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Sample records for lipid membranes potential

  1. Lipid membranes for membrane proteins.

    PubMed

    Kukol, Andreas

    2015-01-01

    The molecular dynamics (MD) simulation of membrane proteins requires the setup of an accurate representation of lipid bilayers. This chapter describes the setup of a lipid bilayer system from scratch using generally available tools, starting with a definition of the lipid molecule POPE, generation of a lipid bilayer, energy minimization, MD simulation, and data analysis. The data analysis includes the calculation of area and volume per lipid, deuterium order parameters, self-diffusion constant, and the electron density profile. PMID:25330959

  2. Unconventional Mechanics of Lipid Membranes: A Potential Role for Mechanotransduction of Hair Cell Stereocilia

    PubMed Central

    Kim, Jichul

    2015-01-01

    A force-conveying role of the lipid membrane across various mechanoreceptors is now an accepted hypothesis. However, such a mechanism is still not fully understood for mechanotransduction in the hair bundle of auditory sensory hair cells. A major goal of this theoretical assessment was to investigate the role of the lipid membrane in auditory mechanotransduction, especially in generating nonlinear bundle force versus displacement measurements, one of the main features of auditory mechanotransduction. To this end, a hair bundle model that generates lipid membrane tented deformation in the stereocilia was developed. A computational analysis of the model not only reproduced nonlinear bundle force measurements but also generated membrane energy that is potentially sufficient to activate the mechanosensitive ion channel of the hair cell. In addition, the model provides biophysical insight into 1) the likelihood that the channel must be linked in some way to the tip link; 2) how the interplay of the bending and stretching of the lipid bilayer may be responsible for the nonlinear force versus displacement response; 3) how measurements of negative stiffness may be a function of the rotational stiffness of the rootlets; and 4) how the standing tension of the tip link is required to interpret migration of the nonlinear force versus displacement and activation curves. These are all features of hair cell mechanotransduction, but the underlying biophysical mechanism has proved elusive for the last three decades. PMID:25650928

  3. Painted supported lipid membranes

    PubMed Central

    Florin, E.-L.; Gaub, H. E.

    1993-01-01

    We report herein measurements on a novel type of supported lipid films, which we call painted supported membranes (PSM). These membranes are formed in a self-assembly process on alkylated gold films from an organic solution. The formation process was investigated with surface plasmon resonance microscopy. The optical and electrical properties of the films were determined for various types of lipids and as a function of temperature by means of cyclic voltammetry and potential relaxation after charge injection. We could show that these films exhibit an extraordinarily high specific resistivity which, depending on the lipid, may be as high as 109 ohm/cm2. We could also show that due to this low conductivity, an electrical polarization across the PSM relaxes with characteristic time constants of up to 20 min. The electrical properties together with their high mechanical stability and accessibility to surface sensitive techniques make these films well suitable model membranes for optical and electrical investigations. Examples for such applications are given in the subsequent article by Seifert et al. ImagesFIGURE 3FIGURE 4 PMID:19431873

  4. Sensing voltage across lipid membranes

    PubMed Central

    Swartz, Kenton J.

    2009-01-01

    The detection of electrical potentials across lipid bilayers by specialized membrane proteins is required for many fundamental cellular processes such as the generation and propagation of nerve impulses. These membrane proteins possess modular voltage-sensing domains, a notable example being the S1-S4 domains of voltage-activated ion channels. Ground-breaking structural studies on these domains explain how voltage sensors are designed and reveal important interactions with the surrounding lipid membrane. Although further structures are needed to fully understand the conformational changes that occur during voltage sensing, the available data help to frame several key concepts that are fundamental to the mechanism of voltage sensing. PMID:19092925

  5. Regulation of Lipid Droplet Size in Mammary Epithelial Cells by Remodeling of Membrane Lipid Composition—A Potential Mechanism

    PubMed Central

    Cohen, Bat-Chen; Shamay, Avi; Argov-Argaman, Nurit

    2015-01-01

    Milk fat globule size is determined by the size of its precursors—intracellular lipid droplets—and is tightly associated with its composition. We examined the relationship between phospholipid composition of mammary epithelial cells and the size of both intracellular and secreted milk fat globules. Primary culture of mammary epithelial cells was cultured in medium without free fatty acids (control) or with 0.1 mM free capric, palmitic or oleic acid for 24 h. The amount and composition of the cellular lipids and the size of the lipid droplets were determined in the cells and medium. Mitochondrial quantity and expression levels of genes associated with mitochondrial biogenesis and polar lipid composition were determined. Cells cultured with oleic and palmitic acids contained similar quantities of triglycerides, 3.1- and 3.8-fold higher than in controls, respectively (P < 0.0001). When cultured with oleic acid, 22% of the cells contained large lipid droplets (>3 μm) and phosphatidylethanolamine concentration was higher by 23 and 63% compared with that in the control and palmitic acid treatments, respectively (P < 0.0001). In the presence of palmitic acid, only 4% of the cells contained large lipid droplets and the membrane phosphatidylcholine concentration was 22% and 16% higher than that in the control and oleic acid treatments, respectively (P < 0.0001). In the oleic acid treatment, approximately 40% of the lipid droplets were larger than 5 μm whereas in that of the palmitic acid treatment, only 16% of the droplets were in this size range. Triglyceride secretion in the oleic acid treatment was 2- and 12-fold higher compared with that in the palmitic acid and control treatments, respectively. Results imply that membrane composition of bovine mammary epithelial cells plays a role in controlling intracellular and secreted lipid droplets size, and that this process is not associated with cellular triglyceride content. PMID:25756421

  6. Lipid-II forms potential “landing terrain” for lantibiotics in simulated bacterial membrane

    PubMed Central

    Chugunov, Anton; Pyrkova, Darya; Nolde, Dmitry; Polyansky, Anton; Pentkovsky, Vladimir; Efremov, Roman

    2013-01-01

    Bacterial cell wall is targeted by many antibiotics. Among them are lantibiotics, which realize their function via interaction with plasma membrane lipid-II molecule — a chemically conserved part of the cell wall synthesis pathway. To investigate structural and dynamic properties of this molecule, we have performed a series of nearly microsecond-long molecular dynamics simulations of lipid-II and some of its analogs in zwitterionic single component and charged mixed simulated phospholipid bilayers (the reference and the mimic of the bacterial plasma membrane, respectively). Extensive analysis revealed that lipid-II forms a unique “amphiphilic pattern” exclusively on the surface of the simulated bacterial membrane (and not in the reference one). We hypothesize that many lantibiotics exploit the conserved features of lipid-II along with characteristic modulation of the bacterial membrane as the “landing site”. This putative recognition mechanism opens new opportunities for studies on lantibiotics action and design of novel armament against resistant bacterial strains. PMID:23588060

  7. Electrostatics of Deformable Lipid Membranes

    PubMed Central

    Vorobyov, Igor; Bekker, Borislava; Allen, Toby W.

    2010-01-01

    Abstract It was recently demonstrated that significant local deformations of biological membranes take place due to the fields of charged peptides and ions, challenging the standard model of membrane electrostatics. The ability of ions to retain their immediate hydration environment, combined with the lack of sensitivity of permeability to ion type or even ion pairs, led us to question the extent to which hydration energetics and electrostatics control membrane ion permeation. Using the arginine analog methyl-guanidinium as a test case, we find that although hydrocarbon electronic polarizability causes dramatic changes in ion solvation free energy, as well as a significant change (∼0.4 V) in the membrane dipole potential, little change in membrane permeation energetics occurs. We attribute this to compensation of solvation terms from polar and polarizable nonpolar components within the membrane, and explain why the dipole potential is not fully sensed in terms of the locally deformed bilayer interface. Our descriptions provide a deeper understanding of the translocation process and allow predictions for poly-ions, ion pairs, charged lipids, and lipid flip-flop. We also report simulations of large hydrophobic-ion-like membrane defects and the ionophore valinomycin, which exhibit little membrane deformation, as well as hydrophilic defects and the ion channel gramicidin A, to provide parallels to membranes deformed by unassisted ion permeation. PMID:20550903

  8. Influence of the membrane dipole potential on peptide binding to lipid bilayers

    PubMed Central

    Zhan, Huan; Lazaridis, Themis

    2011-01-01

    The implicit membrane model IMM1 is extended to include the membrane dipole potential and applied to molecular dynamics simulations of the helical peptides alamethicin, WALP23, influenza hemagglutinin fusion peptide, HIV fusion peptide, magainin, and the pre-sequence of cytochrome c oxidase subunit IV (p25). The results show that the orientation of the peptides in the membrane can be influenced by the dipole potential. The binding affinity of all peptides except for the hemagglutinin fusion peptide decreases upon increase of the dipole potential. The changes in both orientation and binding affinity are explained by the interaction of the dipole potential with the helix backbone dipole and ionic side-chains. In general, peptides that tend to insert the N-terminus in the membrane and/or have positively charged side chains will lose binding affinity upon increase of the dipole potential. PMID:22100997

  9. Permeability across lipid membranes.

    PubMed

    Shinoda, Wataru

    2016-10-01

    Molecular permeation through lipid membranes is a fundamental biological process that is important for small neutral molecules and drug molecules. Precise characterization of free energy surface and diffusion coefficients along the permeation pathway is required in order to predict molecular permeability and elucidate the molecular mechanisms of permeation. Several recent technical developments, including improved molecular models and efficient sampling schemes, are illustrated in this review. For larger penetrants, explicit consideration of multiple collective variables, including orientational, conformational degrees of freedom, are required to be considered in addition to the distance from the membrane center along the membrane normal. Although computationally demanding, this method can provide significant insights into the molecular mechanisms of permeation for molecules of medical and pharmaceutical importance. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg. PMID:27085977

  10. Potentiation of ethanol-induced lipid peroxidation of biological membranes by vitamin C

    SciTech Connect

    Ahmad, F.F.; Cowan, D.L.; Sun, A.Y.

    1988-01-01

    The hydroxyl free radical (/sup ./OH) was generated by the system of ADP-Fe/sup + +/ and H/sub 2/O/sub 2/, trapped by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and analyzed by electron spin resonance (ESR) spectroscopy. The addition of vitamin C to the system decreased considerably the amount of hydroxyl adduct of DMPO formed. In the presence of ethanol, the ESR spectrum observed was a composite signal of the hydroxyl and hydroxyethyl (HE) adducts of DMPO. However, in the presence of vitamin C and ethanol, pure HE adduct of DMPO was detected. We also detected the increase in lipid peroxidation in the presence of ethanol and vitamin C. These data lead us to hypothesize that in the biological system, formation of these long-lived HE free radicals may result in membrane damage due to an increase in lipid peroxidation.

  11. Tension moderation and fluctuation spectrum in simulated lipid membranes under an applied electric potential.

    PubMed

    Loubet, Bastien; Lomholt, Michael Andersen; Khandelia, Himanshu

    2013-10-28

    We investigate the effect of an applied electric potential on the mechanics of a coarse grained POPC bilayer under tension. The size and duration of our simulations allow for a detailed and accurate study of the fluctuations. Effects on the fluctuation spectrum, tension, bending rigidity, and bilayer thickness are investigated in detail. In particular, the least square fitting technique is used to calculate the fluctuation spectra. The simulations confirm a recently proposed theory that the effect of an applied electric potential on the membrane will be moderated by the elastic properties of the membrane. In agreement with the theory, we find that the larger the initial tension the larger the effect of the electric potential. Application of the electric potential increases the amplitude of the long wavelength part of the spectrum and the bending rigidity is deduced from the short wavelength fluctuations. The effect of the applied electric potential on the bending rigidity is non-existent within error bars. However, when the membrane is stretched there is a point where the bending rigidity is lowered due to a decrease of the thickness of the membrane. All these effects should prove important for mechanosensitive channels and biomembrane mechanics in general. PMID:24182074

  12. A Crystal Structure of a Dimer of the Antibiotic Ramoplanin Illustrates Membrane Positioning and a Potential Lipid II Docking Interface

    SciTech Connect

    Hamburger, J.; Hoertz, A; Lee, A; Senturia, R; McCafferty, D; Loll, P

    2009-01-01

    The glycodepsipeptide antibiotic ramoplanin A2 is in late stage clinical development for the treatment of infections from Gram-positive pathogens, especially those that are resistant to first line antibiotics such as vancomycin. Ramoplanin A2 achieves its antibacterial effects by interfering with production of the bacterial cell wall; it indirectly inhibits the transglycosylases responsible for peptidoglycan biosynthesis by sequestering their Lipid II substrate. Lipid II recognition and sequestration occur at the interface between the extracellular environment and the bacterial membrane. Therefore, we determined the structure of ramoplanin A2 in an amphipathic environment, using detergents as membrane mimetics, to provide the most physiologically relevant structural context for mechanistic and pharmacological studies. We report here the X-ray crystal structure of ramoplanin A2 at a resolution of 1.4 {angstrom}. This structure reveals that ramoplanin A2 forms an intimate and highly amphipathic dimer and illustrates the potential means by which it interacts with bacterial target membranes. The structure also suggests a mechanism by which ramoplanin A2 recognizes its Lipid II ligand.

  13. Two photon fluorescence imaging of lipid membrane domains and potentials using advanced fluorescent probes

    NASA Astrophysics Data System (ADS)

    Kilin, Vasyl; Darwich, Zeinab; Richert, Ludovic; Didier, Pascal; Klymchenko, Andrey; Mély, Yves

    2013-02-01

    Biomembranes are ordered and dynamic nanoscale structures critical for cell functions. The biological functions of the membranes strongly depend on their physicochemical properties, such as electrostatics, phase state, viscosity, polarity and hydration. These properties are essential for the membrane structure and the proper folding and function of membrane proteins. To monitor these properties, fluorescence techniques and notably, two-photon microscopy appear highly suited due to their exquisite sensitivity and their capability to operate in complex biological systems, such as living cells and tissues. In this context, we have developed multiparametric environment-sensitive fluorescent probes tailored for precise location in the membrane bilayer. We notably developed probes of the 3-hydroxychromone family, characterized by an excited state intramolecular proton transfer reaction, which generates two tautomeric emissive species with well-separated emission bands. As a consequence, the response of these probes to changes in their environment could be monitored through changes in the ratios of the two bands, as well as through changes in the fluorescence lifetimes. Using two-photon ratiometric imaging and FLIM, these probes were used to monitor the surface membrane potential, and were applied to detect apoptotic cells and image membrane domains.

  14. S-layer stabilized lipid membranes (Review)

    PubMed Central

    Schuster, Bernhard; Pum, Dietmar; Sleytr, Uwe B.

    2010-01-01

    The present review focuses on a unique bio-molecular construction kit based on surface-layer (S-layer) proteins as building blocks and patterning elements, but also major classes of biological molecules such as lipids, membrane-active peptides and membrane proteins, and glycans for the design of functional supported lipid membranes. The biomimetic approach copying the supramolecular building principle of most archaeal cell envelopes merely composed of a plasma membrane and a closely associated S-layer lattice has resulted in robust and fluid lipid membranes. Most importantly, S-layer supported lipid membranes spanning an aperture or generated on solid and porous substrates constitute highly interesting model membranes for the reconstitution of responsive transmembrane proteins and membrane-active peptides. This is of particular challenge as one-third of all proteins are membrane proteins such as pore-forming proteins, ion channels, and receptors. S-layer supported lipid membranes are seen as one of the most innovative strategies in membrane protein-based nanobiotechnology with potential applications that range from pharmaceutical (high-throughput) drug screening over lipid chips to the detection of biological warfare agents. PMID:20408666

  15. Lipid exchange between membranes.

    PubMed Central

    Jähnig, F

    1984-01-01

    The exchange of lipid molecules between vesicle bilayers in water and a monolayer forming at the water surface was investigated theoretically within the framework of thermodynamics. The total number of exchanged molecules was found to depend on the bilayer curvature as expressed by the vesicle radius and on the boundary condition for exchange, i.e., whether during exchange the radius or the packing density of the vesicles remains constant. The boundary condition is determined by the rate of flip-flop within the bilayer relative to the rate of exchange between bi- and monolayer. If flip-flop is fast, exchange is independent of the vesicle radius; if flip-flop is slow, exchange increases with the vesicle radius. Available experimental results agree with the detailed form of this dependence. When the theory was extended to exchange between two bilayers of different curvature, the direction of exchange was also determined by the curvatures and the boundary conditions for exchange. Due to the dependence of the boundary conditions on flip-flop and, consequently, on membrane fluidity, exchange between membranes may partially be regulated by membrane fluidity. PMID:6518251

  16. Electronic polymers in lipid membranes

    PubMed Central

    Johansson, Patrik K.; Jullesson, David; Elfwing, Anders; Liin, Sara I.; Musumeci, Chiara; Zeglio, Erica; Elinder, Fredrik; Solin, Niclas; Inganäs, Olle

    2015-01-01

    Electrical interfaces between biological cells and man-made electrical devices exist in many forms, but it remains a challenge to bridge the different mechanical and chemical environments of electronic conductors (metals, semiconductors) and biosystems. Here we demonstrate soft electrical interfaces, by integrating the metallic polymer PEDOT-S into lipid membranes. By preparing complexes between alkyl-ammonium salts and PEDOT-S we were able to integrate PEDOT-S into both liposomes and in lipid bilayers on solid surfaces. This is a step towards efficient electronic conduction within lipid membranes. We also demonstrate that the PEDOT-S@alkyl-ammonium:lipid hybrid structures created in this work affect ion channels in the membrane of Xenopus oocytes, which shows the possibility to access and control cell membrane structures with conductive polyelectrolytes. PMID:26059023

  17. Lipid membranes on nanostructured silicon.

    SciTech Connect

    Slade, Andrea Lynn; Lopez, Gabriel P.; Ista, Linnea K.; O'Brien, Michael J.; Sasaki, Darryl Yoshio; Bisong, Paul; Zeineldin, Reema R.; Last, Julie A.; Brueck, Stephen R. J.

    2004-12-01

    A unique composite nanoscale architecture that combines the self-organization and molecular dynamics of lipid membranes with a corrugated nanotextured silicon wafer was prepared and characterized with fluorescence microscopy and scanning probe microscopy. The goal of this project was to understand how such structures can be assembled for supported membrane research and how the interfacial interactions between the solid substrate and the soft, self-assembled material create unique physical and mechanical behavior through the confinement of phases in the membrane. The nanometer scale structure of the silicon wafer was produced through interference lithography followed by anisotropic wet etching. For the present study, a line pattern with 100 nm line widths, 200 nm depth and a pitch of 360 nm pitch was fabricated. Lipid membranes were successfully adsorbed on the structured silicon surface via membrane fusion techniques. The surface topology of the bilayer-Si structure was imaged using in situ tapping mode atomic force microscopy (AFM). The membrane was observed to drape over the silicon structure producing an undulated topology with amplitude of 40 nm that matched the 360 nm pitch of the silicon structure. Fluorescence recovery after photobleaching (FRAP) experiments found that on the microscale those same structures exhibit anisotropic lipid mobility that was coincident with the silicon substructure. The results showed that while the lipid membrane maintains much of its self-assembled structure in the composite architecture, the silicon substructure indeed influences the dynamics of the molecular motion within the membrane.

  18. Lipid metabolism in mitochondrial membranes.

    PubMed

    Mayr, Johannes A

    2015-01-01

    Mitochondrial membranes have a unique lipid composition necessary for proper shape and function of the organelle. Mitochondrial lipid metabolism involves biosynthesis of the phospholipids phosphatidylethanolamine, cardiolipin and phosphatidylglycerol, the latter is a precursor of the late endosomal lipid bis(monoacylglycero)phosphate. It also includes mitochondrial fatty acid synthesis necessary for the formation of the lipid cofactor lipoic acid. Furthermore the synthesis of coenzyme Q takes place in mitochondria as well as essential parts of the steroid and vitamin D metabolism. Lipid transport and remodelling, which are necessary for tailoring and maintaining specific membrane properties, are just partially unravelled. Mitochondrial lipids are involved in organelle maintenance, fission and fusion, mitophagy and cytochrome c-mediated apoptosis. Mutations in TAZ, SERAC1 and AGK affect mitochondrial phospholipid metabolism and cause Barth syndrome, MEGDEL and Sengers syndrome, respectively. In these disorders an abnormal mitochondrial energy metabolism was found, which seems to be due to disturbed protein-lipid interactions, affecting especially enzymes of the oxidative phosphorylation. Since a growing number of enzymes and transport processes are recognised as parts of the mitochondrial lipid metabolism, a further increase of lipid-related disorders can be expected. PMID:25082432

  19. Modification of ion transport in lipid bilayer membranes in the presence of 2,4-dichlorophenoxyacetic acid. II. Suppression of tetraphenylborate conductance and changes of interfacial potentials.

    PubMed Central

    Smejtek, P; Paulis-Illangasekare, M

    1979-01-01

    It has been shown that the blocking of negatively charged tetraphenylborate ion transport in phosphatidylcholine (PC)-cholesterol membranes by the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is dominated by suppression of TPhB- diffusion across the membrane interior, rather than by the decrease of adsorption of TPhB- ions at the membrane surface. The blocking effect can be associated with the decrease of electric potential inside the membrane with respect to that of the aqueous medium, this decreases being proportional to the concentration of 2,4-D in the aqueous solution. It has been estimated that 25 - 30% of the total 2,4-D-induced change of the potential difference is between the plane of absorption of TPhB- and the aqueous solution, and the remaining fraction is between the membrane interior and the absorption plane. The results of this study support the dipolar hypothesis of 2,4-D action in lipid membranes. These conclusions are further supported by measurements changes of electric potential difference across air/water and air/lipid monolayer/water interfaces. It has been found that the electric potential of the nonpolar side of the interface decreases in the presence of neutral molecules of 2,4-D and that this effect becomes more prominent in presence of electrolyte. We have confirmed that PC-cholesterol monolayer cannot be considered as a model for half of the bilayer membrane because of the disagreement between the changes of the interfacial potential difference of PC-cholesterol monolayers and those determined from studied of transport of positive and negative ions across bilayer membranes. In contract, we have found close agreement between the 2,4-D-induced changes of electric potential of the lipid hydrocarbon region in glycerolmonooleate (GMO) membranes and GMO monolayers. We suggest that the action of 2,4-D in lipid membranes is not associated with the changes of orientation of dipoles of lipids constituting the membranes, but rather with a layer

  20. Modification of ion transport in lipid bilayer membranes in the presence of 2,4-dichlorophenoxyacetic acid. II. Suppression of tetraphenylborate conductance and changes of interfacial potentials.

    PubMed

    Smejtek, P; Paulis-Illangasekare, M

    1979-06-01

    It has been shown that the blocking of negatively charged tetraphenylborate ion transport in phosphatidylcholine (PC)-cholesterol membranes by the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is dominated by suppression of TPhB- diffusion across the membrane interior, rather than by the decrease of adsorption of TPhB- ions at the membrane surface. The blocking effect can be associated with the decrease of electric potential inside the membrane with respect to that of the aqueous medium, this decreases being proportional to the concentration of 2,4-D in the aqueous solution. It has been estimated that 25 - 30% of the total 2,4-D-induced change of the potential difference is between the plane of absorption of TPhB- and the aqueous solution, and the remaining fraction is between the membrane interior and the absorption plane. The results of this study support the dipolar hypothesis of 2,4-D action in lipid membranes. These conclusions are further supported by measurements changes of electric potential difference across air/water and air/lipid monolayer/water interfaces. It has been found that the electric potential of the nonpolar side of the interface decreases in the presence of neutral molecules of 2,4-D and that this effect becomes more prominent in presence of electrolyte. We have confirmed that PC-cholesterol monolayer cannot be considered as a model for half of the bilayer membrane because of the disagreement between the changes of the interfacial potential difference of PC-cholesterol monolayers and those determined from studied of transport of positive and negative ions across bilayer membranes. In contract, we have found close agreement between the 2,4-D-induced changes of electric potential of the lipid hydrocarbon region in glycerolmonooleate (GMO) membranes and GMO monolayers. We suggest that the action of 2,4-D in lipid membranes is not associated with the changes of orientation of dipoles of lipids constituting the membranes, but rather with a layer

  1. How Membrane-Active Peptides Get into Lipid Membranes.

    PubMed

    Sani, Marc-Antoine; Separovic, Frances

    2016-06-21

    mechanism by which these membrane-active peptides lyse membranes. The last class of membrane-active peptides discussed are the CPPs, which translocate across the lipid bilayer without inducing severe disruption and have potential as drug vehicles. CPPs are typically highly charged and can show antimicrobial activity by targeting an intracellular target rather than via a direct membrane lytic mechanism. A critical aspect in the structure-function relationship of membrane-active peptides is their specific activity relative to the lipid membrane composition of the cell target. Cell membranes have a wide diversity of lipids, and those of eukaryotic and prokaryotic species differ greatly in composition and structure. The activity of AMPs from Australian tree frogs, toxins, and CPPs has been investigated within various lipid systems to assess whether a relationship between peptide and membrane composition could be identified. NMR spectroscopy techniques are being used to gain atomistic details of how these membrane-active peptides interact with model membranes and cells, and in particular, competitive assays demonstrate the difference between affinity and activity for a specific lipid environment. Overall, the interactions between these relatively small sized peptides and various lipid bilayers give insight into how these peptides function at the membrane interface. PMID:27187572

  2. Membrane lipids of Mycoplasma fermentans.

    PubMed

    Salman, M; Deutsch, I; Tarshis, M; Naot, Y; Rottem, S

    1994-11-01

    Membranes of Mycoplasma fermentans, incognitus strain, were isolated by a combination of osmotic lysis and sonication. Analysis of membrane lipids revealed, in addition to free and esterified cholesterol, six major polar lipids dominated by a de novo synthesized compound (compound X), which accounts for 64% of the total lipid phosphorus. Compound X was labeled by palmitate, but not by oleate. Mass spectrometry and gas liquid chromatography analyses of compound X revealed two molecular species with molecular masses of 1048 and 1076 representing, a dipalmitoyl- and a stearoyl-palmitoyl-glycerodiphosphatidylcholine. Compound X has the ability to stimulate human monocytes to secret TNF alpha and to enhance the fusion of small unilamellar vesicles with MOLT-3 lymphocytes. PMID:7988908

  3. Atomistic Monte Carlo Simulation of Lipid Membranes

    PubMed Central

    Wüstner, Daniel; Sklenar, Heinz

    2014-01-01

    Biological membranes are complex assemblies of many different molecules of which analysis demands a variety of experimental and computational approaches. In this article, we explain challenges and advantages of atomistic Monte Carlo (MC) simulation of lipid membranes. We provide an introduction into the various move sets that are implemented in current MC methods for efficient conformational sampling of lipids and other molecules. In the second part, we demonstrate for a concrete example, how an atomistic local-move set can be implemented for MC simulations of phospholipid monomers and bilayer patches. We use our recently devised chain breakage/closure (CBC) local move set in the bond-/torsion angle space with the constant-bond-length approximation (CBLA) for the phospholipid dipalmitoylphosphatidylcholine (DPPC). We demonstrate rapid conformational equilibration for a single DPPC molecule, as assessed by calculation of molecular energies and entropies. We also show transition from a crystalline-like to a fluid DPPC bilayer by the CBC local-move MC method, as indicated by the electron density profile, head group orientation, area per lipid, and whole-lipid displacements. We discuss the potential of local-move MC methods in combination with molecular dynamics simulations, for example, for studying multi-component lipid membranes containing cholesterol. PMID:24469314

  4. Lipidic phase membrane protein serial femtosecond crystallography

    PubMed Central

    Johansson, Linda C; Arnlund, David; White, Thomas A; Katona, Gergely; DePonte, Daniel P; Weierstall, Uwe; Doak, R Bruce; Shoeman, Robert L; Lomb, Lukas; Malmerberg, Erik; Davidsson, Jan; Nass, Karol; Liang, Mengning; Andreasson, Jakob; Aquila, Andrew; Bajt, Sasa; Barthelmess, Miriam; Barty, Anton; Bogan, Michael J; Bostedt, Christoph; Bozek, John D; Caleman, Carl; Coffee, Ryan; Coppola, Nicola; Ekeberg, Tomas; Epp, Sascha W; Erk, Benjamin; Fleckenstein, Holger; Foucar, Lutz; Graafsma, Heinz; Gumprecht, Lars; Hajdu, Janos; Hampton, Christina Y; Hartmann, Robert; Hartmann, Andreas; Hauser, Günter; Hirsemann, Helmut; Holl, Peter; Hunter, Mark S; Kassemeyer, Stephan; Kimmel, Nils; Kirian, Richard A; Maia, Filipe R N C; Marchesini, Stefano; Martin, Andrew V; Reich, Christian; Rolles, Daniel; Rudek, Benedikt; Rudenko, Artem; Schlichting, Ilme; Schulz, Joachim; Seibert, M Marvin; Sierra, Raymond G; Soltau, Heike; Starodub, Dmitri; Stellato, Francesco; Stern, Stephan; Strüder, Lothar; Timneanu, Nicusor; Ullrich, Joachim; Wahlgren, Weixiao Y; Wang, Xiaoyu; Weidenspointner, Georg; Wunderer, Cornelia; Fromme, Petra; Chapman, Henry N; Spence, John C H; Neutze, Richard

    2012-01-01

    X-ray free electron laser (X-feL)-based serial femtosecond crystallography is an emerging method with potential to rapidly advance the challenging field of membrane protein structural biology. here we recorded interpretable diffraction data from micrometer-sized lipidic sponge phase crystals of the Blastochloris viridis photosynthetic reaction center delivered into an X-feL beam using a sponge phase micro-jet. PMID:22286383

  5. Menthol-induced action potentials in Conocephalum conicum as a result of unspecific interactions between menthol and the lipid phase of the plasma membrane.

    PubMed

    Kupisz, Kamila; Trebacz, Kazimierz; Gruszecki, Wiesław I

    2015-07-01

    Our previous study has shown that the liverwort Conocephalum conicum generates action potentials (APs) in response to both temperature drop and menthol, which are also activators of the TRPM8 (transient receptor potential melastatin 8) receptor in animals. Not only similarities but also differences between electrical reactions to menthol and cooling observed in the liverwort aroused our interest in the action of menthol at the molecular level. Patch-clamp investigations have shown that menthol causes a reduction of current flowing through slow vacuolar (SV) channels to 29 ± 10% of the initial value (n = 9); simultaneously, it does not influence magnitudes of currents passing through a single SV channel. This may point to an unspecific interaction between menthol and the lipid phase of the membrane. An influence of menthol on lipid organization in membranes was investigated in two-component monomolecular layers formed with menthol and dipalmitoylphosphatidylcholine (DPPC) at the argon-water interface. Analyses of the mean molecular area parameters vs the molar fraction of the menthol component have shown over-additivity (approximately 20 Å(2) ) in the region of high molar fractions of menthol. Infrared absorption spectroscopy studies have shown that menthol, most probably, induces breaking of a hydrogen bond network formed by ester carbonyl groups and water bridges in the lipid membrane and binds to the polar head group region of DPPC. We conclude that the disruption in the lipid phase of the membrane influences ion channels and/or pumps and subsequently causes generation of APs in excitable plants such as C. conicum. PMID:25256908

  6. Electrodiffusion of lipids on membrane surfaces

    NASA Astrophysics Data System (ADS)

    Zhou, Y. C.

    2012-05-01

    Lateral translocation of lipids and proteins is a universal process on membrane surfaces. Local aggregation or organization of lipids and proteins can be induced when the random lateral motion is mediated by the electrostatic interactions and membrane curvature. Although the lateral diffusion rates of lipids on membranes of various compositions are measured and the electrostatic free energies of predetermined protein-membrane-lipid systems can be computed, the process of the aggregation and the evolution to the electrostatically favorable states remain largely undetermined. Here we propose an electrodiffusion model, based on the variational principle of the free energy functional, for the self-consistent lateral drift-diffusion of multiple species of charged lipids on membrane surfaces. Finite sizes of lipids are modeled to enforce the geometrical constraint of the lipid concentration on membrane surfaces. A surface finite element method is developed to appropriate the Laplace-Beltrami operators in the partial differential equations of the model. Our model properly describes the saturation of lipids on membrane surfaces, and correctly predicts that the MARCKS peptide can consistently sequester three multivalent phosphatidylinositol 4,5-bisphosphate lipids through its basic amino acid residues, regardless of a wide range of the percentage of monovalent phosphatidylserine in the membrane.

  7. Potential scorpionate antibiotics: targeted hydrolysis of lipid II containing model membranes by vancomycin-TACzyme conjugates and modulation of their antibacterial activity by Zn-ions.

    PubMed

    Bauke Albada, H; Arnusch, Christopher J; Branderhorst, Hilbert M; Verel, Anne-Marie; Janssen, Wouter T M; Breukink, Eefjan; de Kruijff, Ben; Pieters, Roland J; Liskamp, Rob M J

    2009-07-15

    The antibiotic vancomycin-that binds lipid II in the bacterial cell membrane-was conjugated to a mono- and tetravalent mimic of the tris-histidine catalytic triad of metalloenzymes. Targeted hydrolysis by the conjugate was observed using model membranes containing lipid II, and in vitro MIC-values of the targeted mimic constructs could be modulated by Zn-ions. PMID:19524434

  8. Effect of surface-potential modulators on the opening of lipid pores in liposomal and mitochondrial inner membranes induced by palmitate and calcium ions.

    PubMed

    Belosludtsev, Konstantin N; Belosludtseva, Natalia V; Agafonov, Alexey V; Penkov, Nikita V; Samartsev, Victor N; Lemasters, John J; Mironova, Galina D

    2015-10-01

    The effect of surface-potential modulators on palmitate/Ca2+-induced formation of lipid pores was studied in liposomal and inner mitochondrial membranes. Pore formation was monitored by sulforhodamine B release from liposomes and swelling of mitochondria. ζ-potential in liposomes was determined from electrophoretic mobility. Replacement of sucrose as the osmotic agent with KCl decreased negative ζ-potential in liposomes and increased resistance of both mitochondria and liposomes to the pore inducers, palmitic acid, and Ca2+. Micromolar Mg2+ also inhibited palmitate/Ca2+-induced permeabilization of liposomes. The rate of palmitate/Ca2+-induced, cyclosporin A-insensitive swelling of mitochondria increased 22% upon increasing pH from 7.0 to 7.8. At below the critical micelle concentration, the cationic detergent cetyltrimethylammonium bromide (10 μM) and the anionic surfactant sodium dodecylsulfate (10-50 μM) made the ζ-potential less and more negative, respectively, and inhibited and stimulated opening of mitochondrial palmitate/Ca2+-induced lipid pores. Taken together, the findings indicate that surface potential regulates palmitate/Ca2+-induced lipid pore opening. PMID:26014488

  9. Effect of surface-potential modulators on the opening of lipid pores in liposomal and mitochondrial inner membranes induced by palmitate and calcium ions

    PubMed Central

    Belosludtsev, Konstantin N.; Belosludtseva, Natalia V.; Agafonov, Alexey V.; Penkov, Nikita V.; Samartsev, Victor N.; Lemasters, John J.; Mironova, Galina D.

    2016-01-01

    The effect of surface-potential modulators on palmitate/Ca2+-induced formation of lipid pores was studied in liposomal and inner mitochondrial membranes. Pore formation was monitored by sulforhodamine B release from liposomes and swelling of mitochondria. ζ-potential in liposomes was determined from electrophoretic mobility. Replacement of sucrose as the osmotic agent with KCl decreased negative ζ-potential in liposomes and increased resistance of both mitochondria and liposomes to the pore inducers, palmitic acid, and Ca2+. Micromolar Mg2+ also inhibited palmitate/Ca2+-induced permeabilization of liposomes. The rate of palmitate/Ca2+-induced, cyclosporin A-insensitive swelling of mitochondria increased 22% upon increasing pH from 7.0 to 7.8. At below the critical micelle concentration, the cationic detergent cetyltrimethylammonium bromide (10 μM) and the anionic surfactant sodium dodecylsulfate (10–50 μM) made the ζ-potential less and more negative, respectively, and inhibited and stimulated opening of mitochondrial palmitate/Ca2+-induced lipid pores. Taken together, the findings indicate that surface potential regulates palmitate/Ca2+-induced lipid pore opening. PMID:26014488

  10. Insights into thermophilic archaebacterial membrane stability from simplified models of lipid membranes

    NASA Astrophysics Data System (ADS)

    Davis, Charles H.; Nie, Huifen; Dokholyan, Nikolay V.

    2007-05-01

    Lipid aggregation into fluid bilayers is an essential process for sustaining life. Simplified models of lipid structure, which allow for long time scales or large length scales not obtainable with all-atom simulations, have recently been developed and show promise for describing lipid dynamics in biological systems. Here, we describe two simplified models, a reduced-lipid model and a bola-lipid model for thermophilic bacterial membranes, developed for use with the rapid discrete molecular dynamics simulation method. In the reduced-lipid model, we represent the lipid chain by a series of three beads interacting through pairwise discrete potentials that model hydrophobic attractions between hydrocarbon tails in implicit solvent. Our phase diagram recapitulates those produced by continuous potential models with similar coarse-grained lipid representations. We also find that phase transition temperatures for our reduced-lipid model are dependent upon the flexibility of the lipid chain, giving an insight into archaebacterial membrane stability and prompting development of a bola-lipid model specific for archaebacteria lipids. With both the reduced-lipid and bola-lipid model, we find that the reduced flexibility inherent in archaebacteria lipids yields more stable bilayers as manifested by increased phase transition temperatures. The results of these studies provide a simulation methodology for lipid molecules in biological systems and show that discrete molecular dynamics is applicable to lipid aggregation and dynamics.

  11. Model answers to lipid membrane questions.

    PubMed

    Mouritsen, Ole G

    2011-09-01

    Ever since it was discovered that biological membranes have a core of a bimolecular sheet of lipid molecules, lipid bilayers have been a model laboratory for investigating physicochemical and functional properties of biological membranes. Experimental and theoretical models help the experimental scientist to plan experiments and interpret data. Theoretical models are the theoretical scientist's preferred toys to make contact between membrane theory and experiments. Most importantly, models serve to shape our intuition about which membrane questions are the more fundamental and relevant ones to pursue. Here we review some membrane models for lipid self-assembly, monolayers, bilayers, liposomes, and lipid-protein interactions and illustrate how such models can help answering questions in modern lipid cell biology. PMID:21610116

  12. Characterization of lipid domains in erythrocyte membranes.

    PubMed Central

    Rodgers, W; Glaser, M

    1991-01-01

    Fluorescence digital imaging microscopy was used to study the lateral distribution of the lipid components in erythrocyte membranes. Intact erythrocytes labeled with phospholipids containing a fluorophore attached to one fatty acid chain showed an uneven distribution of the phospholipids in the membrane thereby demonstrating the presence of membrane domains. The enrichment of the lipotropic compound chlor-promazine in domains in intact erythrocytes also suggested that the domains are lipid-enriched regions. Similar membrane domains were present in erythrocyte ghosts. The phospholipid enrichment was increased in the domains by inducing membrane protein aggregation. Double-labeling experiments were done to determine the relative distributions of different phospholipids in the membrane. Vesicles made from extracted lipids did not show the presence of domains consistent with the conclusion that membrane proteins were responsible for creating the domains. Overall, it was found that large domains exist in the red blood cell membrane with unequal enrichment of the different phospholipid species. Images PMID:1996337

  13. Single molecule dynamics in lipid membranes

    NASA Astrophysics Data System (ADS)

    Skaug, Michael James

    Lipid membranes are self-assembled molecular materials that form the membranes of cells. Because of their biological function, lipid membranes are important from a biomedical and biotechnological standpoint. Because of their complex fluid properties, they also provide a rich testbed for studying the structure and dynamics in self-assembled materials and for developing other bio-mimetic structures. In this work, we studied the dynamics of single lipid molecules using experimental and computational techniques. Using single molecule fluorescence microscopy, we tracked the diffusive motion of lipids in phase separated lipid membranes. With the additional techniques of atomic force microscopy and Monte Carlo simulation, we were able to, for the first time experimentally, directly correlate the observed obstructed diffusion with lipid membrane organization. The single molecule tracking tracking experiments required the addition of impurity fluorescent molecules and the assumption that the impurities do not alter the dynamics of the system. To test this assumption, we performed atomistic molecular dynamics simulations of a fluorescently labeled lipid in a lipid membrane. We showed that the fluorescent impurity could have a significant impact on some membrane properties, such as phase behavior, but that relative changes in diffusive behavior are unaffected.

  14. S-layer-supported lipid membranes.

    PubMed

    Schuster, B; Sleytr, U B

    2000-09-01

    Many prokaryotic organisms (archaea and bacteria) are covered by a regularly ordered surface layer (S-layer) as the outermost cell wall component. S-layers are built up of a single protein or glycoprotein species and represent the simplest biological membrane developed during evolution. Pores in S-layers are of regular size and morphology, and functional groups on the protein lattice are aligned in well-defined positions and orientations. Due to the high degree of structural regularity S-layers represent unique systems for studying the structure, morphogenesis, and function of layered supramolecular assemblies. Isolated S-layer subunits of numerous organisms are able to assemble into monomolecular arrays either in suspension, at air/water interfaces, on planar mono- and bilayer lipid films, on liposomes and on solid supports (e.g. silicon wafers). Detailed studies on composite S-layer/lipid structures have been performed with Langmuir films, freestanding bilayer lipid membranes, solid supported lipid membranes, and liposomes. Lipid molecules in planar films and liposomes interact via their head groups with defined domains on the S-layer lattice. Electrostatic interactions are the most prevalent forces. The hydrophobic chains of the lipid monolayers are almost unaffected by the attachment of the S-layer and no impact on the hydrophobic thickness of the membranes has been observed. Upon crystallization of a coherent S-layer lattice on planar and vesicular lipid membranes, an increase in molecular order is observed, which is reflected in a decrease of the membrane tension and an enhanced mobility of probe molecules within an S-layer-supported bilayer. Thus, the terminology 'semifluid membrane' has been introduced for describing S-layer-supported lipid membranes. The most important feature of composite S-layer/lipid membranes is an enhanced stability in comparison to unsupported membranes. PMID:11143799

  15. DMSO induces dehydration near lipid membrane surfaces.

    PubMed

    Cheng, Chi-Yuan; Song, Jinsuk; Pas, Jolien; Meijer, Lenny H H; Han, Songi

    2015-07-21

    Dimethyl sulfoxide (DMSO) has been broadly used in biology as a cosolvent, a cryoprotectant, and an enhancer of membrane permeability, leading to the general assumption that DMSO-induced structural changes in cell membranes and their hydration water play important functional roles. Although the effects of DMSO on the membrane structure and the headgroup dehydration have been extensively studied, the mechanism by which DMSO invokes its effect on lipid membranes and the direct role of water in this process are unresolved. By directly probing the translational water diffusivity near unconfined lipid vesicle surfaces, the lipid headgroup mobility, and the repeat distances in multilamellar vesicles, we found that DMSO exclusively weakens the surface water network near the lipid membrane at a bulk DMSO mole fraction (XDMSO) of <0.1, regardless of the lipid composition and the lipid phase. Specifically, DMSO was found to effectively destabilize the hydration water structure at the lipid membrane surface at XDMSO <0.1, lower the energetic barrier to dehydrate this surface water, whose displacement otherwise requires a higher activation energy, consequently yielding compressed interbilayer distances in multilamellar vesicles at equilibrium with unaltered bilayer thicknesses. At XDMSO >0.1, DMSO enters the lipid interface and restricts the lipid headgroup motion. We postulate that DMSO acts as an efficient cryoprotectant even at low concentrations by exclusively disrupting the water network near the lipid membrane surface, weakening the cohesion between water and adhesion of water to the lipid headgroups, and so mitigating the stress induced by the volume change of water during freeze-thaw. PMID:26200868

  16. Model Answers to Lipid Membrane Questions

    PubMed Central

    Mouritsen, Ole G.

    2011-01-01

    Ever since it was discovered that biological membranes have a core of a bimolecular sheet of lipid molecules, lipid bilayers have been a model laboratory for investigating physicochemical and functional properties of biological membranes. Experimental and theoretical models help the experimental scientist to plan experiments and interpret data. Theoretical models are the theoretical scientist’s preferred toys to make contact between membrane theory and experiments. Most importantly, models serve to shape our intuition about which membrane questions are the more fundamental and relevant ones to pursue. Here we review some membrane models for lipid self-assembly, monolayers, bilayers, liposomes, and lipid–protein interactions and illustrate how such models can help answering questions in modern lipid cell biology. PMID:21610116

  17. Biosynthesis of archaeal membrane ether lipids

    PubMed Central

    Jain, Samta; Caforio, Antonella; Driessen, Arnold J. M.

    2014-01-01

    A vital function of the cell membrane in all living organism is to maintain the membrane permeability barrier and fluidity. The composition of the phospholipid bilayer is distinct in archaea when compared to bacteria and eukarya. In archaea, isoprenoid hydrocarbon side chains are linked via an ether bond to the sn-glycerol-1-phosphate backbone. In bacteria and eukarya on the other hand, fatty acid side chains are linked via an ester bond to the sn-glycerol-3-phosphate backbone. The polar head groups are globally shared in the three domains of life. The unique membrane lipids of archaea have been implicated not only in the survival and adaptation of the organisms to extreme environments but also to form the basis of the membrane composition of the last universal common ancestor (LUCA). In nature, a diverse range of archaeal lipids is found, the most common are the diether (or archaeol) and the tetraether (or caldarchaeol) lipids that form a monolayer. Variations in chain length, cyclization and other modifications lead to diversification of these lipids. The biosynthesis of these lipids is not yet well understood however progress in the last decade has led to a comprehensive understanding of the biosynthesis of archaeol. This review describes the current knowledge of the biosynthetic pathway of archaeal ether lipids; insights on the stability and robustness of archaeal lipid membranes; and evolutionary aspects of the lipid divide and the LUCA. It examines recent advances made in the field of pathway reconstruction in bacteria. PMID:25505460

  18. Electro-hydrodynamic effects on lipid membranes in giant vesicles

    NASA Astrophysics Data System (ADS)

    Staykova, Margarita; Yamamoto, Tetsuya; Lipowsky, Reinhard; Dimova, Rumiana

    2009-11-01

    Electric fields are widely applied for cell manipulation in numerous micron-scale systems. Here, we show for the first time that alternating electric fields may cause pronounced flows in the membrane of giant lipid vesicles as well as in the surrounding fluid media.^ The lipid vesicles are not only biomimetic model for the cell membrane but also have many potential biotechnological applications, e.g. as drug-delivery systems and micro-reactors. The reported effects should be considered in electric micro-manipulation procedures on cells and vesicles. They might be useful for applications in microfluidic technologies, for lipid mixing, trapping and displacement, as will be demonstrated. We also believe that our method for visualization of the lipid flows by fluorescently labeled intra-membrane domains will be helpful for studies on membrane behavior in vesicles subjected to shear or mechanical stresses.

  19. Radiosensitization by fullerene-C60 dissolved in squalene on human malignant melanoma through lipid peroxidation and enhanced mitochondrial membrane potential

    NASA Astrophysics Data System (ADS)

    Kato, Shinya; Kimura, Masatsugu; Miwa, Nobuhiko

    2014-04-01

    We examined fullerene-C60 dissolved in squalene (C60/Sqe) for the ability to potentiate the radiosensitization under X-ray irradiation on human malignant melanoma HMV-II cells, which were treated with C60/Sqe and thereafter irradiated with X-ray. The cell proliferation for C60/Sqe was inhibited more markedly than for Sqe alone. Meanwhile, cell proliferation was almost unaltered for C60/squalane (Sqa) or Sqa, a hydrogenated form of Sqe, as compared to no-additive control. Thus radiosensitization of C60/Sqe is attributed to peroxidation of unsaturated bonds of squalene by X-ray-excited C60 in contrast to squalane. The fluorescence images of HMV-II cells stained with Rhodamine123, an indicator for mitochondrial membrane potential, were monitored for 6 h after X-ray irradiation. C60/Sqe obviously exhibited more augmented fluorescence intensity on perinuclear region of HMV-II cells than Sqe alone. TBARS assay showed that the lipid peroxidation level as malondialdehyde-equivalent increased by combination of C60/Sqe and X-ray dose-dependently on X-ray doses. C60/Sqe exhibited lipid peroxidation more markedly by 1.2-fold than Sqe alone. Thus the level of lipid peroxidation of squalene was sufficiently higher in C60/Sqe than in Sqe in the absence of C60 under X-ray irradiation, suggesting the combination of C60/Sqe and X-ray irradiation induced radiosensitization on HMV-II cells by peroxidation of absorbed Sqe in mitochondrial membrane via oxidative stress mediated by fullerene-C60.

  20. Critical dynamics in multicomponent lipid membranes.

    PubMed

    Haataja, Mikko

    2009-08-01

    The formation and dynamics of spatially extended compositional domains in multicomponent lipid membranes both in vivo and in vitro lie at the heart of many important biological and biophysical phenomena. While the thermodynamic basis for domain formation has been explored extensively in the past, the roles of membrane and exterior fluid hydrodynamics on domain formation kinetics have received less attention. A case in point is the impact of hydrodynamics on the dynamics of compositional heterogeneities in lipid membranes in the vicinity of a critical point. In this Rapid Communication it is argued that the asymptotic dynamic behavior of a lipid membrane system in the vicinity of a critical point is strongly influenced by hydrodynamic interactions. More specifically, a mode-coupling argument is developed which predicts a scaling behavior of lipid transport coefficients near the critical point for both symmetric and asymmetric bilayers immersed in a bulk fluid. PMID:19792068

  1. DNA nanostructures interacting with lipid bilayer membranes.

    PubMed

    Langecker, Martin; Arnaut, Vera; List, Jonathan; Simmel, Friedrich C

    2014-06-17

    CONSPECTUS: DNA has been previously shown to be useful as a material for the fabrication of static nanoscale objects, and also for the realization of dynamic molecular devices and machines. In many cases, nucleic acid assemblies directly mimic biological structures, for example, cytoskeletal filaments, enzyme scaffolds, or molecular motors, and many of the applications envisioned for such structures involve the study or imitation of biological processes, and even the interaction with living cells and organisms. An essential feature of biological systems is their elaborate structural organization and compartmentalization, and this most often involves membranous structures that are formed by dynamic assemblies of lipid molecules. Imitation of or interaction with biological systems using the tools of DNA nanotechnology thus ultimately and necessarily also involves interactions with lipid membrane structures, and thus the creation of DNA-lipid hybrid assemblies. Due to their differing chemical nature, however, highly charged nucleic acids and amphiphilic lipids do not seem the best match for the construction of such systems, and in fact they are rarely found in nature. In recent years, however, a large variety of lipid-interacting DNA conjugates were developed, which are now increasingly being applied also for the realization of DNA nanostructures interacting with lipid bilayer membranes. In this Account, we will present the current state of this emerging class of nanosystems. After a brief overview of the basic biophysical and biochemical properties of lipids and lipid bilayer membranes, we will discuss how DNA molecules can interact with lipid membranes through electrostatic interactions or via covalent modification with hydrophobic moieties. We will then show how such DNA-lipid interactions have been utilized for the realization of DNA nanostructures attached to or embedded within lipid bilayer membranes. Under certain conditions, DNA nanostructures remain mobile on

  2. Crystallizing Membrane Proteins in Lipidic Mesophases. A Host Lipid Screen

    SciTech Connect

    Li, Dianfan; Lee, Jean; Caffrey, Martin

    2011-11-30

    The default lipid for the bulk of the crystallogenesis studies performed to date using the cubic mesophase method is monoolein. There is no good reason, however, why this 18-carbon, cis-monounsaturated monoacylglycerol should be the preferred lipid for all target membrane proteins. The latter come from an array of biomembrane types with varying properties that include hydrophobic thickness, intrinsic curvature, lateral pressure profile, lipid and protein makeup, and compositional asymmetry. Thus, it seems reasonable that screening for crystallizability based on the identity of the lipid creating the hosting mesophase would be worthwhile. For this, monoacylglycerols with differing acyl chain characteristics, such as length and olefinic bond position, must be available. A lipid synthesis and purification program is in place in the author's laboratory to serve this need. In the current study with the outer membrane sugar transporter, OprB, we demonstrate the utility of host lipid screening as a means for generating diffraction-quality crystals. Host lipid screening is likely to prove a generally useful strategy for mesophase-based crystallization of membrane proteins.

  3. Membrane species mobility under in-lipid-membrane forced convection.

    PubMed

    Hu, Shu-Kai; Huang, Ling-Ting; Chao, Ling

    2016-08-17

    Processing and managing cell membrane proteins for characterization while maintaining their intact structure is challenging. Hydrodynamic flow has been used to transport membrane species in supported lipid bilayers (SLBs) where the hydrophobic cores of the membrane species can be protected during processing. However, the forced convection mechanism of species embedded in lipid bilayers is still unclear. Developing a controlled SLB platform with a practical model to predict the membrane species mobility in the platform under in-lipid-membrane forced convection is imperative to ensure the practical applicability of SLBs in processing and managing membrane species with various geometrical properties. The mobility of membrane species is affected by the driving force from the aqueous environment in addition to the frictions from the lipid bilayer, in which both lipid leaflets may exhibit different speeds relative to that of the moving species. In this study, we developed a model, based on the applied driving force and the possible frictional resistances that the membrane species encounter, to predict how the mobility under in-lipid-membrane forced convection is influenced by the sizes of the species' hydrophilic portion in the aqueous environment and the hydrophobic portion embedded in the membrane. In addition, we used a microfluidic device for controlling the flow to arrange the lipid membrane and the tested membrane species in the desirable locations in order to obtain a SLB platform which can provide clear mobility responses of the species without disturbance from the species dispersion effect. The model predictions were consistent with the experimental observations, with the sliding friction coefficient between the upper leaflet and the hydrophilic portion of the species as the only regressed parameter. The result suggests that not only the lateral drag frictions from the lipid layers but also the sliding frictions between the species and the lipid layer planes

  4. Interaction of mammalian Hsp22 with lipid membranes

    PubMed Central

    Chowdary, Tirumala Kumar; Raman, Bakthisaran; Ramakrishna, Tangirala; Rao, Ch. Mohan

    2006-01-01

    Hsp22/HspB8 is a member of the small heat-shock protein family, whose function is not yet completely understood. Our immunolocalization studies in a human neuroblastoma cell line, SK-N-SH, using confocal microscopy show that a significant fraction of Hsp22 is localized to the plasma membrane. We therefore investigated its interactions with lipid vesicles in vitro. Intrinsic tryptophan fluorescence is quenched in the presence of lipid vesicles derived from either bovine brain lipid extract or purified lipids. Time-resolved fluorescence studies show a decrease in the lifetimes of the tryptophan residues. Both of these results indicate burial of some tryptophan residues of Hsp22 upon interaction with lipid vesicles. Membrane interactions also lead to increase in fluorescence polarization of Hsp22. Gel-filtration chromatography shows that Hsp22 binds stably with lipid vesicles; the extent of binding depends on the nature of the lipid. Hsp22 binds more strongly to vesicles made of lipids containing a phosphatidic acid, phosphatidylinositol or phosphatidylserine headgroup (known to be present in the inner leaflet of plasma membrane) compared with lipid vesicles made of a phosphatidylcholine head-group alone. Far-UV CD spectra reveal conformational changes upon binding to the lipid vesicles or in membrane-mimetic solvent, trifluoroethanol. Thus our fluorescence, CD and gel-filtration studies show that Hsp22 interacts with membrane and this interaction leads to stable binding and conformational changes. The present study therefore clearly demonstrates that Hsp22 exhibits potential membrane interaction that may play an important role in its cellular functions. PMID:17020537

  5. Solvent-exposed lipid tail protrusions depend on lipid membrane composition and curvature.

    PubMed

    Tahir, Mukarram A; Van Lehn, Reid C; Choi, S H; Alexander-Katz, Alfredo

    2016-06-01

    The stochastic protrusion of hydrophobic lipid tails into solution, a subclass of hydrophobic membrane defects, has recently been shown to be a critical step in a number of biological processes like membrane fusion. Understanding the factors that govern the appearance of lipid tail protrusions is critical for identifying membrane features that affect the rate of fusion or other processes that depend on contact with solvent-exposed lipid tails. In this work, we utilize atomistic molecular dynamics simulations to characterize the likelihood of tail protrusions in phosphotidylcholine lipid bilayers of varying composition, curvature, and hydration. We distinguish two protrusion modes corresponding to atoms near the end of the lipid tail or near the glycerol group. Through potential of mean force calculations, we demonstrate that the thermodynamic cost for inducing a protrusion depends on tail saturation but is insensitive to other bilayer structural properties or hydration above a threshold value. Similarly, highly curved vesicles or micelles increase both the overall frequency of lipid tail protrusions as well as the preference for splay protrusions, both of which play an important role in driving membrane fusion. In multi-component bilayers, however, the incidence of protrusion events does not clearly depend on the mismatch between tail length or tail saturation of the constituent lipids. Together, these results provide significant physical insight into how system components might affect the appearance of protrusions in biological membranes, and help explain the roles of composition or curvature-modifying proteins in membrane fusion. PMID:26828121

  6. Pushing the lipid envelope: using bio-inspired nanocomposites to understand and exploit lipid membrane limitations

    NASA Astrophysics Data System (ADS)

    Montano, Gabriel

    Lipids serve as the organizing matrix material for biological membranes, the site of interaction of cells with the external environment. . As such, lipids play a critical role in structure/function relationships of an extraordinary number of critical biological processes. In this talk, we will look at bio-inspired membrane assemblies to better understand the roles of lipids in biological systems as well as attempt to generate materials that can mimic and potentially advance upon biological membrane processes. First, we will investigate the response of lipids to adverse conditions. In particular, I will present data that demonstrates the response of lipids to harsh conditions and how such responses can be exploited to generate nanocomposite rearrangements. I will also show the effect of adding the endotoxin lipopolysaccharide (LPS) to lipid bilayer assemblies and describe implications on our understanding of LPS organization in biological systems as well as describe induced lipid modifications that can be exploited to organize membrane composites with precise, two-dimensional geometric control. Lastly, I will describe the use of amphiphilic block copolymers to create membrane nanocomposites capable of mimicking biological systems. In particular, I will describe the use of our polymer-based membranes in creating artificial photosynthetic assemblies that rival biological systems in function in a more flexible, dynamic matrix.

  7. Micropattern formation in supported lipid membranes.

    PubMed

    Groves, Jay T; Boxer, Steven G

    2002-03-01

    Phospholipid vesicles exhibit a natural tendency to fuse and assemble into a continuous single bilayer membrane on silica and several other substrate materials. The resulting supported membrane maintains many of the physical and biological characteristics of free membranes, including lateral fluidity. Recent advances, building on the supported membrane configuration, have created a wealth of opportunities for the manipulation, control, and analysis of membranes and the reaction environments they provide. The work reviewed in this Account, which can be broadly characterized as the science and technology of membrane patterning, contains three basic components: lateral diffusion control (barriers), membrane deposition techniques (microarrays), and electric field-induced lateral reorganization. Collectively, these preparative and analytical patterned membrane techniques offer a broad experimental platform for the study and utilization of lipid membranes. PMID:11900518

  8. Interactions of surfactants with lipid membranes.

    PubMed

    Heerklotz, Heiko

    2008-01-01

    Surfactants are surface-active, amphiphilic compounds that are water-soluble in the micro- to millimolar range, and self-assemble to form micelles or other aggregates above a critical concentration. This definition comprises synthetic detergents as well as amphiphilic peptides and lipopeptides, bile salts and many other compounds. This paper reviews the biophysics of the interactions of surfactants with membranes of insoluble, naturally occurring lipids. It discusses structural, thermodynamic and kinetic aspects of membrane-water partitioning, changes in membrane properties induced by surfactants, membrane solubilisation to micelles and other phases formed by lipid-surfactant systems. Each section defines and derives key parameters, mentions experimental methods for their measurement and compiles and discusses published data. Additionally, a brief overview is given of surfactant-like effects in biological systems, technical applications of surfactants that involve membrane interactions, and surfactant-based protocols to study biological membranes. PMID:19079805

  9. Lipid landscapes and pipelines in membrane homeostasis.

    PubMed

    Holthuis, Joost C M; Menon, Anant K

    2014-06-01

    The lipid composition of cellular organelles is tailored to suit their specialized tasks. A fundamental transition in the lipid landscape divides the secretory pathway in early and late membrane territories, allowing an adaptation from biogenic to barrier functions. Defending the contrasting features of these territories against erosion by vesicular traffic poses a major logistical problem. To this end, cells evolved a network of lipid composition sensors and pipelines along which lipids are moved by non-vesicular mechanisms. We review recent insights into the molecular basis of this regulatory network and consider examples in which malfunction of its components leads to system failure and disease. PMID:24899304

  10. Pore dynamics in lipid membranes

    NASA Astrophysics Data System (ADS)

    Gozen, I.; Dommersnes, P.

    2014-09-01

    Transient circular pores can open in plasma membrane of cells due to mechanical stress, and failure to repair such pores lead to cell death. Similar pores in the form of defects also exist among smectic membranes, such as in myelin sheaths or mitochondrial membranes. The formation and growth of membrane defects are associated with diseases, for example multiple sclerosis. A deeper understanding of membrane pore dynamics can provide a more refined picture of membrane integrity-related disease development, and possibly also treatment options and strategies. Pore dynamics is also of great importance regarding healthcare applications such as drug delivery, gene or as recently been implied, cancer therapy. The dynamics of pores significantly differ in stacks which are confined in 2D compared to those in cells or vesicles. In this short review, we will summarize the dynamics of different types of pores that can be observed in biological membranes, which include circular transient, fusion and hemi-fusion pores. We will dedicate a section to floral and fractal pores which were discovered a few years ago and have highly peculiar characteristics. Finally, we will discuss the repair mechanisms of large area pores in conjunction with the current cell membrane repair hypotheses.

  11. Why Hydrophilic Water can Permeate Hydrophobic Interior of Lipid Membranes

    NASA Astrophysics Data System (ADS)

    Qiao, Baofu; Olvera de La Cruz, Monica

    2014-03-01

    Water molecules as well as some small molecules have long been found to be able to diffuse across lipid membranes. Such permeation is of significant biological and biotechnological importance. For instance, the permeation of water across lipid membrane plays a important role in regulating ionic concentrations inside of cells. Such water permeation without the assistance of proteins embedded in membranes has been found to be a energetically unfavorable process. We, for the first time, explicitly depict the driving force for such an energetically unfavorable process. Atomistic molecular dynamics simulations are employed to investigate water diffusion in both liquid-crystalline and ordered gel phases of membranes containing zwitterionic DPPC or anionic DLPS lipid. The membrane conformation is calculated to have a critical role in water permeation, regardless of the type of lipid. The fluctuations in the potential energy are found to have a significant, if not the exclusive, role in the transportation of water across lipid membranes. Our results are also informative for the diffusion of small molecules of CO2, O2 and drug molecules, the absence of diffusion of ions, and the diffusion of water into the hydrophobic pores of carbon nanotubes. The authors acknowledge the support from the Office of the Director of Defense Research and Engineering (DDR & E) under Award No. FA9550-10-1-0167.

  12. The physics of stratum corneum lipid membranes.

    PubMed

    Das, Chinmay; Olmsted, Peter D

    2016-07-28

    The stratum corneum (SC), the outermost layer of skin, comprises rigid corneocytes (keratin-filled dead cells) in a specialized lipid matrix. The continuous lipid matrix provides the main barrier against uncontrolled water loss and invasion of external pathogens. Unlike all other biological lipid membranes (such as intracellular organelles and plasma membranes), molecules in the SC lipid matrix show small hydrophilic groups and large variability in the length of the alkyl tails and in the numbers and positions of groups that are capable of forming hydrogen bonds. Molecular simulations provide a route for systematically probing the effects of each of these differences separately. In this article, we present the results from atomistic molecular dynamics of selected lipid bilayers and multi-layers to probe the effect of these polydispersities. We address the nature of the tail packing in the gel-like phase, the hydrogen bond network among head groups, the bending moduli expected for leaflets comprising SC lipids and the conformation of very long ceramide lipids in multi-bilayer lipid assemblies.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'. PMID:27298438

  13. Molecular Transport Studies Through Unsupported Lipid Membranes

    NASA Astrophysics Data System (ADS)

    Rock, William; Parekh, Sapun; Bonn, Mischa

    2014-03-01

    Dendrimers, spherical polymeric nanoparticles made from branched monomers around a central core, show great promise as drug delivery vehicles. Dendrimer size, core contents, and surface functionality can be synthetically tuned, providing unprecedented versatility. Polyamidoamine (PAMAM) dendrimers have been shown to enter cells; however, questions remain about their biophysical interactions with the cell membrane, specifically about the presence and size of transient pores. We monitor dendrimer-lipid bilayer interactions using unsupported black lipid membranes (BLMs) as model cell membranes. Custom bilayer slides contain two vertically stacked aqueous chambers separated by a 25 μm Teflon sheet with a 120 μm aperture where the bilayer is formed. We vary the composition of model membranes (cholesterol content and lipid phase) to create biomimetic systems and study the interaction of PAMAM G6 and G3 dendrimers with these bilayers. Dendrimers, dextran cargo, and bilayers are monitored and quantified using time-lapse fluorescence imaging. Electrical capacitance measurements are simultaneously recorded to determine if the membrane is porous, and the pore size is deduced by monitoring transport of fluorescent dextrans of increasing molecular weight. These experiments shed light on the importance of cholesterol content and lipid phase on the interaction of dendrimer nanoparticles with membranes.

  14. Nanosecond Lipid Dynamics in Membranes Containing Cholesterol

    SciTech Connect

    Armstrong, Clare L; Haeussler, Wolfgang; Seydel, Tilo; Katsaras, John; Rheinstadter, Maikel C

    2014-01-01

    Lipid dynamics in the cholesterol-rich (40 mol%) liquid-ordered (lo) phase of dimyristoylphosphatidylcholine membranes were studied using neutron spin-echo and neutron backscattering. Recent theoretical and experimental evidence supports the notion of the liquid-ordered phase in phospholipid membranes as a locally structured liquid, with small ordered domains of a highly dynamic nature in equilibrium with a disordered matrix [S. Meinhardt, R. L. C. Vink and F. Schmid, Proc. Natl. Acad. Sci. U. S. A., 2013, 110(12), 4476 4481, C. L. Armstrong et al., PLoS One, 2013, 8(6), e66162]. This local structure was found to have a pronounced impact on the membranes' dynamical properties. We found that the long-wavelength dynamics in the liquid-ordered phase, associated with the elastic properties of the membranes, were faster by two orders of magnitude as compared to the liquid disordered phase. At the same time, collective nanoscale diffusion was significantly slower. The presence of a soft-mode (a slowing down) in the longwavelength dispersion relationship suggests an upper size limit for the ordered lipid domain of ~220 A. Moreover, from the relaxation rate of the collective lipid diffusion of lipid lipid distances, the lifetime of these domains was estimated to be about 100 nanoseconds.

  15. Engineering Lipid Bilayer Membranes for Protein Studies

    PubMed Central

    Khan, Muhammad Shuja; Dosoky, Noura Sayed; Williams, John Dalton

    2013-01-01

    Lipid membranes regulate the flow of nutrients and communication signaling between cells and protect the sub-cellular structures. Recent attempts to fabricate artificial systems using nanostructures that mimic the physiological properties of natural lipid bilayer membranes (LBM) fused with transmembrane proteins have helped demonstrate the importance of temperature, pH, ionic strength, adsorption behavior, conformational reorientation and surface density in cellular membranes which all affect the incorporation of proteins on solid surfaces. Much of this work is performed on artificial templates made of polymer sponges or porous materials based on alumina, mica, and porous silicon (PSi) surfaces. For example, porous silicon materials have high biocompatibility, biodegradability, and photoluminescence, which allow them to be used both as a support structure for lipid bilayers or a template to measure the electrochemical functionality of living cells grown over the surface as in vivo. The variety of these media, coupled with the complex physiological conditions present in living systems, warrant a summary and prospectus detailing which artificial systems provide the most promise for different biological conditions. This study summarizes the use of electrochemical impedance spectroscopy (EIS) data on artificial biological membranes that are closely matched with previously published biological systems using both black lipid membrane and patch clamp techniques. PMID:24185908

  16. Model lipid bilayer with facile diffusion of lipids and integral membrane proteins.

    PubMed

    Wang, Tingting; Ingram, Colin; Weisshaar, James C

    2010-07-01

    A model membrane system is formed by the rupture of giant unilamellar vesicles (GUVs) onto a passivating layer comprising a PEG polymer cushion anchored in a lipid bilayer supported on glass. The novel use of pH-dependent electrostatic interactions between NeutrAvidin in the passivating layer and anionic lipids in the GUV drives vesicle rupture. The resulting "GUV pancakes" are single, planar lipid bilayer patches whose diameters vary from approximately 20 to 50 microm. The pancakes have several potential advantages for the in vitro study of protein-lipid interactions and integral membrane protein function. All components are commercially available. The pancakes resist nonspecific binding of vesicles containing protein. Both lipids and integral membrane proteins exhibit good lateral mobility in the GUV pancakes, as evidenced by single-particle tracking (SPT) of the DiD double-tailed fluorescent probe and of the integral membrane protein syntaxin-1A, labeled with AlexaFluor 633 (AF633-Syx). At least 80% of both probes exhibit free, homogeneous diffusion with a diffusion coefficient of approximately 5.5 microm(2) s(-1), which is more than 10 times faster than diffusion in a GUV pancake supported on bare glass. Atomic force microscopy (AFM) suggests that the polymer cushion has a height of approximately 4 nm. The mobility of a large fraction of the AF633-Syx probe suggests that even integral membrane proteins with large domains on both sides of the lipid bilayer should exhibit free diffusion within a GUV pancake. PMID:20459075

  17. Nonlinear adhesion dynamics of confined lipid membranes

    NASA Astrophysics Data System (ADS)

    To, Tung; Le Goff, Thomas; Pierre-Louis, Olivier

    Lipid membranes, which are ubiquitous objects in biological environments are often confined. For example, they can be sandwiched between a substrate and the cytoskeleton between cell adhesion, or between other membranes in stacks, or in the Golgi apparatus. We present a study of the nonlinear dynamics of membranes in a model system, where the membrane is confined between two flat walls. The dynamics derived from the lubrication approximation is highly nonlinear and nonlocal. The solution of this model in one dimension exhibits frozen states due to oscillatory interactions between membranes caused by the bending rigidity. We develope a kink model for these phenomena based on the historical work of Kawasaki and Otha. In two dimensions, the dynamics is more complex, and depends strongly on the amount of excess area in the system. We discuss the relevance of our findings for experiments on model membranes, and for biological systems. Supported by the grand ANR Biolub.

  18. Dynamic Response of Model Lipid Membranes to Ultrasonic Radiation Force

    PubMed Central

    Prieto, Martin Loynaz; Oralkan, Ömer; Khuri-Yakub, Butrus T.; Maduke, Merritt C.

    2013-01-01

    Low-intensity ultrasound can modulate action potential firing in neurons in vitro and in vivo. It has been suggested that this effect is mediated by mechanical interactions of ultrasound with neural cell membranes. We investigated whether these proposed interactions could be reproduced for further study in a synthetic lipid bilayer system. We measured the response of protein-free model membranes to low-intensity ultrasound using electrophysiology and laser Doppler vibrometry. We find that ultrasonic radiation force causes oscillation and displacement of lipid membranes, resulting in small (<1%) changes in membrane area and capacitance. Under voltage-clamp, the changes in capacitance manifest as capacitive currents with an exponentially decaying sinusoidal time course. The membrane oscillation can be modeled as a fluid dynamic response to a step change in pressure caused by ultrasonic radiation force, which disrupts the balance of forces between bilayer tension and hydrostatic pressure. We also investigated the origin of the radiation force acting on the bilayer. Part of the radiation force results from the reflection of the ultrasound from the solution/air interface above the bilayer (an effect that is specific to our experimental configuration) but part appears to reflect a direct interaction of ultrasound with the bilayer, related to either acoustic streaming or scattering of sound by the bilayer. Based on these results, we conclude that synthetic lipid bilayers can be used to study the effects of ultrasound on cell membranes and membrane proteins. PMID:24194863

  19. Permeability and electrical properties of planar lipid membranes from thylakoid lipids.

    PubMed Central

    Fuks, B; Homblé, F

    1994-01-01

    Electrical measurements were carried out on planar lipid membranes from thylakoid lipids. The specific capacitance of membranes formed from decane-containing monogalactosyldiacylglycerol (MGDG), which accounts for 57% of the total lipid content of thylakoids, showed that it adopted a bilayer structure. Solvent-free bilayers of MGDG were not formed, with very rare exceptions, indicating that decane is required to stabilize the planar conformation. However, this cone-shaped lipid produces bilayer structures in combination with other cylindrical thylakoid lipids even in the absence of organic solvent. We compared the properties of solvent-free and decane-containing bilayers from MGDG, soybean lecithin, and the quaternary mixture of lipids similar to that found in vivo. The conductance of decane-MGDG was 26 times higher than that of decane-lecithin. The flux through the decane-lecithin bilayer was found to be slightly dependent on pH, whereas the decane-MGDG membrane was not. The specific conductance of bilayers formed from the quaternary mixture of lipids was 5 to 10 times larger than lecithin (with alkane or not). Further experiments with bilayers made in the presence of a KCl gradient showed that decane-MGDG, decane-MGDG/DGDG/SQDG/PG, and solvent-free MGDG/DGDG/SQDG/PG were cation-selective. The permeability coefficient for potassium ranged from 4.9 to 8.3 x 10(-11) cm s-1. The permeability coefficient for protons in galactolipids, however, was determined to be about six orders of magnitude higher than the value for potassium ions. The HCl permeation mechanism through the lipid membranes was determined from diffusion potentials measured in HCl gradients. Our results suggest that HCl was not transported as neutral molecules. The data is discussed with regard to the function of galactolipids in the ion transport through thylakoid membranes. PMID:8061192

  20. Tryptophan orientation in model lipid membranes

    SciTech Connect

    Esbjoerner, Elin K.

    2007-09-28

    Tryptophans in membrane proteins display strong preference for the lipid membrane interface and are important for anchoring proteins at the proper longitudinal level. Linear dichroism spectroscopy on indoles in shear-deformed liposomes has been used to show that this positioning is accompanied by an intrinsically adopted orientation, also observed for tryptophans in membrane-bound peptides. Similarities in orientation of different indoles suggest that tryptophan will adopt this orientation independent of the protein it is part of. From the orientation of indole electronic transition moments L{sub a}, L{sub b} and B{sub b}, a binding model is proposed where the indole long axis is {approx}60-65 deg. from the membrane normal and the indole plane is at an oblique angle. We propose that dipole-dipole interactions and steric constraints in the membrane hydrocarbon region determine positioning and orientation of tryptophans whereas hydrogen bonding and cation-{pi} interactions with lipid head-groups, though contributing to the membrane affinity of indoles, are less important.

  1. Membrane lipids and the origin of life

    NASA Technical Reports Server (NTRS)

    Oro, J.; Holzer, G.; Rao, M.; Tornabene, T. G.

    1981-01-01

    The current state of knowledge regarding the development of biological systems is briefly reviewed. At a crucial stage concerning the evolution of such systems, the mechanisms leading to more complex structures must have evolved within the confines of a protected microenvironment, similar to those provided by the contemporary cell membranes. The major components found normally in biomembranes are phospholipids. The structure of the biomembrane is examined, and attention is given to questions concerning the availability of the structural components which are necessary in the formation of primitive lipid membranes. Two approaches regarding the study of protomembranes are discussed. The probability of obtaining ether lipids under prebiotic conditions is considered, taking into account the formation of cyclic and acyclic isoprenoids by the irradiation of isoprene with UV.

  2. [Lipid oxidation in bilayer lipid membranes linked with the reaction of oxidation of NAD.H by atmospheric oxygen].

    PubMed

    Shchipumov, Iu A; Sokolov, V S; Iaguzhinskiĭ, L S; Boguslavskiĭ, L I

    1976-01-01

    It is shown that along with NAD.H oxidation with air oxygen peroxide oxidation of lipids forming the membrane takes place in bilayer lipid membranes modified with ubiquinone. During nicotin amide oxidation proton absorption takes place. Peroxide oxidation of lipids results in the liberation of H+ ions, which in its turn brings about the formation of protone-deficient or enriched (against aqueous solution) layers adjacent to the membrane. The potential value on the membrane is shown to depend on nicotine amide and oxygen concentration, on ubiquinone presence and lipid composition of the membrane. It has been also indicated that the transmembrane potential difference is initiated with a sharp change of aqueous solution pH by 0.05--0.4 units. PMID:178383

  3. Multichannel taste sensors with lipid, lipid like polymer membranes

    NASA Astrophysics Data System (ADS)

    Szpakowska, M.; Szwacki, J.; Marjańska, E.

    2008-08-01

    The elaboration of a sensitive taste sensor for discrimination of different soft drinks is very important in food industry. The short review of taste sensors described in the literature is presented. Two types of potentiometric taste sensors, one with lipophilic compound-polymer membranes (ISE) and the other with lipid polymer membrane and a conducting polymer film (All solid state electrode, ASSE) were tested in appropriate taste solutions. Five channel ISE sensor was examined in acid, sour and sweet solutions. This sensor was sensitive to bitter and sour substances and not too sensitive to sucrose concentration. It was successfully used for discrimination of different kind of soft drinks. Four channel ASSE sensor was examined in sour solutions. It was found that stability and sensitivity of ASSE are lower than ISE. Therefore, it seems that the previous one cannot be applied in taste sensor.

  4. Lipid Gymnastics: Tethers and Fingers in membrane

    NASA Astrophysics Data System (ADS)

    Tayebi, Lobat; Miller, Gregory; Parikh, Atul

    2009-03-01

    A significant body of evidence now links local mesoscopic structure (e.g., shape and composition) of the cell membrane with its function; the mechanisms by which cellular membranes adopt the specific shapes remain poorly understood. Among all the different structures adopted by cellular membranes, the tubular shape is one of the most surprising one. While their formation is typically attributed to the reorganization of membrane cytoskeleton, many exceptions exist. We report the instantaneous formation of tubular membrane mesophases following the hydration under specific thermal conditions. The shapes emerge in a bimodal way where we have two distinct diameter ranges for tubes, ˜20μm and ˜1μm, namely fat fingers and narrow tethers. We study the roughening of hydrated drops of 3 lipids in 3 different spontaneous curvatures at various temp. and ionic strength to figure out the dominant effect in selection of tethers and fingers. Dynamics of the tubes are of particular interest where we observe four distinct steps of birth, coiling, uncoiling and retraction with different lifetime on different thermal condition. These dynamics appear to reflect interplay between membrane elasticity, surface adhesion, and thermal or hydrodynamic gradient.

  5. Concise theory of chiral lipid membranes

    NASA Astrophysics Data System (ADS)

    Tu, Z. C.; Seifert, U.

    2007-09-01

    A theory of chiral lipid membranes is proposed on the basis of a concise free energy density which includes the contributions of the bending and the surface tension of membranes, as well as the chirality and orientational variation of tilting molecules. This theory is consistent with the previous experiments [J.M. Schnur , Science 264, 945 (1994); M.S. Spector , Langmuir 14, 3493 (1998); Y. Zhao, , Proc. Natl. Acad. Sci. USA 102, 7438 (2005)] on self-assembled chiral lipid membranes of DC8,9PC . A torus with the ratio between its two generated radii larger than 2 is predicted from the Euler-Lagrange equations. It is found that tubules with helically modulated tilting state are not admitted by the Euler-Lagrange equations and that they are less energetically favorable than helical ripples in tubules. The pitch angles of helical ripples are theoretically estimated to be about 0° and 35°, which are close to the most frequent values 5° and 28° observed in the experiment [N. Mahajan , Langmuir 22, 1973 (2006)]. Additionally, the present theory can explain twisted ribbons of achiral cationic amphiphiles interacting with chiral tartrate counterions. The ratio between the width and pitch of twisted ribbons is predicted to be proportional to the relative concentration difference of left- and right-handed enantiomers in the low relative concentration difference region, which is in good agreement with the experiment [R. Oda , Nature (London) 399, 566 (1999)].

  6. Structure and dynamics of water and lipid molecules in charged anionic DMPG lipid bilayer membranes

    NASA Astrophysics Data System (ADS)

    Rønnest, A. K.; Peters, G. H.; Hansen, F. Y.; Taub, H.; Miskowiec, A.

    2016-04-01

    Molecular dynamics simulations have been used to investigate the influence of the valency of counter-ions on the structure of freestanding bilayer membranes of the anionic 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) lipid at 310 K and 1 atm. At this temperature, the membrane is in the fluid phase with a monovalent counter-ion and in the gel phase with a divalent counter-ion. The diffusion constant of water as a function of its depth in the membrane has been determined from mean-square-displacement calculations. Also, calculated incoherent quasielastic neutron scattering functions have been compared to experimental results and used to determine an average diffusion constant for all water molecules in the system. On extrapolating the diffusion constants inferred experimentally to a temperature of 310 K, reasonable agreement with the simulations is obtained. However, the experiments do not have the sensitivity to confirm the diffusion of a small component of water bound to the lipids as found in the simulations. In addition, the orientation of the dipole moment of the water molecules has been determined as a function of their depth in the membrane. Previous indirect estimates of the electrostatic potential within phospholipid membranes imply an enormous electric field of 108-109 V m-1, which is likely to have great significance in controlling the conformation of translocating membrane proteins and in the transfer of ions and molecules across the membrane. We have calculated the membrane potential for DMPG bilayers and found ˜1 V (˜2 ṡ 108 V m-1) when in the fluid phase with a monovalent counter-ion and ˜1.4 V (˜2.8 ṡ 108 V m-1) when in the gel phase with a divalent counter-ion. The number of water molecules for a fully hydrated DMPG membrane has been estimated to be 9.7 molecules per lipid in the gel phase and 17.5 molecules in the fluid phase, considerably smaller than inferred experimentally for 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine (DMPC

  7. Membrane Contact Sites: Complex Zones for Membrane Association and Lipid Exchange

    PubMed Central

    Quon, Evan; Beh, Christopher T.

    2015-01-01

    Lipid transport between membranes within cells involves vesicle and protein carriers, but as agents of nonvesicular lipid transfer, the role of membrane contact sites has received increasing attention. As zones for lipid metabolism and exchange, various membrane contact sites mediate direct associations between different organelles. In particular, membrane contact sites linking the plasma membrane (PM) and the endoplasmic reticulum (ER) represent important regulators of lipid and ion transfer. In yeast, cortical ER is stapled to the PM through membrane-tethering proteins, which establish a direct connection between the membranes. In this review, we consider passive and facilitated models for lipid transfer at PM–ER contact sites. Besides the tethering proteins, we examine the roles of an additional repertoire of lipid and protein regulators that prime and propagate PM–ER membrane association. We conclude that instead of being simple mediators of membrane association, regulatory components of membrane contact sites have complex and multilayered functions. PMID:26949334

  8. Force Field Development for Lipid Membrane Simulations.

    PubMed

    Lyubartsev, Alexander P; Rabinovich, Alexander L

    2016-10-01

    With the rapid development of computer power and wide availability of modelling software computer simulations of realistic models of lipid membranes, including their interactions with various molecular species, polypeptides and membrane proteins have become feasible for many research groups. The crucial issue of the reliability of such simulations is the quality of the force field, and many efforts, especially in the latest several years, have been devoted to parametrization and optimization of the force fields for biomembrane modelling. In this review, we give account of the recent development in this area, covering different classes of force fields, principles of the force field parametrization, comparison of the force fields, and their experimental validation. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg. PMID:26766518

  9. Negatively Charged Lipid Membranes Catalyze Supramolecular Hydrogel Formation.

    PubMed

    Versluis, Frank; van Elsland, Daphne M; Mytnyk, Serhii; Perrier, Dayinta L; Trausel, Fanny; Poolman, Jos M; Maity, Chandan; le Sage, Vincent A A; van Kasteren, Sander I; van Esch, Jan H; Eelkema, Rienk

    2016-07-20

    In this contribution we show that biological membranes can catalyze the formation of supramolecular hydrogel networks. Negatively charged lipid membranes can generate a local proton gradient, accelerating the acid-catalyzed formation of hydrazone-based supramolecular gelators near the membrane. Synthetic lipid membranes can be used to tune the physical properties of the resulting multicomponent gels as a function of lipid concentration. Moreover, the catalytic activity of lipid membranes and the formation of gel networks around these supramolecular structures are controlled by the charge and phase behavior of the lipid molecules. Finally, we show that the insights obtained from synthetic membranes can be translated to biological membranes, enabling the formation of gel fibers on living HeLa cells. PMID:27359373

  10. Lipid diffusibility in the intact erythrocyte membrane.

    PubMed Central

    Bloom, J A; Webb, W W

    1983-01-01

    The lateral diffusion of fluorescent lipid analogues in the plasma membrane of intact erythrocytes from man, mouse, rabbit, and frog has been measured by fluorescence photobleaching recovery (FPR). Intact cells from dystrophic, normoblastic, hemolytic, and spherocytotic mouse mutants; from hypercholesterolemic rabbits and humans; and from prenatal, neonatal, and juvenile mice have been compared with corresponding normals. The lateral diffusion coefficient (D) for 3,3'-dioctadecylindodicarbocyanine iodide (DiI[5]) in intact normal human erythrocytes is D = 8.2 +/- 1.2 X 10(-9) cm2/s at 25 degrees C and D = 2.1 +/- 0.4 X 10(-8) cm2/s at 37 degrees C, and varies approximately 50-fold between 1 degree and 42 degrees C. The diffusion constants of lipid analogue rhodamine-B phosphatidylethanolamine (RBPE) are about twice those of DiI[5]. The temperature dependence and magnitude of D vary by up to a factor of 3 between species and are only influenced by donor age in prenatals. DiI[5] diffusibility is not perturbed by the presence of calcium or local anesthetics or by spectrin depletion (via mutation). However, lipid-analogue diffusibility in erythrocyte ghosts may differ from intact cells. Dietary hypercholesterolemia in rabbits reduces the diffusion coefficient and eliminates the characteristic break in Arrhenius plots of D found in all other cells studied except frog. PMID:6603237

  11. Crystallizing Membrane Proteins Using Lipidic Mesophases

    PubMed Central

    Caffrey, Martin; Cherezov, Vadim

    2009-01-01

    A detailed protocol for crystallizing membrane proteins that makes use of lipidic mesophases is described. This has variously been referred to as the lipid cubic phase or in meso method. The method has been shown to be quite general in that it has been used to solve X-ray crystallographic structures of prokaryotic and eukaryotic proteins, proteins that are monomeric, homo- and hetero-multimeric, chromophore-containing and chromophore-free, and α-helical and β-barrel proteins. Its most recent successes are the human engineered β2-adrenergic and adenosine A2A G protein-coupled receptors. Protocols are provided for preparing and characterizing the lipidic mesophase, for reconstituting the protein into the monoolein-based mesophase, for functional assay of the protein in the mesophase, and for setting up crystallizations in manual mode. Methods for harvesting micro-crystals are also described. The time required to prepare the protein-loaded mesophase and to set up a crystallization plate manually is about one hour. PMID:19390528

  12. Illuminating the lipidome to advance biomedical research: peptide-based probes of membrane lipids

    PubMed Central

    Gao, Jianmin; Zheng, Hong

    2014-01-01

    Systematic investigation of the lipidome will reveal new opportunities for disease diagnosis and intervention. However, lipidomic research has been hampered by the lack of molecular tools to track specific lipids of interest. Accumulating reports indicate lipid recognition can be achieved with properly constructed short peptides in addition to large proteins. This review summarizes the key developments of this area within the past decade. Select lantibiotic peptides present the best examples of low-molecular-weight probes of membrane lipids, displaying selectivity comparable to lipid-binding proteins. Designed peptides, through biomimetic approaches and combinational screening, have begun to demonstrate their potential for lipid tracking in cultured cells and even in living organisms. Biophysical characterization of these lipid-targeting peptides has revealed certain features critical for selective membrane binding, including preorganized scaffolds and the balance of polar and nonpolar interactions. The knowledge summarized herein should facilitate the development of molecular tools to target a variety of membrane lipids. PMID:23682570

  13. Order of lipid phases in model and plasma membranes

    PubMed Central

    Kaiser, Hermann-Josef; Lingwood, Daniel; Levental, Ilya; Sampaio, Julio L.; Kalvodova, Lucie; Rajendran, Lawrence; Simons, Kai

    2009-01-01

    Lipid rafts are nanoscopic assemblies of sphingolipids, cholesterol, and specific membrane proteins that contribute to lateral heterogeneity in eukaryotic membranes. Separation of artificial membranes into liquid-ordered (Lo) and liquid-disordered phases is regarded as a common model for this compartmentalization. However, tight lipid packing in Lo phases seems to conflict with efficient partitioning of raft-associated transmembrane (TM) proteins. To assess membrane order as a component of raft organization, we performed fluorescence spectroscopy and microscopy with the membrane probes Laurdan and C-laurdan. First, we assessed lipid packing in model membranes of various compositions and found cholesterol and acyl chain dependence of membrane order. Then we probed cell membranes by using two novel systems that exhibit inducible phase separation: giant plasma membrane vesicles [Baumgart et al. (2007) Proc Natl Acad Sci USA 104:3165–3170] and plasma membrane spheres. Notably, only the latter support selective inclusion of raft TM proteins with the ganglioside GM1 into one phase. We measured comparable small differences in order between the separated phases of both biomembranes. Lateral packing in the ordered phase of giant plasma membrane vesicles resembled the Lo domain of model membranes, whereas the GM1 phase in plasma membrane spheres exhibited considerably lower order, consistent with different partitioning of lipid and TM protein markers. Thus, lipid-mediated coalescence of the GM1 raft domain seems to be distinct from the formation of a Lo phase, suggesting additional interactions between proteins and lipids to be effective. PMID:19805351

  14. Film Balance Studies of Membrane Lipids and Related Molecules

    ERIC Educational Resources Information Center

    Cadenhead, D. A.

    1972-01-01

    Discusses apparatus, techniques, and measurements used to determine cell membrane composition. The use of a film balance to study monolayer membranes of selected lipids is described and results reported. (TS)

  15. Ion-Induced Defect Permeation of Lipid Membranes

    PubMed Central

    Vorobyov, Igor; Olson, Timothy E.; Kim, Jung H.; Koeppe, Roger E.; Andersen, Olaf S.; Allen, Toby W.

    2014-01-01

    We have explored the mechanisms of uncatalyzed membrane ion permeation using atomistic simulations and electrophysiological recordings. The solubility-diffusion mechanism of membrane charge transport has prevailed since the 1960s, despite inconsistencies in experimental observations and its lack of consideration for the flexible response of lipid bilayers. We show that direct lipid bilayer translocation of alkali metal cations, Cl–, and a charged arginine side chain analog occurs via an ion-induced defect mechanism. Contrary to some previous suggestions, the arginine analog experiences a large free-energy barrier, very similar to those for Na+, K+, and Cl–. Our simulations reveal that membrane perturbations, due to the movement of an ion, are central for explaining the permeation process, leading to both free-energy and diffusion-coefficient profiles that show little dependence on ion chemistry and charge, despite wide-ranging hydration energies and the membrane’s dipole potential. The results yield membrane permeabilities that are in semiquantitative agreement with experiments in terms of both magnitude and selectivity. We conclude that ion-induced defect-mediated permeation may compete with transient pores as the dominant mechanism of uncatalyzed ion permeation, providing new understanding for the actions of a range of membrane-active peptides and proteins. PMID:24507599

  16. [Role of membrane lipids in myocardial cytoprotection

    NASA Technical Reports Server (NTRS)

    Grynberg, A.

    2000-01-01

    The cardiomyocyte capacity to regulate ATP production to face any change in energy demand is a major determinant of cardiac function. This process is based on a balanced fatty acid (FA) metabolism, because FA is the main fuel of the heart, although the most expensive one in oxygen. The pathway is, however, weakly controlled by the cardiac myocyte which can well regulate FA mitochondrial entry but not cell FA uptake. For this reason, several pathological situations often result from either harmful accumulation of FA and derivatives or excess FA-oxidation. Control of the FA/glucose balance by decreased energy production from FA would thus offer an alternative strategy in the treatment of ischaemia, providing the cardiomyocytes weak ability in handling the non-metabolised FA is controlled. The initiation and the regulation of cardiac contraction both result from membrane activity; the other major role of lipids in the heart is their contribution to membrane homeostasis through phospholipid synthesis pathways and phospholipases. The anti-anginal activity of Trimetazidine, reported as a cytoprotective effect without a haemo-dynamic component; is associated with reduced use of FA for energy. However, accumulation of FA and derivatives has never been observed. Trimetazidine is reported to increase significantly the synthesis of phospholipids without influencing the other lipid classes, thus increasing the incorporation of FA in membrane structures. This cytoprotection appears to be based on the redirection of the use of FA to phospholipid synthesis, which would decrease their availability for energy production. This class of compounds, with the same properties as Trimetazidine, offers a metabolic approach to the treatment of ischaemia.

  17. Polymer-Induced Swelling of Solid-Supported Lipid Membranes

    PubMed Central

    Kreuzer, Martin; Trapp, Marcus; Dahint, Reiner; Steitz, Roland

    2015-01-01

    In this paper, we study the interaction of charged polymers with solid-supported 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membranes by in-situ neutron reflectivity. We observe an enormous swelling of the oligolamellar lipid bilayer stacks after incubation in solutions of poly(allylamine hydrochloride) (PAH) in D2O. The positively charged polyelectrolyte molecules interact with the lipid bilayers and induce a drastic increase in their d-spacing by a factor of ~4. Temperature, time, and pH influence the swollen interfacial lipid linings. From our study, we conclude that electrostatic interactions introduced by the adsorbed PAH are the main cause for the drastic swelling of the lipid coatings. The DMPC membrane stacks do not detach from their solid support at T > Tm. Steric interactions, also introduced by the PAH molecules, are held responsible for the stabilizing effect. We believe that this novel system offers great potential for fundamental studies of biomembrane properties, keeping the membrane’s natural fluidity and freedom, decoupled from a solid support at physiological conditions. PMID:26703746

  18. Different modes of lipid binding to membrane proteins probed by mass spectrometry.

    PubMed

    Bechara, Chérine; Robinson, Carol V

    2015-04-29

    The realization that the lipid environment is crucial for maintaining the structure and function of membrane proteins prompts new methods to understand lipid interactions. One such method, mass spectrometry, is emerging with the potential to monitor different modes of lipid binding to membrane protein complexes. Initial studies monitored the addition of lipids and deduced the kinetic and thermodynamic effects of lipid binding to proteins. Recent efforts however have focused on identifying lipids already present, explicitly in plugs, annular rings, or cavities. Lipids that bind within these orifices to membrane proteins will have higher residence times than those in the bulk lipid bilayer and consequently can be quantified and characterized by mass spectrometry. In special cases, lipids identified within cavities have been proposed as substrates following activity assays. Alternatively, a gas-phase unfolding protocol can be used to distinguish lipids that are important for stability. These lipids can subsequently be added during crystallization for the characterization of lipid-bound protein complexes. Overall therefore this Perspective provides an overview of recent advances in mass spectrometry, with a particular focus on the distinction of the various modes of lipid binding, and their implications for structure and function as well as new directions that lie ahead. PMID:25860341

  19. Study of polytopic membrane protein topological organization as a function of membrane lipid composition.

    PubMed

    Bogdanov, Mikhail; Heacock, Philip N; Dowhan, William

    2010-01-01

    A protocol is described using lipid mutants and thiol-specific chemical reagents to study lipid-dependent and host-specific membrane protein topogenesis by the substituted-cysteine accessibility method as applied to transmembrane domains (SCAM). SCAM is adapted to follow changes in membrane protein topology as a function of changes in membrane lipid composition. The strategy described can be adapted to any membrane system. PMID:20419405

  20. Mixtures of Cationic Lipid O-Ethylphosphatidylcholine with Membrane Lipids and DNA: Phase Diagrams

    PubMed Central

    Koynova, Rumiana; MacDonald, Robert C.

    2003-01-01

    Ethylphosphatidylcholines are positively charged membrane lipid derivatives, which effectively transfect DNA into cells and are metabolized by the cells. For this reason, they are promising nonviral transfection agents. With the aim of revealing the kinds of lipid phases that may arise when lipoplexes interact with cellular lipids during DNA transfection, temperature-composition phase diagrams of mixtures of the O-ethyldipalmitoylphosphatidylcholine with representatives of the major lipid classes (phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, cholesterol) were constructed. Phase boundaries were determined using differential scanning calorimetry and synchrotron x-ray diffraction. The effects of ionic strength and of DNA presence were examined. A large variety of polymorphic and mesomorphic structures were observed. Surprisingly, marked enhancement of the affinity for nonlamellar phases was observed in mixtures with phosphatidylethanolamine and cholesterol as well as with phosphatidylglycerol (previously reported). Because of the potential relevance to transfection, it is noteworthy that such phases form at close to physiological conditions, and in the presence of DNA. All four mixtures exhibit a tendency to molecular clustering in the gel phase, presumably due to the specific interdigitated molecular arrangement of the O-ethyldipalmitoylphosphatidylcholine gel bilayers. It is evident that a remarkably broad array of lipid phases could arise in transfected cells and that these could have significant effects on transfection efficiency. The data may be particularly useful for selecting possible “helper” lipids in the lipoplex formulations, and in searches for correlations between lipoplex structure and transfection activity. PMID:14507708

  1. Interaction measurement of particles bound to a lipid membrane

    NASA Astrophysics Data System (ADS)

    Sarfati, Raphael; Dufresne, Eric

    2015-03-01

    The local shape and dynamics of the plasma membrane play important roles in many cellular processes. Local membrane deformations are often mediated by the adsorption of proteins (notably from the BAR family), and their subsequent self-assembly. The emerging hypothesis is that self-assembly arises from long-range interactions of individual proteins through the membrane's deformation field. We study these interactions in a model system of micron-sized colloidal particles adsorbed onto a lipid bilayer. We use fluorescent microscopy, optical tweezers and particle tracking to measure dissipative and conservative forces as a function of the separation between the particles. We find that particles are driven together with forces of order 100 fN and remain bound in a potential well with a stiffness of order 100 fN/micron.

  2. MemProtMD: Automated Insertion of Membrane Protein Structures into Explicit Lipid Membranes

    PubMed Central

    Stansfeld, Phillip J.; Goose, Joseph E.; Caffrey, Martin; Carpenter, Elisabeth P.; Parker, Joanne L.; Newstead, Simon; Sansom, Mark S.P.

    2015-01-01

    Summary There has been exponential growth in the number of membrane protein structures determined. Nevertheless, these structures are usually resolved in the absence of their lipid environment. Coarse-grained molecular dynamics (CGMD) simulations enable insertion of membrane proteins into explicit models of lipid bilayers. We have automated the CGMD methodology, enabling membrane protein structures to be identified upon their release into the PDB and embedded into a membrane. The simulations are analyzed for protein-lipid interactions, identifying lipid binding sites, and revealing local bilayer deformations plus molecular access pathways within the membrane. The coarse-grained models of membrane protein/bilayer complexes are transformed to atomistic resolution for further analysis and simulation. Using this automated simulation pipeline, we have analyzed a number of recently determined membrane protein structures to predict their locations within a membrane, their lipid/protein interactions, and the functional implications of an enhanced understanding of the local membrane environment of each protein. PMID:26073602

  3. A Critical Reassessment of Penetratin Translocation Across Lipid Membranes

    PubMed Central

    Bárány-Wallje, Elsa; Keller, Sandro; Serowy, Steffen; Geibel, Sebastian; Pohl, Peter; Bienert, Michael; Dathe, Margitta

    2005-01-01

    Penetratin is a short, basic cell-penetrating peptide able to induce cellular uptake of a vast variety of large, hydrophilic cargos. We have reassessed the highly controversial issue of direct permeation of the strongly cationic peptide across negatively charged lipid membranes. Confocal laser scanning microscopy on rhodamine-labeled giant vesicles incubated with carboxyfluorescein-labeled penetratin yielded no evidence of transbilayer movement, in contradiction to previously reported results. Confocal fluorescence spectroscopy on black lipid membranes confirmed this finding, which was also not affected by application of a transmembrane electric potential difference. A novel dialysis assay based on tryptophan absorbance and fluorescence spectroscopy demonstrated that the permeability of small and large unilamellar vesicles to penetratin is <10−13 m/s. Taken together, the results show that penetratin is not capable of overcoming model membrane systems irrespective of the bilayer curvature or the presence of a transmembrane voltage. Thus, direct translocation across the hydrophobic core of the plasma membrane cannot account for the efficient uptake of penetratin into live cells, which is in accord with recent in vitro studies underlining the importance of endocytosis in the internalization process of cationic cell-penetrating peptides. PMID:16040762

  4. Theoretical analysis of protein organization in lipid membranes.

    PubMed

    Gil, T; Ipsen, J H; Mouritsen, O G; Sabra, M C; Sperotto, M M; Zuckermann, M J

    1998-11-10

    The fundamental physical principles of the lateral organization of trans-membrane proteins and peptides as well as peripheral membrane proteins and enzymes are considered from the point of view of the lipid-bilayer membrane, its structure, dynamics, and cooperative phenomena. Based on a variety of theoretical considerations and model calculations, the nature of lipid-protein interactions is considered both for a single protein and an assembly of proteins that can lead to aggregation and protein crystallization in the plane of the membrane. Phenomena discussed include lipid sorting and selectivity at protein surfaces, protein-lipid phase equilibria, lipid-mediated protein-protein interactions, wetting and capillary condensation as means of protein organization, mechanisms of two-dimensional protein crystallization, as well as non-equilibrium organization of active proteins in membranes. The theoretical findings are compared with a variety of experimental data. PMID:9804966

  5. Role of Alcohols in Growth, Lipid Composition, and Membrane Fluidity of Yeasts, Bacteria, and Archaea ▿

    PubMed Central

    Huffer, Sarah; Clark, Melinda E.; Ning, Jonathan C.; Blanch, Harvey W.; Clark, Douglas S.

    2011-01-01

    Increased membrane fluidity, which causes cofactor leakage and loss of membrane potential, has long been documented as a cause for decreased cell growth during exposure to ethanol, butanol, and other alcohols. Reinforcement of the membrane with more complex lipid components is thus thought to be beneficial for the generation of more tolerant organisms. In this study, organisms with more complex membranes, namely, archaea, did not maintain high growth rates upon exposure to alcohols, indicating that more complex lipids do not necessarily fortify the membrane against the fluidizing effects of alcohols. In the presence of alcohols, shifts in lipid composition to more saturated and unbranched lipids were observed in most of the organisms tested, including archaea, yeasts, and bacteria. However, these shifts did not always result in a decrease in membrane fluidity or in greater tolerance of the organism to alcohol exposure. In general, organisms tolerating the highest concentrations of alcohols maintained membrane fluidity after alcohol exposure, whereas organisms that increased membrane rigidity were less tolerant. Altered lipid composition was a common response to alcohol exposure, with the most tolerant organisms maintaining a modestly fluid membrane. Our results demonstrate that increased membrane fluidity is not the sole cause of growth inhibition and that alcohols may also denature proteins within the membrane and cytosol, adversely affecting metabolism and decreasing cell growth. PMID:21784917

  6. Membrane-Protein Interactions in a Generic Coarse-Grained Model for Lipid Bilayers

    PubMed Central

    West, Beate; Brown, Frank L.H.; Schmid, Friederike

    2009-01-01

    Abstract We study membrane-protein interactions and membrane-mediated protein-protein interactions by Monte Carlo simulations of a generic coarse-grained model for lipid bilayers with cylindrical hydrophobic inclusions. The strength of the hydrophobic force and the hydrophobic thickness of the proteins are systematically varied. The results are compared with analytical predictions of two popular analytical theories: The Landau-de Gennes theory and the elastic theory. The elastic theory provides an excellent description of the fluctuation spectra of pure membranes and successfully reproduces the deformation profiles of membranes around single proteins. However, its prediction for the potential of mean force between proteins is not compatible with the simulation data for large distances. The simulations show that the lipid-mediated interactions are governed by five competing factors: direct interactions; lipid-induced depletion interactions; lipid bridging; lipid packing; and a smooth long-range contribution. The mechanisms leading to hydrophobic mismatch interactions are critically analyzed. PMID:18835907

  7. TOPICAL REVIEW: Stability of macroion-decorated lipid membranes

    NASA Astrophysics Data System (ADS)

    May, Sylvio

    2005-08-01

    Adsorption of macroions such as colloidal particles, proteins, or other rigid biopolymers onto oppositely charged, mixed lipid membranes is a ubiquitous phenomenon encountered in biotechnology, drug delivery, and cellular biology. The softness and self-assembled nature of the membrane enable the macroion-membrane complex to laterally reorganize via forming macroion clusters, lipid domains, or separate phases, and to exhibit curvature modulations or even morphological transitions. Almost always, the lateral organization of the membrane and associated macroion layer mutually depend on each other so that neither of the two extreme views—macroion-induced membrane domain formation or membrane-mediated macroion clustering—strictly accounts for the underlying energetics. We review and discuss some recent efforts to describe the lateral organization and stability of macroion-decorated lipid membranes using different levels of mean-field electrostatics, thereby focusing on binary membranes and the destabilizing role of compositional gradients.

  8. Label-free surface-enhanced infrared spectro-electro-chemical analysis of the Redox potential shift of cytochrome c complexed with a cardiolipin-containing lipid membrane of varied composition

    NASA Astrophysics Data System (ADS)

    Liu, Li; Wu, Lie; Zeng, Li; Jiang, Xiu-E.

    2015-12-01

    In this study, a lipid membrane was fabricated by fusing cardiolipin-phosphatidylcholine (CL_PC, 1:4) vesicles onto a hydrophobic surface of 1-dodecanethiol (DT) preadsorbed on a nanostructured gold film. By changing the concentration of the DT adsorption solution, we constructed a series of CL_PC-DT bilayers with different hydrophobicity to study the effects of lipid membrane characteristics on the adsorption conformation of cytochrome c (Cyt c). Electrochemical analysis showed that the formal potential is 0.24 V for Cyt c-CL_PC-DT(10), 0.2 V for Cyt c-CL_PC-DT(20), and 0.16 V for Cyt c-CL_PC-DT(40) — a gradual positive shift with the decreasing DT concentration — relative to the potential of native cyt c (0.02 V). Potential-induced surface-enhanced infrared adsorption difference spectroscopy revealed that the gradual positive shift of the formal potential of CL-bound cyt c is determined by the environment with the gradually lowered dielectric constant for the heme cofactor in CL-bound cyt c (Fe3+). Project supported by the National Natural Science Foundation of China (Grant Nos. 91227114, 21322510, and 21105097), the China Postdoctoral Science Foundation (Grant No. 2013M530998), the Natural Science Foundation of Jilin Province, China (Grant No. 201215092), and the President Funds of the Chinese Academy of Sciences.

  9. Counterion-mediated pattern formation in membranes containing anionic lipids

    PubMed Central

    Slochower, David R.; Wang, Yu-Hsiu; Tourdot, Richard W.; Radhakrishnan, Ravi; Janmey, Paul A.

    2014-01-01

    Most lipid components of cell membranes are either neutral, like cholesterol, or zwitterionic, like phosphatidylcholine and sphingomyelin. Very few lipids, such as sphingosine, are cationic at physiological pH. These generally interact only transiently with the lipid bilayer, and their synthetic analogs are often designed to destabilize the membrane for drug or DNA delivery. However, anionic lipids are common in both eukaryotic and prokaryotic cell membranes. The net charge per anionic phospholipid ranges from −1 for the most abundant anionic lipids such has phosphatidylserine, to near −7 for phosphatidylinositol 3,4,5 trisphosphate, although the effective charge depends on many environmental factors. Anionic phospholipids and other negatively charged lipids such as lipopolysaccharides are not randomly distributed in the lipid bilayer, but are highly restricted to specific leaflets of the bilayer and to regions near transmembrane proteins or other organized structures within the plane of the membrane. This review highlights some recent evidence that counterions, in the form of monovalent or divalent metal ions, polyamines, or cationic protein domains, have a large influence of the lateral distribution of anionic lipids within the membrane, and that lateral demixing of anionic lipids has effects on membrane curvature and protein function that are important for biological control. PMID:24556233

  10. Lipid oxidation induces structural changes in biomimetic membranes.

    PubMed

    Weber, Georges; Charitat, Thierry; Baptista, Maurício S; Uchoa, Adjaci F; Pavani, Christiane; Junqueira, Helena C; Guo, Yachong; Baulin, Vladimir A; Itri, Rosangela; Marques, Carlos M; Schroder, André P

    2014-06-28

    Oxidation can intimately influence and structurally compromise the levels of biological self-assembly embodied by intracellular and plasma membranes. Lipid peroxidation, a natural metabolic outcome of life with oxygen under light, is also a salient oxidation reaction in photomedicine treatments. However, the effect of peroxidation on the fate of lipid membranes remains elusive. Here we use a new photosensitizer that anchors and disperses in the membrane to achieve spatial control of the oxidizing species. We find, surprisingly, that the integrity of unsaturated unilamellar vesicles is preserved even for fully oxidized membranes. Membrane survival allows for the quantification of the transformations of the peroxidized bilayers, providing key physical and chemical information to understand the effect of lipid oxidation on protein insertion and on other mechanisms of cell function. We anticipate that spatially controlled oxidation will emerge as a new powerful strategy for tuning and evaluating lipid membranes in biomimetic media under oxidative stress. PMID:24871383

  11. Curvature Forces in Membrane Lipid-Protein Interactions

    NASA Astrophysics Data System (ADS)

    Brown, Michael F.

    2012-02-01

    Membrane protein conformational changes, folding, and stability may all involve elastic deformation of the bilayer. Non-specific properties of the bilayer play a significant role in modulating protein conformational energetics. A flexible-surface model (FSM) describes the balance of curvature and hydrophobic forces in lipid-protein interactions. The FSM describes elastic coupling of membrane lipids to integral membrane proteins. Curvature and hydrophobic matching to the lipid bilayer entails a stress field that explains membrane protein stability. Rhodopsin provides an important example, where solid-state NMR and FTIR spectroscopy characterize the energy landscape of the dynamically activated receptor. Time-resolved UV-visible and FTIR spectroscopic studies show how membrane lipids affect the metarhodopsin equilibrium due to non-specific material properties. Influences of bilayer thickness, nonlamellar-forming lipids, detergents, and osmotic stress on rhodopsin function are all explained by the new biomembrane model. By contrast, the older fluid-mosaic model fails to account for such effects on membrane protein activity. According to the FSM proteins are regulated by membrane lipids whose spontaneous curvature most closely matches the activated state within the lipid membrane.

  12. Electric Characteristics of Hybrid Polymer Membranes Composed of Two Lipid Species

    NASA Astrophysics Data System (ADS)

    Oohira, Koji; Toko, Kiyoshi; Akiyama, Hideyuki; Yoshihara, Hiroshi; Yamafuji, Kaoru

    1995-09-01

    Electric characteristics of hybrid polymer membranes composed of two lipid species were studied, where one lipid species is positively charged in aqueous solution and the other is negatively charged. As a result, it was found that the hybrid membranes responded to taste substances in different ways according to the molar mixing ratio of these two kinds of lipids, and also showed different response characteristics from those of the single-lipid membranes. The membranes with the mixing ratio around 50% exhibited the largest responses to HCl (sourness) and monosodium glutamate (umami). Moreover, good quantitative agreements with the observed data on the response electric potential were obtained using a theory describing both the changes in surface electric potential and surface charge density with taste substances.

  13. Lipid membrane domains in cell surface and vacuolar systems.

    PubMed

    Kobayashi, T; Hirabayashi, Y

    2000-01-01

    Detergent insoluble sphingolipid-cholesterol enriched 'raft'-like membrane microdomains have been implicated in a variety of biological processes including sorting, trafficking, and signaling. Mutant cells and knockout animals of sphingolipid biosynthesis are clearly useful to understand the biological roles of lipid components in raft-like domains. It is suggested that raft-like domains distribute in internal vacuolar membranes as well as plasma membranes. In addition to sphingolipid-cholesterol-rich membrane domains, recent studies suggest the existence of another lipid-membrane domain in the endocytic pathway. This domain is enriched with a unique phospholipid, lysobisphosphatidic acid (LBPA) and localized in the internal membrane of multivesicular endosome. LBPA-rich membrane domains are involved in lipid and protein sorting within the endosomal system. Possible interaction between sphingolipids and LBPA in sphingolipid-storage disease is discussed. PMID:11201787

  14. Mechanism of proton permeation through chloroplast lipid membranes.

    PubMed Central

    Fuks, B; Homblé, F

    1996-01-01

    Electrical measurements were carried out to investigate the contribution of chloroplast lipids to the passive proton permeability of both the thylakoid and inner-envelope membranes. Permeability coefficient and conductance to protons were measured for solvent-free bilayers made from monogalactosyldiglyceride:digalactosyldiglycerid: sulfoquinovosyldiglyceride:phosphatidylglycerol (2:1:0.5:0.5, w/w) in the presence of a pH gradient of 7.4/8.1. The permeability coefficient for protons in glycolipids was 5.5 +/- 1.1 x 10(-4) cm s-1 (n = 14). To determine whether this high H+ permeability could be explained by the presence of lipid contaminants such as weak acids, we investigated the effects of (a) bovine serum albumin, which can remove some amphiphilic molecules such as free fatty acids, (b) 6-ketocholestanol, which increases the membrane dipole potential, (c) oleic acid, and (d) chlorodecane, which increases the dielectric constant of the lipid bilayer. Our results show that free fatty acids are inefficient protonophores, as compared with carbonylcyanide-m-chlorphenythydrazone, and that the hypothesis of a weak acid mechanism is not valid with glycolipid bilayers. In the presence of deuterium oxide the H+ conductane was reduced significantly, indicating that proton transport through the glycolipid matrix could occur directly by a hydrogen bond process. The passive transport of H+ through the glycolipid matrix is discussed with regard to the activity of the thylakoid ATP synthase and the inner-envelope H(+)-ATPase. PMID:8883387

  15. Functional crosstalk between membrane lipids and TLR biology.

    PubMed

    Köberlin, Marielle S; Heinz, Leonhard X; Superti-Furga, Giulio

    2016-04-01

    Toll-like receptors (TLRs) are important transmembrane proteins of the innate immune system that detect invading pathogens and subsequently orchestrate an immune response. The ensuing inflammatory processes are connected to lipid metabolism at multiple levels. Here, we describe different aspects of how membrane lipids can shape the response of TLRs. Recent reports have uncovered the role of individual lipid species on membrane protein function and mouse models have contributed to the understanding of how changes in lipid metabolism alter TLR signaling, endocytosis, and cytokine secretion. Finally, we discuss the importance of systematic approaches to identify the function of individual lipid species or the composition of membrane lipids in TLR-related processes. PMID:26895312

  16. Concerted diffusion of lipids in raft-like membranes.

    PubMed

    Apajalahti, Touko; Niemelä, Perttu; Govindan, Praveen Nedumpully; Miettinen, Markus S; Salonen, Emppu; Marrink, Siewert-Jan; Vattulainen, Ilpo

    2010-01-01

    Currently, there is no comprehensive model for the dynamics of cellular membranes. The understanding of even the basic dynamic processes, such as lateral diffusion of lipids, is still quite limited. Recent studies of one-component membrane systems have shown that instead of single-particle motions, the lateral diffusion is driven by a more complex, concerted mechanism for lipid diffusion (E. Falck et al., J. Am. Chem. Soc., 2008, 130, 44-45), where a lipid and its neighbors move in unison in terms of loosely defined clusters. In this work, we extend the previous study by considering the concerted lipid diffusion phenomena in many-component raft-like membranes. This nature of diffusion phenomena emerge in all the cases we have considered, including both atom-scale simulations of lateral diffusion within rafts and coarse-grained MARTINI simulations of diffusion in membranes characterized by coexistence of raft and non-raft domains. The data allows us to identify characteristic time scales for the concerted lipid motions, which turn out to range from hundreds of nanoseconds to several microseconds. Further, we characterize typical length scales associated with the correlated lipid diffusion patterns and find them to be about 10 nm, or even larger if weak correlations are taken into account. Finally, the concerted nature of lipid motions is also found in dissipative particle dynamics simulations of lipid membranes, clarifying the role of hydrodynamics (local momentum conservation) in membrane diffusion phenomena. PMID:20158041

  17. How Lipid Membranes Affect Pore Forming Toxin Activity.

    PubMed

    Rojko, Nejc; Anderluh, Gregor

    2015-12-15

    Pore forming toxins (PFTs) evolved to permeate the plasma membrane of target cells. This is achieved in a multistep mechanism that usually involves binding of soluble protein monomer to the lipid membrane, oligomerization at the plane of the membrane, and insertion of part of the polypeptide chain across the lipid membrane to form a conductive channel. Introduced pores allow uncontrolled transport of solutes across the membrane, inflicting damage to the target cell. PFTs are usually studied from the perspective of structure-function relationships, often neglecting the important role of the bulk membrane properties on the PFT mechanism of action. In this Account, we discuss how membrane lateral heterogeneity, thickness, and fluidity influence the pore forming process of PFTs. In general, lipid molecules are more accessible for binding in fluid membranes due to steric reasons. When PFT specifically binds ordered domains, it usually recognizes a specific lipid distribution pattern, like sphingomyelin (SM) clusters or SM/cholesterol complexes, and not individual lipid species. Lipid domains were also suggested to act as an additional concentration platform facilitating PFT oligomerization, but this is yet to be shown. The last stage in PFT action is the insertion of the transmembrane segment across the membranes to build the transmembrane pore walls. Conformational changes are a spontaneous process, and sufficient free energy has to be available for efficient membrane penetration. Therefore, fluid bilayers are permeabilized more readily in comparison to highly ordered and thicker liquid ordered lipid phase (Lo). Energetically more costly insertion into the Lo phase can be driven by the hydrophobic mismatch between the thinner liquid disordered phase (Ld) and large protein complexes, which are unable to tilt like single transmembrane segments. In the case of proteolipid pores, membrane properties can directly modulate pore size, stability, and even selectivity. Finally

  18. Anomalous diffusion of proteins in sheared lipid membranes.

    PubMed

    Khoshnood, Atefeh; Jalali, Mir Abbas

    2013-09-01

    We use coarse grained molecular dynamics simulations to investigate diffusion properties of sheared lipid membranes with embedded transmembrane proteins. In membranes without proteins, we find normal in-plane diffusion of lipids in all flow conditions. Protein embedded membranes behave quite differently: by imposing a simple shear flow and sliding the monolayers of the membrane over each other, the motion of protein clusters becomes strongly superdiffusive in the shear direction. In such a circumstance, the subdiffusion regime is predominant perpendicular to the flow. We show that superdiffusion is a result of accelerated chaotic motions of protein-lipid complexes within the membrane voids, which are generated by hydrophobic mismatch or the transport of lipids by proteins. PMID:24125292

  19. Membrane lipid rafts and neurobiology: age-related changes in membrane lipids and loss of neuronal function.

    PubMed

    Egawa, Junji; Pearn, Matthew L; Lemkuil, Brian P; Patel, Piyush M; Head, Brian P

    2016-08-15

    A better understanding of the cellular physiological role that plasma membrane lipids, fatty acids and sterols play in various cellular systems may yield more insight into how cellular and whole organ function is altered during the ageing process. Membrane lipid rafts (MLRs) within the plasma membrane of most cells serve as key organizers of intracellular signalling and tethering points of cytoskeletal components. MLRs are plasmalemmal microdomains enriched in sphingolipids, cholesterol and scaffolding proteins; they serve as a platform for signal transduction, cytoskeletal organization and vesicular trafficking. Within MLRs are the scaffolding and cholesterol binding proteins named caveolin (Cav). Cavs not only organize a multitude of receptors including neurotransmitter receptors (NMDA and AMPA receptors), signalling proteins that regulate the production of cAMP (G protein-coupled receptors, adenylyl cyclases, phosphodiesterases (PDEs)), and receptor tyrosine kinases involved in growth (Trk), but also interact with components that modulate actin and tubulin cytoskeletal dynamics (e.g. RhoGTPases and actin binding proteins). MLRs are essential for the regulation of the physiology of organs such as the brain, and age-related loss of cholesterol from the plasma membrane leads to loss of MLRs, decreased presynaptic vesicle fusion, and changes in neurotransmitter release, all of which contribute to different forms of neurodegeneration. Thus, MLRs provide an active membrane domain that tethers and reorganizes the cytoskeletal machinery necessary for membrane and cellular repair, and genetic interventions that restore MLRs to normal cellular levels may be exploited as potential therapeutic means to reverse the ageing and neurodegenerative processes. PMID:26332795

  20. Carrier-mediated ion transport in lipid bilayer membranes.

    PubMed

    Laprade, R; Grenier, F; Pagé-Dansereau, M; Dansereau, J

    1984-08-01

    The electrical properties predicted by a widely accepted model for carrier-mediated ion transport in lipid bilayers are described. The different steps leading to ion transport and their associated rate constants are reaction at the interface between an ion in the aqueous phase and a carrier in the membrane (kRi), followed by translocation of the ion-carrier complex across the membrane interior (kis) and its dissociation at the other interface (kDi) after which the free carrier crosses back the membrane interior (ks). Results on glyceryl monooleate (GMO) membranes for a family of homologue carriers, the macrotetralide actin antibiotics (nonactin, monactin, dinactin, trinactin, and tetranactin) and a variety of ions (Na+, Cs+, Rb+, K+, NH4+, and Tl+) are presented. Internally consistent data obtained from steady-state electrical measurements (zero-current potential and conductance, current-voltage relationship) allow us to obtain the equilibrium permeability ratios for the different ions and show that for a given carrier kRi is relatively invariant from one ion to the other, except for Tl+ (larger), which implies that the ionic selectivity is controlled by the dissociation of the complex. The values of the individual rate constants obtained from current relaxation experiments are also presented and confirm the findings from steady-state measurements, as well as the isostericity concept for complexes of different ions with the same carrier (kis invariant). These also allow us to determine the aqueous phase membrane and torus membrane partition coefficients. Finally, the observed increase in kis from nonactin to tetranactin and, for all homologues, from GMO-decane to solvent-free GMO membranes, together with the concomitant decrease in kDi, can be explained in terms of modifications of electrostatic energy profiles induced by variations in carrier size and membrane thickness. PMID:6498590

  1. Optimization of fluorimetric lipid membrane biosensor sensitivity through manipulation of membrane structure and nitrobenzoxadiazole dipalmitoylphosphatidylethanolamine concentration

    NASA Astrophysics Data System (ADS)

    Shrive, Jason D. A.; Krull, Ulrich J.

    1995-01-01

    In the work reported here, surface concentrations of 0.027 and 0.073 molecules nm-2 of the fluorescent membrane probe molecule nitrobenzoxadiazole dipalmitoylphosphatidylethanolamine (NBD-PE) were shown to yield optimum sensitivity for fluorimetric transduction of membrane structural perturbations for lipid membrane-based biosensor development. These optima were obtained through correlation of experimental data with theoretical predictions of optimum surface concentrations based on a model for NBD-PE self quenching previously published by our group. It was also determined that membrane structural heterogeneity improves the sensitivity of NBD-PE labeled membrane transducers. Together with fluorescence microscopy, observations of surface potential change upon compression or expansion of phosphatidylcholine (PC)/phosphatidic acid (PA) monolayers were used to qualitatively indicate the degree of structural heterogeneity in these membranes. It was determined that sub-microscopic domains must exist in microscopically homogeneous egg PC/egg PA membranes in order to facilitate the observed NBD-PE self-quenching responses upon alteration of bulk pH and therefore, membrane surface electrostatics and structure.

  2. Amino acid-containing membrane lipids in bacteria.

    PubMed

    Geiger, Otto; González-Silva, Napoleón; López-Lara, Isabel M; Sohlenkamp, Christian

    2010-01-01

    In the bacterial model organism Escherichia coli only the three major membrane lipids phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin occur, all of which belong to the glycerophospholipids. The amino acid-containing phosphatidylserine is a major lipid in eukaryotic membranes but in most bacteria it occurs only as a minor biosynthetic intermediate. In some bacteria, the anionic glycerophospholipids phosphatidylglycerol and cardiolipin can be decorated with aminoacyl residues. For example, phosphatidylglycerol can be decorated with lysine, alanine, or arginine whereas in the case of cardiolipin, lysine or d-alanine modifications are known. In few bacteria, diacylglycerol-derived lipids can be substituted with lysine or homoserine. Acyl-oxyacyl lipids in which the lipidic part is amide-linked to the alpha-amino group of an amino acid are widely distributed among bacteria and ornithine-containing lipids are the most common version of this lipid type. Only few bacterial groups form glycine-containing lipids, serineglycine-containing lipids, sphingolipids, or sulfonolipids. Although many of these amino acid-containing bacterial membrane lipids are produced in response to certain stress conditions, little is known about the specific molecular functions of these lipids. PMID:19703488

  3. Molecular dynamics study of electrostatic potential along lipid bilayer with gramicidin A

    NASA Astrophysics Data System (ADS)

    Saito, Hiroaki; Nishimura, Megumi; Takagi, Hiroyuki; Miyakawa, Takeshi; Kawaguchi, Kazutomo; Nagao, Hidemi

    2013-02-01

    The structure and electrostatic potential profile of the DMPC lipid bilayers with a gramicidin A (GA) were studied by molecular dynamics (MD) simulation. The MD simulation reproduced the effect of GA on the membrane structure; the area per lipid decreases and membrane thickness increases, and the observed membrane structures correspond to the experimental data. The polar headgroup of lipid was found to orient toward the membrane normal as the lipid approaches the GA. The observed electrostatic potential map showed that the electrostatic potential around the region of GA gate was lower than the others at the same level of the membrane normal and the values of electrostatic potential in the pore region of GA were negative. These results indicate that a cation in the aqueous region of membrane can be electrostatically led to the GA entrance and penetrate the GA channel following the gradient of ion concentration.

  4. Molecular Dynamics Study of Bipolar Tetraether Lipid Membranes

    PubMed Central

    Shinoda, Wataru; Shinoda, Keiko; Baba, Teruhiko; Mikami, Masuhiro

    2005-01-01

    Membranes composed of bipolar tetraether lipids have been studied by a series of 25-ns molecular dynamics simulations to understand the microscopic structure and dynamics as well as membrane area elasticity. By comparing macrocyclic and acyclic tetraether and diether archaeal lipids, the effect of tail linkage of the two phytanyl-chained lipids on the membrane properties is elucidated. Tetraether lipids show smaller molecular area and lateral mobility. For the latter, calculated diffusion coefficients are indeed one order-of-magnitude smaller than that of the diether lipid. These two tetraether membranes are alike in many physical properties except for membrane area elasticity. The macrocyclic tetraether membrane shows a higher elastic area expansion modulus than its acyclic counterpart by a factor of three. Free energy profiles of a water molecule crossing the membranes show no major difference in barrier height; however, a significant difference is observed near the membrane center due to the lack of the slip-plane in tetraether membranes. PMID:16100279

  5. Dynamics and instabilities of lipid bilayer membrane shapes

    PubMed Central

    Shi, Zheng; Baumgart, Tobias

    2014-01-01

    Biological membranes undergo constant shape remodeling involving the formation of highly curved structures. The lipid bilayer represents the fundamental architecture of the cellular membrane with its shapes determined by the Helfrich curvature bending energy. However, the dynamics of bilayer shape transitions, especially their modulation by membrane proteins, and the resulting shape instabilities, are still not well understood. Here, we review in a unifying manner several theories that describe the fluctuations (i.e. undulations) of bilayer shapes as well as their local coupling with lipid or protein density variation. The coupling between local membrane curvature and lipid density gives rise to a ‘slipping mode’ in addition to the conventional ‘bending mode’ for damping the membrane fluctuation. This leads to a number of interesting experimental phenomena regarding bilayer shape dynamics. More importantly, curvature-inducing proteins can couple with membrane shape and eventually render the membrane unstable. A criterion for membrane shape instability is derived from a linear stability analysis. The instability criterion reemphasizes the importance of membrane tension in regulating the stability and dynamics of membrane geometry. Recent progresses in understanding the role of membrane tension in regulating dynamical cellular processes are also reviewed. Protein density is emphasized as a key factor in regulating membrane shape transitions: a threshold density of curvature coupling proteins is required for inducing membrane morphology transitions. PMID:24529968

  6. Dynamics and instabilities of lipid bilayer membrane shapes.

    PubMed

    Shi, Zheng; Baumgart, Tobias

    2014-06-01

    Biological membranes undergo constant shape remodeling involving the formation of highly curved structures. The lipid bilayer represents the fundamental architecture of the cellular membrane with its shapes determined by the Helfrich curvature bending energy. However, the dynamics of bilayer shape transitions, especially their modulation by membrane proteins, and the resulting shape instabilities, are still not well understood. Here, we review in a unifying manner several theories that describe the fluctuations (i.e. undulations) of bilayer shapes as well as their local coupling with lipid or protein density variation. The coupling between local membrane curvature and lipid density gives rise to a 'slipping mode' in addition to the conventional 'bending mode' for damping the membrane fluctuation. This leads to a number of interesting experimental phenomena regarding bilayer shape dynamics. More importantly, curvature-inducing proteins can couple with membrane shape and eventually render the membrane unstable. A criterion for membrane shape instability is derived from a linear stability analysis. The instability criterion reemphasizes the importance of membrane tension in regulating the stability and dynamics of membrane geometry. Recent progresses in understanding the role of membrane tension in regulating dynamical cellular processes are also reviewed. Protein density is emphasized as a key factor in regulating membrane shape transitions: a threshold density of curvature coupling proteins is required for inducing membrane morphology transitions. PMID:24529968

  7. Membrane-lipid unsaturation and mitochondrial function in Saacharomyces cerevisiae.

    PubMed Central

    Watson, K; Houghton, R L; Bertoli, E; Griffiths, D E

    1975-01-01

    The lipid composition of yeast cells was manipulated by the use of an unsaturated fatty acid auxotroph of Saccharomyces cerevisiae. There was a 2-3-fold decrease in the concentration of cytochromes a+a3 when the unsaturated fatty acid content of the cells was decreased from 60-70% of the total fatty acid to 20-30%. The amounts of cytochromes b and c were also decreased under these conditions, but to a lesser extent. Further lipid depletion, to proportions of less than 20% unsaturated fatty acid, led to a dramatic decrease in the content of all cytochromes, particularly cytochromes a+a3. The ATPase (adenosine triphosphatase), succinate oxidase and NADH oxidase activities of the isolated mitochondria also varied with the degree of unsaturation of the membrane lipids. The lower the percentage of unsaturated fatty acid, the lower was the enzymic activity. Inhibition of mitochondrial ATPase by oligomycin, on the other hand, was not markedly influenced by the membrane-lipid unsaturation. Npn-linear Arrenius plots of mitochondrial membrane-bound enzymes showed transition temperatures that were dependent on the degree of membrane-lipid unsaturation. The greater the degree of lipid unsaturation, the lower was the transition temperature. It was concluded that the degree of unsaturation of the membrane lipids plays an important role in determining the properties of mitochondrial membrane-bound enzymes. PMID:125585

  8. Lipid-engineered Escherichia coli Membranes Reveal Critical Lipid Headgroup Size for Protein Function*

    PubMed Central

    Wikström, Malin; Kelly, Amélie A.; Georgiev, Alexander; Eriksson, Hanna M.; Klement, Maria Rosén; Bogdanov, Mikhail; Dowhan, William; Wieslander, Åke

    2009-01-01

    Escherichia coli membranes have a substantial bilayer curvature stress due to a large fraction of the nonbilayer-prone lipid phosphatidylethanolamine, and a mutant (AD93) lacking this lipid is severely crippled in several membrane-associated processes. Introduction of four lipid glycosyltransferases from Acholeplasma laidlawii and Arabidopsis thaliana, synthesizing large amounts of two nonbilayer-prone, and two bilayer-forming gluco- and galacto-lipids, (i) restored the curvature stress with the two nonbilayer lipids, and (ii) diluted the high negative lipid surface charge in all AD93 bilayers. Surprisingly, the bilayer-forming diglucosyl-diacylglycerol was almost as good in improving AD93 membrane processes as the two nonbilayer-prone glucosyl-diacylglycerol and galactosyl-diacylglycerol lipids, strongly suggesting that lipid surface charge dilution by these neutral lipids is very important for E. coli. Increased acyl chain length and unsaturation, plus cardiolipin (nonbilayer-prone) content, were probably also beneficial in the modified strains. However, despite a correct transmembrane topology for the transporter LacY in the diglucosyl-diacylglycerol clone, active transport failed in the absence of a nonbilayer-prone glycolipid. The corresponding digalactosyl-diacylglycerol bilayer lipid did not restore AD93 membrane processes, despite analogous acyl chain and cardiolipin contents. Chain ordering, probed by bis-pyrene lipids, was substantially lower in the digalactosyl-diacylglycerol strain lipids due to its extended headgroup. Hence, a low surface charge density of anionic lipids is important in E. coli membranes, but is inefficient if the headgroup of the diluting lipid is too large. This strongly indicates that a certain magnitude of the curvature stress is crucial for the bilayer in vivo. PMID:18981182

  9. Chain ordering of hybrid lipids can stabilize domains in saturated/hybrid/cholesterol lipid membranes

    NASA Astrophysics Data System (ADS)

    Yamamoto, T.; Brewster, R.; Safran, S. A.

    2010-07-01

    We use a liquid-crystal model to predict that hybrid lipids (lipids that have one saturated and one unsaturated tail) can stabilize line interfaces between domains in mixed membranes of saturated lipids, hybrid lipids, and cholesterol (SHC membranes). The model predicts the phase separation of SHC membranes with both parabolic and loop binodals depending on the cholesterol concentration, modeled via an effective pressure. In some cases, the hybrid lipids can reduce the line tension to zero in SHC membranes at temperatures that approach the critical temperature as the pressure is increased. The differences in the hybrid saturated tail conformational order in bulk and at the interface are responsible for the reduction of the line tension.

  10. Autonomous Transmembrane Segment S4 of the Voltage Sensor Domain Partitions into the Lipid Membrane

    PubMed Central

    Tiriveedhi, Venkataswarup; Miller, Melissa; Butko, Peter; Li, Min

    2012-01-01

    The S4 transmembrane segment in voltage-gated ion channels, a highly basic α helix, responds to changes in membrane potential and induces channel opening. Earlier work by others indicates that the S4 segment interacts with lipids in plasma membrane, but its mechanism is unclear. Working with synthetic tryptophan-labeled S4 peptides, we characterized binding of autonomous S4 to lipid membranes. The binding free energy (5.2 ± 0.2 kcal/mol) of the peptide-lipid interaction was estimated from the apparent dissociation constants, determined from the changes in anisotropy of tryptophan fluorescence induced by addition of lipid vesicles with 30 mol% phosphatidylglycerol. The results are in good agreement with the prediction based on the Wimley-White hydrophobicity scale for interfacial (IF) binding of an alpha-helical peptide to the lipid bilayer (6.98 kcal/mol). High salt inhibited the interaction, thus indicating that the peptide/membrane interaction has both electrostatic and non-electrostatic components. Furthermore, the synthetic S4 corresponding to the Shaker potassium channel was found to spontaneously penetrate into the negatively charged lipid membrane to a depth of about 9 Å. Our results revealed important biophysical parameters that influence the interaction of S4 with the membrane: they include fluidity, surface charge, and surface pressure of the membrane, and the α helicity and regular spacing of basic amino-acid residues in the S4 sequence. PMID:22465069

  11. Differential Effect of Plant Lipids on Membrane Organization

    PubMed Central

    Grosjean, Kevin; Mongrand, Sébastien; Beney, Laurent; Simon-Plas, Françoise; Gerbeau-Pissot, Patricia

    2015-01-01

    The high diversity of the plant lipid mixture raises the question of their respective involvement in the definition of membrane organization. This is particularly the case for plant plasma membrane, which is enriched in specific lipids, such as free and conjugated forms of phytosterols and typical phytosphingolipids, such as glycosylinositolphosphoceramides. This question was here addressed extensively by characterizing the order level of membrane from vesicles prepared using various plant lipid mixtures and labeled with an environment-sensitive probe. Fluorescence spectroscopy experiments showed that among major phytosterols, campesterol exhibits a stronger ability than β-sitosterol and stigmasterol to order model membranes. Multispectral confocal microscopy, allowing spatial analysis of membrane organization, demonstrated accordingly the strong ability of campesterol to promote ordered domain formation and to organize their spatial distribution at the membrane surface. Conjugated sterol forms, alone and in synergy with free sterols, exhibit a striking ability to order membrane. Plant sphingolipids, particularly glycosylinositolphosphoceramides, enhanced the sterol-induced ordering effect, emphasizing the formation and increasing the size of sterol-dependent ordered domains. Altogether, our results support a differential involvement of free and conjugated phytosterols in the formation of ordered domains and suggest that the diversity of plant lipids, allowing various local combinations of lipid species, could be a major contributor to membrane organization in particular through the formation of sphingolipid-sterol interacting domains. PMID:25575593

  12. The electrical interplay between proteins and lipids in membranes.

    PubMed

    Richens, Joanna L; Lane, Jordan S; Bramble, Jonathan P; O'Shea, Paul

    2015-09-01

    All molecular interactions that are relevant to cellular and molecular structures are electrical in nature but manifest in a rich variety of forms that each has its own range and influences on the net effect of how molecular species interact. This article outlines how electrical interactions between the protein and lipid membrane components underlie many of the activities of membrane function. Particular emphasis is placed on spatially localised behaviour in membranes involving modulation of protein activity and microdomain structure. The interactions between membrane lipids and membrane proteins together with their role within cell biology represent an enormous body of work. Broad conclusions are not easy given the complexities of the various systems and even consensus with model membrane systems containing two or three lipid types is difficult. By defining two types of broad lipid-protein interaction, respectively Type I as specific and Type II as more non-specific and focussing on the electrical interactions mostly in the extra-membrane regions it is possible to assemble broad rules or a consensus of the dominant features of the interplay between these two fundamentally important classes of membrane component. This article is part of a special issue entitled: Lipid-protein interactions. PMID:25817548

  13. Designing lipids for selective partitioning into liquid ordered membrane domains.

    PubMed

    Momin, Noor; Lee, Stacey; Gadok, Avinash K; Busch, David J; Bachand, George D; Hayden, Carl C; Stachowiak, Jeanne C; Sasaki, Darryl Y

    2015-04-28

    Self-organization of lipid molecules into specific membrane phases is key to the development of hierarchical molecular assemblies that mimic cellular structures. While the packing interaction of the lipid tails should provide the major driving force to direct lipid partitioning to ordered or disordered membrane domains, numerous examples show that the headgroup and spacer play important but undefined roles. We report here the development of several new biotinylated lipids that examine the role of spacer chemistry and structure on membrane phase partitioning. The new lipids were prepared with varying lengths of low molecular weight polyethylene glycol (EGn) spacers to examine how spacer hydrophilicity and length influence their partitioning behavior following binding with FITC-labeled streptavidin in liquid ordered (Lo) and liquid disordered (Ld) phase coexisting membranes. Partitioning coefficients (Kp Lo/Ld) of the biotinylated lipids were determined using fluorescence measurements in studies with giant unilamellar vesicles (GUVs). Compared against DPPE-biotin, DPPE-cap-biotin, and DSPE-PEG2000-biotin lipids, the new dipalmityl-EGn-biotin lipids exhibited markedly enhanced partitioning into liquid ordered domains, achieving Kp of up to 7.3 with a decaethylene glycol spacer (DP-EG10-biotin). We further demonstrated biological relevance of the lipids with selective partitioning to lipid raft-like domains observed in giant plasma membrane vesicles (GPMVs) derived from mammalian cells. Our results found that the spacer group not only plays a pivotal role for designing lipids with phase selectivity but may also influence the structural order of the domain assemblies. PMID:25772372

  14. Protein-lipid interactions and non-lamellar lipidic structures in membrane pore formation and membrane fusion.

    PubMed

    Gilbert, Robert J C

    2016-03-01

    Pore-forming proteins and peptides act on their targeted lipid bilayer membranes to increase permeability. This approach to the modulation of biological function is relevant to a great number of living processes, including; infection, parasitism, immunity, apoptosis, development and neurodegeneration. While some pore-forming proteins/peptides assemble into rings of subunits to generate discrete, well-defined pore-forming structures, an increasing number is recognised to form pores via mechanisms which co-opt membrane lipids themselves. Among these, membrane attack complex-perforin/cholesterol-dependent cytolysin (MACPF/CDC) family proteins, Bax/colicin family proteins and actinoporins are especially prominent and among the mechanisms believed to apply are the formation of non-lamellar (semi-toroidal or toroidal) lipidic structures. In this review I focus on the ways in which lipids contribute to pore formation and contrast this with the ways in which lipids are co-opted also in membrane fusion and fission events. A variety of mechanisms for pore formation that involve lipids exists, but they consistently result in stable hybrid proteolipidic structures. These structures are stabilised by mechanisms in which pore-forming proteins modify the innate capacity of lipid membranes to respond to their environment, changing shape and/or phase and binding individual lipid molecules directly. In contrast, and despite the diversity in fusion protein types, mechanisms for membrane fusion are rather similar to each other, mapping out a pathway from pairs of separated compartments to fully confluent fused membranes. Fusion proteins generate metastable structures along the way which, like long-lived proteolipidic pore-forming complexes, rely on the basic physical properties of lipid bilayers. Membrane fission involves similar intermediates, in the reverse order. I conclude by considering the possibility that at least some pore-forming and fusion proteins are evolutionarily related

  15. 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

  16. Lipid partitioning at the nuclear envelope controls membrane biogenesis

    PubMed Central

    Barbosa, Antonio Daniel; Sembongi, Hiroshi; Su, Wen-Min; Abreu, Susana; Reggiori, Fulvio; Carman, George M.; Siniossoglou, Symeon

    2015-01-01

    Partitioning of lipid precursors between membranes and storage is crucial for cell growth, and its disruption underlies pathologies such as cancer, obesity, and type 2 diabetes. However, the mechanisms and signals that regulate this process are largely unknown. In yeast, lipid precursors are mainly used for phospholipid synthesis in nutrient-rich conditions in order to sustain rapid proliferation but are redirected to triacylglycerol (TAG) stored in lipid droplets during starvation. Here we investigate how cells reprogram lipid metabolism in the endoplasmic reticulum. We show that the conserved phosphatidate (PA) phosphatase Pah1, which generates diacylglycerol from PA, targets a nuclear membrane subdomain that is in contact with growing lipid droplets and mediates TAG synthesis. We find that cytosol acidification activates the master regulator of Pah1, the Nem1-Spo7 complex, thus linking Pah1 activity to cellular metabolic status. In the absence of TAG storage capacity, Pah1 still binds the nuclear membrane, but lipid precursors are redirected toward phospholipids, resulting in nuclear deformation and a proliferation of endoplasmic reticulum membrane. We propose that, in response to growth signals, activation of Pah1 at the nuclear envelope acts as a switch to control the balance between membrane biogenesis and lipid storage. PMID:26269581

  17. Planar asymmetric lipid bilayers of glycosphingolipid or lipopolysaccharide on one side and phospholipids on the other: membrane potential, porin function, and complement activation.

    PubMed Central

    Wiese, A; Reiners, J O; Brandenburg, K; Kawahara, K; Zähringer, U; Seydel, U

    1996-01-01

    We have determined some physicochemical properties of the monosaccharide-type fraction (GSL-1) of glycosphingolipids, the major glycolipid components of the outer leaflet of the Gram-negative species Sphingomonas paucimobilis. These properties included the state of order of the hydrocarbon moiety, the effective molecular area, surface charge density, and intrinsic transmembrane potential profile of reconstituted planar asymmetric GSL-1/phospholipid bilayer membranes. We have, furthermore, investigated the insertion into and the function of porin channels in the reconstituted bilayers and the complement-activating capability of GSL-1 surfaces. All results were compared with respective data for deep rough mutant lipopolysaccharide of Salmonella minnesota R595. We found a remarkable agreement in most functional properties of the two glycolipids. PMID:8770208

  18. Aspirin Increases the Solubility of Cholesterol in Lipid Membranes

    NASA Astrophysics Data System (ADS)

    Alsop, Richard; Barrett, Matthew; Zheng, Sonbo; Dies, Hannah; Rheinstadter, Maikel

    2014-03-01

    Aspirin (ASA) is often prescribed for patients with high levels of cholesterol for the secondary prevention of myocardial events, a regimen known as the Low-Dose Aspirin Therapy. We have recently shown that Aspirin partitions in lipid bilayers. However, a direct interplay between ASA and cholesterol has not been investigated. Cholesterol is known to insert itself into the membrane in a dispersed state at moderate concentrations (under ~37.5%) and decrease fluidity of membranes. We prepared model lipid membranes containing varying amounts of both ASA and cholesterol molecules. The structure of the bilayers as a function of ASA and cholesterol concentration was determined using high-resolution X-ray diffraction. At cholesterol levels of more than 40mol%, immiscible cholesterol plaques formed. Adding ASA to the membranes was found to dissolve the cholesterol plaques, leading to a fluid lipid bilayer structure. We present first direct evidence for an interaction between ASA and cholesterol on the level of the cell membrane.

  19. Tolerance to Changes in Membrane Lipid Composition as a Selected Trait of Membrane Proteins†

    PubMed Central

    Sanders, Charles R.; Mittendorf, Kathleen F.

    2011-01-01

    Membrane lipid composition can vary dramatically across the three domains of life and even within single organisms. Here we review evidence that the lipid-exposed surfaces of membrane proteins have generally evolved to maintain correct structure and function in the face of major changes in lipid composition. Such tolerance has allowed evolution to extensively remodel membrane lipid compositions during the emergence of new species without having to extensively remodel the associated membrane proteins. The tolerance of membrane proteins also permits single-celled organisms to vary membrane lipid composition in response to their changing environments and enables dynamic and organelle-specific variations in the lipid compositions of eukaryotic cells. Membrane protein structural biology has greatly benefited from this seemingly intrinsic property of membrane proteins: the majority of structures determined to date have been characterized under model membrane conditions that little-resemble native membranes. Nevertheless, with a few notable exceptions most experimentally-determined membrane protein structures appear, to a good approximation, to faithfully report on native structure. PMID:21848311

  20. [The effect of ionizing radiation in a wide dosage range on the structural-functional characteristics of the protein and lipid components of erythrocyte plasma membranes].

    PubMed

    Zima, G V; Dreval', V I

    2000-01-01

    The erythrocyte ghosts were irradiated with doses of 4 x 10(-3) Gy-10(3) Gy. Changes in the membrane lipid microviscosity, membrane proteins' structural mobility, membrane surface potential and intensity of the lipid peroxidation processes were determined. It has been established that the features of membrane structural changes are characterised, by polyphase changes of examined parameters. PMID:10907401

  1. Effects of Phospholipase A2 Inhibitors on Bilayer Lipid Membranes.

    PubMed

    Dubinin, Mikhail V; Astashev, Maxim E; Penkov, Nikita V; Gudkov, Sergey V; Dyachenko, Igor A; Samartsev, Victor N; Belosludtsev, Konstantin N

    2016-06-01

    The work examines the effect of inhibitors of cytosolic Ca(2+)-dependent and Ca(2+)-independent phospholipases A2 on bilayer lipid membranes. It was established that trifluoroperazine (TFP) and, to a lesser extent, arachidonyl trifluoromethyl ketone (AACOCF3) and palmitoyl trifluoromethyl ketone (PACOCF3) were able to permeabilize artificial lipid membranes (BLM and liposomes). It was shown that AACOCF3 lowered the temperature of phase transition of DMPC liposomes, inducing disordering of the hydrophobic region of lipid bilayer. TFP disordered membranes both in the hydrophobic region and in the region of hydrophilic heads, this being accompanied by changes in the membrane permeability: appearance of a channel-like BLM activity and leakage of sulforhodamine B from liposomes. In contrast to AACOCF3 and TFP, PACOCF3 increased membrane orderliness in the hydrophobic region (heightened the temperature of phase transition of DMPC liposomes) and in the region of lipid heads. The effectiveness of AACOCF3 and PACOCF3 as inductors of BLM and liposome permeabilization was considerably lower comparatively to TFP. As revealed by dynamic light scattering, incorporation of TFP, AACOCF3 and PACOCF3 into the membrane of liposomes resulted in the increase of the average size of particles in the suspension, presumably due to their aggregation or fusion. The paper discusses possible mechanisms of the influence of phospholipase A2 inhibitors on bilayer lipid membranes. PMID:26762382

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

    PubMed

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

    2016-04-01

    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. PMID:27015007

  3. Structural interactions of a voltage sensor toxin with lipid membranes

    PubMed Central

    Mihailescu, Mihaela; Krepkiy, Dmitriy; Milescu, Mirela; Gawrisch, Klaus; Swartz, Kenton J.; White, Stephen

    2014-01-01

    Protein toxins from tarantula venom alter the activity of diverse ion channel proteins, including voltage, stretch, and ligand-activated cation channels. Although tarantula toxins have been shown to partition into membranes, and the membrane is thought to play an important role in their activity, the structural interactions between these toxins and lipid membranes are poorly understood. Here, we use solid-state NMR and neutron diffraction to investigate the interactions between a voltage sensor toxin (VSTx1) and lipid membranes, with the goal of localizing the toxin in the membrane and determining its influence on membrane structure. Our results demonstrate that VSTx1 localizes to the headgroup region of lipid membranes and produces a thinning of the bilayer. The toxin orients such that many basic residues are in the aqueous phase, all three Trp residues adopt interfacial positions, and several hydrophobic residues are within the membrane interior. One remarkable feature of this preferred orientation is that the surface of the toxin that mediates binding to voltage sensors is ideally positioned within the lipid bilayer to favor complex formation between the toxin and the voltage sensor. PMID:25453087

  4. Anthrax toxin-induced rupture of artificial lipid bilayer membranes.

    PubMed

    Nablo, Brian J; Panchal, Rekha G; Bavari, Sina; Nguyen, Tam L; Gussio, Rick; Ribot, Wil; Friedlander, Art; Chabot, Donald; Reiner, Joseph E; Robertson, Joseph W F; Balijepalli, Arvind; Halverson, Kelly M; Kasianowicz, John J

    2013-08-14

    We demonstrate experimentally that anthrax toxin complexes rupture artificial lipid bilayer membranes when isolated from the blood of infected animals. When the solution pH is temporally acidified to mimic that process in endosomes, recombinant anthrax toxin forms an irreversibly bound complex, which also destabilizes membranes. The results suggest an alternative mechanism for the translocation of anthrax toxin into the cytoplasm. PMID:23947891

  5. Structural interactions of a voltage sensor toxin with lipid membranes.

    PubMed

    Mihailescu, Mihaela; Krepkiy, Dmitriy; Milescu, Mirela; Gawrisch, Klaus; Swartz, Kenton J; White, Stephen

    2014-12-16

    Protein toxins from tarantula venom alter the activity of diverse ion channel proteins, including voltage, stretch, and ligand-activated cation channels. Although tarantula toxins have been shown to partition into membranes, and the membrane is thought to play an important role in their activity, the structural interactions between these toxins and lipid membranes are poorly understood. Here, we use solid-state NMR and neutron diffraction to investigate the interactions between a voltage sensor toxin (VSTx1) and lipid membranes, with the goal of localizing the toxin in the membrane and determining its influence on membrane structure. Our results demonstrate that VSTx1 localizes to the headgroup region of lipid membranes and produces a thinning of the bilayer. The toxin orients such that many basic residues are in the aqueous phase, all three Trp residues adopt interfacial positions, and several hydrophobic residues are within the membrane interior. One remarkable feature of this preferred orientation is that the surface of the toxin that mediates binding to voltage sensors is ideally positioned within the lipid bilayer to favor complex formation between the toxin and the voltage sensor. PMID:25453087

  6. Anthrax toxin-induced rupture of artificial lipid bilayer membranes

    NASA Astrophysics Data System (ADS)

    Nablo, Brian J.; Panchal, Rekha G.; Bavari, Sina; Nguyen, Tam L.; Gussio, Rick; Ribot, Wil; Friedlander, Art; Chabot, Donald; Reiner, Joseph E.; Robertson, Joseph W. F.; Balijepalli, Arvind; Halverson, Kelly M.; Kasianowicz, John J.

    2013-08-01

    We demonstrate experimentally that anthrax toxin complexes rupture artificial lipid bilayer membranes when isolated from the blood of infected animals. When the solution pH is temporally acidified to mimic that process in endosomes, recombinant anthrax toxin forms an irreversibly bound complex, which also destabilizes membranes. The results suggest an alternative mechanism for the translocation of anthrax toxin into the cytoplasm.

  7. Melittin-induced cholesterol reorganization in lipid bilayer membranes.

    PubMed

    Qian, Shuo; Heller, William T

    2015-10-01

    The peptide melittin, a 26 amino acid, cationic peptide from honey bee (Apis mellifera) venom, disrupts lipid bilayer membranes in a concentration-dependent manner. Rather than interacting with a specific receptor, the peptide interacts directly with the lipid matrix of the membrane in a manner dependent on the lipid composition. Here, a small-angle neutron scattering study of the interaction of melittin with lipid bilayers made of mixtures of dimyristoylphosphatidylcholine (DMPC) and cholesterol (Chol) is presented. Through the use of deuterium-labeled DMPC, changes in the distribution of the lipid and cholesterol in unilamellar vesicles were observed for peptide concentrations below those that cause pores to form. In addition to disrupting the in-plane organization of Chol, melittin produces vesicles having inner and outer leaflet compositions that depend on the lipid-Chol molar ratio and on the peptide concentration. The changes seen at high cholesterol and low peptide concentration are similar to those produced by alamethicin (Qian, S. et al., J. Phys. Chem. B 2014, 118, 11200-11208), which points to an underlying physical mechanism driving the redistribution of Chol, but melittin displays an additional effect not seen with alamethicin. A model for how the peptide drives the redistribution of Chol is proposed. The results suggest that redistribution of the lipids in a target cell membrane by membrane active peptides takes places as a prelude to the lysis of the cell. PMID:26074009

  8. Lipid Bilayer Membrane Perturbation by Embedded Nanopores: A Simulation Study.

    PubMed

    Garcia-Fandiño, Rebeca; Piñeiro, Ángel; Trick, Jemma L; Sansom, Mark S P

    2016-03-22

    A macromolecular nanopore inserted into a membrane may perturb the dynamic organization of the surrounding lipid bilayer. To better understand the nature of such perturbations, we have undertaken a systematic molecular dynamics simulation study of lipid bilayer structure and dynamics around three different classes of nanopore: a carbon nanotube, three related cyclic peptide nanotubes differing in the nature of their external surfaces, and a model of a β-barrel nanopore protein. Periodic spatial distributions of several lipid properties as a function of distance from the nanopore were observed. This was especially clear for the carbon nanotube system, for which the density of lipids, the bilayer thickness, the projection of lipid head-to-tail vectors onto the membrane plane, and lipid lateral diffusion coefficients exhibited undulatory behavior as a function of the distance from the surface of the channel. Overall, the differences in lipid behavior as a function of the nanopore structure reveal local adaptation of the bilayer structure and dynamics to different embedded nanopore structures. Both the local structure and dynamic behavior of lipids around membrane-embedded nanopores are sensitive to the geometry and nature of the outer surface of the macromolecule/molecular assembly forming the pore. PMID:26943498

  9. The adrenal specific toxicant mitotane directly interacts with lipid membranes and alters membrane properties depending on lipid composition.

    PubMed

    Scheidt, Holger A; Haralampiev, Ivan; Theisgen, Stephan; Schirbel, Andreas; Sbiera, Silviu; Huster, Daniel; Kroiss, Matthias; Müller, Peter

    2016-06-15

    Mitotane (o,p'.-DDD) is an orphan drug approved for the treatment of adrenocortical carcinoma. The mechanisms, which are responsible for this activity of the drug, are not completely understood. It can be hypothesized that an impact of mitotane is mediated by the interaction with cellular membranes. However, an interaction of mitotane with (lipid) membranes has not yet been investigated in detail. Here, we characterized the interaction of mitotane and its main metabolite o,p'-dichlorodiphenyldichloroacetic acid (o,p'-DDA) with lipid membranes by applying a variety of biophysical approaches of nuclear magnetic resonance, electron spin resonance, and fluorescence spectroscopy. We found that mitotane and o,p'-DDA bind to lipid membranes by inserting into the lipid-water interface of the bilayer. Mitotane but not o,p'-DDA directly causes a disturbance of bilayer structure leading to an increased permeability of the membrane for polar molecules. Mitotane induced alterations of the membrane integrity required the presence of phosphatidylethanolamine and/or cholesterol. Collectively, our data for the first time characterize the impact of mitotane on the lipid membrane structure and dynamics, which may contribute to a better understanding of specific mitotane effects and side effects. PMID:27002491

  10. Stabilization of concentration fluctuations in mixed membranes by hybrid lipids

    NASA Astrophysics Data System (ADS)

    Palmieri, Benoit; Safran, Samuel

    2012-02-01

    Finite-size domains have been observed at the surface of cells. These lipids ``rafts'' are stable nanodomains enriched in saturated lipids and cholesterol. While line tension favors macrodomains, one explanation for raft stabilization suggests that the membrane composition is tuned close to a spinodal temperature. From this point of view, rafts are long-lived concentration fluctuations in the mixed phase. We propose a ternary mixture model for the cell membrane that includes hybrid lipids which have one saturated and one unsaturated hydrocarbon chain. Finite amount of hybrid lipids reduces the packing incompatibility at the saturated/unsaturated lipid interface and stabilizes the concentration fluctuations. Hybrid-Hybrid interactions are included in the model and further increase the life-time of the rafts and decrease their length-scales. Moreover, the hybrid has extra orientational degrees of freedom that may lead to modulated phases.

  11. High-throughput formation of lipid bilayer membrane arrays with an asymmetric lipid composition

    PubMed Central

    Watanabe, Rikiya; Soga, Naoki; Yamanaka, Tomoko; Noji, Hiroyuki

    2014-01-01

    We present a micro-device in which more than 10,000 asymmetric lipid bilayer membranes are formed at a time on micro-chamber arrays. The arrayed asymmetric lipid bilayers, where lipid compositions are different between the inner and outer leaflets, are formed with high efficiency of over 97% by injecting several types of liquids into a micro-device that has hydrophilic-in-hydrophobic surfaces. The lipid compositional asymmetry is an intrinsic property of bio-membranes, and therefore, this micro-device extends the versatility of artificial lipid-bilayer systems, which were previously limited to symmetric bilayer formation, and could contribute to the understanding of the role of lipid compositional asymmetry in cell physiology and also to further analytical and pharmacological applications. PMID:25399694

  12. Influence of membrane phospholipid composition and structural organization on spontaneous lipid transfer between membranes.

    PubMed

    Pankov, R; Markovska, T; Antonov, P; Ivanova, L; Momchilova, A

    2006-09-01

    Investigations were carried out on the influence of phospholipid composition of model membranes on the processes of spontaneous lipid transfer between membranes. Acceptor vesicles were prepared from phospholipids extracted from plasma membranes of control and ras-transformed fibroblasts. Acceptor model membranes with manipulated levels of phosphatidylethanolamine (PE), sphingomyelin and phosphatidic acid were also used in the studies. Donor vesicles were prepared of phosphatidylcholine (PC) and contained two fluorescent lipid analogues, NBD-PC and N-Rh-PE, at a self-quenching concentration. Lipid transfer rate was assessed by measuring the increase of fluorescence in acceptor membranes due to transfer of fluorescent lipid analogues from quenched donor to unquenched acceptor vesicles. The results showed that spontaneous NBD-PC transfer increased upon fluidization of acceptor vesicles. In addition, elevation of PE concentration in model membranes was also accompanied by an increase of lipid transfer to all series of acceptor vesicles. The results are discussed with respect to the role of lipid composition and structural order of cellular plasma membranes in the processes of spontaneous lipid exchange between membrane bilayers. PMID:17197729

  13. Probing DNA-lipid membrane interactions with a lipopeptide nanopore.

    PubMed

    Bessonov, Andrey; Takemoto, Jon Y; Simmel, Friedrich C

    2012-04-24

    Association of DNA molecules with lipid bilayer membranes is of considerable interest for a large variety of applications in biotechnology. Here we introduce syringomycin E (SRE), a small pore-forming lipopeptide produced by the bacterium Pseudomonas syringae, as a facile sensor for the detection of DNA interactions with lipid membranes. SRE forms highly reproducible pores in cellular and artificial membranes. The pore structure involves bilayer lipids, which have a pronounced influence on open channel conductance and gating. SRE channels act as ionic diodes that serve as current rectifiers sensitive to the charge of the bilayer. We employ this intrinsic property to electronically monitor the association of DNA molecules with the membrane in a variety of different settings. We show that SRE can be used for quantitatively probing electrostatic interactions of DNA and DNA-cholesterol conjugates with a lipid membrane. Furthermore, we demonstrate that SRE channels allow monitoring of hybridization reactions between lipid-anchored probe strands and complementary strands in solution. In the presence of double-stranded DNA, SRE channels display a particularly high degree of rectification. Finally, the formation of multilayered structures assembled from poly-(L)-lysine and DNA oligonucleotides on the membrane was precisely monitored with SRE. PMID:22424398

  14. Elastic deformation and failure of lipid bilayer membranes containing cholesterol.

    PubMed Central

    Needham, D; Nunn, R S

    1990-01-01

    Giant bilayer vesicles were reconstituted from several lipids and lipid/cholesterol (CHOL) mixtures: stearolyloleoylphosphatidylcholine (SOPC), bovine sphingomyelin (BSM), diarachidonylphosphatidylcholine (DAPC), SOPC/CHOL, BSM/CHOL, DAPC/CHOL, and extracted red blood cell (RBC) lipids with native cholesterol. Single-walled vesicles were manipulated by micropipette suction and several membrane material properties were determined. The properties measured were the elastic area compressibility modulus K, the critical areal strain alpha c, and the tensile strength tau lys, from which the failure energy or membrane toughness Tf was calculated. The elastic area expansion moduli for these lipid and lipid/cholesterol bilayers ranged from 57 dyn/cm for DAPC to 1,734 dyn/cm for BSM/CHOL. The SOPC/CHOL series and RBC lipids had intermediate values. The results indicated that the presence of cholesterol is the single most influential factor in increasing bilayer cohesion, but only for lipids where both chains are saturated, or mono- or diunsaturated. Multiple unsaturation in both lipid chains inhibits the condensing effect of cholesterol in bilayers. The SOPC/CHOL system was studied in more detail. The area expansion modulus showed a nonlinear increase with increasing cholesterol concentration up to a constant plateau, indicating a saturation limit for cholesterol in the bilayer phase of approximately 55 mol% CHOL. The membrane compressibility was modeled by a property-averaging composite theory involving two bilayer components, namely, uncomplexed lipid and a lipid/cholesterol complex of stoichiometry 1/1.22. The area expansion modulus of this molecular composite membrane was evaluated by a combination of the expansion moduli of each component scaled by their area fractions in the bilayer. Bilayer toughness, which is the energy stored in the bilayer at failure, showed a maximum value at approximately 40 mol% CHOL. This breakdown energy was found to be only a fraction of the

  15. Preparation of supported lipid membranes for aquaporin Z incorporation.

    PubMed

    Li, Xuesong; Wang, Rong; Tang, Chuyang; Vararattanavech, Ardcharaporn; Zhao, Yang; Torres, Jaume; Fane, Tony

    2012-06-01

    There has been a recent surge of interest to mimic the performance of natural cellular membranes by incorporating water channel proteins-aquaporins (AQPs) into various ultrathin films for water filtration applications. To make biomimetic membranes one of the most crucial steps is preparing a defect-free platform for AQPs incorporation on a suitable substrate. In this study two methods were used to prepare supported lipid membranes on NF membrane surfaces under a benign pH condition of 7.8. One method was direct vesicle fusion on a hydrophilic membrane NF-270; the other was vesicle fusion facilitated by hydraulic pressure on a modified hydrophilic NF-270 membrane whose surface has been spin-coated with positively charged lipids. Experiments revealed that the supported lipid membrane without AQPs prepared by the spin coating plus vesicle fusion had a much lower defect density than that prepared by vesicle fusion alone. It appears that the surface roughness and charge are the main factors determining the quality of the supported lipid membrane. Aquaporin Z (AqpZ) proteins were successfully incorporated into 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes and its permeability was measured by the stopped-flow experimental procedure. However, after the proteoliposomes have been fused onto the modified substrate, the AqpZ function in the resultant membrane was not observed and AFM images showed distinct aggregations of unfused proteoliposomes or AqpZ proteins on the substrate surface. It is speculated that the inhibition of AqpZ function may be caused by the low lipid mobility on the NF membrane surface. Further investigations to evaluate and optimize the structure-performance relationship are required. PMID:22386862

  16. Interactions of Polyethylenimines with Zwitterionic and Anionic Lipid Membranes.

    PubMed

    Kwolek, Urszula; Jamróz, Dorota; Janiczek, Małgorzata; Nowakowska, Maria; Wydro, Paweł; Kepczynski, Mariusz

    2016-05-17

    Interactions between polyethylenimines (PEIs) and phospholipid membranes are of fundamental importance for various biophysical applications of these polymers such as gene delivery. Despite investigations into the nature of these interactions, their molecular basis remains poorly understood. In this article, we combined experimental methods and atomistic molecular dynamics (MD) simulations to obtain comprehensive insight into the effect of linear and branched PEIs on zwitterionic and anionic bilayers used as simple models of mammalian cellular membranes. Our results show that PEIs adsorb only partially on the surface of zwitterionic membranes by forming hydrogen bonds to the lipid headgroups, whereas a large part of the polymer chains dangles freely in the aqueous phase. In contrast, PEIs readily adhere to and insert into the anionic membrane. The attraction of the polymer chains to the membrane is due to electrostatic interactions as well as hydrogen bonding between the amine groups of PEI and the phosphate groups of lipids. These interactions were found to induce a substantial reorganization of the bilayer in the polymer vicinity due to the reorientation of lipid molecules. The lipid headgroups were pulled toward the center of the membrane, which can facilitate transmembrane translocations of anionic lipids. Furthermore, the PEI-lipid interactions affect the stability of liposomal dispersions, but we did not see any evidence of disruption of the vesicular structures into small fragments at polymer concentrations typically used in gene therapy. Our results provide a detailed molecular-level description of the lipid organization in the membrane in the presence of polycations that can be useful in understanding their mechanisms of in vitro and in vivo cytotoxicity. PMID:27115556

  17. Characterization of 3D Voronoi Tessellation Nearest Neighbor Lipid Shells Provides Atomistic Lipid Disruption Profile of Protein Containing Lipid Membranes

    PubMed Central

    Cheng, Sara Y.; Duong, Hai V.; Compton, Campbell; Vaughn, Mark W.; Nguyen, Hoa; Cheng, Kwan H.

    2015-01-01

    Quantifying protein-induced lipid disruptions at the atomistic level is a challenging problem in membrane biophysics. Here we propose a novel 3D Voronoi tessellation nearest-atom-neighbor shell method to classify and characterize lipid domains into discrete concentric lipid shells surrounding membrane proteins in structurally heterogeneous lipid membranes. This method needs only the coordinates of the system and is independent of force fields and simulation conditions. As a proof-of-principle, we use this multiple lipid shell method to analyze the lipid disruption profiles of three simulated membrane systems: phosphatidylcholine, phosphatidylcholine/cholesterol, and beta-amyloid/phosphatidylcholine/cholesterol. We observed different atomic volume disruption mechanisms due to cholesterol and beta-amyloid Additionally, several lipid fractional groups and lipid-interfacial water did not converge to their control values with increasing distance or shell order from the protein. This volume divergent behavior was confirmed by bilayer thickness and chain orientational order calculations. Our method can also be used to analyze high-resolution structural experimental data. PMID:25637891

  18. 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.

  19. Membrane curvature and cholesterol effects on lipids packing and spin-labelled lipids conformational distributions

    NASA Astrophysics Data System (ADS)

    Manukovsky, Nurit; Sanders, Ella; Matalon, Erez; Wolf, Sharon G.; Goldfarb, Daniella

    2013-10-01

    Nitroxide spin-labelled lipid analogues are often used to study model membrane properties using EPR spectroscopy. Whereas in liquid phase membranes the spin label assumes, on average, its putative location, in gel phases and frozen membrane, depending on its position along the acyl chain, it may exhibit a different average location. Here we used 2H three-pulse Electron Spin Echo Envelope Modulation (ESEEM) of phospholipid spin probes, combined with various deuteration schemes to detect the effect of the model membrane curvature and cholesterol on vertical migrations of the spin label. We compared large and small unilamellar 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) vesicles with and without cholesterol (10%). The vertical displacement of the spin label was manifested as an apparently flat trans-membrane profile of water concentration and of label proximity to the head group choline. The spin-label propensity to migrate was found to increase with vesicle curvature and decrease in the presence of cholesterol. This in turn reflects the effect of packing and ordering of the membrane lipids. The results show that in curved vesicles lacking cholesterol, the label attached to carbon 16 may travel as far high along the membrane normal as the location of the label on carbon 5, due to the presence of U-shaped lipid conformations. This phenomenon must be taken into account when using spin-labelled lipids as membrane depth markers or to trace trans-membrane profiles.

  20. Bioavailability of endocrine disrupting chemicals (EDCs): Liposome-water partitioning and lipid membrane permeation

    NASA Astrophysics Data System (ADS)

    Kwon, Jung-Hwan

    The bioavailability of endocrine disrupting chemicals (EDCs) is a function of a number of parameters including the ability of the chemical to partition into organic tissue and reach receptor sites within an organism. In this dissertation, equilibrium partition coefficients between water and lipid membrane vesicles and artificial lipid membrane permeability were investigated for evaluating bioavailability of aqueous pollutants. Structurally diverse endocrine disrupting chemicals were chosen as model compounds for partitioning experiments and simple hydrophobic organic chemicals were used for the evaluation of a parallel artificial membrane device developed to mimic bioconcentration rates in fish. Hydrophobic interactions represented by octanol/water partition coefficients (KOWs) were not appropriate for estimating lipid membrane/water partition coefficients (Klipws) for the selected EDCs having a relatively large molar liquid volume (MLV) and containing polar functional groups. Correlations that include MLV and polar surface area (PSA) reduce the predicted value of log K lipw, suggesting that lipid membranes are less favorable than 1-octanol for a hydrophobic solute because of the changes in membrane fluidity and the amount of cholesterol in the lipid bilayers. These results suggested that KOW alone has limited potential for estimating K lipw, and MLV or PSA may be used as additional descriptors for developing quantitative structure-activity relationships (QSARs). The poor correlations between KOW and Klipw observed in this research may be due to the highly organized structure of lipid bilayers. Measured thermodynamic constants demonstrated that the entropy contribution becomes more dominant for more organized liposomes having saturated lipid tails. This implies that entropy-driven partitioning process makes Klipw different from KOW especially for more saturated lipid bilayer membranes. In the parallel artificial membrane system developed, a membrane filter

  1. Transbilayer coupling mechanism for the formation of lipid asymmetry in biological membranes. Application to the photoreceptor disc membrane.

    PubMed Central

    Hubbell, W L

    1990-01-01

    An equilibrium transmembrane asymmetry in charged lipids is shown to arise as a result of oriented, bipolar proteins in the membrane. The basic interaction giving rise to the asymmetry is between a lipid molecule and a transbilayer potential generated by the asymmetric charge distribution in the protein. Thus, a protein can generate a lipid asymmetry without a direct binding interaction between lipid and protein. The generation of an asymmetry in charged lipid by this mechanism can also lead to a concomitant asymmetry in neutral lipids if deviations from ideality in the lipid mixture are taken into account. It is shown that regular solution theory applied to the lipid phase predicts an asymmetry in all components of a ternary mixture as long as one component is electrostatically oriented according to the mechanism mentioned above. The resulting asymmetry is not strongly salt dependent. The mechanism quantitatively accounts for the experimentally determined phospholipid asymmetry in the rod outer segment disc membrane of the vertebrate photoreceptor. PMID:2297564

  2. Applications of Mass Spectrometry to Lipids and Membranes

    PubMed Central

    Harkewicz, Richard; Dennis, Edward A.

    2012-01-01

    Lipidomics, a major part of metabolomics, constitutes the detailed analysis and global characterization, both spatial and temporal, of the structure and function of lipids (the lipidome) within a living system. As with proteomics, mass spectrometry has earned a central analytical role in lipidomics, and this role will continue to grow with technological developments. Currently, there exist two mass spectrometry-based lipidomics approaches, one based on a division of lipids into categories and classes prior to analysis, the “comprehensive lipidomics analysis by separation simplification” (CLASS), and the other in which all lipid species are analyzed together without prior separation, shotgun. In exploring the lipidome of various living systems, novel lipids are being discovered, and mass spectrometry is helping characterize their chemical structure. Deuterium exchange mass spectrometry (DXMS) is being used to investigate the association of lipids and membranes with proteins and enzymes, and imaging mass spectrometry (IMS) is being applied to the in situ analysis of lipids in tissues. PMID:21469951

  3. Analysis of a Lipid/Polymer Membrane for Bitterness Sensing with a Preconditioning Process.

    PubMed

    Yatabe, Rui; Noda, Junpei; Tahara, Yusuke; Naito, Yoshinobu; Ikezaki, Hidekazu; Toko, Kiyoshi

    2015-01-01

    It is possible to evaluate the taste of foods or medicines using a taste sensor. The taste sensor converts information on taste into an electrical signal using several lipid/polymer membranes. A lipid/polymer membrane for bitterness sensing can evaluate aftertaste after immersion in monosodium glutamate (MSG), which is called "preconditioning". However, we have not yet analyzed the change in the surface structure of the membrane as a result of preconditioning. Thus, we analyzed the change in the surface by performing contact angle and surface zeta potential measurements, Fourier transform infrared spectroscopy (FTIR), X-ray photon spectroscopy (XPS) and gas cluster ion beam time-of-flight secondary ion mass spectrometry (GCIB-TOF-SIMS). After preconditioning, the concentrations of MSG and tetradodecylammonium bromide (TDAB), contained in the lipid membrane were found to be higher in the surface region than in the bulk region. The effect of preconditioning was revealed by the above analysis methods. PMID:26404301

  4. Simulation modeling of supported lipid membranes - a review.

    PubMed

    Hirtz, Michael; Kumar, Naresh; Chi, Lifeng

    2014-03-01

    Lipid membranes are of great importance for many biological systems and biotechnological applications. One method to gain a profound understanding of the dynamics in lipid membranes and their interaction with other system components is by modeling these systems by computer simulations. Many different approaches have been undertaken in this endeavor that have led to molecular level insights into the underlying mechanisms of several experimental observations and biological processes with an extremely high temporal resolution. As compared to the free-standing lipid bilayers, there are fewer simulation studies addressing the systems of supported lipid membranes. Nevertheless, these have significantly enhanced our understanding of the behavior of lipid layers employed in applications spanning from biosensors to drug delivery and for biological processes such as the breathing cycle of lung surfactants. In this review, we give an account of the state of the art of methods and applications of the simulations of supported lipid bilayers, interfacial membranes at the air/water interface and on solid surfaces. PMID:24444165

  5. Melittin-induced cholesterol reorganization in lipid bilayer membranes

    SciTech Connect

    Qian, Shuo; Heller, William T.

    2015-06-12

    The peptide melittin, a 26 amino acid, cationic peptide from honey bee (Apis mellifera) venom, disrupts lipid bilayer membranes in a concentration-dependent manner. Rather than interacting with a specific receptor, the peptide interacts directly with the lipid matrix of the membrane in a manner dependent on the lipid composition. Here, a small-angle neutron scattering study of the interaction of melittin with lipid bilayers made of mixtures of dimyristoylphosphatidylcholine (DMPC) and cholesterol (Chol) is presented. Through the use of deuterium-labeled DMPC, changes in the distribution of the lipid and cholesterol in unilamellar vesicles were observed for peptide concentrations below those that cause pores to form. In addition to disrupting the in-plane organization of Chol, melittin produces vesicles having inner and outer leaflet compositions that depend on the lipid–Chol molar ratio and on the peptide concentration. The changes seen at high cholesterol and low peptide concentration are similar to those produced by alamethicin (Qian, S. et al., J. Phys. Chem. B 2014, 118, 11200–11208), which points to an underlying physical mechanism driving the redistribution of Chol, but melittin displays an additional effect not seen with alamethicin. Furthermore, a model for how the peptide drives the redistribution of Chol is proposed. The results suggest that redistribution of the lipids in a target cell membrane by membrane active peptides takes places as a prelude to the lysis of the cell.

  6. Melittin-induced cholesterol reorganization in lipid bilayer membranes

    DOE PAGESBeta

    Qian, Shuo; Heller, William T.

    2015-06-12

    The peptide melittin, a 26 amino acid, cationic peptide from honey bee (Apis mellifera) venom, disrupts lipid bilayer membranes in a concentration-dependent manner. Rather than interacting with a specific receptor, the peptide interacts directly with the lipid matrix of the membrane in a manner dependent on the lipid composition. Here, a small-angle neutron scattering study of the interaction of melittin with lipid bilayers made of mixtures of dimyristoylphosphatidylcholine (DMPC) and cholesterol (Chol) is presented. Through the use of deuterium-labeled DMPC, changes in the distribution of the lipid and cholesterol in unilamellar vesicles were observed for peptide concentrations below those thatmore » cause pores to form. In addition to disrupting the in-plane organization of Chol, melittin produces vesicles having inner and outer leaflet compositions that depend on the lipid–Chol molar ratio and on the peptide concentration. The changes seen at high cholesterol and low peptide concentration are similar to those produced by alamethicin (Qian, S. et al., J. Phys. Chem. B 2014, 118, 11200–11208), which points to an underlying physical mechanism driving the redistribution of Chol, but melittin displays an additional effect not seen with alamethicin. Furthermore, a model for how the peptide drives the redistribution of Chol is proposed. The results suggest that redistribution of the lipids in a target cell membrane by membrane active peptides takes places as a prelude to the lysis of the cell.« less

  7. Equilibrium Potentials of Membrane Electrodes

    PubMed Central

    Wang, Jui H.; Copeland, Eva

    1973-01-01

    A simple thermodynamic theory of the equilibrium potentials of membrane electrodes is formulated and applied to the glass electrode for measurement of pH. The new formulation assumes the selective adsorption or binding of specific ions on the surface of the membrane which may or may not be permeable to the ion, and includes the conventional derivation based on reversible ion transport across membranes as a special case. To test the theory, a platinum wire was coated with a mixture of stearic acid and methyl-tri-n-octyl-ammonium stearate. When this coated electrode was immersed in aqueous phosphate solution, its potential was found to be a linear function of pH from pH 2 to 12 with a slope equal to the theoretical value of 59.0 mV per pH unit at 24°. PMID:4516194

  8. DNA release from lipoplexes by anionic lipids: correlation with lipid mesomorphism, interfacial curvature, and membrane fusion

    SciTech Connect

    Tarahovsky, Yury S.; Koynova, Rumiana; MacDonald, Robert C.

    2010-01-18

    DNA release from lipoplexes is an essential step during lipofection and is probably a result of charge neutralization by cellular anionic lipids. As a model system to test this possibility, fluorescence resonance energy transfer between DNA and lipid covalently labeled with Cy3 and BODIPY, respectively, was used to monitor the release of DNA from lipid surfaces induced by anionic liposomes. The separation of DNA from lipid measured this way was considerably slower and less complete than that estimated with noncovalently labeled DNA, and depends on the lipid composition of both lipoplexes and anionic liposomes. This result was confirmed by centrifugal separation of released DNA and lipid. X-ray diffraction revealed a clear correlation of the DNA release capacity of the anionic lipids with the interfacial curvature of the mesomorphic structures developed when the anionic and cationic liposomes were mixed. DNA release also correlated with the rate of fusion of anionic liposomes with lipoplexes. It is concluded that the tendency to fuse and the phase preference of the mixed lipid membranes are key factors for the rate and extent of DNA release. The approach presented emphasizes the importance of the lipid composition of both lipoplexes and target membranes and suggests optimal transfection may be obtained by tailoring lipoplex composition to the lipid composition of target cells.

  9. Effect of membrane tension on the physical properties of DOPC lipid bilayer membrane

    PubMed Central

    Reddy, A. Srinivas; Warshaviak, Dora Toledo; Chachisvilis, Mirianas

    2013-01-01

    Molecular dynamics simulations of a dioleoylphosphocholine (DOPC) lipid bilayer were performed to explore its mechanosensitivity. Variations in the bilayer properties, such as area per lipid, volume, thickness, hydration depth (HD), hydration thickness (HT), lateral diffusion coefficient, and changes in lipid structural order were computed in the membrane tension range 0 to 15 dyn/cm. We determined that an increase in membrane tension results in a decrease in the bilayer thickness and HD of ∼5% and ∼5.7% respectively, whereas area per lipid, volume, and HT/HD increased by 6.8%, 2.4%, and 5% respectively. The changes in lipid conformation and orientation were characterized using orientational (S2) and deuterium (SCD) order parameters. Upon increase of membrane tension both order parameters indicated an increase in lipid disorder by 10– 20%, mostly in the tail end region of the hydrophobic chains. The effect of membrane tension on lipid lateral diffusion in the DOPC bilayer was analyzed on three different time scales corresponding to inertial motion, anomalous diffusion and normal diffusion. The results showed that lateral diffusion of lipid molecules is anomalous in nature due to the non-exponential distribution of waiting times. The anomalous and normal diffusion coefficients increased by 20% and 52% when the membrane tension changed from 0 to 15 dyn/cm, respectively. In conclusion, our studies showed that membrane tension causes relatively significant changes in the area per lipid, volume, polarity, membrane thickness, and fluidity of the membrane suggesting multiple mechanisms by which mechanical perturbation of the membrane could trigger mechanosensitive response in cells. PMID:22588133

  10. Stability of DNA-Tethered Lipid Membranes with Mobile Tethers

    PubMed Central

    Chung, Minsub; Boxer, Steven G.

    2011-01-01

    We recently introduced two approaches for tethering planar lipid bilayers as membrane patches to either a supported lipid bilayer or DNA-functionalized surface using DNA hybridization (Chung, M., Lowe, R. D., Chan, Y-H. M., Ganesan, P. V., Boxer, S. G. J. Struct. Biol. 2009, 168, 190–9). When mobile DNA tethers are used, the tethered bilayer patches become unstable, while they are stable if the tethers are fixed on the surface. Because the mobile tethers between a patch and a supported lipid bilayer offer a particularly interesting architecture for studying the dynamics of membrane-membrane interactions, we have investigated the sources of instability, focusing on membrane composition. The most stable patches were made with a mixture of saturated lipids and cholesterol, suggesting an important role for membrane stiffness. Other factors such as the effect of tether length, lateral mobility and patch membrane edge were also investigated. Based on these results, a model for the mechanism of patch destruction is developed. PMID:21452847

  11. Membrane-Sculpting BAR Domains Generate Stable Lipid Microdomains

    PubMed Central

    Zhao, Hongxia; Michelot, Alphée; Koskela, Essi V.; Tkach, Vadym; Stamou, Dimitrios; Drubin, David G.; Lappalainen, Pekka

    2014-01-01

    SUMMARY Bin-Amphiphysin-Rvs (BAR) domain proteins are central regulators of many cellular processes involving membrane dynamics. BAR domains sculpt phosphoinositide-rich membranes to generate membrane protrusions or invaginations. Here, we report that, in addition to regulating membrane geometry, BAR domains can generate extremely stable lipid microdomains by “freezing” phosphoinositide dynamics. This is a general feature of BAR domains, because the yeast endocytic BAR and Fes/CIP4 homology BAR (F-BAR) domains, the inverse BAR domain of Pinkbar, and the eisosomal BAR protein Lsp1 induced phosphoinositide clustering and halted lipid diffusion, despite differences in mechanisms of membrane interactions. Lsp1 displays comparable low diffusion rates in vitro and in vivo, suggesting that BAR domain proteins also generate stable phosphoinositide microdomains in cells. These results uncover a conserved role for BAR superfamily proteins in regulating lipid dynamics within membranes. Stable microdomains induced by BAR domain scaffolds and specific lipids can generate phase boundaries and diffusion barriers, which may have profound impacts on diverse cellular processes. PMID:24055060

  12. 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

    2015-10-01

    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. PMID:26327393

  13. The Unsaturation of Membrane Lipids Stabilizes Photosynthesis against Heat Stress.

    PubMed Central

    Gombos, Z.; Wada, H.; Hideg, E.; Murata, N.

    1994-01-01

    The effect of the unsaturation of glycerolipids of thylakoid membranes on the heat tolerance of the photosynthetic evolution of oxygen was studied in vivo by mutation and transformation of fatty-acid desaturases in the cyanobacterium Synechocystis PCC6803. The experimental results indicate that elimination of dienoic lipid molecules decreases, to a small but distinct extent, the heat tolerance of photosynthetic oxygen evolution, but that elimination of trienoic lipid molecules has no effect on the heat tolerance. This conclusion contrasts with the previous hypothesis that the heat tolerance of photosynthesis is enhanced upon an increase in the level of saturation of membrane lipids. It is also shown that light does not affect the nature of the effect of lipid unsaturation on the heat tolerance of photosynthesis. PMID:12232106

  14. Membrane protein biosensing with plasmonic nanopore arrays and pore-spanning lipid membranes

    PubMed Central

    Im, Hyungsoon; Wittenberg, Nathan J.; Lesuffleur, Antoine; Lindquist, Nathan C.; Oh, Sang-Hyun

    2010-01-01

    Integration of solid-state biosensors and lipid bilayer membranes is important for membrane protein research and drug discovery. In these sensors, it is critical that the solid-state sensing material does not have adverse effects on the conformation or functionality of membrane-bound molecules. In this work, pore-spanning lipid membranes are formed over an array of periodic nanopores in free-standing gold films for surface plasmon resonance (SPR) kinetic binding assays. The ability to perform kinetic assays with a transmembrane protein is demonstrated with α-hemolysin (α-HL). The incorporation of α-HL into the membrane followed by specific antibody binding (anti-α-HL) red-shifts the plasmon resonance of the gold nanopore array, which is optically monitored in real time. Subsequent fluorescence imaging reveals that the antibodies primarily bind in nanopore regions, indicating that α-HL incorporation preferentially occurs into areas of pore-spanning lipid membranes. PMID:21218136

  15. Oxygen permeability of the lipid bilayer membrane made of calf lens lipids

    PubMed Central

    Widomska, Justyna; Raguz, Marija; Subczynski, Witold K.

    2007-01-01

    The oxygen permeability coefficient across the membrane made of the total lipid extract from the plasma membrane of calf lens was estimated from the profile of the oxygen transport parameter (local oxygen diffusion-concentration product) and compared with those estimated for membranes made of an equimolar 1-palmitoyl-2-oleoylphosphatidylcholine/cholesterol (POPC/Chol) mixture and of pure POPC. Profiles of the oxygen transport parameter were obtained by observing the collision of molecular oxygen with nitroxide radical spin labels placed at different depths in the membrane using the saturation-recovery EPR technique and were published by us earlier (J. Widomska, M. Raguz, J. Dillon, E. R. Gaillard, W. K. Subczynski, Biochim. Biophys. Acta. Epub 2007 March 20). At 35°C, the estimated oxygen permeability coefficients were 51.3, 49.7, and 157.4 cm/s for lens lipid, POPC/Chol, and POPC membranes, respectively (compared with 53.3 cm/s for a water layer with the same thickness as a membrane). Membrane permeability significantly decreases at lower temperatures. In the lens lipid membrane, resistance to the oxygen transport is located in and near the polar headgroup region of the membrane to the depth of the ninth carbon, which is approximately where the steroid-ring structure of cholesterol reaches into the membrane. In the central region of the membrane, oxygen transport is enhanced, significantly exceeding that in bulk water. It is concluded that the high level of cholesterol in lens lipids is responsible for these unique membrane properties. PMID:17662231

  16. Tethered and Polymer Supported Bilayer Lipid Membranes: Structure and Function

    PubMed Central

    Andersson, Jakob; Köper, Ingo

    2016-01-01

    Solid supported bilayer lipid membranes are model systems to mimic natural cell membranes in order to understand structural and functional properties of such systems. The use of a model system allows for the use of a wide variety of analytical tools including atomic force microscopy, impedance spectroscopy, neutron reflectometry, and surface plasmon resonance spectroscopy. Among the large number of different types of model membranes polymer-supported and tethered lipid bilayers have been shown to be versatile and useful systems. Both systems consist of a lipid bilayer, which is de-coupled from an underlying support by a spacer cushion. Both systems will be reviewed, with an emphasis on the effect that the spacer moiety has on the bilayer properties. PMID:27249006

  17. Tethered and Polymer Supported Bilayer Lipid Membranes: Structure and Function.

    PubMed

    Andersson, Jakob; Köper, Ingo

    2016-01-01

    Solid supported bilayer lipid membranes are model systems to mimic natural cell membranes in order to understand structural and functional properties of such systems. The use of a model system allows for the use of a wide variety of analytical tools including atomic force microscopy, impedance spectroscopy, neutron reflectometry, and surface plasmon resonance spectroscopy. Among the large number of different types of model membranes polymer-supported and tethered lipid bilayers have been shown to be versatile and useful systems. Both systems consist of a lipid bilayer, which is de-coupled from an underlying support by a spacer cushion. Both systems will be reviewed, with an emphasis on the effect that the spacer moiety has on the bilayer properties. PMID:27249006

  18. Domain formation in membranes caused by lipid wetting of protein.

    PubMed

    Akimov, Sergey A; Frolov, Vladimir A J; Kuzmin, Peter I; Zimmerberg, Joshua; Chizmadzhev, Yuri A; Cohen, Fredric S

    2008-05-01

    Formation of rafts and other domains in cell membranes is considered as wetting of proteins by lipids. The membrane is modeled as a continuous elastic medium. Thermodynamic functions of the lipid films that wet proteins are calculated using a mean-field theory of liquid crystals as adapted to biomembranes. This approach yields the conditions necessary for a macroscopic wetting film to form; its thickness could also be determined. It is shown that films of macroscopic thicknesses form around large (tens nanometers in diameter) lipid-protein aggregates; only thin adsorption films form around single proteins or small complexes. The means by which wetting films can facilitate the merger of these aggregates is considered. It is shown that a wetting film prevents a protein from leaving an aggregate. Using experimentally derived values of elastic moduli and spontaneous curvatures as well as height mismatch between aggregates and bulk membrane, we obtained numerical results, which can be compared with the experimental data. PMID:18643096

  19. Impact of monoolein on aquaporin1-based supported lipid bilayer membranes

    NASA Astrophysics Data System (ADS)

    Wang, Zhining; Wang, Xida; Ding, Wande; Wang, Miaoqi; Qi, Xin; Gao, Congjie

    2015-08-01

    Aquaporin (AQP) based biomimetic membranes have attracted considerable attention for their potential water purification applications. In this paper, AQP1 incorporated biomimetic membranes were prepared and characterized. The morphology and structure of the biomimetic membranes were characterized by in situ atomic force microscopy (AFM), infrared absorption spectroscopy, fluorescence microscopy, and contact angle measurements. The nanofiltration performance of the AQP1 incorporated membranes was investigated at 4 bar by using 2 g l-1 NaCl as feed solution. Lipid mobility plays an important role in the performance of the AQP1 incorporated supported lipid bilayer (SLB) membranes. We demonstrated that the lipid mobility is successfully tuned by the addition of monoolein (MO). Through in situ AFM and fluorescence recovery after photo-bleaching (FRAP) measurements, the membrane morphology and the molecular mobility were studied. The lipid mobility increased in the sequence DPPC < DPPC/MO (RMO = 5/5) < DOPC/MO (RMO = 5/5) < DOPC, which is consistent with the flux increment and salt rejection. This study may provide some useful insights for improving the water purification performance of biomimetic membranes.

  20. Micrometric segregation of fluorescent membrane lipids: relevance for endogenous lipids and biogenesis in erythrocytes[S

    PubMed Central

    D'Auria, Ludovic; Fenaux, Marisa; Aleksandrowicz, Paulina; Van Der Smissen, Patrick; Chantrain, Christophe; Vermylen, Christiane; Vikkula, Miikka; Courtoy, Pierre J.; Tyteca, Donatienne

    2013-01-01

    Micrometric membrane lipid segregation is controversial. We addressed this issue in attached erythrocytes and found that fluorescent boron dipyrromethene (BODIPY) analogs of glycosphingolipids (GSLs) [glucosylceramide (BODIPY-GlcCer) and monosialotetrahexosylganglioside (GM1BODIPY)], sphingomyelin (BODIPY-SM), and phosphatidylcholine (BODIPY-PC inserted into the plasma membrane spontaneously gathered into distinct submicrometric domains. GM1BODIPY domains colocalized with endogenous GM1 labeled by cholera toxin. All BODIPY-lipid domains disappeared upon erythrocyte stretching, indicating control by membrane tension. Minor cholesterol depletion suppressed BODIPY-SM and BODIPY-PC but preserved BODIPY-GlcCer domains. Each type of domain exchanged constituents but assumed fixed positions, suggesting self-clustering and anchorage to spectrin. Domains showed differential association with 4.1R versus ankyrin complexes upon antibody patching. BODIPY-lipid domains also responded differentially to uncoupling at 4.1R complexes [protein kinase C (PKC) activation] and ankyrin complexes (in spherocytosis, a membrane fragility disease). These data point to micrometric compartmentation of polar BODIPY-lipids modulated by membrane tension, cholesterol, and differential association to the two nonredundant membrane:spectrin anchorage complexes. Micrometric compartmentation might play a role in erythrocyte membrane deformability and fragility. PMID:23322884

  1. Role of lipids in the translocation of proteins across membranes.

    PubMed Central

    Van Voorst, F; De Kruijff, B

    2000-01-01

    The architecture of cells, with various membrane-bound compartments and with the protein synthesizing machinery confined to one location, dictates that many proteins have to be transported through one or more membranes during their biogenesis. A lot of progress has been made on the identification of protein translocation machineries and their sorting signals in various organelles and organisms. Biochemical characterization has revealed the functions of several individual protein components. Interestingly, lipid components were also found to be essential for the correct functioning of these translocases. This led to the idea that there is a very intimate relationship between the lipid and protein components that enables them to fulfil their intriguing task of transporting large biopolymers through a lipid bilayer without leaking their contents. In this review we focus on the Sec translocases in the endoplasmic reticulum and the bacterial inner membrane. We also highlight the interactions of lipids and proteins during the process of translocation and integrate this into a model that enables us to understand the role of membrane lipid composition in translocase function. PMID:10769162

  2. Divergent Diffusion Coefficients in Simulations of Fluids and Lipid Membranes.

    PubMed

    Vögele, Martin; Hummer, Gerhard

    2016-08-25

    We investigate the dependence of single-particle diffusion coefficients on the size and shape of the simulation box in molecular dynamics simulations of fluids and lipid membranes. We find that the diffusion coefficients of lipids and a carbon nanotube embedded in a lipid membrane diverge with the logarithm of the box width. For a neat Lennard-Jones fluid in flat rectangular boxes, diffusion becomes anisotropic, diverging logarithmically in all three directions with increasing box width. In elongated boxes, the diffusion coefficients normal to the long axis diverge linearly with the height-to-width ratio. For both lipid membranes and neat fluids, this behavior is predicted quantitatively by hydrodynamic theory. Mean-square displacements in the neat fluid exhibit intermediate regimes of anomalous diffusion, with t ln t and t(3/2) components in flat and elongated boxes, respectively. For membranes, the large finite-size effects, and the apparent inability to determine a well-defined lipid diffusion coefficient from simulation, rationalize difficulties in comparing simulation results to each other and to those from experiments. PMID:27385207

  3. Investigating lipid-lipid and lipid-protein interactions in model membranes by ToF-SIMS

    NASA Astrophysics Data System (ADS)

    Zheng, L.; McQuaw, C. M.; Baker, M. J.; Lockyer, N. P.; Vickerman, J. C.; Ewing, A. G.; Winograd, N.

    2008-12-01

    With the chemical imaging capability of ToF-SIMS, biological molecules are identified and localized in membranes without any chemical labels. We have developed a model membrane system made with supported Langmuir-Blodgett (LB) monolayers. This simplified model can be used with different combinations of molecules to form a membrane, and thus represents a bottom-up approach to study individual lipid-lipid or lipid-protein interactions. We have used ternary mixtures of sphingomyelin (SM), phosphatidylcholine (PC), and cholesterol (CH) in the model membrane to study the mechanism of domain formation and interactions between phospholipids and cholesterol. Domain structures are observed only when the acyl chain saturation is different for SM and PC in the mixture. The saturated lipid, whether it is SM or PC, is found to be localized with cholesterol, while the unsaturated one is excluded from the domain area. More complicated model membranes which involve a functional membrane protein glycophorin are also investigated and different membrane properties are observed compared to the systems without glycophorin.

  4. Lipid Bilayer Domain Fluctuations as a Probe of Membrane Viscosity

    PubMed Central

    Camley, Brian A.; Esposito, Cinzia; Baumgart, Tobias; Brown, Frank L.H.

    2010-01-01

    We argue that membrane viscosity, ηm, plays a prominent role in the thermal fluctuation dynamics of micron-scale lipid domains. A theoretical expression is presented for the timescales of domain shape relaxation, which reduces to the well-known ηm = 0 result of Stone and McConnell in the limit of large domain sizes. Experimental measurements of domain dynamics on the surface of ternary phospholipid and cholesterol vesicles confirm the theoretical results and suggest domain flicker spectroscopy as a convenient means to simultaneously measure both the line tension, σ, and the membrane viscosity, ηm, governing the behavior of individual lipid domains. PMID:20858410

  5. Computational redesign of the lipid-facing surface of the outer membrane protein OmpA

    PubMed Central

    Stapleton, James A.; Whitehead, Timothy A.; Nanda, Vikas

    2015-01-01

    Advances in computational design methods have made possible extensive engineering of soluble proteins, but designed β-barrel membrane proteins await improvements in our understanding of the sequence determinants of folding and stability. A subset of the amino acid residues of membrane proteins interact with the cell membrane, and the design rules that govern this lipid-facing surface are poorly understood. We applied a residue-level depth potential for β-barrel membrane proteins to the complete redesign of the lipid-facing surface of Escherichia coli OmpA. Initial designs failed to fold correctly, but reversion of a small number of mutations indicated by backcross experiments yielded designs with substitutions to up to 60% of the surface that did support folding and membrane insertion. PMID:26199411

  6. Lipocarbazole, an efficient lipid peroxidation inhibitor anchored in the membrane.

    PubMed

    Fabre, Gabin; Hänchen, Anne; Calliste, Claude-Alain; Berka, Karel; Banala, Srinivas; Otyepka, Michal; Süssmuth, Roderich D; Trouillas, Patrick

    2015-08-01

    Lipid peroxidation is a major deleterious effect caused by oxidative stress. It is involved in various diseases such as atherosclerosis, rheumatoid arthritis and neurodegenerative diseases. In order to inhibit lipid peroxidation, antioxidants must efficiently scavenge free radicals and penetrate inside biological membranes. Lipocarbazole has recently been shown to be a powerful antioxidant in solution. Here, we show its powerful capacity as lipid peroxidation inhibitor. Its mechanism of action is rationalized based on molecular dynamics simulations on a biomembrane model, quantum calculations and experimental evaluation. The role of the lipocarbazole side chain is particularly highlighted as a critical chemical feature responsible for its antioxidant activity. PMID:26068016

  7. Intermonolayer Friction and Surface Shear Viscosity of Lipid Bilayer Membranes

    PubMed Central

    den Otter, W. K.; Shkulipa, S. A.

    2007-01-01

    The flow behavior of lipid bilayer membranes is characterized by a surface viscosity for in-plane shear deformations, and an intermonolayer friction coefficient for slip between the two leaflets of the bilayer. Both properties have been studied for a variety of coarse-grained double-tailed model lipids, using equilibrium and nonequilibrium molecular dynamics simulations. For lipids with two identical tails, the surface shear viscosity rises rapidly with tail length, while the intermonolayer friction coefficient is less sensitive to the tail length. Interdigitation of lipid tails across the bilayer midsurface, as observed for lipids with two distinct tails, strongly enhances the intermonolayer friction coefficient, but hardly affects the surface shear viscosity. The simulation results are compared against the available experimental data. PMID:17468168

  8. Hybrid lipids increase nanoscale fluctuation lifetimes in mixed membranes

    NASA Astrophysics Data System (ADS)

    Palmieri, Benoit; Safran, Samuel A.

    2013-09-01

    A recently proposed ternary mixture model is used to predict fluctuation domain lifetimes in the one phase region. The membrane is made of saturated, unsaturated, and hybrid lipids that have one saturated and one unsaturated hydrocarbon chain. The hybrid lipid is a natural linactant which can reduce the packing incompatibility between saturated and unsaturated lipids. The fluctuation lifetimes are predicted as a function of the hybrid lipid fraction and the fluctuation domain size. These lifetimes can be increased by up to three orders of magnitude compared to the case of no hybrids. With hybrid, small length scale fluctuations have sizable amplitudes even close to the critical temperature and, hence, benefit from enhanced critical slowing down. The increase in lifetime is particularly important for nanometer scale fluctuation domains where the hybrid orientation and the other lipids composition are highly coupled.

  9. Watching individual molecules flex within lipid membranes using SERS

    PubMed Central

    Taylor, Richard W.; Benz, Felix; Sigle, Daniel O.; Bowman, Richard W.; Bao, Peng; Roth, Johannes S.; Heath, George R.; Evans, Stephen D.; Baumberg, Jeremy J.

    2014-01-01

    Interrogating individual molecules within bio-membranes is key to deepening our understanding of biological processes essential for life. Using Raman spectroscopy to map molecular vibrations is ideal to non-destructively ‘fingerprint’ biomolecules for dynamic information on their molecular structure, composition and conformation. Such tag-free tracking of molecules within lipid bio-membranes can directly connect structure and function. In this paper, stable co-assembly with gold nano-components in a ‘nanoparticle-on-mirror’ geometry strongly enhances the local optical field and reduces the volume probed to a few nm3, enabling repeated measurements for many tens of minutes on the same molecules. The intense gap plasmons are assembled around model bio-membranes providing molecular identification of the diffusing lipids. Our experiments clearly evidence measurement of individual lipids flexing through telltale rapid correlated vibrational shifts and intensity fluctuations in the Raman spectrum. These track molecules that undergo bending and conformational changes within the probe volume, through their interactions with the environment. This technique allows for in situ high-speed single-molecule investigations of the molecules embedded within lipid bio-membranes. It thus offers a new way to investigate the hidden dynamics of cell membranes important to a myriad of life processes. PMID:25113088

  10. Membrane-Active Peptides and the Clustering of Anionic Lipids

    PubMed Central

    Wadhwani, P.; Epand, R.F.; Heidenreich, N.; Bürck, J.; Ulrich, A.S.; Epand, R.M.

    2012-01-01

    There is some overlap in the biological activities of cell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs). We compared nine AMPs, seven CPPs, and a fusion peptide with regard to their ability to cluster anionic lipids in a mixture mimicking the cytoplasmic membrane of Gram-negative bacteria, as measured by differential scanning calorimetry. We also studied their bacteriostatic effect on several bacterial strains, and examined their conformational changes upon membrane binding using circular dichroism. A remarkable correlation was found between the net positive charge of the peptides and their capacity to induce anionic lipid clustering, which was independent of their secondary structure. Among the peptides studied, six AMPs and four CPPs were found to have strong anionic lipid clustering activity. These peptides also had bacteriostatic activity against several strains (particularly Gram-negative Escherichia coli) that are sensitive to lipid clustering agents. AMPs and CPPs that did not cluster anionic lipids were not toxic to E. coli. As shown previously for several types of AMPs, anionic lipid clustering likely contributes to the mechanism of antibacterial action of highly cationic CPPs. The same mechanism could explain the escape of CPPs from intracellular endosomes that are enriched with anionic lipids. PMID:22853904

  11. A Variational Approach to Particles in Lipid Membranes

    NASA Astrophysics Data System (ADS)

    Elliott, Charles M.; Gräser, Carsten; Hobbs, Graham; Kornhuber, Ralf; Wolf, Maren-Wanda

    2016-06-01

    A variety of models for the membrane-mediated interaction of particles in lipid membranes, mostly well-established in theoretical physics, is reviewed from a mathematical perspective. We provide mathematically consistent formulations in a variational framework, relate apparently different modelling approaches in terms of successive approximation, and investigate existence and uniqueness. Numerical computations illustrate that the new variational formulations are directly accessible to effective numerical methods.

  12. Lipidic cubic phase injector facilitates membrane protein serial femtosecond crystallography

    PubMed Central

    Weierstall, Uwe; James, Daniel; Wang, Chong; White, Thomas A.; Wang, Dingjie; Liu, Wei; Spence, John C.H.; Doak, R. Bruce; Nelson, Garrett; Fromme, Petra; Fromme, Raimund; Grotjohann, Ingo; Kupitz, Christopher; Zatsepin, Nadia A.; Liu, Haiguang; Basu, Shibom; Wacker, Daniel; Han, Gye Won; Katritch, Vsevolod; Boutet, Sébastien; Messerschmidt, Marc; Williams, Garth J.; Koglin, Jason E.; Seibert, M. Marvin; Klinker, Markus; Gati, Cornelius; Shoeman, Robert L.; Barty, Anton; Chapman, Henry N.; Kirian, Richard A.; Beyerlein, Kenneth R.; Stevens, Raymond C.; Li, Dianfan; Shah, Syed T.A.; Howe, Nicole; Caffrey, Martin; Cherezov, Vadim

    2014-01-01

    Lipidic cubic phase (LCP) crystallization has proven successful for high-resolution structure determination of challenging membrane proteins. Here we present a technique for extruding gel-like LCP with embedded membrane protein microcrystals, providing a continuously-renewed source of material for serial femtosecond crystallography. Data collected from sub-10 μm-sized crystals produced with less than 0.5 mg of purified protein yield structural insights regarding cyclopamine binding to the Smoothened receptor. PMID:24525480

  13. Archaeal Lipid Genes: Clues to Life in Acid and the Evolution of Membranes

    NASA Astrophysics Data System (ADS)

    Macalady, J. L.; Croft, L.; Vestling, M. M.; Harms, A. C.; Zheng, L.; Baumler, D. J.; Kaspar, C. W.; Banfield, J. F.

    2002-12-01

    Microorganisms living in acid mine drainage environments face extraordinary challenges. Acid-loving archaea such as Ferroplasma acidarmanus maintain pH gradients of 4 to 5 pH units across their membranes and thrive in hot, extremely low pH (0-1), metal-rich, solutions. New lipid analyses for two extremely acidophilic archaea, F. acidarmanus and F. acidiphilum, reveal that all known archaeal acidophiles have cell membranes composed primarily of tetraether-linked lipids. Because tetraether lipids assemble in rigid monolayers that exclude protons and metals, we suggest that tetraether synthesis genes are essential for archaeal survival in acid. Fusion of two diether-linked lipids to form a tetraether-linked lipid is a distinctive biochemical reaction with no analogy in bacteria and eukaryotes. In addition to archaeal acidophiles, tetraethers are present in members of every archaeal lineage except halophiles. Genes responsible for tetraether synthesis and subsequent biochemical steps which "tune" membrane lipid properties in response to environmental changes have not been identified to date. Comparative genomic analyses using the newly completed genome of F. acidarmanus and available genomes from Bacteria, Archaea and Eukarya have generated candidate tetraether synthase genes found only in archaea. Because tetraether-linked lipids are advantageous for acid-loving and possibly also for heat-loving archaea, the phylogeny of these genes has the potential to shed new light on role of hot, acid environments in early evolution.

  14. Reconstitution of a plasma-membrane H(+)-ATPase into bilayer lipid membrane.

    PubMed

    Ziegler, W; Slayman, C L; Cartwright, C P

    1993-10-01

    The plasma membrane H(+)-ATPase of Neurospora has been reconstituted into planar lipid bilayer membranes by means of the vesicle-fusion technique described by Finkelstein and his collaborators (Zimmerberg et al., 1980; Cohen et al., 1980, 1984; Akabas et al., 1984). Enzyme was first transferred from isolated plasma membrane fragments into asolectin vesicles by a detergent-dialysis procedure (Perlin et al., 1984). After H(+)-pumping activity had been checked by quenching of acridine orange fluorescence, the vesicles were fused into performed bilayers. Critical features of the fusion process include (i) attachment of the vesicles to the bilayer in the presence of divalent cations (Mg++), and (ii) rapid osmotic swelling, which was enhanced by prior sonication or freeze-thawing of the vesicles, and/or by inclusions of physiologic channels. Enough proton pumps could be thus incorporated into bilayers to achieve ATP-driven, vanadate-sensitive currents of 0.04-0.4 pA. Aqueous solutions of low ionic strength were used to suppress conductance fluctuations due to the channels, and when that precaution was taken, we could demonstrate the proton pump the work against membrane potentials of at least 50 mV. PMID:8181690

  15. Adaptable Lipid Matrix Promotes Protein-Protein Association in Membranes.

    PubMed

    Kuznetsov, Andrey S; Polyansky, Anton A; Fleck, Markus; Volynsky, Pavel E; Efremov, Roman G

    2015-09-01

    The cell membrane is "stuffed" with proteins, whose transmembrane (TM) helical domains spontaneously associate to form functionally active complexes. For a number of membrane receptors, a modulation of TM domains' oligomerization has been shown to contribute to the development of severe pathological states, thus calling for detailed studies of the atomistic aspects of the process. Despite considerable progress achieved so far, several crucial questions still remain: How do the helices recognize each other in the membrane? What is the driving force of their association? Here, we assess the dimerization free energy of TM helices along with a careful consideration of the interplay between the structure and dynamics of protein and lipids using atomistic molecular dynamics simulations in the hydrated lipid bilayer for three different model systems - TM fragments of glycophorin A, polyalanine and polyleucine peptides. We observe that the membrane driven association of TM helices exhibits a prominent entropic character, which depends on the peptide sequence. Thus, a single TM peptide of a given composition induces strong and characteristic perturbations in the hydrophobic core of the bilayer, which may facilitate the initial "communication" between TM helices even at the distances of 20-30 Å. Upon tight helix-helix association, the immobilized lipids accommodate near the peripheral surfaces of the dimer, thus disturbing the packing of the surrounding. The dimerization free energy of the modeled peptides corresponds to the strength of their interactions with lipids inside the membrane being the lowest for glycophorin A and similarly higher for both homopolymers. We propose that the ability to accommodate lipid tails determines the dimerization strength of TM peptides and that the lipid matrix directly governs their association. PMID:26575933

  16. Solid-Supported Lipid Membranes: Formation, Stability and Applications

    NASA Astrophysics Data System (ADS)

    Goh, Haw Zan

    This thesis presents a comprehensive investigation of the formation of supported lipid membranes with vesicle hemifusion, their stability under detergents and organic solvents and their applications in molecular biology. In Chapter 3, we describe how isolated patches of DOPC bilayers supported on glass surfaces are dissolved by various detergents (decyl maltoside, dodecyl maltoside, CHAPS, CTAB, SDS, TritonX-100 and Tween20) at their CMC, as investigated by fluorescence video microscopy. In general, detergents partition into distal leaflets of bilayers and lead to the expansion of the bilayers through a rolling motion of the distal over the proximal leaflets, in agreement with the first stage of the established 3-stage model of lipid vesicle solubilization by detergents. Subsequently, we study the partitioning of organic solvents (methanol, ethanol, isopropanol, propanol, acetone and chloroform) into isolated bilayer patches on glass in Chapter 4 with fluorescence microscopy. The area expansion of bilayers due to the partitioning of organic solvents is measured. From the titration of organic solvents, we measured the rate of area expansion as a function of the volume fraction of organic solvents, which is proposed to be a measure of strength of interactions between solvents and membranes. From the same experiments, we also measure the maximum expansion of bilayers (or the maximum binding stoichiometry between organic solvents and lipids) before structural breakdown, which depends on the depth of penetration of solvents to the membranes. In Chapter 5, we investigate the formation of sparsely-tethered bilayer lipid membranes (stBLMs) with vesicle hemifusion. In vesicle hemifusion, lipid vesicles in contact with a hydrophobic alkyl-terminated self-assembled monolayer (SAM) deposit a lipid monolayer to the SAM surface, thus completing the bilayer. Electrical Impedance Spectroscopy and Neutron Reflectivity are used to probe the integrity of stBLMs in terms of their

  17. α-Synuclein Senses Lipid Packing Defects and Induces Lateral Expansion of Lipids Leading to Membrane Remodeling*

    PubMed Central

    Ouberai, Myriam M.; Wang, Juan; Swann, Marcus J.; Galvagnion, Celine; Guilliams, Tim; Dobson, Christopher M.; Welland, Mark E.

    2013-01-01

    There is increasing evidence for the involvement of lipid membranes in both the functional and pathological properties of α-synuclein (α-Syn). Despite many investigations to characterize the binding of α-Syn to membranes, there is still a lack of understanding of the binding mode linking the properties of lipid membranes to α-Syn insertion into these dynamic structures. Using a combination of an optical biosensing technique and in situ atomic force microscopy, we show that the binding strength of α-Syn is related to the specificity of the lipid environment (the lipid chemistry and steric properties within a bilayer structure) and to the ability of the membranes to accommodate and remodel upon the interaction of α-Syn with lipid membranes. We show that this interaction results in the insertion of α-Syn into the region of the headgroups, inducing a lateral expansion of lipid molecules that can progress to further bilayer remodeling, such as membrane thinning and expansion of lipids out of the membrane plane. We provide new insights into the affinity of α-Syn for lipid packing defects found in vesicles of high curvature and in planar membranes with cone-shaped lipids and suggest a comprehensive model of the interaction between α-Syn and lipid bilayers. The ability of α-Syn to sense lipid packing defects and to remodel membrane structure supports its proposed role in vesicle trafficking. PMID:23740253

  18. Reversible control of current across lipid membranes by local heating

    NASA Astrophysics Data System (ADS)

    Urban, Patrick; Kirchner, Silke R.; Mühlbauer, Christian; Lohmüller, Theobald; Feldmann, Jochen

    2016-03-01

    Lipid membranes are almost impermeable for charged molecules and ions that can pass the membrane barrier only with the help of specialized transport proteins. Here, we report how temperature manipulation at the nanoscale can be employed to reversibly control the electrical resistance and the amount of current that flows through a bilayer membrane with pA resolution. For this experiment, heating is achieved by irradiating gold nanoparticles that are attached to the bilayer membrane with laser light at their plasmon resonance frequency. We found that controlling the temperature on the nanoscale renders it possible to reproducibly regulate the current across a phospholipid membrane and the membrane of living cells in absence of any ion channels.

  19. Reversible control of current across lipid membranes by local heating

    PubMed Central

    Urban, Patrick; Kirchner, Silke R.; Mühlbauer, Christian; Lohmüller, Theobald; Feldmann, Jochen

    2016-01-01

    Lipid membranes are almost impermeable for charged molecules and ions that can pass the membrane barrier only with the help of specialized transport proteins. Here, we report how temperature manipulation at the nanoscale can be employed to reversibly control the electrical resistance and the amount of current that flows through a bilayer membrane with pA resolution. For this experiment, heating is achieved by irradiating gold nanoparticles that are attached to the bilayer membrane with laser light at their plasmon resonance frequency. We found that controlling the temperature on the nanoscale renders it possible to reproducibly regulate the current across a phospholipid membrane and the membrane of living cells in absence of any ion channels. PMID:26940847

  20. Automated Lipid Bilayer Membrane Formation Using a Polydimethylsiloxane Thin Film.

    PubMed

    Choi, Sangbaek; Yoon, Sunhee; Ryu, Hyunil; Kim, Sun Min; Jeon, Tae-Joon

    2016-01-01

    An artificial lipid bilayer, or black lipid membrane (BLM), is a powerful tool for studying ion channels and protein interactions, as well as for biosensor applications. However, conventional BLM formation techniques have several drawbacks and they often require specific expertise and laborious processes. In particular, conventional BLMs suffer from low formation success rates and inconsistent membrane formation time. Here, we demonstrate a storable and transportable BLM formation system with controlled thinning-out time and enhanced BLM formation rate by replacing conventionally used films (polytetrafluoroethylene, polyoxymethylene, polystyrene) to polydimethylsiloxane (PDMS). In this experiment, a porous-structured polymer such as PDMS thin film is used. In addition, as opposed to conventionally used solvents with low viscosity, the use of squalene permitted a controlled thinning-out time via slow solvent absorption by PDMS, prolonging membrane lifetime. In addition, by using a mixture of squalene and hexadecane, the freezing point of the lipid solution was increased (~16 °C), in addition, membrane precursors were produced that can be indefinitely stored and readily transported. These membrane precursors have reduced BLM formation time of < 1 hr and achieved a BLM formation rate of ~80%. Moreover, ion channel experiments with gramicidin A demonstrated the feasibility of the membrane system. PMID:27501114

  1. Temperature-induced membrane-lipid adaptation in Acanthamoeba castellanii.

    PubMed

    Jones, A L; Hann, A C; Harwood, J L; Lloyd, D

    1993-02-15

    A method has been developed for the separation of the major membrane fractions of Acanthamoeba castellanii after growth at different temperatures. The acyl-lipid compositions of individual membrane fractions, microsomal membranes, plasma membrane and mitochondria were analysed after a shift in culture temperature from 30 degrees C to 15 degrees C. The major change in lipid composition observed was an alteration in the relative proportions of oleate and linoleate. This reciprocal change was seen in all the membrane fractions, but occurred most rapidly in the phosphatidylcholine of the microsomal fraction. Thus, there appears to be a rapid induction of delta 12-desaturase activity in A. castellanii after a downward shift in growth temperature. Changes were also seen in the proportions of the n-6 C20 fatty acids, with a decrease in the proportions of icosadienoate and increases of icosatrienoate and arachidonate. However, unlike the alteration in oleate/linoleate ratios, this change was not seen in all the individual lipids of each membrane fraction. PMID:8439295

  2. Controlling water flow inside carbon nanotube with lipid membranes

    SciTech Connect

    Feng, Jia-Wei; Ding, Hong-Ming; Ma, Yu-Qiang

    2014-09-07

    Understanding and controlling the transportation of water molecules across carbon nanotube (CNT) is of great importance in bio-nanotechnology. In this paper, we systematically investigate the water transporting behaviors (i.e., water flow rate) inside the CNT in the presence of lipid membranes by using all atom molecular dynamic simulations. Our results show that the hydrophilicity of CNT as well as membrane thickness can have important impacts on the water flow rate. Interestingly, since the membrane thickness is temperature-dependent, the water flow rate can exhibit thermo-responsive behaviors. Further, we also provide insights into the effect of CNT on lipid membranes. It is found that all CNTs can increase the lipid tail order parameters and thicken the membrane at 320 K; while these effects are not obvious at 290 K. Importantly, we observe that the CNT with specific hydrophobicity has the least effect on membranes. The present study may give some useful advice on future experimental design of novel devices and sensors.

  3. Lipid bilayer membrane affinity rationalizes inhibition of lipid peroxidation by a natural lignan antioxidant.

    PubMed

    Podloucká, Pavlína; Berka, Karel; Fabre, Gabin; Paloncýová, Markéta; Duroux, Jean-Luc; Otyepka, Michal; Trouillas, Patrick

    2013-05-01

    Lipid peroxidation is a degenerative oxidative process that modifies the structure of membranes, influencing their biological functions. Lignans, natural polyphenolic antioxidants widely distributed in plants, can prevent this membrane damage by free-radical scavenging. Here, we rationalize the difference in lipid peroxidation inhibition activity of argenteane, a natural dilignan isolated from wild nutmeg, and 3,3'-dimethoxy-1,1'-biphenyl-2,2'-diol, which represents the central part of argenteane responsible for its antioxidant activity. Although both compounds have the same capacity to scavenge free radicals, argenteane is a more active inhibitor of lipid peroxidation. We show that both compounds penetrate into DOPC and PLPC lipid bilayers and adopt similar positions and orientations, which therefore does not explain the difference in their lipid peroxidation inhibition activity. However, free energy profiles indicate that argenteane has a significantly higher affinity to the lipid bilayer, and thus a higher effective concentration to scavenge radicals formed during lipid peroxidation. This finding explains the higher activity of argenteane to inhibit lipid peroxidation. PMID:23560800

  4. Modeling Lipid-Lipid Correlations across a Bilayer Membrane Using the Quasi-chemical Approximation.

    PubMed

    Bossa, Guilherme Volpe; Roth, Joseph; May, Sylvio

    2015-09-15

    Mixed fluid-like lipid membranes exhibit interactions not only among the lipids within a given leaflet but also across the bilayer. The ensuing collective interleaflet coupling of entire membrane domains has been modeled previously using various mean-field approaches. Yet, also on the level of individual lipids have correlations across the bilayer been observed experimentally for binary mixtures of charged/uncharged lipids with mismatching combinations of short and long acyl chain lengths. The present study proposes a lattice gas model to quantify these correlations. To this end, we represent a macroscopically homogeneous lipid bilayer by two coupled two-dimensional lattice gases that we study using the quasi-chemical approximation. We demonstrate that the rationalization of previous experimental results is only possible if besides two-body lipid-lipid interactions within and across the bilayer our model also accounts for an additional multibody interaction mechanism, namely the local hydrophobic height mismatch created by pairing short and long chain lipids together. The robustness of the quasi-chemical approximation is verified by comparison with Monte Carlo simulations. PMID:26302019

  5. Membrane texture induced by specific protein binding and receptor clustering: active roles for lipids in cellular function.

    PubMed

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

    2011-04-26

    Biological membranes are complex, self-organized structures that define boundaries and compartmentalize space in living matter. Composed of a wide variety of lipid and protein molecules, these responsive surfaces mediate transmembrane signaling and material transport within the cell and with its environment. It is well known that lipid membrane properties change as a function of composition and phase state, and that protein-lipid interactions can induce changes in the membrane's properties and biochemical response. Here, molecular level changes in lipid organization induced by multivalent toxin binding were investigated using grazing incidence X-ray diffraction. Structural changes to lipid monolayers at the air-water interface and bilayers at the solid-water interface were studied before and after specific binding of cholera toxin to membrane embedded receptors. At biologically relevant surface pressures, protein binding perturbed lipid packing within monolayers and bilayers resulting in topological defects and the emergence of a new orientationally textured lipid phase. In bilayers this altered lipid order was transmitted from the receptor laden exterior membrane leaflet to the inner leaflet, representing a potential mechanism for lipid mediated outside-in signaling by multivalent protein binding. It is further hypothesized that cell-surface micro-domains exhibiting this type of lipid order may serve as nucleation sites for vesicle formation in clathrin independent endocytosis of cholera toxin. PMID:21474780

  6. Undulation instability in a bilayer lipid membrane due to electric field interaction with lipid dipoles

    NASA Astrophysics Data System (ADS)

    Bingham, Richard J.; Olmsted, Peter D.; Smye, Stephen W.

    2010-05-01

    Bilayer lipid membranes (BLMs) are an essential component of all biological systems, forming a functional barrier for cells and organelles from the surrounding environment. The lipid molecules that form membranes contain both permanent and induced dipoles, and an electric field can induce the formation of pores when the transverse field is sufficiently strong (electroporation). Here, a phenomenological free energy is constructed to model the response of a BLM to a transverse static electric field. The model contains a continuum description of the membrane dipoles and a coupling between the headgroup dipoles and the membrane tilt. The membrane is found to become unstable through buckling modes, which are weakly coupled to thickness fluctuations in the membrane. The thickness fluctuations, along with the increase in interfacial area produced by membrane buckling, increase the probability of localized membrane breakdown, which may lead to pore formation. The instability is found to depend strongly on the strength of the coupling between the dipolar headgroups and the membrane tilt as well as the degree of dipolar ordering in the membrane.

  7. Impact of two different saponins on the organization of model lipid membranes.

    PubMed

    Korchowiec, Beata; Gorczyca, Marcelina; Wojszko, Kamila; Janikowska, Maria; Henry, Max; Rogalska, Ewa

    2015-10-01

    Saponins, naturally occurring plant compounds are known for their biological and pharmacological activity. This activity is strongly related to the amphiphilic character of saponins that allows them to aggregate in aqueous solution and interact with membrane components. In this work, Langmuir monolayer techniques combined with polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and Brewster angle microscopy were used to study the interaction of selected saponins with lipid model membranes. Two structurally different saponins were used: digitonin and a commercial Merck Saponin. Membranes of different composition, namely, cholesterol, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine or 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) were formed at the air/water and air/saponin solution interfaces. The saponin-lipid interaction was characterized by changes in surface pressure, surface potential, surface morphology and PM-IRRAS signal. Both saponins interact with model membranes and change the physical state of membranes by perturbing the lipid acyl chain orientation. The changes in membrane fluidity were more significant upon the interaction with Merck Saponin. A higher affinity of saponins for cholesterol than phosphatidylglycerols was observed. Moreover, our results indicate that digitonin interacts strongly with cholesterol and solubilize the cholesterol monolayer at higher surface pressures. It was shown, that digitonin easily penetrate to the cholesterol monolayer and forms a hydrogen bond with the hydroxyl groups. These findings might be useful in further understanding of the saponin action at the membrane interface and of the mechanism of membrane lysis. PMID:26055895

  8. Lipid packing drives the segregation of transmembrane helices into disordered lipid domains in model membranes

    PubMed Central

    Schäfer, Lars V.; de Jong, Djurre H.; Holt, Andrea; Rzepiela, Andrzej J.; de Vries, Alex H.; Poolman, Bert; Killian, J. Antoinette; Marrink, Siewert J.

    2011-01-01

    Cell membranes are comprised of multicomponent lipid and protein mixtures that exhibit a complex partitioning behavior. Regions of structural and compositional heterogeneity play a major role in the sorting and self-assembly of proteins, and their clustering into higher-order oligomers. Here, we use computer simulations and optical microscopy to study the sorting of transmembrane helices into the liquid-disordered domains of phase-separated model membranes, irrespective of peptide–lipid hydrophobic mismatch. Free energy calculations show that the enthalpic contribution due to the packing of the lipids drives the lateral sorting of the helices. Hydrophobic mismatch regulates the clustering into either small dynamic or large static aggregates. These results reveal important molecular driving forces for the lateral organization and self-assembly of transmembrane helices in heterogeneous model membranes, with implications for the formation of functional protein complexes in real cells. PMID:21205902

  9. Effect of lipid head group interactions on membrane properties and membrane-induced cationic β-hairpin folding.

    PubMed

    Ganesan, Sai J; Xu, Hongcheng; Matysiak, Silvina

    2016-07-21

    Stages in POPS membrane induced SVS-1 folding. One key characteristic of mIFs is the dielectric gradient and subsequently, electrostatic potential that arises from dipolar interactions in the head group region. In this work, we present a coarse-grained (CG) model for anionic and zwitterionic lipids that accounts for dipolar intricacies in the head group region. Prior work on adding dipolar interactions in a coarse grained (CG) model for peptides enabled us to achieve α/β secondary structure content de novo, without any added bias. We have now extended this idea to lipids. To mimic dipolar interactions, two dummy particles with opposite charges are added to CG polar beads. These two dummy charges represent a fluctuating dipole that introduces structural polarization into the head group region. We have used POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and POPS (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine) as our model lipids. We characterize structural, dynamic, and dielectric properties of our CG bilayer, along with the effect of monovalent ions. We observe head group dipoles to play a significant role in membrane dielectric gradient and lipid clustering induced by dipole-dipole interactions in POPS lipids. In addition, we studied membrane-induced peptide folding of a cationic antimicrobial peptide with anticancer activity, SVS-1. We find that membrane-induced peptide folding is driven by both (a) cooperativity in peptide self-interaction and (b) cooperativity in membrane-peptide interaction. In particular, dipolar interactions between the peptide backbone and lipid head groups contribute to stabilizing folded conformations. PMID:27165814

  10. Stabilization of composition fluctuations in mixed membranes by hybrid lipids

    NASA Astrophysics Data System (ADS)

    Safran, Samuel; Palmieri, Benoit

    2013-03-01

    A ternary mixture model is proposed to describe composition fluctuations in mixed membranes composed of saturated, unsaturated and hybrid lipids. The asymmetric hybrid lipid has one saturated and one unsaturated hydrocarbon chain and it can reduce the packing incompatibility between saturated and unsaturated lipids. A methodology to recast the free-energy of the lattice in terms of a continuous isotropic field theory is proposed and used to analyze composition fluctuations above the critical temperature. The effect of hybrid lipids on fluctuations domains rich in saturated/unsaturated lipids is predicted. The correlation length of such fluctuations decreases significantly with increasing amounts of hybrids even if the temperature is maintained close to the critical temperature. This provides an upper bound for the domain sizes expected in rafts stabilized by hybrids, above the critical temperature. When the hybrid composition of the membrane is increased further, a crossover value is found above which ``stripe-like'' fluctuations are observed. The wavelength of these fluctuations decreases with increasing hybrid fraction and tends toward a molecular size in a membrane that contains only hybrids.

  11. Ordered Nanoclusters in Lipid-Cholesterol Membranes

    NASA Astrophysics Data System (ADS)

    Ratajczak, Maria K.; Chi, Eva Y.; Frey, Shelli L.; Cao, Kathleen D.; Luther, Laura M.; Lee, Ka Yee C.; Majewski, Jaroslaw; Kjaer, Kristian

    2009-07-01

    X-ray diffraction of sphingomyelin-dihydrocholesterol (SM-DChol) monolayers revealed short-ranged (˜25Å) 2D ordering. These nanoclusters show two distinct regions: below the cusp point of the phase diagram (35 mol% DChol), a constant d spacing was observed; above the cusp, the d spacing increases linearly with DChol in accordance to Vegard’s law for binary alloys. The components in this lipidic alloy are thus a 65∶35 SM-DChol entity and excess DChol. Reflectivity data further support the emergence above the cusp of an uncomplexed DChol population with greater vertical mobility.

  12. Respiration and ecological niche influence bacterial membrane lipid compositions.

    PubMed

    Bay, Denice C; Booth, Sean C; Turner, Raymond J

    2015-05-01

    Bacterial membrane compositions vary widely between phyla and within related species. The types of lipids within membranes are as diverse as the selective pressures that influence bacterial lifestyles such as their mode of respiration and habitat. This study has examined the extent that respiration and habitat affect bacterial fatty acid (FA) and polar lipid (PL) compositions. To accomplish this, over 300 FA and PL profiles from 380 previously characterized species were assembled and subjected to multivariate statistical analyses in order to determine lipid to habitat/respiration associations. It was revealed that PL profiles showed a slight advantage over FA profiles for discriminating taxonomic relationships between species. FA profiles showed greater correlation with respiration and habitat than PL. This study identified that respiration did not consistently favour uniform FA or PL changes when lipid profiles were compared between examined phyla. This suggests that although phyla may adopt similar respiration methods, it does not result in consistent lipid attributes within one respiration state. Examination of FA and PL compositions were useful to identify taxonomic relationships between related species and provides insight into lipid variations influenced by the niche of its host. PMID:25297716

  13. Golgi Membrane Dynamics Viewed Through a Lens of Lipids

    PubMed Central

    Bankaitis, Vytas A.; Garcia-Mata, Rafael; Mousley, Carl J.

    2012-01-01

    Summary The striking morphology of the Golgi complex has fascinated cell biologists since its discovery over 100 years ago. Yet, despite intense efforts to understand how membrane flow relates to Golgi form and function, this organelle continues to baffle cell biologists and biochemists alike. Fundamental questions regarding Golgi function, while hotly debated, remain unresolved. While Golgi function is historically described from a protein-centric point of view, we now appreciate that conceptual frameworks for how lipid metabolism is integrated with Golgi biogenesis and function are essential for a mechanistic understanding of this fascinating organelle. It is from a lipid-centric perspective that we discuss the larger question of Golgi dynamics and membrane trafficking. We review the growing body of evidence for how lipid metabolism is integrally written into the engineering of the Golgi system, and highlight questions for future study. PMID:22625862

  14. Lipid Bilayer Membrane-Triggered Presynaptic Vesicle Assembly

    PubMed Central

    2009-01-01

    The formation of functional synapses on artificial substrates is a very important step in the development of engineered in vitro neural networks. Spherical supported bilayer lipid membranes (SS-BLMs) are used here as a novel substrate to demonstrate presynaptic vesicle accumulation at an in vitro synaptic junction. Confocal fluorescence microscopy, cryo-transmission electron microscopy (cryo-TEM), and fluorescence recovery after photobleaching (FRAP) experiments have been used to characterize the SS-BLMs. Conventional immunocytochemistry combined with confocal fluorescence microscopy was used to observe the formation of presynaptic vesicles at the neuron−SS-BLM contacts. These results indicate that lipid phases may play a role in the observed phenomenon, in addition to the chemical and electrostatic interactions between the neurons and SS-BLMs. The biocompatibility of lipid bilayers along with their membrane tunability makes the suggested approach a useful “toolkit” for many neuroengineering applications including artificial synapse formation and synaptogenesis in vivo. PMID:22778819

  15. Anesthetic Diffusion Through Lipid Membranes Depends on the Protonation Rate

    PubMed Central

    Pérez-Isidoro, Rosendo; Sierra-Valdez, F. J.; Ruiz-Suárez, J. C.

    2014-01-01

    Hundreds of substances possess anesthetic action. However, despite decades of research and tests, a golden rule is required to reconcile the diverse hypothesis behind anesthesia. What makes an anesthetic to be local or general in the first place? The specific targets on proteins, the solubility in lipids, the diffusivity, potency, action time? Here we show that there could be a new player equally or even more important to disentangle the riddle: the protonation rate. Indeed, such rate modulates the diffusion speed of anesthetics into lipid membranes; low protonation rates enhance the diffusion for local anesthetics while high ones reduce it. We show also that there is a pH and membrane phase dependence on the local anesthetic diffusion across multiple lipid bilayers. Based on our findings we incorporate a new clue that may advance our understanding of the anesthetic phenomenon. PMID:25520016

  16. Membrane potential generated by ion adsorption.

    PubMed

    Tamagawa, Hirohisa; Morita, Sachi

    2014-01-01

    It has been widely acknowledged that the Goldman-Hodgkin-Katz (GHK) equation fully explains membrane potential behavior. The fundamental facet of the GHK equation lies in its consideration of permeability of membrane to ions, when the membrane serves as a separator for separating two electrolytic solutions. The GHK equation describes that: variation of membrane permeability to ion in accordance with ion species results in the variation of the membrane potential. However, nonzero potential was observed even across the impermeable membrane (or separator) separating two electrolytic solutions. It gave rise to a question concerning the validity of the GHK equation for explaining the membrane potential generation. In this work, an alternative theory was proposed. It is the adsorption theory. The adsorption theory attributes the membrane potential generation to the ion adsorption onto the membrane (or separator) surface not to the ion passage through the membrane (or separator). The computationally obtained potential behavior based on the adsorption theory was in good agreement with the experimentally observed potential whether the membrane (or separator) was permeable to ions or not. It was strongly speculated that the membrane potential origin could lie primarily in the ion adsorption on the membrane (or separator) rather than the membrane permeability to ions. It might be necessary to reconsider the origin of membrane potential which has been so far believed explicable by the GHK equation. PMID:24957176

  17. Membrane Potential Generated by Ion Adsorption

    PubMed Central

    Tamagawa, Hirohisa; Morita, Sachi

    2014-01-01

    It has been widely acknowledged that the Goldman-Hodgkin-Katz (GHK) equation fully explains membrane potential behavior. The fundamental facet of the GHK equation lies in its consideration of permeability of membrane to ions, when the membrane serves as a separator for separating two electrolytic solutions. The GHK equation describes that: variation of membrane permeability to ion in accordance with ion species results in the variation of the membrane potential. However, nonzero potential was observed even across the impermeable membrane (or separator) separating two electrolytic solutions. It gave rise to a question concerning the validity of the GHK equation for explaining the membrane potential generation. In this work, an alternative theory was proposed. It is the adsorption theory. The adsorption theory attributes the membrane potential generation to the ion adsorption onto the membrane (or separator) surface not to the ion passage through the membrane (or separator). The computationally obtained potential behavior based on the adsorption theory was in good agreement with the experimentally observed potential whether the membrane (or separator) was permeable to ions or not. It was strongly speculated that the membrane potential origin could lie primarily in the ion adsorption on the membrane (or separator) rather than the membrane permeability to ions. It might be necessary to reconsider the origin of membrane potential which has been so far believed explicable by the GHK equation. PMID:24957176

  18. Cyclohexane Rings Reduce Membrane Permeability to Small Ions in Archaea-Inspired Tetraether Lipids.

    PubMed

    Koyanagi, Takaoki; Leriche, Geoffray; Onofrei, David; Holland, Gregory P; Mayer, Michael; Yang, Jerry

    2016-01-26

    Extremophile archaeal organisms overcome problems of membrane permeability by producing lipids with structural elements that putatively improve membrane integrity compared to lipids from other life forms. Herein, we describe a series of lipids that mimic some key structural features of archaeal lipids, such as: 1) single tethering of lipid tails to create fully transmembrane tetraether lipids and 2) the incorporation of small rings into these tethered segments. We found that membranes formed from pure tetraether lipids leaked small ions at a rate that was about two orders of magnitude slower than common bilayer-forming lipids. Incorporation of cyclopentane rings into the tetraether lipids did not affect membrane leakage, whereas a cyclohexane ring reduced leakage by an additional 40 %. These results show that mimicking certain structural features of natural archaeal lipids results in improved membrane integrity, which may help overcome limitations of many current lipid-based technologies. PMID:26695717

  19. Poloxamer 188 decreases susceptibility of artificial lipid membranes to electroporation.

    PubMed Central

    Sharma, V; Stebe, K; Murphy, J C; Tung, L

    1996-01-01

    The effect of a nontoxic, nonionic block co-polymeric surface active agent, poloxamer 188, on electroporation of artificial lipid membranes made of azolectin, was investigated. Two different experimental protocols were used in our study: charge pulse and voltage clamp. For the charge pulse protocol, membranes were pulsed with a 10-micronsecond rectangular voltage waveform, after which membrane voltage decay was observed through an external 1-M omega resistance. For the voltage clamp protocol the membranes were pulsed with a waveform that consisted of an initial 10-microsecond rectangular phase, followed by a negative sloped ramp that decayed to zero in the subsequent 500 microseconds. Several parameters characterizing the electroporation process were measured and compared for the control membranes and membranes treated with 1.0 mM poloxamer 188. For both the charge pulse and voltage clamp experiments, the threshold voltage (amplitude of initial rectangular phase) and latency time (time elapsed between the end of rectangular phase and the onset of membrane electroporation) were measured. Membrane conductance (measured 200 microseconds after the initial rectangular phase) and rise time (tr; the time required for the porated membrane to reach a certain conductance value) were also determined for the voltage clamp experiments, and postelectroporation time constant (PE tau; the time constant for transmembrane voltage decay after onset of electroporation) for the charge pulse experiments. The charge pulse experiments were performed on 23 membranes with 10 control and 13 poloxamer-treated membranes, and voltage pulse experiments on 49 membranes with 26 control and 23 poloxamer-treated membranes. For both charge pulse and voltage clamp experiments, poloxamer 188-treated membranes exhibited a statistically higher threshold voltage (p = 0.1 and p = 0.06, respectively), and longer latency time (p = 0.04 and p = 0.05, respectively). Also, poloxamer 188-treated membranes were

  20. Measuring Lipid Membrane Viscosity Using Rotational and Translational Probe Diffusion

    NASA Astrophysics Data System (ADS)

    Hormel, Tristan T.; Kurihara, Sarah Q.; Brennan, M. Kathleen; Wozniak, Matthew C.; Parthasarathy, Raghuveer

    2014-05-01

    The two-dimensional fluidity of lipid bilayers enables the motion of membrane-bound macromolecules and is therefore crucial to biological function. Microrheological methods that measure fluid viscosity via the translational diffusion of tracer particles are challenging to apply and interpret for membranes, due to uncertainty about the local environment of the tracers. Here, we demonstrate a new technique in which determination of both the rotational and translational diffusion coefficients of membrane-linked particles enables quantification of viscosity, measurement of the effective radii of the tracers, and assessment of theoretical models of membrane hydrodynamics. Surprisingly, we find a wide distribution of effective tracer radii, presumably due to a variable number of lipids linked to each tracer particle. Furthermore, we show for the first time that a protein involved in generating membrane curvature, the vesicle trafficking protein Sar1p, dramatically increases membrane viscosity. Using the rheological method presented here, therefore, we are able to reveal a class of previously unknown couplings between protein activity and membrane mechanics.

  1. Determining the pivotal plane of fluid lipid membranes in simulations.

    PubMed

    Wang, Xin; Deserno, Markus

    2015-10-28

    Each leaflet of a curved lipid membrane contains a surface at which the area strain vanishes, the so-called pivotal plane. Its distance z0 from the bilayer's midplane arises in numerous contexts, for instance the connection between monolayer and bilayer moduli, stress-profile moments, or area-difference elasticity theories. Here, we propose two precise methods for determining the location of the pivotal plane in computer simulations, both of which rely on monitoring the lipid imbalance across a curved bilayer. The first method considers the ratio of lipid number between the two leaflets of cylindrical or spherical vesicles; it hence requires lipid flip-flop for equilibration. The second method looks at the leaflet difference across local sections cut out from a buckled membrane; this observable equilibrates even in the absence of flip-flop. We apply our methods to two different coarse-grained lipid models, the generic three-bead solvent-free Cooke model and a ten-bead representation of dimyristoylphosphocholine with the explicit solvent MARTINI model. The Cooke model is amenable to both methods and gives results that agree at the percent level. Using it, we also show that the pivotal plane moves outward as lipid curvature becomes more positive. The MARTINI model can only be analyzed with the buckling method; the obtained value z0 = 0.850(11) nm lies about 0.4 nm inwards of the glycerol backbone and is hence unexpectedly small. We attribute this to limitations of the coarse-grained description, suggesting that the location of the pivotal plane might be a good indicator for how well lipid models capture the microscopic origins of curvature elasticity. Finally, we also show that the pivotal plane position itself moves as the membrane is bent. The leading correction is linear in curvature, dependent on the Poisson ratio, and can matter when analyzing experimental results obtained from highly curved inverse hexagonal phases. PMID:26520500

  2. Determining the pivotal plane of fluid lipid membranes in simulations

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Deserno, Markus

    2015-10-01

    Each leaflet of a curved lipid membrane contains a surface at which the area strain vanishes, the so-called pivotal plane. Its distance z0 from the bilayer's midplane arises in numerous contexts, for instance the connection between monolayer and bilayer moduli, stress-profile moments, or area-difference elasticity theories. Here, we propose two precise methods for determining the location of the pivotal plane in computer simulations, both of which rely on monitoring the lipid imbalance across a curved bilayer. The first method considers the ratio of lipid number between the two leaflets of cylindrical or spherical vesicles; it hence requires lipid flip-flop for equilibration. The second method looks at the leaflet difference across local sections cut out from a buckled membrane; this observable equilibrates even in the absence of flip-flop. We apply our methods to two different coarse-grained lipid models, the generic three-bead solvent-free Cooke model and a ten-bead representation of dimyristoylphosphocholine with the explicit solvent MARTINI model. The Cooke model is amenable to both methods and gives results that agree at the percent level. Using it, we also show that the pivotal plane moves outward as lipid curvature becomes more positive. The MARTINI model can only be analyzed with the buckling method; the obtained value z0 = 0.850(11) nm lies about 0.4 nm inwards of the glycerol backbone and is hence unexpectedly small. We attribute this to limitations of the coarse-grained description, suggesting that the location of the pivotal plane might be a good indicator for how well lipid models capture the microscopic origins of curvature elasticity. Finally, we also show that the pivotal plane position itself moves as the membrane is bent. The leading correction is linear in curvature, dependent on the Poisson ratio, and can matter when analyzing experimental results obtained from highly curved inverse hexagonal phases.

  3. Simulations of Pore Formation in Lipid Membranes: Reaction Coordinates, Convergence, Hysteresis, and Finite-Size Effects.

    PubMed

    Awasthi, Neha; Hub, Jochen S

    2016-07-12

    Transmembrane pores play an important role in various biophysical processes such as membrane permeation, membrane fusion, and antimicrobial peptide activity. In principal, all-atom molecular dynamics (MD) simulations provide an accurate model of pore formation in lipid membranes. However, the free energy landscape of transmembrane pore formation remains poorly understood, partly because potential of mean force (PMF) calculations of pore formation strongly depend on the choice of the reaction coordinate. In this study, we used umbrella sampling to compute PMFs for pore formation using three different reaction coordinates, namely, (i) a coordinate that steers the lipids in the lateral direction away from the pore center, (ii) the distance of a single lipid phosphate group from the membrane center, and (iii) the average water density inside a membrane-spanning cylinder. Our results show that while the three reaction coordinates efficiently form pores in membranes, they suffer from strong hysteresis between pore-opening and pore-closing simulations, suggesting that they do not restrain the systems close to the transition state for pore formation. The two reaction coordinates that act via restraining the lipids lead to more pronounced hysteresis compared with the coordinate acting on the water molecules. By comparing PMFs computed from membranes with different numbers of lipids, we observed significant artifacts from the periodic boundary conditions in small simulation systems. Further analysis suggests that the formation and disruption of a continuous hydrogen-bonding network across the membrane corresponds to the transition state for pore formation. Our study provides molecular insights into the critical steps of transmembrane pore formation, and it may guide the development of efficient reaction coordinates for pore formation. PMID:27254744

  4. The role of blood cell membrane lipids on the mode of action of HIV-1 fusion inhibitor sifuvirtide

    SciTech Connect

    Matos, Pedro M.; Freitas, Teresa; Castanho, Miguel A.R.B.; Santos, Nuno C.

    2010-12-17

    Research highlights: {yields} Sifuvirtide interacts with erythrocyte and lymphocyte membrane in a concentration dependent manner by decreasing its dipole potential. {yields} Dipole potential variations in lipid vesicles show sifuvirtide's lipid selectivity towards saturated phosphatidylcholines. {yields} This peptide-membrane interaction may direct the drug towards raft-like membrane domains where the receptors used by HIV are located, facilitating its inhibitory action. -- Abstract: Sifuvirtide is a gp41 based peptide that inhibits HIV-1 fusion with the host cells and is currently under clinical trials. Previous studies showed that sifuvirtide partitions preferably to saturated phosphatidylcholine lipid membranes, instead of fluid-phase lipid vesicles. We extended the study to the interaction of the peptide with circulating blood cells, by using the dipole potential sensitive probe di-8-ANEPPS. Sifuvirtide decreased the dipole potential of erythrocyte and lymphocyte membranes in a concentration dependent manner, demonstrating its interaction. Also, the lipid selectivity of the peptide towards more rigid phosphatidylcholines was confirmed based on the dipole potential variations. Overall, the interaction of the peptide with the cell membranes is a contribution of different lipid preferences that presumably directs the peptide towards raft-like domains where the receptors are located, facilitating the reach of the peptide to its molecular target, the gp41 in its pre-fusion conformation.

  5. Lipids and Membrane Microdomains in HIV-1 Replication

    PubMed Central

    Waheed, Abdul A.; Freed, Eric O.

    2009-01-01

    Several critical steps in the replication cycle of human immunodeficiency virus type 1 (HIV-1) – entry, assembly and budding – are complex processes that take place at the plasma membrane of the host cell. A growing body of data indicates that these early and late steps in HIV-1 replication take place in specialized plasma membrane microdomains, and that many of the viral and cellular components required for entry, assembly, and budding are concentrated in these microdomains. In particular, a number of studies have shown that cholesterol- and sphingolipid-enriched microdomains known as lipid rafts play important roles in multiple steps in the virus replication cycle. In this review, we provide an overview of what is currently known about the involvement of lipids and membrane microdomains in HIV-1 replication. PMID:19383519

  6. Protein-lipid interactions in bilayer membranes: A lattice model

    PubMed Central

    Pink, David A.; Chapman, Dennis

    1979-01-01

    A lattice model has been developed to study the effects of intrinsic membrane proteins upon the thermodynamic properties of a lipid bilayer membrane. We assume that only nearest-neighbor van der Waals and steric interactions are important and that the polar group interactions can be represented by effective pressure—area terms. Phase diagrams, the temperature T0, which locates the gel—fluid melting, the transition enthalpy, and correlations were calculated by mean field and cluster approximations. Average lipid chain areas and chain areas when the lipid is in a given protein environment were obtained. Proteins that have a “smooth” homogeneous surface (“cholesterol-like”) and those that have inhomogeneous surfaces or that bind lipids specifically were considered. We find that T0 can vary depending upon the interactions and that another peak can appear upon the shoulder of the main peak which reflects the melting of a eutectic mixture. The transition enthalpy decreases generally, as was found before, but when a second peak appears departures from this behavior reflect aspects of the eutectic mixture. We find that proteins have significant nonzero probabilities for being adjacent to one another so that no unbroken “annulus” of lipid necessarily exists around a protein. If T0 does not increase much, or decreases, with increasing c, then lipids adjacent to a protein cannot all be all-trans on the time scale (10-7 sec) of our system. Around a protein the lipid correlation depth is about one lipid layer, and this increases with c. Possible consequences of ignoring changes in polar group interactions due to clustering of proteins are discussed. PMID:286996

  7. AFM Study on the Electric-Field Effects on Supported Bilayer Lipid Membranes

    PubMed Central

    Jeuken, Lars J. C.

    2008-01-01

    Electric-field induced changes in structure and conductivity of supported bilayer lipid membranes (SLM) have been studied at submicroscopic resolution using atomic force microscopy and electrochemical impedance spectroscopy. The SLMs are formed on gold surfaces modified with mixed self-assembled monolayers of a cholesterol-tether and 6-mercaptohexanol. At applied potentials of ≤−0.25 V versus standard hydrogen electrode, the conductance of the SLM increases and membrane areas of <150 nm in size are found to elevate from the surface up to 15 nm in height. To estimate the electric field experienced by the lipid membrane, electrowetting has been used to determine the point of zero charge of a 6-mercaptohexanol-modified surface (0.19 ± 0.13 V versus standard hydrogen electrode). The effects of electric fields on the structure and conductance of supported membranes are discussed. PMID:18326663

  8. Atomic Structure of a Voltage-Dependent K+ Channel in a Lipid Membrane-Like Environment

    SciTech Connect

    Long,S.; Tao, X.; Campbell, E.; MacKinnon, R.

    2007-01-01

    Voltage-dependent K+ (Kv) channels repolarize the action potential in neurons and muscle. This type of channel is gated directly by membrane voltage through protein domains known as voltage sensors, which are molecular voltmeters that read the membrane voltage and regulate the pore. Here we describe the structure of a chimaeric voltage-dependent K+ channel, which we call the 'paddle-chimaera channel', in which the voltage-sensor paddle has been transferred from Kv2.1 to Kv1.2. Crystallized in complex with lipids, the complete structure at 2.4 Angstroms resolution reveals the pore and voltage sensors embedded in a membrane-like arrangement of lipid molecules. The detailed structure, which can be compared directly to a large body of functional data, explains charge stabilization within the membrane and suggests a mechanism for voltage-sensor movements and pore gating.

  9. PrP106-126 peptide disrupts lipid membranes: Influence of C-terminal amidation

    SciTech Connect

    Zheng Wenfu; Wang Lijun; Hong Yuankai; Sha Yinlin

    2009-02-06

    PrP106-126 is located within the important domain concerning membrane related conformational conversion of human Prion protein (from cellular isoform PrP{sup C} to scrapie isoform PrP{sup Sc}). Recent advances reveal that the pathological and physicochemical properties of PrP106-126 peptide are very sensitive to its N-terminal amidation, however, the detailed mechanism remains unclear. In this work, we studied the interactions of the PrP106-126 isoforms (PrP106-126{sub CONH2} and PrP106-126{sub COOH}) with the neutral lipid bilayers by atomic force microscopy, surface plasmon resonance and fluorescence spectroscopy. The membrane structures were disturbed by the two isoforms in a similarly stepwise process. The distinct morphological changes of the membrane were characterized by formation of semi-penetrated defects and sigmoidal growth of flat high-rise domains on the supported lipid bilayers. However, PrP106-126{sub COOH} displayed a higher peptide-lipid binding affinity than PrP106-126{sub CONH2} ({approx}2.9 times) and facilitated the peptide-lipid interactions by shortening the lag time. These results indicate that the C-terminal amidation may influence the pathological actions of PrP106-126 by lowering the interaction potentials with lipid membranes.

  10. The membrane dipole potential in a total membrane potential model. Applications to hydrophobic ion interactions with membranes.

    PubMed Central

    Flewelling, R F; Hubbell, W L

    1986-01-01

    The total potential energy profile for hydrophobic ion interactions with lipid bilayers can be written as the sum of four terms: the electrical Born, image and dipole contributions, and a neutral energy term. We introduce a specific model for the membrane dipole potential, treating it as a two-dimensional array of point dipoles located near each membrane-water interface. Together with specific theoretical models for the other energy terms, a total potential profile is developed that successfully describes the complete set of thermodynamic parameters for binding and translocation for the two hydrophobic ion structural analogues, tetraphenylphosphonium (TPP+) and tetraphenylboron (TPB-). A reasonable fit to the data is possible if the dipole potential energy has a magnitude of 5.5 + 0.5 kcal/mol (240 + 20 mV), positive inside, and if the neutral energy contribution for TPP+ and TPB- is -7.0 + 1.0 kcal/mol. These results may also have important implications for small ion interactions with membranes and the energetics of charged groups in membrane proteins. PMID:3955184

  11. Protein-fluctuation-induced water-pore formation in ion channel voltage-sensor translocation across a lipid bilayer membrane

    NASA Astrophysics Data System (ADS)

    Rajapaksha, Suneth P.; Pal, Nibedita; Zheng, Desheng; Lu, H. Peter

    2015-11-01

    We have applied a combined fluorescence microscopy and single-ion-channel electric current recording approach, correlating with molecular dynamics (MD) simulations, to study the mechanism of voltage-sensor domain translocation across a lipid bilayer. We use the colicin Ia ion channel as a model system, and our experimental and simulation results show the following: (1) The open-close activity of an activated colicin Ia is not necessarily sensitive to the amplitude of the applied cross-membrane voltage when the cross-membrane voltage is around the resting potential of excitable membranes; and (2) there is a significant probability that the activation of colicin Ia occurs by forming a transient and fluctuating water pore of ˜15 Å diameter in the lipid bilayer membrane. The location of the water-pore formation is nonrandom and highly specific, right at the insertion site of colicin Ia charged residues in the lipid bilayer membrane, and the formation is intrinsically associated with the polypeptide conformational fluctuations and solvation dynamics. Our results suggest an interesting mechanistic pathway for voltage-sensitive ion channel activation, and specifically for translocation of charged polypeptide chains across the lipid membrane under a transmembrane electric field: the charged polypeptide domain facilitates the formation of hydrophilic water pore in the membrane and diffuses through the hydrophilic pathway across the membrane; i.e., the charged polypeptide chain can cross a lipid membrane without entering into the hydrophobic core of the lipid membrane but entirely through the aqueous and hydrophilic environment to achieve a cross-membrane translocation. This mechanism sheds light on the intensive and fundamental debate on how a hydrophilic and charged peptide domain diffuses across the biologically inaccessible high-energy barrier of the hydrophobic core of a lipid bilayer: The peptide domain does not need to cross the hydrophobic core to move across a

  12. Carotenoid binding to proteins: Modeling pigment transport to lipid membranes.

    PubMed

    Reszczynska, Emilia; Welc, Renata; Grudzinski, Wojciech; Trebacz, Kazimierz; Gruszecki, Wieslaw I

    2015-10-15

    Carotenoid pigments play numerous important physiological functions in human organism. Very special is a role of lutein and zeaxanthin in the retina of an eye and in particular in its central part, the macula lutea. In the retina, carotenoids can be directly present in the lipid phase of the membranes or remain bound to the protein-pigment complexes. In this work we address a problem of binding of carotenoids to proteins and possible role of such structures in pigment transport to lipid membranes. Interaction of three carotenoids, beta-carotene, lutein and zeaxanthin with two proteins: bovine serum albumin and glutathione S-transferase (GST) was investigated with application of molecular spectroscopy techniques: UV-Vis absorption, circular dichroism and Fourier transform infrared spectroscopy (FTIR). Interaction of pigment-protein complexes with model lipid bilayers formed with egg yolk phosphatidylcholine was investigated with application of FTIR, Raman imaging of liposomes and electrophysiological technique, in the planar lipid bilayer models. The results show that in all the cases of protein and pigment studied, carotenoids bind to protein and that the complexes formed can interact with membranes. This means that protein-carotenoid complexes are capable of playing physiological role in pigment transport to biomembranes. PMID:26361975

  13. Controlled Transport of Functionalized Nanochannel though Lipid Membrane

    NASA Astrophysics Data System (ADS)

    Dutt, Meenakshi; Kuksenok, Olga; Balazs, Anna C.

    2012-02-01

    Via the Dissipative Particle Dynamics approach, we study the directed transport of a transmembrane nanochannel to a desired location within a lipid bilayer. Each nanochannel encompasses an ABA architecture, with a hydrophobic shaft (B) with two hydrophilic ends (A). One of the ends of the nanochannel is functionalized with hydrophilic functional groups, or hairs. The hydrophilic hairs serve a dual role: (a) control transport across the membrane barrier, and (b) enable the channel relocation to a specific membrane site. Our system comprises a lipid membrane with an embedded transmembrane nanochannel with the hairs extending into solution. First, we hold a suitably functionalized pipette above the membrane while the nanochannel freely diffuses within the membrane. For an optimal range of parameters, we demonstrate that the hairs find the pipette and spontaneously anchor onto it. We then show that by moving the pipette for a range of velocities, we can effectively transport the channel to any location within the membrane. This prototype assembly can provide guidelines for designing a number of systems for biomimetic applications.

  14. Single Molecule Kinetics of ENTH Binding to Lipid Membranes

    SciTech Connect

    Rozovsky, Sharon; Forstner, Martin B.; Sondermann, Holger; Groves, Jay T.

    2012-04-03

    Transient recruitment of proteins to membranes is a fundamental mechanism by which the cell exerts spatial and temporal control over proteins’ localization and interactions. Thus, the specificity and the kinetics of peripheral proteins’ membrane residence are an attribute of their function. In this article, we describe the membrane interactions of the interfacial epsin N-terminal homology (ENTH) domain with its target lipid phosphatidylinositol (4,5)-bisphosphate (PtdIns(4,5)P2). The direct visualization and quantification of interactions of single ENTH molecules with supported lipid bilayers is achieved using total internal reflection fluorescence microscopy (TIRFM) with a time resolution of 13 ms. This enables the recording of the kinetic behavior of ENTH interacting with membranes with physiologically relevant concentrations of PtdIns(4,5)P2 despite the low effective binding affinity. Subsequent single fluorophore tracking permits us to build up distributions of residence times and to measure ENTH dissociation rates as a function of membrane composition. In addition, due to the high time resolution, we are able to resolve details of the motion of ENTH associated with a simple, homogeneous membrane. In this case ENTH’s diffusive transport appears to be the result of at least three different diffusion processes.

  15. Micropatterned composite membranes of polymerized and fluid lipid bilayers.

    PubMed

    Morigaki, Kenichi; Kiyosue, Kazuyuki; Taguchi, Takahisa

    2004-08-31

    Micropatterned composite membranes of polymerized and fluid lipid bilayers were constructed on solid substrates. Lithographic photopolymerization of a diacetylene-containing phospholipid, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DiynePC), and subsequent removal of nonreacted monomers by a detergent solution (0.1 M sodium dodecyl sulfate (SDS)) yielded a patterned polymeric bilayer matrix on the substrate. Fluid lipid bilayers of phosphatidylcholine from egg yolk (egg-PC) were incorporated into the lipid-free wells surrounded by the polymeric bilayers through the process of fusion and reorganization of suspended small unilamellar vesicles. Spatial distribution of the fluid bilayers in the patterned bilayer depended on the degree of photopolymerization that in turn could be modulated by varying the applied UV irradiation dose. The polymeric bilayer domains blocked lateral diffusion of the fluid lipid bilayers and confined them in the defined areas (corrals), if the polymerization was conducted with a sufficiently large UV dose. On the other hand, lipid molecules of the fluid bilayers penetrated into the polymeric bilayer domains, if the UV dose was relatively small. A direct correlation was observed between the applied UV dose and the lateral diffusion coefficient of fluorescent marker molecules in the fluid bilayers embedded within the polymeric bilayer domains. Artificial control of lateral diffusion by polymeric bilayers may lead to the creation of complex and versatile biomimetic model membrane arrays. PMID:15323525

  16. Adaptive Lipid Packing and Bioactivity in Membrane Domains

    PubMed Central

    Sezgin, Erdinc; Gutmann, Theresia; Buhl, Tomasz; Dirkx, Ron; Grzybek, Michal; Coskun, Ünal; Solimena, Michele; Simons, Kai; Levental, Ilya; Schwille, Petra

    2015-01-01

    Lateral compositional and physicochemical heterogeneity is a ubiquitous feature of cellular membranes on various length scales, from molecular assemblies to micrometric domains. Segregated lipid domains of increased local order, referred to as rafts, are believed to be prominent features in eukaryotic plasma membranes; however, their exact nature (i.e. size, lifetime, composition, homogeneity) in live cells remains difficult to define. Here we present evidence that both synthetic and natural plasma membranes assume a wide range of lipid packing states with varying levels of molecular order. These states may be adapted and specifically tuned by cells during active cellular processes, as we show for stimulated insulin secretion. Most importantly, these states regulate both the partitioning of molecules between coexisting domains and the bioactivity of their constituent molecules, which we demonstrate for the ligand binding activity of the glycosphingolipid receptor GM1. These results confirm the complexity and flexibility of lipid-mediated membrane organization and reveal mechanisms by which this flexibility could be functionalized by cells. PMID:25905447

  17. Model for the dynamic responses of taste receptor cells to salty stimuli. I. Function of lipid bilayer membranes.

    PubMed

    Naito, M; Fuchikami, N; Sasaki, N; Kambara, T

    1991-06-01

    The dynamic response of the lipid bilayer membrane is studied theoretically using a microscopic model of the membrane. The time courses of membrane potential variations due to monovalent salt stimulation are calculated explicitly under various conditions. A set of equations describing the time evolution of membrane surface potential and diffusion potential is derived and solved numerically. It is shown that a rather simple membrane such as lipid bilayer has functions capable of reproducing the following properties of dynamic response observed in gustatory receptor potential. Initial transient depolarization does not occur under Ringer adaptation but does under water. It appears only for comparatively rapid flows of stimuli, the peak height of transient response is expressed by a power function of the flow rate, and the membrane potential gradually decreases after reaching its peak under long and strong stimulation. The dynamic responses in the present model arise from the differences between the time dependences in the surface potential phi s and the diffusion potential phi d across a membrane. Under salt stimulation phi d cannot immediately follow the variation in phi s because of the delay due to the charging up of membrane capacitance. It is suggested that lipid bilayer in the apical membrane is the most probable agency producing the initial phasic response to the stimulation. PMID:1873461

  18. Computational Investigation of the Effect of Lipid Membranes on Ion Permeation in Gramicidin A

    PubMed Central

    Setiadi, Jeffry; Kuyucak, Serdar

    2016-01-01

    Membrane proteins are embedded in a lipid bilayer and interact with the lipid molecules in subtle ways. This can be studied experimentally by examining the effect of different lipid bilayers on the function of membrane proteins. Understanding the causes of the functional effects of lipids is difficult to dissect experimentally but more amenable to a computational approach. Here we perform molecular dynamics simulations and free energy calculations to study the effect of two lipid types (POPC and NODS) on the conductance of the gramicidin A (gA) channel. A larger energy barrier is found for the K+ potential of mean force in gA embedded in POPC compared to that in NODS, which is consistent with the enhanced experimental conductance of cations in gA embedded in NODS. Further analysis of the contributions to the potential energy of K+ reveals that gA and water molecules in gA make similar contributions in both bilayers but there are significant differences between the two bilayers when the lipid molecules and interfacial waters are considered. It is shown that the stronger dipole moments of the POPC head groups create a thicker layer of interfacial waters with better orientation, which ultimately is responsible for the larger energy barrier in the K+ PMF in POPC. PMID:26999229

  19. Computational Investigation of the Effect of Lipid Membranes on Ion Permeation in Gramicidin A.

    PubMed

    Setiadi, Jeffry; Kuyucak, Serdar

    2016-01-01

    Membrane proteins are embedded in a lipid bilayer and interact with the lipid molecules in subtle ways. This can be studied experimentally by examining the effect of different lipid bilayers on the function of membrane proteins. Understanding the causes of the functional effects of lipids is difficult to dissect experimentally but more amenable to a computational approach. Here we perform molecular dynamics simulations and free energy calculations to study the effect of two lipid types (POPC and NODS) on the conductance of the gramicidin A (gA) channel. A larger energy barrier is found for the K⁺ potential of mean force in gA embedded in POPC compared to that in NODS, which is consistent with the enhanced experimental conductance of cations in gA embedded in NODS. Further analysis of the contributions to the potential energy of K⁺ reveals that gA and water molecules in gA make similar contributions in both bilayers but there are significant differences between the two bilayers when the lipid molecules and interfacial waters are considered. It is shown that the stronger dipole moments of the POPC head groups create a thicker layer of interfacial waters with better orientation, which ultimately is responsible for the larger energy barrier in the K⁺ PMF in POPC. PMID:26999229

  20. A C-terminal Membrane Anchor Affects the Interactions of Prion Proteins with Lipid Membranes*

    PubMed Central

    Chu, Nam K.; Shabbir, Waheed; Bove-Fenderson, Erin; Araman, Can; Lemmens-Gruber, Rosa; Harris, David A.; Becker, Christian F. W.

    2014-01-01

    Membrane attachment via a C-terminal glycosylphosphatidylinositol anchor is critical for conversion of PrPC into pathogenic PrPSc. Therefore the effects of the anchor on PrP structure and function need to be deciphered. Three PrP variants, including full-length PrP (residues 23–231, FL_PrP), N-terminally truncated PrP (residues 90–231, T_PrP), and PrP missing its central hydrophobic region (Δ105–125, ΔCR_PrP), were equipped with a C-terminal membrane anchor via a semisynthesis strategy. Analyses of the interactions of lipidated PrPs with phospholipid membranes demonstrated that C-terminal membrane attachment induces a different binding mode of PrP to membranes, distinct from that of non-lipidated PrPs, and influences the biochemical and conformational properties of PrPs. Additionally, fluorescence-based assays indicated pore formation by lipidated ΔCR_PrP, a variant that is known to be highly neurotoxic in transgenic mice. This finding was supported by using patch clamp electrophysiological measurements of cultured cells. These results provide new evidence for the role of the membrane anchor in PrP-lipid interactions, highlighting the importance of the N-terminal and the central hydrophobic domain in these interactions. PMID:25217642

  1. Maleimide-functionalized lipids that anchor polypeptides to lipid bilayers and membranes.

    PubMed

    Elliott, J T; Prestwich, G D

    2000-01-01

    Two maleimide-containing diacylglycerol derivatives were synthesized to permit the anchoring of short peptides and longer polypeptides to phospholipid bilayers and membranes. The maleimide was introduced at the site normally occupied by a phospholipid headgroup. The first lipid, the dipalmitoyl ester of 1-maleimido-2,3-propanediol, was developed as a membrane anchor for extracellular domains of transmembrane proteins. The second anchoring lipid, in which the 3-position contained a 6-aminohexanoate, was designed for convenient modification with amine-reactive reporter groups. Specifically, the NBD fluorophore, 7-nitrobenzo-2-oxa-1, 3-diazole-aminohexanoic-N-hydroxysuccinimide ester, was attached to give an fluorescent anchoring reagent. Next, these reagents were applied to the anchoring of a C-terminally cysteamine-modified 8 kDa polypeptide that comprises the extracellular N-terminal domain of the human thrombin receptor, a transmembrane protease-activated receptor (PAR-1). Gel filtration and fluorescence analysis showed that the fluorescent lipopolypeptide spontaneously inserted into preformed phospholipid vesicles, but it did not insert into whole cell membranes. In contrast, the dipalmitoyl derivative could only be reconstituted into artificial membranes by mixing the lipopolypeptide and phospholipid before vesicle formation. These results suggest that biophysical interactions governing the lipopolypeptide insertion into artificial and cellular membranes may differ. The thiol-reactive lipidating reagents should be valuable materials for studying the structure and function of peptides and polypeptides at phospholipid bilayer surfaces. PMID:11087332

  2. Tubular lipid membranes pulled from vesicles: Dependence of system equilibrium on lipid bilayer curvature

    NASA Astrophysics Data System (ADS)

    Golushko, I. Yu.; Rochal, S. B.

    2016-01-01

    Conditions of joint equilibrium and stability are derived for a spherical lipid vesicle and a tubular lipid membrane (TLM) pulled from this vesicle. The obtained equations establish relationships between the geometric and physical characteristics of the system and the external parameters, which have been found to be controllable in recent experiments. In particular, the proposed theory shows that, in addition to the pressure difference between internal and external regions of the system, the variable spontaneous average curvature of the lipid bilayer (forming the TLM) also influences the stability of the lipid tube. The conditions for stability of the cylindrical phase of TLMs after switching off the external force that initially formed the TLM from a vesicle are discussed. The loss of system stability under the action of a small axial force compressing the TLM is considered.

  3. Femtosecond crystallography of membrane proteins in the lipidic cubic phase

    PubMed Central

    Liu, Wei; Wacker, Daniel; Wang, Chong; Abola, Enrique; Cherezov, Vadim

    2014-01-01

    Despite recent technological advances in heterologous expression, stabilization and crystallization of membrane proteins (MPs), their structural studies remain difficult and require new transformative approaches. During the past two years, crystallization in lipidic cubic phase (LCP) has started gaining a widespread acceptance, owing to the spectacular success in high-resolution structure determination of G protein-coupled receptors (GPCRs) and to the introduction of commercial instrumentation, tools and protocols. The recent appearance of X-ray free-electron lasers (XFELs) has enabled structure determination from substantially smaller crystals than previously possible with minimal effects of radiation damage, offering new exciting opportunities in structural biology. The unique properties of LCP material have been exploited to develop special protocols and devices that have established a new method of serial femtosecond crystallography of MPs in LCP (LCP-SFX). In this method, microcrystals are generated in LCP and streamed continuously inside the same media across the intersection with a pulsed XFEL beam at a flow rate that can be adjusted to minimize sample consumption. Pioneering studies that yielded the first room temperature GPCR structures, using a few hundred micrograms of purified protein, validate the LCP-SFX approach and make it attractive for structure determination of difficult-to-crystallize MPs and their complexes with interacting partners. Together with the potential of femtosecond data acquisition to interrogate unstable intermediate functional states of MPs, LCP-SFX holds promise to advance our understanding of this biomedically important class of proteins. PMID:24914147

  4. Membrane potential and cancer progression

    PubMed Central

    Yang, Ming; Brackenbury, William J.

    2013-01-01

    Membrane potential (Vm), the voltage across the plasma membrane, arises because of the presence of different ion channels/transporters with specific ion selectivity and permeability. Vm is a key biophysical signal in non-excitable cells, modulating important cellular activities, such as proliferation and differentiation. Therefore, the multiplicities of various ion channels/transporters expressed on different cells are finely tuned in order to regulate the Vm. It is well-established that cancer cells possess distinct bioelectrical properties. Notably, electrophysiological analyses in many cancer cell types have revealed a depolarized Vm that favors cell proliferation. Ion channels/transporters control cell volume and migration, and emerging data also suggest that the level of Vm has functional roles in cancer cell migration. In addition, hyperpolarization is necessary for stem cell differentiation. For example, both osteogenesis and adipogenesis are hindered in human mesenchymal stem cells (hMSCs) under depolarizing conditions. Therefore, in the context of cancer, membrane depolarization might be important for the emergence and maintenance of cancer stem cells (CSCs), giving rise to sustained tumor growth. This review aims to provide a broad understanding of the Vm as a bioelectrical signal in cancer cells by examining several key types of ion channels that contribute to its regulation. The mechanisms by which Vm regulates cancer cell proliferation, migration, and differentiation will be discussed. In the long term, Vm might be a valuable clinical marker for tumor detection with prognostic value, and could even be artificially modified in order to inhibit tumor growth and metastasis. PMID:23882223

  5. Supported lipid bilayer membranes for water purification by reverse osmosis.

    PubMed

    Kaufman, Yair; Berman, Amir; Freger, Viatcheslav

    2010-05-18

    Some biological plasma membranes pass water with a permeability and selectivity largely exceeding those of commercial membranes for water desalination using specialized trans-membrane proteins aquaporins. However, highly selective transport of water through aquaporins is usually driven by an osmotic rather mechanical pressure, which is not as attractive from the engineering point of view. The feasibility of adopting biomimetic membranes for water purification driven by a mechanical pressure, i.e., filtration is explored in this paper. Toward this goal, it is proposed to use a commercial nanofiltration (NF) membrane as a support for biomimetic lipid bilayer membranes to render them robust enough to withstand the required pressures. It is shown in this paper for the first time that by properly tuning molecular interactions supported phospholipid bilayers (SPB) can be prepared on a commercial NF membrane. The presence of SPB on the surface was verified and quantified by several spectroscopic and microscopic techniques, which showed morphology close to the desired one with very few defects. As an ultimate test it is shown that hydraulic permeability of the SPB supported on the NF membrane (NTR-7450) approaches the values deduced from the typical osmotic permeabilities of intact continuous bilayers. This permeability was unaffected by the trans-membrane flow of water and by repeatedly releasing and reapplying a 10 bar pressure. Along with a parallel demonstration that aquaporins could be incorporated in a similar bilayer on mica, this demonstrates the feasibility of the proposed approach. The prepared SPB structure may be used as a platform for preparing biomimetic filtration membranes with superior performance based on aquaporins. The concept of SPBs on permeable substrates of the present type may also be useful in the future for studying transport of various molecules through trans-membrane proteins. PMID:20099798

  6. Effects of Dipole Potential Modifiers on Heterogenic Lipid Bilayers.

    PubMed

    Efimova, Svetlana S; Malev, Valery V; Ostroumova, Olga S

    2016-04-01

    In this work, we examine the ability of dipole modifiers, flavonoids, and RH dyes to affect the dipole potential (φ d) and phase separation in membranes composed of ternary mixtures of POPC with different sphingolipids and sterols. Changes in the steady-state conductance induced by cation-ionophore complexes have been measured to evaluate the changes in dipole potential of planar lipid bilayers. Confocal fluorescence microscopy has been employed to investigate lipid segregation in giant unilamellar vesicles. The effects of flavonoids on φ d depend on lipid composition and dipole modifier type. The effectiveness of RH dyes to increase φ d depends on sphingolipid type but is not influenced by sterol content. Tested modifiers lead to partial or complete disruption of gel domains in bilayers composed of POPC, sphingomyelin, and cholesterol. Substitution of cholesterol to ergosterol or 7-dehydrocholesterol leads to a loss of fluidizing effects of modifiers except phloretin. This may be due to various compositions of gel domains. The lack of influence of modifiers on phase scenario in vesicles composed of ternary mixtures of POPC, cholesterol, and phytosphingosine or sphinganine is related to an absence of gel-like phase. It was concluded that the membrane lateral heterogeneity affects the dipole-modifying abilities of the agents that influence the magnitude of φ d by intercalation into the bilayer and orientation of its own large dipole moments (phloretin and RH dyes). The efficacy of modifiers that do not penetrate deeply and affect φ d through water adsorption (phlorizin, quercetin, and myricetin) is not influenced by lateral heterogeneity of membrane. PMID:26454655

  7. Photopolymerization of Dienoyl Lipids Creates Planar Supported Poly(lipid) Membranes with Retained Fluidity.

    PubMed

    Orosz, Kristina S; Jones, Ian W; Keogh, John P; Smith, Christopher M; Griffin, Kaitlyn R; Xu, Juhua; Comi, Troy J; Hall, H K; Saavedra, S Scott

    2016-02-16

    Polymerization of substrate-supported bilayers composed of dienoylphosphatidylcholine (PC) lipids is known to greatly enhance their chemical and mechanical stability; however, the effects of polymerization on membrane fluidity have not been investigated. Here planar supported lipid bilayers (PSLBs) composed of dienoyl PCs on glass substrates were examined to assess the degree to which UV-initiated polymerization affects lateral lipid mobility. Fluorescence recovery after photobleaching (FRAP) was used to measure the diffusion coefficients (D) and mobile fractions of rhodamine-DOPE in unpolymerized and polymerized PSLBs composed of bis-sorbyl phosphatidylcholine (bis-SorbPC), mono-sorbyl-phosphatidylcholine (mono-SorbPC), bis-dienoyl-phosphatidylcholine (bis-DenPC), and mono-dienoyl phosphatidylcholine (mono-DenPC). Polymerization was performed in both the Lα and Lβ phase for each lipid. In all cases, polymerization reduced membrane fluidity; however, measurable lateral diffusion was retained which is attributed to a low degree of polymerization. The D values for sorbyl lipids were less than those of the denoyl lipids; this may be a consequence of the distal location of polymerizable group in the sorbyl lipids which may facilitate interleaflet bonding. The D values measured after polymerization were 0.1-0.8 of those measured before polymerization, a range that corresponds to fluidity intermediate between that of a Lα phase and a Lβ phase. This D range is comparable to ratios of D values reported for liquid-disordered (Ld) and liquid-ordered (Lo) lipid phases and indicates that the effect of UV polymerization on lateral diffusion in a dienoyl PSLB is similar to the transition from a Ld phase to a Lo phase. The partial retention of fluidity in UV-polymerized PSLBs, their enhanced stability, and the activity of incorporated transmembrane proteins and peptides is discussed. PMID:26794208

  8. Exploiting lipopolysaccharide-induced deformation of lipid bilayers to modify membrane composition and generate two-dimensional geometric membrane array patterns

    SciTech Connect

    Adams, Peter G.; Swingle, Kirstie L.; Paxton, Walter F.; Nogan, John J.; Stromberg, Loreen R.; Firestone, Millicent A.; Mukundan, Harshini; Montaño, Gabriel A.

    2015-05-27

    Supported lipid bilayers have proven effective as model membranes for investigating biophysical processes and in development of sensor and array technologies. The ability to modify lipid bilayers after their formation and in situ could greatly advance membrane technologies, but is difficult via current state-of-the-art technologies. Here we demonstrate a novel method that allows the controlled post-formation processing and modification of complex supported lipid bilayer arrangements, under aqueous conditions. We exploit the destabilization effect of lipopolysaccharide, an amphiphilic biomolecule, interacting with lipid bilayers to generate voids that can be backfilled to introduce desired membrane components. We further demonstrate that when used in combination with a single, traditional soft lithography process, it is possible to generate hierarchically-organized membrane domains and microscale 2-D array patterns of domains. Significantly, this technique can be used to repeatedly modify membranes allowing iterative control over membrane composition. This approach expands our toolkit for functional membrane design, with potential applications for enhanced materials templating, biosensing and investigating lipid-membrane processes.

  9. Exploiting lipopolysaccharide-induced deformation of lipid bilayers to modify membrane composition and generate two-dimensional geometric membrane array patterns

    PubMed Central

    Adams, Peter G.; Swingle, Kirstie L.; Paxton, Walter F.; Nogan, John J.; Stromberg, Loreen R.; Firestone, Millicent A.; Mukundan, Harshini; Montaño, Gabriel A.

    2015-01-01

    Supported lipid bilayers have proven effective as model membranes for investigating biophysical processes and in development of sensor and array technologies. The ability to modify lipid bilayers after their formation and in situ could greatly advance membrane technologies, but is difficult via current state-of-the-art technologies. Here we demonstrate a novel method that allows the controlled post-formation processing and modification of complex supported lipid bilayer arrangements, under aqueous conditions. We exploit the destabilization effect of lipopolysaccharide, an amphiphilic biomolecule, interacting with lipid bilayers to generate voids that can be backfilled to introduce desired membrane components. We further demonstrate that when used in combination with a single, traditional soft lithography process, it is possible to generate hierarchically-organized membrane domains and microscale 2-D array patterns of domains. Significantly, this technique can be used to repeatedly modify membranes allowing iterative control over membrane composition. This approach expands our toolkit for functional membrane design, with potential applications for enhanced materials templating, biosensing and investigating lipid-membrane processes. PMID:26015293

  10. Exploiting lipopolysaccharide-induced deformation of lipid bilayers to modify membrane composition and generate two-dimensional geometric membrane array patterns

    DOE PAGESBeta

    Adams, Peter G.; Swingle, Kirstie L.; Paxton, Walter F.; Nogan, John J.; Stromberg, Loreen R.; Firestone, Millicent A.; Mukundan, Harshini; Montaño, Gabriel A.

    2015-05-27

    Supported lipid bilayers have proven effective as model membranes for investigating biophysical processes and in development of sensor and array technologies. The ability to modify lipid bilayers after their formation and in situ could greatly advance membrane technologies, but is difficult via current state-of-the-art technologies. Here we demonstrate a novel method that allows the controlled post-formation processing and modification of complex supported lipid bilayer arrangements, under aqueous conditions. We exploit the destabilization effect of lipopolysaccharide, an amphiphilic biomolecule, interacting with lipid bilayers to generate voids that can be backfilled to introduce desired membrane components. We further demonstrate that when usedmore » in combination with a single, traditional soft lithography process, it is possible to generate hierarchically-organized membrane domains and microscale 2-D array patterns of domains. Significantly, this technique can be used to repeatedly modify membranes allowing iterative control over membrane composition. This approach expands our toolkit for functional membrane design, with potential applications for enhanced materials templating, biosensing and investigating lipid-membrane processes.« less

  11. Electrochemical characterization of bilayer lipid membrane-semiconductor junctions

    SciTech Connect

    Zhao, Xiao Kang; Baral, S.; Fendler, J.H. )

    1990-03-08

    Three different systems of glyceryl monooleate (GMO), bilayer lipid membrane (BLM) supported semiconductor particles have been prepared and characterized. A single composition of particulate semiconductor deposited only on one side of the BLM constituted system A, two different compositions of particulate semiconductors sequentially deposited on the same side of the BLM represented system B, and two different compositions of particulate semiconductors deposited on the opposite sides of the BLM made up system C.

  12. Nonbilayer lipids affect peripheral and integral membrane proteins via changes in the lateral pressure profile.

    PubMed

    van den Brink-van der Laan, Els; Killian, J Antoinette; de Kruijff, Ben

    2004-11-01

    Nonbilayer lipids can be defined as cone-shaped lipids with a preference for nonbilayer structures with a negative curvature, such as the hexagonal phase. All membranes contain these lipids in large amounts. Yet, the lipids in biological membranes are organized in a bilayer. This leads to the question: what is the physiological role of nonbilayer lipids? Different models are discussed in this review, with a focus on the lateral pressure profile within the membrane. Based on this lateral pressure model, predictions can be made for the effect of nonbilayer lipids on peripheral and integral membrane proteins. Recent data on the catalytic domain of Leader Peptidase and the potassium channel KcsA are discussed in relation to these predictions and in relation to the different models on the function of nonbilayer lipids. The data suggest a general mechanism for the interaction between nonbilayer lipids and membrane proteins via the membrane lateral pressure. PMID:15519321

  13. Interaction of pyridinium bis-retinoid (A2E) with bilayer lipid membranes.

    PubMed

    Sokolov, V S; Sokolenko, E A; Sokolov, A V; Dontsov, A E; Chizmadzhev, Y A; Ostrovsky, M A

    2007-02-01

    The accumulation of lipofuscin granules within the retinal pigment epithelium (RPE) cells is correlated with the progression of age-related macular degeneration. One of the fluorophores contained in lipofiscin granules is pyridinium bis-retinoid (A2E). To test its membrane-toxic effect, the interaction of A2E with bilayer lipid membranes (BLM) was studied. The incorporation of charged A2E molecules into the membranes has been detected as a change of either zeta-potential of multilayer liposomes or boundary potential of BLM. It was shown that the presence of up to 25mol% of A2E did not destabilize the bilayers made of saturated phosphatidylcholine (PC). However, the destabilizing effect became very significant when BLM contained negatively charged lipids such as cardiolipin or phosphatidylserine. The electrical breakdown measurements revealed that the A2E-induced decrease of BLM stability was primarily associated with the growing probability of lipid pore formation. It was found from the measurements of boundary potential of BLM that exposure of A2E to light initiates its transformation into at least two products. One of them is epoxy-A2E, which, being hydrophilic, moves from the membrane into water solution. The other product is a non-identified hydrophobic substance. Illumination of A2E-containing BLM made from unsaturated PC by visible light caused the membrane damage presumably due to oxidation of these lipids by singlet oxygen generated by excited A2E molecules. However, this effect was very weak compared to the effect of known photosensitizers. The illumination of BLM with A2E also leads to the damage of gramicidin incorporated into the membrane, as was detected by measuring the conductance of channels formed by this peptide. PMID:17070694

  14. Forming lipid bilayer membrane arrays on micropatterned polyelectrolyte film surfaces.

    PubMed

    Zhang, Ying; Wang, Lei; Wang, Xuejing; Qi, Guodong; Han, Xiaojun

    2013-07-01

    A novel method of forming lipid bilayer membrane arrays on micropatterned polyelectrolyte film surfaces is introduced. Polyelectrolyte films were fabricated by the layer-by-layer technique on a silicon oxide surface modified with a 3-aminopropyltriethoxysilane (APTES) monolayer. The surface pK(a) value of the APTES monolayer was determined by cyclic voltammetry to be approximately 5.61, on the basis of which a pH value of 2.0 was chosen for layer-by-layer assembly. Micropatterned polyelectrolyte films were obtained by deep-UV (254 nm) photolysis though a mask. Absorbed fluorescent latex beads were used to visualize the patterned surfaces. Lipid bilayer arrays were fabricated on the micropatterned surfaces by immersing the patterned substrates into a solution containing egg phosphatidylcholine vesicles. Fluorescence recovery after photobleaching studies yielded a lateral diffusion coefficient for probe molecules of 1.31±0.17 μm(2) s(-1) in the bilayer region, and migration of the lipid NBD PE in bilayer lipid membrane arrays was observed in an electric field. PMID:23695862

  15. Formation of functional cell membrane domains: the interplay of lipid- and protein-mediated interactions.

    PubMed Central

    Harder, Thomas

    2003-01-01

    Numerous cell membrane associated processes, including signal transduction, membrane sorting, protein processing and virus trafficking take place in membrane subdomains. Protein-protein interactions provide the frameworks necessary to generate biologically functional membrane domains. For example, coat proteins define membrane areas destined for sorting processes, viral proteins self-assemble to generate a budding virus, and adapter molecules organize multimolecular signalling assemblies, which catalyse downstream reactions. The concept of raft lipid-based membrane domains provides a different principle for compartmentalization and segregation of membrane constituents. Accordingly, rafts are defined by the physical properties of the lipid bilayer and function by selective partitioning of membrane lipids and proteins into membrane domains of specific phase behaviour and lipid packing. Here, I will discuss the interplay of these independent principles of protein scaffolds and raft lipid microdomains leading to the generation of biologically functional membrane domains. PMID:12803918

  16. Fractional hereditariness of lipid membranes: Instabilities and linearized evolution.

    PubMed

    Deseri, L; Pollaci, P; Zingales, M; Dayal, K

    2016-05-01

    In this work lipid ordering phase changes arising in planar membrane bilayers is investigated both accounting for elasticity alone and for effective viscoelastic response of such assemblies. The mechanical response of such membranes is studied by minimizing the Gibbs free energy which penalizes perturbations of the changes of areal stretch and their gradients only (Deseri and Zurlo, 2013). As material instabilities arise whenever areal stretches characterizing homogeneous configurations lie inside the spinoidal zone of the free energy density, bifurcations from such configurations are shown to occur as oscillatory perturbations of the in-plane displacement. Experimental observations (Espinosa et al., 2011) show a power-law in-plane viscous behavior of lipid structures allowing for an effective viscoelastic behavior of lipid membranes, which falls in the framework of Fractional Hereditariness. A suitable generalization of the variational principle invoked for the elasticity is applied in this case, and the corresponding Euler-Lagrange equation is found together with a set of boundary and initial conditions. Separation of variables allows for showing how Fractional Hereditariness owes bifurcated modes with a larger number of spatial oscillations than the corresponding elastic analog. Indeed, the available range of areal stresses for material instabilities is found to increase with respect to the purely elastic case. Nevertheless, the time evolution of the perturbations solving the Euler-Lagrange equation above exhibits time-decay and the large number of spatial oscillation slowly relaxes, thereby keeping the features of a long-tail type time-response. PMID:26897568

  17. On the Importance of Hydrodynamic Interactions in Lipid Membrane Formation

    PubMed Central

    Ando, Tadashi; Skolnick, Jeffrey

    2013-01-01

    Hydrodynamic interactions (HI) give rise to collective motions between molecules, which are known to be important in the dynamics of random coil polymers and colloids. However, their role in the biological self-assembly of many molecule systems has not been investigated. Here, using Brownian dynamics simulations, we evaluate the importance of HI on the kinetics of self-assembly of lipid membranes. One-thousand coarse-grained lipid molecules in periodic simulation boxes were allowed to assemble into stable bilayers in the presence and absence of intermolecular HI. Hydrodynamic interactions reduce the monomer-monomer association rate by 50%. In contrast, the rate of association of lipid clusters is much faster in the presence of intermolecular HI. In fact, with intermolecular HI, the membrane self-assembly rate is 3–10 times faster than that without intermolecular HI. We introduce an analytical model to describe the size dependence of the diffusive encounter rate of particle clusters, which can qualitatively explain our simulation results for the early stage of the membrane self-assembly process. These results clearly suggest that HI greatly affects the kinetics of self-assembly and that simulations without HI will significantly underestimate the kinetic parameters of such processes. PMID:23332062

  18. Lipid membrane-mediated attraction between curvature inducing objects.

    PubMed

    van der Wel, Casper; Vahid, Afshin; Šarić, Anđela; Idema, Timon; Heinrich, Doris; Kraft, Daniela J

    2016-01-01

    The interplay of membrane proteins is vital for many biological processes, such as cellular transport, cell division, and signal transduction between nerve cells. Theoretical considerations have led to the idea that the membrane itself mediates protein self-organization in these processes through minimization of membrane curvature energy. Here, we present a combined experimental and numerical study in which we quantify these interactions directly for the first time. In our experimental model system we control the deformation of a lipid membrane by adhering colloidal particles. Using confocal microscopy, we establish that these membrane deformations cause an attractive interaction force leading to reversible binding. The attraction extends over 2.5 times the particle diameter and has a strength of three times the thermal energy (-3.3 kBT). Coarse-grained Monte-Carlo simulations of the system are in excellent agreement with the experimental results and prove that the measured interaction is independent of length scale. Our combined experimental and numerical results reveal membrane curvature as a common physical origin for interactions between any membrane-deforming objects, from nanometre-sized proteins to micrometre-sized particles. PMID:27618764

  19. Liquid membrane potential in nonisothermal systems.

    PubMed Central

    Scibona, G; Fabiani, C; Scuppa, B; Danesi, P R

    1976-01-01

    Electrical membrane potential equations for liquid ion exchange membranes, characterized by the presence of uncharged associated species and by exclusion of co-ions (no electrolyte uptake) have been derived. The irreversible thermodynamic theories already developed for solid membranes with fixed charged site density have been extended to include the different physicochemical aspects of the liquid membranes. To this purpose the dissipation function has been written with reference to the fluxes of all the species present in the membrane. It has been found that the mobile charged site, the counterions, and the uncharged associated species contribute to the electrical membrane potential through their phenomenological coefficients. The electrical membrane potential equations have been integrated in isothermal and nonisothermal conditions for monoionic and biionic systems. The theoretical predictions have been experimentally tested by studying the electrical potential of liquid membranes formed with solutions of tetraheptylammonium salts in omicron-dichlorobenzene. PMID:1276391

  20. The fusogenic lipid phosphatidic acid promotes the biogenesis of mitochondrial outer membrane protein Ugo1

    PubMed Central

    Keller, Michael; Taskin, Asli A.; Horvath, Susanne E.; Guan, Xue Li; Prinz, Claudia; Opalińska, Magdalena; Zorzin, Carina; van der Laan, Martin; Wenk, Markus R.; Schubert, Rolf; Wiedemann, Nils; Holzer, Martin

    2015-01-01

    Import and assembly of mitochondrial proteins depend on a complex interplay of proteinaceous translocation machineries. The role of lipids in this process has been studied only marginally and so far no direct role for a specific lipid in mitochondrial protein biogenesis has been shown. Here we analyzed a potential role of phosphatidic acid (PA) in biogenesis of mitochondrial proteins in Saccharomyces cerevisiae. In vivo remodeling of the mitochondrial lipid composition by lithocholic acid treatment or by ablation of the lipid transport protein Ups1, both leading to an increase of mitochondrial PA levels, specifically stimulated the biogenesis of the outer membrane protein Ugo1, a component of the mitochondrial fusion machinery. We reconstituted the import and assembly pathway of Ugo1 in protein-free liposomes, mimicking the outer membrane phospholipid composition, and found a direct dependency of Ugo1 biogenesis on PA. Thus, PA represents the first lipid that is directly involved in the biogenesis pathway of a mitochondrial membrane protein. PMID:26347140

  1. A macroscopic H+ and Cl- ions pump via reconstitution of EcClC membrane proteins in lipidic cubic mesophases.

    PubMed

    Speziale, Chiara; Salvati Manni, Livia; Manatschal, Cristina; Landau, Ehud M; Mezzenga, Raffaele

    2016-07-01

    Functional reconstitution of membrane proteins within lipid bilayers is crucial for understanding their biological function in living cells. While this strategy has been extensively used with liposomes, reconstitution of membrane proteins in lipidic cubic mesophases presents significant challenges related to the structural complexity of the lipid bilayer, organized on saddle-like minimal surfaces. Although reconstitution of membrane proteins in lipidic cubic mesophases plays a prominent role in membrane protein crystallization, nanotechnology, controlled drug delivery, and pathology of diseased cells, little is known about the molecular mechanism of protein reconstitution and about how transport properties of the doped mesophase mirror the original molecular gating features of the reconstituted membrane proteins. In this work we design a general strategy to demonstrate correct functional reconstitution of active and selective membrane protein transporters in lipidic mesophases, exemplified by the bacterial ClC exchanger from Escherichia coli (EcClC) as a model ion transporter. We show that its correct reconstitution in the lipidic matrix can be used to generate macroscopic proton and chloride pumps capable of selectively transporting charges over the length scale of centimeters. By further exploiting the coupled chloride/proton exchange of this membrane protein and by combining parallel or antiparallel chloride and proton gradients, we show that the doped mesophase can operate as a charge separation device relying only on the reconstituted EcClC protein and an external bias potential. These results may thus also pave the way to possible applications in supercapacitors, ion batteries, and molecular pumps. PMID:27313210

  2. Lipid-Free Antigen B Subunits from Echinococcus granulosus: Oligomerization, Ligand Binding, and Membrane Interaction Properties

    PubMed Central

    Silva-Álvarez, Valeria; Franchini, Gisela R.; Pórfido, Jorge L.; Kennedy, Malcolm W.; Ferreira, Ana M.; Córsico, Betina

    2015-01-01

    Background The hydatid disease parasite Echinococcus granulosus has a restricted lipid metabolism, and needs to harvest essential lipids from the host. Antigen B (EgAgB), an abundant lipoprotein of the larval stage (hydatid cyst), is thought to be important in lipid storage and transport. It contains a wide variety of lipid classes, from highly hydrophobic compounds to phospholipids. Its protein component belongs to the cestode-specific Hydrophobic Ligand Binding Protein family, which includes five 8-kDa isoforms encoded by a multigene family (EgAgB1-EgAgB5). How lipid and protein components are assembled into EgAgB particles remains unknown. EgAgB apolipoproteins self-associate into large oligomers, but the functional contribution of lipids to oligomerization is uncertain. Furthermore, binding of fatty acids to some EgAgB subunits has been reported, but their ability to bind other lipids and transfer them to acceptor membranes has not been studied. Methodology/Principal Findings Lipid-free EgAgB subunits obtained by reverse-phase HPLC were used to analyse their oligomerization, ligand binding and membrane interaction properties. Size exclusion chromatography and cross-linking experiments showed that EgAgB8/2 and EgAgB8/3 can self-associate, suggesting that lipids are not required for oligomerization. Furthermore, using fluorescent probes, both subunits were found to bind fatty acids, but not cholesterol analogues. Analysis of fatty acid transfer to phospholipid vesicles demonstrated that EgAgB8/2 and EgAgB8/3 are potentially capable of transferring fatty acids to membranes, and that the efficiency of transfer is dependent on the surface charge of the vesicles. Conclusions/Significance We show that EgAgB apolipoproteins can oligomerize in the absence of lipids, and can bind and transfer fatty acids to phospholipid membranes. Since imported fatty acids are essential for Echinococcus granulosus, these findings provide a mechanism whereby EgAgB could engage in lipid

  3. The assembly and use of tethered bilayer lipid membranes (tBLMs).

    PubMed

    Cranfield, Charles; Carne, Sonia; Martinac, Boris; Cornell, Bruce

    2015-01-01

    Because they are firmly held in place, tethered bilayer lipid membranes (tBLMs) are considerably more robust than supported lipid bilayers such as black lipid membranes (BLMs) (Cornell et al. Nature 387(6633): 580-583, 1997). Here we describe the procedures required to assemble and test tethered lipid bilayers that can incorporate various lipid species, peptides, and ion channel proteins. PMID:25331126

  4. Alteration of macrophage membrane lipids following processing of bacterial peptidoglycan

    SciTech Connect

    Polanski, M.; Gray, G.R.

    1986-03-01

    As part of the continuing investigation into the role played by macrophages in antigen presentation and bacterial adjuvant activation, the authors have examined the metabolites produced by macrophages after encounter with peptidoglycan. Peptidoglycan was chosen because it contains N-acetyl-muramyl-L-alanyl-D-isoglutamine (muramyl dipeptide), a known adjuvant whose primary target cell is the macrophage. In previous work, the authors established that a series of muramyl dipeptide-like glycopeptides was released into the medium following phagocytosis of peptidoglycan by a macrophage cell line. Here the authors report on the finding that, additionally, a membrane lipid has been covalently altered by the addition of a peptidoglycan fragment. Bacillus subtilis cell walls which had been radiolabeled in their muramic acid, glucosamine and alanine residues, were incubated with the murine macrophage cell line RAW264. Using standard lipid extraction procedures, a lipid was isolated and found to contain equal molar ratios of alanine, glutamic acid and diaminopimelic acid. Since lipidated peptidoglycan peptides have been shown to be immunoactivators, the isolated lipid derivative may serve as a signal for interactions with other lymphocytes.

  5. How Tolerant are Membrane Simulations with Mismatch in Area per Lipid between Leaflets?

    PubMed

    Park, Soohyung; Beaven, Andrew H; Klauda, Jeffery B; Im, Wonpil

    2015-07-14

    Difficulties in estimating the correct number of lipids in each leaflet of complex bilayer membrane simulation systems make it inevitable to introduce a mismatch in lipid packing (i.e., area per lipid) and thus alter the lateral pressure of each leaflet. To investigate potential impacts of such mismatch on simulation results, we performed molecular dynamics simulations of saturated and monounsaturated lipid bilayers with and without gramicidin A or WALP23 at various mismatches by adjusting the number of lipids in the lower leaflet from no mismatch to a 25% reduction compared to that in the upper leaflet. All simulations were stable under the constant pressure barostat, but the mismatch induces asymmetric lipid packing between the leaflets, so that the upper leaflet becomes more ordered, and the lower leaflet becomes less ordered. The mismatch impacts on various bilayer properties are mild up to 5-10% mismatch, and bilayers with fully saturated chains appear to be more prone to these impacts than those with unsaturated tails. The nonvanishing leaflet surface tensions and the free energy derivatives with respect to the bilayer curvature indicate that the bilayer would be energetically unstable in the presence of mismatch. We propose a quantitative criterion for allowable mismatch based on the energetics derived from a continuum elastic model, which grows as a square root of the number of the lipids in the system. On the basis of this criterion, we infer that the area per lipid mismatch up to 5% would be tolerable in various membrane simulations of reasonable all-atom system sizes (40-160 lipids per leaflet). PMID:26575780

  6. 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

  7. Phospholipid-cationic lipid interactions: influences on membrane and vesicle properties.

    PubMed

    Campbell, R B; Balasubramanian, S V; Straubinger, R M

    2001-05-01

    Liposomes composed of synthetic dialkyl cationic lipids and zwitterionic phospholipids such as dioleoylphosphatidylethanolamine have been studied extensively as vehicles for gene delivery, but the broader potentials of these cationic liposomes for drug delivery have not. An understanding of phospholipid-cationic lipid interactions is essential for rational development of this potential. We evaluated the effect of the cationic lipid DOTAP (N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium) on liposome physical properties such as size and membrane domain structure. DSC (differential scanning calorimetry) showed progressive decrease and broadening of the phase transition temperature of dipalmitoylphosphatidylcholine (DPPC) with increasing fraction of DOTAP, in the range of 0.4-20 mol%. Laurdan (6-dodecanolyldimethylamino-naphthalene), a fluorescent probe of membrane domain structure, showed that DOTAP and DPPC remained miscible at all ratios tested. DOTAP reduced the size of spontaneously-forming PC-containing liposomes, regardless of the acyl chain length and degree of saturation. The anionic lipid DOPG (dioleoylphosphatidylglycerol) had similar effects on DPPC membrane fluidity and size. However, DOTAP/DOPC (50/50) vesicles were taken up avidly by OVCAR-3 human ovarian tumor cells, in contrast to DOPG/DOPC (50/50) liposomes. Overall, DOTAP exerts potent effects on bilayer physical properties, and may provide advantages for drug delivery. PMID:11334622

  8. Evidence for a discrete charge effect within lipid bilayer membranes.

    PubMed Central

    Wang, C C; Bruner, L J

    1978-01-01

    A high amplitude voltage step technique has been used to meausre the surface density of dipicrylamine anions adsorbed at the surfaces of lipid bilayer membranes. Accompanying low amplitude measurements have determined the relaxation time for transient current flow across the membranes, a parameter governed by the height of the central energy barrier which dipicrylamine anions must cross in moving from one membrane surface to the other. Measured relaxation times and surface charge densities have been related by a quasi-continuum model of the discrete charge effect, which predicts that the membrane central barrier height will increase with increasing density of adsorbed surface charge. The experimentally determined relationship is in satisfactory agreement with the predictions of the model. The model does not provide a complete description of the membrane/solution interface, however, because it cannot be applied to the description of previously measured isotherms for the adsorption of dipicrylamine anions onto bilayer membranes surfaces. Possible reasons for this discrepancy are discussed. PMID:737286

  9. Fluid lipid membranes: from differential geometry to curvature stresses.

    PubMed

    Deserno, Markus

    2015-01-01

    A fluid lipid membrane transmits stresses and torques that are fully determined by its geometry. They can be described by a stress- and torque-tensor, respectively, which yield the force or torque per length through any curve drawn on the membrane's surface. In the absence of external forces or torques the surface divergence of these tensors vanishes, revealing them as conserved quantities of the underlying Euler-Lagrange equation for the membrane's shape. This review provides a comprehensive introduction into these concepts without assuming the reader's familiarity with differential geometry, which instead will be developed as needed, relying on little more than vector calculus. The Helfrich Hamiltonian is then introduced and discussed in some depth. By expressing the quest for the energy-minimizing shape as a functional variation problem subject to geometric constraints, as proposed by Guven (2004), stress- and torque-tensors naturally emerge, and their connection to the shape equation becomes evident. How to reason with both tensors is then illustrated with a number of simple examples, after which this review concludes with four more sophisticated applications: boundary conditions for adhering membranes, corrections to the classical micropipette aspiration equation, membrane buckling, and membrane mediated interactions. PMID:24835737

  10. A fluctuating elastic plate and a cell model for lipid membranes

    NASA Astrophysics Data System (ADS)

    Liang, Xiaojun; Purohit, Prashant K.

    2016-05-01

    The thermal fluctuations of lipid bi-layer membranes are key to their interaction with cellular components as well as the measurement of their mechanical properties. Typically, membrane fluctuations are analyzed by decomposing into normal modes or by molecular simulations. Here we propose two new approaches to calculate the partition function of a membrane. In the first approach we view the membrane as a fluctuating von Karman plate and discretize it into triangular elements. We express its energy as a function of nodal displacements, and then compute the partition function and co-variance matrix using Gaussian integrals. We recover well-known results for the dependence of the projected area of the membrane on the applied tension and recent simulation results on the dependence of membrane free energy on geometry, spontaneous curvature and tension. As new applications we compute the fluctuations of the membrane of a malaria infected cell and analyze the effects of boundary conditions on fluctuations. Our second approach is based on the cell model of Lennard-Jones and Devonshire. This model, which was developed for liquids, assumes that each molecule fluctuates within a cell on which a potential is imposed by all the surrounding molecules. We adapt the cell model to a lipid membrane by recognizing that it is a 2D liquid with the ability to deform out of plane whose energetic penalty must be factored into the partition function of a cell. We show, once again, that some results on membrane fluctuations can be recovered using this new cell model. However, unlike some well established results, our cell model gives an entropy that scales with the number of molecules in a membrane. Our model makes predictions about the heat capacity of the membrane that can be tested in experiments.