

Ligand- and drug-binding studies of membrane proteins revealed through circular dichroism spectroscopy.

PubMed

Siligardi, Giuliano; Hussain, Rohanah; Patching, Simon G; Phillips-Jones, Mary K

2014-01-01

A great number of membrane proteins have proven difficult to crystallise for use in X-ray crystallographic structural determination or too complex for NMR structural studies. Circular dichroism (CD) is a fast and relatively easy spectroscopic technique to study protein conformational behaviour. In this review examples of the applications of CD and synchrotron radiation CD (SRCD) to membrane protein ligand binding interaction studies are discussed. The availability of SRCD has been an important advancement in recent progress, most particularly because it can be used to extend the spectral region in the far-UV region (important for increasing the accuracy of secondary structure estimations) and for working with membrane proteins available in only small quantities for which SRCD has facilitated molecular recognition studies. Such studies have been accomplished by probing in the near-UV region the local tertiary structure of aromatic amino acid residues upon addition of chiral or non-chiral ligands using long pathlength cells of small volume capacity. In particular, this review describes the most recent use of the technique in the following areas: to obtain quantitative data on ligand binding (exemplified by the FsrC membrane sensor kinase receptor); to distinguish between functionally similar drugs that exhibit different mechanisms of action towards membrane proteins (exemplified by secretory phospholipase A2); and to identify suitable detergent conditions to observe membrane protein-ligand interactions using stabilised proteins (exemplified by the antiseptic transporter SugE). Finally, the importance of characterising in solution the conformational behaviour and ligand binding properties of proteins in both far- and near-UV regions is discussed. This article is part of a Special Issue entitled: Structural and biophysical characterisation of membrane protein-ligand binding. © 2013.

Microimaging of Bacillus thuringiensis Toxin-binding proteins in gypsy moth larval gut using confocal fluorescence microscopy

Treesearch

Daniel J. Krofcheck; Algimantas P. Valaitis

2010-01-01

After ingestion by susceptible insect larvae, Bacillus thuringiensis (Bt) insecticidal proteins bind to the brush border membranes of gut epithelial cells and disrupt the integrity of the plasma membrane by forming...

Mutagenesis of Paramyxovirus Hemagglutinin-Neuraminidase Membrane-Proximal Stalk Region Influences Stability, Receptor Binding, and Neuraminidase Activity.

PubMed

Adu-Gyamfi, Emmanuel; Kim, Lori S; Jardetzky, Theodore S; Lamb, Robert A

2016-09-01

Paramyxoviridae consist of a large family of enveloped, negative-sense, nonsegmented single-stranded RNA viruses that account for a significant number of human and animal diseases. The fusion process for nearly all paramyxoviruses involves the mixing of the host cell plasma membrane and the virus envelope in a pH-independent fashion. Fusion is orchestrated via the concerted action of two surface glycoproteins: an attachment protein called hemagglutinin-neuraminidase (HN [also called H or G depending on virus type and substrate]), which acts as a receptor binding protein, and a fusion (F) protein, which undergoes a major irreversible refolding process to merge the two membranes. Recent biochemical evidence suggests that receptor binding by HN is dispensable for cell-cell fusion. However, factors that influence the stability and/or conformation of the HN 4-helix bundle (4HB) stalk have not been studied. Here, we used oxidative cross-linking as well as functional assays to investigate the role of the structurally unresolved membrane-proximal stalk region (MPSR) (residues 37 to 58) of HN in the context of headless and full-length HN membrane fusion promotion. Our data suggest that the receptor binding head serves to stabilize the stalk to regulate fusion. Moreover, we found that the MPSR of HN modulates receptor binding and neuraminidase activity without a corresponding regulation of F triggering. Paramyxoviruses require two viral membrane glycoproteins, the attachment protein variously called HN, H, or G and the fusion protein (F), to couple host receptor recognition to virus-cell fusion. The HN protein has a globular head that is attached to a membrane-anchored flexible stalk of ∼80 residues and has three activities: receptor binding, neuraminidase, and fusion activation. In this report, we have identified the functional significance of the membrane-proximal stalk region (MPSR) (HN, residues 37 to 56) of the paramyxovirus parainfluenza virus (PIV5), a region of the HN stalk that has not had its structure determined by X-ray crystallography. Our data suggest that the MPSR influences receptor binding and neuraminidase activity via an indirect mechanism. Moreover, the receptor binding head group stabilizes the 4HB stalk as part of the general mechanism to fine-tune F-activation. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

Binding of Thyrotropin-Releasing Hormone to Plasma Membranes of Bovine Anterior Pituitary Gland

PubMed Central

Labrie, Fernand; Barden, Nicholas; Poirier, Guy; De Lean, Andre

1972-01-01

An assay for the binding of [3H]thyrotropin-releasing hormone ([3H]TRH) is described. Plasma membranes isolated from bovine anterior pituitary gland bind about 600 femtomoles of this hormone per mg of protein, as compared to 15 femtomoles per mg of protein in the total adenohypophyseal homogenate (40-fold purification). The equilibrium constant of membrane receptor-[3H]TRH binding at 0°C is 4.3 × 107 L·M-1, or a half-maximal binding of this hormone at 23 nM. The binding is time-dependent; addition of unlabeled hormone induces dissociation of the receptor-[3H]TRH complex with a half-life of 14 min. The binding of TRH is not altered by 10 μM melanocyte-stimulating hormone-release inhibiting hormone, lysine-vasopressin, adrenocorticotropin, growth hormone, prolactin, luteinizing hormone, insulin, glucagon, L-thyroxine, or L-triiodothyronine. K+ and Mg++ increase formation of the receptor-TRH complex at optimal concentrations of 5-25 mM and 0.5-2.5 mM, respectively, with inhibition at higher concentrations. Ca++ inhibits binding of TRH at all concentrations tested. PMID:4621548

Quantitation of the calcium and membrane binding properties of the C2 domains of dysferlin.

PubMed

Abdullah, Nazish; Padmanarayana, Murugesh; Marty, Naomi J; Johnson, Colin P

2014-01-21

Dysferlin is a large membrane protein involved in calcium-triggered resealing of the sarcolemma after injury. Although it is generally accepted that dysferlin is Ca(2+) sensitive, the Ca(2+) binding properties of dysferlin have not been characterized. In this study, we report an analysis of the Ca(2+) and membrane binding properties of all seven C2 domains of dysferlin as well as a multi-C2 domain construct. Isothermal titration calorimetry measurements indicate that all seven dysferlin C2 domains interact with Ca(2+) with a wide range of binding affinities. The C2A and C2C domains were determined to be the most sensitive, with Kd values in the tens of micromolar, whereas the C2D domain was least sensitive, with a near millimolar Kd value. Mutagenesis of C2A demonstrates the requirement for negatively charged residues in the loop regions for divalent ion binding. Furthermore, dysferlin displayed significantly lower binding affinity for the divalent cations magnesium and strontium. Measurement of a multidomain construct indicates that the solution binding affinity does not change when C2 domains are linked. Finally, sedimentation assays suggest all seven C2 domains bind lipid membranes, and that Ca(2+) enhances but is not required for interaction. This report reveals for the first time, to our knowledge, that all dysferlin domains bind Ca(2+) albeit with varying affinity and stoichiometry. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Interaction of Gramicidin S and its Aromatic Amino-Acid Analog with Phospholipid Membranes

PubMed Central

Jelokhani-Niaraki, Masoud; Hodges, Robert S.; Meissner, Joseph E.; Hassenstein, Una E.; Wheaton, Laura

2008-01-01

To investigate the mechanism of interaction of gramicidin S-like antimicrobial peptides with biological membranes, a series of five decameric cyclic cationic β-sheet-β-turn peptides with all possible combinations of aromatic D-amino acids, Cyclo(Val-Lys-Leu-D-Ar1-Pro-Val-Lys-Leu-D-Ar2-Pro) (Ar ≡ Phe, Tyr, Trp), were synthesized. Conformations of these cyclic peptides were comparable in aqueous solutions and lipid vesicles. Isothermal titration calorimetry measurements revealed entropy-driven binding of cyclic peptides to POPC and POPE/POPG lipid vesicles. Binding of peptides to both vesicle systems was endothermic—exceptions were peptides containing the Trp-Trp and Tyr-Trp pairs with exothermic binding to POPC vesicles. Application of one- and two-site binding (partitioning) models to binding isotherms of exothermic and endothermic binding processes, respectively, resulted in determination of peptide-lipid membrane binding constants (Kb). The Kb1 and Kb2 values for endothermic two-step binding processes corresponded to high and low binding affinities (Kb1 ≥ 100 Kb2). Conformational change of cyclic peptides in transferring from buffer to lipid bilayer surfaces was estimated using fluorescence resonance energy transfer between the Tyr-Trp pair in one of the peptide constructs. The cyclic peptide conformation expands upon adsorption on lipid bilayer surface and interacts more deeply with the outer monolayer causing bilayer deformation, which may lead to formation of nonspecific transient peptide-lipid porelike zones causing membrane lysis. PMID:18621820

Activation mechanism of erythrocyte cathepsin E. evidence for the occurrence of the membrane-associated active enzyme.

PubMed

Ueno, E; Sakai, H; Kato, Y; Yamamoto, K

1989-06-01

Activation of the erythrocyte cathepsin E located on the cytoplasmic surface of the membrane in a latent form was studied in stripped inside-out membrane vesicles prepared from human erythrocyte membranes. Incubation of the vesicles at 40 degrees C at pH 4 resulted in increased degradation of the membrane proteins, especially band 3. This proteolysis was selectively inhibited by the inclusion of pepstatin (isovaleryl-Val-Val-statyl-Ala-statine) or H 297 [Pro-Thr-Glu-Phe(CH2-NH)Nle-Arg-Leu] in the incubation mixtures, indicating that cathepsin E, as the only aspartic proteinase in erythrocytes, is responsible for the proteolysis. Two potential active-site-directed inhibitors of aspartic proteinases, pepstatin and H 297, were used to prove the occurrence of the membrane-associated active enzyme. To minimize potential errors arising from non-specific binding, the concentrations of the inhibitors used in the binding assay (pepstatin, 5 x 10(-8) M; H 297, 1 x 10(-5) M) were determined by calibration for purified and membrane-associated cathepsin E. The inhibition of the membrane-associated cathepsin E by each inhibitor, which showed the binding of the inhibitor to the activated enzyme, was temperature- and time-dependent. The binding of each inhibitor to the enzyme on the exposed surface of the membrane at pH 4 was highly specific, saturable, and reversible. The present study thus provides the first evidence that cathepsin E tightly bound to the membrane is converted to the active enzyme in the membrane-associated form, and suggests that this enzyme may be responsible for the degradation of band 3.

Ankyrin binding activity shared by the neurofascin/L1/NrCAM family of nervous system cell adhesion molecules.

PubMed

Davis, J Q; Bennett, V

1994-11-04

Neurofascin, L1, NrCAM, NgCAM, and neuroglian are membrane-spanning cell adhesion molecules with conserved cytoplasmic domains that are believed to play important roles in development of the nervous system. This report presents biochemical evidence that the cytoplasmic domains of these molecules associate directly with ankyrins, a family of spectrin-binding proteins located on the cytoplasmic surface of specialized plasma membrane domains. Rat neurofascin and NrCAM together comprise over 0.5% of the membrane protein in adult brain tissue. Linkage of these ankyrin-binding cell adhesion molecules to spectrin-based structures may provide a major class of membrane-cytoskeletal connections in adult brain as well as earlier stages of development.

The interaction of substituted benzamides with brain benzodiazepine binding sites in vitro.

PubMed

Horton, R W; Lowther, S; Chivers, J; Jenner, P; Marsden, C D; Testa, B

1988-08-01

1. The interaction of substituted benzamides with brain benzodiazepine (BDZ) binding sites was examined by their ability to displace [3H]-flunitrazepam ([3H]-FNM) from specific binding sites in bovine cortical membranes in vitro. 2. Clebopride, Delagrange 2674, Delagrange 2335 and BRL 20627 displayed concentration-dependent displacement of [3H]-FNM with IC50 values of 73 nM, 132 nM, 7.7 microM and 5.9 microM, respectively. Other substituted benzamides including metoclopramide, sulpiride, tiapride, sultopride and cisapride were inactive at 10(-5) M. 3. Inhibition by clebopride and Delagrange 2674 of [3H]-FNM binding was apparently competitive and readily reversible. 4. In the presence of gamma-aminobutyric acid (GABA), the ability of diazepam and Delagrange 2674 to displace [3H]-Ro 15-1788 binding was increased 3.6 and 1.6 fold respectively, compared to the absence of GABA, while ethyl beta-carboline-3-carboxylate (beta CCE) and clebopride were less potent in the presence of GABA. 5. Diazepam was 30 fold less potent at displacing [3H]-Ro 15-1788 in membranes that had been photoaffinity labelled with FNM than in control membranes, whereas the potency of beta CCE did not differ. Clebopride and Delagrange 2674 showed a less than two fold loss of potency in photoaffinity labelled membranes. 6. The pattern of binding of clebopride and Delagrange 2674 in these in vitro tests is similar to that found previously with partial agonists or antagonists at BDZ binding sites. 7. Clebopride and Delagrange 2674 inhibited [3H]-FNM binding with similar potency in rat cerebellar and hippocampal membranes, suggesting they have no selectivity for BDZ1 and BDZ2 binding sites. 8. Clebopride and Delagrange 2674 are structurally dissimilar to other BDZ ligands and represent another chemical structure to probe brain BDZ binding sites.

Development of a Novel Tetravalent Synthetic Peptide That Binds to Phosphatidic Acid.

PubMed

Ogawa, Rina; Nagao, Kohjiro; Taniuchi, Kentaro; Tsuchiya, Masaki; Kato, Utako; Hara, Yuji; Inaba, Takehiko; Kobayashi, Toshihide; Sasaki, Yoshihiro; Akiyoshi, Kazunari; Watanabe-Takahashi, Miho; Nishikawa, Kiyotaka; Umeda, Masato

2015-01-01

We employed a multivalent peptide-library screening technique to identify a peptide motif that binds to phosphatidic acid (PA), but not to other phospholipids such as phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS). A tetravalent peptide with the sequence motif of MARWHRHHH, designated as PAB-TP (phosphatidic acid-binding tetravalent peptide), was shown to bind as low as 1 mol% of PA in the bilayer membrane composed of PC and cholesterol. Kinetic analysis of the interaction between PAB-TP and the membranes containing 10 mol% of PA showed that PAB-TP associated with PA with a low dissociation constant of KD = 38 ± 5 nM. Coexistence of cholesterol or PE with PA in the membrane enhanced the PAB-TP binding to PA by increasing the ionization of the phosphomonoester head group as well as by changing the microenvironment of PA molecules in the membrane. Amino acid replacement analysis demonstrated that the tryptophan residue at position 4 of PAB-TP was involved in the interaction with PA. Furthermore, a series of amino acid substitutions at positions 5 to 9 of PAB-TP revealed the involvement of consecutive histidine and arginine residues in recognition of the phosphomonoester head group of PA. Our results demonstrate that the recognition of PA by PAB-TP is achieved by a combination of hydrophobic, electrostatic and hydrogen-bond interactions, and that the tetravalent structure of PAB-TP contributes to the high affinity binding to PA in the membrane. The novel PA-binding tetravalent peptide PAB-TP will provide insight into the molecular mechanism underlying the recognition of PA by PA-binding proteins that are involved in various cellular events.

The Association of Myosin IB with Actin Waves in Dictyostelium Requires Both the Plasma Membrane-Binding Site and Actin-Binding Region in the Myosin Tail

PubMed Central

Brzeska, Hanna; Pridham, Kevin; Chery, Godefroy; Titus, Margaret A.; Korn, Edward D.

2014-01-01

F-actin structures and their distribution are important determinants of the dynamic shapes and functions of eukaryotic cells. Actin waves are F-actin formations that move along the ventral cell membrane driven by actin polymerization. Dictyostelium myosin IB is associated with actin waves but its role in the wave is unknown. Myosin IB is a monomeric, non-filamentous myosin with a globular head that binds to F-actin and has motor activity, and a non-helical tail comprising a basic region, a glycine-proline-glutamine-rich region and an SH3-domain. The basic region binds to acidic phospholipids in the plasma membrane through a short basic-hydrophobic site and the Gly-Pro-Gln region binds F-actin. In the current work we found that both the basic-hydrophobic site in the basic region and the Gly-Pro-Gln region of the tail are required for the association of myosin IB with actin waves. This is the first evidence that the Gly-Pro-Gln region is required for localization of myosin IB to a specific actin structure in situ. The head is not required for myosin IB association with actin waves but binding of the head to F-actin strengthens the association of myosin IB with waves and stabilizes waves. Neither the SH3-domain nor motor activity is required for association of myosin IB with actin waves. We conclude that myosin IB contributes to anchoring actin waves to the plasma membranes by binding of the basic-hydrophobic site to acidic phospholipids in the plasma membrane and binding of the Gly-Pro-Gln region to F-actin in the wave. PMID:24747353

Disclosure of key stereoelectronic factors for efficient H2 binding and cleavage in the active site of [NiFe]-hydrogenases.

PubMed

Bruschi, Maurizio; Tiberti, Matteo; Guerra, Alessandro; De Gioia, Luca

2014-02-05

A comparative analysis of a series of DFT models of [NiFe]-hydrogenases, ranging from minimal NiFe clusters to very large systems including both the first and second coordination sphere of the bimetallic cofactor, was carried out with the aim of unraveling which stereoelectronic properties of the active site of [NiFe]-hydrogenases are crucial for efficient H2 binding and cleavage. H2 binding to the Ni-SIa redox state is energetically favored (by 4.0 kcal mol(-1)) only when H2 binds to Ni, the NiFe metal cluster is in a low spin state, and the Ni cysteine ligands have a peculiar seesaw coordination geometry, which in the enzyme is stabilized by the protein environment. The influence of the Ni coordination geometry on the H2 binding affinity was then quantitatively evaluated and rationalized analyzing frontier molecular orbitals and populations. Several plausible reaction pathways leading to H2 cleavage were also studied. It turned out that a two-step pathway, where H2 cleavage takes place on the Ni-SIa redox state of the enzyme, is characterized by very low reaction barriers and favorable reaction energies. More importantly, the seesaw coordination geometry of Ni was found to be a key feature for facile H2 cleavage. The discovery of the crucial influence of the Ni coordination geometry on H2 binding and activation in the active site of [NiFe]-hydrogenases could be exploited in the design of novel biomimetic synthetic catalysts.

Rotenone Activates Phagocyte NADPH Oxidase through Binding to Its Membrane Subunit gp91phox

PubMed Central

Zhou, Hui; Zhang, Feng; Chen, Shih-heng; Zhang, Dan; Wilson, Belinda; Hong, Jau-shyong; Gao, Hui-Ming

2011-01-01

Rotenone, a widely used pesticide, reproduces Parkinsonism in rodents and associates with increased risk for Parkinson’s disease. We previously reported rotenone increased superoxide production through stimulating microglial phagocyte NADPH oxidase (PHOX). The present study identified a novel mechanism by which rotenone activates PHOX. Ligand-binding assay revealed that rotenone directly bound to membrane gp91phox, the catalytic subunit of PHOX; such binding was inhibited by diphenyleneiodonium, a PHOX inhibitor with a binding site on gp91phox. Functional studies showed both membrane and cytosolic subunits were required for rotenone-induced superoxide production in cell-free systems, intact phagocytes, and COS7 cells transfected with membrane subunits (gp91phox/p22phox) and cytosolic subunits (p67phox and p47phox). Rotenone-elicited extracellular superoxide release in p47phox-deficient macrophages suggested rotenone enabled to activate PHOX through a p47phox-independent mechanism. Increased membrane translocation of p67phox, elevated binding of p67phox to rotenone-treated membrane fractions, and co-immunoprecipitation of p67phox and gp91phox in rotenone-treated wild-type and p47phox-deficient macrophages indicated p67phox played a critical role in rotenone-induced PHOX activation via its direct interaction with gp91phox. Rac1, a Rho-like small GTPase, enhanced p67phox-gp91phox interaction; Rac1 inhibition decreased rotenone-elicited superoxide release. In conclusion, rotenone directly interacted with gp91phox; such an interaction triggered membrane translocation of p67phox, leading to PHOX activation and superoxide production. PMID:22094225

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bidlack, J.M.; Frey, D.K.; Seyed-Mozaffari, A.

The binding properties of 14{beta}-(bromoacetamido)morphine (BAM) and the ability of BAM to irreversibly inhibit opioid binding to rat brain membranes were examined to characterize the affinity and selectivity of BAM as an irreversible affinity ligand for opioid receptors. BAM had the same receptor selectivity as morphine, with a 3-5-fold decrease in affinity for the different types of opioid receptors. When brain membranes were incubated with BAM, followed by extensive washing, opioid binding was restored to control levels. However, when membranes were incubated with dithiothreitol (DTT), followed by BAM, and subsequently washed, 90% of the 0.25 nM ({sup 3}H)(D-Ala{sup 2},(Me)Phe{sup 4},Gly(ol){supmore » 5})enkephalin (DAGO) binding was irreversibly inhibited as a result of the specific alkylation of a sulfhydryl group at the {mu} binding site. This inhibition was dependent on the concentrations of both DTT and BAM. The {mu} receptor specificity of BAM alkylation was demonstrated by the ability of BAM alkylated membranes to still bind the {delta}-selective peptide ({sup 3}H)(D-penicillamine{sup 2},D-penicillamine{sup 5})enkephalin (DPDPE) and (-)-({sup 3}H)bremazocine in the presence of {mu} and {delta} blockers, selective for {kappa} binding sites. Morphine and naloxone partially protected the binding site from alkylation with BAM, while ligands that did not bind to the {mu}s site did not afford protection. These studies have demonstrated that when a disulfide bond at or near {mu} opioid binding sites was reduced, BAM could then alkylate this site, resulting in the specific irreversible labeling of {mu} opioid receptors.« less

Location and ion-binding of membrane-associated valinomycin, a proton nuclear magnetic resonance study.

PubMed

Meers, P; Feigenson, G W

1988-03-03

Valinomycin, incorporated in small unilamellar vesicles of perdeuterated dimyristoylphosphatidylcholine, reveals several well-resolved 1H-NMR resonances. These resonances were used to examine the location, orientation and ion-binding of membrane-bound valinomycin. The order of affinity of membrane-bound valinomycin for cations is Rb+ greater than K+ greater than Cs+ greater than Ba2+, and binding is sensitive to surface change. The exchange between bound and free forms is fast on the NMR time scale. The intrinsic binding constants, extrapolated to zero anion concentration, are similar to those determined in aqueous solution. Rb+ and K+ show 1:1 binding to valinomycin, whereas the stoichiometry of Cs+ and Ba2+ is not certain. Paramagnetic chemical shift reagents and nitroxide spin label relaxation probes were used to study the location and orientation of valinomycin in the membrane. Despite relatively fast exchange of bound cations, the time average location of the cation-free form of valinomycin is deep within the bilayer under the conditions of these experiments. Upon complexation to K+, valinomycin moves closer to the interfacial region.

A Structure-Based Mechanism for Arf1-Dependent Recruitment of Coatomer to Membranes

PubMed Central

Yu, Xinchao; Breitman, Marianna; Goldberg, Jonathan

2012-01-01

Summary Budding of COPI-coated vesicles from Golgi membranes requires an Arf-family G protein and the coatomer complex recruited from cytosol. Arf is also required with coatomer-related clathrin adaptor complexes to bud vesicles from the trans-Golgi network and endosomal compartments. To understand the structural basis for Arf-dependent recruitment of a vesicular coat to the membrane, we determined the structure of Arf1 bound to the γζ-COP subcomplex of coatomer. Structure-guided biochemical analysis reveals that a second Arf1-GTP molecule binds to βδ-COP at a site common to the γ- and β-COP subunits. The Arf1-binding sites on coatomer are spatially related to PtdIns4,5P2-binding sites on the endocytic AP2 complex, providing evidence that the orientation of membrane binding is general for this class of vesicular coat proteins. A bivalent GTP-dependent binding mode has implications for the dynamics of coatomer interaction with the Golgi and for the selection of cargo molecules. PMID:22304919

Interactions between antimicrobial polynorbornenes and phospholipid vesicles monitored by light scattering and microcalorimetry.

PubMed

Gabriel, Gregory J; Pool, Joanna G; Som, Abhigyan; Dabkowski, Jeffrey M; Coughlin, E Bryan; Muthukumar, M; Tew, Gregory N

2008-11-04

Antimicrobial polynorbornenes composed of facially amphiphilic monomers have been previously reported to accurately emulate the antimicrobial activity of natural host-defense peptides (HDPs). The lethal mechanism of most HDPs involves binding to the membrane surface of bacteria leading to compromised phospholipid bilayers. In this paper, the interactions between biomimetic vesicle membranes and these cationic antimicrobial polynorbornenes are reported. Vesicle dye-leakage experiments were consistent with previous biological assays and corroborated a mode of action involving membrane disruption. Dynamic light scattering (DLS) showed that these antimicrobial polymers cause extensive aggregation of vesicles without complete bilayer disintegration as observed with surfactants that efficiently solubilize the membrane. Fluorescence microscopy on vesicles and bacterial cells also showed polymer-induced aggregation of both synthetic vesicles and bacterial cells. Isothermal titration calorimetry (ITC) afforded free energy of binding values (Delta G) and polymer to lipid binding ratios, plus revealed that the interaction is entropically favorable (Delta S>0, Delta H>0). It was observed that the strength of vesicle binding was similar between the active polymers while the binding stoichiometries were dramatically different.

Expression of senescent antigen on erythrocytes infected with a knobby variant of the human malaria parasite Plasmodium falciparum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Winograd, E.; Greenan, J.R.T.; Sherman, I.W.

Erythrocytes infected with a knobby variant of Plasmodium falciparum selectively bind IgG autoantibodies in normal human serum. Quantification of membrane-bound IgG, by use of /sup 125/I-labeled protein A, revealed that erythrocytes infected with the knobby variant bound 30 times more protein A than did noninfected erythrocytes; infection with a knobless variant resulted in less than a 2-fold difference compared with noninfected erythrocytes. IgG binding to knobby erythrocytes appeared to be related to parasite development, since binding of /sup 125/I-labeled protein A to cells bearing young trophozoites (less than 20 hr after parasite invasion) was similar to binding to uninfected erythrocytes.more » By immunoelectron microscopy, the membrane-bound IgG on erythrocytes infected with the knobby variant was found to be preferentially associated with the protuberances (knobs) of the plasma membrane. The removal of aged or senescent erythrocytes from the peripheral circulation is reported to involve the binding of specific antibodies to an antigen (senescent antigen) related to the major erythrocyte membrane protein band 3. Since affinity-purified autoantibodies against band 3 specifically bound to the plasma membrane of erythrocytes infected with the knobby variant of P. falciparum, it is clear that the malaria parasite induces expression of senescent antigen.« less

Lipid-binding analysis using a fat blot assay.

PubMed

Munnik, Teun; Wierzchowiecka, Magdalena

2013-01-01

Protein-lipid interactions play an important role in lipid metabolism, membrane trafficking and cell -signaling by regulating protein localization, activation, and function. The Fat Blot assay is a relatively simple and inexpensive method to examine these interactions using nitrocellulose membrane-immobilized lipids. The assay is adapted from the method by Dowler et al. (Sci STKE 129:pl6, 2002) and provides qualitative and quantitative information on the relative affinity with which a protein binds to a particular lipid. To perform a Fat Blot assay, serial dilutions of different phospholipids are spotted onto a nitrocellulose membrane. These membranes are then incubated with a lipid-binding protein possessing a GST (or other epitope) tag. The membranes are washed and the protein, which is bound to the membrane by virtue of its interaction with the lipid's head group, is detected by immunoblotting with an antibody against GST (or other epitope). The procedure only requires a few micrograms of protein and is quick, simple and cheap to perform.

Comparison of Saccharomyces cerevisiae F-BAR domain structures reveals a conserved inositol phosphate binding site.

PubMed

Moravcevic, Katarina; Alvarado, Diego; Schmitz, Karl R; Kenniston, Jon A; Mendrola, Jeannine M; Ferguson, Kathryn M; Lemmon, Mark A

2015-02-03

F-BAR domains control membrane interactions in endocytosis, cytokinesis, and cell signaling. Although they are generally thought to bind curved membranes containing negatively charged phospholipids, numerous functional studies argue that differences in lipid-binding selectivities of F-BAR domains are functionally important. Here, we compare membrane-binding properties of the Saccharomyces cerevisiae F-BAR domains in vitro and in vivo. Whereas some F-BAR domains (such as Bzz1p and Hof1p F-BARs) bind equally well to all phospholipids, the F-BAR domain from the RhoGAP Rgd1p preferentially binds phosphoinositides. We determined X-ray crystal structures of F-BAR domains from Hof1p and Rgd1p, the latter bound to an inositol phosphate. The structures explain phospholipid-binding selectivity differences and reveal an F-BAR phosphoinositide binding site that is fully conserved in a mammalian RhoGAP called Gmip and is partly retained in certain other F-BAR domains. Our findings reveal previously unappreciated determinants of F-BAR domain lipid-binding specificity and provide a basis for its prediction from sequence. Copyright © 2015 Elsevier Ltd. All rights reserved.

Comparison of Saccharomyces cerevisiae F-BAR Domain Structures Reveals a Conserved Inositol Phosphate Binding Site

DOE PAGES

Moravcevic, Katarina; Alvarado, Diego; Schmitz, Karl R.; ...

2015-01-22

F-BAR domains control membrane interactions in endocytosis, cytokinesis, and cell signaling. Although they are generally thought to bind curved membranes containing negatively charged phospholipids, numerous functional studies argue that differences in lipid-binding selectivities of F-BAR domains are functionally important. Here in this paper, we compare membrane-binding properties of the Saccharomyces cerevisiae F-BAR domains in vitro and in vivo. Whereas some F-BAR domains (such as Bzz1p and Hof1p F-BARs) bind equally well to all phospholipids, the F-BAR domain from the RhoGAP Rgd1p preferentially binds phosphoinositides. We determined X-ray crystal structures of F-BAR domains from Hof1p and Rgd1p, the latter bound tomore » an inositol phosphate. The structures explain phospholipid-binding selectivity differences and reveal an F-BAR phosphoinositide binding site that is fully conserved in a mammalian RhoGAP called Gmip and is partly retained in certain other F-BAR domains. In conclusion, our findings reveal previously unappreciated determinants of F-BAR domain lipid-binding specificity and provide a basis for its prediction from sequence.« less

Structural and mechanistic insights into phospholipid transfer by Ups1–Mdm35 in mitochondria

PubMed Central

Watanabe, Yasunori; Tamura, Yasushi; Kawano, Shin; Endo, Toshiya

2015-01-01

Eukaryotic cells are compartmentalized into membrane-bounded organelles whose functions rely on lipid trafficking to achieve membrane-specific compositions of lipids. Here we focused on the Ups1–Mdm35 system, which mediates phosphatidic acid (PA) transfer between the outer and inner mitochondrial membranes, and determined the X-ray structures of Mdm35 and Ups1–Mdm35 with and without PA. The Ups1–Mdm35 complex constitutes a single domain that has a deep pocket and flexible Ω-loop lid. Structure-based mutational analyses revealed that a basic residue at the pocket bottom and the Ω-loop lid are important for PA extraction from the membrane following Ups1 binding. Ups1 binding to the membrane is enhanced by the dissociation of Mdm35. We also show that basic residues around the pocket entrance are important for Ups1 binding to the membrane and PA extraction. These results provide a structural basis for understanding the mechanism of PA transfer between mitochondrial membranes. PMID:26235513

The sodium channel in membranes of electroplax. Binding of batrachotoxinin-a [(3)H]benzoate to particulate preparations from electric eel (electrophorus).

PubMed

McNeal, E T; Daly, J W

1986-01-01

Batrachotoxinin-A [(3)H]benzoate ([(3)H]BTX-B) binds specifically and with high affinity (K(D) 48 nM) to sites (B(max) 2.1 pmol/mg protein) associated with voltage-dependent sodium channels in rodent brain vesicular preparations. High affinity binding requires the presence of scorpion (Leiurus) venom and a membrane potential. Local anesthetics antagonize the binding. Nonspecific binding is defined in the presence of veratridine. In particulate preparations from electroplax of the eel Electrophorus electricus, [(3)H]BTX-B binds with a K(D) of about 140 nM and a B(max) of 2.5 pmol/mg protein in the presence of scorpion venom. Higher concentrations of scorpion venom are required to enhance binding in Electrophorus preparations than in brain preparations. Local anesthetics antagonize binding in Electrophorus preparations with potencies similar to those in brain preparations. Veratridine and batrachotoxin are less potent in blocking binding in Electrophorus than in brain preparations. It appears likely that binding in Electrophorus preparations is primarily to membrane fragments rather than vesicular entities as in brain. Binding of [(3)H]BTX-B to particulate preparations from electroplax of the ray Torpedo californica and the catfish Malapterurus electricus is mainly nonspecific. Scorpion venom does not enhance total binding and local anesthetics are not effective in antagonizing binding.

Aerobic sn-glycerol-3-phosphate dehydrogenase from Escherichia coli binds to the cytoplasmic membrane through an amphipathic alpha-helix.

PubMed Central

Walz, Antje-Christine; Demel, Rudy A; de Kruijff, Ben; Mutzel, Rupert

2002-01-01

sn-Glycerol-3-phosphate dehydrogenase (GlpD) from Escherichia coli is a peripheral membrane enzyme involved in respiratory electron transfer. For it to display its enzymic activity, binding to the inner membrane is required. The way the enzyme interacts with the membrane and how this controls activity has not been elucidated. In the present study we provide evidence for direct protein-lipid interaction. Using the monolayer technique, we observed insertion of GlpD into lipid monolayers with a clear preference for anionic phospholipids. GlpD variants with point mutations in their predicted amphipathic helices showed a decreased ability to penetrate anionic phospholipid monolayers. From these data we propose that membrane binding of GlpD occurs by insertion of an amphipathic helix into the acyl-chain region of lipids mediated by negatively charged phospholipids. PMID:11955283

Vitamin E: A Role in Signal Transduction.

PubMed

Zingg, Jean-Marc

2015-01-01

Vitamin E modulates the activity of several signal transduction enzymes with consequent alterations of gene expression. At the molecular level, vitamin E may directly bind to these enzymes and compete with their substrates, or it may change their activity by redox regulation. The translocation of several of these enzymes to the plasma membrane is regulated by vitamin E, suggesting the modulation of protein-membrane interactions as a common mechanism for vitamin E action. Enzyme-membrane interactions can be affected by vitamin E by interference with binding to specific membrane lipids or by altering cellular structures such as membrane microdomains (lipid rafts). Moreover, competition by vitamin E for common binding sites within lipid transport proteins may alter the traffic of lipid mediators and thus affect their signaling and enzymatic conversion. In this review, the main effects of vitamin E on enzymes involved in signal transduction are summarized and possible molecular mechanisms leading to enzyme modulation are evaluated.

Interaction of the Full-length Bax Protein with Biomimetic Mitochondrial Liposomes: A Small-Angle Neutron Scattering and Fluorescence Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Satsoura, D; Kucerka, Norbert; Shivakumar, S

2012-01-01

In response to apoptotic stimuli, the pro-apoptotic protein Bax inserts in the outer mitochondrial membrane, resulting in the formation of pores and the release of several mitochondrial components, and sealing the cell's fate. To study the binding of Bax to membranes, we used an in vitro system consisting of 50 nm diameter liposomes prepared with a lipid composition mimicking that of mitochondrial membranes in which recombinant purified full-length Bax was inserted via activation with purified tBid. We detected the association of the protein with the membrane using fluorescence fluctuation methods, and found that it could well be described by anmore » equilibrium between soluble and membrane-bound Bax and that at a high protein-toliposome ratio the binding seemed to saturate at about 15 Bax proteins per 50 nm diameter liposome. We then obtained structural data for samples in this saturated binding regime using small-angle neutron scattering under different contrast matching conditions. Utilizing a simple model to fit the neutron data, we observed that a significant amount of the protein mass protrudes above the membrane, in contrast to the conjecture that all of the membrane-associated Bax states are umbrella-like. Upon protein binding, we also observed a thinning of the lipid bilayer accompanied by an increase in liposome radius, an effect reminiscent of the action of antimicrobial peptides on membranes.« less

Retinal isomerization in bacteriorhodopsin captured by a femtosecond x-ray laser.

PubMed

Nogly, Przemyslaw; Weinert, Tobias; James, Daniel; Carbajo, Sergio; Ozerov, Dmitry; Furrer, Antonia; Gashi, Dardan; Borin, Veniamin; Skopintsev, Petr; Jaeger, Kathrin; Nass, Karol; Båth, Petra; Bosman, Robert; Koglin, Jason; Seaberg, Matthew; Lane, Thomas; Kekilli, Demet; Brünle, Steffen; Tanaka, Tomoyuki; Wu, Wenting; Milne, Christopher; White, Thomas; Barty, Anton; Weierstall, Uwe; Panneels, Valerie; Nango, Eriko; Iwata, So; Hunter, Mark; Schapiro, Igor; Schertler, Gebhard; Neutze, Richard; Standfuss, Jörg

2018-06-14

Ultrafast isomerization of retinal is the primary step in photoresponsive biological functions including vision in humans and ion-transport across bacterial membranes. We studied the sub-picosecond structural dynamics of retinal isomerization in the light-driven proton pump bacteriorhodopsin using an x-ray laser. A series of structural snapshots with near-atomic spatial and temporal resolution in the femtosecond regime show how the excited all- trans retinal samples conformational states within the protein binding pocket prior to passing through a twisted geometry and emerging in the 13 -cis conformation. Our findings suggest ultrafast collective motions of aspartic acid residues and functional water molecules in the proximity of the retinal Schiff base as a key ingredient for this stereo-selective and efficient photochemical reaction. Copyright © 2018, American Association for the Advancement of Science.

Effect of ceramic membrane channel geometry and uniform transmembrane pressure on limiting flux and serum protein removal during skim milk microfiltration.

PubMed

Adams, Michael C; Hurt, Emily E; Barbano, David M

2015-11-01

Our objectives were to determine the effects of a ceramic microfiltration (MF) membrane's retentate flow channel geometry (round or diamond-shaped) and uniform transmembrane pressure (UTP) on limiting flux (LF) and serum protein (SP) removal during skim milk MF at a temperature of 50°C, a retentate protein concentration of 8.5%, and an average cross-flow velocity of 7 m·s(-1). Performance of membranes with round and diamond flow channels was compared in UTP mode. Performance of the membrane with round flow channels was compared with and without UTP. Using UTP with round flow channel MF membranes increased the LF by 5% when compared with not using UTP, but SP removal was not affected by the use of UTP. Using membranes with round channels instead of diamond-shaped channels in UTP mode increased the LF by 24%. This increase was associated with a 25% increase in Reynolds number and can be explained by lower shear at the vertices of the diamond-shaped channel's surface. The SP removal factor of the diamond channel system was higher than the SP removal factor of the round channel system below the LF. However, the diamond channel system passed more casein into the MF permeate than the round channel system. Because only one batch of each membrane was tested in our study, it was not possible to determine if the differences in protein rejection between channel geometries were due to the membrane design or random manufacturing variation. Despite the lower LF of the diamond channel system, the 47% increase in membrane module surface area of the diamond channel system produced a modular permeate removal rate that was at least 19% higher than the round channel system. Consequently, using diamond channel membranes instead of round channel membranes could reduce some of the costs associated with ceramic MF of skim milk if fewer membrane modules could be used to attain the required membrane area. Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Inhibition of (/sup 3/H)nitrendipine binding by phospholipase A/sub 2/

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldman, M.E.; Pisano, J.J.

Phospholipase A/sub 2/ from several sources inhibited (/sup 3/H)nitrendipine binding to membranes from brain, heart and ileal longitudinal muscle. The enzymes from bee venom and Russell's viper venom were most potent, having IC/sub 50/ values of approximately 5 and 14 ng/ml, respectively, in all three membrane preparations. Inhibition of binding by bee venom phospholipase A/sub 2/ was time- and dose-dependent. Mastoparan, a known facilitator of phospholipase A/sub 2/ enzymatic activity, shifted the bee venom phospholipase A/sub 2/ dose-response curve to the left. Pretreatment of brain membranes with bee venom phospholipase A/sub 2/ (10 ng/ml) for 15 min caused a 2-foldmore » increase in the K/sub d/ without changing the B/sub max/ compared with untreated membranes. Extension of the preincubation period to 30 min caused no further increase in the K/sub d/ but significantly decreased the B/sub max/ to 71% the value for untreated membranes. (/sup 3/H)Nitrendipine, preincubated with bee venom phospholipase A/sub 2/, was recovered and found to be fully active, indicating that the phospholipase A/sub 2/ did not modify the ligand. It is concluded that phospholipase A/sub 2/ acts on the membrane at or near the (/sup 3/H)nitrendipine binding site and that phospholipids play a key role in the interactions of 1,4 dihydropyridine calcium channel antagonists with the dihydropyridine binding site. 33 references, 3 figures, 1 table.« less

Interaction of KMP-11 with Phospholipid Membranes and Its Implications in Leishmaniasis: Effects of Single Tryptophan Mutations and Cholesterol.

PubMed

Sannigrahi, Achinta; Maity, Pabitra; Karmakar, Sanat; Chattopadhyay, Krishnananda

2017-03-02

KMP-11 is a small protein that is believed to control the overall bilayer pressure of the Leishmania parasite. Recent results have suggested that membrane binding and the presence of cholesterol affect the efficacy of Leishmanial infection, in which KMP-11 plays an important role. Nevertheless, there exists no systematic study of membrane interaction with KMP-11 either in the absence or presence of cholesterol. In this article, we investigated the interaction between KMP-11 and phospholipid membranes using an unsaturated (PC 18:1; 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)) and saturated (PC 12:0; 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC)) lipid as membrane mimics. Additionally, we studied the effect of cholesterol on the protein-membrane interaction. Steady-state as well as time-resolved fluorescence spectroscopy, isothermal titration calorimetry (ITC), and ζ-potential measurements were used for the determination of the binding constants for the wild-type (WT) and single-site tryptophan mutants. Single-site tryptophan mutants were designed to make sure that the tryptophan residues sample different surface exposures in different mutants. In the absence of cholesterol, the membrane-binding affinities of the partially exposed and buried tryptophan mutants (Y5W and Y48W, respectively) were found to be greater than those of the WT protein. In the presence of cholesterol, the binding constants of the WT and Y48W mutant were found to decrease with an increase in cholesterol concentration. This was in contrast to that in the Y5W and F77W mutants, in which the binding constants increased on adding cholesterol. The present study highlights the interplay among the conformational architecture of a protein, its interaction with the membrane, and membrane composition in modulating the survival of a Leishmania parasite inside host macrophages.

Functionalized Anodic Aluminum Oxide Membrane–Electrode System for Enzyme Immobilization

PubMed Central

2015-01-01

A nanoporous membrane system with directed flow carrying reagents to sequentially attached enzymes to mimic nature’s enzyme complex system was demonstrated. Genetically modified glycosylation enzyme, OleD Loki variant, was immobilized onto nanometer-scale electrodes at the pore entrances/exits of anodic aluminum oxide membranes through His6-tag affinity binding. The enzyme activity was assessed in two reactions—a one-step “reverse” sugar nucleotide formation reaction (UDP-Glc) and a two-step sequential sugar nucleotide formation and sugar nucleotide-based glycosylation reaction. For the one-step reaction, enzyme specific activity of 6–20 min–1 on membrane supports was seen to be comparable to solution enzyme specific activity of 10 min–1. UDP-Glc production efficiencies as high as 98% were observed at a flow rate of 0.5 mL/min, at which the substrate residence time over the electrode length down pore entrances was matched to the enzyme activity rate. This flow geometry also prevented an unwanted secondary product hydrolysis reaction, as observed in the test homogeneous solution. Enzyme utilization increased by a factor of 280 compared to test homogeneous conditions due to the continuous flow of fresh substrate over the enzyme. To mimic enzyme complex systems, a two-step sequential reaction using OleD Loki enzyme was performed at membrane pore entrances then exits. After UDP-Glc formation at the entrance electrode, aglycon 4-methylumbelliferone was supplied at the exit face of the reactor, affording overall 80% glycosylation efficiency. The membrane platform showed the ability to be regenerated with purified enzyme as well as directly from expression crude, thus demonstrating a single-step immobilization and purification process. PMID:25025628

The Antibiotic Novobiocin Binds and Activates the ATPase That Powers Lipopolysaccharide Transport.

PubMed

May, Janine M; Owens, Tristan W; Mandler, Michael D; Simpson, Brent W; Lazarus, Michael B; Sherman, David J; Davis, Rebecca M; Okuda, Suguru; Massefski, Walter; Ruiz, Natividad; Kahne, Daniel

2017-12-06

Novobiocin is an orally active antibiotic that inhibits DNA gyrase by binding the ATP-binding site in the ATPase subunit. Although effective against Gram-positive pathogens, novobiocin has limited activity against Gram-negative organisms due to the presence of the lipopolysaccharide-containing outer membrane, which acts as a permeability barrier. Using a novobiocin-sensitive Escherichia coli strain with a leaky outer membrane, we identified a mutant with increased resistance to novobiocin. Unexpectedly, the mutation that increases novobiocin resistance was not found to alter gyrase, but the ATPase that powers lipopolysaccharide (LPS) transport. Co-crystal structures, biochemical, and genetic evidence show novobiocin directly binds this ATPase. Novobiocin does not bind the ATP binding site but rather the interface between the ATPase subunits and the transmembrane subunits of the LPS transporter. This interaction increases the activity of the LPS transporter, which in turn alters the permeability of the outer membrane. We propose that novobiocin will be a useful tool for understanding how ATP hydrolysis is coupled to LPS transport.

Increased lectin binding capacity of trophoblastic cells of late day 5 rat blastocysts.

PubMed Central

Stein, B A; Shaw, T J; Turner, V F; Murphy, C R

1994-01-01

The binding of lectins to the trophoblast of rat blastocysts has been studied using quantitative ultrastructural cytochemistry. Rat blastocysts from early, mid and late d 5 of gestation were stained using biotinylated lectins (Phytolacca americana [Phy am], fucose binding protein [FBP] and soybean agglutinin [SBA]) and a sensitive avidin-ferritin cytochemical method. Electron micrographs of ferritin particles along the membrane were processed to produce images for which grey scale levels could be established and the ferritin particles automatically counted. The ferritin:membrane ratio was then calculated. Increased binding with Phy am (which detects short chain oligosaccharides) was found after midday of d 5, i.e. after hatching. Binding of FBP and SBA did not alter during the period studied. The increased concentration of oligosaccharides on the blastocyst surface membrane after hatching may have important implications for blastocyst attachment to the endometrium. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 PMID:7649802

Topographical localization of the C-terminal region of the voltage-dependent sodium channel from Electrophorus electricus using antibodies raised against a synthetic peptide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gordon, R.D.; Fieles, W.E.; Schotland, D.L.

1987-01-01

A peptide corresponding to amino acid residues 1783-1794 near the C terminus of the electric eel sodium channel primary sequence of the eel (Electrophorus electricus) sodium channel has been synthesized and used to raise an antiserum in rabbits. This antiserum specifically recognized the peptide in a solid-phase radioimmunoassay. Specificity of the antiserum for the native channel protein was shown by its specific binding to a 280-kDa protein in immunoblots of eel electroplax membrane proteins. The antiserum also specifically labeled the innervated membrane of the eel electroplax in immunofluorescent studies. The membrane topology of the peptide recognized by this antiserum wasmore » proved in binding studies using oriented electroplax membrane vesicles. These vesicles were 98% right-side-out as determined by (/sup 3/H)saxitoxin binding. Binding of the antipeptide antiserum to this fraction was measured before and after permeabilization with 0.01% saponin. Specific binding to intact vesicles was low, but this binding increased 10-fold after permeabilization, implying a cytoplasmic orientation for the peptide. Confirmation for this orientation was then sought by localizing the antibody bound to intact electroplax cells with immunogold electron microscopy. The data imply that the region of the sodium channel primary sequence near the C terminus that is recognized by the anitserum is localized on the cytoplasmic side of the membrane; this localization provides some further constraints on models of sodium channel tertiary structure.« less

Transient potentials in dendritic systems of arbitrary geometry.

PubMed

Butz, E G; Cowan, J D

1974-09-01

A simple graphical calculus is developed that generates analytic solutions for membrane potential transforms at any point on the dendritic tree of neurons with arbitrary dendritic geometries, in response to synaptic "current" inputs. Such solutions permit the computation of transients in neurons with arbitrary geometry and may facilitate analysis of the role of dendrites in such cells.

Binding of Sudan II and IV to lecithin liposomes and E. coli membranes: insights into the toxicity of hydrophobic azo dyes

PubMed Central

Li, Lu; Gao, Hong-Wen; Ren, Jiao-Rong; Chen, Ling; Li, Yu-Cheng; Zhao, Jian-Fu; Zhao, He-Ping; Yuan, Yuan

2007-01-01

Background Sudan red compounds are hydrophobic azo dyes, still used as food additives in some countries. However, they have been shown to be unsafe, causing tumors in the liver and urinary bladder in rats. They have been classified as category 3 human carcinogens by the International Agency for Research on Cancer. A number of hypotheses that could explain the mechanism of carcinogenesis have been proposed for dyes similar to the Sudan red compounds. Traditionally, investigations of the membrane toxicity of organic substances have focused on hydrocarbons, e.g. polycyclic aromatic hydrocarbons (PAHs), and DDT. In contrast to hydrocarbons, Sudan red compounds contain azo and hydroxy groups, which can form hydrogen bonds with the polar head groups of membrane phospholipids. Thus, entry may be impeded. They could have different toxicities from other lipophilic hydrocarbons. The available data show that because these compounds are lipophilic, interactions with hydrophobic parts of the cell are important for their toxicity. Lipophilic compounds accumulate in the membrane, causing expansion of the membrane surface area, inhibition of primary ion pumps and increased proton permeability. Results This work investigated the interactions of the amphiphilic compounds Sudan II and IV with lecithin liposomes and live Escherichia coli (E. coli). Sudan II and IV binding to lecithin liposomes and live E. coli corresponds to the Langmuir adsorption isotherm. In the Sudan red compounds – lecithin liposome solutions, the binding ratio of Sudan II to lecithin is 1/31 and that of Sudan IV to 1/314. The binding constant of the Sudan II-lecithin complex is 1.75 × 104 and that of the Sudan IV-lecithin complex 2.92 × 105. Besides, the influences of pH, electrolyte and temperature were investigated and analyzed quantitatively. In the Sudan red compounds – E.coli mixture, the binding ratios of Sudan II and Sudan IV to E.coli membrane phospholipid are 1/29 and 1/114. The binding constants of the Sudan II – and Sudan IV- E.coli membrane phospholipid complexes are 1.86 × 104 and 6.02 × 104. Over 60% of Sudan II and 75% of Sudan IV penetrated into E.coli, in which 90% of them remained in the E.coli membrane. Conclusion Experiments of Sudan II and IV binding to lecithin liposomes and live E. coli indicates that amphiphilic compounds may besequestered in thelecithin liposomes and membrane phospholipid bilayer according to the Langmuir adsorption law. Penetration into the cytosol was impeded and inhibited for Sudan red compounds. It is possible for such compounds themselves (excluding their metabolites and by-products)not result directly in terminal toxicity. Therefore, membrane toxicity could be manifested as membrane blocking and membrane expansion. The method established here may be useful for evaluating the interaction of toxins with membranes. PMID:17389047

IgG red blood cell autoantibodies in autoimmune hemolytic anemia bind to epitopes on red blood cell membrane band 3 glycoprotein

DOE Office of Scientific and Technical Information (OSTI.GOV)

Victoria, E.J.; Pierce, S.W.; Branks, M.J.

1990-01-01

Red blood cell (RBC) autoantibodies from patients with IgG warm-type autoimmune hemolytic anemia were labeled with iodine 125 and their RBC binding behavior characterized. Epitope-bearing RBC membrane polypeptides were identified after autoantibody immunoprecipitation of labeled membranes and immunoblotting. Immunoaffinity isolation of labeled membrane proteins with 12 different IgG hemolytic autoantibodies with protein A-agarose revealed a major polypeptide at Mr 95 to 110 kd, which coelectrophoresed on sodium dodecylsulfate-polyacrylamide gel electrophoresis with a membrane component isolated with sheep IgG anti-band 3. Immunoprecipitation studies with chymotrypsinized RBCs resulted in the recovery of two labeled membrane polypeptides with molecular weights characteristically resulting frommore » the chymotryptic fragmentation of band 3. Immunoblotting with sheep IgG anti-band 3 of the immunoprecipitated polypeptides confirmed that hemolytic autoantibody binding led to recovery of band 3 or its fragments. Two 125I-labeled IgG hemolytic autoantibodies showed binding behavior consistent with epitope localization on band 3. The labeled RBC autoantibodies bound immunospecifically to all types of human RBC tested, including those of rare Rh type (Rh-null, D--) at a site density of approximately 10(6) per RBC. The 125I-IgG in two labeled autoantibodies was 84% and 92% adsorbable by human and higher nonhuman primate RBCs. Antigen-negative animal RBC bound less than 10%, consistent with immunospecific RBC binding. IgG-1 was the major subclass in five autoantibodies tested; one of six fixed complement; and autoantibody IgG appeared polyclonal by isoelectric focusing. We conclude that IgG eluted from RBCs of patients with autoimmune hemolytic anemia consists predominantly of a single totally RBC-adsorbable antibody population that binds to antigenic determinants on band 3.« less

Evaluation of water binding, seed coat permeability and germination characteristics of wheat seeds equilibrated at different relative humidities.

PubMed

Chatterjee, Nabamita; Nagarajan, Shantha

2006-08-01

The relative binding of seed water and seed coat membrane stability were measured in two contrasting wheat (Triticum aestivum L) varieties, HDR 77 (drought-tolerant) and HD 2009 (susceptible) using seed water sorption isotherms, electrical conductivity (EC) of leachates and desorption-absorption isotherms. Analysis of sorption isotherm at 25 degrees C showed that the seeds of HDR 77 had significantly higher number of strong binding sites, with correspondingly greater amount of seed water as strongly bound water, as compared to HD 2009. Total number of binding sites was also higher in HDR 77 than HD 2009, which explained the better desiccation tolerance and higher capacity to bind water in seeds of HDR 77. EC of seed leachate in both varieties did not change with respect to change in equilibrium relative humidity (RII), indicating the general seed coat membrane stability of wheat seeds. However, absolute conductivity values were higher for HD 2009. showing its relatively porous seed coat membrane. Significantly lower area enclosed by the desorption-absorption isotherm loop in HDR 77, as compared to HD 2009 also indicated the greater membrane integrity of HDR 77. Germination and seedling vigour of HD 2009 were reduced when equilibrated over very low and very high RH. In contrast, germination and vigour in HDR 77 were maintained high, except at very high RH, indicating again its desiccation tolerance. Thus, the study demonstrated the relative drought tolerance of HDR 77, on the basis of seed water-binding characteristics and seed membrane stability. Seed membrane stability as measured by seed leachate conductivity or as area under dehydration-rehydration loop may be used as a preliminary screening test for drought tolerance in wheat.

A 115 kDa calmodulin-binding protein is located in rat liver endosome fractions.

PubMed Central

Enrich, C; Bachs, O; Evans, W H

1988-01-01

The distribution of calmodulin-binding polypeptides in various rat liver subcellular fractions was investigated. Plasma-membrane, endosome, Golgi and lysosome fractions were prepared by established procedures. The calmodulin-binding polypeptides present in the subcellular fractions were identified by using an overlay technique after transfer from gels to nitrocellulose sheets. Distinctive populations of calmodulin-binding polypeptides were present in all the fractions examined except lysosomes. A major 115 kDa calmodulin-binding polypeptide of pI 4.3 was located to the endosome subfractions, and it emerges as a candidate endosome-specific protein. Partitioning of endosome fractions between aqueous and Triton X-114 phases indicated that the calmodulin-binding polypeptide was hydrophobic. Major calmodulin-binding polypeptides of 140 and 240 kDa and minor polypeptides of 40-60 kDa were present in plasma membranes. The distribution of calmodulin in the various endosome and plasma-membrane fractions was also analysed, and the results indicated that the amounts were high compared with those in the cytosol. Images Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5. PMID:3214436

Specific receptors for epidermal growth factor in rat intestinal microvillus membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thompson, J.F.

Epidermal growth factor (EGF) is present in high concentrations in milk, salivary, and pancreaticobiliary secretions. EGF, delivered to the intestinal lumen by these fluids, appears to influence intestinal proliferation. Because EGF exerts its mitogenic effect through binding to specific membrane-bound receptors, binding studies of {sup 125}I-labeled EGF to purified microvillus membrane (MVM) preparations fetal, newborn, and adult rat small intestine were performed. Using the membrane filter technique, binding of {sup 125}I-EGF to adult MVM was specific, saturable, and reversible. Adult and fetal MVM binding was rapid and reached a plateau after 30 min at both 20 and 37{degree}C. No bindingmore » was detected at 4{degree}C. Specific binding increased linearly from 0 to 75 {mu}g MVM protein. Scatchard analysis revealed a single class of receptors in fetal and adult MVM with an association constant of 1.0 {+-} 0.35 {times} 10{sup 9} and 2.3 {+-} 1.6 {times} 10{sup 9} M{sup {minus}1}, respectively. Binding capacity was 435.0 {+-} 89 and 97.7 {+-} 41.3 fmol {sup 125}I-EGF bound/mg MVM protein for fetal and adult MVM, respectively. Newborn MVM binding was negligible. After binding, cross-linking utilizing disuccinimidyl suberate, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, autoradiography revealed a 170-kDa receptor. These data demonstrate specific receptors for EGF on MVM of rat small intestine and, thus, suggest a mechanism for the intraluminal regulation of enterocyte proliferation by EGF.« less

L-phenylalanyl-L-glutamate-stimulated, chloride-dependent glutamate binding represents glutamate sequestration mediated by an exchange system.

PubMed

Kessler, M; Petersen, G; Vu, H M; Baudry, M; Lynch, G

1987-04-01

Stimulation of glutamate binding by the dipeptide L-phenylalanyl-L-glutamate (Phe-Glu) was inhibited by the peptidase inhibitor bestatin, suggesting that the stimulation was caused by glutamate liberated from the dipeptide and not by the dipeptide itself. It further suggests that this form of glutamate binding should be reinterpreted as glutamate sequestration and that stimulation of binding both by dipeptides and after preincubation with high concentrations of glutamate is likely to be due to counterflow accumulation. Several other criteria indicate that most of glutamate binding stimulated by chloride represents glutamate sequestration: Binding is reduced when the osmolarity of the incubation medium is increased, when membranes incubated with [3H]glutamate are lysed before filtration, and when membranes are made permeable by transient exposure to saponin. Moreover, dissociation of bound glutamate after a 100-fold dilution of the incubation medium is accelerated about 50 times by the addition of glutamate to the dilution medium. This result would be anomalous if glutamate were bound to a receptor site; it suggests instead that glutamate is transported in and out of membrane vesicles by a transport system that preferentially mediates exchange between internal and external glutamate. Glutamate binding contains a component of glutamate sequestration even when measured in the absence of chloride. Sequestration is adequately abolished only after treating membranes with detergents; even extensive lysis, sonication, and freezing/thawing may be insufficient.

Hybrid In Silico/In Vitro Approaches for the Identification of Functional Cholesterol-Binding Domains in Membrane Proteins.

PubMed

Di Scala, Coralie; Fantini, Jacques

2017-01-01

In eukaryotic cells, cholesterol is an important regulator of a broad range of membrane proteins, including receptors, transporters, and ion channels. Understanding how cholesterol interacts with membrane proteins is a difficult task because structural data of these proteins complexed with cholesterol are scarce. Here, we describe a dual approach based on in silico studies of protein-cholesterol interactions, combined with physico-chemical measurements of protein insertion into cholesterol-containing monolayers. Our algorithm is validated through careful analysis of the effect of key mutations within and outside the predicted cholesterol-binding site. Our method is illustrated by a complete analysis of cholesterol-binding to Alzheimer's β-amyloid peptide, a protein that penetrates the plasma membrane of brain cells through a cholesterol-dependent process.

Tropomyosin modulates erythrocyte membrane stability

PubMed Central

An, Xiuli; Salomao, Marcela; Guo, Xinhua; Gratzer, Walter; Mohandas, Narla

2007-01-01

The ternary complex of spectrin, actin, and 4.1R (human erythrocyte protein 4.1) defines the nodes of the erythrocyte membrane skeletal network and is inseparable from membrane stability under mechanical stress. These junctions also contain tropomyosin (TM) and the other actin-binding proteins, adducin, protein 4.9, tropomodulin, and a small proportion of capZ, the functions of which are poorly defined. Here, we have examined the consequences of selective elimination of TM from the membrane. We have shown that the mechanical stability of the membranes of resealed ghosts devoid of TM is grossly, but reversibly, impaired. That the decreased membrane stability of TM-depleted membranes is the result of destabilization of the ternary complex of the network junctions is demonstrated by the strongly facilitated entry into the junctions in situ of a β-spectrin peptide, containing the actin- and 4.1R-binding sites, after extraction of the TM. The stabilizing effect of TM is highly specific, in that it is only the endogenous isotype, and not the slightly longer muscle TM that can bind to the depleted membranes and restore their mechanical stability. These findings have enabled us identify a function for TM in elevating the mechanical stability of erythrocyte membranes by stabilizing the spectrin-actin-4.1R junctional complex. PMID:17008534

Perfringolysin O Theta Toxin as a Tool to Monitor the Distribution and Inhomogeneity of Cholesterol in Cellular Membranes

PubMed Central

Maekawa, Masashi; Yang, Yanbo; Fairn, Gregory D.

2016-01-01

Cholesterol is an essential structural component of cellular membranes in eukaryotes. Cholesterol in the exofacial leaflet of the plasma membrane is thought to form membrane nanodomains with sphingolipids and specific proteins. Additionally, cholesterol is found in the intracellular membranes of endosomes and has crucial functions in membrane trafficking. Furthermore, cellular cholesterol homeostasis and regulation of de novo synthesis rely on transport via both vesicular and non-vesicular pathways. Thus, the ability to visualize and detect intracellular cholesterol, especially in the plasma membrane, is critical to understanding the complex biology associated with cholesterol and the nanodomains. Perfringolysin O (PFO) theta toxin is one of the toxins secreted by the anaerobic bacteria Clostridium perfringens and this toxin forms pores in the plasma membrane that causes cell lysis. It is well understood that PFO recognizes and binds to cholesterol in the exofacial leaflets of the plasma membrane, and domain 4 of PFO (D4) is sufficient for the binding of cholesterol. Recent studies have taken advantage of this high-affinity cholesterol-binding domain to create a variety of cholesterol biosensors by using a non-toxic PFO or the D4 in isolation. This review highlights the characteristics and usefulness of, and the principal findings related to, these PFO-derived cholesterol biosensors. PMID:27005662

Perfringolysin O Theta Toxin as a Tool to Monitor the Distribution and Inhomogeneity of Cholesterol in Cellular Membranes.

PubMed

Maekawa, Masashi; Yang, Yanbo; Fairn, Gregory D

2016-03-08

Cholesterol is an essential structural component of cellular membranes in eukaryotes. Cholesterol in the exofacial leaflet of the plasma membrane is thought to form membrane nanodomains with sphingolipids and specific proteins. Additionally, cholesterol is found in the intracellular membranes of endosomes and has crucial functions in membrane trafficking. Furthermore, cellular cholesterol homeostasis and regulation of de novo synthesis rely on transport via both vesicular and non-vesicular pathways. Thus, the ability to visualize and detect intracellular cholesterol, especially in the plasma membrane, is critical to understanding the complex biology associated with cholesterol and the nanodomains. Perfringolysin O (PFO) theta toxin is one of the toxins secreted by the anaerobic bacteria Clostridium perfringens and this toxin forms pores in the plasma membrane that causes cell lysis. It is well understood that PFO recognizes and binds to cholesterol in the exofacial leaflets of the plasma membrane, and domain 4 of PFO (D4) is sufficient for the binding of cholesterol. Recent studies have taken advantage of this high-affinity cholesterol-binding domain to create a variety of cholesterol biosensors by using a non-toxic PFO or the D4 in isolation. This review highlights the characteristics and usefulness of, and the principal findings related to, these PFO-derived cholesterol biosensors.

Continuum electromechanical modeling of protein-membrane interactions

NASA Astrophysics Data System (ADS)

Zhou, Y. C.; Lu, Benzhuo; Gorfe, Alemayehu A.

2010-10-01

A continuum electromechanical model is proposed to describe the membrane curvature induced by electrostatic interactions in a solvated protein-membrane system. The model couples the macroscopic strain energy of membrane and the electrostatic solvation energy of the system, and equilibrium membrane deformation is obtained by minimizing the electroelastic energy functional with respect to the dielectric interface. The model is illustrated with the systems with increasing geometry complexity and captures the sensitivity of membrane curvature to the permanent and mobile charge distributions.

Checking transfer efficiency and equal loading via qualitative optical way in western blotting.

PubMed

Gong, Jun-Hua; Gong, Jian-Ping; Zheng, Kai-Wen

2017-11-01

The ability to determine that successful transfer and equal loading occur prior to using primary antibodies is important. And total protein staining is commonly used to check transfer efficiency and normalization, which play a crucial role in western blotting. Ponceau S and coomassie blue are commonly used, but there are disadvantages reported in recent years. Therefore, we are interested in finding another method, which is cheap, easy and fast. As we know, protein binding region of PVDF membrane is still hydrophilic when carbinol volatilizes, however, the non-protein binding region of PVDF membrane became hydrophobic again. And this different wettability between non-protein binding region and protein binding region of Polyvinylidene difluoride membrane may be used to check transfer efficiency and equal loading in western blotting. Based on the principle above, we describe an optical approach where an experimenter can observe that the proteins have been transferred to the membrane without any staining within minutes. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The binding of Varp to VAMP7 traps VAMP7 in a closed, fusogenically inactive conformation

PubMed Central

Schäfer, Ingmar B.; Hesketh, Geoffrey G.; Bright, Nicholas A.; Gray, Sally R.; Pryor, Paul R.; Evans, Philip R; Luzio, J. Paul; Owen, David J.

2012-01-01

SNAREs provide energy and specificity to membrane fusion events. Fusogenic trans-SNARE complexes are assembled from Q-SNAREs embedded in one membrane and an R–SNARE embedded in the other. Regulation of membrane fusion events is crucial for intracellular trafficking. We identify the endosomal protein Varp as an R-SNARE-binding regulator of SNARE complex formation. Varp co-localises with and binds to VAMP7, an R-SNARE involved in both endocytic and secretory pathways. We present the structure of the second ankyrin repeat domain of mammalian Varp in complex with the cytosolic portion of VAMP7. The VAMP7 SNARE motif is trapped between Varp and the VAMP7 longin domain and hence Varp kinetically inhibits VAMP7’s ability to form SNARE complexes. This inhibition will be increased when Varp can also bind to other proteins present on the same membrane as the VAMP7 such as Rab32:GTP. PMID:23104059

Effectors of animal and plant pathogens use a common domain to bind host phosphoinositides.

PubMed

Salomon, Dor; Guo, Yirui; Kinch, Lisa N; Grishin, Nick V; Gardner, Kevin H; Orth, Kim

2013-01-01

Bacterial Type III Secretion Systems deliver effectors into host cells to manipulate cellular processes to the advantage of the pathogen. Many host targets of these effectors are found on membranes. Therefore, to identify their targets, effectors often use specialized membrane-localization domains to localize to appropriate host membranes. However, the molecular mechanisms used by many domains are unknown. Here we identify a conserved bacterial phosphoinositide-binding domain (BPD) that is found in functionally diverse Type III effectors of both plant and animal pathogens. We show that members of the BPD family functionally bind phosphoinositides and mediate localization to host membranes. Moreover, NMR studies reveal that the BPD of the newly identified Vibrio parahaemolyticus Type III effector VopR is unfolded in solution, but folds into a specific structure upon binding its ligand phosphatidylinositol-(4,5)-bisphosphate. Thus, our findings suggest a possible mechanism for promoting refolding of Type III effectors after delivery into host cells.

Snake Cytotoxins Bind to Membranes via Interactions with Phosphatidylserine Head Groups of Lipids

PubMed Central

Konshina, Anastasia G.; Boldyrev, Ivan A.; Utkin, Yuri N.; Omel'kov, Anton V.; Efremov, Roman G.

2011-01-01

The major representatives of Elapidae snake venom, cytotoxins (CTs), share similar three-fingered fold and exert diverse range of biological activities against various cell types. CT-induced cell death starts from the membrane recognition process, whose molecular details remain unclear. It is known, however, that the presence of anionic lipids in cell membranes is one of the important factors determining CT-membrane binding. In this work, we therefore investigated specific interactions between one of the most abundant of such lipids, phosphatidylserine (PS), and CT 4 of Naja kaouthia using a combined, experimental and modeling, approach. It was shown that incorporation of PS into zwitterionic liposomes greatly increased the membrane-damaging activity of CT 4 measured by the release of the liposome-entrapped calcein fluorescent dye. The CT-induced leakage rate depends on the PS concentration with a maximum at approximately 20% PS. Interestingly, the effects observed for PS were much more pronounced than those measured for another anionic lipid, sulfatide. To delineate the potential PS binding sites on CT 4 and estimate their relative affinities, a series of computer simulations was performed for the systems containing the head group of PS and different spatial models of CT 4 in aqueous solution and in an implicit membrane. This was done using an original hybrid computational protocol implementing docking, Monte Carlo and molecular dynamics simulations. As a result, at least three putative PS-binding sites with different affinities to PS molecule were delineated. Being located in different parts of the CT molecule, these anion-binding sites can potentially facilitate and modulate the multi-step process of the toxin insertion into lipid bilayers. This feature together with the diverse binding affinities of the sites to a wide variety of anionic targets on the membrane surface appears to be functionally meaningful and may adjust CT action against different types of cells. PMID:21559494

Effects of Lys to Glu mutations in GsMTx4 on membrane binding, peptide orientation, and self-association propensity, as analyzed by molecular dynamics simulations.

PubMed

Nishizawa, Kazuhisa; Nishizawa, Manami; Gnanasambandam, Radhakrishnan; Sachs, Frederick; Sukharev, Sergei I; Suchyna, Thomas M

2015-11-01

GsMTx4, a gating modifier peptide acting on cationic mechanosensitive channels, has a positive charge (+5e) due to six Lys residues. The peptide does not have a stereospecific binding site on the channel but acts from the boundary lipids within a Debye length of the pore probably by changing local stress. To gain insight into how these Lys residues interact with membranes, we performed molecular dynamics simulations of Lys to Glu mutants in parallel with our experimental work. In silico, K15E had higher affinity for 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine bilayers than wild-type (WT) peptide or any other mutant tested, and showed deeper penetration than WT, a finding consistent with the experimental data. Experimentally, the inhibitory activities of K15E and K25E were most compromised, whereas K8E and K28E inhibitory activities remained similar to WT peptide. Binding of WT in an interfacial mode did not influence membrane thickness. With interfacial binding, the direction of the dipole moments of K15E and K25E was predicted to differ from WT, whereas those of K8E and K28E oriented similarly to that of WT. These results support a model in which binding of GsMTx4 to the membrane acts like an immersible wedge that serves as a membrane expansion buffer reducing local stress and thus inhibiting channel activity. In simulations, membrane-bound WT attracted other WT peptides to form aggregates. This may account for the positive cooperativity observed in the ion channel experiments. The Lys residues seem to fine-tune the depth of membrane binding, the tilt angle, and the dipole moments. Copyright © 2015 Elsevier B.V. All rights reserved.

Isolation and partial characterization of gypsy moth BTR-270, an anionic brush border membrane glycoconjugate that binds Bacillus thuringiensis Cry1A toxins with high affinity

Treesearch

Algimantas P. Valaitis; Jeremy L. Jenkins; Mi Kyong Lee; Donald H. Dean; Karen J. Garner

2001-01-01

BTR-270, a gypsy moth (Lymantria dispar) brush border membrane molecule that binds Bacillus thuringiensis (Bt) Cry1A toxins with high affinity, was purified by preparative gel electrophoresis. Rabbit antibodies specific for the Bt toxin-binding molecule were raised. Attempts to label BTR-270 by protein-directed techniques were...

SIRT3 and SIRT5 Regulate the Enzyme Activity and Cardiolipin Binding of Very Long-Chain Acyl-CoA Dehydrogenase

PubMed Central

Zhang, Yuxun; Bharathi, Sivakama S.; Rardin, Matthew J.; Uppala, Radha; Verdin, Eric; Gibson, Bradford W.; Goetzman, Eric S.

2015-01-01

SIRT3 and SIRT5 have been shown to regulate mitochondrial fatty acid oxidation but the molecular mechanisms behind the regulation are lacking. Here, we demonstrate that SIRT3 and SIRT5 both target human very long-chain acyl-CoA dehydrogenase (VLCAD), a key fatty acid oxidation enzyme. SIRT3 deacetylates and SIRT5 desuccinylates K299 which serves to stabilize the essential FAD cofactor in the active site. Further, we show that VLCAD binds strongly to cardiolipin and isolated mitochondrial membranes via a domain near the C-terminus containing lysines K482, K492, and K507. Acetylation or succinylation of these residues eliminates binding of VLCAD to cardiolipin. SIRT3 deacetylates K507 while SIRT5 desuccinylates K482, K492, and K507. Sirtuin deacylation of recombinant VLCAD rescues membrane binding. Endogenous VLCAD from SIRT3 and SIRT5 knockout mouse liver shows reduced binding to cardiolipin. Thus, SIRT3 and SIRT5 promote fatty acid oxidation by converging upon VLCAD to promote its activity and membrane localization. Regulation of cardiolipin binding by reversible lysine acylation is a novel mechanism that is predicted to extrapolate to other metabolic proteins that localize to the inner mitochondrial membrane. PMID:25811481

Uptake of oleate by isolated rat adipocytes is mediated by a 40-kDa plasma membrane fatty acid binding protein closely related to that in liver and gut

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwieterman, W.; Sorrentino, D.; Potter, B.J.

1988-01-01

A portion of the hepatocellular uptake of nonesterified long-chain fatty acids is mediated by a specific 40-kDa plasma membrane fatty acid binding protein, which has also been isolated from the gut. To investigate whether a similar transport process exists in other tissues with high transmembrane fatty acid fluxes, initial rates (V/sub O/) of (/sup 3/H)-oleate uptake into isolated rat adipocytes were studied as a function of the concentration of unbound (/sup 3/H)oleate in the medium. V/sub O/ reached a maximum as the concentration of unbound oleate was increased and was significantly inhibited both by phloretin and by prior incubation ofmore » the cells with Pronase. A rabbit antibody to the rat liver plasma membrane fatty acid binding protein inhibited adipocyte fatty acid uptake by up to 63% in dose-dependent fashion. Inhibition was noncompetitive; at an immunoglobulin concentration of 250 ..mu..g/ml V/sub max/ was reduced from 2480 /plus minus/ 160 to 1870 /plus minus/ 80 pmol/min per 5 /times/ 10/sup 4/ adipocytes, with no change in K/sub m/. A basic kDa adipocyte plasma membrane fatty acid binding protein, isolated from crude adipocyte plasma membrane fractions, reacted strongly in both agar gel diffusion and electrophoretic blots with the antibody raised against the corresponding hepatic plasma membrane protein. These data indicate that the uptake of oleate by rat adipocytes is mediated by a 40-kDa plasma membrane fatty acid binding protein closely related to that in liver and gut.« less

Higher-order assemblies of BAR domain proteins for shaping membranes.

PubMed

Suetsugu, Shiro

2016-06-01

Most cellular organelles contain lipid bilayer membranes. The earliest characterization of cellular organelles was performed by electron microscopy observation of such membranes. However, the precise mechanisms for shaping the membrane in particular subcellular organelles is poorly understood. Classically, the overall cellular shape, i.e. the shape of the plasma membrane, was thought to be governed by the reorganization of cytoskeletal components such as actin and microtubules. The plasma membrane contains various submicron structures such as clathrin-coated pits, caveolae, filopodia and lamellipodia. These subcellular structures are either invaginations or protrusions and are associated with the cytoskeleton. Therefore, it could be hypothesized that there are membrane-binding proteins that cooperates with cytoskeleton in shaping of plasma membrane organelles. Proteins with the Bin-Amphiphysin-Rvs (BAR) domain connect a variety of membrane shapes to actin filaments. The BAR domains themselves bend the membranes by their rigidity and then mold the membranes into tubules through their assembly as spiral polymers, which are thought to be involved in the various submicron structures. Membrane tubulation by polymeric assembly of the BAR domains is supposed to be regulated by binding proteins, binding lipids and the mechanical properties of the membrane. This review gives an overview of BAR protein assembly, describes the significance of the assembly and discusses how to study the assembly in the context of membrane and cellular morphology. The technical problems encountered in microscopic observation of BAR domain assembly are also discussed. © The Author 2016. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Novel approach for extraction of quercetin using molecular imprinted membranes

NASA Astrophysics Data System (ADS)

Kamarudin, Siti Fatimah; Ahmad, Mohd Noor; Dzahir, Irfan Hatim Mohamed; Nasir, Azalina Mohamed; Ishak, Noorhidayah; Halim, Nurul Farhanah

2017-12-01

Quercetin imprinted membrane (QIM) was synthesized and applied for the extraction of quercetin. The quercetin imprinted membranes (QIM) were fabricated through a non-covalent approach via surface thermal polymerization. Polyvinylidene fluoride (PVDF) microfiltration membrane was used as a support to improve mechanical stability of the membrane. The thin imprinted layer was formed by copolymerization of acrylamide (AA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinker in the presence of quercetin as template in tetrahydrofuran (THF) solution. The Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscope (FESEM) were used to visualize the surface of membrane. Batch rebinding and binding kinetic experiments proved that the binding properties of the QIM are higher than non-imprinted membranes (NIM). QIM also have higher selectivity towards quercetin compared to sinensetin and rosmarinic acid.

Pertussis toxin modifies the characteristics of both the inhibitory GTP binding proteins and the somatostatin receptor in anterior pituitary tumor cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahy, N.; Woolkalis, M.; Thermos, K.

1988-08-01

The effects of pertussis toxin treatment on the characteristics of somatostatin receptors in the anterior pituitary tumor cell line AtT-20 were examined. Pertussis toxin selectively catalyzed the ADP ribosylation of the alpha subunits of the inhibitory GTP binding proteins in AtT-20 cells. Toxin treatment abolished somatostatin inhibition of forskolin-stimulated adenylyl cyclase activity and somatostatin stimulation of GTPase activity. To examine the effects of pertussis toxin treatment on the characteristics of the somatostatin receptor, the receptor was labeled by the somatostatin analog (125I)CGP 23996. (125I)CGP 23996 binding to AtT-20 cell membranes was saturable and within a limited concentration range was tomore » a single high affinity site. Pertussis toxin treatment reduced the apparent density of the high affinity (125I)CGP 23996 binding sites in AtT-20 cell membranes. Inhibition of (125I)CGP 23996 binding by a wide concentration range of CGP 23996 revealed the presence of two binding sites. GTP predominantly reduced the level of high affinity sites in control membranes. Pertussis toxin treatment also diminished the amount of high affinity sites. GTP did not affect (125I)CGP 23996 binding in the pertussis toxin-treated membranes. The high affinity somatostatin receptors were covalently labeled with (125I) CGP 23996 and the photoactivated crosslinking agent n-hydroxysuccinimidyl-4-azidobenzoate. No high affinity somatostatin receptors, covalently bound to (125I)CGP 23996, were detected in the pertussis toxin-treated membranes. These results are most consistent with pertussis toxin uncoupling the inhibitory G proteins from the somatostatin receptor thereby converting the receptor from a mixed population of high and low affinity sites to only low affinity receptors.« less

Arrestin-rhodopsin binding stoichiometry in isolated rod outer segment membranes depends on the percentage of activated receptors.

PubMed

Sommer, Martha E; Hofmann, Klaus Peter; Heck, Martin

2011-03-04

In the rod cell of the retina, arrestin is responsible for blocking signaling of the G-protein-coupled receptor rhodopsin. The general visual signal transduction model implies that arrestin must be able to interact with a single light-activated, phosphorylated rhodopsin molecule (Rho*P), as would be generated at physiologically relevant low light levels. However, the elongated bi-lobed structure of arrestin suggests that it might be able to accommodate two rhodopsin molecules. In this study, we directly addressed the question of binding stoichiometry by quantifying arrestin binding to Rho*P in isolated rod outer segment membranes. We manipulated the "photoactivation density," i.e. the percentage of active receptors in the membrane, with the use of a light flash or by partially regenerating membranes containing phosphorylated opsin with 11-cis-retinal. Curiously, we found that the apparent arrestin-Rho*P binding stoichiometry was linearly dependent on the photoactivation density, with one-to-one binding at low photoactivation density and one-to-two binding at high photoactivation density. We also observed that, irrespective of the photoactivation density, a single arrestin molecule was able to stabilize the active metarhodopsin II conformation of only a single Rho*P. We hypothesize that, although arrestin requires at least a single Rho*P to bind the membrane, a single arrestin can actually interact with a pair of receptors. The ability of arrestin to interact with heterogeneous receptor pairs composed of two different photo-intermediate states would be well suited to the rod cell, which functions at low light intensity but is routinely exposed to several orders of magnitude more light.

Plasmodium falciparum aldolase and the C-terminal cytoplasmic domain of certain apical organellar proteins promote actin polymerization.

PubMed

Diaz, Suraya A; Martin, Stephen R; Grainger, Munira; Howell, Steven A; Green, Judith L; Holder, Anthony A

2014-10-01

The current model of Apicomplexan motility and host cell invasion is that both processes are driven by an actomyosin motor located beneath the plasma membrane, with the force transduced to the outside of the cell via coupling through aldolase and the cytoplasmic tail domains (CTDs) of certain type 1 membrane proteins. In Plasmodium falciparum (Pf), aldolase is thought to bind to the CTD of members of the thrombospondin-related anonymous protein (TRAP) family, which are micronemal proteins and represented by MTRAP in merozoites. Other type 1 membrane proteins including members of the erythrocyte binding antigen (EBA) and reticulocyte binding protein homologue (RH) protein families, which are also apical organellar proteins, have also been implicated in host cell binding in erythrocyte invasion. However, recent studies with Toxoplasma gondii have questioned the importance of aldolase in these processes. Using biolayer interferometry we show that Pf aldolase binds with high affinity to both rabbit and Pf actin, with a similar affinity for filamentous (F-) actin and globular (G-) actin. The interaction between Pf aldolase and merozoite actin was confirmed by co-sedimentation assays. Aldolase binding was shown to promote rabbit actin polymerization indicating that the interaction is more complicated than binding alone. The CTDs of some but not all type 1 membrane proteins also promoted actin polymerization in the absence of aldolase; MTRAP and RH1 CTDs promoted actin polymerization but EBA175 CTD did not. Direct actin polymerization mediated by membrane protein CTDs may contribute to actin recruitment, filament formation and stability during motor assembly, and actin-mediated movement, independent of aldolase. Copyright © 2014 The Authors. Published by Elsevier B.V. All rights reserved.

Initial targets and cellular responses to PDT

NASA Astrophysics Data System (ADS)

Rodriguez, Myriam E.; Azizuddin, Kashif; Chiu, Song-mao; Delos Santos, Grace; Joseph, Sheeba; Xue, Liang-yan; Oleinick, Nancy L.

2007-02-01

Pc 4, a photosensitizer first synthesized at Case Western Reserve University and now in clinical trial at University Hospitals of Cleveland, has been shown to bind preferentially and with high affinity to mitochondrial and endoplasmic reticulum membranes. Upon photoirradiation of Pc 4-loaded cells, membrane components are photodamaged. In most cancer cells, apoptosis is triggered by the initial photodamage; however, in cells deficient in one of the critical intermediates of apoptosis, this process does not occur, although the cells remain as sensitive to the lethal effects of Pc 4-PDT as the apoptosis-competent cells, when cell death is determined by colony formation. Here we report that an alternative death process, autophagy, is induced in all cells tested and becomes the dominant pathway for elimination of lethally damaged cells when apoptosis is compromised. The anti-apoptotic protein Bcl-2, when overexpressed, protects only apoptosis-competent cells against loss of clonogenicity, while the autophagy inhibitor 3-methyladenine provides a markedly greater protection to apoptosis-deficient cells. The results suggest that the primary determinant of cell death is not the final pathway for elimination of the cells but the initial photodamage to critical membrane targets. In attempts to identify those targets, we have studied the role of different membrane phospholipids in the localization of Pc 4. Cardiolipin (CL) is a phospholipid found exclusively in the mitochondrial inner membrane and at the contact sites between the inner and outer membranes. Previous fluorescence resonance energy transfer studies revealed colocalization of Pc 4 and CL, which points to CL as a possible binding site and target for Pc 4. Unilamellar liposomes with different lipid compositions were used as membrane models to test the affinity of Pc 4. As revealed by the binding constants, Pc 4 does not display preferential binding to CL in these systems. Moreover, binding affinities appear to be independent of lipid composition. Localization of Pc 4 in mitochondrial membranes is likely determined by proteins or other factors not replicated in the liposomes. Studies in cells with modified CL content could report modified binding affinities.

Identification of spinal 5-HT sub 3 receptors and their role in the modulation of nociceptive responses in the rat

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glaum, S.R.

1988-01-01

The project consisted of two related studies: (1) the characterization of serotonin binding sites in crude and purified synaptic membranes prepared from the rat spinal cord, and (2) the association of serotonin binding sites with functional 5-HT receptor responses in the modulation of nociceptive information at the level of the spinal cord. The first series of experiments involved the preparation of membranes from the dorsal and ventral halves of the rat spinal cord and the demonstration of specific ({sup 3}H)serotonin binding to these membranes. High affinity binding sites which conformed to the 5-HT{sub 3} subtype were identified in dorsal, butmore » not ventral spinal cord synaptic membranes. These experiments also confirmed the presence of high affinity ({sup 3}H)5-HT binding sites in dorsal spinal cord synaptic membranes of the 5-HT{sub 1} subtype. The second group of studies demonstrated the ability of selective 5-HT{sub 3} antagonists to inhibit the antinociceptive response to intrathecally administered 5-HT, as measured by a change in tail flick and hot plate latencies. Intrathecal pretreatment with the selective 5-HT{sub 3} antagonists ICS 205-930 or MDL 72222 abolished the antinociceptive effects of 5-HT. Furthermore, the selective 5-HT{sub 3} agonist 2-methyl-5-HT mimicked the antinociceptive effects of 5-HT.« less

Transient Potentials in Dendritic Systems of Arbitrary Geometry

PubMed Central

Butz, Edward G.; Cowan, Jack D.

1974-01-01

A simple graphical calculus is developed that generates analytic solutions for membrane potential transforms at any point on the dendritic tree of neurons with arbitrary dendritic geometries, in response to synaptic “current” inputs. Such solutions permit the computation of transients in neurons with arbitrary geometry and may facilitate analysis of the role of dendrites in such cells. PMID:4416699

Global transformation of erythrocyte properties via engagement of an SH2-like sequence in band 3

PubMed Central

Turrini, Francesco M.; Li, Yen-Hsing; Low, Philip S.

2016-01-01

Src homology 2 (SH2) domains are composed of weakly conserved sequences of ∼100 aa that bind phosphotyrosines in signaling proteins and thereby mediate intra- and intermolecular protein–protein interactions. In exploring the mechanism whereby tyrosine phosphorylation of the erythrocyte anion transporter, band 3, triggers membrane destabilization, vesiculation, and fragmentation, we discovered a SH2 signature motif positioned between membrane-spanning helices 4 and 5. Evidence that this exposed cytoplasmic sequence contributes to a functional SH2-like domain is provided by observations that: (i) it contains the most conserved sequence of SH2 domains, GSFLVR; (ii) it binds the tyrosine phosphorylated cytoplasmic domain of band 3 (cdb3-PO4) with Kd = 14 nM; (iii) binding of cdb3-PO4 to erythrocyte membranes is inhibited both by antibodies against the SH2 signature sequence and dephosphorylation of cdb3-PO4; (iv) label transfer experiments demonstrate the covalent transfer of photoactivatable biotin from isolated cdb3-PO4 (but not cdb3) to band 3 in erythrocyte membranes; and (v) phosphorylation-induced binding of cdb3-PO4 to the membrane-spanning domain of band 3 in intact cells causes global changes in membrane properties, including (i) displacement of a glycolytic enzyme complex from the membrane, (ii) inhibition of anion transport, and (iii) rupture of the band 3–ankyrin bridge connecting the spectrin-based cytoskeleton to the membrane. Because SH2-like motifs are not retrieved by normal homology searches for SH2 domains, but can be found in many tyrosine kinase-regulated transport proteins using modified search programs, we suggest that related cases of membrane transport proteins containing similar motifs are widespread in nature where they participate in regulation of cell properties. PMID:27856737

Global transformation of erythrocyte properties via engagement of an SH2-like sequence in band 3.

PubMed

Puchulu-Campanella, Estela; Turrini, Francesco M; Li, Yen-Hsing; Low, Philip S

2016-11-29

Src homology 2 (SH2) domains are composed of weakly conserved sequences of ∼100 aa that bind phosphotyrosines in signaling proteins and thereby mediate intra- and intermolecular protein-protein interactions. In exploring the mechanism whereby tyrosine phosphorylation of the erythrocyte anion transporter, band 3, triggers membrane destabilization, vesiculation, and fragmentation, we discovered a SH2 signature motif positioned between membrane-spanning helices 4 and 5. Evidence that this exposed cytoplasmic sequence contributes to a functional SH2-like domain is provided by observations that: (i) it contains the most conserved sequence of SH2 domains, GSFLVR; (ii) it binds the tyrosine phosphorylated cytoplasmic domain of band 3 (cdb3-PO 4 ) with K d = 14 nM; (iii) binding of cdb3-PO 4 to erythrocyte membranes is inhibited both by antibodies against the SH2 signature sequence and dephosphorylation of cdb3-PO 4 ; (iv) label transfer experiments demonstrate the covalent transfer of photoactivatable biotin from isolated cdb3-PO 4 (but not cdb3) to band 3 in erythrocyte membranes; and (v) phosphorylation-induced binding of cdb3-PO 4 to the membrane-spanning domain of band 3 in intact cells causes global changes in membrane properties, including (i) displacement of a glycolytic enzyme complex from the membrane, (ii) inhibition of anion transport, and (iii) rupture of the band 3-ankyrin bridge connecting the spectrin-based cytoskeleton to the membrane. Because SH2-like motifs are not retrieved by normal homology searches for SH2 domains, but can be found in many tyrosine kinase-regulated transport proteins using modified search programs, we suggest that related cases of membrane transport proteins containing similar motifs are widespread in nature where they participate in regulation of cell properties.

Glycosphingolipid-facilitated membrane insertion and internalization of cobra cardiotoxin. The sulfatide.cardiotoxin complex structure in a membrane-like environment suggests a lipid-dependent cell-penetrating mechanism for membrane binding polypeptides.

PubMed

Wang, Chia-Hui; Liu, Jyung-Hurng; Lee, Shao-Chen; Hsiao, Chwan-Deng; Wu, Wen-Guey

2006-01-06

Cobra cardiotoxins, a family of basic polypeptides having lipid- and heparin-binding capacities similar to the cell-penetrating peptides, induce severe tissue necrosis and systolic heart arrest in snakebite victims. Whereas cardiotoxins are specifically retained on the cell surface via heparan sulfate-mediated processes, their lipid binding ability appears to be responsible, at least in part, for cardiotoxin-induced membrane leakage and cell death. Although the exact role of lipids involved in toxin-mediated cytotoxicity remains largely unknown, monoclonal anti-sulfatide antibody O4 has recently been shown to inhibit the action of CTX A3, the major cardiotoxin from Taiwan cobra venom, on cardiomyocytes by preventing cardiotoxin-induced membrane leakage and CTX A3 internalization into mitochondria. Here, we show that anti-sulfatide acts by blocking the binding of CTX A3 to the sulfatides in the plasma membrane to prevent sulfatide-dependent CTX A3 membrane pore formation and internalization. We also describe the crystal structure of a CTX A3-sulfatide complex in a membrane-like environment at 2.3 angstroms resolution. The unexpected orientation of the sulfatide fatty chains in the structure allows prediction of the mode of toxin insertion into the plasma membrane. CTX A3 recognizes both the headgroup and the ceramide interfacial region of sulfatide to induce a lipid conformational change that may play a key role in CTX A3 oligomerization and cellular internalization. This proposed lipid-mediated toxin translocation mechanism may also shed light on the cellular uptake mechanism of the amphiphilic cell-penetrating peptides known to involve multiple internalization pathways.

Design of Microporosity in Membrane Distillation

NASA Astrophysics Data System (ADS)

Zhao, Tom; Patankar, Neelesh

2017-11-01

Membrane Distillation (MD) is a desalination method where only vapor can pass through pores in a hydrophobic membrane. Unlike reverse osmosis, MD is insensitive to feed salinity (osmotic pressure) and demonstrates near 100% salt rejection in processing wastewater with a high concentration of nonvolatile impurities. To maximize vapor flux and maintain salt rejection, we demonstrate using molecular dynamics the critical pore radius below which the liquid feed will not intrude or nucleate inside the pores for cylindrical, re-entrant and conical pore geometries. We note that re-entrant structures not only can process low surface-tension wastewater due to its inherent oleophobicity, but can also be optimized to achieve maximum vapor transport compared to all other pore geometries as a function of the material hydrophobicity.

AC impedance investigations of proton conduction in Nafion(sup TM)

NASA Astrophysics Data System (ADS)

Cahan, B. D.; Wainright, J. S.

1993-12-01

AC impedance spectroscopy has been employed to study the conduction of protons in Nafion 117 polymer electrolyte membrane. Both two- and four-electrode geometries have been used to uniquely distinguish between the membrane impedance and the interfacial impedances. The results show that the impedance of Nafion for frequencies up to 100 kHz is characterized by a pure resistance, similar to conventional liquid electrolytes. The frequency dependent features observed using a two-electrode geometry are shown to be consistent will well-characterized interfacial impedances and do not arise from ionic conduction in the membrane. These results show that previous two-electrode studies reported in the literature have misinterpreted the impedance of the electrode interfaces as belonging to the conduction process in the electrolyte.

Electrically generated eddies at an eightfold stagnation point within a nanopore

PubMed Central

Sherwood, J. D.; Mao, M.; Ghosal, S.

2014-01-01

Electrically generated flows around a thin dielectric plate pierced by a cylindrical hole are computed numerically. The geometry represents that of a single nanopore in a membrane. When the membrane is uncharged, flow is due solely to induced charge electroosmosis, and eddies are generated by the high fields at the corners of the nanopore. These eddies meet at stagnation points. If the geometry is chosen correctly, the stagnation points merge to form a single stagnation point at which four streamlines cross at a point and eight eddies meet. PMID:25489206

Analysis of molecular assemblies by flow cytometry: determinants of Gi1 and by binding

NASA Astrophysics Data System (ADS)

Sarvazyan, Noune A.; Neubig, Richard R.

1998-05-01

We report here a novel application of flow cytometry for the quantitative analysis of the high affinity interaction between membrane proteins both in detergent solutions and when reconstituted into lipid vesicles. The approach is further advanced to permit the analysis of binding to expressed protein complexes in native cell membranes. The G protein heterotrimer signal transduction function links the extracellularly activated transmembrane receptors and intracellular effectors. Upon activation, (alpha) and (beta) (gamma) subunits of G protein undergo a dissociation/association cycle on the cell membrane interface. The binding parameters of solubilized G protein (alpha) and (beta) (gamma) subunits have been defined but little is known quantitatively about their interactions in the membrane. Using a novel flow cytometry approach, the binding of low nanomolar concentrations of fluorescein-labeled G(alpha) i1 (F- (alpha) ) to (beta) (gamma) both in detergent solution and in a lipid environment was quantitatively compared. Unlabeled (beta) $gama reconstituted in biotinylated phospholipid vesicles bound F-(alpha) tightly (Kd 6 - 12 nM) while the affinity for biotinylated-(beta) (gamma) in Lubrol was even higher (Kd of 2.9 nM). The application of this approach to proteins expressed in native cell membranes will advance our understanding of G protein function in context of receptor and effector interaction. More generally, this approach can be applied to study the interaction of any fluorescently labeled protein with a membrane protein which can be expressed in Sf9 plasma membranes.

Effects of Serine 129 Phosphorylation on α-Synuclein Aggregation, Membrane Association, and Internalization*

PubMed Central

Samuel, Filsy; Flavin, William P.; Iqbal, Sobia; Pacelli, Consiglia; Sri Renganathan, Sri Dushyaanthan; Trudeau, Louis-Eric; Campbell, Edward M.; Fraser, Paul E.; Tandon, Anurag

2016-01-01

Although trace levels of phosphorylated α-synuclein (α-syn) are detectable in normal brains, nearly all α-syn accumulated within Lewy bodies in Parkinson disease brains is phosphorylated on serine 129 (Ser-129). The role of the phosphoserine residue and its effects on α-syn structure, function, and intracellular accumulation are poorly understood. Here, co-expression of α-syn and polo-like kinase 2 (PLK2), a kinase that targets Ser-129, was used to generate phosphorylated α-syn for biophysical and biological characterization. Misfolding and fibril formation of phosphorylated α-syn isoforms were detected earlier, although the fibrils remained phosphatase- and protease-sensitive. Membrane binding of α-syn monomers was differentially affected by phosphorylation depending on the Parkinson disease-linked mutation. WT α-syn binding to presynaptic membranes was not affected by phosphorylation, whereas A30P α-syn binding was greatly increased, and A53T α-syn was slightly lower, implicating distal effects of the carboxyl- on amino-terminal membrane binding. Endocytic vesicle-mediated internalization of pre-formed fibrils into non-neuronal cells and dopaminergic neurons matched the efficacy of α-syn membrane binding. Finally, the disruption of internalized vesicle membranes was enhanced by the phosphorylated α-syn isoforms, a potential means for misfolded extracellular or lumenal α-syn to access cytosolic α-syn. Our results suggest that the threshold for vesicle permeabilization is evident even at low levels of α-syn internalization and are relevant to therapeutic strategies to reduce intercellular propagation of α-syn misfolding. PMID:26719332

Augmenting β-augmentation: structural basis of how BamB binds BamA and may support folding of outer membrane proteins.

PubMed

Heuck, Alexander; Schleiffer, Alexander; Clausen, Tim

2011-03-11

β-Barrel proteins are frequently found in the outer membrane of mitochondria, chloroplasts and Gram-negative bacteria. In Escherichia coli, these proteins are inserted in the outer membrane by the Bam (β-barrel assembly machinery) complex, a multiprotein machinery formed by the β-barrel protein BamA and the four peripheral membrane proteins BamB, BamC, BamD and BamE. The periplasmic part of BamA binds prefolded β-barrel proteins by a β-augmentation mechanism, thereby stabilizing the precursors prior to their membrane insertion. However, the role of the associated proteins within the Bam complex remains unknown. Here, we describe the crystal structure of BamB, a nonessential component of the Bam complex. The structure shows a typical eight-bladed β-propeller fold. Two sequence stretches of BamB were previously identified to be important for interaction with BamA. In our structure, both motifs are located in close proximity to each other and contribute to a conserved region forming a narrow groove on the top of the propeller. Moreover, crystal contacts reveal two interaction modes of how BamB might bind unfolded β-barrel proteins. In the crystal lattice, BamB binds to exposed β-strands by β-augmentation, whereas peptide stretches rich in aromatic residues can be accommodated in hydrophobic pockets located at the bottom of the propeller. Thus, BamB could simultaneously bind to BamA and prefolded β-barrel proteins, thereby enhancing the folding and membrane insertion capability of the Bam complex. Copyright © 2011 Elsevier Ltd. All rights reserved.

Modes of Interaction of Pleckstrin Homology Domains with Membranes: Toward a Computational Biochemistry of Membrane Recognition.

PubMed

Naughton, Fiona B; Kalli, Antreas C; Sansom, Mark S P

2018-02-02

Pleckstrin homology (PH) domains mediate protein-membrane interactions by binding to phosphatidylinositol phosphate (PIP) molecules. The structural and energetic basis of selective PH-PIP interactions is central to understanding many cellular processes, yet the molecular complexities of the PH-PIP interactions are largely unknown. Molecular dynamics simulations using a coarse-grained model enables estimation of free-energy landscapes for the interactions of 12 different PH domains with membranes containing PIP 2 or PIP 3 , allowing us to obtain a detailed molecular energetic understanding of the complexities of the interactions of the PH domains with PIP molecules in membranes. Distinct binding modes, corresponding to different distributions of cationic residues on the PH domain, were observed, involving PIP interactions at either the "canonical" (C) and/or "alternate" (A) sites. PH domains can be grouped by the relative strength of their C- and A-site interactions, revealing that a higher affinity correlates with increased C-site interactions. These simulations demonstrate that simultaneous binding of multiple PIP molecules by PH domains contributes to high-affinity membrane interactions, informing our understanding of membrane recognition by PH domains in vivo. Copyright © 2017. Published by Elsevier Ltd.

The “Electrostatic-Switch” Mechanism: Monte Carlo Study of MARCKS-Membrane Interaction

PubMed Central

Tzlil, Shelly; Murray, Diana; Ben-Shaul, Avinoam

2008-01-01

The binding of the myristoylated alanine-rich C kinase substrate (MARCKS) to mixed, fluid, phospholipid membranes is modeled with a recently developed Monte Carlo simulation scheme. The central domain of MARCKS is both basic (ζ = +13) and hydrophobic (five Phe residues), and is flanked with two long chains, one ending with the myristoylated N-terminus. This natively unfolded protein is modeled as a flexible chain of “beads” representing the amino acid residues. The membranes contain neutral (ζ = 0), monovalent (ζ = −1), and tetravalent (ζ = −4) lipids, all of which are laterally mobile. MARCKS-membrane interaction is modeled by Debye-Hückel electrostatic potentials and semiempirical hydrophobic energies. In agreement with experiment, we find that membrane binding is mediated by electrostatic attraction of the basic domain to acidic lipids and membrane penetration of its hydrophobic moieties. The binding is opposed by configurational entropy losses and electrostatic membrane repulsion of the two long chains, and by lipid demixing upon adsorption. The simulations provide a physical model for how membrane-adsorbed MARCKS attracts several PIP2 lipids (ζ = −4) to its vicinity, and how phosphorylation of the central domain (ζ = +13 to ζ = +7) triggers an “electrostatic switch”, which weakens both the membrane interaction and PIP2 sequestration. This scheme captures the essence of “discreteness of charge” at membrane surfaces and can examine the formation of membrane-mediated multicomponent macromolecular complexes that function in many cellular processes. PMID:18502797

Immobilization of sodium alginate sulfates on polysulfone ultrafiltration membranes for selective adsorption of low-density lipoprotein.

PubMed

Wang, Wei; Huang, Xiao-Jun; Cao, Jian-Da; Lan, Ping; Wu, Wen

2014-01-01

A novel method for the immobilization of sodium alginate sulfates (SAS) on polysulfone (PSu) ultrafiltration membranes to achieve selective adsorption of low-density lipoprotein (LDL) was developed, which involved the photoinduced graft polymerization of acrylamide on the membrane and the Hofmann rearrangement reaction of grafted acrylamide followed by chemical binding of SAS with glutaraldehyde. The surface modification processes were confirmed by attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy characterization. Zeta potential and water contact angle measurements were performed to investigate the surface charge and wettability of the membranes. An enzyme-linked immunosorbent assay was used to measure the binding of LDL on plain and modified PSu membranes. It was found that the PSu membrane immobilized with sodium alginate sulfates (PSu-SAS) greatly enhanced the selective adsorption of LDL from protein solutions and the absorbed LDL could be easily eluted with sodium chloride solution, indicating a specific and reversible binding of LDL to SAS, mainly driven by electrostatic forces. Furthermore, the PSu-SAS membrane showed good blood compatibility as examined by platelet adhesion. The results suggest that the PSu-SAS membranes are promising for application in simultaneous hemodialysis and LDL apheresis therapy. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Flexible Charged Macromolecules on Mixed Fluid Lipid Membranes: Theory and Monte Carlo Simulations

PubMed Central

Tzlil, Shelly; Ben-Shaul, Avinoam

2005-01-01

Fluid membranes containing charged lipids enhance binding of oppositely charged proteins by mobilizing these lipids into the interaction zone, overcoming the concomitant entropic losses due to lipid segregation and lower conformational freedom upon macromolecule adsorption. We study this energetic-entropic interplay using Monte Carlo simulations and theory. Our model system consists of a flexible cationic polyelectrolyte, interacting, via Debye-Hückel and short-ranged repulsive potentials, with membranes containing neutral lipids, 1% tetravalent, and 10% (or 1%) monovalent anionic lipids. Adsorption onto a fluid membrane is invariably stronger than to an equally charged frozen or uniform membrane. Although monovalent lipids may suffice for binding rigid macromolecules, polyvalent counter-lipids (e.g., phosphatidylinositol 4,5 bisphosphate), whose entropy loss upon localization is negligible, are crucial for binding flexible macromolecules, which lose conformational entropy upon adsorption. Extending Rosenbluth's Monte Carlo scheme we directly simulate polymer adsorption on fluid membranes. Yet, we argue that similar information could be derived from a biased superposition of quenched membrane simulations. Using a simple cell model we account for surface concentration effects, and show that the average adsorption probabilities on annealed and quenched membranes coincide at vanishing surface concentrations. We discuss the relevance of our model to the electrostatic-switch mechanism of, e.g., the myristoylated alanine-rich C kinase substrate protein. PMID:16126828

Two nucleotide binding sites modulate ( sup 3 H) glyburide binding to rat cortex membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, D.E.; Gopalakrishnan, M.; Triggle, D.J.

1991-03-11

The effects of nucleotides on the binding of the ATP-dependent K{sup +}-channel antagonist ({sup 3}H)glyburide (GLB) to rat cortex membranes were examined. Nucleotide triphosphates (NTPs) and nucleotide diphosphate (NDPs) inhibited the binding of GLB. This effect was dependent on the presence of dithiothreitol (DTT). Inhibition of binding by NTPs, with the exception of ATP{gamma}S, was dependent on the presence of Mg{sup 2+}. GLB binding showed a biphasic response to ADP: up to 3 mM, ADP inhibited binding, and above this concentration GLB binding increased rapidly, and was restored to normal levels by 10 mM ADP. In the presence of Mg{supmore » 2+}, ADP did not stimulate binding. Saturation analysis in the presence of Mg{sup 2+} and increasing concentrations of ADP showed that ADP results primarily in a change of the B{sub max} for GLB binding. The differential effects of NTPS and NDPs indicate that two nucleotide binding sites regulate GLB binding.« less

Inactivation by Phenylglyoxal of the Specific Binding of 1-Naphthyl Acetic Acid with Membrane-Bound Auxin Binding Sites from Maize Coleoptiles

PubMed Central

Navé, Jean-François; Benveniste, Pierre

1984-01-01

The specific binding of 1-[3H]naphthyl acetic acid (NAA) to membrane-bound binding sites from maize (Zea mays cv INRA 258) coleoptiles is inactivated by phenylglyoxal. The inactivation obeys pseudo first-order kinetics. The rate of inactivation is proportional to phenylglyoxal concentration. Under conditions at which significant binding occurs, NAA, R and S-1-naphthyl 2-propionic acids protect the auxin binding site against inactivation by phenylglyoxal. Scatchard analysis shows that the inhibition of binding corresponds to a decrease in the concentration of sites but not in the affinity. The results of the present chemical modification study indicate that at least one arginyl residue is involved in the positively charged recognition site of the carboxylate anion of NAA. PMID:16663499

New insights into the organization of plasma membrane and its role in signal transduction.

PubMed

Suzuki, Kenichi G N

2015-01-01

Plasma membranes have heterogeneous structures for efficient signal transduction, required to perform cell functions. Recent evidence indicates that the heterogeneous structures are produced by (1) compartmentalization by actin-based membrane skeleton, (2) raft domains, (3) receptor-receptor interactions, and (4) the binding of receptors to cytoskeletal proteins. This chapter provides an overview of recent studies on diffusion, clustering, raft association, actin binding, and signal transduction of membrane receptors, especially glycosylphosphatidylinositol (GPI)-anchored receptors. Studies on diffusion of GPI-anchored receptors suggest that rafts may be small and/or short-lived in plasma membranes. In steady state conditions, GPI-anchored receptors form transient homodimers, which may represent the "standby state" for the stable homodimers and oligomers upon ligation. Furthermore, It is proposed that upon ligation, the binding of GPI-anchored receptor clusters to cytoskeletal actin filaments produces a platform for downstream signaling, and that the pulse-like signaling easily maintains the stability of the overall signaling activity. Copyright © 2015 Elsevier Inc. All rights reserved.

Functionalizing Microporous Membranes for Protein Purification and Protein Digestion

NASA Astrophysics Data System (ADS)

Dong, Jinlan; Bruening, Merlin L.

2015-07-01

This review examines advances in the functionalization of microporous membranes for protein purification and the development of protease-containing membranes for controlled protein digestion prior to mass spectrometry analysis. Recent studies confirm that membranes are superior to bead-based columns for rapid protein capture, presumably because convective mass transport in membrane pores rapidly brings proteins to binding sites. Modification of porous membranes with functional polymeric films or TiO2 nanoparticles yields materials that selectively capture species ranging from phosphopeptides to His-tagged proteins, and protein-binding capacities often exceed those of commercial beads. Thin membranes also provide a convenient framework for creating enzyme-containing reactors that afford control over residence times. With millisecond residence times, reactors with immobilized proteases limit protein digestion to increase sequence coverage in mass spectrometry analysis and facilitate elucidation of protein structures. This review emphasizes the advantages of membrane-based techniques and concludes with some challenges for their practical application.

Functionalizing Microporous Membranes for Protein Purification and Protein Digestion.

PubMed

Dong, Jinlan; Bruening, Merlin L

2015-01-01

This review examines advances in the functionalization of microporous membranes for protein purification and the development of protease-containing membranes for controlled protein digestion prior to mass spectrometry analysis. Recent studies confirm that membranes are superior to bead-based columns for rapid protein capture, presumably because convective mass transport in membrane pores rapidly brings proteins to binding sites. Modification of porous membranes with functional polymeric films or TiO₂ nanoparticles yields materials that selectively capture species ranging from phosphopeptides to His-tagged proteins, and protein-binding capacities often exceed those of commercial beads. Thin membranes also provide a convenient framework for creating enzyme-containing reactors that afford control over residence times. With millisecond residence times, reactors with immobilized proteases limit protein digestion to increase sequence coverage in mass spectrometry analysis and facilitate elucidation of protein structures. This review emphasizes the advantages of membrane-based techniques and concludes with some challenges for their practical application.

A novel substance P binding site in rat brain regions modulates TRH receptor binding.

PubMed

Sharif, N A

1990-10-01

Binding sites for thyrotropin-releasing hormone (TRH) were labelled with [3H](2-Me-His3)TRH ([3H]MeTRH) on membranes from rat brain regions at 0 degrees C for 5 h. Amygdaloid membranes bound [3H]MeTRH with high-affinity (Kd = 3.1 +/- 0.5 nM (n = 4)). Five TRH analogs competed for this binding with the same rank order and with affinities that matched the pharmacological specificity of pituitary TRH receptors. Substance P (SP) and its C-terminal fragments reduced amygdaloid TRH receptor binding in a concentration dependent manner (IC50 for SP = 65 microM). The rank order of potency of SP analogs at inhibiting TRH receptor binding was: SP greater than nonapeptide (3-11) greater than hexapeptide (6-11) greater than heptapeptide (5-11) greater than pentapeptide (7-11). However, other tachykinins were inactive in this system. SP was a potent inhibitor of [3H]MeTRH binding in hippocampus greater than spinal cord greater than retina greater than n. accumbens greater than hypothalamus greater than amygdaloid greater than olfactory bulb greater than or equal to pituitary greater than pons/medulla in parallel assays. In amygdaloid membranes SP (50 microM) reduced the apparent maximum receptor density by 39% (p less than 0.01) without altering the binding affinity, and 100 microM SP induced a biphasic dissociation of [3H]MeTRH with kinetics faster than those induced by both TRH (10 microM) and serotonin (100 microM). In contrast, other neuropeptides such as neurotensin, proctolin, angiotensin II, bombesin and luteinizing hormone releasing hormone did not significantly inhibit [3H]MeTRH binding to amygdaloid membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

(+)-3-( sup 123 I)Iodo-MK-801: Synthesis and characterization of binding to the N-methyl-D-aspartate receptor complex

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ransom, R.W.; Wai-si Eng; Burns, H.D.

1990-01-01

Synthetic methods have been established for preparing high specific activity (+)-3-({sup 123}I)Iodo-MK-801 in high radiochemical yield. The binding of the radiotracer to rat cortical membranes has been examine to assess its potential use as an in vivo imaging agent for the N-methyl-D-aspartate (NMDA) receptor-ion channel complex. Under the conditions of the assay, specific (+)-3-({sup 123}I)Iodo-MK-801 binding to membrane homogenates represented greater than 95% of the total binding. Several structurally distinct, noncompetitive NMDA receptor antagonists inhibited binding with potencies in accordance with their reported inhibitory activity at the receptor complex. The concentration of ({plus minus})-3-Iodo-MK-801 required to inhibit 50% of (+)-3-({supmore » 123}I)Iodo-MK-801 binding (IC{sub 50}) was 3.4 nM when using a low ionic strength assay buffer and 5.5 nM in a physiological buffer. In a thoroughly washed membrane preparation, (+)-3-({sup 123}I)Iodo-MK-801 binding was enhanced by L-glutamate and glycine at concentrations known to activate the NMDA receptor. The results indicate that (+)-3-({sup 123}I)Iodo-MK-801 specifically labels the NMDA receptor complex in rat brain membranes and the retention of high affinity under near physiological assay conditions suggests that it may be useful as a SPECT imaging agent for the receptor in vivo.« less

Identification of Peroxiredoxin-5 in Bovine Cauda Epididymal Sperm

PubMed Central

Nagdas, Subir K; Buchanan, Teresa; Raychoudhury, Samir

2013-01-01

Developing spermatozoa require a series of post-testicular modifications within the luminal environment of the epididymis to achieve maturation; this involves several surface modifications including changes in plasma membrane lipids, proteins, carbohydrates, and alterations in the outer acrosomal membrane. Epididymal maturation can therefore allow sperm to gain forward motility and fertilization capabilities. The objective of this study was to identify maturation dependent protein(s) and to investigate their role with the production of functionally competent spermatozoa. Lectin blot analyses of caput and cauda sperm plasma membrane fractions identified a 17.5kDa Wheat Germ Agglutinin (WGA) binding polypeptide present in the cauda sperm plasma membrane not in the caput sperm plasma membrane. Among the several WGA stained bands, the presence of a 17.5kDa WGA binding polypeptide band was detected only in cauda epididymal fluid not in caput epididymal fluid suggesting that the 17.5kDa WGA-binding polypeptide is secreted from the cauda epididymis and binds to the cauda sperm plasma membrane during epididymal transit. Proteomic identification of the 17.5kDa polypeptide yielded 13 peptides that matched the sequence of peroxiredoxin-5 (PRDX5) protein (Bos Taurus). We propose that bovine cauda sperm PRDX5 acts as an antioxidant enzyme in the epididymal environment, which is crucial in protecting the viable sperm population against the damage caused by endogeneous or exogeneous peroxide. PMID:24186847

Transition metal ion FRET to measure short-range distances at the intracellular surface of the plasma membrane

PubMed Central

Senning, Eric N.; Aman, Teresa K.

2016-01-01

Biological membranes are complex assemblies of lipids and proteins that serve as platforms for cell signaling. We have developed a novel method for measuring the structure and dynamics of the membrane based on fluorescence resonance energy transfer (FRET). The method marries four technologies: (1) unroofing cells to isolate and access the cytoplasmic leaflet of the plasma membrane; (2) patch-clamp fluorometry (PCF) to measure currents and fluorescence simultaneously from a membrane patch; (3) a synthetic lipid with a metal-chelating head group to decorate the membrane with metal-binding sites; and (4) transition metal ion FRET (tmFRET) to measure short distances between a fluorescent probe and a transition metal ion on the membrane. We applied this method to measure the density and affinity of native and introduced metal-binding sites in the membrane. These experiments pave the way for measuring structural rearrangements of membrane proteins relative to the membrane. PMID:26755772

Postprocessing of docked protein-ligand complexes using implicit solvation models.

PubMed

Lindström, Anton; Edvinsson, Lotta; Johansson, Andreas; Andersson, C David; Andersson, Ida E; Raubacher, Florian; Linusson, Anna

2011-02-28

Molecular docking plays an important role in drug discovery as a tool for the structure-based design of small organic ligands for macromolecules. Possible applications of docking are identification of the bioactive conformation of a protein-ligand complex and the ranking of different ligands with respect to their strength of binding to a particular target. We have investigated the effect of implicit water on the postprocessing of binding poses generated by molecular docking using MM-PB/GB-SA (molecular mechanics Poisson-Boltzmann and generalized Born surface area) methodology. The investigation was divided into three parts: geometry optimization, pose selection, and estimation of the relative binding energies of docked protein-ligand complexes. Appropriate geometry optimization afforded more accurate binding poses for 20% of the complexes investigated. The time required for this step was greatly reduced by minimizing the energy of the binding site using GB solvation models rather than minimizing the entire complex using the PB model. By optimizing the geometries of docking poses using the GB(HCT+SA) model then calculating their free energies of binding using the PB implicit solvent model, binding poses similar to those observed in crystal structures were obtained. Rescoring of these poses according to their calculated binding energies resulted in improved correlations with experimental binding data. These correlations could be further improved by applying the postprocessing to several of the most highly ranked poses rather than focusing exclusively on the top-scored pose. The postprocessing protocol was successfully applied to the analysis of a set of Factor Xa inhibitors and a set of glycopeptide ligands for the class II major histocompatibility complex (MHC) A(q) protein. These results indicate that the protocol for the postprocessing of docked protein-ligand complexes developed in this paper may be generally useful for structure-based design in drug discovery.

High-affinity receptors for bombesin-like peptides in normal guinea pig lung membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lach, E.; Trifilieff, A.; Landry, Y.

1991-01-01

The binding of the radiolabeled bombesin analogue ({sup 125}I-Tyr{sup 4})bombesin to guinea-pig lung membranes was investigated. Binding of ({sup 125}I-Tyr{sup 4})bombesin was specific, saturable, reversible and linearly related to the protein concentration. Scatchard analysis of equilibrium binding data at 25C indicated the presence of a single class of non-interacting binding sites for bombesin (B{sub max} = 7.7 fmol/mg protein). The value of the equilibrium dissociation constant (K{sub D} = 90 pM) agrees with a high-affinity binding site. Bombesin and structurally related peptides such as ({sup 125}I-Tyr{sup 4})bombesin, neuromedin B and neuromedin C inhibited the binding of ({sup 125}I-Tyr{sup 4})bombesin inmore » an order of potencies as follows: ({sup 125}I-Tyr{sup 4})bombesin {gt} bombesin {ge} neuromedin C {much gt} neuromedin B. These results indicate that guinea-pig lung membranes possess a single class of bombesin receptors with a high affinity for bombesin and a lower one for neuromedin B.« less

Methyl-branched lipids promote the membrane adsorption of α-synuclein by enhancing shallow lipid-packing defects.

PubMed

Garten, Matthias; Prévost, Coline; Cadart, Clotilde; Gautier, Romain; Bousset, Luc; Melki, Ronald; Bassereau, Patricia; Vanni, Stefano

2015-06-28

Alpha-synuclein (AS) is a synaptic protein that is directly involved in Parkinson's disease due to its tendency to form protein aggregates. Since AS aggregation can be dependent on the interactions between the protein and the cell plasma membrane, elucidating the membrane binding properties of AS is of crucial importance to establish the molecular basis of AS aggregation into toxic fibrils. Using a combination of in vitro reconstitution experiments based on Giant Unilamellar Vesicles (GUVs), confocal microscopy and all-atom molecular dynamics simulations, we have investigated the membrane binding properties of AS, with a focus on the relative contribution of hydrophobic versus electrostatic interactions. In contrast with previous observations, we did not observe any binding of AS to membranes containing the ganglioside GM1, even at relatively high GM1 content. AS, on the other hand, showed a stronger affinity for neutral flat membranes consisting of methyl-branched lipids. To rationalize these results, we used all-atom molecular dynamics simulations to investigate the influence of methyl-branched lipids on interfacial membrane properties. We found that methyl-branched lipids promote the membrane adsorption of AS by creating shallow lipid-packing defects to a larger extent than polyunsaturated and monounsaturated lipids. Our findings suggest that methyl-branched lipids may constitute a remarkably adhesive substrate for peripheral proteins that adsorb on membranes via hydrophobic insertions.

Nanofiber Ion-Exchange Membranes for the Rapid Uptake and Recovery of Heavy Metals from Water

PubMed Central

Chitpong, Nithinart; Husson, Scott M.

2016-01-01

An evaluation of the performance of polyelectrolyte-modified nanofiber membranes was undertaken to determine their efficacy in the rapid uptake and recovery of heavy metals from impaired waters. The membranes were prepared by grafting poly(acrylic acid) (PAA) and poly(itaconic acid) (PIA) to cellulose nanofiber mats. Performance measurements quantified the dynamic ion-exchange capacity for cadmium (Cd), productivity, and recovery of Cd(II) from the membranes by regeneration. The dynamic binding capacities of Cd(II) on both types of nanofiber membrane were independent of the linear flow velocity, with a residence time of as low as 2 s. Analysis of breakthrough curves indicated that the mass flow rate increased rapidly at constant applied pressure after membranes approached equilibrium load capacity for Cd(II), apparently due to a collapse of the polymer chains on the membrane surface, leading to an increased porosity. This mechanism is supported by hydrodynamic radius (Rh) measurements for PAA and PIA obtained from dynamic light scattering, which show that Rh values decrease upon Cd(II) binding. Volumetric productivity was high for the nanofiber membranes, and reached 0.55 mg Cd/g/min. The use of ethylenediaminetetraacetic acid as regeneration reagent was effective in fully recovering Cd(II) from the membranes. Ion-exchange capacities were constant over five cycles of binding-regeneration. PMID:27999394

Nanofiber Ion-Exchange Membranes for the Rapid Uptake and Recovery of Heavy Metals from Water.

PubMed

Chitpong, Nithinart; Husson, Scott M

2016-12-20

An evaluation of the performance of polyelectrolyte-modified nanofiber membranes was undertaken to determine their efficacy in the rapid uptake and recovery of heavy metals from impaired waters. The membranes were prepared by grafting poly(acrylic acid) (PAA) and poly(itaconic acid) (PIA) to cellulose nanofiber mats. Performance measurements quantified the dynamic ion-exchange capacity for cadmium (Cd), productivity, and recovery of Cd(II) from the membranes by regeneration. The dynamic binding capacities of Cd(II) on both types of nanofiber membrane were independent of the linear flow velocity, with a residence time of as low as 2 s. Analysis of breakthrough curves indicated that the mass flow rate increased rapidly at constant applied pressure after membranes approached equilibrium load capacity for Cd(II), apparently due to a collapse of the polymer chains on the membrane surface, leading to an increased porosity. This mechanism is supported by hydrodynamic radius (R h ) measurements for PAA and PIA obtained from dynamic light scattering, which show that R h values decrease upon Cd(II) binding. Volumetric productivity was high for the nanofiber membranes, and reached 0.55 mg Cd/g/min. The use of ethylenediaminetetraacetic acid as regeneration reagent was effective in fully recovering Cd(II) from the membranes. Ion-exchange capacities were constant over five cycles of binding-regeneration.

Aβ1-25-Derived Sphingolipid-Domain Tracer Peptide SBD Interacts with Membrane Ganglioside Clusters via a Coil-Helix-Coil Motif

PubMed Central

Wang, Yaofeng; Kraut, Rachel; Mu, Yuguang

2015-01-01

The Amyloid-β (Aβ)-derived, sphingolipid binding domain (SBD) peptide is a fluorescently tagged probe used to trace the diffusion behavior of sphingolipid-containing microdomains in cell membranes through binding to a constellation of glycosphingolipids, sphingomyelin, and cholesterol. However, the molecular details of the binding mechanism between SBD and plasma membrane domains remain unclear. Here, to investigate how the peptide recognizes the lipid surface at an atomically detailed level, SBD peptides in the environment of raft-like bilayers were examined in micro-seconds-long molecular dynamics simulations. We found that SBD adopted a coil-helix-coil structural motif, which binds to multiple GT1b gangliosides via salt bridges and CH–π interactions. Our simulation results demonstrate that the CH–π and electrostatic forces between SBD monomers and GT1b gangliosides clusters are the main driving forces in the binding process. The presence of the fluorescent dye and linker molecules do not change the binding mechanism of SBD probes with gangliosides, which involves the helix-turn-helix structural motif that was suggested to constitute a glycolipid binding domain common to some sphingolipid interacting proteins, including HIV gp120, prion, and Aβ. PMID:26540054

Tunable graphene quantum point contact transistor for DNA detection and characterization

PubMed Central

Girdhar, Anuj; Sathe, Chaitanya; Schulten, Klaus; Leburton, Jean-Pierre

2015-01-01

A graphene membrane conductor containing a nanopore in a quantum point contact (QPC) geometry is a promising candidate to sense, and potentially sequence, DNA molecules translocating through the nanopore. Within this geometry, the shape, size, and position of the nanopore as well as the edge configuration influences the membrane conductance caused by the electrostatic interaction between the DNA nucleotides and the nanopore edge. It is shown that the graphene conductance variations resulting from DNA translocation can be enhanced by choosing a particular geometry as well as by modulating the graphene Fermi energy, which demonstrates the ability to detect conformational transformations of a double-stranded DNA, as well as the passage of individual base pairs of a single-stranded DNA molecule through the nanopore. PMID:25765702

Differences in the protein composition of bovine retinal rod outer segment disk and plasma membranes isolated by a ricin-gold-dextran density perturbation method

PubMed Central

1987-01-01

The plasma membrane and disk membranes of bovine retinal rod outer segments (ROS) have been purified by a novel density-gradient perturbation method for analysis of their protein compositions. Purified ROS were treated with neuraminidase to expose galactose residues on plasma membrane-specific glycoproteins and labeled with ricin-gold-dextran particles. After the ROS were lysed in hypotonic buffer, the plasma membrane was dissociated from the disks by either mild trypsin digestion or prolonged exposure to low ionic strength buffer. The dense ricin-gold-dextran-labeled plasma membrane was separated from disks by sucrose gradient centrifugation. Electron microscopy was used to follow this fractionation procedure. The dense red pellet primarily consisted of inverted plasma membrane vesicles containing gold particles; the membrane fraction of density 1.13 g/cc consisted of unlabeled intact disks and vesicles. Ricin-binding studies indicated that the plasma membrane from trypsin-treated ROS was purified between 10-15-fold. The protein composition of plasma membranes and disks was significantly different as analyzed by SDS gels and Western blots labeled with lectins and monoclonal antibodies. ROS plasma membrane exhibited three major proteins of 36 (rhodopsin), 38, and 52 kD, three ricin-binding glycoproteins of 230, 160, and 110 kD, and numerous minor proteins in the range of 14-270 kD. In disk membranes rhodopsin appeared as the only major protein. A 220-kD concanavalin A-binding glycoprotein and peripherin, a rim-specific protein, were also present along with minor proteins of 43 and 57-63 kD. Radioimmune assays indicated that the ROS plasma membrane contained about half as much rhodopsin as disk membranes. PMID:2447095

Conformational antibody binding to a native, cell-free expressed GPCR in block copolymer membranes.

PubMed

de Hoog, Hans-Peter M; Lin JieRong, Esther M; Banerjee, Sourabh; Décaillot, Fabien M; Nallani, Madhavan

2014-01-01

G-protein coupled receptors (GPCRs) play a key role in physiological processes and are attractive drug targets. Their biophysical characterization is, however, highly challenging because of their innate instability outside a stabilizing membrane and the difficulty of finding a suitable expression system. We here show the cell-free expression of a GPCR, CXCR4, and its direct embedding in diblock copolymer membranes. The polymer-stabilized CXCR4 is readily immobilized onto biosensor chips for label-free binding analysis. Kinetic characterization using a conformationally sensitive antibody shows the receptor to exist in the correctly folded conformation, showing binding behaviour that is commensurate with heterologously expressed CXCR4.

Conformational Antibody Binding to a Native, Cell-Free Expressed GPCR in Block Copolymer Membranes

PubMed Central

de Hoog, Hans-Peter M.; Lin JieRong, Esther M.; Banerjee, Sourabh; Décaillot, Fabien M.; Nallani, Madhavan

2014-01-01

G-protein coupled receptors (GPCRs) play a key role in physiological processes and are attractive drug targets. Their biophysical characterization is, however, highly challenging because of their innate instability outside a stabilizing membrane and the difficulty of finding a suitable expression system. We here show the cell-free expression of a GPCR, CXCR4, and its direct embedding in diblock copolymer membranes. The polymer-stabilized CXCR4 is readily immobilized onto biosensor chips for label-free binding analysis. Kinetic characterization using a conformationally sensitive antibody shows the receptor to exist in the correctly folded conformation, showing binding behaviour that is commensurate with heterologously expressed CXCR4. PMID:25329156

Allosteric Signaling Is Bidirectional in an Outer-Membrane Transport Protein.

PubMed

Sikora, Arthur; Joseph, Benesh; Matson, Morgan; Staley, Jacob R; Cafiso, David S

2016-11-01

In BtuB, the Escherichia coli TonB-dependent transporter for vitamin B 12 , substrate binding to the extracellular surface unfolds a conserved energy coupling motif termed the Ton box into the periplasm. This transmembrane signaling event facilitates an interaction between BtuB and the inner-membrane protein TonB. In this study, continuous-wave and pulse electron paramagnetic resonance in a native outer-membrane preparation demonstrate that signaling also occurs from the periplasmic to the extracellular surface in BtuB. The binding of a TonB fragment to the periplasmic interface alters the configuration of the second extracellular loop and partially dissociates a spin-labeled substrate analog. Moreover, mutants in the periplasmic Ton box that are transport-defective alter the binding site for vitamin B 12 in BtuB. This work demonstrates that the Ton box and the extracellular substrate binding site are allosterically coupled in BtuB, and that TonB binding may initiate a partial round of transport. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

[Propranolol beta-blocker decrease in the concentration of high-affinity binding sites for calcium ions by sarcolemma membranes of the rat heart].

PubMed

Seleznev, Iu M; Martynov, A V; Smirnov, V N

1982-05-01

In vivo administration of propranolol considerably inhibits the isoproterenol-stimulated increase in 45Ca accumulation by the myocardium and completely eliminates the potentiation of isoproterenol effect by hydrocortisone. A significant lowering of the concentration of high affinity binding sites for calcium in the sarcolemmal membranes can be produced by propranolol in vitro. Under these conditions, the glucocorticoids do not change the sarcolemmal Ca2+-binding parameters or modulate the propranolol effect. Therefore, for the manifestation of glucocorticoid action to be brought about, the integrity of the cells is apparently required, while propranolol seems to change calcium binding by direct interaction with the sarcolemmal membranes. It is suggested that in vivo propranolol inhibition of catecholamine effect on calcium ion accumulation by the myocardium depends on the interaction with the beta-receptors and direct modulation of the concentration of high affinity binding sites for calcium ions on the surface of the sarcolemma.

Structure of colicin I receptor bound to the R-domain of colicin Ia: implications for protein import

PubMed Central

Buchanan, Susan K; Lukacik, Petra; Grizot, Sylvestre; Ghirlando, Rodolfo; Ali, Maruf M U; Barnard, Travis J; Jakes, Karen S; Kienker, Paul K; Esser, Lothar

2007-01-01

Colicin Ia is a 69 kDa protein that kills susceptible Escherichia coli cells by binding to a specific receptor in the outer membrane, colicin I receptor (70 kDa), and subsequently translocating its channel forming domain across the periplasmic space, where it inserts into the inner membrane and forms a voltage-dependent ion channel. We determined crystal structures of colicin I receptor alone and in complex with the receptor binding domain of colicin Ia. The receptor undergoes large and unusual conformational changes upon colicin binding, opening at the cell surface and positioning the receptor binding domain of colicin Ia directly above it. We modelled the interaction with full-length colicin Ia to show that the channel forming domain is initially positioned 150 Å above the cell surface. Functional data using full-length colicin Ia show that colicin I receptor is necessary for cell surface binding, and suggest that the receptor participates in translocation of colicin Ia across the outer membrane. PMID:17464289

Goodpasture Antigen-binding Protein/Ceramide Transporter Binds to Human Serum Amyloid P-Component and Is Present in Brain Amyloid Plaques*

PubMed Central

Mencarelli, Chiara; Bode, Gerard H.; Losen, Mario; Kulharia, Mahesh; Molenaar, Peter C.; Veerhuis, Robert; Steinbusch, Harry W. M.; De Baets, Marc H.; Nicolaes, Gerry A. F.; Martinez-Martinez, Pilar

2012-01-01

Serum amyloid P component (SAP) is a non-fibrillar glycoprotein belonging to the pentraxin family of the innate immune system. SAP is present in plasma, basement membranes, and amyloid deposits. This study demonstrates, for the first time, that the Goodpasture antigen-binding protein (GPBP) binds to human SAP. GPBP is a nonconventional Ser/Thr kinase for basement membrane type IV collagen. Also GPBP is found in plasma and in the extracellular matrix. In the present study, we demonstrate that GPBP specifically binds SAP in its physiological conformations, pentamers and decamers. The START domain in GPBP is important for this interaction. SAP and GPBP form complexes in blood and partly colocalize in amyloid plaques from Alzheimer disease patients. These data suggest the existence of complexes of SAP and GPBP under physiological and pathological conditions. These complexes are important for understanding basement membrane, blood physiology, and plaque formation in Alzheimer disease. PMID:22396542

A Tenebrio molitor GPI-anchored alkaline phosphatase is involved in binding of Bacillus thuringiensis Cry3Aa to brush border membrane vesicles.

PubMed

Zúñiga-Navarrete, Fernando; Gómez, Isabel; Peña, Guadalupe; Bravo, Alejandra; Soberón, Mario

2013-03-01

Bacillus thuringiensis Cry toxins recognizes their target cells in part by the binding to glycosyl-phosphatidyl-inositol (GPI) anchored proteins such as aminopeptidase-N (APN) or alkaline phosphatases (ALP). Treatment of Tenebrio molitor brush border membrane vesicles (BBMV) with phospholipase C that cleaves out GPI-anchored proteins from the membranes, showed that GPI-anchored proteins are involved in binding of Cry3Aa toxin to BBMV. A 68 kDa GPI-anchored ALP was shown to bind Cry3Aa by toxin overlay assays. The 68 kDa GPI-anchored ALP was preferentially expressed in early instar larvae in comparison to late instar larvae. Our work shows for the first time that GPI-anchored ALP is important for Cry3Aa binding to T. molitor BBMV suggesting that the mode of action of Cry toxins is conserved in different insect orders. Copyright © 2012 Elsevier Inc. All rights reserved.

Coupling of guanine nucleotide inhibitory protein to somatostatin receptors on pancreatic acinar membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakamoto, C.; Matozaki, T.; Nagao, M.

1987-09-01

Guanine nucleotides and pertussis toxin were used to investigate whether somatostatin receptors interact with the guanine nucleotide inhibitory protein (NI) on pancreatic acinar membranes in the rat. Guanine nucleotides reduced /sup 125/I-(Tyr/sup 1/)somatostatin binding to acinar membranes up to 80%, with rank order of potency being 5'-guanylyl imidodiphosphate (Gpp(NH)p)>GTP>TDP>GMP. Scatchard analysis revealed that the decrease in somatostatin binding caused by Gpp(NH)p was due to the decrease in the maximum binding capacity without a significant change in the binding affinity. The inhibitory effect of Gpp(NH)p was partially abolished in the absence of Mg/sup 2 +/. When pancreatic acini were treated withmore » 1 ..mu..g/ml pertussis toxin for 4 h, subsequent /sup 125/I-(Tyr/sup 1/)somatostatin binding to acinar membranes was reduced. Pertussis toxin treatment also abolished the inhibitory effect of somatostatin on vasoactive intestinal peptide-stimulated increase in cellular content of adenosine 3',5'-cyclic monophosphate (cAMP) in the acini. The present results suggest that 1) somatostatin probably functions in the pancreas to regulate adenylate cyclase enzyme system via Ni, 2) the extent of modification of Ni is correlated with the ability of somatostatin to inhibit cAMP accumulation in acini, and 3) guanine nucleotides also inhibit somatostatin binding to its receptor.« less

The binding of calcium ions by erythrocytes and `ghost'-cell membranes

PubMed Central

Long, C.; Mouat, Barbara

1971-01-01

1. Washed human erythrocytes, suspended in iso-osmotic sucrose containing 2.5mm-calcium chloride, bind about 400μg-atoms of calcium/litre of packed cells. Sucrose may be replaced by other sugars. 2. Partial replacement of sucrose by iso-osmotic potassium chloride diminishes the uptake of calcium, 50% inhibition occurring at about 50mm-potassium chloride. 3. Other univalent cations behave like potassium, whereas bivalent cations are much more inhibitory. The tervalent cations, yttrium and lanthanum, however, are the most effective inhibitors of calcium uptake. 4. An approximate correlation exists between the calcium uptake and the sialic acid content of erythrocytes of various species and of human erythrocytes that have been partially depleted of sialic acid by treatment with neuraminidase. However, even after complete removal of sialic acid, human erythrocytes still bind about 140μg-atoms of calcium/litre of packed cells. 5. A Scatchard (1949) plot of calcium uptake at various Ca2+ concentrations in the suspending media shows the presence of three different binding sites on the external surface of the human erythrocyte membrane. 6. Erythrocyte `ghost' cells, the membranes of which appear to be permeable to Ca2+ ions, can bind about 1000μg-atoms of calcium per `ghost'-cell equivalent of 1 litre of packed erythrocytes. This indicates that there are also binding sites for calcium on the internal surface of the erythrocyte membrane. PMID:5124387

Effect of heterogeneity of carcinoembryonic antigen on liver cell membrane binding and its kinetics of removal from circulation.

PubMed

Byrn, R A; Medrek, P; Thomas, P; Jeanloz, R W; Zamcheck, N

1985-07-01

Carcinoembryonic antigen (CEA) is a glycoprotein metabolized primarily by the liver. Subcellular fractions of rat liver were examined for CEA binding activity. Hepatocyte plasma membrane and microsome fractions bound CEA, and this binding shared the calcium requirement, neuraminidase sensitivity, and carbohydrate specificity of the hepatocyte asialoglycoprotein receptor. CEA had previously been shown to react with this galactose-specific receptor, in vivo, only following neuraminidase treatment. Galactose receptor binding of CEA was measured in three different purified CEA preparations. The fraction of CEA capable of binding to excess levels of galactose receptor on membranes varied (46.5%, 40.2%, and 4.7% for CEA-1, -2, and -3, respectively). These CEAs were shown to be 2.3%, 7.9%, and 0.7% as effective, respectively, as asialo-alpha 1-acid glycoprotein in inhibiting the binding of radiolabeled asialo-alpha 1-acid glycoprotein to liver cell membranes. Each of the three CEA preparations showed different clearance kinetics from the circulation of mice. Coinjection of asialo-alpha 1-acid glycoprotein with the CEAs revealed differing inhibition of the clearances. These results show that differences in the carbohydrate components of purified CEA preparations affect their rate of removal from circulation and thus possibly the relationship between CEA production and observed plasma levels in patients. The possible origin of these CEA differences is discussed with their clinical implications.

Progesterone receptor membrane component-1 (PGRMC1) is the mediator of progesterone's antiapoptotic action in spontaneously immortalized granulosa cells as revealed by PGRMC1 small interfering ribonucleic acid treatment and functional analysis of PGRMC1 mutations.

PubMed

Peluso, John J; Romak, Jonathan; Liu, Xiufang

2008-02-01

Progesterone (P4) receptor membrane component-1 (PGRMC1) and its binding partner, plasminogen activator inhibitor 1 RNA binding protein (PAIRBP1) are thought to form a complex that functions as membrane receptor for P4. The present investigations confirm PGRMC1's role in this membrane receptor complex by demonstrating that depleting PGMRC1 with PGRMC1 small interfering RNA results in a 60% decline in [(3)H]P4 binding and the loss of P4's antiapoptotic action. Studies conducted on partially purified GFP-PGRMC1 fusion protein indicate that [(3)H]P4 specifically binds to PGRMC1 at a single site with an apparent K(d) of about 35 nm. In addition, experiments using various deletion mutations reveal that the entire PGRMC1 molecule is required for maximal [(3)H]P4 binding and P4 responsiveness. Analysis of the binding data also suggests that the P4 binding site is within a segment of PGRMC1 that is composed of the transmembrane domain and the initial segment of the C terminus. Interestingly, PAIRBP1 appears to bind to the C terminus between amino acids 70-130, which is distal to the putative P4 binding site. Taken together, these data provide compelling evidence that PGRMC1 is the P4 binding protein that mediates P4's antiapoptotic action. Moreover, the deletion mutation studies indicate that each domain of PGRMC1 plays an essential role in modulating PGRMC1's capacity to both bind and respond to P4. Additional studies are required to more precisely delineate the role of each PGRMC1 domain in transducing P4's antiapoptotic action.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawamoto, Shuhei; Shinoda, Wataru, E-mail: w.shinoda@apchem.nagoya-u.ac.jp; Klein, Michael L.

The effects of membrane curvature on the free energy barrier for membrane fusion have been investigated using coarse-grained molecular dynamics (CG-MD) simulations, assuming that fusion takes place through a stalk intermediate. Free energy barriers were estimated for stalk formation as well as for fusion pore formation using the guiding potential method. Specifically, the three different geometries of two apposed membranes were considered: vesicle–vesicle, vesicle–planar, and planar–planar membranes. The free energy barriers for the resulting fusion were found to depend importantly on the fusing membrane geometries; the lowest barrier was obtained for vesicular membranes. Further, lipid sorting was observed in fusionmore » of the mixed membranes of dimyristoyl phosphatidylcholine and dioleoyl phosphatidylethanolamine (DOPE). Specifically, DOPE molecules were found to assemble around the stalk to support the highly negative curved membrane surface. A consistent result for lipid sorting was observed when a simple continuum model (CM) was used, where the Helfrich energy and mixing entropy of the lipids were taken into account. However, the CM predicts a much higher free energy barrier than found using CG-MD. This discrepancy originates from the conformational changes of lipids, which were not considered in the CM. The results of the CG-MD simulations reveal that a large conformational change in the lipid takes place around the stalk region, which results in a reduction of free energy barriers along the stalk mechanism of membrane fusion.« less

Histochemical study of lectin binding sites in fourth and fifth instar gypsy moth larval midgut epithelium

Treesearch

Algimantas P. Valaitis

2011-01-01

There is evidence that the gypsy moth, Lymantria dispar, midgut epithelial brush border membrane has membrane-bound glycoconjugates, such as BTR-270 and aminopeptidase N (APN), which function as high affinity binding sites (receptors) for the insecticidal proteins produced by Bacillus thuringiensis (Bt). As gypsy...

[Molecular organization of glutamate-sensitive chemoexcitable membranes of nerve cells. Function of glutamate-binding proteins of the central nervous system when incorporated into liposomes].

PubMed

Besedin, V I; Kuznetsov, A S; Dambinova, S A

1985-03-01

The functioning of the glutamate-binding protein of rat brain cortex synaptic membranes was studied by its incorporation into liposomes. The optimal conditions for the receptor protein incorporation were established and the kinetics of 22Na+ and 86Rb+ incorporation into the liposomes in the presence of L-glutamate were analyzed. Modelling of the CNS glutamate receptor functions was found to be dependent on the lipid composition and amount of the incorporated membrane protein. The selective transport of 22Na+ into the liposomes was stimulated in the presence of 10(-4) M glutamate. Addition of monoclonal antibodies against glutamate-binding proteins blocked the incorporation of Na+ into the liposomes. The experimental results are suggestive of the nativity of the liposome-incorporated membrane protein, which is capable of binding glutamate and regulating selective transport of Na+. It was assumed that the glutamate receptor macromolecule represents an integral complex made up of several low molecular weight subunits of glucoprotein nature that form a selective ionic channel.

A validated methodology for the 3D reconstruction of cochlea geometries using human microCT images

NASA Astrophysics Data System (ADS)

Sakellarios, A. I.; Tachos, N. S.; Rigas, G.; Bibas, T.; Ni, G.; Böhnke, F.; Fotiadis, D. I.

2017-05-01

Accurate reconstruction of the inner ear is a prerequisite for the modelling and understanding of the inner ear mechanics. In this study, we present a semi-automated methodology for accurate reconstruction of the major inner ear structures (scalae, basilar membrane, stapes and semicircular canals). For this purpose, high resolution microCT images of a human specimen were used. The segmentation methodology is based on an iterative level set algorithm which provides the borders of the structures of interest. An enhanced coupled level set method which allows the simultaneous multiple image labeling without any overlapping regions has been developed for this purpose. The marching cube algorithm was applied in order to extract the surface from the segmented volume. The reconstructed geometries are then post-processed to improve the basilar membrane geometry to realistically represent physiologic dimensions. The final reconstructed model is compared to the available data from the literature. The results show that our generated inner ear structures are in good agreement with the published ones, while our approach is the most realistic in terms of the basilar membrane thickness and width reconstruction.

Single-cell mechanics--An experimental-computational method for quantifying the membrane-cytoskeleton elasticity of cells.

PubMed

Tartibi, M; Liu, Y X; Liu, G-Y; Komvopoulos, K

2015-11-01

The membrane-cytoskeleton system plays a major role in cell adhesion, growth, migration, and differentiation. F-actin filaments, cross-linkers, binding proteins that bundle F-actin filaments to form the actin cytoskeleton, and integrins that connect the actin cytoskeleton network to the cell plasma membrane and extracellular matrix are major cytoskeleton constituents. Thus, the cell cytoskeleton is a complex composite that can assume different shapes. Atomic force microscopy (AFM)-based techniques have been used to measure cytoskeleton material properties without much attention to cell shape. A recently developed surface chemical patterning method for long-term single-cell culture was used to seed individual cells on circular patterns. A continuum-based cell model, which uses as input the force-displacement response obtained with a modified AFM setup and relates the membrane-cytoskeleton elastic behavior to the cell geometry, while treating all other subcellular components suspended in the cytoplasmic liquid (gel) as an incompressible fluid, is presented and validated by experimental results. The developed analytical-experimental methodology establishes a framework for quantifying the membrane-cytoskeleton elasticity of live cells. This capability may have immense implications in cell biology, particularly in studies seeking to establish correlations between membrane-cytoskeleton elasticity and cell disease, mortality, differentiation, and migration, and provide insight into cell infiltration through nonwoven fibrous scaffolds. The present method can be further extended to analyze membrane-cytoskeleton viscoelasticity, examine the role of other subcellular components (e.g., nucleus envelope) in cell elasticity, and elucidate the effects of mechanical stimuli on cell differentiation and motility. This is the first study to decouple the membrane-cytoskeleton elasticity from cell stiffness and introduce an effective approach for measuring the elastic modulus. The novelty of this study is the development of new technology for quantifying the elastic stiffness of the membrane-cytoskeleton system of cells. This capability could have immense implications in cell biology, particularly in establishing correlations between various cell diseases, mortality, and differentiation with membrane-cytoskeleton elasticity, examining through-tissue cell migration, and understanding cell infiltration in porous scaffolds. The present method can be further extended to analyze membrane-cytoskeleton viscous behavior, identify the contribution of other subcellular components (e.g., nucleus envelope) to load sharing, and elucidate mechanotransduction effects due to repetitive compressive loading and unloading on cell differentiation and motility. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

TGD4 involved in endoplasmic reticulum-to-chloroplast lipid trafficking is a phosphatidic acid binding protein

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang Z.; Xu C.; Benning, C.

The synthesis of galactoglycerolipids, which are prevalent in photosynthetic membranes, involves enzymes at the endoplasmic reticulum (ER) and the chloroplast envelope membranes. Genetic analysis of trigalactosyldiacylglycerol (TGD) proteins in Arabidopsis has demonstrated their role in polar lipid transfer from the ER to the chloroplast. The TGD1, 2, and 3 proteins resemble components of a bacterial-type ATP-binding cassette (ABC) transporter, with TGD1 representing the permease, TGD2 the substrate binding protein, and TGD3 the ATPase. However, the function of the TGD4 protein in this process is less clear and its location in plant cells remains to be firmly determined. The predicted C-terminalmore » {beta}-barrel structure of TGD4 is weakly similar to proteins of the outer cell membrane of Gram-negative bacteria. Here, we show that, like TGD2, the TGD4 protein when fused to DsRED specifically binds phosphatidic acid (PtdOH). As previously shown for tgd1 mutants, tgd4 mutants have elevated PtdOH content, probably in extraplastidic membranes. Using highly purified and specific antibodies to probe different cell fractions, we demonstrated that the TGD4 protein was present in the outer envelope membrane of chloroplasts, where it appeared to be deeply buried within the membrane except for the N-terminus, which was found to be exposed to the cytosol. It is proposed that TGD4 is either directly involved in the transfer of polar lipids, possibly PtdOH, from the ER to the outer chloroplast envelope membrane or in the transfer of PtdOH through the outer envelope membrane.« less

Development of high-productivity, strong cation-exchange adsorbers for protein capture by graft polymerization from membranes with different pore sizes

PubMed Central

Chenette, Heather C.S.; Robinson, Julie R.; Hobley, Eboni; Husson, Scott M.

2012-01-01

This paper describes the surface modification of macroporous membranes using ATRP (atom transfer radical polymerization) to create cation-exchange adsorbers with high protein binding capacity at high product throughput. The work is motivated by the need for a more economical and rapid capture step in downstream processing of protein therapeutics. Membranes with three reported nominal pore sizes (0.2, 0.45, 1.0 μm) were modified with poly(3-sulfopropyl methacrylate, potassium salt) tentacles, to create a high density of protein binding sites. A special formulation was used in which the monomer was protected by a crown ether to enable surface-initiated ATRP of this cationic polyelectrolyte. Success with modification was supported by chemical analysis using Fourier-transform infrared spectroscopy and indirectly by measurement of pure water flux as a function of polymerization time. Uniformity of modification within the membranes was visualized with confocal laser scanning microscopy. Static and dynamic binding capacities were measured using lysozyme protein to allow comparisons with reported performance data for commercial cation-exchange materials. Dynamic binding capacities were measured for flow rates ranging from 13 to 109 column volumes (CV)/min. Results show that this unique ATRP formulation can be used to fabricate cation-exchange membrane adsorbers with dynamic binding capacities as high as 70 mg/mL at a throughput of 100 CV/min and unprecedented productivity of 300 mg/mL/min. PMID:23175597

Conformational changes in the M2 muscarinic receptor induced by membrane voltage and agonist binding

PubMed Central

Navarro-Polanco, Ricardo A; Galindo, Eloy G Moreno; Ferrer-Villada, Tania; Arias, Marcelo; Rigby, J Ryan; Sánchez-Chapula, José A; Tristani-Firouzi, Martin

2011-01-01

Abstract The ability to sense transmembrane voltage is a central feature of many membrane proteins, most notably voltage-gated ion channels. Gating current measurements provide valuable information on protein conformational changes induced by voltage. The recent observation that muscarinic G-protein-coupled receptors (GPCRs) generate gating currents confirms their intrinsic capacity to sense the membrane electrical field. Here, we studied the effect of voltage on agonist activation of M2 muscarinic receptors (M2R) in atrial myocytes and how agonist binding alters M2R gating currents. Membrane depolarization decreased the potency of acetylcholine (ACh), but increased the potency and efficacy of pilocarpine (Pilo), as measured by ACh-activated K+ current, IKACh. Voltage-induced conformational changes in M2R were modified in a ligand-selective manner: ACh reduced gating charge displacement while Pilo increased the amount of charge displaced. Thus, these ligands manifest opposite voltage-dependent IKACh modulation and exert opposite effects on M2R gating charge displacement. Finally, mutations in the putative ligand binding site perturbed the movement of the M2R voltage sensor. Our data suggest that changes in voltage induce conformational changes in the ligand binding site that alter the agonist–receptor interaction in a ligand-dependent manner. Voltage-dependent GPCR modulation has important implications for cellular signalling in excitable tissues. Gating current measurement allows for the tracking of subtle conformational changes in the receptor that accompany agonist binding and changes in membrane voltage. PMID:21282291

Influence of N-ethylmaleimide on cholinoceptors and responses in longitudinal muscles from guinea-pig ileum.

PubMed Central

Aronstam, R. S.; Carrier, G. O.

1982-01-01

1 The binding of carbamylcholine to membranes prepared from the longitudinal muscle of guinea-pig ileum was determined from its inhibition of the binding of [3H]-3-quinuclidinyl benzilate. Carbamylcholine binding was resolved into high and low affinity components with apparent dissociation constants of 0.11 +/- 0.02 and 11 +/- 1 microM; 42% of the receptors displayed high affinity carbamylcholine binding. 2 Alkylation of longitudinal muscle membranes with N-ethylmaleimide increased muscarinic receptor affinity for carbamylcholine in a manner consistent with a conversion of low affinity to high affinity receptors. After exposure the muscle membrane fragments to 1 mM N-ethylmaleimide for 20 min at 35 degrees C, carbamylcholine binding was resolved into two components with apparent dissociation constants of 0.11 +/- 0.01 and 9 +/- 2 microM, with 74% of the receptors displaying the higher affinity. 3 Exposure of longitudinal membranes mounted in an organ chamber to 1 mM N-ethylmaleimide for 30s depressed isometric contractions in response to acetylcholine by 80%, while contractions induced by K+ and Ba2+ were reduced by less than 20% and 10%, respectively. Acetylcholine dose-response curves were shifted to the right while Ba2+ curves were unaffected. 4 It is suggested that N-ethylmaleimide has a selective effect on muscarinic responses in the longitudinal muscle by disrupting processes occurring after receptor occupancy but before the induction of phospholipid turnover or calcium influx in the postsynaptic membrane. PMID:7126999

Coordination of golgin tethering and SNARE assembly: GM130 binds syntaxin 5 in a p115-regulated manner.

PubMed

Diao, Aipo; Frost, Laura; Morohashi, Yuichi; Lowe, Martin

2008-03-14

During membrane traffic, transport carriers are first tethered to the target membrane prior to undergoing fusion. Mechanisms exist to connect tethering with fusion, but in most cases, the details remain poorly understood. GM130 is a member of the golgin family of coiled-coil proteins tat is involved in membrane tethering at the endoplasmic reticulum (ER) to Golgi intermediate compartment and cis-Golgi. Here, we demonstrate that GM130 interacts with syntaxin 5, a t-SNARE also localized to the early secretory pathway. Binding to syntaxin 5 is specific, direct, and mediated by the membrane-proximal region of GM130. Interestingly, interaction with syntaxin 5 is inhibited by the binding of the vesicle docking protein p115 to a distal binding site in GM130. The interaction between GM130 and the small GTPase Rab1 is also inhibited by p115 binding. Our findings suggest a mechanism for coupling membrane tethering and fusion at the ER to Golgi intermediate compartment and cis-Golgi, with GM130 playing a central role in linking these processes. Consistent with this hypothesis, we find that depletion of GM130 by RNA interference slows the rate of ER to Golgi trafficking in vivo. The interactions of GM130 with syntaxin 5 and Rab1 are also regulated by mitotic phosphorylation, which is likely to contribute to the inhibition of ER to Golgi trafficking that occurs when mammalian cells enter mitosis.

Mapping structural landmarks, ligand binding sites and missense mutations to the collagen IV heterotrimers predicts major functional domains, novel interactions and variation in phenotypes in inherited diseases affecting basement membranes

PubMed Central

Des Parkin, J.; San Antonio, James D.; Pedchenko, Vadim; Hudson, Billy; Jensen, Shane T.; Savige, Judy

2016-01-01

Collagen IV is the major protein found in basement membranes. It comprises 3 heterotrimers (α1α1α2, α3α4α5, and α5α5α6) that form distinct networks, and are responsible for membrane strength and integrity. We constructed linear maps of the collagen IV heterotrimers (‘interactomes’) that indicated major structural landmarks, known and predicted ligand-binding sites, and missense mutations, in order to identify functional and disease-associated domains, potential interactions between ligands, and genotype-phenotype relationships. The maps documented more than 30 known ligand-binding sites as well as motifs for integrins, heparin, von Willebrand factor (VWF), decorin and bone morphogenetic protein (BMP). They predicted functional domains for angiogenesis and haemostasis, and disease domains for autoimmunity, tumor growth and inhibition, infection and glycation. Cooperative ligand interactions were indicated by binding site proximity, for example, between integrins, matrix metalloproteinases and heparin. The maps indicated that mutations affecting major ligand-binding sites, for example for Von Hippel Lindau (VHL) protein in the α1 chain or integrins in the α5 chain, resulted in distinctive phenotypes (Hereditary Angiopathy, Nephropathy, Aneurysms and muscle Cramps (HANAC) syndrome, and early onset Alport syndrome respectively). These maps further our understanding of basement membrane biology and disease, and suggest novel membrane interactions, functions, and therapeutic targets. PMID:21280145

Actin-Binding Protein Requirement for Cortical Stability and Efficient Locomotion

NASA Astrophysics Data System (ADS)

Cunningham, C. Casey; Gorlin, Jed B.; Kwiatkowski, David J.; Hartwig, John H.; Janmey, Paul A.; Randolph Byers, H.; Stossel, Thomas P.

1992-01-01

Three unrelated tumor cell lines derived from human malignant melanomas lack actin-binding protein (ABP), which cross-links actin filaments in vitro and connects these filaments to plasma membrane glycoproteins. The ABP-deficient cells have impaired locomotion and display circumferential blebbing of the plasma membrane. Expression of ABP in one of the lines after transfection restored translocational motility and reduced membrane blebbing. These findings establish that ABP functions to stabilize cortical actin in vivo and is required for efficient cell locomotion.

Frizzled 7 and PIP2 binding by syntenin PDZ2 domain supports Frizzled 7 trafficking and signalling

NASA Astrophysics Data System (ADS)

Egea-Jimenez, Antonio Luis; Gallardo, Rodrigo; Garcia-Pino, Abel; Ivarsson, Ylva; Wawrzyniak, Anna Maria; Kashyap, Rudra; Loris, Remy; Schymkowitz, Joost; Rousseau, Frederic; Zimmermann, Pascale

2016-07-01

PDZ domain-containing proteins work as intracellular scaffolds to control spatio-temporal aspects of cell signalling. This function is supported by the ability of their PDZ domains to bind other proteins such as receptors, but also phosphoinositide lipids important for membrane trafficking. Here we report a crystal structure of the syntenin PDZ tandem in complex with the carboxy-terminal fragment of Frizzled 7 and phosphatidylinositol 4,5-bisphosphate (PIP2). The crystal structure reveals a tripartite interaction formed via the second PDZ domain of syntenin. Biophysical and biochemical experiments establish co-operative binding of the tripartite complex and identify residues crucial for membrane PIP2-specific recognition. Experiments with cells support the importance of the syntenin-PIP2 interaction for plasma membrane targeting of Frizzled 7 and c-jun phosphorylation. This study contributes to our understanding of the biology of PDZ proteins as key players in membrane compartmentalization and dynamics.

Energy design for protein-protein interactions

PubMed Central

Ravikant, D. V. S.; Elber, Ron

2011-01-01

Proteins bind to other proteins efficiently and specifically to carry on many cell functions such as signaling, activation, transport, enzymatic reactions, and more. To determine the geometry and strength of binding of a protein pair, an energy function is required. An algorithm to design an optimal energy function, based on empirical data of protein complexes, is proposed and applied. Emphasis is made on negative design in which incorrect geometries are presented to the algorithm that learns to avoid them. For the docking problem the search for plausible geometries can be performed exhaustively. The possible geometries of the complex are generated on a grid with the help of a fast Fourier transform algorithm. A novel formulation of negative design makes it possible to investigate iteratively hundreds of millions of negative examples while monotonically improving the quality of the potential. Experimental structures for 640 protein complexes are used to generate positive and negative examples for learning parameters. The algorithm designed in this work finds the correct binding structure as the lowest energy minimum in 318 cases of the 640 examples. Further benchmarks on independent sets confirm the significant capacity of the scoring function to recognize correct modes of interactions. PMID:21842951

Pyrrolic tripodal receptors for carbohydrates. Role of functional groups and binding geometry on carbohydrate recognition.

PubMed

Cacciarini, Martina; Nativi, Cristina; Norcini, Martina; Staderini, Samuele; Francesconi, Oscar; Roelens, Stefano

2011-02-21

The contribution from several H-bonding groups and the impact of geometric requirements on the binding ability of benzene-based tripodal receptors toward carbohydrates have been investigated by measuring the affinity of a set of structures toward octyl β-D-glucopyranoside, selected as a representative monosaccharide. The results reported in the present study demonstrate that a judicious choice of correct geometry and appropriate functional groups is critical to achieve the complementary hydrogen bonding interactions required for an effective carbohydrate recognition.

Interaction analysis of chimeric metal-binding green fluorescent protein and artificial solid-supported lipid membrane by quartz crystal microbalance and atomic force microscopy.

PubMed

Prachayasittikul, Virapong; Isarankura Na Ayudhya, Chartchalerm; Hilterhaus, Lutz; Hinz, Andreas; Tantimongcolwat, Tanawut; Galla, Hans-Joachim

2005-02-04

Non-specific adsorption and specific interaction between a chimeric green fluorescent protein (GFP) carrying metal-binding region and the immobilized zinc ions on artificial solid-supported lipid membranes was investigated using the quartz crystal microbalance technique and the atomic force microscopy (AFM). Supported lipid bilayer, composed of octanethiol and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/1,2-dioleoyl-sn-glycero-3-[N-(5-amino-1-carboxypentyl iminodiacetic acid)succinyl] (NTA-DOGS)-Zn2+, was formed on the gold electrode of quartz resonator (5 MHz). Binding of the chimeric GFP to zinc ions resulted in a rapid decrease of resonance frequency. Reversibility of the process was demonstrated via the removal of metal ions by EDTA. Nanoscale structural orientation of the chimeric GFP on the membrane was imaged by AFM. Association constant of the specific binding to metal ions was 2- to 3-fold higher than that of the non-specific adsorption, which was caused by the fluidization effect of the metal-chelating lipid molecules as well as the steric hindrance effect. This infers a possibility for a further development of biofunctionalized membrane. However, maximization is needed in order to attain closer advancement to a membrane-based sensor device.

The geometry of the ionic chànnel lumen formed by alpha-latroinsectotoxin from black widow spider venom in the bilayer lipid membranes.

PubMed

Shatursky, Oleg Ya; Volkova, Tatyana M; Himmelreich, Nina H; Grishin, Eugene V

2007-11-01

The dependence of single channel conductance formed by alpha-latroinsectotoxin (alpha-LIT) from black widow spider venom in the planar phospholipid membrane on the hydrodynamic radii of different nonelectrolytes allowed to determine the geometry of alpha-LIT water lumen. It was found that the cis- and trans-entrances of alpha-LIT channel had the same effective radii of 0.55-0.58 nm. Relatively small conductance of alpha-LIT channel (23.5+3.7 pS) in a symmetrical membrane bathing solution of 100 mM KCl (pH 7.4) may result from the constriction inside the channel with apparent radius of 0.37 nm located 32.5% of channel length away from the cis-entrance.

The GTP- and Phospholipid-Binding Protein TTD14 Regulates Trafficking of the TRPL Ion Channel in Drosophila Photoreceptor Cells

PubMed Central

Cerny, Alexander C.; Altendorfer, André; Schopf, Krystina; Baltner, Karla; Maag, Nathalie; Sehn, Elisabeth; Wolfrum, Uwe; Huber, Armin

2015-01-01

Recycling of signaling proteins is a common phenomenon in diverse signaling pathways. In photoreceptors of Drosophila, light absorption by rhodopsin triggers a phospholipase Cβ-mediated opening of the ion channels transient receptor potential (TRP) and TRP-like (TRPL) and generates the visual response. The signaling proteins are located in a plasma membrane compartment called rhabdomere. The major rhodopsin (Rh1) and TRP are predominantly localized in the rhabdomere in light and darkness. In contrast, TRPL translocates between the rhabdomeral plasma membrane in the dark and a storage compartment in the cell body in the light, from where it can be recycled to the plasma membrane upon subsequent dark adaptation. Here, we identified the gene mutated in trpl translocation defective 14 (ttd14), which is required for both TRPL internalization from the rhabdomere in the light and recycling of TRPL back to the rhabdomere in the dark. TTD14 is highly conserved in invertebrates and binds GTP in vitro. The ttd14 mutation alters a conserved proline residue (P75L) in the GTP-binding domain and abolishes binding to GTP. This indicates that GTP binding is essential for TTD14 function. TTD14 is a cytosolic protein and binds to PtdIns(3)P, a lipid enriched in early endosome membranes, and to phosphatidic acid. In contrast to TRPL, rhabdomeral localization of the membrane proteins Rh1 and TRP is not affected in the ttd14 P75L mutant. The ttd14 P75L mutation results in Rh1-independent photoreceptor degeneration and larval lethality suggesting that other processes are also affected by the ttd14 P75L mutation. In conclusion, TTD14 is a novel regulator of TRPL trafficking, involved in internalization and subsequent sorting of TRPL into the recycling pathway that enables this ion channel to return to the plasma membrane. PMID:26509977

Prediction of binding free energy for adsorption of antimicrobial peptide lactoferricin B on a POPC membrane

NASA Astrophysics Data System (ADS)

Vivcharuk, Victor; Tomberli, Bruno; Tolokh, Igor S.; Gray, C. G.

2008-03-01

Molecular dynamics (MD) simulations are used to study the interaction of a zwitterionic palmitoyl-oleoyl-phosphatidylcholine (POPC) bilayer with the cationic antimicrobial peptide bovine lactoferricin (LFCinB) in a 100 mM NaCl solution at 310 K. The interaction of LFCinB with POPC is used as a model system for studying the details of membrane-peptide interactions, with the peptide selected because of its antimicrobial nature. Seventy-two 3 ns MD simulations, with six orientations of LFCinB at 12 different distances from a POPC membrane, are carried out to determine the potential of mean force (PMF) or free energy profile for the peptide as a function of the distance between LFCinB and the membrane surface. To calculate the PMF for this relatively large system a new variant of constrained MD and thermodynamic integration is developed. A simplified method for relating the PMF to the LFCinB-membrane binding free energy is described and used to predict a free energy of adsorption (or binding) of -1.05±0.39kcal/mol , and corresponding maximum binding force of about 20 pN, for LFCinB-POPC. The contributions of the ions-LFCinB and the water-LFCinB interactions to the PMF are discussed. The method developed will be a useful starting point for future work simulating peptides interacting with charged membranes and interactions involved in the penetration of membranes, features necessary to understand in order to rationally design peptides as potential alternatives to traditional antibiotics.

Prediction of binding free energy for adsorption of antimicrobial peptide lactoferricin B on a POPC membrane.

PubMed

Vivcharuk, Victor; Tomberli, Bruno; Tolokh, Igor S; Gray, C G

2008-03-01

Molecular dynamics (MD) simulations are used to study the interaction of a zwitterionic palmitoyl-oleoyl-phosphatidylcholine (POPC) bilayer with the cationic antimicrobial peptide bovine lactoferricin (LFCinB) in a 100 mM NaCl solution at 310 K. The interaction of LFCinB with POPC is used as a model system for studying the details of membrane-peptide interactions, with the peptide selected because of its antimicrobial nature. Seventy-two 3 ns MD simulations, with six orientations of LFCinB at 12 different distances from a POPC membrane, are carried out to determine the potential of mean force (PMF) or free energy profile for the peptide as a function of the distance between LFCinB and the membrane surface. To calculate the PMF for this relatively large system a new variant of constrained MD and thermodynamic integration is developed. A simplified method for relating the PMF to the LFCinB-membrane binding free energy is described and used to predict a free energy of adsorption (or binding) of -1.05+/-0.39 kcal/mol , and corresponding maximum binding force of about 20 pN, for LFCinB-POPC. The contributions of the ions-LFCinB and the water-LFCinB interactions to the PMF are discussed. The method developed will be a useful starting point for future work simulating peptides interacting with charged membranes and interactions involved in the penetration of membranes, features necessary to understand in order to rationally design peptides as potential alternatives to traditional antibiotics.

Osmotically-induced tension and the binding of N-BAR protein to lipid vesicles.

PubMed

Hutchison, Jaime B; Karunanayake Mudiyanselage, Aruni P K K; Weis, Robert M; Dinsmore, Anthony D

2016-02-28

The binding affinity of a curvature-sensing protein domain (N-BAR) is measured as a function of applied osmotic stress while the membrane curvature is nearly constant. Varying the osmotic stress allows us to control membrane tension, which provides a probe of the mechanism of binding. We study the N-BAR domain of the Drosophila amphiphysin and monitor its binding on 50 nm-radius vesicles composed of 90 mol% DOPC and 10 mol% PIP. We find that the bound fraction of N-BAR is enhanced by a factor of approximately 6.5 when the tension increases from zero to 2.6 mN m(-1). This tension-induced response can be explained by the hydrophobic insertion mechanism. From the data we extract a hydrophobic domain area that is consistent with known structure. These results indicate that membrane stress and strain could play a major role in the previously reported curvature-affinity of N-BAR.

Chlamydia trachomatis elementary bodies possess proteins which bind to eucaryotic cell membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wenman, W.M.; Meuser, R.U.

1986-02-01

Chlamydia trachomatis proteins were electrophoresed and then transferred to nitrocellulose paper to detect chlamydial proteins which bind to eucaryotic cell membranes. Resolved polypeptides of C. trachomatis serovars J and L/sub 2/ were reacted with iodinated HeLa cell membranes and autoradiographed. Infectious elementary bodies of both serovars possess 31,000- and 18,000-dalton proteins which bind to HeLa cells. In contrast, noninfectious reticulate bodies do not possess eucaryotic cell-binding proteins. Both proteins are antigenic when reacted with hyperimmune rabbit antisera in immunoblots and antisera raised against the 31,000- and 18,000-dalton proteins are inhibitory to chlamydia-host cell association. In addition, these antisera exhibit neutralizingmore » activity. These data suggest that these putative chlamydial adhesions play a key role in the early steps of chlamydia-host cell interaction and that antibody directed against them may be protective.« less

Influence of volatile anesthetics on muscarinic receptor adenylate cyclase coupling in brain and heart

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anthony, B.L.

In the present study, the influence of four volatile anesthetics (enflurane, isoflurane, diethyl ether, and chloroform) on (1) muscarinic receptor binding parameters and (2) muscarnic regulation of adenylate cyclase activity was examined using membranes isolated from rat brain and heart. Membranes were equilibrated with each of the four anesthetics for 30 minutes and then during the binding assay. The data obtained can be summarized as follows: (1) volatile anesthetics increased receptor affinity for a radiolabeled antagonists, ({sup 3}H)N-methylscopolamine (({sup 3}H)MS), by decreasing its rate of dissociation in brain stem, but not in cardiac, membranes, (2) volatile anesthetics decreased high affinitymore » ({sup 3}H)Oxotremorine-M binding, (3) volatile anesthetics depressed or eliminated the guanine nucleotide sensitivity of agonist binding. The influence of volatile anesthetics on muscarinic regulation of adenylate cyclase enzyme activity was studied using {alpha}({sup 32}P)ATP as the substrate.« less

Analysis of Protein Interactions at Native Chloroplast Membranes by Ellipsometry

PubMed Central

Kriechbaumer, Verena; Nabok, Alexei; Mustafa, Mohd K.; Al-Ammar, Rukaiah; Tsargorodskaya, Anna; Smith, David P.; Abell, Ben M.

2012-01-01

Membrane bound receptors play vital roles in cell signaling, and are the target for many drugs, yet their interactions with ligands are difficult to study by conventional techniques due to the technical difficulty of monitoring these interactions in lipid environments. In particular, the ability to analyse the behaviour of membrane proteins in their native membrane environment is limited. Here, we have developed a quantitative approach to detect specific interactions between low-abundance chaperone receptors within native chloroplast membranes and their soluble chaperone partners. Langmuir-Schaefer film deposition was used to deposit native chloroplasts onto gold-coated glass slides, and interactions between the molecular chaperones Hsp70 and Hsp90 and their receptors in the chloroplast membranes were detected and quantified by total internal reflection ellipsometry (TIRE). We show that native chloroplast membranes deposited on gold-coated glass slides using Langmuir-Schaefer films retain functional receptors capable of binding chaperones with high specificity and affinity. Taking into account the low chaperone receptor abundance in native membranes, these binding properties are consistent with data generated using soluble forms of the chloroplast chaperone receptors, OEP61 and Toc64. Therefore, we conclude that chloroplasts have the capacity to selectively bind chaperones, consistent with the notion that chaperones play an important role in protein targeting to chloroplasts. Importantly, this method of monitoring by TIRE does not require any protein labelling. This novel combination of techniques should be applicable to a wide variety of membranes and membrane protein receptors, thus presenting the opportunity to quantify protein interactions involved in fundamental cellular processes, and to screen for drugs that target membrane proteins. PMID:22479632

Toxin studies using an integrated biophysical and structural biology approach.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Last, Julie A.; Schroeder, Anne E.; Slade, Andrea Lynn

2005-03-01

Clostridial neurotoxins, such as botulinum and tetanus, are generally thought to invade neural cells through a process of high affinity binding mediated by gangliosides, internalization via endosome formation, and subsequent membrane penetration of the catalytic domain activated by a pH drop in the endosome. This surface recognition and internalization process is still not well understood with regard to what specific membrane features the toxins target, the intermolecular interactions between bound toxins, and the molecular conformational changes that occur as a result of pH lowering. In an effort to elucidate the mechanism of tetanus toxin binding and permeation through the membranemore » a simple yet representative model was developed that consisted of the ganglioside G{sub tlb} incorporated in a bilayer of cholesterol and DPPC (dipalmitoylphosphatidyl choline). The bilayers were stable over time yet sensitive towards the binding and activity of whole toxin. A liposome leakage study at constant pH as well as with a pH gradient, to mimic the processes of the endosome, was used to elucidate the effect of pH on the toxin's membrane binding and permeation capability. Topographic imaging of the membrane surface, via in situ tapping mode AFM, provided nanoscale characterization of the toxin's binding location and pore formation activity.« less

[Molecular organization of glutamate-sensitive chemoexcitatory membranes of nerve cells. Comparative analysis of glutamate-binding membrane proteins from the cerebral cortex of rats and humans].

PubMed

Dambinova, S A; Gorodinskiĭ, A I; Lekomtseva, T M; Koreshonkov, O N

1987-10-01

The kinetics of 3H-L-glutamate binding to human brain synaptic membranes revealed the existence of one type of binding sites with Kd and Vmax comparable with those for freshly isolated rat brain membranes. The fraction of glutamate-binding proteins (GBP) was shown to contain three components with Mr of 14, 60 and 280 kD whose stoichiometry is specific for human and rat brain. All fractions were found to bind the radiolabeled neurotransmitter and to dissociate into subunits with Mr of 14 kD after treatment with-potent detergents (with the exception of the 56-60 kD component). Study of association-dissociation of GBP protein subunits by high performance liquid chromatography confirmed the hypothesis on the oligomeric structure of glutamate receptors which are made up of low molecular weight glycoprotein-lipid subunits and which form ionic channels by way of repeated association. Despite the similarity of antigen determinants in the active center of glutamate receptors from human and rat brain, it was assumed that the stoichiometry of structural organization of receptor subunits isolated from different sources is different. The functional role of structural complexity of human brain glutamate receptors is discussed.

Massive Ca-induced Membrane Fusion and Phospholipid Changes Triggered by Reverse Na/Ca Exchange in BHK Fibroblasts

PubMed Central

Yaradanakul, Alp; Wang, Tzu-Ming; Lariccia, Vincenzo; Lin, Mei-Jung; Shen, Chengcheng; Liu, Xinran; Hilgemann, Donald W.

2008-01-01

Baby hamster kidney (BHK) fibroblasts increase their cell capacitance by 25–100% within 5 s upon activating maximal Ca influx via constitutively expressed cardiac Na/Ca exchangers (NCX1). Free Ca, measured with fluo-5N, transiently exceeds 0.2 mM with total Ca influx amounting to ∼5 mmol/liter cell volume. Capacitance responses are half-maximal when NCX1 promotes a free cytoplasmic Ca of 0.12 mM (Hill coefficient ≈ 2). Capacitance can return to baseline in 1–3 min, and responses can be repeated several times. The membrane tracer, FM 4-64, is taken up during recovery and can be released at a subsequent Ca influx episode. Given recent interest in signaling lipids in membrane fusion, we used green fluorescent protein (GFP) fusions with phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and diacylglycerol (DAG) binding domains to analyze phospholipid changes in relation to these responses. PI(4,5)P2 is rapidly cleaved upon activating Ca influx and recovers within 2 min. However, PI(4,5)P2 depletion by activation of overexpressed hM1 muscarinic receptors causes only little membrane fusion, and subsequent fusion in response to Ca influx remains massive. Two results suggest that DAG may be generated from sources other than PI(4,5)P in these protocols. First, acylglycerols are generated in response to elevated Ca, even when PI(4,5)P2 is metabolically depleted. Second, DAG-binding C1A-GFP domains, which are brought to the cell surface by exogenous ligands, translocate rapidly back to the cytoplasm in response to Ca influx. Nevertheless, inhibitors of PLCs and cPLA2, PI(4,5)P2-binding peptides, and PLD modification by butanol do not block membrane fusion. The cationic agents, FM 4-64 and heptalysine, bind profusely to the extracellular cell surface during membrane fusion. While this binding might reflect phosphatidylserine (PS) “scrambling” between monolayers, it is unaffected by a PS-binding protein, lactadherin, and by polylysine from the cytoplasmic side. Furthermore, the PS indicator, annexin-V, binds only slowly after fusion. Therefore, we suggest that the luminal surfaces of membrane vesicles that fuse to the plasmalemma may be rather anionic. In summary, our results provide no support for any regulatory or modulatory role of phospholipids in Ca-induced membrane fusion in fibroblasts. PMID:18562498

Structure of the tandem PX-PH domains of Bem3 from Saccharomyces cerevisiae.

PubMed

Ali, Imtiaz; Eu, Sungmin; Koch, Daniel; Bleimling, Nathalie; Goody, Roger S; Müller, Matthias P

2018-05-01

The structure of the tandem lipid-binding PX and pleckstrin-homology (PH) domains of the Cdc42 GTPase-activating protein Bem3 from Saccharomyces cerevisiae (strain S288c) has been determined to a resolution of 2.2 Å (R work = 21.1%, R free = 23.4%). It shows that the domains adopt a relative orientation that enables them to simultaneously bind to a membrane and suggests possible cooperativity in membrane binding. open access.

Structure of the tandem PX-PH domains of Bem3 from Saccharomyces cerevisiae

PubMed Central

Ali, Imtiaz; Eu, Sungmin; Bleimling, Nathalie

2018-01-01

The structure of the tandem lipid-binding PX and pleckstrin-homology (PH) domains of the Cdc42 GTPase-activating protein Bem3 from Saccharomyces cerevisiae (strain S288c) has been determined to a resolution of 2.2 Å (R work = 21.1%, R free = 23.4%). It shows that the domains adopt a relative orientation that enables them to simultaneously bind to a membrane and suggests possible cooperativity in membrane binding. PMID:29718000

Posttranslational events leading to the assembly of photosystem II protein complex: a study using photosynthesis mutants from Chlamydomonas reinhardtii

PubMed Central

1989-01-01

We studied the assembly of photosystem II (PSII) in several mutants from Chlamydomonas reinhardtii which were unable to synthesize either one PSII core subunit (P6 [43 kD], D1, or D2) or one oxygen-evolving enhancer (OEE1 or OEE2) subunit. Synthesis of the PSII subunits was analyzed on electrophoretograms of cells pulse labeled with [14C]acetate. Their accumulation in thylakoid membranes was studied on immunoblots, their chlorophyll-binding ability on nondenaturating gels, their assembly by detergent fractionation, their stability by pulse- chase experiments and determination of in vitro protease sensitivity, and their localization by immunocytochemistry. In Chlamydomonas, the PSII core subunits P5 (47 kD), D1, and D2 are synthesized in a concerted manner while P6 synthesis is independent. P5 and P6 accumulate independently of each other in the stacked membranes. They bind chlorophyll soon after, or concomitantly with, their synthesis and independently of the presence of the other PSII subunits. Resistance to degradation increases step by step: beginning with assembly of P5, D1, and D2, then with binding of P6, and, finally, with binding of the OEE subunits on two independent high affinity sites (one for OEE1 and another for OEE2 to which OEE3 binds). In the absence of PSII cores, the OEE subunits accumulate independently in the thylakoid lumen and bind loosely to the membranes; OEE1 was found on stacked membranes, but OEE2 was found on either stacked or unstacked membranes depending on whether or not P6 was synthesized. PMID:2670960

Posttranslational events leading to the assembly of photosystem II protein complex: a study using photosynthesis mutants from Chlamydomonas reinhardtii.

PubMed

de Vitry, C; Olive, J; Drapier, D; Recouvreur, M; Wollman, F A

1989-09-01

We studied the assembly of photosystem II (PSII) in several mutants from Chlamydomonas reinhardtii which were unable to synthesize either one PSII core subunit (P6 [43 kD], D1, or D2) or one oxygen-evolving enhancer (OEE1 or OEE2) subunit. Synthesis of the PSII subunits was analyzed on electrophoretograms of cells pulse labeled with [14C]acetate. Their accumulation in thylakoid membranes was studied on immunoblots, their chlorophyll-binding ability on nondenaturating gels, their assembly by detergent fractionation, their stability by pulse-chase experiments and determination of in vitro protease sensitivity, and their localization by immunocytochemistry. In Chlamydomonas, the PSII core subunits P5 (47 kD), D1, and D2 are synthesized in a concerted manner while P6 synthesis is independent. P5 and P6 accumulate independently of each other in the stacked membranes. They bind chlorophyll soon after, or concomitantly with, their synthesis and independently of the presence of the other PSII subunits. Resistance to degradation increases step by step: beginning with assembly of P5, D1, and D2, then with binding of P6, and, finally, with binding of the OEE subunits on two independent high affinity sites (one for OEE1 and another for OEE2 to which OEE3 binds). In the absence of PSII cores, the OEE subunits accumulate independently in the thylakoid lumen and bind loosely to the membranes; OEE1 was found on stacked membranes, but OEE2 was found on either stacked or unstacked membranes depending on whether or not P6 was synthesized.

A stepwise mechanism for the permeation of phloretin through a lipid bilayer

PubMed Central

1982-01-01

The thermodynamics of interactions between phloretin and a phosphatidylcholine (PC) vesicle membrane are characterized using equilibrium spectrophotometric titration, stopped-flow, and temperature- jump techniques. Binding of phloretin to a PC vesicle membrane is diffusion limited, with an association rate constant greater than 10(8) M-1s-1, and an interfacial activation free energy of less than 2 kcal/mol. Equilibrium binding of phloretin to a vesicle membrane is characterized by a single class of high-affinity (8 micro M), noninteracting sites. Binding is enthalpy driven (delta H = -4.9 kcal/mol) at 23 degrees C. Analysis of amplitudes of kinetic processes shows that 66 +/- 3% of total phloretin binding sites are exposed at the external vesicle surface. The rate of phloretin movement between binding sites located near the external and internal interfaces is proportional to the concentration of un-ionized phloretin, with a rate constant of 5.7 X 10(4) M-1s-1 at 23 degrees C. The rate of this process is limited by a large enthalpic (9 kcal/mol) and entropic (-31 entropy units) barrier. An analysis of the concentration dependence of the rate of transmembrane movement suggests the presence of multiple intramembrane potential barriers. Permeation of phloretin through a lipid bilayer is modeled quantitatively in terms of discrete steps: binding to a membrane surface, translocation across a series of intramembrane barriers, and dissociation from the opposite membrane surface. The permeability coefficient for phloretin is calculated as 1.9 X 10(-3) cm/s on the basis of the model presented. Structure- function relationships are examined for a number of phloretin analogues. PMID:7142954

Recognition and stabilization of geranylgeranylated human Rab5 by the GDP Dissociation Inhibitor (GDI).

PubMed

Edler, Eileen; Stein, Matthias

2017-10-25

The small GTPase Rab5 is the key regulator of early endosomal fusion. It is post-translationally modified by covalent attachment of two geranylgeranyl (GG) chains to adjacent cysteine residues of the C-terminal hypervariable region (HVR). The GDP dissociation inhibitor (GDI) recognizes membrane-associated Rab5(GDP) and serves to release it into the cytoplasm where it is kept in a soluble state. A detailed new structural and dynamic model for human Rab5(GDP) recognition and binding with human GDI at the early endosome membrane and in its dissociated state is presented. In the cytoplasm, the GDI protein accommodates the GG chains in a transient hydrophobic binding pocket. In solution, two different binding modes of the isoprenoid chains inserted into the hydrophobic pocket of the Rab5(GDP):GDI complex can be identified. This equilibrium between the two states helps to stabilize the protein-protein complex in solution. Interprotein contacts between the Rab5 switch regions and characteristic patches of GDI residues from the Rab binding platform (RBP) and the C-terminus coordinating region (CCR) reveal insight on the formation of such a stable complex. GDI binding to membrane-anchored Rab5(GDP) is initially mediated by the solvent accessible switch regions of the Rab-specific RBP. Formation of the membrane-associated Rab5(GDP):GDI complex induces a GDI reorientation to establish additional interactions with the Rab5 HVR. These results allow to devise a detailed structural model for the process of extraction of GG-Rab5(GDP) by GDI from the membrane and the dissociation from targeting factors and effector proteins prior to GDI binding.

Analyte detection using an active assay

DOEpatents

Morozov, Victor; Bailey, Charles L.; Evanskey, Melissa R.

2010-11-02

Analytes using an active assay may be detected by introducing an analyte solution containing a plurality of analytes to a lacquered membrane. The lacquered membrane may be a membrane having at least one surface treated with a layer of polymers. The lacquered membrane may be semi-permeable to nonanalytes. The layer of polymers may include cross-linked polymers. A plurality of probe molecules may be arrayed and immobilized on the lacquered membrane. An external force may be applied to the analyte solution to move the analytes towards the lacquered membrane. Movement may cause some or all of the analytes to bind to the lacquered membrane. In cases where probe molecules are presented, some or all of the analytes may bind to probe molecules. The direction of the external force may be reversed to remove unbound or weakly bound analytes. Bound analytes may be detected using known detection types.

Detection of cholesterol-rich microdomains in the inner leaflet of the plasma membrane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hayashi, Masami; Shimada, Yukiko; Inomata, Mitsushi

2006-12-22

The C-terminal domain (D4) of perfringolysin O binds selectively to cholesterol in cholesterol-rich microdomains. To address the issue of whether cholesterol-rich microdomains exist in the inner leaflet of the plasma membrane, we expressed D4 as a fusion protein with EGFP in MEF cells. More than half of the EGFP-D4 expressed in stable cell clones was bound to membranes in raft fractions. Depletion of membrane cholesterol with {beta}-cyclodextrin reduced the amount of EGFP-D4 localized in raft fractions, confirming EGFP-D4 binding to cholesterol-rich microdomains. Subfractionation of the raft fractions showed most of the EGFP-D4 bound to the plasma membrane rather than tomore » intracellular membranes. Taken together, these results strongly suggest the existence of cholesterol-rich microdomains in the inner leaflet of the plasma membrane.« less

The distal short consensus repeats 1 and 2 of the membrane cofactor protein CD46 and their distance from the cell membrane determine productive entry of species B adenovirus serotype 35.

PubMed

Fleischli, Christoph; Verhaagh, Sandra; Havenga, Menzo; Sirena, Dominique; Schaffner, Walter; Cattaneo, Roberto; Greber, Urs F; Hemmi, Silvio

2005-08-01

The human regulator of complement activation membrane cofactor protein (CD46) has recently been identified as an attachment receptor for most species B adenoviruses (Ads), including Ad type 3 (Ad3), Ad11, and Ad35, as well as species D Ad37. To characterize the interaction between Ad35 and CD46, hybrid receptors composed of different CD46 short consensus repeat (SCR) domains fused to immunoglobulin-like domains of CD4 and a set of 36 CD46 mutants containing semiconservative changes of single amino acids within SCR domains I and II were tested in binding and in Ad35-mediated luciferase transduction assays. In addition, anti-CD46 antibodies and soluble polypeptides constituting various CD46 domains were used in binding inhibition studies. Our data indicate that (i) CD46 SCR I or SCR II alone confers low but significant Ad35 binding; (ii) the presence of SCR I and II is required for optimal binding and transgene expression; (iii) transduction efficiencies equivalent to that of full-length CD46 are obtained if SCR I and II are at an appropriate distance from the cell membrane; (iv) ablation of the N-glycan attached to SCR I has no influence on receptor function, whereas ablation of the SCR II N-glycan results in about a two- to threefold reduction of binding and transgene expression; (v) most putative Ad35 binding residues are located on the same solvent-exposed face of the SCR I or SCR II domain, which are twisted by about 90 degrees ; and (vi) the putative Ad35 binding sites partly overlap with the measles virus binding surface.

The Distal Short Consensus Repeats 1 and 2 of the Membrane Cofactor Protein CD46 and Their Distance from the Cell Membrane Determine Productive Entry of Species B Adenovirus Serotype 35

PubMed Central

Fleischli, Christoph; Verhaagh, Sandra; Havenga, Menzo; Sirena, Dominique; Schaffner, Walter; Cattaneo, Roberto; Greber, Urs F.; Hemmi, Silvio

2005-01-01

The human regulator of complement activation membrane cofactor protein (CD46) has recently been identified as an attachment receptor for most species B adenoviruses (Ads), including Ad type 3 (Ad3), Ad11, and Ad35, as well as species D Ad37. To characterize the interaction between Ad35 and CD46, hybrid receptors composed of different CD46 short consensus repeat (SCR) domains fused to immunoglobulin-like domains of CD4 and a set of 36 CD46 mutants containing semiconservative changes of single amino acids within SCR domains I and II were tested in binding and in Ad35-mediated luciferase transduction assays. In addition, anti-CD46 antibodies and soluble polypeptides constituting various CD46 domains were used in binding inhibition studies. Our data indicate that (i) CD46 SCR I or SCR II alone confers low but significant Ad35 binding; (ii) the presence of SCR I and II is required for optimal binding and transgene expression; (iii) transduction efficiencies equivalent to that of full-length CD46 are obtained if SCR I and II are at an appropriate distance from the cell membrane; (iv) ablation of the N-glycan attached to SCR I has no influence on receptor function, whereas ablation of the SCR II N-glycan results in about a two- to threefold reduction of binding and transgene expression; (v) most putative Ad35 binding residues are located on the same solvent-exposed face of the SCR I or SCR II domain, which are twisted by about 90°; and (vi) the putative Ad35 binding sites partly overlap with the measles virus binding surface. PMID:16014961

Interaction of human synovial phospholipase A2 with mixed lipid bilayers: a coarse-grain and all-atom molecular dynamics simulation study.

PubMed

Qin, Shan-Shan; Yu, Yang-Xin; Li, Qi-Kai; Yu, Zhi-Wu

2013-02-26

Human secreted phospholipase A2s have been shown to promote inflammation in mammals by catalyzing the first step of the arachidonic acid pathway by breaking down phospholipids, producing fatty acids, including arachidonic acid. They bind to the membrane water interface to access their phospholipid substrates from the membrane. Their binding modes on membrane surfaces are regulated by diverse factors, including membrane charge, fluidity, and heterogeneity. The influence of these factors on the binding modes of the enzymes is not well understood. Here we have studied several human synovial phospholipase A2 (hs-PLA2)/mixed bilayer systems through a combined coarse-grain and all-atom molecular dynamics simulation. It was found that hydrophobic residues Leu2, Val3, Ala18, Leu19, Phe23, Gly30, and Phe63 that form the edge of the entrance of the hydrophobic binding pocket in hs-PLA2 tend to penetrate into the hydrophobic area of lipid bilayers, and more than half of the total amino acid residues make contact with the lipid headgroups. Each enzyme molecule forms 19-38 hydrogen bonds with the bilayer to which it binds, most of which are with the phosphate groups. Analysis of the root-mean-square deviation (rmsd) shows that residues Val30-Thr40, Tyr66-Gln80, and Lys107-Arg118 have relatively large rmsds during all-atom molecular dynamics simulations, in accordance with the observation of an enlarged entrance region of the hydrophobic binding pocket. The amino acid sequences forming the entrance of the binding pocket prefer to interact with lipid molecules that are more fluid or negatively charged, and the opening of the binding pocket would be larger when the lipid components are more fluid.

The interaction of albumin and fatty-acid-binding protein with membranes: oleic acid dissociation.

PubMed

Catalá, A

1984-10-01

Bovine serum albumin or fatty-acid-binding protein rapidly lose oleic acid when incubated in the presence of dimyristoyl lecithin liposomes. The phenomenon is dependent on vesicle concentration and no measurable quantities of protein are found associated with liposomes. Upon gel filtration on Sepharose CL-2B of incubated mixtures of microsomes containing [1-14C] oleic acid and albumin or fatty-acid-binding protein, association of fatty acid with the soluble proteins could be demonstrated. Both albumin and fatty-acid-binding protein stimulated the transfer of oleic acid from rat liver microsomes to egg lecithin liposomes. These results indicate that albumin is more effective in the binding of oleic acid than fatty-acid-binding protein, which allows a selective oleic acid dissociation during its interaction with membranes.

Sum Frequency Generation of Interfacial Lipid Monolayers Shows Polarization Dependence on Experimental Geometries.

PubMed

Li, Bolin; Li, Xu; Ma, Yong-Hao; Han, Xiaofeng; Wu, Fu-Gen; Guo, Zhirui; Chen, Zhan; Lu, Xiaolin

2016-07-19

Sum frequency generation (SFG) vibrational spectroscopy has been widely employed to investigate molecular structures of biological surfaces and interfaces including model cell membranes. A variety of lipid monolayers or bilayers serving as model cell membranes and their interactions with many different molecules have been extensively studied using SFG. Here, we conducted an in-depth investigation on polarization-dependent SFG signals collected from interfacial lipid monolayers using different experimental geometries, i.e., the prism geometry (total internal reflection) and the window geometry (external reflection). The different SFG spectral features of interfacial lipid monolayers detected using different experimental geometries are due to the interplay between the varied Fresnel coefficients and second-order nonlinear susceptibility tensor terms of different vibrational modes (i.e., ss and as modes of methyl groups), which were analyzed in detail in this study. Therefore, understanding the interplay between the interfacial Fresnel coefficients and χ((2)) tensors is a prerequisite for correctly understanding the SFG spectral features with respect to different experimental geometries. More importantly, the derived information in this paper should not be limited to the methyl groups with a C3v symmetry; valid extension to interfacial functional groups with different molecular symmetries and even chiral interfaces could be expected.

Solubilization and characterization of haloperidol-sensitive (+)-( sup 3 H)SKF-10,047 binding sites (sigma sites) from rat liver membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCann, D.J.; Su, T.P.

1991-05-01

The zwitterionic detergent 3-((3-cholamidopropyl)dimethylamino)-1-propanesulfonate (CHAPS) produced optimal solubilization of (+)-({sup 3}H)SKF-10,047 binding sites from rat liver membranes at a concentration of 0.2%, well below the critical micellular concentration of the detergent. The pharmacological selectivity of the liver (+)-({sup 3}H)SKF-10,047 binding sites corresponds to that of sigma sites from rat and guinea pig brain. When the affinities of 18 different drugs at (+)-({sup 3}H)SKF-10,047 binding sites in membranes and solubilized preparations were compared, a correlation coefficient of 0.99 and a slope of 1.03 were obtained, indicating that the pharmacological selectivity of rat liver sigma sites is retained after solubilization. In addition,more » the binding of 20 nM ({sup 3}H)progesterone to solubilized rat liver preparations was found to exhibit a pharmacological selectivity appropriate for sigma sites. A stimulatory effect of phenytoin on (+)-({sup 3}H)SKF-10,047 binding to sigma sites persisted after solubilization. When the solubilized preparation was subjected to molecular sizing chromatography, a single peak exhibiting specific (+)-({sup 3}H)SKF-10,047 binding was obtained. The binding activity of this peak was stimulated symmetrically when assays were performed in the presence of 300 microM phenytoin. The molecular weight of the CHAPS-solubilized sigma site complex was estimated to be 450,000 daltons. After solubilization with CHAPS, rat liver sigma sites were enriched to 12 pmol/mg of protein. The present results demonstrate a successful solubilization of sigma sites from rat liver membranes and provide direct evidence that the gonadal steroid progesterone binds to sigma sites. The results also suggest that the anticonvulsant phenytoin binds to an associated allosteric site on the sigma site complex.« less

Coordinated autoinhibition of F-BAR domain membrane binding and WASp activation by Nervous Wreck.

PubMed

Stanishneva-Konovalova, Tatiana B; Kelley, Charlotte F; Eskin, Tania L; Messelaar, Emily M; Wasserman, Steven A; Sokolova, Olga S; Rodal, Avital A

2016-09-20

Membrane remodeling by Fes/Cip4 homology-Bin/Amphiphysin/Rvs167 (F-BAR) proteins is regulated by autoinhibitory interactions between their SRC homology 3 (SH3) and F-BAR domains. The structural basis of autoregulation, and whether it affects interactions of SH3 domains with other cellular ligands, remain unclear. Here we used single-particle electron microscopy to determine the structure of the F-BAR protein Nervous Wreck (Nwk) in both soluble and membrane-bound states. On membrane binding, Nwk SH3 domains do not completely dissociate from the F-BAR dimer, but instead shift from its concave surface to positions on either side of the dimer. Unexpectedly, along with controlling membrane binding, these autoregulatory interactions inhibit the ability of Nwk-SH3a to activate Wiskott-Aldrich syndrome protein (WASp)/actin related protein (Arp) 2/3-dependent actin filament assembly. In Drosophila neurons, Nwk autoregulation restricts SH3a domain-dependent synaptopod formation, synaptic growth, and actin organization. Our results define structural rearrangements in Nwk that control F-BAR-membrane interactions as well as SH3 domain activities, and suggest that these two functions are tightly coordinated in vitro and in vivo.

Molecular Basis of the Membrane Interaction of the β2e Subunit of Voltage-Gated Ca2+ Channels

PubMed Central

Kim, Dong-Il; Kang, Mooseok; Kim, Sangyeol; Lee, Juhwan; Park, Yongsoo; Chang, Iksoo; Suh, Byung-Chang

2015-01-01

The auxiliary β subunit plays an important role in the regulation of voltage-gated calcium (CaV) channels. Recently, it was revealed that β2e associates with the plasma membrane through an electrostatic interaction between N-terminal basic residues and anionic phospholipids. However, a molecular-level understanding of β-subunit membrane recruitment in structural detail has remained elusive. In this study, using a combination of site-directed mutagenesis, liposome-binding assays, and multiscale molecular-dynamics (MD) simulation, we developed a physical model of how the β2e subunit is recruited electrostatically to the plasma membrane. In a fluorescence resonance energy transfer assay with liposomes, binding of the N-terminal peptide (23 residues) to liposome was significantly increased in the presence of phosphatidylserine (PS) and phosphatidylinositol 4,5-bisphosphate (PIP2). A mutagenesis analysis suggested that two basic residues proximal to Met-1, Lys-2 (K2) and Trp-5 (W5), are more important for membrane binding of the β2e subunit than distal residues from the N-terminus. Our MD simulations revealed that a stretched binding mode of the N-terminus to PS is required for stable membrane attachment through polar and nonpolar interactions. This mode obtained from MD simulations is consistent with experimental results showing that K2A, W5A, and K2A/W5A mutants failed to be targeted to the plasma membrane. We also investigated the effects of a mutated β2e subunit on inactivation kinetics and regulation of CaV channels by PIP2. In experiments with voltage-sensing phosphatase (VSP), a double mutation in the N-terminus of β2e (K2A/W5A) increased the PIP2 sensitivity of CaV2.2 and CaV1.3 channels by ∼3-fold compared with wild-type β2e subunit. Together, our results suggest that membrane targeting of the β2e subunit is initiated from the nonspecific electrostatic insertion of N-terminal K2 and W5 residues into the membrane. The PS-β2e interaction observed here provides a molecular insight into general principles for protein binding to the plasma membrane, as well as the regulatory roles of phospholipids in transporters and ion channels. PMID:26331250

Elucidating the Functional Roles of Spatial Organization in Cross-Membrane Signal Transduction by a Hybrid Simulation Method.

PubMed

Chen, Jiawen; Xie, Zhong-Ru; Wu, Yinghao

2016-07-01

The ligand-binding of membrane receptors on cell surfaces initiates the dynamic process of cross-membrane signal transduction. It is an indispensable part of the signaling network for cells to communicate with external environments. Recent experiments revealed that molecular components in signal transduction are not randomly mixed, but spatially organized into distinctive patterns. These patterns, such as receptor clustering and ligand oligomerization, lead to very different gene expression profiles. However, little is understood about the molecular mechanisms and functional impacts of this spatial-temporal regulation in cross-membrane signal transduction. In order to tackle this problem, we developed a hybrid computational method that decomposes a model of signaling network into two simulation modules. The physical process of binding between receptors and ligands on cell surfaces are simulated by a diffusion-reaction algorithm, while the downstream biochemical reactions are modeled by stochastic simulation of Gillespie algorithm. These two processes are coupled together by a synchronization framework. Using this method, we tested the dynamics of a simple signaling network in which the ligand binding of cell surface receptors triggers the phosphorylation of protein kinases, and in turn regulates the expression of target genes. We found that spatial aggregation of membrane receptors at cellular interfaces is able to either amplify or inhibit downstream signaling outputs, depending on the details of clustering mechanism. Moreover, by providing higher binding avidity, the co-localization of ligands into multi-valence complex modulates signaling in very different ways that are closely related to the binding affinity between ligand and receptor. We also found that the temporal oscillation of the signaling pathway that is derived from genetic feedback loops can be modified by the spatial clustering of membrane receptors. In summary, our method demonstrates the functional importance of spatial organization in cross-membrane signal transduction. The method can be applied to any specific signaling pathway in cells.

Oncogenic and RASopathy-associated K-RAS mutations relieve membrane-dependent occlusion of the effector-binding site.

PubMed

Mazhab-Jafari, Mohammad T; Marshall, Christopher B; Smith, Matthew J; Gasmi-Seabrook, Geneviève M C; Stathopulos, Peter B; Inagaki, Fuyuhiko; Kay, Lewis E; Neel, Benjamin G; Ikura, Mitsuhiko

2015-05-26

K-RAS4B (Kirsten rat sarcoma viral oncogene homolog 4B) is a prenylated, membrane-associated GTPase protein that is a critical switch for the propagation of growth factor signaling pathways to diverse effector proteins, including rapidly accelerated fibrosarcoma (RAF) kinases and RAS-related protein guanine nucleotide dissociation stimulator (RALGDS) proteins. Gain-of-function KRAS mutations occur frequently in human cancers and predict poor clinical outcome, whereas germ-line mutations are associated with developmental syndromes. However, it is not known how these mutations affect K-RAS association with biological membranes or whether this impacts signal transduction. Here, we used solution NMR studies of K-RAS4B tethered to nanodiscs to investigate lipid bilayer-anchored K-RAS4B and its interactions with effector protein RAS-binding domains (RBDs). Unexpectedly, we found that the effector-binding region of activated K-RAS4B is occluded by interaction with the membrane in one of the NMR-observable, and thus highly populated, conformational states. Binding of the RAF isoform ARAF and RALGDS RBDs induced marked reorientation of K-RAS4B from the occluded state to RBD-specific effector-bound states. Importantly, we found that two Noonan syndrome-associated mutations, K5N and D153V, which do not affect the GTPase cycle, relieve the occluded orientation by directly altering the electrostatics of two membrane interaction surfaces. Similarly, the most frequent KRAS oncogenic mutation G12D also drives K-RAS4B toward an exposed configuration. Further, the D153V and G12D mutations increase the rate of association of ARAF-RBD with lipid bilayer-tethered K-RAS4B. We revealed a mechanism of K-RAS4B autoinhibition by membrane sequestration of its effector-binding site, which can be disrupted by disease-associated mutations. Stabilizing the autoinhibitory interactions between K-RAS4B and the membrane could be an attractive target for anticancer drug discovery.

Cholera toxin binding affinity and specificity for gangliosides determined by surface plasmon resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuziemko, G.M.; Stroh, M.; Stevens, R.C.

1996-05-21

The present study determines the affinity of cholera toxin for the ganglioside series GM1, GM2, GM3, GD1A, GD1B, GT1B, asialo GM1, globotriosyl ceramide, and lactosyl ceramide using real time biospecific interaction analysis (surface plasmon resonance, SPR). SPR shows that cholera toxin preferably binds to gangliosides in the following sequence: GM1 > GM2 > GD1A > GM3 > GT1B > GD1B > asialo-GM1. The measured binding affinity of cholera toxin for the ganglioside sequence ranges from 4.61 {times} 10{sup {minus}12} M for GM1 to 1.88 {times} 10{sup {minus}10} M for asialo GM1. The picomolar values obtained by surface plasmon resonance aremore » similar to K{sub d} values determined with whole-cell binding assays. Both whole-cell assays ans SPR measurements on synthetic membranes are higher than free solution measurements by several orders of magnitude. This difference may be caused by the effects of avidity and charged lipid head-groups, which may play a major role in the binding between cholera toxin, the receptor, and the membrane surface. The primary difference between free solution binding studies and surface plasmon resonance studies is that the latter technique is performed on surfaces resembling the cell membrane. Surface plasmon resonance has the further advantage of measuring apparent kinetic association and dissociation rates in real time, providing direct information about binding events at the membrane surface. 34 refs., 8 figs., 2 tabs.« less

A role for carbohydrate recognition in mammalian sperm-egg binding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clark, Gary F., E-mail: clarkgf@health.missouri.edu

Highlights: • Mammalian sperm-egg binding as a carbohydrate dependent species recognition event. • The role of carbohydrate recognition in human, mouse and pig sperm-egg binding. • Historical perspective and future directions for research focused on gamete binding. - Abstract: Mammalian fertilization usually requires three sequential cell–cell interactions: (i) initial binding of sperm to the specialized extracellular matrix coating the egg known as the zona pellucida (ZP); (ii) binding of sperm to the ZP via the inner acrosomal membrane that is exposed following the induction of acrosomal exocytosis; and (iii) adhesion of acrosome-reacted sperm to the plasma membrane of the eggmore » cell, enabling subsequent fusion of these gametes. The focus of this review is on the initial binding of intact sperm to the mammalian ZP. Evidence collected over the past fifty years has confirmed that this interaction relies primarily on the recognition of carbohydrate sequences presented on the ZP by lectin-like egg binding proteins located on the plasma membrane of sperm. There is also evidence that the same carbohydrate sequences that mediate binding also function as ligands for lectins on lymphocytes that can inactivate immune responses, likely protecting the egg and the developing embryo up to the stage of blastocyst hatching. The literature related to initial sperm-ZP binding in the three major mammalian models (human, mouse and pig) is discussed. Historical perspectives and future directions for research related to this aspect of gamete adhesion are also presented.« less

Interaction of Plasmodium falciparum knob-associated histidine-rich protein (KAHRP) with erythrocyte ankyrin R is required for its attachment to the erythrocyte membrane.

PubMed

Weng, Haibo; Guo, Xinhua; Papoin, Julien; Wang, Jie; Coppel, Ross; Mohandas, Narla; An, Xiuli

2014-01-01

The malaria parasite Plasmodium falciparum exports a large number of proteins into the erythrocyte cytoplasm during the asexual intraerythrocytic stage of its life cycle. A subset of these proteins interacts with erythrocyte membrane skeletal proteins and grossly alters the structure and function of the membrane. Several of the exported proteins, such as PfEMP1, PfEMP3, RESA and KAHRP, interact with the preponderant erythrocyte skeleton protein, spectrin. Here we have searched for possible interaction of these four malaria proteins with another major erythrocyte skeleton protein, ankyrin R. We have shown that KAHRP, but none of the other three, binds to ankyrin R. We have mapped the binding site for ankyrin R to a 79-residue segment of the KAHRP sequence, and the reciprocal binding site for KAHRP in ankyrin R to a subdomain (D3) of the 89kDa ankyrin R membrane-binding domain. Interaction of intact ankyrin R with KAHRP was inhibited by the free D3 subdomain. When, moreover, red cells loaded with the soluble D3 subdomain were infected with P. falciparum, KAHRP secreted by the intraerythrocytic parasite no longer migrated to the host cell membrane, but remained diffusely distributed throughout the cytosol. Our findings suggest a potentially important role for interaction of KAHRP with red cell membrane skeleton in promoting the adhesion of malaria-infected red cells to endothelial surfaces, a central element in the pathophysiology of malaria. © 2013.

Protein-membrane interaction and fatty acid transfer from intestinal fatty acid-binding protein to membranes. Support for a multistep process.

PubMed

Falomir-Lockhart, Lisandro J; Laborde, Lisandro; Kahn, Peter C; Storch, Judith; Córsico, Betina

2006-05-19

Fatty acid transfer from intestinal fatty acid-binding protein (IFABP) to phospholipid membranes occurs during protein-membrane collisions. Electrostatic interactions involving the alpha-helical "portal" region of the protein have been shown to be of great importance. In the present study, the role of specific lysine residues in the alpha-helical region of IFABP was directly examined. A series of point mutants in rat IFABP was engineered in which the lysine positive charges in this domain were eliminated or reversed. Using a fluorescence resonance energy transfer assay, we analyzed the rates and mechanism of fatty acid transfer from wild type and mutant proteins to acceptor membranes. Most of the alpha-helical domain mutants showed slower absolute fatty acid transfer rates to zwitterionic membranes, with substitution of one of the lysines of the alpha2 helix, Lys27, resulting in a particularly dramatic decrease in the fatty acid transfer rate. Sensitivity to negatively charged phospholipid membranes was also reduced, with charge reversal mutants in the alpha2 helix the most affected. The results support the hypothesis that the portal region undergoes a conformational change during protein-membrane interaction, which leads to release of the bound fatty acid to the membrane and that the alpha2 segment is of particular importance in the establishment of charge-charge interactions between IFABP and membranes. Cross-linking experiments with a phospholipid-photoactivable reagent underscored the importance of charge-charge interactions, showing that the physical interaction between wild-type intestinal fatty acid-binding protein and phospholipid membranes is enhanced by electrostatic interactions. Protein-membrane interactions were also found to be enhanced by the presence of ligand, suggesting different collisional complex structures for holo- and apo-IFABP.

Downregulation of surface sodium pumps by endocytosis during meiotic maturation of Xenopus laevis oocytes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmalzing, G.; Eckard, P.; Kroener, S.P.

1990-01-01

During meiotic maturation, plasma membranes of Xenopus laevis oocytes completely lose the capacity to transport Na and K and to bind ouabain. To explore whether the downregulation might be due to an internalization of the sodium pump molecules, the intracellular binding of ouabain was determined. Selective permeabilization of the plasma membrane of mature oocytes (eggs) by digitonin almost failed to disclose ouabain binding sites. However, when the eggs were additionally treated with 0.02% sodium dodecyl sulfate (SDS) to permeabilize inner membranes, all sodium pumps present before maturation were recovered. Phosphorylation by (gamma-32P)ATP combined with SDS-polyacrylamide gel electrophoresis (PAGE) and autoradiographymore » showed that sodium pumps were greatly reduced in isolated plasma membranes of eggs. According to sucrose gradient fractionation, maturation induced a shift of sodium pumps from the plasma membrane fraction to membranes of lower buoyant density with a protein composition different from that of the plasma membrane. Endocytosed sodium pumps identified on the sucrose gradient from (3H)ouabain bound to the cell surface before maturation could be phosphorylated with inorganic (32P)phosphate. The findings suggest that downregulation of sodium pumps during maturation is brought about by translocation of surface sodium pumps to an intracellular compartment, presumably endosomes. This contrasts the mechanism of downregulation of Na-dependent cotransport systems, the activities of which are reduced as a consequence of a maturation-induced depolarization of the membrane without a removal of the corresponding transporter from the plasma membrane.« less

Integrable structure in discrete shell membrane theory

PubMed Central

Schief, W. K.

2014-01-01

We present natural discrete analogues of two integrable classes of shell membranes. By construction, these discrete shell membranes are in equilibrium with respect to suitably chosen internal stresses and external forces. The integrability of the underlying equilibrium equations is proved by relating the geometry of the discrete shell membranes to discrete O surface theory. We establish connections with generalized barycentric coordinates and nine-point centres and identify a discrete version of the classical Gauss equation of surface theory. PMID:24808755

Integrable structure in discrete shell membrane theory.

PubMed

Schief, W K

2014-05-08

We present natural discrete analogues of two integrable classes of shell membranes. By construction, these discrete shell membranes are in equilibrium with respect to suitably chosen internal stresses and external forces. The integrability of the underlying equilibrium equations is proved by relating the geometry of the discrete shell membranes to discrete O surface theory. We establish connections with generalized barycentric coordinates and nine-point centres and identify a discrete version of the classical Gauss equation of surface theory.

Effect of geometry on the pressure induced donor binding energy in semiconductor nanostructures

NASA Astrophysics Data System (ADS)

Kalpana, P.; Jayakumar, K.; Nithiananthi, P.

2015-09-01

The effect of geometry on an on-center hydrogenic donor impurity in a GaAs/(Ga,Al)As quantum wire (QWW) and quantum dot (QD) under the influence of Γ-X band mixing due to an applied hydrostatic pressure is theoretically studied. Numerical calculations are performed in an effective mass approximation. The ground state impurity energy is obtained by variational procedure. Both the effects of pressure and geometry are to exert an additional confinement on the impurity inside the wire as well as dot. We found that the donor binding energy is modified by the geometrical effects as well as by the confining potential when it is subjected to external pressure. The results are presented and discussed.

Apical targeting of the formin Diaphanous in Drosophila tubular epithelia

PubMed Central

Rousso, Tal; Shewan, Annette M; Mostov, Keith E; Schejter, Eyal D; Shilo, Ben-Zion

2013-01-01

Apical secretion from epithelial tubes of the Drosophila embryo is mediated by apical F-actin cables generated by the formin-family protein Diaphanous (Dia). Apical localization and activity of Dia are at the core of restricting F-actin formation to the correct membrane domain. Here we identify the mechanisms that target Dia to the apical surface. PI(4,5)P2 levels at the apical membrane regulate Dia localization in both the MDCK cyst model and in Drosophila tubular epithelia. An N-terminal basic domain of Dia is crucial for apical localization, implying direct binding to PI(4,5)P2. Dia apical targeting also depends on binding to Rho1, which is critical for activation-induced conformational change, as well as physically anchoring Dia to the apical membrane. We demonstrate that binding to Rho1 facilitates interaction with PI(4,5)P2 at the plane of the membrane. Together these cues ensure efficient and distinct restriction of Dia to the apical membrane. DOI: http://dx.doi.org/10.7554/eLife.00666.001 PMID:23853710

Binding affinity of amyloid oligomers to cellular membranes is a generic indicator of cellular dysfunction in protein misfolding diseases

PubMed Central

Evangelisti, Elisa; Cascella, Roberta; Becatti, Matteo; Marrazza, Giovanna; Dobson, Christopher M.; Chiti, Fabrizio; Stefani, Massimo; Cecchi, Cristina

2016-01-01

The conversion of peptides or proteins from their soluble native states into intractable amyloid deposits is associated with a wide range of human disorders. Misfolded protein oligomers formed during the process of aggregation have been identified as the primary pathogenic agents in many such conditions. Here, we show the existence of a quantitative relationship between the degree of binding to neuronal cells of different types of oligomers formed from a model protein, HypF-N, and the GM1 content of the plasma membranes. In addition, remarkably similar behavior is observed for oligomers of the Aβ42 peptide associated with Alzheimer’s disease. Further analysis has revealed the existence of a linear correlation between the level of the influx of Ca2+ across neuronal membranes that triggers cellular damage, and the fraction of oligomeric species bound to the membrane. Our findings indicate that the susceptibility of neuronal cells to different types of misfolded oligomeric assemblies is directly related to the extent of binding of such oligomers to the cellular membrane. PMID:27619987

Conformational dynamics underlie the activity of the auxin-binding protein, Nt-abp1.

PubMed

David, K; Carnero-Diaz, E; Leblanc, N; Monestiez, M; Grosclaude, J; Perrot-Rechenmann, C

2001-09-14

The auxin-binding protein 1 (ABP1) has been proposed to be involved in the perception of the phytohormone at the plasma membrane. Site-directed mutagenesis was performed on highly conserved residues at the C terminus of ABP1 to investigate their relative importance in protein folding and activation of a functional response at the plasma membrane. Detailed analysis of the dynamic interaction of the wild-type ABP1 and mutated proteins with three distinct monoclonal antibodies recognizing conformation-dependent epitopes was performed by surface plasmon resonance. The influence of auxin on these interactions was also investigated. The Cys(177) as well as Asp(175) and Glu(176) were identified as critical residues for ABP1 folding and action at the plasma membrane. On the contrary, the C-terminal KDEL sequence was demonstrated not to be essential for auxin binding, interaction with the plasma membrane, or activation of the transduction cascade although it does appear to be involved in the stability of ABP1. Taken together, the results confirmed that ABP1 conformational change is the critical step for initiating the signal from the plasma membrane.

The amphiphilic peptide adenoregulin enhances agonist binding to A1-adenosine receptors and [35S]GTP gamma S to brain membranes.

PubMed

Moni, R W; Romero, F S; Daly, J W

1995-08-01

1. Adenoregulin is an amphilic peptide isolated from skin mucus of the tree frog, Phyllomedusa bicolor. Synthetic adenoregulin enhanced the binding of agonists to several G-protein-coupled receptors in rat brain membranes. 2. The maximal enhancement of agonist binding, and in parentheses, the concentration of adenoregulin affording maximal enhancement were as follows: 60% (20 microM) for A1-adenosine receptors, 30% (100 microM) for A2a-adenosine receptors, 20% (2 microM) for alpha 2-adrenergic receptors, and 30% (10 microM) for 5HT1A receptors. High affinity agonist binding for A1-, alpha 2-, and 5HT1A-receptors was virtually abolished by GTP gamma S in the presence of adenoregulin, but was only partially abolished in its absence. Magnesium ions increased the binding of agonists to receptors and reduced the enhancement elicited by adenoregulin. 3. The effect of adenoregulin on binding of N6-cyclohexyladenosine ([3H]CHA) to A1-receptors was relatively slow and was irreversible. Adenoregulin increased the Bmax value for [3H]CHA binding sites, and the proportion of high affinity states, and slowed the rate of [3H]CHA dissociation. Binding of the A1-selective antagonist, [3H]DPCPX, was maximally enhanced by only 13% at 2 microM adenoregulin. Basal and A1-adenosine receptor-stimulated binding of [35S]GTP gamma S were maximally enhanced 45% and 23%, respectively, by 50 microM adenoregulin. In CHAPS-solubilized membranes from rat cortex, the binding of both [3H]CHA and [3H]DPCPX were enhanced by adenoregulin. Binding of [3H]CHA to membranes from DDT1 MF-2 cells was maximally enhanced 17% at 20 microM adenoregulin. In intact DDT1 MF-2 cells, 20 microM adenoregulin did not potentiate the inhibition of cyclic AMP accumulation mediated via the adenosine A1 receptor. 4. It is proposed that adenoregulin enhances agonist binding through a mechanism involving enhancement of guanyl nucleotide exchange at G-proteins, resulting in a conversion of receptors into a high affinity state complexed with guanyl nucleotide-free G-protein.

Interaction of arginine oligomer with model membrane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yi, Dandan; Guoming, Li; Gao, Li

2007-08-10

Short oligomers of arginine (R8) have been shown to cross readily a variety of biological barriers. A hypothesis was put forward that inverted micelles form in biological membranes in the presence of arginine oligomer peptides, facilitating their transfer through the membranes. In order to define the role of peptide-lipid interaction in this mechanism, we prepared liposomes as the model membrane to study the ability of R8 inducing calcein release from liposomes, the fusion of liposomes, R8 binding to liposomes and membrane disturbing activity of the bound R8. The results show that R8 binding to liposome membrane depends on lipid compositions,more » negative surface charge density and interior water phase pH values of liposomes. R8 has no activity to induce the leakage of calcein from liposomes or improve liposome fusion. R8 does not permeabilize through the membrane spontaneously. These peptides delivering drugs through membranes may depend on receptors and energy.« less

An activating mutant of Rac1 that fails to interact with Rho GDP-dissociation inhibitor stimulates membrane ruffling in mammalian cells.

PubMed Central

Gandhi, Payal N; Gibson, Richard M; Tong, Xiaofeng; Miyoshi, Jun; Takai, Yoshimi; Konieczkowski, Martha; Sedor, John R; Wilson-Delfosse, Amy L

2004-01-01

Rac1, a member of the Rho family of small GTP-binding proteins, is involved in the regulation of the actin cytoskeleton via activation of lamellipodia and membrane ruffle formation. RhoGDI (Rho-family-specific GDP-dissociation inhibitor) forms a complex with Rho proteins in the cytosol of mammalian cells. It not only regulates guanine nucleotide binding to Rho proteins, but may also function as a molecular shuttle to carry Rho proteins from an inactive cytosolic pool to the membrane for activation. These studies tested if RhoGDI is necessary for the translocation of Rac1 from the cytosol to the plasma membrane for the formation of membrane ruffles. We describe a novel mutant of Rac1, R66E (Arg66-->Glu), that fails to bind RhoGDI. This RhoGDI-binding-defective mutation is combined with a Rac1-activating mutation G12V, resulting in a double-mutant [Rac1(G12V/R66E)] that fails to interact with RhoGDI in COS-7 cells, but remains constitutively activated. This double mutant stimulates membrane ruffling to a similar extent as that observed after epidermal growth factor treatment of non-transfected cells. To confirm that Rac1 can signal ruffle formation in the absence of interaction with RhoGDI, Rac1(G12V) was overexpressed in cultured mesangial cells derived from a RhoGDI knockout mouse. Rac1-mediated membrane ruffling was indistinguishable between the RhoGDI(-/-) and RhoGDI(+/+) cell lines. In both the COS-7 and cultured mesangial cells, Rac1(G12V) and Rac1(G12V/R66E) co-localize with membrane ruffles. These findings suggest that interaction with RhoGDI is not essential in the mechanism by which Rac1 translocates to the plasma membrane to stimulate ruffle formation. PMID:14629200

A major integral protein of the plant plasma membrane binds flavin.

PubMed

Lorenz, Astrid; Kaldenhoff, Ralf; Hertel, Rainer

2003-05-01

Abundant flavin binding sites have been found in membranes of plants and fungi. With flavin mononucleotide-agarose affinity columns, riboflavin-binding activity from microsomes of Cucurbita pepoL. hypocotyls was purified and identified as a specific PIP1-homologous protein of the aquaporin family. Sequences such as gi|2149955 in Phaseolus vulgaris, PIP1b of Arabidopsis thaliana, and NtAQP1 of tobacco are closely related. The identification as a riboflavin-binding protein was confirmed by binding tests with an extract of Escherichia coli cells expressing the tobacco NtAQP1 as well as leaves of transgenic tobacco plants that overexpress NtAQP1 or were inhibited in PIP1 expression by antisense constructs. When binding was assayed in the presence of dithionite, the reduced flavin formed a relatively stable association with the protein. Upon dilution under oxidizing conditions, the adduct was resolved, and free flavin reappeared with a half time of about 30 min. Such an association can also be induced photochemically, with oxidized flavin by blue light at 450 nm, in the presence of an electron donor. Several criteria, localization in the plasma membrane, high abundance, affinity to roseoflavin, and photochemistry, argue for a role of the riboflavin-binding protein PIP1 as a photoreceptor.

Probing the functions of the paramyxovirus glycoproteins F and HN with a panel of synthetic antibodies.

PubMed

Welch, Brett D; Paduch, Marcin; Leser, George P; Bergman, Zachary; Kors, Christopher A; Paterson, Reay G; Jardetzky, Theodore S; Kossiakoff, Anthony A; Lamb, Robert A

2014-10-01

Paramyxoviruses are enveloped negative-strand RNA viruses that are significant human and animal pathogens. Most paramyxoviruses infect host cells via the concerted action of a tetrameric attachment protein (variously called HN, H, or G) that binds either sialic acid or protein receptors on target cells and a trimeric fusion protein (F) that merges the viral envelope with the plasma membrane at neutral pH. F initially folds to a metastable prefusion conformation that becomes activated via a cleavage event during cellular trafficking. Upon receptor binding, the attachment protein, which consists of a globular head anchored to the membrane via a helical tetrameric stalk, triggers a major conformation change in F which results in fusion of virus and host cell membranes. We recently proposed a model for F activation in which the attachment protein head domains move following receptor binding to expose HN stalk residues critical for triggering F. To test the model in the context of wild-type viral glycoproteins, we used a restricted-diversity combinatorial Fab library and phage display to rapidly generate synthetic antibodies (sAbs) against multiple domains of the paramyxovirus parainfluenza 5 (PIV5) pre- and postfusion F and HN. As predicted by the model, sAbs that bind to the critical F-triggering region of the HN stalk do not disrupt receptor binding or neuraminidase (NA) activity but are potent inhibitors of fusion. An inhibitory prefusion F-specific sAb recognized a quaternary antigenic site and may inhibit fusion by preventing F refolding or by blocking the F-HN interaction. Importance: The paramyxovirus family of negative-strand RNA viruses cause significant disease in humans and animals. The viruses bind to cells via their receptor binding protein and then enter cells by fusion of their envelope with the host cell plasma membrane, a process mediated by a metastable viral fusion (F) protein. To understand the steps in viral membrane fusion, a library of synthetic antibodies to F protein and the receptor binding protein was generated in bacteriophage. These antibodies bound to different regions of the F protein and the receptor binding protein, and the location of antibody binding affected different processes in viral entry into cells. Copyright © 2014, American Society for Microbiology. All Rights Reserved.

Ultimate Osmosis Engineered by the Pore Geometry and Functionalization of Carbon Nanostructures

PubMed Central

Song, Zhigong; Xu, Zhiping

2015-01-01

Osmosis is the key process in establishing versatile functions of cellular systems and enabling clean-water harvesting technologies. Membranes with single-atom thickness not only hold great promises in approaching the ultimate limit of these functions, but also offer an ideal test-bed to explore the underlying physical mechanisms. In this work, we explore diffusive and osmotic transport of water and ions through carbon nanotube and porous graphene based membranes by performing molecular dynamics simulations. Our comparative study shows that the cylindrical confinement in carbon nanotubes offers much higher salt rejection at similar permeability in osmosis compared to porous graphene. Moreover, chemical functionalization of the pores modulates the membrane performance by its steric and electrostatic nature, especially at small-size pores due to the fact that the optimal transport is achieved by ordered water transport near pore edges. These findings lay the ground for the ultimate design of forward osmosis membranes with optimized performance trade-off, given the capability of nano-engineering nanostructures by their geometry and chemistry. PMID:26037602

Load Adaptation of Lamellipodial Actin Networks.

PubMed

Mueller, Jan; Szep, Gregory; Nemethova, Maria; de Vries, Ingrid; Lieber, Arnon D; Winkler, Christoph; Kruse, Karsten; Small, J Victor; Schmeiser, Christian; Keren, Kinneret; Hauschild, Robert; Sixt, Michael

2017-09-21

Actin filaments polymerizing against membranes power endocytosis, vesicular traffic, and cell motility. In vitro reconstitution studies suggest that the structure and the dynamics of actin networks respond to mechanical forces. We demonstrate that lamellipodial actin of migrating cells responds to mechanical load when membrane tension is modulated. In a steady state, migrating cell filaments assume the canonical dendritic geometry, defined by Arp2/3-generated 70° branch points. Increased tension triggers a dense network with a broadened range of angles, whereas decreased tension causes a shift to a sparse configuration dominated by filaments growing perpendicularly to the plasma membrane. We show that these responses emerge from the geometry of branched actin: when load per filament decreases, elongation speed increases and perpendicular filaments gradually outcompete others because they polymerize the shortest distance to the membrane, where they are protected from capping. This network-intrinsic geometrical adaptation mechanism tunes protrusive force in response to mechanical load. Copyright © 2017 Elsevier Inc. All rights reserved.

Evidence of proteolipid domain formation in an inner mitochondrial membrane mimicking model.

PubMed

Cheniour, Mouhedine; Brewer, Jonathan; Bagatolli, Luis; Marcillat, Olivier; Granjon, Thierry

2017-05-01

Mitochondrial creatine kinase (mtCK) is highly abundant in mitochondria; its quantity is equimolecular to the Adenylic Nucleotide Translocator and represents 1% of the mitochondrial proteins. It is a multitask protein localized in the mitochondria intermembrane space where it binds to the specific cardiolipin (CL) phospholipid. If mtCK was initially thought to be exclusively implicated in energy transfer between mitochondria and cytosol through a mechanism referred to as the phosphocreatine shuttle, several recent studies suggested an additional role in maintaining mitochondria membrane structure. To further characterized mtCK binding process we used multiphoton excitation fluorescence microscopy coupled with Giant Unilamellar Vesicles (GUV) and laurdan as fluorescence probe. We gathered structural and dynamical information on the molecular events occurring during the binding of mtCK to the mitochondria inner membrane. We present the first visualization of mtCK-induced CL segregation on a bilayer model forming micrometer-size proteolipid domains at the surface of the GUV. Those microdomains, which only occurred when CL is included in the lipid mixture, were accompanied by the formation of protein multimolecular assembly, vesicle clamping, and changes in both vesicle curvature and membrane fluidity CONCLUSION: Those results highlighted the importance of the highly abundant mtCK in the lateral organization of the mitochondrial inner membrane. Microdomains were induced in mitochondria-mimicking membranes composed of natural phospholipids without cholesterol and/or sphingolipids differing from the proposed cytoplasmic membrane rafts. Those findings as well as membrane curvature modification were discussed in relation with protein-membrane interaction and protein cluster involvement in membrane morphology. Copyright © 2017 Elsevier B.V. All rights reserved.

Agonist properties of a stable hexapeptide analog of neurotensin, N alpha MeArg-Lys-Pro-Trp-tLeu-Leu (NT1).

PubMed

Akunne, H C; Demattos, S B; Whetzel, S Z; Wustrow, D J; Davis, D M; Wise, L D; Cody, W L; Pugsley, T A; Heffner, T G

1995-04-18

The major signal transduction pathway for neurotensin (NT) receptors is the G-protein-dependent stimulation of phospholipase C, leading to the mobilization of intracellular free Ca2+ ([Ca2+]i) and the stimulation of cyclic GMP. We investigated the functional actions of an analog of NT(8-13), N alpha MeArg-Lys-Pro-Trp-tLeu-Leu (NT1), and other NT related analogs by quantitative measurement of the cytosolic free Ca2+ concentration in HT-29 (human colonic adenocarcinoma) cells using the Ca(2+)-sensitive dye fura-2/AM and by effects on cyclic GMP levels in rat cerebellar slices. The NT receptor binding affinities for these analogs to HT-29 cell membranes and newborn (10-day-old) mouse brain membranes were also investigated. Data obtained from HT-29 cell and mouse brain membrane preparations showed saturable single high-affinity sites and binding densities (Bmax) of 130.2 and 87.5 fmol/mg protein, respectively. The respective KD values were 0.47 and 0.39 nM, and the Hill coefficients were 0.99 and 0.92. The low-affinity levocabastine-sensitive site was not present (K1 > 10,000) in either membrane preparation. Although the correlation of binding between HT-29 cell membranes and mouse brain membranes was quite significant (r = 0.92), some of the reference agents had lower binding affinities in the HT-29 cell membranes. The metabolically stable compound NT1 plus other NT analogs and related peptides [NT, NT(8-13), xenopsin, neuromedin N, NT(9-13), kinetensin and (D-Trp11)-NT] increased intracellular Ca2+ levels in HT-29 cells, indicating NT receptor agonist properties. The effect of NT1 in mobilizing [Ca2+]i blocked by SR 48692, a non-peptide NT antagonist. Receptor binding affinities of NT analogs to HT-29 cell membranes were positively correlated with potencies for mobilizing intracellular calcium in the same cells. In addition, NT1 increased cyclic GMP levels in rat cerebellar slices, confirming the latter findings of its NT agonist action. These results substantiate the in vitro NT agonist properties of the hexapeptide NT analog NT1.

Myristoylation Restricts Orientation of the GRASP Domain on Membranes and Promotes Membrane Tethering*

PubMed Central

Heinrich, Frank; Nanda, Hirsh; Goh, Haw Zan; Bachert, Collin; Lösche, Mathias; Linstedt, Adam D.

2014-01-01

The mammalian Golgi reassembly stacking protein (GRASP) proteins are Golgi-localized homotypic membrane tethers that organize Golgi stacks into a long, contiguous ribbon-like structure. It is unknown how GRASPs undergo trans pairing given that cis interactions between the proteins in the plane of the membrane are intrinsically favored. To test the hypothesis that myristoylation of the self-interacting GRASP domain restricts its orientation on the membrane to favor trans pairing, we established an in vitro assay that recapitulates GRASP-dependent membrane tethering and used neutron reflection under similar conditions to determine the orientation of the GRASP domain. In vivo, the membrane association of GRASP proteins is conferred by the simultaneous insertion of an N-terminal myristic acid and binding to a Golgi-associated binding partner. In our assay, the latter contact was replaced using a C-terminal hexa-His moiety, which bound to Ni2+-conjugated lipids incorporated into a substrate-supported bilayer lipid membrane. Nonmyristoylated protein lacked a fixed orientation on the membrane and inefficiently tethered liposomes. In contrast, myristoylated GRASP promoted tethering and exhibited a unique membrane complex. Thus, myristoylation restricts the membrane orientation of the GRASP domain favoring interactions in trans for membrane tethering. PMID:24505136

Novel interactions of CAPS (Ca2+-dependent activator protein for secretion) with the three neuronal SNARE proteins required for vesicle fusion.

PubMed

Daily, Neil J; Boswell, Kristin L; James, Declan J; Martin, Thomas F J

2010-11-12

CAPS (aka CADPS) is required for optimal vesicle exocytosis in neurons and endocrine cells where it functions to prime the exocytic machinery for Ca(2+)-triggered fusion. Fusion is mediated by trans complexes of the SNARE proteins VAMP-2, syntaxin-1, and SNAP-25 that bridge vesicle and plasma membrane. CAPS promotes SNARE complex formation on liposomes, but the SNARE binding properties of CAPS are unknown. The current work revealed that CAPS exhibits high affinity binding to syntaxin-1 and SNAP-25 and moderate affinity binding to VAMP-2. CAPS binding is specific for a subset of exocytic SNARE protein isoforms and requires membrane integration of the SNARE proteins. SNARE protein binding by CAPS is novel and mediated by interactions with the SNARE motifs in the three proteins. The C-terminal site for CAPS binding on syntaxin-1 does not overlap the Munc18-1 binding site and both proteins can co-reside on membrane-integrated syntaxin-1. As expected for a C-terminal binding site on syntaxin-1, CAPS stimulates SNARE-dependent liposome fusion with N-terminal truncated syntaxin-1 but exhibits impaired activity with C-terminal syntaxin-1 mutants. Overall the results suggest that SNARE complex formation promoted by CAPS may be mediated by direct interactions of CAPS with each of the three SNARE proteins required for vesicle exocytosis.

Novel Interactions of CAPS (Ca2+-dependent Activator Protein for Secretion) with the Three Neuronal SNARE Proteins Required for Vesicle Fusion*

PubMed Central

Daily, Neil J.; Boswell, Kristin L.; James, Declan J.; Martin, Thomas F. J.

2010-01-01

CAPS (aka CADPS) is required for optimal vesicle exocytosis in neurons and endocrine cells where it functions to prime the exocytic machinery for Ca2+-triggered fusion. Fusion is mediated by trans complexes of the SNARE proteins VAMP-2, syntaxin-1, and SNAP-25 that bridge vesicle and plasma membrane. CAPS promotes SNARE complex formation on liposomes, but the SNARE binding properties of CAPS are unknown. The current work revealed that CAPS exhibits high affinity binding to syntaxin-1 and SNAP-25 and moderate affinity binding to VAMP-2. CAPS binding is specific for a subset of exocytic SNARE protein isoforms and requires membrane integration of the SNARE proteins. SNARE protein binding by CAPS is novel and mediated by interactions with the SNARE motifs in the three proteins. The C-terminal site for CAPS binding on syntaxin-1 does not overlap the Munc18-1 binding site and both proteins can co-reside on membrane-integrated syntaxin-1. As expected for a C-terminal binding site on syntaxin-1, CAPS stimulates SNARE-dependent liposome fusion with N-terminal truncated syntaxin-1 but exhibits impaired activity with C-terminal syntaxin-1 mutants. Overall the results suggest that SNARE complex formation promoted by CAPS may be mediated by direct interactions of CAPS with each of the three SNARE proteins required for vesicle exocytosis. PMID:20826818

Zinc can increase the activity of protein kinase C and contributes to its binding to plasma membranes in T lymphocytes.

PubMed

Csermely, P; Szamel, M; Resch, K; Somogyi, J

1988-05-15

In the primary structure of protein kinase C, the presence of a putative metal-binding site has been suggested (Parker, P.J., Coussens, L., Totty, N., Rhee, L., Young, S., Chen, E., Stabel, S., Waterfield, M.D., and Ullrich, A. (1986) Science 233, 853-859). In the present report, we demonstrate that the most abundant intracellular heavy metal, zinc, can increase the activity of cytosolic protein kinase C. Zinc reversibly binds the enzyme to plasma membranes, and it may contribute to the calcium-induced binding as well. The intracellular heavy metal chelator N,N,N',N'-tetrakis(2-pyridylmethyl) ethylenediamine prevents the phorbol ester- and antigen-induced translocation of protein kinase C. This effect can be totally reversed by the concomitant addition of Zn2+, while Fe2+ and Mn2+ are only partially counteractive. Our results suggest that zinc can activate protein kinase C and contributes to its binding to plasma membranes in T lymphocytes induced by Ca2+, phorbol ester, or antigen.

CTP:phosphocholine cytidylyltransferase binds anionic phospholipid vesicles in a cross-bridging mode.

PubMed

Taneva, Svetla G; Patty, Philipus J; Frisken, Barbara J; Cornell, Rosemary B

2005-07-05

CTP:phosphocholine cytidylyltransferase (CCT) catalyzes the rate-limiting step in phosphatidylcholine (PC) synthesis, and its activity is regulated by reversible association with membranes, mediated by an amphipathic helical domain M. Here we describe a new feature of the CCTalpha isoform, vesicle tethering. We show, using dynamic light scattering and transmission electron microscopy, that dimers of CCTalpha can cross-bridge separate vesicles to promote vesicle aggregation. The vesicles contained either class I activators (anionic phospholipids) or the less potent class II activators, which favor nonlamellar phase formation. CCT increased the apparent hydrodynamic radius and polydispersity of anionic phospholipid vesicles even at low CCT concentrations corresponding to only one or two dimers per vesicle. Electron micrographs of negatively stained phosphatidylglycerol (PG) vesicles confirmed CCT-mediated vesicle aggregation. CCT conjugated to colloidal gold accumulated on the vesicle surfaces and in areas of vesicle-vesicle contact. PG vesicle aggregation required both the membrane-binding domain and the intact CCT dimer, suggesting binding of CCT to apposed membranes via the two M domains situated on opposite sides of the dimerization domain. In contrast to the effects on anionic phospholipid vesicles, CCT did not induce aggregation of PC vesicles containing the class II lipids, oleic acid, diacylglycerol, or phosphatidylethanolamine. The different behavior of the two lipid classes reflected differences in measured binding affinity, with only strongly binding phospholipid vesicles being susceptible to CCT-induced aggregation. Our findings suggest a new model for CCTalpha domain organization and membrane interaction, and a potential involvement of the enzyme in cellular events that implicate close apposition of membranes.

Free and membrane-bound calcium in microgravity and microgravity effects at the membrane level

NASA Astrophysics Data System (ADS)

Belyavskaya, N. A.

The changes of [Ca^2+]_i controlled is known to play a key regulatory role in numerous cellular processes especially associated with membranes. Previous studies from our laboratory have demonstrated an increase in calcium level in root cells of pea seedlings grown aboard orbital station ``Salyut 6'' /1/. These results: 1) indicate that observed Ca^2+-binding sites of membranes also consist in proteins and phospholipids; 2) suggest that such effects of space flight in membrane Ca-binding might be due to the enhancement of Ca^2+ influx through membranes. In model presented, I propose that Ca^2+-activated channels in plasma membrane in response to microgravity allow the movement of Ca^2+ into the root cells, causing a rise in cytoplasmic free Ca^2+ levels. The latter, in its turn, may induce the inhibition of a Ca^2+ efflux by Ca^2+-activated ATPases and through a Ca^2+/H^+ antiport. It is possible that increased cytosolic levels of Ca^2+ ions have stimulated hydrolysis and turnover of phosphatidylinositols, with a consequent elevation of cytosolic [Ca^2+]_i. Plant cell can response to such a Ca^2+ rise by an enhancement of membranous Ca^2+-binding activities to rescue thus a cell from an abundance of a cytotoxin. A Ca^2+-induced phase separation of membranous lipids assists to appear the structure nonstable zones with high energy level at the boundary of microdomains which are rich by some phospholipid components; there is mixing of molecules of the membranes contacted in these zones, the first stage of membranous fusion, which was found in plants exposed to microgravity. These results support the hypothesis that a target for microgravity effect is the flux mechanism of Ca^2+ to plant cell.

Exploring Molecular-Biomembrane Interactions with Surface Plasmon Resonance and Dual Polarization Interferometry Technology: Expanding the Spotlight onto Biomembrane Structure.

PubMed

Lee, Tzong-Hsien; Hirst, Daniel J; Kulkarni, Ketav; Del Borgo, Mark P; Aguilar, Marie-Isabel

2018-06-13

The molecular analysis of biomolecular-membrane interactions is central to understanding most cellular systems but has emerged as a complex technical challenge given the complexities of membrane structure and composition across all living cells. We present a review of the application of surface plasmon resonance and dual polarization interferometry-based biosensors to the study of biomembrane-based systems using both planar mono- or bilayers or liposomes. We first describe the optical principals and instrumentation of surface plasmon resonance, including both linear and extraordinary transmission modes and dual polarization interferometry. We then describe the wide range of model membrane systems that have been developed for deposition on the chips surfaces that include planar, polymer cushioned, tethered bilayers, and liposomes. This is followed by a description of the different chemical immobilization or physisorption techniques. The application of this broad range of engineered membrane surfaces to biomolecular-membrane interactions is then overviewed and how the information obtained using these techniques enhance our molecular understanding of membrane-mediated peptide and protein function. We first discuss experiments where SPR alone has been used to characterize membrane binding and describe how these studies yielded novel insight into the molecular events associated with membrane interactions and how they provided a significant impetus to more recent studies that focus on coincident membrane structure changes during binding of peptides and proteins. We then discuss the emerging limitations of not monitoring the effects on membrane structure and how SPR data can be combined with DPI to provide significant new information on how a membrane responds to the binding of peptides and proteins.

Detection of lipid-induced structural changes of the Marburg virus matrix protein VP40 using hydrogen/deuterium exchange-mass spectrometry

PubMed Central

Wijesinghe, Kaveesha J.; Urata, Sarah; Bhattarai, Nisha; Kooijman, Edgar E.; Gerstman, Bernard S.; Chapagain, Prem P.; Li, Sheng; Stahelin, Robert V.

2017-01-01

Marburg virus (MARV) is a lipid-enveloped virus from the Filoviridae family containing a negative sense RNA genome. One of the seven MARV genes encodes the matrix protein VP40, which forms a matrix layer beneath the plasma membrane inner leaflet to facilitate budding from the host cell. MARV VP40 (mVP40) has been shown to be a dimeric peripheral protein with a broad and flat basic surface that can associate with anionic phospholipids such as phosphatidylserine. Although a number of mVP40 cationic residues have been shown to facilitate binding to membranes containing anionic lipids, much less is known on how mVP40 assembles to form the matrix layer following membrane binding. Here we have used hydrogen/deuterium exchange (HDX) mass spectrometry to determine the solvent accessibility of mVP40 residues in the absence and presence of phosphatidylserine and phosphatidylinositol 4,5-bisphosphate. HDX analysis demonstrates that two basic loops in the mVP40 C-terminal domain make important contributions to anionic membrane binding and also reveals a potential oligomerization interface in the C-terminal domain as well as a conserved oligomerization interface in the mVP40 N-terminal domain. Lipid binding assays confirm the role of the two basic patches elucidated with HD/X measurements, whereas molecular dynamics simulations and membrane insertion measurements complement these studies to demonstrate that mVP40 does not appreciably insert into the hydrocarbon region of anionic membranes in contrast to the matrix protein from Ebola virus. Taken together, we propose a model by which association of the mVP40 dimer with the anionic plasma membrane facilitates assembly of mVP40 oligomers. PMID:28167534

Detection of lipid-induced structural changes of the Marburg virus matrix protein VP40 using hydrogen/deuterium exchange-mass spectrometry.

PubMed

Wijesinghe, Kaveesha J; Urata, Sarah; Bhattarai, Nisha; Kooijman, Edgar E; Gerstman, Bernard S; Chapagain, Prem P; Li, Sheng; Stahelin, Robert V

2017-04-14

Marburg virus (MARV) is a lipid-enveloped virus from the Filoviridae family containing a negative sense RNA genome. One of the seven MARV genes encodes the matrix protein VP40, which forms a matrix layer beneath the plasma membrane inner leaflet to facilitate budding from the host cell. MARV VP40 (mVP40) has been shown to be a dimeric peripheral protein with a broad and flat basic surface that can associate with anionic phospholipids such as phosphatidylserine. Although a number of mVP40 cationic residues have been shown to facilitate binding to membranes containing anionic lipids, much less is known on how mVP40 assembles to form the matrix layer following membrane binding. Here we have used hydrogen/deuterium exchange (HDX) mass spectrometry to determine the solvent accessibility of mVP40 residues in the absence and presence of phosphatidylserine and phosphatidylinositol 4,5-bisphosphate. HDX analysis demonstrates that two basic loops in the mVP40 C-terminal domain make important contributions to anionic membrane binding and also reveals a potential oligomerization interface in the C-terminal domain as well as a conserved oligomerization interface in the mVP40 N-terminal domain. Lipid binding assays confirm the role of the two basic patches elucidated with HD/X measurements, whereas molecular dynamics simulations and membrane insertion measurements complement these studies to demonstrate that mVP40 does not appreciably insert into the hydrocarbon region of anionic membranes in contrast to the matrix protein from Ebola virus. Taken together, we propose a model by which association of the mVP40 dimer with the anionic plasma membrane facilitates assembly of mVP40 oligomers. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

(/sup 3/H)forskolin- and (/sup 3/H)dihydroalprenolol-binding sites and adenylate cyclase activity in heart of rats fed diets containing different oils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alam, S.Q.; Ren, Y.F.; Alam, B.S.

1988-03-01

The characteristics of the cardiac adenylate cyclase system were studied in rats fed diets containing fish oil (menhaden oil) and other oils. Adenylate cyclase activity generally was higher in cardiac homogenates and membranes of rats fed diet containing 10% menhaden oil than in the other oils. The increase in enzyme activity, especially in forskolin-stimulated activity, was associated with an increase in the concentration of the (/sup 3/H) forskolin-binding sites in cardiac membranes of rats fed menhaden oil. The beta-adrenergic receptor concentration was not significantly altered although the affinity for (/sup 3/H)dihydroalprenolol-binding was lower in membranes of rats fed menhaden oilmore » than those fed the other oils. omega-3 fatty acids from menhaden oil were incorporated into the cardiac membrane phospholipids. The results suggest that the observed increase in myocardial adenylate cyclase activity of rats fed menhaden oil may be due to an increase in the number of the catalytic subunits of the enzyme or due to a greater availability of the forskolin-binding sites.« less

Assembly of streptolysin O pores assessed by quartz crystal microbalance and atomic force microscopy provides evidence for the formation of anchored but incomplete oligomers.

PubMed

Stewart, Sarah E; D'Angelo, Michael E; Paintavigna, Stefania; Tabor, Rico F; Martin, Lisandra L; Bird, Phillip I

2015-01-01

Streptolysin O (SLO) is a bacterial pore forming protein that is part of the cholesterol dependent cytolysin (CDC) family. We have used quartz crystal microbalance with dissipation monitoring (QCM-D) to examine SLO membrane binding and pore formation. In this system, SLO binds tightly to cholesterol-containing membranes, and assembles into partial and complete pores confirmed by atomic force microscopy. SLO binds to the lipid bilayer at a single rate consistent with the Langmuir isotherm model of adsorption. Changes in dissipation illustrate that SLO alters the viscoelastic properties of the bilayer during pore formation, but there is no loss of material from the bilayer as reported for small membrane-penetrating peptides. SLO mutants were used to further dissect the assembly and insertion processes by QCM-D. This shows the signature of SLO in QCM-D changes when pore formation is inhibited, and that bound and inserted SLO forms can be distinguished. Furthermore a pre-pore locked SLO mutant binds reversibly to lipid, suggesting that the partially complete wtSLO forms observed by AFM are anchored to the membrane. Copyright © 2014 Elsevier B.V. All rights reserved.

Cargo self-assembly rescues affinity of cell-penetrating peptides to lipid membranes

NASA Astrophysics Data System (ADS)

Weinberger, Andreas; Walter, Vivien; MacEwan, Sarah R.; Schmatko, Tatiana; Muller, Pierre; Schroder, André P.; Chilkoti, Ashutosh; Marques, Carlos M.

2017-03-01

Although cationic cell-penetrating peptides (CPPs) are able to bind to cell membranes, thus promoting cell internalization by active pathways, attachment of cargo molecules to CPPs invariably reduces their cellular uptake. We show here that CPP binding to lipid bilayers, a simple model of the cell membrane, can be recovered by designing cargo molecules that self-assemble into spherical micelles and increase the local interfacial density of CPP on the surface of the cargo. Experiments performed on model giant unilamellar vesicles under a confocal laser scanning microscope show that a family of thermally responsive elastin-like polypeptides that exhibit temperature-triggered micellization can promote temperature triggered attachment of the micelles to membranes, thus rescuing by self-assembly the cargo-induced loss of the CPP affinity to bio-membranes.

Pharmacophore screening of the protein data bank for specific binding site chemistry.

PubMed

Campagna-Slater, Valérie; Arrowsmith, Andrew G; Zhao, Yong; Schapira, Matthieu

2010-03-22

A simple computational approach was developed to screen the Protein Data Bank (PDB) for putative pockets possessing a specific binding site chemistry and geometry. The method employs two commonly used 3D screening technologies, namely identification of cavities in protein structures and pharmacophore screening of chemical libraries. For each protein structure, a pocket finding algorithm is used to extract potential binding sites containing the correct types of residues, which are then stored in a large SDF-formatted virtual library; pharmacophore filters describing the desired binding site chemistry and geometry are then applied to screen this virtual library and identify pockets matching the specified structural chemistry. As an example, this approach was used to screen all human protein structures in the PDB and identify sites having chemistry similar to that of known methyl-lysine binding domains that recognize chromatin methylation marks. The selected genes include known readers of the histone code as well as novel binding pockets that may be involved in epigenetic signaling. Putative allosteric sites were identified on the structures of TP53BP1, L3MBTL3, CHEK1, KDM4A, and CREBBP.

Visualization of membrane RNAs

PubMed Central

JANAS, TADEUSZ; YARUS, MICHAEL

2003-01-01

Using fluorescence microscopy, we show that previously isolated membrane-binding RNAs coat artificial phospholipid membranes relatively uniformly, except for a frequent tendency to concentrate at bends, membrane junctions, and other unusual sites. Membrane RNAs can also be visualized as single molecules or isolated complexes by atomic force microscopy (AFM) of free RNAs on mica. Finally, RNAs can be seen within membranes by AFM of RNA-liposomes immobilized on hydrophobic mica surfaces. Monomer RNAs appear globular, as expected for small RNAs. When mixed under conditions in which RNAs bind bilayers, RNA 9 and RNA 10 combine to yield about 80% of RNAs as mainly linear oligomers of ≈2–8 molecules. Once inserted in membranes, the RNAs oligomerize further, yielding larger, irregular ropelike structures that prefer the edges of altered lipid patches. These properties can be interpreted in terms of RNA–RNA loop interactions, and the RNA effects on membranes can be explained in terms of an RNA preference for irregular lipid conformations. The RNA-bilayer system poses new opportunities for combining the properties of membranes and RNA in contemporary cells, and also in the ribocytes of an RNA world. PMID:14561885

Molecular basis of the specific subcellular localization of the C2-like domain of 5-lipoxygenase.

PubMed

Kulkarni, Shilpa; Das, Sudipto; Funk, Colin D; Murray, Diana; Cho, Wonhwa

2002-04-12

The activation of 5-lipoxygenase (5-LO) involves its calcium-dependent translocation to the nuclear envelope, where it catalyzes the two-step transformation of arachidonic acid into leukotriene A(4), leading to the synthesis of various leukotrienes. To understand the mechanism by which 5-LO is specifically targeted to the nuclear envelope, we studied the membrane binding properties of the amino-terminal domain of 5-LO, which has been proposed to have a C2 domain-like structure. The model building, electrostatic potential calculation, and in vitro membrane binding studies of the isolated C2-like domain of 5-LO and selected mutants show that this Ca(2+)-dependent domain selectively binds zwitterionic phosphatidylcholine, which is conferred by tryptophan residues (Trp(13), Trp(75), and Trp(102)) located in the putative Ca(2+)-binding loops. The spatiotemporal dynamics of the enhanced green fluorescence protein-tagged C2-like domain of 5-LO and mutants in living cells also show that the phosphatidylcholine selectivity of the C2-like domain accounts for the specific targeting of 5-LO to the nuclear envelope. Together, these results show that the C2-like domain of 5-LO is a genuine Ca(2+)-dependent membrane-targeting domain and that the subcellular localization of the domain is governed in large part by its membrane binding properties.

Biochemical characterization of P-type copper ATPases

PubMed Central

Inesi, Giuseppe; Pilankatta, Rajendra; Tadini-Buoninsegni, Francesco

2014-01-01

Copper ATPases, in analogy with other members of the P-ATPase superfamily, contain a catalytic headpiece including an aspartate residue reacting with ATP to form a phosphoenzyme intermediate, and transmembrane helices containing cation-binding sites [TMBS (transmembrane metal-binding sites)] for catalytic activation and cation translocation. Following phosphoenzyme formation by utilization of ATP, bound copper undergoes displacement from the TMBS to the lumenal membrane surface, with no H+ exchange. Although PII-type ATPases sustain active transport of alkali/alkali-earth ions (i.e. Na+, Ca2+) against electrochemical gradients across defined membranes, PIB-type ATPases transfer transition metal ions (i.e. Cu+) from delivery to acceptor proteins and, prominently in mammalian cells, undergo trafficking from/to various membrane compartments. A specific component of copper ATPases is the NMBD (N-terminal metal-binding domain), containing up to six copper-binding sites in mammalian (ATP7A and ATP7B) enzymes. Copper occupancy of NMBD sites and interaction with the ATPase headpiece are required for catalytic activation. Furthermore, in the presence of copper, the NMBD allows interaction with protein kinase D, yielding phosphorylation of serine residues, ATP7B trafficking and protection from proteasome degradation. A specific feature of ATP7A is glycosylation and stabilization on plasma membranes. Cisplatin, a platinum-containing anti-cancer drug, binds to copper sites of ATP7A and ATP7B, and undergoes vectorial displacement in analogy with copper. PMID:25242165

Autoradiographic visualization of the mouse egg's sperm receptor bound to sperm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bleil, J.D.; Wassarman, P.M.

1986-04-01

The extracellular coat, or zona pellucida, of mammalian eggs contains species-specific receptors to which sperm bind as a prelude to fertilization. In mice, ZP3, one of only three zona pellucida glycoproteins, serves as sperm receptor. Acrosome-intact, but not acrosome-reacted, mouse sperm recognize and interact with specific O-linked oligosaccharides of ZP3 resulting in sperm-egg binding. Binding, in turn, causes sperm to undergo the acrosome reaction; a membrane fusion event that results in loss of plasma membrane at the anterior region of the head and exposure of inner acrosomal membrane with its associated acrosomal contents. Bound, acrosome-reacted sperm are able to penetratemore » the zona pellucida and fuse with the egg's plasma membrane (fertilization). In the present report, we examined binding of radioiodinated, purified, egg ZP3 to both acrosome intact and acrosome reacted sperm by whole-mount autoradiography. Silver grains due to bound 125I-ZP3 were found localized to the acrosomal cap region of heads of acrosome-reacted sperm. Under the same conditions, 125I-fetuin bound at only background levels to heads of both acrosome-intact and -reacted sperm, and 125I-ZP2, another zona pellucida glycoprotein, bound preferentially to acrosome-reacted sperm. These results provide visual evidence that ZP3 binds preferentially and specifically to heads of acrosome intact sperm; properties expected of the mouse egg's sperm receptor.« less

Structural insights into a StART-like domain in Lam4 and its interaction with sterol ligands.

PubMed

Gatta, Alberto T; Sauerwein, Andrea C; Zhuravleva, Anastasia; Levine, Tim P; Matthews, Stephen

2018-01-15

Sterols are essential components of cellular membranes and shape their biophysical properties. The recently discovered family of Lipid transfer proteins Anchored at Membrane contact sites (LAMs) has been suggested to carry out intracellular sterol traffic using StART-like domains. Here, we studied the second StART-like domain of Lam4p from S. cerevisiae by NMR. We show that NMR data are consistent with the StART-like domain structure, and that several functionally important regions within the domain exhibit significant conformational dynamics. NMR titration experiments confirm sterol binding to the canonical sterol-binding site and suggest a role of membrane interactions on the thermodynamics and kinetics of sterol binding. Copyright © 2017 Elsevier Inc. All rights reserved.

IMPROVING THE QUALITY, AVAILABILITY AND SUSTAINABILITY OF DRINKING WATER SUPPLIES THROUGH ANTIFOULING AND ANTISCALING DESALINATION MEMBRANES

EPA Science Inventory

Surface modification with the selected polymers is expected to reduce the fouling and scaling propensity of desalination membranes by strongly binding water at the membrane surface. Foulants will interact with this bound water layer and not with the membrane surface itself....

Pharmacological evaluation of an [(123)I] labelled imidazopyridine-3-acetamide for the study of benzodiazepine receptors.

PubMed

Mattner, Filomena; Mardon, Karine; Loc'h, Christian; Katsifis, Andrew

2006-06-13

In vitro binding of the iodinated imidazopyridine, N',N'-dimethyl-6-methyl-(4'-[(123)I]iodophenyl)imidazo[1,2-a]pyridine-3-acetamide [(123)I]IZOL to benzodiazepine binding sites on brain cortex, adrenal and kidney membranes is reported. Saturation experiments showed that [(123)I]IZOL, bound to a single class of binding site (n(H)=0.99) on adrenal and kidney mitochondrial membranes with a moderate affinity (K(d)=30 nM). The density of binding sites was 22+/-6 and 1.2+/-0.4 pmol/mg protein on adrenal and kidney membranes, respectively. No specific binding was observed in mitochondrial-synaptosomal membranes of brain cortex. In biodistribution studies in rats, the highest uptake of [(123)I]IZOL was found 30 min post injection in adrenals (7.5% ID/g), followed by heart, kidney, lung (1% ID/g) and brain (0.12% ID/g), consistent with the distribution of peripheral benzodiazepine binding sites. Pre-administration of unlabelled IZOL and the specific PBBS drugs, PK 11195 and Ro 5-4864 significantly reduced the uptake of [(123)I]IZOL by 30% (p<0.05) in olfactory bulbs and by 51-86% (p<0.01) in kidney, lungs, heart and adrenals, while it increased by 30% to 50% (p<0.01) in the rest of the brain and the blood. Diazepam, a mixed CBR-PBBS drug, inhibited the uptake in kidney, lungs, heart, adrenals and olfactory bulbs by 32% to 44% (p<0.01) but with no effect on brain uptake and in blood concentration. Flumazenil, a central benzodiazepine drug and haloperidol (dopamine antagonist/sigma receptor drug) displayed no effect in [(123)I]IZOL in peripheral organs and in the brain. [(123)I]IZOL may deserve further development for imaging selectively peripheral benzodiazepine binding sites.

A Role for Weak Electrostatic Interactions in Peripheral Membrane Protein Binding

PubMed Central

Khan, Hanif M.; He, Tao; Fuglebakk, Edvin; Grauffel, Cédric; Yang, Boqian; Roberts, Mary F.; Gershenson, Anne; Reuter, Nathalie

2016-01-01

Bacillus thuringiensis phosphatidylinositol-specific phospholipase C (BtPI-PLC) is a secreted virulence factor that binds specifically to phosphatidylcholine (PC) bilayers containing negatively charged phospholipids. BtPI-PLC carries a negative net charge and its interfacial binding site has no obvious cluster of basic residues. Continuum electrostatic calculations show that, as expected, nonspecific electrostatic interactions between BtPI-PLC and membranes vary as a function of the fraction of anionic lipids present in the bilayers. Yet they are strikingly weak, with a calculated ΔGel below 1 kcal/mol, largely due to a single lysine (K44). When K44 is mutated to alanine, the equilibrium dissociation constant for small unilamellar vesicles increases more than 50 times (∼2.4 kcal/mol), suggesting that interactions between K44 and lipids are not merely electrostatic. Comparisons of molecular-dynamics simulations performed using different lipid compositions reveal that the bilayer composition does not affect either hydrogen bonds or hydrophobic contacts between the protein interfacial binding site and bilayers. However, the occupancies of cation-π interactions between PC choline headgroups and protein tyrosines vary as a function of PC content. The overall contribution of basic residues to binding affinity is also context dependent and cannot be approximated by a rule-of-thumb value because these residues can contribute to both nonspecific electrostatic and short-range protein-lipid interactions. Additionally, statistics on the distribution of basic amino acids in a data set of membrane-binding domains reveal that weak electrostatics, as observed for BtPI-PLC, might be a less unusual mechanism for peripheral membrane binding than is generally thought. PMID:27028646

Resveratrol inhibits phorbol ester-induced membrane translocation of presynaptic Munc13-1.

PubMed

Pany, Satyabrata; Ghosh, Anamitra; You, Youngki; Nguyen, Nga; Das, Joydip

2017-11-01

Resveratrol (1) is a naturally occurring polyphenol that has been implicated in neuroprotection. One of resveratrol's several biological targets is Ca 2+ -sensitive protein kinase C alpha (PKCα). Resveratrol inhibits PKCα by binding to its activator-binding C1 domain. Munc13-1 is a C1 domain-containing Ca 2+ -sensitive SNARE complex protein essential for vesicle priming and neurotransmitter release. To test if resveratrol could also bind and inhibit Munc13-1, we studied the interaction of resveratrol and its derivatives, (E)-1,3-dimethoxy-5-(4-methoxystyryl)benzene, (E)-5,5'-(ethene-1,2-diyl)bis(benzene-1,2,3-triol), (E)-1,2-bis(3,4,5-trimethoxyphenyl)ethane, and (E)-5-(4-(hexadecyloxy)-3,5-dihydroxystyryl)benzene-1,2,3-triol with Munc13-1 by studying its membrane translocation from cytosol to plasma membrane in HT22 cells and primary hippocampal neurons. Resveratrol, but not the derivatives inhibited phorbol ester-induced Munc13-1 translocation from cytosol to membrane in HT22 cells and primary hippocampal neurons, as evidenced by immunoblot analysis and confocal microscopy. Resveratrol did not show any effect on Munc13-1 H567K , a mutant which is not sensitive to phorbol ester. Binding studies with Munc13-1 C1 indicated that resveratrol competes with phorbol ester for the binding site. Molecular docking and dynamics studies suggested that hydroxyl groups of resveratrol interact with phorbol-ester binding residues in the binding pocket. This study characterizes Munc13-1 as a target of resveratrol and highlights the importance of dietary polyphenol in the management of neurodegenerative diseases. Copyright © 2017 Elsevier B.V. All rights reserved.

Role of surfactant protein A (SP-A)/lipid interactions for SP-A functions in the lung.

PubMed

Casals, C

2001-01-01

Surfactant protein A (SP-A), an oligomeric glycoprotein, is a member of a group of proteins named collectins that contain collagen-like and Ca(2+)-dependent carbohydrate recognition domains. SP-A interacts with a broad range of amphipathic lipids (glycerophospholipids, sphingophospholipids, glycosphingolipids, lipid A, and lipoglycans) that are present in surfactant or microbial membranes. This review summarizes SP-A/lipid interaction studies regarding the lipid system used (i.e., phospholipid vesicles, phospholipid monolayers, and lipids immobilized on silica or adsorbed on a solid support). The effect of calcium, ionic strength, and pH on the binding of SP-A to lipids and the subsequent lipid aggregation process is discussed. Current evidence suggests that hydrophobic-binding forces are involved in the peripherical association of SP-A to membranes. It is also proposed that fluid and liquid-ordered phase coexistence in surfactant membranes might favor partition of SP-A into those membranes. The binding of SP-A to surfactant membranes containing hydrophobic surfactant peptides makes possible the formation of a membrane reservoir in the alveolar fluid that is protected by SP-A against inactivation and improves the rate of surfactant film formation. In addition, the interaction of SP-A with membranes might enhance the affinity of SP-A for terminal carbohydrates of glycolipids or glycoproteins on the surface of invading microorganisms.

Decreased content of protein 4.2 in ankyrin-deficient normoblastosis (nb/nb) mouse red blood cells: evidence for ankyrin enhancement of protein 4.2 membrane binding.

PubMed

Rybicki, A C; Musto, S; Schwartz, R S

1995-11-01

Homozygous normoblastosis (nb/nb) mice, whose red blood cell (RBC) membranes are nearly completely deficient in full-length 210-kD ankyrin, were used to study interactions between ankyrin and protein 4.2 (P4.2). Although it is unclear whether or not these proteins interact in the membrane, both ankyrin and P4.2 bind to the cytoplasmic domain of band 3 (cdb3). In addition to the complete deficiency of full-length ankyrin, nb/nb RBC membranes are also partially spectrin deficient, resulting in morphologically spherocytic and mechanically fragile cells. A new finding was that nb/nb RBC membranes are severely (approximately 73%) P4.2 deficient compared with wild type (+/+) or high reticulocyte mouse RBC membranes. Metabolic labeling of nb/nb reticulocytes showed active P4.2 synthesis at levels comparable with high reticulocyte controls suggesting that the nb/nb P4.2 deficiency was not the result of defective P4.2 synthesis. Reconstitution of nb/nb inside-out vesicles (IOVs) with human RBC ankyrin restored ankyrin levels to approximately 80% of +/+ IOV levels and increased binding of exogenously added human RBC P4.2 by approximately 60%. These results suggest that ankyrin is required for normal associations of P4.2 with the RBC membrane.

Lipophilic oligonucleotides spontaneously insert into lipid membranes, bind complementary DNA strands, and sequester into lipid-disordered domains.

PubMed

Bunge, Andreas; Kurz, Anke; Windeck, Anne-Kathrin; Korte, Thomas; Flasche, Wolfgang; Liebscher, Jürgen; Herrmann, Andreas; Huster, Daniel

2007-04-10

For the development of surface functionalized bilayers, we have synthesized lipophilic oligonucleotides to combine the molecular recognition mechanism of nucleic acids and the self-assembly characteristics of lipids in planar membranes. A lipophilic oligonucleotide consisting of 21 thymidine units and two lipophilic nucleotides with an alpha-tocopherol moiety as a lipophilic anchor was synthesized using solid-phase methods with a phosphoramadite strategy. The interaction of the water soluble lipophilic oligonucleotide with vesicular lipid membranes and its capability to bind complementary DNA strands was studied using complementary methods such as NMR, EPR, DSC, fluorescence spectroscopy, and fluorescence microscopy. This oligonucleotide inserted stably into preformed membranes from the aqueous phase. Thereby, no significant perturbation of the lipid bilayer and its stability was observed. However, the non-lipidated end of the oligonucleotide is exposed to the aqueous environment, is relatively mobile, and is free to interact with complementary DNA strands. Binding of the complementary single-stranded DNA molecules is fast and accomplished by the formation of Watson-Crick base pairs, which was confirmed by 1H NMR chemical shift analysis and fluorescence resonance energy transfer. The molecular structure of the membrane bound DNA double helix is very similar to the free double-stranded DNA. Further, the membrane bound DNA double strands also undergo regular melting. Finally, in raft-like membrane mixtures, the lipophilic oligonucleotide was shown to preferentially sequester into liquid-disordered membrane domains.

Binding free energy and counterion release for adsorption of the antimicrobial peptide lactoferricin B on a POPG membrane.

PubMed

Tolokh, Igor S; Vivcharuk, Victor; Tomberli, Bruno; Gray, C G

2009-09-01

Molecular dynamics (MD) simulations are used to study the interaction of an anionic palmitoyl-oleoyl-phosphatidylglycerol (POPG) bilayer with the cationic antimicrobial peptide bovine lactoferricin (LFCinB) in a 100 mM NaCl solution at 310 K. The interaction of LFCinB with a POPG bilayer is employed as a model system for studying the details of membrane adsorption selectivity of cationic antimicrobial peptides. Seventy eight 4 ns MD production run trajectories of the equilibrated system, with six restrained orientations of LFCinB at 13 different separations from the POPG membrane, are generated to determine the free energy profile for the peptide as a function of the distance between LFCinB and the membrane surface. To calculate the profile for this relatively large system, a variant of constrained MD and thermodynamic integration is used. A simplified method for relating the free energy profile to the LFCinB-POPG membrane binding constant is employed to predict a free energy of adsorption of -5.4+/-1.3 kcal/mol and a corresponding maximum adsorption binding force of about 58 pN. We analyze the results using Poisson-Boltzmann theory. We find the peptide-membrane attraction to be dominated by the entropy increase due to the release of counterions and polarized water from the region between the charged membrane and peptide, as the two approach each other. We contrast these results with those found earlier for adsorption of LFCinB on the mammalianlike palmitoyl-oleoyl-phosphatidylcholine membrane.

Salt bridge dynamics control substrate-induced conformational change in the membrane transporter GlpT

PubMed Central

Law, Christopher J.; Almqvist, Jonas; Bernstein, Adam; Goetz, Regina M.; Huang, Yafei; Soudant, Celine; Laaksonen, Aatto; Hovmöller, Sven; Wang, Da-Neng

2008-01-01

Summary Active transport of substrates across cytoplasmic membranes is of great physiological, medical and pharmaceutical importance. The glycerol-3-phosphate (G3P) transporter (GlpT) of the E. coli inner membrane is a secondary active antiporter from the ubiquitous major facilitator superfamily that couples the import of G3P to the efflux of inorganic phosphate (Pi) down its concentration gradient. Integrating information from a novel combination of structural, molecular dynamics simulations and biochemical studies, we identify the residues involved directly in binding of substrate to the inward-facing conformation of GlpT, thus defining the structural basis for the substrate-specificity of this transporter. The substrate binding mechanism involves protonation of a histidine residue at the binding site. Furthermore, our data suggest that the formation and breaking of inter- and intradomain salt bridges control the conformational change of the transporter that accompanies substrate translocation across the membrane. The mechanism we propose may be a paradigm for organophosphate/phosphate antiporters. PMID:18395745

Charge-Triggered Membrane Insertion of Matrix Metalloproteinase-7, Supporter of Innate Immunity and Tumors.

PubMed

Prior, Stephen H; Fulcher, Yan G; Koppisetti, Rama K; Jurkevich, Alexander; Van Doren, Steven R

2015-11-03

Matrix metalloproteinase-7 (MMP-7) sheds signaling proteins from cell surfaces to activate bacterial killing, wound healing, and tumorigenesis. The mechanism targeting soluble MMP-7 to membranes has been investigated. Nuclear magnetic resonance structures of the zymogen, free and bound to membrane mimics without and with anionic lipid, reveal peripheral binding to bilayers through paramagnetic relaxation enhancements. Addition of cholesterol sulfate partially embeds the protease in the bilayer, restricts its diffusion, and tips the active site away from the bilayer. Its insertion of hydrophobic residues organizes the lipids, pushing the head groups and sterol sulfate outward toward the enzyme's positive charge on the periphery of the enlarged interface. Fluorescence probing demonstrates a similar mode of binding to plasma membranes and internalized vesicles of colon cancer cells. Binding of bilayered micelles induces allosteric activation and conformational change in the auto-inhibitory peptide and the adjacent scissile site, illustrating a potential intermediate in the activation of the zymogen. Copyright © 2015 Elsevier Ltd. All rights reserved.

Structure of an E. coli integral membrane sulfurtransferase and its structural transition upon SCN- binding defined by EPR-based hybrid method

NASA Astrophysics Data System (ADS)

Ling, Shenglong; Wang, Wei; Yu, Lu; Peng, Junhui; Cai, Xiaoying; Xiong, Ying; Hayati, Zahra; Zhang, Longhua; Zhang, Zhiyong; Song, Likai; Tian, Changlin

2016-01-01

Electron paramagnetic resonance (EPR)-based hybrid experimental and computational approaches were applied to determine the structure of a full-length E. coli integral membrane sulfurtransferase, dimeric YgaP, and its structural and dynamic changes upon ligand binding. The solution NMR structures of the YgaP transmembrane domain (TMD) and cytosolic catalytic rhodanese domain were reported recently, but the tertiary fold of full-length YgaP was not yet available. Here, systematic site-specific EPR analysis defined a helix-loop-helix secondary structure of the YagP-TMD monomers using mobility, accessibility and membrane immersion measurements. The tertiary folds of dimeric YgaP-TMD and full-length YgaP in detergent micelles were determined through inter- and intra-monomer distance mapping and rigid-body computation. Further EPR analysis demonstrated the tight packing of the two YgaP second transmembrane helices upon binding of the catalytic product SCN-, which provides insight into the thiocyanate exportation mechanism of YgaP in the E. coli membrane.

Substrate binding site for nitrate reductase of Escherichia coli is on the inner aspect of the membrane.

PubMed Central

Kristjansson, J K; Hollocher, T C

1979-01-01

Escherichia coli grown anaerobically on nitrate exhibited the same transport barrier to reduction of chlorate, relative to nitrate, as that exhibited by Paracoccus denitrificans. This establishes that the nitrate binding site of nitrate reductase (EC 1.7.99.4) in E. coli must also lie on the cell side of the nitrate transporter which is associated with the plasma membrane. Because nitrate reductase is membrane bound, the nitrate binding site is thus located on the inner aspect of the membrane. Nitrate pulse studies on E. coli in the absence of valinomycin showed a small transient alkalinization (leads to H+/NO3- congruent to --0.07) which did not occur with oxygen pulses. By analogy with P. denitrificans, the alkaline transient is interpreted to arise from proton-linked nitrate uptake which is closely followed by nitrite efflux. The result is consistent with internal reduction of nitrate, whereas external reduction would be expected to give leads to H+/NO3-ratios approaching --2. PMID:374343

Monitoring glycolipid transfer protein activity and membrane interaction with the surface plasmon resonance technique.

PubMed

Ohvo-Rekilä, Henna; Mattjus, Peter

2011-01-01

The glycolipid transfer protein (GLTP) is a protein capable of binding and transferring glycolipids. GLTP is cytosolic and it can interact through its FFAT-like (two phenylalanines in an acidic tract) motif with proteins localized on the surface of the endoplasmic reticulum. Previous in vitro work with GLTP has focused mainly on the complete transfer reaction of the protein, that is, binding and subsequent removal of the glycolipid from the donor membrane, transfer through the aqueous environment, and the final release of the glycolipid to an acceptor membrane. Using bilayer vesicles and surface plasmon resonance spectroscopy, we have now, for the first time, analyzed the binding and lipid removal capacity of GLTP with a completely label-free technique. This technique is focused on the initial steps in GLTP-mediated transfer and the parameters affecting these steps can be more precisely determined. We used the new approach for detailed structure-function studies of GLTP by examining the glycolipid transfer capacity of specific GLTP tryptophan mutants. Tryptophan 96 is crucial for the transfer activity of the protein and tryptophan 142 is an important part of the proteins membrane interacting domain. Further, we varied the composition of the used lipid vesicles and gained information on the effect of membrane properties on GLTP activity. GLTP prefers to interact with more tightly packed membranes, although GLTP-mediated transfer is faster from more fluid membranes. This technique is very useful for the study of membrane-protein interactions and lipid-transfer rates and it can easily be adapted to other membrane-interacting proteins. Copyright © 2010 Elsevier B.V. All rights reserved.

Cholesterol Promotes Protein Binding by Affecting Membrane Electrostatics and Solvation Properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doktorova, Milka; Heberle, Frederick A.; Kingston, Richard L.

Binding of the retroviral structural protein Gag to the cellular plasma membrane is mediated by the protein’s matrix (MA) domain. Prominent among MA-PM interactions is electrostatic attraction between the positively charged MA domain and the negatively charged plasma membrane inner leaflet. Previously, we reported that membrane association of HIV-1 Gag, as well as purified Rous sarcoma virus (RSV) MA and Gag, depends strongly on the presence of acidic lipids and is enhanced by cholesterol (Chol). The mechanism underlying this enhancement was unclear. Here in this paper, using a broad set of in vitro and in silico techniques we addressed molecularmore » mechanisms of association between RSV MA and model membranes, and investigated how Chol enhances this association. In neutron scattering experiments with liposomes in the presence or absence of Chol, MA preferentially interacted with preexisting POPS-rich clusters formed by nonideal lipid mixing, binding peripherally to the lipid headgroups with minimal perturbation to the bilayer structure. Molecular dynamics simulations showed a stronger MA-bilayer interaction in the presence of Chol, and a large Chol-driven increase in lipid packing and membrane surface charge density. Although in vitro MA-liposome association is influenced by disparate variables, including ionic strength and concentrations of Chol and charged lipids, continuum electrostatic theory revealed an underlying dependence on membrane surface potential. Together, these results conclusively show that Chol affects RSV MA-membrane association by making the electrostatic potential at the membrane surface more negative, while decreasing the penalty for lipid headgroup desolvation. The presented approach can be applied to other viral and nonviral proteins.« less

BamA POTRA Domain Interacts with a Native Lipid Membrane Surface.

PubMed

Fleming, Patrick J; Patel, Dhilon S; Wu, Emilia L; Qi, Yifei; Yeom, Min Sun; Sousa, Marcelo Carlos; Fleming, Karen G; Im, Wonpil

2016-06-21

The outer membrane of Gram-negative bacteria is an asymmetric membrane with lipopolysaccharides on the external leaflet and phospholipids on the periplasmic leaflet. This outer membrane contains mainly β-barrel transmembrane proteins and lipidated periplasmic proteins (lipoproteins). The multisubunit protein β-barrel assembly machine (BAM) catalyzes the insertion and folding of the β-barrel proteins into this membrane. In Escherichia coli, the BAM complex consists of five subunits, a core transmembrane β-barrel with a long periplasmic domain (BamA) and four lipoproteins (BamB/C/D/E). The BamA periplasmic domain is composed of five globular subdomains in tandem called POTRA motifs that are key to BAM complex formation and interaction with the substrate β-barrel proteins. The BAM complex is believed to undergo conformational cycling while facilitating insertion of client proteins into the outer membrane. Reports describing variable conformations and dynamics of the periplasmic POTRA domain have been published. Therefore, elucidation of the conformational dynamics of the POTRA domain in full-length BamA is important to understand the function of this molecular complex. Using molecular dynamics simulations, we present evidence that the conformational flexibility of the POTRA domain is modulated by binding to the periplasmic surface of a native lipid membrane. Furthermore, membrane binding of the POTRA domain is compatible with both BamB and BamD binding, suggesting that conformational selection of different POTRA domain conformations may be involved in the mechanism of BAM-facilitated insertion of outer membrane β-barrel proteins. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Cholesterol Promotes Protein Binding by Affecting Membrane Electrostatics and Solvation Properties

DOE PAGES

Doktorova, Milka; Heberle, Frederick A.; Kingston, Richard L.; ...

2017-11-07

Binding of the retroviral structural protein Gag to the cellular plasma membrane is mediated by the protein’s matrix (MA) domain. Prominent among MA-PM interactions is electrostatic attraction between the positively charged MA domain and the negatively charged plasma membrane inner leaflet. Previously, we reported that membrane association of HIV-1 Gag, as well as purified Rous sarcoma virus (RSV) MA and Gag, depends strongly on the presence of acidic lipids and is enhanced by cholesterol (Chol). The mechanism underlying this enhancement was unclear. Here in this paper, using a broad set of in vitro and in silico techniques we addressed molecularmore » mechanisms of association between RSV MA and model membranes, and investigated how Chol enhances this association. In neutron scattering experiments with liposomes in the presence or absence of Chol, MA preferentially interacted with preexisting POPS-rich clusters formed by nonideal lipid mixing, binding peripherally to the lipid headgroups with minimal perturbation to the bilayer structure. Molecular dynamics simulations showed a stronger MA-bilayer interaction in the presence of Chol, and a large Chol-driven increase in lipid packing and membrane surface charge density. Although in vitro MA-liposome association is influenced by disparate variables, including ionic strength and concentrations of Chol and charged lipids, continuum electrostatic theory revealed an underlying dependence on membrane surface potential. Together, these results conclusively show that Chol affects RSV MA-membrane association by making the electrostatic potential at the membrane surface more negative, while decreasing the penalty for lipid headgroup desolvation. The presented approach can be applied to other viral and nonviral proteins.« less

Evaluation of the Parameters and Conditions of Process in the Ethylbenzene Dehydrogenation with Application of Permselective Membranes to Enhance Styrene Yield.

PubMed

Araújo, Paulo Jardel P; Leite, Manuela Souza; Ravagnani, Teresa M Kakuta

2016-01-01

Styrene is an important monomer in the manufacture of thermoplastic. Most of it is produced by the catalytic dehydrogenation of ethylbenzene. In this process that depends on reversible reactions, the yield is usually limited by the establishment of thermodynamic equilibrium in the reactor. The styrene yield can be increased by using a hybrid process, with reaction and separation simultaneously. It is proposed using permselective composite membrane to remove hydrogen and thus suppress the reverse and secondary reactions. This paper describes the simulation of a dehydrogenation process carried out in a tubular fixed-bed reactor wrapped in a permselective composite membrane. A mathematical model was developed, incorporating the various mass transport mechanisms found in each of the membrane layers and in the catalytic fixed bed. The effects of the reactor feed conditions (temperature, steam-to-oil ratio, and the weight hourly space velocity), the fixed-bed geometry (length, diameter, and volume), and the membrane geometry (thickness of the layers) on the styrene yield were analyzed. These variables were used to determine experimental conditions that favour the production of styrene. The simulation showed that an increase of 40.98% in the styrene yield, compared to a conventional fixed-bed process, could be obtained by wrapping the reactor in a permselective composite membrane.

Quantitative Analysis of Self-Association and Mobility of Annexin A4 at the Plasma Membrane

PubMed Central

Crosby, Kevin C.; Postma, Marten; Hink, Mark A.; Zeelenberg, Christiaan H.C.; Adjobo-Hermans, Merel J.W.; Gadella, Theodorus W.J.

2013-01-01

Annexins, found in most eukaryotic species, are cytosolic proteins that are able to bind negatively-charged phospholipids in a calcium-dependent manner. Annexin A4 (AnxA4) has been implicated in diverse cellular processes, including the regulation of exocytosis and ion-transport; however, its precise mechanistic role is not fully understood. AnxA4 has been shown to aggregate on lipid layers upon Ca2+ binding in vitro, a characteristic that may be critical for its function. We have utilized advanced fluorescence microscopy to discern details on the mobility and self-assembly of AnxA4 after Ca2+ influx at the plasma membrane in living cells. Total internal reflection microscopy in combination with Förster resonance energy transfer reveals that there is a delay between initial plasma membrane binding and the beginning of self-assembly and this process continues after the cytoplasmic pool has completely relocated. Number-and-brightness analysis suggests that the predominant membrane bound mobile form of the protein is trimeric. There also exists a pool of AnxA4 that forms highly immobile aggregates at the membrane. Fluorescence recovery after photobleaching suggests that the relative proportion of these two forms varies and is correlated with membrane morphology. PMID:23663830

Quantitative analysis of self-association and mobility of annexin A4 at the plasma membrane.

PubMed

Crosby, Kevin C; Postma, Marten; Hink, Mark A; Zeelenberg, Christiaan H C; Adjobo-Hermans, Merel J W; Gadella, Theodorus W J

2013-05-07

Annexins, found in most eukaryotic species, are cytosolic proteins that are able to bind negatively-charged phospholipids in a calcium-dependent manner. Annexin A4 (AnxA4) has been implicated in diverse cellular processes, including the regulation of exocytosis and ion-transport; however, its precise mechanistic role is not fully understood. AnxA4 has been shown to aggregate on lipid layers upon Ca(2+) binding in vitro, a characteristic that may be critical for its function. We have utilized advanced fluorescence microscopy to discern details on the mobility and self-assembly of AnxA4 after Ca(2+) influx at the plasma membrane in living cells. Total internal reflection microscopy in combination with Förster resonance energy transfer reveals that there is a delay between initial plasma membrane binding and the beginning of self-assembly and this process continues after the cytoplasmic pool has completely relocated. Number-and-brightness analysis suggests that the predominant membrane bound mobile form of the protein is trimeric. There also exists a pool of AnxA4 that forms highly immobile aggregates at the membrane. Fluorescence recovery after photobleaching suggests that the relative proportion of these two forms varies and is correlated with membrane morphology. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Neutron Reflectometry Study of the Conformation of HIV Nef Bound to Lipid Membranes

PubMed Central

Kent, Michael S.; Murton, Jaclyn K.; Sasaki, Darryl Y.; Satija, Sushil; Akgun, Bulent; Nanda, Hirsh; Curtis, Joseph E.; Majewski, Jaroslaw; Morgan, Christopher R.; Engen, John R.

2010-01-01

Nef is an HIV-1 accessory protein that directly contributes to AIDS progression. Nef is myristoylated on the N-terminus, associates with membranes, and may undergo a transition from a solution conformation to a membrane-associated conformation. It has been hypothesized that conformational rearrangement enables membrane-associated Nef to interact with cellular proteins. Despite its medical relevance, to our knowledge there is no direct information about the conformation of membrane-bound Nef. In this work, we used neutron reflection to reveal what we believe are the first details of the conformation of membrane-bound Nef. The conformation of Nef was probed upon binding to Langmuir monolayers through the interaction of an N-terminal His tag with a synthetic metal-chelating lipid, which models one of the possible limiting cases for myr-Nef. The data indicate that residues are inserted into the lipid headgroups during interaction, and that the core domain lies directly against the lipid headgroups, with a thickness of ∼40 Å. Binding of Nef through the N-terminal His tag apparently facilitates insertion of residues, as no insertion occurred upon binding of Nef through weak electrostatic interactions in the absence of the specific interaction through the His tag. PMID:20858440

19F NMR studies provide insights into lipid membrane interactions of listeriolysin O, a pore forming toxin from Listeria monocytogenes.

PubMed

Kozorog, Mirijam; Sani, Marc-Antoine; Lenarčič Živković, Martina; Ilc, Gregor; Hodnik, Vesna; Separovic, Frances; Plavec, Janez; Anderluh, Gregor

2018-05-02

Listeria monocytogenes is a mammalian pathogen that causes gastroenteritis, miscarriages and infections of the central nervous system in immunocompromised individuals. Its main virulence factor is listeriolysin O (LLO), a pore-forming cholesterol-dependent cytolysin (CDC), which enables bacterial escape from the phagolysosome and contributes to bacterial pathogenicity. Details of cholesterol (Chol) recognition and membrane binding mechanisms by LLO are still not known. Here we used 19 F-NMR spectroscopy in order to assess LLO-Chol interactions in solution and in a Chol-rich membrane environment. LLO has six tryptophan residues located in the region of the molecule that is first in contact with lipid membranes. 19 F-LLO, which contained 5-fluoro-tryptophans, was prepared by using isotopic labelling in an E. coli expression system. Signals in the 19 F-NMR spectrum of 19 F-LLO were unambiguously assigned by using a series of single Trp → Phe point mutations. The results employing various cholesterol preparations in solution indicate that tryptophan residues are not directly involved in Chol binding in solution. However, significant chemical shift changes were observed upon LLO binding to Chol-rich membranes, highlighting the role of tryptophan residues in membrane interactions (W512) and oligomerisation (W189 and W489).

Endothelial cell membrane vesicles in the study of organ preference of metastasis.

PubMed

Johnson, R C; Augustin-Voss, H G; Zhu, D Z; Pauli, B U

1991-01-01

Many malignancies exhibit distinct patterns of metastasis that appear to be mediated by receptor/ligand-like interactions between tumor cells and organ-specific vascular endothelium. In order to study endothelial cell surface molecules involved in the binding of metastatic cells, we developed a perfusion method to isolate outside-out membrane vesicles from the lumenal surface of rat lung microvascular endothelium. Lungs were perfused in situ for 4 h at 37 degrees C with a solution of 100 mM formaldehyde, 2 mM dithiothreitol in phosphate-buffered saline to induce endothelial cell vesiculation. Radioiodinated rat lung endothelial cell membrane vesicles bound lung-metastatic tumor cells (B16F10, R323OAC-MET) in significantly higher numbers than their low or nonmetastatic counterparts (B16F0, R323OAC-LR). In contrast, leg endothelial membrane vesicle showed no binding preference for either cell line. Neuraminidase treatment of vesicles abolished specificity of adhesion of lung-derived vesicles to lung metastatic tumor cells. These results demonstrate that in situ perfusion is an appropriate technique to obtain pure endothelial cell membrane vesicles containing functionally active adhesion molecules. The preferential binding of lung-derived endothelial cell membrane vesicles by lung metastatic tumor cells is evidence of the importance of endothelial cell adhesion molecules in the formation of metastases.

The Sperm-surface glycoprotein, SGP, is necessary for fertilization in the frog, Xenopus laevis.

PubMed

Nagai, Keita; Ishida, Takuya; Hashimoto, Takafumi; Harada, Yuichirou; Ueno, Shuichi; Ueda, Yasushi; Kubo, Hideo; Iwao, Yasuhiro

2009-06-01

To identify a molecule involved in sperm-egg plasma membrane binding at fertilization, a monoclonal antibody against a sperm-surface glycoprotein (SGP) was obtained by immunizing mice with a sperm membrane fraction of the frog, Xenopus laevis, followed by screening of the culture supernatants based on their inhibitory activity against fertilization. The fertilization of both jellied and denuded eggs was effectively inhibited by pretreatment of sperm with intact anti-SGP antibody as well as its Fab fragment, indicating that the antibody recognizes a molecule on the sperm's surface that is necessary for fertilization. On Western blots, the anti-SGP antibody recognized large molecules, with molecular masses of 65-150 kDa and minor smaller molecules with masses of 20-28 kDa in the sperm membrane vesicles. SGP was distributed over nearly the entire surface of the sperm, probably as an integral membrane protein in close association with microfilaments. More membrane vesicles containing SGP bound to the surface were found in the animal hemisphere compared with the vegetal hemisphere in unfertilized eggs, but the vesicle-binding was not observed in fertilized eggs. These results indicate that SGP mediates sperm-egg membrane binding and is responsible for the establishment of fertilization in Xenopus.

Specific Adhesion of Lipid Membranes Can Simultaneously Produce Two Types of Lipid and Protein Heterogeneities

NASA Astrophysics Data System (ADS)

Shindell, Orrin; Micah, Natalie; Ritzer, Max; Gordon, Vernita

2015-03-01

Living cells adhere to one another and their environment. Adhesion is associated with re-organization of the lipid and protein components of the cell membrane. The resulting heterogeneities are functional structures involved in biological processes. We use artificial lipid membranes that contain a single type of binding protein. Before adhesion, the lipid, protein, and dye components in the membrane are well-mixed and constitute a single disordered-liquid phase (Ld) . After adhesion, two distinct types of heterogeneities coexist in the adhesion zone: a central domain of ordered lipid phase that excludes both binding proteins and membrane dye, and a peripheral domain of disordered lipid phase that is densely packed with adhesion proteins and enriched in membrane dye relative to the non-adhered portion of the vesicle. Thus, we show that adhesion that is mediated by only one type of protein can organize the lipid and protein components of the membranes into heterogeneities that resemble those found in biology, for example the immune synapse.

α-SNAP Interferes with the Zippering of the SNARE Protein Membrane Fusion Machinery

PubMed Central

Park, Yongsoo; Vennekate, Wensi; Yavuz, Halenur; Preobraschenski, Julia; Hernandez, Javier M.; Riedel, Dietmar; Walla, Peter Jomo; Jahn, Reinhard

2014-01-01

Neuronal exocytosis is mediated by soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. Before fusion, SNARE proteins form complexes bridging the membrane followed by assembly toward the C-terminal membrane anchors, thus initiating membrane fusion. After fusion, the SNARE complex is disassembled by the AAA-ATPase N-ethylmaleimide-sensitive factor that requires the cofactor α-SNAP to first bind to the assembled SNARE complex. Using chromaffin granules and liposomes we now show that α-SNAP on its own interferes with the zippering of membrane-anchored SNARE complexes midway through the zippering reaction, arresting SNAREs in a partially assembled trans-complex and preventing fusion. Intriguingly, the interference does not result in an inhibitory effect on synaptic vesicles, suggesting that membrane properties also influence the final outcome of α-SNAP interference with SNARE zippering. We suggest that binding of α-SNAP to the SNARE complex affects the ability of the SNARE complex to harness energy or transmit force to the membrane. PMID:24778182

Dietary fat and the diabetic state alter insulin binding and the fatty acyl composition of the adipocyte plasma membrane.

PubMed Central

Field, C J; Ryan, E A; Thomson, A B; Clandinin, M T

1988-01-01

Control and diabetic rats were fed on semi-purified high-fat diets providing a polyunsaturated/saturated fatty acid ratio (P/S) of 1.0 or 0.25, to examine the effect of diet on the fatty acid composition of major phospholipids of the adipocyte plasma membrane. Feeding the high-P/S diet (P/S = 1.0) compared with the low-P/S diet (P/S = 0.25) increased the content of polyunsaturated fatty acids in membrane phospholipids in both control and diabetic animals. The diabetic state decreased the content of polyunsaturated fatty acids, particularly arachidonic acid, in adipocyte membrane phospholipids. The decrease in arachidonic acid in membrane phospholipids of diabetic animals tended to be normalized to within the control values when high-P/S diets were given. For control animals, altered plasma-membrane composition was associated with change in insulin binding, suggesting that change in plasma-membrane composition may have physiological consequences for insulin-stimulated functions in the adipocyte. PMID:3052424

Multiplexed biomimetic lipid membranes on graphene by dip-pen nanolithography

PubMed Central

Hirtz, Michael; Oikonomou, Antonios; Georgiou, Thanasis; Fuchs, Harald; Vijayaraghavan, Aravind

2013-01-01

The application of graphene in sensor devices depends on the ability to appropriately functionalize the pristine graphene. Here we show the direct writing of tailored phospholipid membranes on graphene using dip-pen nanolithography. Phospholipids exhibit higher mobility on graphene compared with the commonly used silicon dioxide substrate, leading to well-spread uniform membranes. Dip-pen nanolithography allows for multiplexed assembly of phospholipid membranes of different functionalities in close proximity to each other. The membranes are stable in aqueous environments and we observe electronic doping of graphene by charged phospholipids. On the basis of these results, we propose phospholipid membranes as a route for non-covalent immobilization of various functional groups on graphene for applications in biosensing and biocatalysis. As a proof of principle, we demonstrate the specific binding of streptavidin to biotin-functionalized membranes. The combination of atomic force microscopy and binding experiments yields a consistent model for the layer organization within phospholipid stacks on graphene. PMID:24107937

Coupled diffusion processes and 2D affinities of adhesion molecules at synthetic membrane junctions

NASA Astrophysics Data System (ADS)

Peel, Christopher; Choudhuri, Kaushik; Schmid, Eva M.; Bakalar, Matthew H.; Ann, Hyoung Sook; Fletcher, Daniel A.; Journot, Celine; Turberfield, Andrew; Wallace, Mark; Dustin, Michael

A more complete understanding of the physically intrinsic mechanisms underlying protein mobility at cellular interfaces will provide additional insights into processes driving adhesion and organization in signalling junctions such as the immunological synapse. We observed diffusional slowing of structurally diverse binding proteins at synthetic interfaces formed by giant unilamellar vesicles (GUVs) on supported lipid bilayers (SLBs) that shows size dependence not accounted for by existing models. To model the effects of size and intermembrane spacing on interfacial reaction-diffusion processes, we describe a multistate diffusion model incorporating entropic effects of constrained binding. This can be merged with hydrodynamic theories of receptor-ligand diffusion and coupling to thermal membrane roughness. A novel synthetic membrane adhesion assay based on reversible and irreversible DNA-mediated interactions between GUVs and SLBs is used to precisely vary length, affinity, and flexibility, and also provides a platform to examine these effects on the dynamics of processes such as size-based segregation of binding and non-binding species.

Solid-phase receptor binding assay for /sup 125/I-hCG

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bortolussi, M.; Selmin, O.; Colombatti, A.

1987-01-01

A solid-phase radioligand-receptor assay (RRA) to measure the binding of /sup 125/I-labelled human chorionic gonadotropin (/sup 125/I-hCG) to target cell membranes has been developed. The binding of /sup 125/I-hCG to membranes immobilized on the wells of microtitration plates reached a maximum at about 3 hours at 37 degrees C, was saturable, displayed a high affinity (Ka = 2.4 X 10(9) M-1) and was specifically inhibited by unlabelled hCG. In comparison with RRAs carried out with membranes in suspension, the solid-phase RRA is significantly simpler and much faster to perform as it avoids centrifugation or filtration procedures. The solid-phase RRA wasmore » adapted profitably to process large numbers of samples at the same time. It proved particularly useful as a screening assay to detect anti-hCG monoclonal antibodies with high inhibitory activity for binding of /sup 125/I-hCG to its receptors.« less

Changes in tau phosphorylation in hibernating rodents.

PubMed

León-Espinosa, Gonzalo; García, Esther; García-Escudero, Vega; Hernández, Félix; Defelipe, Javier; Avila, Jesús

2013-07-01

Tau is a cytoskeletal protein present mainly in the neurons of vertebrates. By comparing the sequence of tau molecule among different vertebrates, it was found that the variability of the N-terminal sequence in tau protein is higher than that of the C-terminal region. The N-terminal region is involved mainly in the binding of tau to cellular membranes, whereas the C-terminal region of the tau molecule contains the microtubule-binding sites. We have compared the sequence of Syrian hamster tau with the sequences of other hibernating and nonhibernating rodents and investigated how differences in the N-terminal region of tau could affect the phosphorylation level and tau binding to cell membranes. We also describe a change, in tau phosphorylation, on a casein kinase 1 (ck1)-dependent site that is found only in hibernating rodents. This ck1 site seems to play an important role in the regulation of tau binding to membranes. Copyright © 2013 Wiley Periodicals, Inc.

Biochemical and pharmacological characterization of the thyrotropin releasing hormone (TRH) receptor from clonal GH sub 4 C sub 1 pituitary cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Phillips, W.J.

1987-01-01

The effect of drugs with anesthetic properties on the activity of the pituitary thyrotropin-releasing hormone (TRH) receptor was determined in the clonal GH{sub 4}C{sub 1} somatomammotropic cell line. Classic local anesthetics and other drugs with anesthetic activity inhibited binding of ({sup 3}H)methyl-TRH to cell receptors at concentrations known to produce anesthetic effects on the membrane. The inhibition of TRH receptor binding by tetracaine was competitive and temperature and pH dependent. Verapamil and tetracaine inhibited TRH-stimulated prolactin secretion at concentrations that inhibited peptide binding. TRH-stimulated prolactin secretion was equivalent with or without Ca{sup 2+} channel activity. Verapamil and tetracaine also inhibitedmore » basal prolactin and secretion stimulated by drugs that bypass membrane receptors, db-cAMP and TPA. These results indicate that inhibition of TRH binding and responses by diverse drugs results from an anesthetic effect on the cell membrane.« less

Host and viral RNA-binding proteins involved in membrane targeting, replication and intercellular movement of plant RNA virus genomes

PubMed Central

Hyodo, Kiwamu; Kaido, Masanori; Okuno, Tetsuro

2014-01-01

Many plant viruses have positive-strand RNA [(+)RNA] as their genome. Therefore, it is not surprising that RNA-binding proteins (RBPs) play important roles during (+)RNA virus infection in host plants. Increasing evidence demonstrates that viral and host RBPs play critical roles in multiple steps of the viral life cycle, including translation and replication of viral genomic RNAs, and their intra- and intercellular movement. Although studies focusing on the RNA-binding activities of viral and host proteins, and their associations with membrane targeting, and intercellular movement of viral genomes have been limited to a few viruses, these studies have provided important insights into the molecular mechanisms underlying the replication and movement of viral genomic RNAs. In this review, we briefly overview the currently defined roles of viral and host RBPs whose RNA-binding activity have been confirmed experimentally in association with their membrane targeting, and intercellular movement of plant RNA virus genomes. PMID:25071804

Host Cell Plasma Membrane Phosphatidylserine Regulates the Assembly and Budding of Ebola Virus

PubMed Central

Adu-Gyamfi, Emmanuel; Johnson, Kristen A.; Fraser, Mark E.; Scott, Jordan L.; Soni, Smita P.; Jones, Keaton R.; Digman, Michelle A.; Gratton, Enrico; Tessier, Charles R.

2015-01-01

ABSTRACT Lipid-enveloped viruses replicate and bud from the host cell where they acquire their lipid coat. Ebola virus, which buds from the plasma membrane of the host cell, causes viral hemorrhagic fever and has a high fatality rate. To date, little has been known about how budding and egress of Ebola virus are mediated at the plasma membrane. We have found that the lipid phosphatidylserine (PS) regulates the assembly of Ebola virus matrix protein VP40. VP40 binds PS-containing membranes with nanomolar affinity, and binding of PS regulates VP40 localization and oligomerization on the plasma membrane inner leaflet. Further, alteration of PS levels in mammalian cells inhibits assembly and egress of VP40. Notably, interactions of VP40 with the plasma membrane induced exposure of PS on the outer leaflet of the plasma membrane at sites of egress, whereas PS is typically found only on the inner leaflet. Taking the data together, we present a model accounting for the role of plasma membrane PS in assembly of Ebola virus-like particles. IMPORTANCE The lipid-enveloped Ebola virus causes severe infection with a high mortality rate and currently lacks FDA-approved therapeutics or vaccines. Ebola virus harbors just seven genes in its genome, and there is a critical requirement for acquisition of its lipid envelope from the plasma membrane of the human cell that it infects during the replication process. There is, however, a dearth of information available on the required contents of this envelope for egress and subsequent attachment and entry. Here we demonstrate that plasma membrane phosphatidylserine is critical for Ebola virus budding from the host cell plasma membrane. This report, to our knowledge, is the first to highlight the role of lipids in human cell membranes in the Ebola virus replication cycle and draws a clear link between selective binding and transport of a lipid across the membrane of the human cell and use of that lipid for subsequent viral entry. PMID:26136573

Fluorescent sensor systems based on nanostructured polymeric membranes for selective recognition of Aflatoxin B1.

PubMed

Sergeyeva, Tetyana; Yarynka, Daria; Piletska, Elena; Lynnik, Rostyslav; Zaporozhets, Olga; Brovko, Oleksandr; Piletsky, Sergey; El'skaya, Anna

2017-12-01

Nanostructured polymeric membranes for selective recognition of aflatoxin B1 were synthesized in situ and used as highly sensitive recognition elements in the developed fluorescent sensor. Artificial binding sites capable of selective recognition of aflatoxin B1 were formed in the structure of the polymeric membranes using the method of molecular imprinting. A composition of molecularly imprinted polymer (MIP) membranes was optimized using the method of computational modeling. The MIP membranes were synthesized using the non-toxic close structural analogue of aflatoxin B1, ethyl-2-oxocyclopentanecarboxylate as a dummy template. The MIP membranes with the optimized composition demonstrated extremely high selectivity towards aflatoxin B1 (AFB1). Negligible binding of close structural analogues of AFB1 - aflatoxins B2 (AFB2), aflatoxin G2 (AFG2), and ochratoxin A (OTA) was demonstrated. Binding of AFB1 by the MIP membranes was investigated as a function of both type and concentration of the functional monomer in the initial monomer composition used for the membranes' synthesis, as well as sample composition. The conditions of the solid-phase extraction of the mycotoxin using the MIP membrane as a stationary phase (pH, ionic strength, buffer concentration, volume of the solution, ratio between water and organic solvent, filtration rate) were optimized. The fluorescent sensor system based on the optimized MIP membranes provided a possibility of AFB1 detection within the range 14-500ngmL -1 demonstrating detection limit (3Ϭ) of 14ngmL -1 . The developed technique was successfully applied for the analysis of model solutions and waste waters from bread-making plants. Copyright © 2017 Elsevier B.V. All rights reserved.

Sigma opiates and certain antipsychotic drugs mutually inhibit (+)-[3H] SKF 10,047 and [3H]haloperidol binding in guinea pig brain membranes.

PubMed Central

Tam, S W; Cook, L

1984-01-01

The relationship between binding of antipsychotic drugs and sigma psychotomimetic opiates to binding sites for the sigma agonist (+)-[3H]SKF 10,047 (N-allylnormetazocine) and to dopamine D2 sites was investigated. In guinea pig brain membranes, (+)-[3H]SKF 10,047 bound to a single class of sites with a Kd of 4 X 10(-8) M and a Bmax of 333 fmol/mg of protein. This binding was different from mu, kappa, or delta opiate receptor binding. It was inhibited by opiates that produce psychotomimetic activities but not by opiates that lack such activities. Some antipsychotic drugs inhibited (+)-[3H]SKF 10,047 binding with high to moderate affinities in the following order of potency: haloperidol greater than perphenazine greater than fluphenazine greater than acetophenazine greater than trifluoperazine greater than molindone greater than or equal to pimozide greater than or equal to thioridazine greater than or equal to chlorpromazine greater than or equal to triflupromazine. However, there were other antipsychotic drugs such as spiperone and clozapine that showed low affinity for the (+)-[3H]SKF 10,047 binding sites. Affinities of antipsychotic drugs for (+)-[3H]SKF 10,047 binding sites did not correlate with those for [3H]spiperone (dopamine D2) sites. [3H]-Haloperidol binding in whole brain membranes was also inhibited by the sigma opiates pentazocine, cyclazocine, and (+)-SKF 10,047. In the striatum, about half of the saturable [3H]haloperidol binding was to [3H]spiperone (D2) sites and the other half was to sites similar to (+)-[3H]SKF 10,047 binding sites. PMID:6147851

Elution of viruses by ionic and nonionic surfactants.

PubMed Central

Fujito, B T; Lytle, C D

1996-01-01

The ionic and nonionic surfactants sodium dodecyl sulfate and Triton X-100, respectively, eluted two viruses, phi X174 and PRD1, which were adsorbed to the ionic and nonionic binding membranes cationic polysulfone and nitrocellulose, respectively. Results indicated that complete elution was readily achieved only when combinations of surfactants and binding membranes were matched (i.e., ionic-ionic or nonionic-nonionic). PMID:8795240

Acetylcholinesterase Chirality and Cellular Mechanisms of Organophosphonate Toxicity

DTIC Science & Technology

1990-06-11

toxin bind- FIG. 4. Decidium modulation of [’H]PCP binding to the Tor- ing. To address this question, we examined the concentration pedo membranes...increasing concen- pedo membranes. Here, meproadifen enhances carbamylcho- trations of decidium displace [3H]PCP, consistent with direct line...central a 2-adrenoceptors in the long lasting vasodepression elicited by the organophosphates was considered. Materials and Methods Cats of both sexes

Binding of Substrates to the Central Pore of the Vps4 ATPase Is Autoinhibited by the Microtubule Interacting and Trafficking (MIT) Domain and Activated by MIT Interacting Motifs (MIMs).

PubMed

Han, Han; Monroe, Nicole; Votteler, Jörg; Shakya, Binita; Sundquist, Wesley I; Hill, Christopher P

2015-05-22

The endosomal sorting complexes required for transport (ESCRT) pathway drives reverse topology membrane fission events within multiple cellular pathways, including cytokinesis, multivesicular body biogenesis, repair of the plasma membrane, nuclear membrane vesicle formation, and HIV budding. The AAA ATPase Vps4 is recruited to membrane necks shortly before fission, where it catalyzes disassembly of the ESCRT-III lattice. The N-terminal Vps4 microtubule-interacting and trafficking (MIT) domains initially bind the C-terminal MIT-interacting motifs (MIMs) of ESCRT-III subunits, but it is unclear how the enzyme then remodels these substrates in response to ATP hydrolysis. Here, we report quantitative binding studies that demonstrate that residues from helix 5 of the Vps2p subunit of ESCRT-III bind to the central pore of an asymmetric Vps4p hexamer in a manner that is dependent upon the presence of flexible nucleotide analogs that can mimic multiple states in the ATP hydrolysis cycle. We also find that substrate engagement is autoinhibited by the Vps4p MIT domain and that this inhibition is relieved by binding of either Type 1 or Type 2 MIM elements, which bind the Vps4p MIT domain through different interfaces. These observations support the model that Vps4 substrates are initially recruited by an MIM-MIT interaction that activates the Vps4 central pore to engage substrates and generate force, thereby triggering ESCRT-III disassembly. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

Binding of cationic pentapeptides with modified side chain lengths to negatively charged lipid membranes: Complex interplay of electrostatic and hydrophobic interactions.

PubMed

Hoernke, Maria; Schwieger, Christian; Kerth, Andreas; Blume, Alfred

2012-07-01

Basic amino acids play a key role in the binding of membrane associated proteins to negatively charged membranes. However, side chains of basic amino acids like lysine do not only provide a positive charge, but also a flexible hydrocarbon spacer that enables hydrophobic interactions. We studied the influence of hydrophobic contributions to the binding by varying the side chain length of pentapeptides with ammonium groups starting with lysine to lysine analogs with shorter side chains, namely omithine (Orn), alpha, gamma-diaminobutyric acid (Dab) and alpha, beta-diaminopropionic acid (Dap). The binding to negatively charged phosphatidylglycerol (PG) membranes was investigated by calorimetry, FT-infrared spectroscopy (FT-IR) and monolayer techniques. The binding was influenced by counteracting and sometimes compensating contributions. The influence of the bound peptides on the lipid phase behavior depends on the length of the peptide side chains. Isothermal titration calorimetry (ITC) experiments showed exothermic and endothermic effects compensating to a different extent as a function of side chain length. The increase in lipid phase transition temperature was more significant for peptides with shorter side chains. FTIR-spectroscopy revealed changes in hydration of the lipid bilayer interface after peptide binding. Using monolayer techniques, the contributions of electrostatic and hydrophobic effects could clearly be observed. Peptides with short side chains induced a pronounced decrease in surface pressure of PG monolayers whereas peptides with additional hydrophobic interactions decreased the surface pressure much less or even lead to an increase, indicating insertion of the hydrophobic part of the side chain into the lipid monolayer.

Binding of Substrates to the Central Pore of the Vps4 ATPase Is Autoinhibited by the Microtubule Interacting and Trafficking (MIT) Domain and Activated by MIT Interacting Motifs (MIMs)*

PubMed Central

Han, Han; Monroe, Nicole; Votteler, Jörg; Shakya, Binita; Sundquist, Wesley I.; Hill, Christopher P.

2015-01-01

The endosomal sorting complexes required for transport (ESCRT) pathway drives reverse topology membrane fission events within multiple cellular pathways, including cytokinesis, multivesicular body biogenesis, repair of the plasma membrane, nuclear membrane vesicle formation, and HIV budding. The AAA ATPase Vps4 is recruited to membrane necks shortly before fission, where it catalyzes disassembly of the ESCRT-III lattice. The N-terminal Vps4 microtubule-interacting and trafficking (MIT) domains initially bind the C-terminal MIT-interacting motifs (MIMs) of ESCRT-III subunits, but it is unclear how the enzyme then remodels these substrates in response to ATP hydrolysis. Here, we report quantitative binding studies that demonstrate that residues from helix 5 of the Vps2p subunit of ESCRT-III bind to the central pore of an asymmetric Vps4p hexamer in a manner that is dependent upon the presence of flexible nucleotide analogs that can mimic multiple states in the ATP hydrolysis cycle. We also find that substrate engagement is autoinhibited by the Vps4p MIT domain and that this inhibition is relieved by binding of either Type 1 or Type 2 MIM elements, which bind the Vps4p MIT domain through different interfaces. These observations support the model that Vps4 substrates are initially recruited by an MIM-MIT interaction that activates the Vps4 central pore to engage substrates and generate force, thereby triggering ESCRT-III disassembly. PMID:25833946

Bridging the gap between structural bioinformatics and receptor research: the membrane-embedded, ligand-gated, P2X glycoprotein receptor.

PubMed

Mager, Peter P; Weber, Anje; Illes, Peter

2004-01-01

No details on P2X receptor architecture had been known at the atomic resolution level. Using comparative homology-based molecular modelling and threading, it was attempted to predict the three-dimensional structure of P2X receptors. This prediction could not be carried out, however, because important properties of the P2X family differ considerably from that of the potential template proteins. This paper reviews an alternative approach consisting of three research fields: bioinformatics, structural modelling, and a variety of the results of biological experiments. Starting point is the amino acid sequence. Using the sequential data, the first step is a secondary structure prediction. The resulting secondary structure is converted into a three-dimensional geometry. Then, the secondary and tertiary structures are optimized by using the quantum chemistry RHF/3-21G minimal basic set and the all-atom molecular mechanics AMBER96 force field. The fold of the membrane-embedded protein is simulated by a suitable dielectricum. The structure is refined using a conjugate gradient minimizer (Fletcher-Reeves modification of the Polak-Ribiere method). The results of the geometry optimization were checked by a Ramanchandran plot, rotamer analysis, all-atom contact dots, and the C(beta) deviation. As additional tools for the model building, multiple alignment analysis and comparative sequence-function analysis were used. The approach is exemplified on the membrane-embedded, ligand-gated P2X3 receptor subunit, a monovalent-bivalent cation channel-forming glycoprotein that is activated by extracellular adenosine 5'-triphosphate. From these results, a topology of the pore-forming motif of the P2X3 receptor subunit was proposed. It is believed that a fully functional P2X channel requires a precise coupling between (i) two distinct peptide modules, an extracellularly occurring ATP-binding module and a pore module that includes a long transmembrane and short intracellular part, (ii) an interaction surface with membranes, and (iii) hydrogen bonding forces of the residues and hydrated cations. Furthermore, this paper demonstrates the role of quantitative structure-activity relationships (QSARs) in P2X research (calcium ion permeability of the wild-type and after site-directed mutagenesis of the rat P2X2 receptor protein, KN-62 analogs as competitive antagonists of the human P2X7 receptor). EXPERIMENTAL PROOFS: The predictions are experimentally testable and may provide an additional interpretation of experimental observations published in literature. In particular, there is the good agreement of the geometry optimized P2X3 structure with experimentally proposed P2X receptor models obtained by neurophysiological, biochemical, pharmacological, and mutation experiments. Although the rat P2X3 receptor subunit is more complex (397 amino acids) than the KcsA protein (160 amino acids), the overall folds of the peptide backbone atoms are similar. To avoid semantic confusion, it should be noted that "prediction" is defined in a probabilistic sense. Matches to generic rules do not mean "this is true" but rather "this might be true". Only biological and chemical knowledge can determine whether or not these predictions are meaningful. Thus, the results from the computational tools are probabilistic predictions and subject to further experimental verification. The geometry optimized P2X3 receptor subunit is freely available for academic researchers on e-mail request (PDB format).

The “gating” residues Ile199 and Tyr326 in human monoamine oxidase B function in substrate and inhibitor recognition

PubMed Central

Milczek, Erika M.; Binda, Claudia; Rovida, Stefano; Mattevi, Andrea; Edmondson, Dale E.

2011-01-01

Summary The major structural difference between human monoamine oxidases A (MAO A) and B (MAO B) is that MAO A has a monopartite substrate cavity of ~550 Å3 volume and MAO B contains a dipartite cavity structure with volumes of ~290 Å3 (entrance cavity) and ~400 Å3 (substrate cavity). Ile199 and Tyr326 side chains separate these two cavities in MAO B. To probe the function of these gating residues, Ile199Ala and Ile199Ala Tyr326Ala mutant forms of MAO B were investigated. Structural data on the Ile199Ala MAO B mutant show no alterations in active site geometries compared to WT enzyme while the Ile199Ala-Tyr326Ala MAO B mutant exhibits alterations in residues 100–103 which are part of the loop gating the entrance to the active site. Both mutant enzymes exhibit catalytic properties with increased amine KM but unaltered kcat values. The altered KM values on mutation are attributed to the influence of the cavity structure in the binding and subsequent deprotonation of the amine substrate. Both mutant enzymes exhibit weaker binding affinities relative to WT enzyme for small reversible inhibitors. Ile199Ala MAO B exhibits an increase in binding affinity for reversible MAO B specific inhibitors which bridge both cavities. The Ile199Ala-Tyr326Ala double mutant exhibits inhibitor binding properties more similar to those of MAO A than to MAO B. These results demonstrate the bipartite cavity structure in MAO B plays an important role in substrate and inhibitor recognition to distinguish its specificities from those of MAO A and provides insights into specific reversible inhibitor design for these membrane-bound enzymes. PMID:21978362

Comparison of cannabinoid binding sites in guinea-pig forebrain and small intestine

PubMed Central

Ross, Ruth A; Brockie, Heather C; Fernando, Susanthi R; Saha, Bijali; Razdan, Raj K; Pertwee, Roger G

1998-01-01

We have investigated the nature of cannabinoid receptors in guinea-pig small intestine by establishing whether this tissue contains cannabinoid receptors with similar binding properties to those of brain CB1 receptors. The cannabinoids used were the CB1-selective antagonist SR141716A, the CB2-selective antagonist SR144528, the novel cannabinoid receptor ligand, 6′-azidohex-2′-yne-Δ8-tetrahydrocannabinol (O-1184), and the agonists CP55940, which binds equally well to CB1 and CB2 receptors, and WIN55212-2, which shows marginal CB2 selectivity.[3H]-CP55940 (1 nM) underwent extensive specific binding both to forebrain membranes (76.3%) and to membranes obtained by sucrose density gradient fractionation of homogenates of myenteric plexus-longitudinal muscle of guinea-pig small intestine (65.2%).Its binding capacity (Bmax) was higher in forebrain (4281 fmol mg−1) than in intestinal membranes (2092 fmol mg−1). However, the corresponding KD values were not significantly different from each other (2.29 and 1.75 nM respectively). Nor did the Ki values for its displacement by CP55940, WIN55212-2, O-1184, SR141716A and SR144528 from forebrain membranes (0.87, 4.15, 2.85, 5.32 and 371.9 respectively) differ significantly from the corresponding Ki values determined in experiments with intestinal membranes (0.99, 5.03, 3.16, 4.95 and 361.5 nM respectively).The Bmax values of [3H]-CP55940 and [3H]-SR141716A in forebrain membranes did not differ significantly from each other (4281 and 5658 fmol mg−1) but were both greater than the Bmax of [3H]-WIN55212-2 (2032 fmol mg−1).O-1184 (10 or 100 nM) produced parallel dextral shifts in the log concentration-response curves of WIN55212-2 and CP55940 for inhibition of electrically-evoked contractions of the myenteric plexus-longitudinal muscle preparation, its KD values being 0.20 nM (against WIN55212-2) and 0.89 nM (against CP55940).We conclude that cannabinoid binding sites in guinea-pig small intestine closely resemble CB1 binding sites of guinea-pig brain and that O-1184 behaves as a cannabinoid receptor antagonist in the guinea-pig myenteric plexus-longitudinal muscle preparation. PMID:9863666

Crystal Structure of the Receptor Binding Domain of the botulinum C-D Mosiac Neurotoxin Reveals Potential Roles of Lysines 1118 and 1136 in Membrane Interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Y Zhang; G Buchko; L Qin

2011-12-31

The botulinum neurotoxins (BoNTs) produced by different strains of the bacterium Clostridium botulinum are responsible for the disease botulism and include a group of immunologically distinct serotypes (A, B, E, and F) that are considered to be the most lethal natural proteins known for humans. Two BoNT serotypes, C and D, while rarely associated with human infection, are responsible for deadly botulism outbreaks afflicting animals. Also associated with animal infections is the BoNT C-D mosaic protein (BoNT/CD), a BoNT subtype that is essentially a hybrid of the BoNT/C ({approx}two-third) and BoNT/D ({approx}one-third) serotypes. While the amino acid sequence of themore » heavy chain receptor binding (HCR) domain of BoNT/CD (BoNT/CD-HCR) is very similar to the corresponding amino acid sequence of BoNT/D, BoNT/CD-HCR binds synaptosome membranes better than BoNT/D-HCR. To obtain structural insights for the different membrane binding properties, the crystal structure of BoNT/CD-HCR (S867-E1280) was determined at 1.56 {angstrom} resolution and compared to previously reported structures for BoNT/D-HCR. Overall, the BoNT/CD-HCR structure is similar to the two sub-domain organization observed for other BoNT HCRs: an N-terminal jellyroll barrel motif and a C-terminal {beta}-trefoil fold. Comparison of the structure of BoNT/CD-HCR with BoNT/D-HCR indicates that K1118 has a similar structural role as the equivalent residue, E1114, in BoNT/D-HCR, while K1136 has a structurally different role than the equivalent residue, G1132, in BoNT/D-HCR. Lysine-1118 forms a salt bridge with E1247 and may enhance membrane interactions by stabilizing the putative membrane binding loop (K1240-N1248). Lysine-1136 is observed on the surface of the protein. A sulfate ion bound to K1136 may mimic a natural interaction with the negatively changed phospholipid membrane surface. Liposome-binding experiments demonstrate that BoNT/CD-HCR binds phosphatidylethanolamine liposomes more tightly than BoNT/D-HCR.« less

Crystal structure of the receptor binding domain of the botulinum C-D mosaic neurotoxin reveals potential roles of lysines 1118 and 1136 in membrane interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yanfeng; Buchko, Garry W.; Qin, Ling

2011-01-07

The botulinum neurotoxins (BoNTs) produced by different strains of the bacterium Clostridium botulinum are responsible for the disease botulism and include a group of immunologically distinct serotypes (A, B, E, and F) that are considered to be the most lethal natural proteins known for humans. Two BoNT serotypes, C and D, while rarely associated with human infection, are responsible for deadly botulism outbreaks afflicting animals. Also associated with animal infections is the BoNT C-D mosaic protein (BoNT/CD), a BoNT subtype that is essentially a hybrid of the BoNT/C (~two-thirds) and BoNT/D (~one-third) serotypes. While the amino acid sequence of themore » heavy chain receptor binding (HCR) domain of BoNT/CD (BoNT/CD-HCR) is very similar to the corresponding amino acid sequence of BoNT/D, BoNT/CD-HCR binds synaptosome membranes better than BoNT/D-HCR. To obtain structural insights for the different membrane binding properties, the crystal structure of BoNT/CD-HCR (S867-E1280) was determined at 1.56 Å resolution and compared to previously reported structures for BoNT/D-HCR. Overall, the BoNT/CD-HCR structure is similar to the two sub-domain organization observed for other BoNT HCRs: an N-terminal jellyroll barrel motif and a C-terminal β-trefoil fold. Comparison of the structure of BoNT/CD-HCR with BoNT/D-HCR indicates that K1118 has a similar structural role as the equivalent residue, E1114, in BoNT/D-HCR, while K1136 has a structurally different role than the equivalent residue, G1132, in BoNT/D-HCR. Lysine-1118 forms a salt bridge with E1247 and may enhance membrane interactions by stabilizing the putative membrane binding loop (K1240-N1248). Lysine-1136 is observed on the surface of the protein. A sulfate ion bound to K1136 may mimic a natural interaction with the negatively changed phospholipid membrane surface. Liposome-binding experiments demonstrate that BoNT/CD-HCR binds phosphatidylethanolamine liposomes more tightly than BoNT/D-HCR« less

Crystal structure of the receptor binding domain of the botulinum C-D mosaic neurotoxin reveals potential roles of lysines 1118 and 1136 in membrane interactions.

PubMed

Zhang, Yanfeng; Buchko, Garry W; Qin, Ling; Robinson, Howard; Varnum, Susan M

2011-01-07

The botulinum neurotoxins (BoNTs) produced by different strains of the bacterium Clostridium botulinum are responsible for the disease botulism and include a group of immunologically distinct serotypes (A, B, E, and F) that are considered to be the most lethal natural proteins known for humans. Two BoNT serotypes, C and D, while rarely associated with human infection, are responsible for deadly botulism outbreaks afflicting animals. Also associated with animal infections is the BoNT C-D mosaic protein (BoNT/CD), a BoNT subtype that is essentially a hybrid of the BoNT/C (∼two-third) and BoNT/D (∼one-third) serotypes. While the amino acid sequence of the heavy chain receptor binding (HCR) domain of BoNT/CD (BoNT/CD-HCR) is very similar to the corresponding amino acid sequence of BoNT/D, BoNT/CD-HCR binds synaptosome membranes better than BoNT/D-HCR. To obtain structural insights for the different membrane binding properties, the crystal structure of BoNT/CD-HCR (S867-E1280) was determined at 1.56 Å resolution and compared to previously reported structures for BoNT/D-HCR. Overall, the BoNT/CD-HCR structure is similar to the two sub-domain organization observed for other BoNT HCRs: an N-terminal jellyroll barrel motif and a C-terminal β-trefoil fold. Comparison of the structure of BoNT/CD-HCR with BoNT/D-HCR indicates that K1118 has a similar structural role as the equivalent residue, E1114, in BoNT/D-HCR, while K1136 has a structurally different role than the equivalent residue, G1132, in BoNT/D-HCR. Lysine-1118 forms a salt bridge with E1247 and may enhance membrane interactions by stabilizing the putative membrane binding loop (K1240-N1248). Lysine-1136 is observed on the surface of the protein. A sulfate ion bound to K1136 may mimic a natural interaction with the negatively changed phospholipid membrane surface. Liposome-binding experiments demonstrate that BoNT/CD-HCR binds phosphatidylethanolamine liposomes more tightly than BoNT/D-HCR. Copyright © 2010 Elsevier Inc. All rights reserved.

The A2 Adenosine Receptor: Guanine Nucleotide Modulation of Agonist Binding Is Enhanced by Proteolysis

PubMed Central

NANOFF, CHRISTIAN; JACOBSON, KENNETH A.; STILES, GARY L.

2012-01-01

SUMMARY Agonist binding to the A2 adenosine receptor (A2AR) and its regulation by guanine nucleotides was studied using the newly developed radioligand 125l-2-[4-(2-{2-[(4-ammnophenyl)methylcarbonylamino]ethylaminnocarbonyl}ethyl)phenyl]ethylamino-5′-N-ethylcarboxamidoadenosine (1251-PAPA-APEC) and its photoaffinity analog 125l-azido-PAPA-APEC. A single protein of Mr 45,000, displaying the appropriate A2AR pharmacology, is Iabeled in membranes from bovine striatum, PC12 cells, and frog erythrocytes. In DDT1 MF2 cells the labeled protein has a slightly lower molecular weight. Incorporation of 125l-azido-PAPA-APEC into membranes from rabbit striatum, however, reveals two specifically labeled peptides (Mr ~47,O00 and 38,000), both of which display A2AR pharmacology. Inhibition of protease activity leads to a decrease in the amount of the Mr 38,000 protein, with only the Mr 47,000 protein remaining. This suggests that the Mr 38,000 peptide is a proteolytic product of the Mr 47,000 A2AR protein. In membranes containing the intact undigested A2AR protein, guanine nucleotides induce a small to insignificant decrease in agonist binding, which is atypical of stimulatory Gs-coupled receptors. This minimal effect is observed in rabbit striatal membranes prepared in the presence of protease inhibitors, as well as in the other tissues studied. Binding to rabbit stnatal membranes that possess the partially digested receptor protein, however, reveals a 50% reduction in maximal specific agonist binding upon addition of guanine nucleotides. Inhibition of proteolysis in rabbit striatum, on the other hand, results in a diminished ability of guanine nucleotides to regulate agonist binding. Thus, the enhanced effectiveness of guanine nucleotides in rabbit striatal membranes is associated with the generation of the Mr 38,000 peptide fragment. Guanosine 5′-(β,γ-imido)triphosphate reduces photoaffinity labeling by 55% in the Mr 38,000 protein, whereas the labeling is decreased by only 28% in the Mr 47,000 receptor protein. Our data, therefore, suggest that, unless proteolysis occurs, the A2AR in all tissues studied is tightly associated with the Gs protein and displays minimal guanine nucleotide modulation of agonist binding, which makes the A2AR an atypical stimulatory receptor. PMID:1899902

DOE Office of Scientific and Technical Information (OSTI.GOV)

Olsen, Brett N.; Bielska, Agata; Lee, Tiffany

Although the majority of free cellular cholesterol is present in the plasma membrane, cholesterol homeostasis is principally regulated through sterol-sensing proteins that reside in the cholesterol-poor endoplasmic reticulum (ER). In response to acute cholesterol loading or depletion, there is rapid equilibration between the ER and plasma membrane cholesterol pools, suggesting a biophysical model in which the availability of plasma membrane cholesterol for trafficking to internal membranes modulates ER membrane behavior. Previous studies have predominantly examined cholesterol availability in terms of binding to extramembrane acceptors, but have provided limited insight into the structural changes underlying cholesterol activation. In this study, wemore » use both molecular dynamics simulations and experimental membrane systems to examine the behavior of cholesterol in membrane bilayers. We find that cholesterol depth within the bilayer provides a reasonable structural metric for cholesterol availability and that this is correlated with cholesterol-acceptor binding. Further, the distribution of cholesterol availability in our simulations is continuous rather than divided into distinct available and unavailable pools. This data provide support for a revised cholesterol activation model in which activation is driven not by saturation of membrane-cholesterol interactions but rather by bulk membrane remodeling that reduces membrane-cholesterol affinity.« less

Mouse SLLP1, a sperm lysozyme-like protein involved in sperm-egg binding and fertilization.

PubMed

Herrero, María Belén; Mandal, Arabinda; Digilio, Laura C; Coonrod, Scott A; Maier, Bernhard; Herr, John C

2005-08-01

This study demonstrates the retention of mouse sperm lysozyme-like protein (mSLLP1) in the equatorial segment of spermatozoa following the acrosome reaction and a role for mSLLP1 in sperm-egg binding and fertilization. Treatment of cumulus intact oocytes with either recmSLLP1 or its antiserum resulted in a significant (P < or = 0.05) inhibition of fertilization. Co-incubation of zona-free mouse oocytes with capacitated mouse spermatozoa in the presence of varying concentrations of anti-recmSLLP1 serum or recmSLLP1 also inhibited sperm-oolemma binding. A complete inhibition of binding and fusion of spermatozoa to the oocyte occurred at 12.5 muM concentration of recmSLLP1, while conventional chicken and human lysozymes did not block sperm-egg binding. mSLLP1 showed receptor sites in the perivitelline space as well as on the microvillar region of the egg plasma membrane. The retention of mSLLP1 in the equatorial segment of acrosome-reacted sperm, the inhibitory effects of both recmSLLP1 and antibodies to SLLP1 on in vitro fertilization with both cumulus intact and zona-free eggs, and the definition of complementary SLLP1-binding sites on the egg plasma membrane together support the hypothesis that a c lysozyme-like protein is involved in the binding of spermatozoa to the egg plasma membrane during fertilization.

Unveiling Stability Criteria of DNA-Carbon Nanotubes Constructs by Scanning Tunneling Microscopy and Computational Modeling

DOE PAGES

Kilina, Svetlana; Yarotski, Dzmitry A.; Talin, A. Alec; ...

2011-01-01

We present a combined approach that relies on computational simulations and scanning tunneling microscopy (STM) measurements to reveal morphological properties and stability criteria of carbon nanotube-DNA (CNT-DNA) constructs. Application of STM allows direct observation of very stable CNT-DNA hybrid structures with the well-defined DNA wrapping angle of 63.4 ° and a coiling period of 3.3 nm. Using force field simulations, we determine how the DNA-CNT binding energy depends on the sequence and binding geometry of a single strand DNA. This dependence allows us to quantitatively characterize the stability of a hybrid structure with an optimal π-stacking between DNA nucleotides and themore » tube surface and better interpret STM data. Our simulations clearly demonstrate the existence of a very stable DNA binding geometry for (6,5) CNT as evidenced by the presence of a well-defined minimum in the binding energy as a function of an angle between DNA strand and the nanotube chiral vector. This novel approach demonstrates the feasibility of CNT-DNA geometry studies with subnanometer resolution and paves the way towards complete characterization of the structural and electronic properties of drug-delivering systems based on DNA-CNT hybrids as a function of DNA sequence and a nanotube chirality.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fedynyshyn, J.P.

The opioid binding characteristics of the rat (PAG) and the signal transduction mechanisms of the opioid receptors were examined with in vitro radioligand binding, GTPase, adenylyl cyclase, and inositol phosphate assays. The nonselective ligand {sup 3}H-ethylketocyclazocine (EKC), the {mu} and {delta} selective ligand {sup 3}H-(D-Ala{sup 2}, D-Leu{sup 5}) enkephalin (DADLE), the {mu} selective ligand {sup 3}H-(D-Ala{sup 2}, N-methyl Phe{sup 4}, Glyol{sup 5}) enkephalin (DAGO), and the {delta} selective ligand {sup 3}H-(D-Pen{sup 2}, D-Pen{sup 5}) enkephalin (DPDPE) were separately used as tracer ligands to label opioid binding sites in rat PAG enriched P{sub 2} membrane in competition with unlabeled DADLE, DAGO,more » DPDPE, or the {kappa} selective ligand trans-3,4-dichloro-N-(2-(1-pyrrolidinyl)cyclohexyl)benzeneacetamide, methane sulfonate, hydrate (U50, 488H). Only {mu} selective high affinity opioid binding was observed. No high affinity {delta} or {kappa} selective binding was detected. {sup 3}H-DAGO was used as a tracer ligand to label {mu} selective high affinity opioid binding sites in PAG enriched P{sub 2} membrane in competition with unlabeled {beta}-endorphin, dynorphin A (1-17), BAM-18, methionine enkephalin, dynorphin A (1-8), and leucine enkephalin. Of these endogenous opioid peptides only those with previously reported high affinity {mu} type opioid binding activity competed with {sup 3}H-DAGO for binding sites in rat PAG enriched P{sub 2} membrane with affinities similar to that of unlabeled DAGO.« less

Class B type I scavenger receptor is responsible for the high affinity cholesterol binding activity of intestinal brush border membrane vesicles

PubMed Central

Labonté, Eric D.; Howles, Philip N.; Granholm, Norman A.; Rojas, Juan C.; Davies, Joanna P.; Ioannou, Yiannis A.; Hui, David Y.

2007-01-01

Recent studies have documented the importance of Niemann Pick C1-like 1 protein (NPC1L1), a putative physiological target of the drug ezetimibe, in mediating intestinal cholesterol absorption. However, whether NPC1L1 is the high affinity cholesterol binding protein on intestinal brush border membranes is still controversial. In this study, brush border membrane vesicles (BBMV) from wild type and NPC1L1−/− mice were isolated and assayed for micellar cholesterol binding in the presence or absence of ezetimibe. Results confirmed the loss of the high affinity component of cholesterol binding when wild type BBMV preparations were incubated with antiserum against the class B type 1 scavenger receptor (SR-BI) in the reaction mixture similar to previous studies. Subsequently, second order binding of cholesterol was observed with BBMV from wild type and NPC1L1−/− mice. The inclusion of ezetimibe in these in vitro reaction assays resulted in the loss of the high affinity component of cholesterol interaction. Surprisingly, BBMVs from NPC1L1−/− mice maintained active binding of cholesterol. These results documented that SR-BI, not NPC1L1, is the major protein responsible for the initial high affinity cholesterol ligand binding process in the cholesterol absorption pathway. Additionally, ezetimibe may inhibit BBM cholesterol binding through targets such as SR-BI in addition to its inhibition of NPC1L1. PMID:17442616

Affinity reagent technology development and application to rapid immunochromatographic pathogen detection

NASA Astrophysics Data System (ADS)

Sooter, Letha J.; Stratis-Cullum, Dimitra N.; Zhang, Yanting; Daugherty, Patrick S.; Soh, H. Tom; Pellegrino, Paul; Stagliano, Nancy

2007-09-01

Immunochromatography is a rapid, reliable, and cost effective method of detecting biowarfare agents. The format is similar to that of an over-the-counter pregnancy test. A sample is applied to one end of a cassette and then a control line, and possibly a sample line, are visualized at the other end of the cassette. The test is based upon a sandwich assay. For the control, a line of Protein A is immobilized on the membrane. Gold nanoparticle bound IgG flows through the membrane and binds the Protein A, creating a visible line on the membrane. For the sample, one epitope is immobilized on the membrane and another epitope is attached to gold nanoparticles. The sample binds gold bound epitope, travels through the membrane, and binds membrane bound epitope. The two epitopes are not cross-reactive, therefore a sample line is only visible if the sample is present. In order to efficiently screen for binders to a sample target, a novel, Continuous Magnetic Activated Cell Sorter (CMACS) has been developed on a disposable, microfluidic platform. The CMACS chip quickly sorts E. coli peptide libraries for target binders with high affinity. Peptide libraries, are composed of approximately ten million bacteria, each displaying a different peptide on their surface. The target of interest is conjugated to a micrometer sized magnetic particle. After the library and the target are incubated together to allow binding, the mixture is applied to the CMACS chip. In the presence of patterned nickel and an external magnet, separation occurs of the bead-bound bacteria from the bulk material. The bead fraction is added to bacterial growth media where any attached E. coli grow and divide. These cells are cloned, sequenced, and the peptides are assayed for target binding affinity. As a proof-of-principle, assays were developed for human C-reactive protein. More defense relevant targets are currently being pursued.

Munc13-4 Is a Rab11-binding Protein That Regulates Rab11-positive Vesicle Trafficking and Docking at the Plasma Membrane.

PubMed

Johnson, Jennifer L; He, Jing; Ramadass, Mahalakshmi; Pestonjamasp, Kersi; Kiosses, William B; Zhang, Jinzhong; Catz, Sergio D

2016-02-12

The small GTPase Rab11 and its effectors control trafficking of recycling endosomes, receptor replenishment and the up-regulation of adhesion and adaptor molecules at the plasma membrane. Despite recent advances in the understanding of Rab11-regulated mechanisms, the final steps mediating docking and fusion of Rab11-positive vesicles at the plasma membrane are not fully understood. Munc13-4 is a docking factor proposed to regulate fusion through interactions with SNAREs. In hematopoietic cells, including neutrophils, Munc13-4 regulates exocytosis in a Rab27a-dependent manner, but its possible regulation of other GTPases has not been explored in detail. Here, we show that Munc13-4 binds to Rab11 and regulates the trafficking of Rab11-containing vesicles. Using a novel Time-resolved Fluorescence Resonance Energy Transfer (TR-FRET) assay, we demonstrate that Munc13-4 binds to Rab11a but not to dominant negative Rab11a. Immunoprecipitation analysis confirmed the specificity of the interaction between Munc13-4 and Rab11, and super-resolution microscopy studies support the interaction of endogenous Munc13-4 with Rab11 at the single molecule level in neutrophils. Vesicular dynamic analysis shows the common spatio-temporal distribution of Munc13-4 and Rab11, while expression of a calcium binding-deficient mutant of Munc13-4 significantly affected Rab11 trafficking. Munc13-4-deficient neutrophils showed normal endocytosis, but the trafficking, up-regulation, and retention of Rab11-positive vesicles at the plasma membrane was significantly impaired. This correlated with deficient NADPH oxidase activation at the plasma membrane in response to Rab11 interference. Our data demonstrate that Munc13-4 is a Rab11-binding partner that regulates the final steps of Rab11-positive vesicle docking at the plasma membrane. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Evaluation of the rate constants of sugar transport through maltoporin (LamB) of Escherichia coli from the sugar-induced current noise

PubMed Central

1995-01-01

LamB (maltoporin) of Escherichia coli outer membrane was reconstituted into artificial lipid bilayer membranes. The channel contains a binding site for sugars and is blocked for ions when the site is occupied by a sugar. The on and off reactions of sugar binding cause an increase of the noise of the current through the channel. The sugar-induced current noise of maltoporin was used for the evaluation of the sugar-binding kinetics for different sugars of the maltooligosaccharide series and for sucrose. The on rate constant for sugar binding was between 10(6) and 10(7) M-1.s-1 for the maltooligosaccharides and corresponds to the movement of the sugars from the aqueous phase to the central binding site. The off rate (corresponding to the release of the sugars from the channel) decreased with increasing number of glucose residues in the maltooligosaccharides from approximately 2,000 s-1 for maltotriose to 180 s-1 for maltoheptaose. The kinetics for sucrose movement was considerably slower. The activation energies of the stability constant and of the rate constants for sugar binding were evaluated from noise experiments at different temperatures. The role of LamB in the transport of maltooligosaccharides across the outer membrane is discussed. PMID:7539481

Unbinding Pathways of an Agonist and an Antagonist from the 5-HT3 Receptor

PubMed Central

Thompson, A. J.; Chau, P.-L.; Chan, S. L.; Lummis, S. C. R.

2006-01-01

The binding sites of 5-HT3 and other Cys-loop receptors have been extensively studied, but there are no data on the entry and exit routes of ligands for these sites. Here we have used molecular dynamics simulations to predict the pathway for agonists and antagonists exiting from the 5-HT3 receptor binding site. The data suggest that the unbinding pathway follows a tunnel at the interface of two subunits, which is ∼8 Å long and terminates ∼20 Å above the membrane. The exit routes for an agonist (5-HT) and an antagonist (granisetron) were similar, with trajectories toward the membrane and outward from the ligand binding site. 5-HT appears to form many hydrogen bonds with residues in the unbinding pathway, and experiments show that mutating these residues significantly affects function. The location of the pathway is also supported by docking studies of granisetron, which show a potential binding site for granisetron on the unbinding route. We propose that leaving the binding pocket along this tunnel places the ligands close to the membrane and prevents their immediate reentry into the binding pocket. We anticipate similar exit pathways for other members of the Cys-loop receptor family. PMID:16387779

A Plasmodium falciparum copper-binding membrane protein with copper transport motifs

PubMed Central

2012-01-01

Background Copper is an essential catalytic co-factor for metabolically important cellular enzymes, such as cytochrome-c oxidase. Eukaryotic cells acquire copper through a copper transport protein and distribute intracellular copper using molecular chaperones. The copper chelator, neocuproine, inhibits Plasmodium falciparum ring-to-trophozoite transition in vitro, indicating a copper requirement for malaria parasite development. How the malaria parasite acquires or secretes copper still remains to be fully elucidated. Methods PlasmoDB was searched for sequences corresponding to candidate P. falciparum copper-requiring proteins. The amino terminal domain of a putative P. falciparum copper transport protein was cloned and expressed as a maltose binding fusion protein. The copper binding ability of this protein was examined. Copper transport protein-specific anti-peptide antibodies were generated in chickens and used to establish native protein localization in P. falciparum parasites by immunofluorescence microscopy. Results Six P. falciparum copper-requiring protein orthologs and a candidate P. falciparum copper transport protein (PF14_0369), containing characteristic copper transport protein features, were identified in PlasmoDB. The recombinant amino terminal domain of the transport protein bound reduced copper in vitro and within Escherichia coli cells during recombinant expression. Immunolocalization studies tracked the copper binding protein translocating from the erythrocyte plasma membrane in early ring stage to a parasite membrane as the parasites developed to schizonts. The protein appears to be a PEXEL-negative membrane protein. Conclusion Plasmodium falciparum parasites express a native protein with copper transporter characteristics that binds copper in vitro. Localization of the protein to the erythrocyte and parasite plasma membranes could provide a mechanism for the delivery of novel anti-malarial compounds. PMID:23190769

Epithelial chloride channel. Development of inhibitory ligands

PubMed Central

1987-01-01

Chloride channels are present in the majority of epithelial cells, where they mediate absorption or secretion of NaCl. Although the absorptive and secretory channels are well characterized in terms of their electrophysiological behavior, there is a lack of pharmacological ligands that can aid us in further functional and eventually molecular characterization. To obtain such ligands, we prepared membrane vesicles from bovine kidney cortex and apical membrane vesicles from trachea and found that they contain a chloride transport process that is electrically conductive. This conductance was reduced by preincubating the vesicles in media containing ATP or ATP-gamma-S, but not beta- methylene ATP, which suggests that the membranes contain a kinase that can close the channels. We then screened compounds derived from three classes: indanyloxyacetic acid (IAA), anthranilic acid (AA), and ethacrynic acid. We identified potent inhibitors from the IAA and the AA series. We tritiated IAA-94 and measured binding of this ligand to the kidney cortex membrane vesicles and found a high-affinity binding site whose dissociation constant (0.6 microM) was similar to the inhibition constant (1 microM). There was a good correlation between the inhibitory potency of several IAA derivatives and their efficacy in displacing [3H]IAA-94 from its binding site. Further, other chloride channel inhibitors, including AA derivatives, ethacrynic acid, bumetanide, and DIDS, also displaced the ligand from its binding site. A similar conductance was found in apical membrane vesicles from bovine trachea that was also inhibited by IAA-94 and AA-130B, but the inhibitory effects of these compounds were weaker than their effects on the renal cortex channel. The two drugs were also less potent in displacing [3H]IAA-94 from the tracheal binding site. PMID:2450168

Abnormal swelling of the peritrophic membrane in Eri silkworm gut caused by MLX56 family defense proteins with chitin-binding and extensin domains.

PubMed

Konno, Kotaro; Shimura, Sachiko; Ueno, Chihiro; Arakawa, Toru; Nakamura, Masatoshi

2018-03-01

MLX56 family defense proteins, MLX56 and its close homolog LA-b, are chitin-binding defense proteins found in mulberry latex that show strong growth-inhibitions against caterpillars when fed at concentrations as low as 0.01%. MLX56 family proteins contain a unique structure with an extensin domain surrounded by two hevein-like chitin-binding domains, but their defensive modes of action remain unclear. Here, we analyzed the effects of MLX56 family proteins on the peritrophic membrane (PM), a thin and soft membrane consisting of chitin that lines the midgut lumen of insects. We observed an abnormally thick (>1/5 the diameter of midgut) hard gel-like membrane consisted of chitin and MLX56 family proteins, MLX56 and LA-b, in the midgut of the Eri silkworms, Samia ricini, fed a diet containing MLX56 family proteins, MLX56 and LA-b. When polyoxin AL, a chitin-synthesis-inhibitor, was added to the diet containing MLX56 family proteins, the toxicity of MLX56 family proteins disappeared and PM became thinner and fragmented. These results suggest that MLX56 family proteins, through their chitin-binding domains, bind to the chitin framework of PM, then through their extensin-domain (gum arabic-like structure), which functions as swelling agent, expands PM into an abnormally thick membrane that inhibits the growth of insects. This study shows that MLX56 family proteins are plant defense lectins with a totally unique mode of action, and reveals the functions of extensin domains and arabinogalactan proteins as swelling (gel-forming) agents of plants. Copyright © 2018 Elsevier Ltd. All rights reserved.

Quantification of Ligand Binding to G-Protein Coupled Receptors on Cell Membranes by Ellipsometry

PubMed Central

Kriechbaumer, Verena; Nabok, Alexei; Widdowson, Robert; Smith, David P.; Abell, Ben M.

2012-01-01

G-protein-coupled receptors (GPCRs) are prime drug targets and targeted by approximately 60% of current therapeutic drugs such as β-blockers, antipsychotics and analgesics. However, no biophysical methods are available to quantify their interactions with ligand binding in a native environment. Here, we use ellipsometry to quantify specific interactions of receptors within native cell membranes. As a model system, the GPCR-ligand CXCL12α and its receptor CXCR4 are used. Human-derived Ishikawa cells were deposited onto gold coated slides via Langmuir-Schaefer film deposition and interactions between the receptor CXCR4 on these cells and its ligand CXCL12α were detected via total internal reflection ellipsometry (TIRE). This interaction could be inhibited by application of the CXCR4-binding drug AMD3100. Advantages of this approach are that it allows measurement of interactions in a lipid environment without the need for labelling, protein purification or reconstitution of membrane proteins. This technique is potentially applicable to a wide variety of cell types and their membrane receptors, providing a novel method to determine ligand or drug interactions targeting GPCRs and other membrane proteins. PMID:23049983

Endocytosis and membrane receptor internalization: implication of F-BAR protein Carom.

PubMed

Xu, Yanjie; Xia, Jixiang; Liu, Suxuan; Stein, Sam; Ramon, Cueto; Xi, Hang; Wang, Luqiao; Xiong, Xinyu; Zhang, Lixiao; He, Dingwen; Yang, William; Zhao, Xianxian; Cheng, Xiaoshu; Yang, Xiaofeng; Wang, Hong

2017-03-01

Endocytosis is a cellular process mostly responsible for membrane receptor internalization. Cell membrane receptors bind to their ligands and form a complex which can be internalized. We previously proposed that F-BAR protein initiates membrane curvature and mediates endocytosis via its binding partners. However, F-BAR protein partners involved in membrane receptor endocytosis and the regulatory mechanism remain unknown. In this study, we established database mining strategies to explore mechanisms underlying receptor-related endocytosis. We identified 34 endocytic membrane receptors and 10 regulating proteins in clathrin-dependent endocytosis (CDE), a major process of membrane receptor internalization. We found that F-BAR protein FCHSD2 (Carom) may facilitate endocytosis via 9 endocytic partners. Carom is highly expressed, along with highly expressed endocytic membrane receptors and partners, in endothelial cells and macrophages. We established 3 models of Carom-receptor complexes and their intracellular trafficking based on protein interaction and subcellular localization. We conclude that Carom may mediate receptor endocytosis and transport endocytic receptors to the cytoplasm for receptor signaling and lysosome/proteasome degradation, or to the nucleus for RNA processing, gene transcription and DNA repair.

Supported Lipid Bilayer/Carbon Nanotube Hybrids

NASA Astrophysics Data System (ADS)

Zhou, Xinjian; Moran-Mirabal, Jose; Craighead, Harold; McEuen, Paul

2007-03-01

We form supported lipid bilayers on single-walled carbon nanotubes and use this hybrid structure to probe the properties of lipid membranes and their functional constituents. We first demonstrate membrane continuity and lipid diffusion over the nanotube. A membrane-bound tetanus toxin protein, on the other hand, sees the nanotube as a diffusion barrier whose strength depends on the diameter of the nanotube. Finally, we present results on the electrical detection of specific binding of streptavidin to biotinylated lipids with nanotube field effect transistors. Possible techniques to extract dynamic information about the protein binding events will also be discussed.

Fast gradient HPLC method to determine compounds binding to human serum albumin. Relationships with octanol/water and immobilized artificial membrane lipophilicity.

PubMed

Valko, Klara; Nunhuck, Shenaz; Bevan, Chris; Abraham, Michael H; Reynolds, Derek P

2003-11-01

A fast gradient HPLC method (cycle time 15 min) has been developed to determine Human Serum Albumin (HSA) binding of discovery compounds using chemically bonded protein stationary phases. The HSA binding values were derived from the gradient retention times that were converted to the logarithm of the equilibrium constants (logK HSA) using data from a calibration set of molecules. The method has been validated using literature plasma protein binding data of 68 known drug molecules. The method is fully automated, and has been used for lead optimization in more than 20 company projects. The HSA binding data obtained for more than 4000 compounds were suitable to set up global and project specific quantitative structure binding relationships that helped compound design in early drug discovery. The obtained HSA binding of known drug molecules were compared to the Immobilized Artificial Membrane binding data (CHI IAM) obtained by our previously described HPLC-based method. The solvation equation approach has been used to characterize the normal binding ability of HSA, and this relationship shows that compound lipophilicity is a significant factor. It was found that the selectivity of the "baseline" lipophilicity governing HSA binding, membrane interaction, and octanol/water partition are very similar. However, the effect of the presence of positive or negative charges have very different effects. It was found that negatively charged compounds bind more strongly to HSA than it would be expected from the lipophilicity of the ionized species at pH 7.4. Several compounds showed stronger HSA binding than can be expected from their lipophilicity alone, and comparison between predicted and experimental binding affinity allows the identification of compounds that have good complementarities with any of the known binding sites. Copyright 2003 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:2236-2248, 2003

Characterization of auxin-binding proteins from zucchini plasma membrane

NASA Technical Reports Server (NTRS)

Hicks, G. R.; Rice, M. S.; Lomax, T. L.

1993-01-01

We have previously identified two auxin-binding polypeptides in plasma membrane (PM) preparations from zucchini (Cucurbita pepo L.) (Hicks et al. 1989, Proc. Natl. Acad. Sci. USA 86, 4948-4952). These polypeptides have molecular weights of 40 kDa and 42 kDa and label specifically with the photoaffinity auxin analog 5-N3-7-3H-IAA (azido-IAA). Azido-IAA permits both the covalent and radioactive tagging of auxin-binding proteins and has allowed us to characterize further the 40-kDa and 42-kDa polypeptides, including the nature of their attachment to the PM, their relationship to each other, and their potential function. The azido-IAA-labeled polypeptides remain in the pelleted membrane fraction following high-salt and detergent washes, which indicates a tight and possibly integral association with the PM. Two-dimensional electrophoresis of partially purified azido-IAA-labeled protein demonstrates that, in addition to the major isoforms of the 40-kDa and 42-kDa polypeptides, which possess isoelectric points (pIs) of 8.2 and 7.2, respectively, several less abundant isoforms that display unique pIs are apparent at both molecular masses. Tryptic and chymotryptic digestion of the auxin-binding proteins indicates that the 40-kDa and 42-kDa polypeptides are closely related or are modifications of the same polypeptide. Phase extraction with the nonionic detergent Triton X-114 results in partitioning of the azido-IAA-labeled polypeptides into the aqueous (hydrophilic) phase. This apparently paradoxical behavior is also exhibited by certain integral membrane proteins that aggregate to form channels. The results of gel filtration indicate that the auxin-binding proteins do indeed aggregate strongly and that the polypeptides associate to form a dimer or multimeric complex in vivo. These characteristics are consistent with the hypothesis that the 40-kDa and 42-kDa polypeptides are subunits of a multimeric integral membrane protein which has an auxin-binding site, and which may possess transporter or channel function.

Characterization of auxin-binding proteins from zucchini plasma membrane.

PubMed

Hicks, G R; Rice, M S; Lomax, T L

1993-01-01

We have previously identified two auxin-binding polypeptides in plasma membrane (PM) preparations from zucchini (Cucurbita pepo L.) (Hicks et al. 1989, Proc. Natl. Acad. Sci. USA 86, 4948-4952). These polypeptides have molecular weights of 40 kDa and 42 kDa and label specifically with the photoaffinity auxin analog 5-N3-7-3H-IAA (azido-IAA). Azido-IAA permits both the covalent and radioactive tagging of auxin-binding proteins and has allowed us to characterize further the 40-kDa and 42-kDa polypeptides, including the nature of their attachment to the PM, their relationship to each other, and their potential function. The azido-IAA-labeled polypeptides remain in the pelleted membrane fraction following high-salt and detergent washes, which indicates a tight and possibly integral association with the PM. Two-dimensional electrophoresis of partially purified azido-IAA-labeled protein demonstrates that, in addition to the major isoforms of the 40-kDa and 42-kDa polypeptides, which possess isoelectric points (pIs) of 8.2 and 7.2, respectively, several less abundant isoforms that display unique pIs are apparent at both molecular masses. Tryptic and chymotryptic digestion of the auxin-binding proteins indicates that the 40-kDa and 42-kDa polypeptides are closely related or are modifications of the same polypeptide. Phase extraction with the nonionic detergent Triton X-114 results in partitioning of the azido-IAA-labeled polypeptides into the aqueous (hydrophilic) phase. This apparently paradoxical behavior is also exhibited by certain integral membrane proteins that aggregate to form channels. The results of gel filtration indicate that the auxin-binding proteins do indeed aggregate strongly and that the polypeptides associate to form a dimer or multimeric complex in vivo. These characteristics are consistent with the hypothesis that the 40-kDa and 42-kDa polypeptides are subunits of a multimeric integral membrane protein which has an auxin-binding site, and which may possess transporter or channel function.

Non-Brownian diffusion in lipid membranes: Experiments and simulations.

PubMed

Metzler, R; Jeon, J-H; Cherstvy, A G

2016-10-01

The dynamics of constituents and the surface response of cellular membranes-also in connection to the binding of various particles and macromolecules to the membrane-are still a matter of controversy in the membrane biophysics community, particularly with respect to crowded membranes of living biological cells. We here put into perspective recent single particle tracking experiments in the plasma membranes of living cells and supercomputing studies of lipid bilayer model membranes with and without protein crowding. Special emphasis is put on the observation of anomalous, non-Brownian diffusion of both lipid molecules and proteins embedded in the lipid bilayer. While single component, pure lipid bilayers in simulations exhibit only transient anomalous diffusion of lipid molecules on nanosecond time scales, the persistence of anomalous diffusion becomes significantly longer ranged on the addition of disorder-through the addition of cholesterol or proteins-and on passing of the membrane lipids to the gel phase. Concurrently, experiments demonstrate the anomalous diffusion of membrane embedded proteins up to macroscopic time scales in the minute time range. Particular emphasis will be put on the physical character of the anomalous diffusion, in particular, the occurrence of ageing observed in the experiments-the effective diffusivity of the measured particles is a decreasing function of time. Moreover, we present results for the time dependent local scaling exponent of the mean squared displacement of the monitored particles. Recent results finding deviations from the commonly assumed Gaussian diffusion patterns in protein crowded membranes are reported. The properties of the displacement autocorrelation function of the lipid molecules are discussed in the light of their appropriate physical anomalous diffusion models, both for non-crowded and crowded membranes. In the last part of this review we address the upcoming field of membrane distortion by elongated membrane-binding particles. We discuss how membrane compartmentalisation and the particle-membrane binding energy may impact the dynamics and response of lipid membranes. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

/sup 3/H)pirenzepine and (-)-(/sup 3/H)quinuclidinyl benzilate binding to rat cerebral cortical and cardiac muscarinic cholinergic sites. I. Characterization and regulation of agonist binding to putative muscarinic subtypes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watson, M.; Yamamura, H.I.; Roeske, W.R.

The binding and regulation of selected muscarinic agonists to putative subtypes in rat cerebral cortex and heart were studied. Parallel inhibition studies of (/sup 3/H)pirenzepine ((/sup 3/H)PZ) and (-)-(/sup 3/H)quinuclidinylbenzilate ((-)-(/sup 3/H)QNB)-labeled membranes were done with and without 30 microM guanyl-5'-yl imidodiphosphate (Gpp(NH)p) at 25 degrees C in 10 mM Na-K-phosphate buffer which enhances PZ binding affinity and in modified Krebs-phosphate buffer, which mimics physiological conditions. Classical agonists such as carbachol, oxotremorine and acetylcholine inhibited (-)-(/sup 3/H)QNB binding to membranes with shallow Hill values (nH less than 1), were better fit to a 2-state model, were Gpp(NH)p-regulated and showed lowermore » affinity in modified Krebs-phosphate buffer than in 10 mM Na-K-phosphate buffer. Some agonists were not significantly better fit to a 2-state model in (/sup 3/H)PZ-labeled cortical membranes, especially in 10 mM Na-K-phosphate buffer. Whereas putative M1 and M2 binding sites distinguished by PZ possessed multiple agonist affinity states, as judged by carbachol, and agonist binding to (/sup 3/H)PZ-labeled sites were Gpp(NH)p modulated, the partial agonist pilocarpine and nonclassical agonist McN-A-343 (3-(m-chlorophenylcarbamoyloxy)-2-butynyl trimethylammonium chloride) showed little Gpp(NH)p-induced shift in (/sup 3/H)PZ-labeled cortical membranes in physiological conditions. Agonist binding to (-)-(/sup 3/H)QNB-labeled putative M2 cardiac sites was more sensitive to Gpp(NH)p than (-)-(/sup 3/H)QNB-labeled cortical sites. Carbachol and acetylcholine showed significant selectivity for putative M2 sites.« less

Choline+ is a low-affinity ligand for alpha 1-adrenoceptors.

PubMed

Unelius, L; Cannon, B; Nedergaard, J

1994-10-07

The effect of choline+, a commonly used Na+ substitute, on ligand binding to alpha 1-adrenoceptors was investigated. It was found that replacement of 25% of the Na+ in a Krebs-Ringer bicarbonate buffer with choline+ led to a 3-fold decrease in the apparent affinity of [3H]prazosin for its binding site (i.e. the alpha 1-receptor) in a membrane preparation from brown adipose tissue, while no decrease in the total number of binding sites was observed. Similar effects were seen in membrane preparations from liver and brain. In competition experiments, it was found that choline+ could inhibit [3H]prazosin binding; from the inhibition curve, an affinity (Ki) of 31 mM choline+ for the [3H]prazosin-binding site could be calculated. In fully choline(+)-substituted buffers, where the level of [3H]prazosin binding was substantially reduced, both phentolamine and norepinephrine could still compete with [3H]prazosin for its binding site, with virtually unaltered affinity; thus choline+ did not substantially affect the characteristics of those receptors to which it did not bind. Choline+ did not affect the binding characteristics of the beta 1/beta 2 radioligand [3H]CGP-12177; thus, the effect on alpha 1-receptors was not due to general, unspecific effects on the membrane preparations. It is concluded that choline+ possesses characteristics similar to those of a competitive ligand for the alpha 1-adrenoceptor; it has a low affinity but the competitive type of interaction of choline may nonetheless under experimental conditions interfere with agonist interaction with the alpha 1-receptor.

Fusicoccin-Binding Proteins in Arabidopsis thaliana (L.) Heynh. 1

PubMed Central

Meyer, Christiane; Feyerabend, Martin; Weiler, Elmar W.

1989-01-01

Using the novel radioligand, [3H]-9′-nor-fusicoccin-8′-alcohol, high affinity binding sites for fusicoccin were characterized in preparations from leaves of Arabidopsis thaliana (L.) Heynh. The binding site copartitioned with the plasmalemma marker, vanadate-sensitive K+, Mg2+-ATPase, when microsomal fractions were further purified by aqueous two-phase partitioning in polyethylene glycol-dextran phase systems and sedimented at an equilibrium density of 1.17 grams per cubic centimeter in continuous sucrose density gradients, as did the ATPase marker. The binding of [3H]-9′-nor-fusicoccin-8′-alcohol was saturable and Scatchard analysis revealed a biphasic plot with two apparent dissociation constants (KD), KD1 = 1.5 nanomolar and KD2 = 42 nanomolar, for the radioligand. Binding was optimal at pH 6, thermolabile, and was reduced by 70% when the membrane vesicles were pretreated with trypsin. The data are consistent with the presence of one or several binding proteins for fusicoccin at the plasma membrane of A. thaliana. Binding of the radioligand was unaffected by pretreatment of the sites with various alkylating and reducing agents, but was reduced by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, diethylpyrocarbonate, chloramine T, and periodate. A number of detergents were tested to find optimum conditions for solubilization. Nonanoyl-N-methylglucamide (50 millimolar) solubilized 70% of the radioligand-binding protein complex in undissociated form. Photoaffinity labeling of membrane preparations with a tritiated azido analog of fusicoccin resulted in the labeling of a 34 ± 1 kilodalton polypeptide. Labeling of this polypeptide, presumably the fusicoccin-binding protein, was severely reduced in the presence of unlabeled fusicoccin. PMID:16666603

Relationship of calcium and membrane guanylate cyclase in adrenocorticotropin-induced steroidogenesis.

PubMed

Nambi, P; Aiyar, N V; Roberts, A N; Sharma, R K

1982-07-01

Chlorpromazine, when incubated with isolated adrenal cells, inhibited the ACTH-stimulated formation of cGMP and corticosterone production. It also inhibited the ACTH-stimulated membrane guanylate cyclase, but did not affect the binding of ACTH to the membrane receptors. cGMP-induced steroidogenesis was not affected by the drug. These data indicate that chlorpromazine interferes with adrenal steroid metabolism at a site between the hormone receptor and guanylate cyclase and also show that guanylate cyclase is composed of separate receptor and catalytic components. Furthermore, based on the premise that chlorpromazine exerts its inhibitory action by blocking the binding of a calcium receptor protein, such as calmodulin, to the receptor-coupled guanylate cyclase, it is proposed that the interaction of calcium, presumably through a calcium-binding protein, is essential for ACTH-dependent guanylate cyclase.

Surface Plasmon Resonance Study of the Binding of PEO-PPO-PEO Triblock Copolymer and PEO Homopolymer to Supported Lipid Bilayers.

PubMed

Kim, Mihee; Vala, Milan; Ertsgaard, Christopher T; Oh, Sang-Hyun; Lodge, Timothy P; Bates, Frank S; Hackel, Benjamin J

2018-06-12

Poloxamer 188 (P188), a poly(ethylene oxide)- b-poly(propylene oxide)- b-poly(ethylene oxide) triblock copolymer, protects cell membranes against various external stresses, whereas poly(ethylene oxide) (PEO; 8600 g/mol) homopolymer lacks protection efficacy. As part of a comprehensive effort to elucidate the protection mechanism, we used surface plasmon resonance (SPR) to obtain direct evidence of binding of the polymers onto supported lipid bilayers. Binding kinetics and coverage of P188 and PEO were examined and compared. Most notably, PEO exhibited membrane association comparable to that of P188, evidenced by comparable association rate constants and coverage. This result highlights the need for additional mechanistic understanding beyond simple membrane association to explain the differential efficacy of P188 in therapeutic applications.

Fluorescent detection of apoptotic cells using a family of zinc coordination complexes with selective affinity for membrane surfaces that are enriched with phosphatidylserine.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Bradley D.; Lambert, Timothy N.; Lakshmi, C.

2005-03-01

The appearance of phosphatidylserine on the membrane surface of apoptotic cells (Jurkat, CHO, HeLa) is monitored by using a family of bis(Zn{sup 2+}-2,2{prime}-dipicolylamine) coordination compounds with appended fluorescein or biotin groups as reporter elements. The phosphatidylserine affinity group is also conjugated directly to a CdSe/CdS quantum dot to produce a probe suitable for prolonged observation without photobleaching. Apoptosis can be detected under a wide variety of conditions, including variations in temperature, incubation time, and binding media. Binding of each probe appears to be restricted to the cell membrane exterior, because no staining of organelles or internal membranes is observed.

Binding characteristics of [125I]Bolton-Hunter [Sar9,Met(O2)11]substance P, a new selective radioligand for the NK1 receptor.

PubMed

Lew, R; Geraghty, D P; Drapeau, G; Regoli, D; Burcher, E

1990-08-02

The selective tachykinin agonist [Sar9,Met(O2)11]substance P (Sar-SP) was radioiodinated with [125I]Bolton-Hunter reagent and the product [125I]Bolton-Hunter-[Sar9,Met(O)2)11]SP (BHSar-SP) purified using reverse phase HPLC. Autoradiographic studies showed dense specific binding of BHSar-SP over the rat submandibular gland and over several regions in rat brain, with very low nonspecific binding, identical with the pattern of binding sites seen in a parallel study with [125I]Bolton-Hunter SP (BHSP). In homogenate binding experiments, BHSar-SP bound with high affinity to a single site in membranes from rat brain (KD 261 pM) and rat submandibular gland (KD 105 pM). Comparative values for BHSP were 495 and 456 pM, i.e. of two and four fold lower affinity than BHSar-SP. Association of BHSar-SP to membranes from brain (k+1 3.7 x 10(9) M-1 min-1) was faster than to membranes from salivary gland (k+1 5.6 x 10(8) M-1 min-1). In competition studies, BHSar-SP was displaced from salivary gland membranes by substance P (SP) approximately physalaemin greater than or equal to Sar-SP approximately SP-(3-11) greater than SP-(5-11) much greater than neurokinin A (NKA) approximately eledoisin = kassinin = SP-methyl ester greater than or equal to neurokinin B (NKB) much greater than [Nle10]NKA-(4-10) greater than [MePhe7]NKB-(4-10). In brain membranes, the rank potency order was SP greater than Sar-SP greater than or equal to physalaemin greater than SP-(3-11) greater than SP-(5-11) greater than NKA greater than or equal to eledoisin much greater than NKB greater than kassinin greater than SP-methyl ester: however [MePhe7]NKB-(4-10) and [Nle10]NKA-(4-10) were ineffective competitors at concentrations up to 1 microM. Both binding patterns are consistent with BHSar-SP binding to an NK1 site. With the exception of SP, Sar-SP, SP-(3-11) and physalaemin, all competitors were 5 to 54 times less potent at BHSar-SP binding sites in brain than in salivary gland. These data reveal some differences in characteristics of NK1 binding sites in brain and submandibular gland. Although of higher affinity, BHSar-SP does not appear greatly more selective than BHSP in its ability to define NK1 binding sites.

Precipitation of the thyrotropin receptor and identification of thyroid autoantigens using Graves' disease immunoglobulins.

PubMed Central

Heyma, P; Harrison, L C

1984-01-01

The thyrotropin (TSH) receptor is a putative target for autoantibodies in Graves' hyperthyroidism and therefore, should be capable of being identified, isolated, and structurally characterized by immunological means. To this end, four sera from patients with hyperthyroidism, three of which inhibited the binding of 125I-TSH to Triton-solubilized human thyroid membranes, were used to isolate TSH receptors by immunoprecipitation. To account for an effect of TSH binding or receptor occupancy on the ability of Graves' immunoglobulins to precipitate TSH receptors, two approaches were taken: (a) specific 125I-TSH binding activity was measured after solubilized thyroid membranes had been incubated with Graves' sera followed by precipitation with Staphylococcus protein A ("receptor depletion"); (b) TSH binding sites were labeled with 125I-TSH and the complexes were precipitated using Graves' sera and Staphylococcus protein A ("receptor precipitation"). The three sera which inhibited 125I-TSH binding depleted 125I-TSH binding activity between 30-80%. Preformed complexes between Staphylococcus protein A and immunoglobulins in these sera were also able to deplete 125I-TSH binding activity. However, after receptor depletion, the one serum that did not inhibit 125I-TSH binding was associated with a significant increase in 125I-TSH binding. All four sera specifically precipitated 80-100% of receptors identified by prelabeling with 125I-TSH. The dilutions of sera that precipitated 50% of 125I-TSH-receptor complexes ranged from 1:150-1:20. Complexes were partially precipitated by high concentrations of control sera (1:20), but the relative potency of control sera was at least fourfold less than Graves' sera. Immunoprecipitates of 125I-labeled thyroid membranes were analysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography to reveal Graves'-specific bands of reduced molecular weights of 100-110,000, 80-90,000, and 70-75,000. These bands were similar to those obtained from 125I-labeled thyroid membranes purified by TSH affinity chromatography. Thus, Graves' immunoglobulins: (a) precipitate unoccupied and occupied TSH receptors, (b) in one case, neither inhibit binding nor immunodeplete the unoccupied receptor but immunoprecipitate 125I-TSH-receptor complexes, suggesting that binding of TSH may initiate an interaction between the binding site and a separate immunoreactive molecule, and (c) identify the molecular structure of Graves' autoantigens, putatively, the TSH receptor. Images PMID:6088581

Multiple sup 3 H-oxytocin binding sites in rat myometrial plasma membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crankshaw, D.; Gaspar, V.; Pliska, V.

1990-01-01

The affinity spectrum method has been used to analyse binding isotherms for {sup 3}H-oxytocin to rat myometrial plasma membranes. Three populations of binding sites with dissociation constants (Kd) of 0.6-1.5 x 10(-9), 0.4-1.0 x 10(-7) and 7 x 10(-6) mol/l were identified and their existence verified by cluster analysis based on similarities between Kd, binding capacity and Hill coefficient. When experimental values were compared to theoretical curves constructed using the estimated binding parameters, good fits were obtained. Binding parameters obtained by this method were not influenced by the presence of GTP gamma S (guanosine-5'-O-3-thiotriphosphate) in the incubation medium. The bindingmore » parameters agree reasonably well with those found in uterine cells, they support the existence of a medium affinity site and may allow for an explanation of some of the discrepancies between binding and response in this system.« less

PI(3,5)P2 controls endosomal branched actin dynamics by regulating cortactin–actin interactions

PubMed Central

Hong, Nan Hyung; Qi, Aidong

2015-01-01

Branched actin critically contributes to membrane trafficking by regulating membrane curvature, dynamics, fission, and transport. However, how actin dynamics are controlled at membranes is poorly understood. Here, we identify the branched actin regulator cortactin as a direct binding partner of phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2) and demonstrate that their interaction promotes turnover of late endosomal actin. In vitro biochemical studies indicated that cortactin binds PI(3,5)P2 via its actin filament-binding region. Furthermore, PI(3,5)P2 competed with actin filaments for binding to cortactin, thereby antagonizing cortactin activity. These findings suggest that PI(3,5)P2 formation on endosomes may remove cortactin from endosome-associated branched actin. Indeed, inhibition of PI(3,5)P2 production led to cortactin accumulation and actin stabilization on Rab7+ endosomes. Conversely, inhibition of Arp2/3 complex activity greatly reduced cortactin localization to late endosomes. Knockdown of cortactin reversed PI(3,5)P2-inhibitor–induced actin accumulation and stabilization on endosomes. These data suggest a model in which PI(3,5)P2 binding removes cortactin from late endosomal branched actin networks and thereby promotes net actin turnover. PMID:26323691

MAA-1, a novel acyl-CoA-binding protein involved in endosomal vesicle transport in Caenorhabditis elegans.

PubMed

Larsen, Morten K; Tuck, Simon; Faergeman, Nils J; Knudsen, Jens

2006-10-01

The budding and fission of vesicles during membrane trafficking requires many proteins, including those that coat the vesicles, adaptor proteins that recruit components of the coat, and small GTPases that initiate vesicle formation. In addition, vesicle formation in vitro is promoted by the hydrolysis of acyl-CoA lipid esters. The mechanisms by which these lipid esters are directed to the appropriate membranes in vivo, and their precise roles in vesicle biogenesis, are not yet understood. Here, we present the first report on membrane associated ACBP domain-containing protein-1 (MAA-1), a novel membrane-associated member of the acyl-CoA-binding protein family. We show that in Caenorhabditis elegans, MAA-1 localizes to intracellular membrane organelles in the secretory and endocytic pathway and that mutations in maa-1 reduce the rate of endosomal recycling. A lack of maa-1 activity causes a change in endosomal morphology. Although in wild type, many endosomal organelles have long tubular protrusions, loss of MAA-1 activity results in loss of the tubular domains, suggesting the maa-1 is required for the generation or maintenance of these domains. Furthermore, we demonstrate that MAA-1 binds fatty acyl-CoA in vitro and that this ligand-binding ability is important for its function in vivo. Our results are consistent with a role for MAA-1 in an acyl-CoA-dependent process during vesicle formation.

Effects of a detergent micelle environment on P-glycoprotein (ABCB1)-ligand interactions

PubMed Central

Shukla, Suneet; Abel, Biebele; Chufan, Eduardo E.; Ambudkar, Suresh V.

2017-01-01

P-glycoprotein (P-gp) is a multidrug transporter that uses energy from ATP hydrolysis to export many structurally dissimilar hydrophobic and amphipathic compounds, including anticancer drugs from cells. Several structural studies on purified P-gp have been reported, but only limited and sometimes conflicting information is available on ligand interactions with the isolated transporter in a dodecyl-maltoside detergent environment. In this report we compared the biochemical properties of P-gp in native membranes, detergent micelles, and when reconstituted in artificial membranes. We found that the modulators zosuquidar, tariquidar, and elacridar stimulated the ATPase activity of purified human or mouse P-gp in a detergent micelle environment. In contrast, these drugs inhibited ATPase activity in native membranes or in proteoliposomes, with IC50 values in the 10–40 nm range. Similarly, a 30–150-fold decrease in the apparent affinity for verapamil and cyclic peptide inhibitor QZ59-SSS was observed in detergent micelles compared with native or artificial membranes. Together, these findings demonstrate that the high-affinity site is inaccessible because of either a conformational change or binding of detergent at the binding site in a detergent micelle environment. The ligands bind to a low-affinity site, resulting in altered modulation of P-gp ATPase activity. We, therefore, recommend studying structural and functional aspects of ligand interactions with purified P-gp and other ATP-binding cassette transporters that transport amphipathic or hydrophobic substrates in a detergent-free native or artificial membrane environment. PMID:28283574

Characterization of pneumolysin from Streptococcus pneumoniae, interacting with carbohydrate moiety and cholesterol as a component of cell membrane.

PubMed

Lim, Jong Eun; Park, Seong Ah; Bong, Seoung Min; Chi, Young Min; Lee, Ki Seog

2013-01-11

The cytolytic mechanism of cholesterol-dependent cytolysins (CDCs) requires the presence of cholesterol in the target cell membrane. Membrane cholesterol was thought to serve as the common receptor for these toxins, but not all CDCs require cholesterol for binding. One member of this toxin family, pneumolysin (PLY) is a major virulence factor of Streptococcus pneumoniae, and the mechanism via which PLY binds to its putative receptor or cholesterol on the cell membrane is still poorly understood. Here, we demonstrated that PLY interacted with carbohydrate moiety and cholesterol as a component of the cell membrane, using the inhibitory effect of hemolytic activity. The hemolytic activity of PLY was inhibited by cholesterol-MβCD, which is in a 3β configuration at the C3-hydroxy group, but is not in a 3α-configuration. In the interaction between PLY and carbohydrate moiety, the mannose showed a dose-dependent increase in the inhibition of PLY hemolytic activity. The binding ability of mannose with truncated PLYs, as determined by the pull-down assay, showed that mannose might favor binding to domain 4 rather than domains 1-3. These studies provide a new model for the mechanism of cellular recognition by PLY, as well as a foundation for future investigations into whether non-sterol molecules can serve as receptors for other members of the CDC family of toxins. Copyright © 2012 Elsevier Inc. All rights reserved.

Membrane Bending by Protein Crowding

NASA Astrophysics Data System (ADS)

Stachowiak, Jeanne

2014-03-01

From endosomes and synaptic vesicles to the cristae of the mitochondria and the annulus of the nuclear pore, highly curved membranes are fundamental to the structure and physiology of living cells. The established view is that specific families of proteins are able to bend membranes by binding to them. For example, inherently curved proteins are thought to impose their structure on the membrane surface, while membrane-binding proteins with hydrophobic motifs are thought to insert into the membrane like wedges, driving curvature. However, computational models have recently revealed that these mechanisms would require specialized membrane-bending proteins to occupy nearly 100% of a curved membrane surface, an improbable physiological situation given the immense density and diversity of membrane-bound proteins, and the low expression levels of these specialized proteins within curved regions of the membrane. How then does curvature arise within the complex and crowded environment of cellular membranes? Our recent work using proteins involved in clathrin-mediated endocytosis, as well as engineered protein-lipid interactions, has suggested a new hypothesis - that lateral pressure generated by collisions between membrane-bound proteins can drive membrane bending. Specifically, by correlating membrane bending with quantitative optical measurements of protein density on synthetic membrane surfaces and simple physical models of collisions among membrane-bound proteins, we have demonstrated that protein-protein steric interactions can drive membrane curvature. These findings suggest that a simple imbalance in the concentration of membrane-bound proteins across a membrane surface can drive a membrane to bend, providing an efficient mechanism by which essentially any protein can contribute to shaping membranes.

sigma opiates and certain antipsychotic drugs mutually inhibit (+)-(/sup 3/H)SKF 10,047 and (/sup 3/H)haloperidol binding in guinea pig brain membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tam, S.W.; Cook, L.

1984-09-01

The relationship between binding of antipsychotic drugs and sigma psychotomimetic opiates to binding sites for the sigma agonist (+)-(/sup 3/H)SKF 10,047 (N-allylnormetazocine) and to dopamine D/sub 2/ sites was investigated. In guinea pig brain membranes, (+)-(/sup 3/H)SKF 10,047 bound to single class of sites with a K/sub d/ of 4 x 10/sup -8/ M and a B/sub max/ of 333 fmol/mg of protein. This binding was different from ..mu.., kappa, or delta opiate receptor binding. It was inhibited by opiates that produce psychotomimetic activities but not by opiates that lack such activities. Some antipsychotic drugs inhibited (+)-(/sup 3/H)SKF 10,047 bindingmore » with high to moderate affinities in the following order of potency: haloperidol > perphenazine > fluphenazine > acetophenazine > trifluoperazine > molindone greater than or equal to pimozide greater than or equal to thioridazine greater than or equal to chlorpromazine greater than or equal to triflupromazine. However, there were other antipsychotic drugs such as spiperone and clozapine that showed low affinity for the (+)-(/sup 3/H)SKF 10,047 binding sites. Affinities of antipsychotic drugs for (+)-(/sup 3/H)SKF 10,047 binding sites did not correlate with those for (/sup 3/H)spiperone (dopamine D/sub 2/) sites. (/sup 3/H)-Haloperidol binding in whole brain membranes was also inhibited by the sigma opiates pentazocine, cyclazocine, and (+)-(/sup 3/H)SKF 10,047. In the striatum, about half of the saturable (/sup 3/H)haloperidol binding was to (/sup 3/H)spiperone (D/sub 2/) sites and the other half was to sites similar to (+)-(/sup 3/H)SKF 10,047 binding sites. 15 references, 4 figures, 1 table.« less

MSC secretes at least 3 EV types each with a unique permutation of membrane lipid, protein and RNA.

PubMed

Lai, Ruenn Chai; Tan, Soon Sim; Yeo, Ronne Wee Yeh; Choo, Andre Boon Hwa; Reiner, Agnes T; Su, Yan; Shen, Yang; Fu, Zhiyan; Alexander, Lezhava; Sze, Siu Kwan; Lim, Sai Kiang

2016-01-01

Mesenchymal stem cell (MSC), a widely used adult stem cell candidate for regenerative medicine, has been shown to exert some of its therapeutic effects through the secretion of extracellular vesicles (EVs). These homogenously sized EVs of 100-150 ηm exhibited many exosome-like biophysical and biochemical properties and carry both proteins and RNAs. Recently, exosome-associated proteins in this MSC EV preparation were found to segregate primarily to those EVs that bind cholera toxin B chain (CTB), a GM1 ganglioside-specific ligand, and pulse-chase experiments demonstrated that these EVs have endosomal origin and carried many of the exosome-associated markers. Here, we report that only a fraction of the MSC EV proteome was found in CTB-bound EVs. Using Annexin V (AV) and Shiga toxin B subunit (ST) with affinities for phosphatidylserine and globotriaosylceramide, respectively, AV- and a ST-binding EV were identified. CTB-, AV- and ST-binding EVs all carried actin. However, the AV-binding EVs carried low or undetectable levels of the exosome-associated proteins. Only the ST-binding EVs carried RNA and EDA-containing fibronectin. Proteins in AV-binding EVs were also different from those released by apoptotic MSCs. CTB- and AV-binding activities were localized to the plasma membrane and cytoplasm of MSCs, while ST-binding activity was localized to the nucleus. Together, this study demonstrates that cells secrete many types of EVs. Specifically, MSCs secrete at least 3 types. They can be differentially isolated based on their affinities for membrane lipid-binding ligands. As the subcellular sites of the binding activities of these ligands and cargo load are different for each EV type, they are likely to have a different biogenesis pathway and possibly different functions.

Structural analysis of the receptor binding domain of botulinum neurotoxin serotype D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yanfeng; Buchko, Garry W.; Qin, Lin

2010-10-28

Botulinum neurotoxins (BoNTs) are the most toxic proteins known. The mechanism for entry into neuronal cells for serotypes A, B, E, F, and G involves a well understood dual receptor (protein and ganglioside) process, however, the mechanism of entry for serotypes C and D remains unclear. To provide structural insights into how BoNT/D enters neuronal cells, the crystal structure of the receptor binding domain (S863-E1276) for this serotype (BoNT/D-HCR) was determined at 1.65 Å resolution. While BoNT/D-HCR adopts an overall fold similar to that observed in other known BoNT HCRs, several major structural differences are present. These structural differences aremore » located at, or near, putative receptor binding sites and may be responsible for BoNT/D host preferences. Two loops, S1195-I1204 and K1236-N1244, located on both sides of the putative protein receptor binding pocket, are displaced >10 Å relative to the corresponding residues in the crystal structures of BoNT/B and G. Obvious clashes were observed in the putative protein receptor binding site when the BoNT/B protein receptor synaptotagmin II was modeled into the BoNT/D-HCR structure. Although a ganglioside binding site has never been unambiguously identified in BoNT/D-HCR, a shallow cavity in an analogous location to the other BoNT serotypes HCR domains is observed in BoNT/D-HCR that has features compatible with membrane binding. A portion of a loop near the putative receptor binding site, K1236-N1244, is hydrophobic and solvent-exposed and may directly bind membrane lipids. Liposome-binding experiments with BoNT/D-HCR demonstrate that this membrane lipid may be phosphatidylethanolamine.« less

Structural Analysis of the Receptor Binding Domain of Botulinum Neurotoxin Serotype D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Y Zhang; G Buchko; L Qin

2011-12-31

Botulinum neurotoxins (BoNTs) are the most toxic proteins known. The mechanism for entry into neuronal cells for serotypes A, B, E, F, and G involves a well understood dual receptor (protein and ganglioside) process, however, the mechanism of entry for serotypes C and D remains unclear. To provide structural insights into how BoNT/D enters neuronal cells, the crystal structure of the receptor binding domain (S863-E1276) for this serotype (BoNT/D-HCR) was determined at 1.65{angstrom} resolution. While BoNT/D-HCR adopts an overall fold similar to that observed in other known BoNT HCRs, several major structural differences are present. These structural differences are locatedmore » at, or near, putative receptor binding sites and may be responsible for BoNT/D host preferences. Two loops, S1195-I1204 and K1236-N1244, located on both sides of the putative protein receptor binding pocket, are displaced >10{angstrom} relative to the corresponding residues in the crystal structures of BoNT/B and G. Obvious clashes were observed in the putative protein receptor binding site when the BoNT/B protein receptor synaptotagmin II was modeled into the BoNT/D-HCR structure. Although a ganglioside binding site has never been unambiguously identified in BoNT/D-HCR, a shallow cavity in an analogous location to the other BoNT serotypes HCR domains is observed in BoNT/D-HCR that has features compatible with membrane binding. A portion of a loop near the putative receptor binding site, K1236-N1244, is hydrophobic and solvent-exposed and may directly bind membrane lipids. Liposome-binding experiments with BoNT/D-HCR demonstrate that this membrane lipid may be phosphatidylethanolamine.« less

Supported Lipid Bilayers with Phosphatidylethanolamine as the Major Component.

PubMed

Sendecki, Anne M; Poyton, Matthew F; Baxter, Alexis J; Yang, Tinglu; Cremer, Paul S

2017-11-21

Phosphatidylethanolamine (PE) is notoriously difficult to incorporate into model membrane systems, such as fluid supported lipid bilayers (SLBs), at high concentrations because of its intrinsic negative curvature. Using fluorescence-based techniques, we demonstrate that having fewer sites of unsaturation in the lipid tails leads to high-quality SLBs because these lipids help to minimize the curvature. Moreover, shorter saturated chains can help maintain the membranes in the fluid phase. Using these two guidelines, we find that up to 70 mol % PE can be incorporated into SLBs at room temperature and up to 90 mol % PE can be incorporated at 37 °C. Curiously, conditions under which three-dimensional tubules project outward from the planar surface as well as conditions under which domain formation occurs can be found. We have employed these model membrane systems to explore the ability of Ni 2+ to bind to PE. It was found that this transition metal ion binds 1000-fold tighter to PE than to phosphatidylcholine lipids. In the future, this platform could be exploited to monitor the binding of other transition metal ions or the binding of antimicrobial peptides. It could also be employed to explore the physical properties of PE-containing membranes, such as phase domain behavior and intermolecular hydrogen bonding.

Effect of alcohol on hepatic receptor of high density lipoproteins (HDL)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, R.C.; Miller, B.M.

1991-03-11

Moderate alcohol intake has been shown to increase HDL cholesterol and proteins. The seemingly protective effect' of moderate alcohol drinking against cardiovascular diseases has been attributed to an increase in serum HDL. In this study, the authors show that a receptor for HDL is present in rat liver. Rat liver membrane was prepared by stepwise ultracentrifugation. Apo Al was iodinated using {sup 125}I-NaI and IODO-beads. HDL was labeled by incubating with {sup 125}I-apo Al then refloated be centrifugation. Binding of {sup 125}I-HDL to rat liver membrane reached equilibrium by 2-3 h and was saturable at 37C. The binding was inhibitedmore » 80% by excess unlabeled HDL, but was inhibited only 25% by excess LDL. It could also be inhibited by preincubating HDL with anti-apo Al or anti-apo E antisera but not with anti-apo AIV or control sera. The binding affinity of HDL to the liver membrane of rats fed alcohol for 5 wk was 50% that of their pair-fed controls. Thus a decrease in the binding of HDL to liver membrane due to alcohol-drinking may result in a slower clearance of HDL by the liver and consequently a higher HDL concentration in the serum.« less

Effect of phloretin on the binding of 1-anilino-8-naphtalene sulfonate (ANS) to 1,2-Dimyristoyl-sn-glycero-3-phosphocoline (DMPC) vesicles in the gel and liquid-crystalline state.

PubMed

Cutró, Andrea C; Montich, Guillermo; Roveri, Oscar A

2015-02-01

Phloretin is a known modifier of the internal dipole potential of lipid membranes. We studied the interaction of phloretin with model lipid membranes and how it influences the membrane dipole organization using ANS as fluorescent probe. The fluorescence increase observed when ANS binds to DMPC liposomes in gel phase (13 °C) was 2.5 times larger in the presence of phloretin. This effect was due to an increase in ANS affinity, which can be related to the known capability of phloretin in decreasing the dipole potential. Conversely, when the experiments were carried out at 33 °C (liquid crystalline phase), phloretin completely inhibited the increase in ANS fluorescence. In addition, phloretin only affected the electrical properties of the membrane in the gel phase, whereas it modifies structural ones in the liquid-crystalline state. We postulate that phloretin was bound only to the DMPC interface in the gel phase decreasing the surface negative charge density without modifying the structural properties of the ANS binding sites. In the liquid-crystalline phase instead, it increased the accessibility of water to the ANS binding sites decreasing the intrinsic affinity and the fluorescence quantum yield of ANS.

Intracellular Trafficking of Clostridium perfringens Iota-Toxin b

PubMed Central

Umezaki, Mariko; Tashiro, Ryo; Oda, Masataka; Kobayashi, Keiko; Shibutani, Masahiro; Takagishi, Teruhisa; Ishidoh, Kazumi; Fukuda, Mitsunori; Sakurai, Jun

2012-01-01

Clostridium perfringens iota-toxin is composed of an enzymatic component (Ia) and a binding component (Ib). Ib binds to a cell surface receptor, undergoes oligomerization in lipid rafts, and binds Ia. The resulting complex is then endocytosed. Here, we show the intracellular trafficking of iota-toxin. After the binding of the Ib monomer with cells at 4°C, oligomers of Ib formed at 37°C and later disappeared. Immunofluorescence staining of Ib revealed that the internalized Ib was transported to early endosomes. Some Ib was returned to the plasma membrane through recycling endosomes, whereas the rest was transported to late endosomes and lysosomes for degradation. Degraded Ib was delivered to the plasma membrane by an increase in the intracellular Ca2+ concentration caused by Ib. Bafilomycin A1, an endosomal acidification inhibitor, caused the accumulation of Ib in endosomes, and both nocodazole and colchicine, microtubule-disrupting agents, restricted Ib's movement in the cytosol. These results indicated that an internalized Ia and Ib complex was delivered to early endosomes and that subsequent delivery of Ia to the cytoplasm occurs mainly in early endosomes. Ib was either sent back to the plasma membranes through recycling endosomes or transported to late endosomes and lysosomes for degradation. Degraded Ib was transported to plasma membranes. PMID:22825447

A superconducting bolometer camera for APEX

NASA Astrophysics Data System (ADS)

Jethava, N.; Kreysa, E.; Siringo, G.; Esch, W.; Gemünd, H.-P.; May, T.; Anders, S.; Fritzsch, L.; Boucher, R.; Zakosarenko, V.; Meyer, H.-G.

2006-06-01

We present the experimental results of voltage-biased superconducting bolometers (VSB) on silicon nitride (Si 3N 4) membranes with niobium wiring developed in collaboration between the Institut fur Physikalische Hochtechnologie (IPHT), Jena, Germany and the Max-Planck-Institut fur Radioastronomie (MPIfR), Bonn, Germany. The bolometer current is measured with the superconducting quantum interference device (SQUID), and as expected, the current responsivity is proportional to the inverse of the bias voltage. The experiments were performed with bilayer gold-palladium molybdenum thermistor at 300 mK 3He cooled cryostat and the desired transition temperature of T c = 450 mK is achieved. The strong negative electro-thermal feedback of the VSB maintains the constant bolometer temperature and reduces the response time from 4 ms to 100 μs. We have tested thermistors of various size and shape on a continuous membrane and achieved a noise equivalent power (NEP) of 3.5 × 10 -16 W/√Hz. The measured NEP is relatively high due to the comparatively high background and high thermal conductance of the unstructured silicon nitride (Si 3N 4) membrane. We have fabricated 8-leg spider structured membranes in three different geometries and the relation between the geometry and the thermal conductance (G) is studied. Using the COSMOS finite element analysis tool, we have modeled the TES bolometers to determine the thermal conductance for different geometries and calculated the various parameters. Due to the demands of large number pixel bolometer camera we plan to implement multiplex readout with integrated SQUIDs in our design.

Internalisation of the bleomycin molecules responsible for bleomycin toxicity: a receptor-mediated endocytosis mechanism.

PubMed

Pron, G; Mahrour, N; Orlowski, S; Tounekti, O; Poddevin, B; Belehradek, J; Mir, L M

1999-01-01

Bleomycin (BLM) does not diffuse through the plasma membrane but nevertheless displays cytotoxic activity due to DNA break generation. The aim of the study was to describe the mechanism of BLM internalisation. We previously provided evidence for the existence of BLM-binding sites at the surface of DC-3F Chinese hamster fibroblasts, as well as of their involvement in BLM cytotoxicity on DC-3F cells and related BLM-resistant sublines. Here we report that A253 human cells and their BLM-resistant subline C-10E also possessed a membrane protein of ca. 250 kDa specifically binding BLM. Part of this C-10E cell resistance could be explained by a decrease in the number of BLM-binding sites exposed at the cell surface with respect to A253 cells. The comparison between A253 and DC-3F cells exposing a similar number of BLM-binding sites revealed that the faster the fluid phase endocytosis, the greater the cell sensitivity to BLM. Moreover, the experimental modification of endocytotic vesicle size showed that BLM cytotoxicity was directly correlated with the flux of plasma membrane area engulfed during endocytosis rather than with the fluid phase volume incorporated. Thus, BLM would be internalised by a receptor-mediated endocytosis mechanism which would first require BLM binding to its membrane receptor and then the transfer of the complex into intracellular endocytotic vesicles, followed by BLM entry into the cytosol, probably from a nonacidic compartment.

Mechanical collapse of confined fluid membrane vesicles.

PubMed

Rim, Jee E; Purohit, Prashant K; Klug, William S

2014-11-01

Compact cylindrical and spherical invaginations are common structural motifs found in cellular and developmental biology. To understand the basic physical mechanisms that produce and maintain such structures, we present here a simple model of vesicles in confinement, in which mechanical equilibrium configurations are computed by energy minimization, balancing the effects of curvature elasticity, contact of the membrane with itself and the confining geometry, and adhesion. For cylindrical confinement, the shape equations are solved both analytically and numerically by finite element analysis. For spherical confinement, axisymmetric configurations are obtained numerically. We find that the geometry of invaginations is controlled by a dimensionless ratio of the adhesion strength to the bending energy of an equal area spherical vesicle. Larger adhesion produces more concentrated curvatures, which are mainly localized to the "neck" region where the invagination breaks away from its confining container. Under spherical confinement, axisymmetric invaginations are approximately spherical. For extreme confinement, multiple invaginations may form, bifurcating along multiple equilibrium branches. The results of the model are useful for understanding the physical mechanisms controlling the structure of lipid membranes of cells and their organelles, and developing tissue membranes.

Brownian dynamics simulations of simplified cytochrome c molecules in the presence of a charged surface

NASA Astrophysics Data System (ADS)

Gorba, C.; Geyer, T.; Helms, V.

2004-07-01

Simulations were performed for up to 150 simplified spherical horse heart cytochrome c molecules in the presence of a charged surface, which serves as an approximate model for a lipid membrane. Screened electrostatic and short-ranged attractive as well as repulsive van der Waals forces for interparticle and particle-membrane interactions are utilized in the simulations. At a distance from the membrane, where particle-membrane interactions are negligible, the simulation is coupled to a noninteraction continuum analogous to a heat bath [Geyer et al., J. Chem. Phys. 120, 4573 (2004)]. From the particles' density profiles perpendicular to the planar surface binding isotherms are derived and compared to experimental results [Heimburg et al. (1999)]. Using a negatively charged structureless membrane surface a saturation effect was found for relatively large particle concentrations. Since biological membranes often contain membrane proteins, we also studied the influence of additional charges on our model membrane mimicking bacterial reaction centers. We find that the onset of the saturation occurs for much lower concentrations and is sensitive to the detailed implementation. Therefore we suggest that local distortion of membrane planarity (undulation), or lipid demixing, or the presence of charged integral membrane proteins create preferential binding sites on the membrane. Only then do we observe saturation at physiological concentrations.

Atomic resolution view into the structure–function relationships of the human myelin peripheral membrane protein P2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruskamo, Salla; University of Oulu, Oulu; Yadav, Ravi P.

2014-01-01

The structure of the human myelin peripheral membrane protein P2 has been refined at 0.93 Å resolution. In combination with functional experiments in vitro, in vivo and in silico, the fine details of the structure–function relationships in P2 are emerging. P2 is a fatty acid-binding protein expressed in vertebrate peripheral nerve myelin, where it may function in bilayer stacking and lipid transport. P2 binds to phospholipid membranes through its positively charged surface and a hydrophobic tip, and accommodates fatty acids inside its barrel structure. The structure of human P2 refined at the ultrahigh resolution of 0.93 Å allows detailed structuralmore » analyses, including the full organization of an internal hydrogen-bonding network. The orientation of the bound fatty-acid carboxyl group is linked to the protonation states of two coordinating arginine residues. An anion-binding site in the portal region is suggested to be relevant for membrane interactions and conformational changes. When bound to membrane multilayers, P2 has a preferred orientation and is stabilized, and the repeat distance indicates a single layer of P2 between membranes. Simulations show the formation of a double bilayer in the presence of P2, and in cultured cells wild-type P2 induces membrane-domain formation. Here, the most accurate structural and functional view to date on P2, a major component of peripheral nerve myelin, is presented, showing how it can interact with two membranes simultaneously while going through conformational changes at its portal region enabling ligand transfer.« less

Insight into the adsorption profiles of the Saprolegnia monoica chitin synthase MIT domain on POPA and POPC membranes by molecular dynamics simulation studies.

PubMed

Kuang, Guanglin; Liang, Lijun; Brown, Christian; Wang, Qi; Bulone, Vincent; Tu, Yaoquan

2016-02-21

The critical role of chitin synthases in oomycete hyphal tip growth has been established. A microtubule interacting and trafficking (MIT) domain was discovered in the chitin synthases of the oomycete model organism, Saprolegnia monoica. MIT domains have been identified in diverse proteins and may play a role in intracellular trafficking. The structure of the Saprolegnia monoica chitin synthase 1 (SmChs1) MIT domain has been recently determined by our group. However, although our in vitro assay identified increased strength in interactions between the MIT domain and phosphatidic acid (PA) relative to other phospholipids including phosphatidylcholine (PC), the mechanism used by the MIT domain remains unknown. In this work, the adsorption behavior of the SmChs1 MIT domain on POPA and POPC membranes was systematically investigated by molecular dynamics simulations. Our results indicate that the MIT domain can adsorb onto the tested membranes in varying orientations. Interestingly, due to the specific interactions between MIT residues and lipid molecules, the binding affinity to the POPA membrane is much higher than that to the POPC membrane. A binding hotspot, which is critical for the adsorption of the MIT domain onto the POPA membrane, was also identified. The lower binding affinity to the POPC membrane can be attributed to the self-saturated membrane surface, which is unfavorable for hydrogen-bond and electrostatic interactions. The present study provides insight into the adsorption profile of SmChs1 and additionally has the potential to improve our understanding of other proteins containing MIT domains.

An ESIPT fluorescent probe sensitive to protein α-helix structures.

PubMed

Jiang, Nan; Yang, Chanli; Dong, Xiongwei; Sun, Xianglang; Zhang, Dan; Liu, Changlin

2014-07-28

A large majority of membrane proteins have one or more transmembrane regions consisting of α-helices. Membrane protein levels differ from one type of cell to another, and the expression of membrane proteins also changes from normal to diseased cells. For example, prostate cancer cells have been reported to have downregulated expression of membrane proteins, including zinc transporters, compared with normal prostate cells. These reports inspired us to design a fluorescence probe sensitive to protein α-helical structures to discriminate individual prostate cancer cells from normal ones. A benzazole derivative ( in this study) was observed to emit strong fluorescence resulting from an excited-state intramolecular proton transfer (ESIPT) in protein α-helical environments. The intensity of ESIPT fluorescence of was observed to be positively correlated with the α-helix content of proteins. The molecular docking simulation suggested that it had low energy for the binding of to proteins when the binding sites were localized within the α-helical regions of protein via H-bonds. Furthermore, was found to be localized in cell membranes through binding to transmembrane α-helical regions of membrane proteins, and was capable of probing differences in the α-helix contents of membrane proteins between normal and cancerous prostate cells through changes in the ESIPT emission intensity. These results indicated that could distinguish individual prostate cancer cells from normal ones, as the changes in the ESIPT fluorescence intensity of could reflect the regulation in expression of the membrane proteins including zinc transporters. This recognition strategy of individual prostate cancer cells might contribute to early diagnosis techniques for prostate cancer.