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Sample records for lipid membrane investigation

  1. Tethered bilayer lipid membranes (tBLMs): interest and applications for biological membrane investigations.

    PubMed

    Rebaud, Samuel; Maniti, Ofelia; Girard-Egrot, Agnès P

    2014-12-01

    Biological membranes play a central role in the biology of the cell. They are not only the hydrophobic barrier allowing separation between two water soluble compartments but also a supra-molecular entity that has vital structural functions. Notably, they are involved in many exchange processes between the outside and inside cellular spaces. Accounting for the complexity of cell membranes, reliable models are needed to acquire current knowledge of the molecular processes occurring in membranes. To simplify the investigation of lipid/protein interactions, the use of biomimetic membranes is an approach that allows manipulation of the lipid composition of specific domains and/or the protein composition, and the evaluation of the reciprocal effects. Since the middle of the 80's, lipid bilayer membranes have been constantly developed as models of biological membranes with the ultimate goal to reincorporate membrane proteins for their functional investigation. In this review, after a brief description of the planar lipid bilayers as biomimetic membrane models, we will focus on the construction of the tethered Bilayer Lipid Membranes, the most promising model for efficient membrane protein reconstitution and investigation of molecular processes occurring in cell membranes. Copyright © 2014 Elsevier Masson SAS. All rights reserved.

  2. Direct affinity of dopamine to lipid membranes investigated by Nuclear Magnetic Resonance spectroscopy.

    PubMed

    Matam, Yashasvi; Ray, Bruce D; Petrache, Horia I

    2016-04-08

    Dopamine, a naturally occurring neurotransmitter, plays an important role in the brain's reward system and acts on sensory receptors in the brain. Neurotransmitters are contained in lipid membraned vesicles and are released by exocytosis. All neurotransmitters interact with transport and receptor proteins in glial cells, on neuronal dendrites, and at the axonal button, and also must interact with membrane lipids. However, the extent of direct interaction between lipid membranes in the absence of receptors and transport proteins has not been extensively investigated. In this report, we use UV and NMR spectroscopy to determine the affinity and the orientation of dopamine interacting with lipid vesicles made of either phosphatidylcholine (PC) or phosphatidylserine (PS) lipids which are primary lipid components of synaptic vesicles. We quantify the interaction of dopamine's aromatic ring with lipid membranes using our newly developed method that involves reference spectra in hydrophobic environments. Our measurements show that dopamine interacts with lipid membranes primarily through the aromatic side opposite to the hydroxyl groups, with this aromatic side penetrating deeper into the hydrophobic region of the membrane. Since dopamine's activity involves its release into extracellular space, we have used our method to also investigate dopamine's release from lipid vesicles. We find that dopamine trapped inside PC and PS vesicles is released into the external solution despite its affinity to membranes. This result suggests that dopamine's interaction with lipid membranes is complex and involves both binding as well as permeation through lipid bilayers, a combination that could be an effective trigger for apoptosis of dopamine-generating cells.

  3. Cell-sized asymmetric lipid vesicles facilitate the investigation of asymmetric membranes

    NASA Astrophysics Data System (ADS)

    Kamiya, Koki; Kawano, Ryuji; Osaki, Toshihisa; Akiyoshi, Kazunari; Takeuchi, Shoji

    2016-09-01

    Asymmetric lipid giant vesicles have been used to model the biochemical reactions in cell membranes. However, methods for producing asymmetric giant vesicles lead to the inclusion of an organic solvent layer that affects the mechanical and physical characteristics of the membrane. Here we describe the formation of asymmetric giant vesicles that include little organic solvent, and use them to investigate the dynamic responses of lipid molecules in the vesicle membrane. We formed the giant vesicles via the inhomogeneous break-up of a lipid microtube generated by applying a jet flow to an asymmetric planar lipid bilayer. The asymmetric giant vesicles showed a lipid flip-flop behaviour in the membrane, superficially similar to the lipid flip-flop activity observed in apoptotic cells. In vitro synthesis of membrane proteins into the asymmetric giant vesicles revealed that the lipid asymmetry in bilayer membranes improves the reconstitution ratio of membrane proteins. Our asymmetric giant vesicles will be useful in elucidating lipid-lipid and lipid-membrane protein interactions involved in the regulation of cellular functions.

  4. Cell-sized asymmetric lipid vesicles facilitate the investigation of asymmetric membranes.

    PubMed

    Kamiya, Koki; Kawano, Ryuji; Osaki, Toshihisa; Akiyoshi, Kazunari; Takeuchi, Shoji

    2016-09-01

    Asymmetric lipid giant vesicles have been used to model the biochemical reactions in cell membranes. However, methods for producing asymmetric giant vesicles lead to the inclusion of an organic solvent layer that affects the mechanical and physical characteristics of the membrane. Here we describe the formation of asymmetric giant vesicles that include little organic solvent, and use them to investigate the dynamic responses of lipid molecules in the vesicle membrane. We formed the giant vesicles via the inhomogeneous break-up of a lipid microtube generated by applying a jet flow to an asymmetric planar lipid bilayer. The asymmetric giant vesicles showed a lipid flip-flop behaviour in the membrane, superficially similar to the lipid flip-flop activity observed in apoptotic cells. In vitro synthesis of membrane proteins into the asymmetric giant vesicles revealed that the lipid asymmetry in bilayer membranes improves the reconstitution ratio of membrane proteins. Our asymmetric giant vesicles will be useful in elucidating lipid-lipid and lipid-membrane protein interactions involved in the regulation of cellular functions.

  5. UV-Visible and Infrared Methods for Investigating Lipid-Rhodopsin Membrane Interactions

    PubMed Central

    Brown, Michael F.

    2017-01-01

    Summary Experimental UV-visible and Fourier transform infrared (FTIR) spectroscopic methods are described for characterizing lipid-protein interactions for the example of rhodopsin in a membrane bilayer environment. The combined use of FTIR and UV-visible difference spectroscopy monitors the structural and functional changes during rhodopsin activation. Such studies investigate how membrane lipids stabilize the various rhodopsin photoproducts, analogous to mutating the protein. Interpretation of the results entails a non-specific flexible surface model for explaining the role of membrane lipid-protein interactions in biological functions. PMID:22976026

  6. UV-visible and infrared methods for investigating lipid-rhodopsin membrane interactions.

    PubMed

    Brown, Michael F

    2012-01-01

    We describe experimental UV-visible and Fourier transform infrared (FTIR) spectroscopic methods for characterizing lipid-protein interactions for rhodopsin in a membrane bilayer environment. The combination of FTIR and UV-visible difference spectroscopy is used to monitor the structural and functional changes during rhodopsin activation. Investigations of how membrane lipids stabilize various rhodopsin photoproducts are analogous to mutating the protein in terms of gain or loss of function. Interpretation of the results entails a flexible surface model for explaining membrane lipid-protein interactions through material properties relevant to biological activity.

  7. Identification and Quantitation of Plasma Membrane Components: A Biochemical Experiment for Lipid Investigations

    NASA Astrophysics Data System (ADS)

    Keys, Susan

    2000-11-01

    In this biochemistry exercise, students isolate and investigate lipid components of erythrocyte membranes. Erythrocytes are separated from sheep's blood by centrifugation. Lipids are extracted using chloroform-methanol (2:1 by volume). Individual lipid components (phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, sphingomyelin, and cholesterol) are separated and identified by thin-layer chromatography using chloroform-methanol-acetic acid-0.9% NaCl (75:45:3:1 by volume) as solvent. Nanomolar amounts of phospholipids are detected and quantified using a spectrophotometric phosphorus assay. Students learn to construct and use a standard concentration curve and test its accuracy.

  8. Investigation of transmembrane protein fused in lipid bilayer membranes supported on porous silicon.

    PubMed

    Tantawi, Khalid Hasan; Cerro, Ramon; Berdiev, Bakhrom; Martin, M Elena Diaz; Montes, Francisco Javier; Patel, Darayas; Williams, John D

    2013-01-01

    This article investigates a device made from a porous silicon structure supporting a lipid bilayer membrane (LBM)fused with Epithelial Sodium Channel protein. The electrochemically-fabricated porous silicon template had pore diameters in the range 0.2~2 µm. Membranes were composed of two synthetic phospholipids: 1,2-diphytanoyl-sn-glycero-3-phosphoserine and 1,2-diphytanoyl-sn-glycero-3-phosphoethanolamine. The LBMwas formed by means of the Langmuir-Blodgett and Langmuir-Schaefer techniques, at a monolayer surface tension of 26 m Nm(-1) in room temperature and on a deionized water subphase, which resulted in an average molecular area of 0.68-0.73 nm(2). Fusion of transmembrane protein was investigated using Atomic Force Microscopy. Initial atomic force microscopy results demonstrate the ability to support lipid bilayers fused with transmembrane proteins across a porous silicon substrate. However, more control of the membrane's surface tension using traditional membrane fusion techniques is required to optimize protein incorporation.

  9. Introduction to membrane lipids.

    PubMed

    Epand, Richard M

    2015-01-01

    Biological membranes are composed largely of lipids and proteins. The most common arrangement of lipids in biological membranes is as a bilayer. This arrangement spontaneously forms a barrier for the passage of polar materials. The bilayer is thin but can have a large area in the dimension perpendicular to its thickness. The physical nature of the bilayer membrane will vary according to the conditions of the environment as well as the chemical structure of the lipid constituents of the bilayer. These physical properties determine the function of the membrane together with specific structural features of the lipids that allow them to have signaling properties. The lipids of the membrane are not uniformly distributed. There is an intrinsic asymmetry between the two monolayers that constitute the bilayer. In addition, some lipids tend to be enriched in particular regions of the membrane, termed domains. There is evidence that certain domains recruit specific proteins into that domain. This has been suggested to be important for allowing interaction among different proteins involved in certain signal transduction pathways. Membrane lipids have important roles in determining the physical properties of the membrane, in modulating the activity of membrane-bound proteins and in certain cases being specific secondary messengers that can interact with specific proteins. A large variety of lipids present in biological membranes result in them possessing many functions.

  10. A new Monte Carlo method for investigating geometrical structures of lipid membranes with atomistic detail

    NASA Astrophysics Data System (ADS)

    Cheng, Sara; Qiu, Liming; Cheng, K.; Vaughn, Mark

    2011-10-01

    The distribution statistics of the surface area, volume and voids of lipid molecules are important parameters to characterize the structures of self-assembling lipid membranes. Traditional methods are mostly based on various assumptions of the thickness of the lipid membrane and the volumes of certain types of lipid molecules. However, those methods usually lead to an over- or underestimation of the average surface area of lipid molecules when compared to the experimental results of the pure lipid systems. We developed a new Monte Carlo method that is able to estimate the distributions and averages of surface area, volume and void space of the lipid molecules in the absence and presence of proteins of the MD simulation results of lipid membranes at the atomistic scale. We successfully validated our new method on an ordered hard-sphere system and on a phospholipid/cholesterol binary lipid system, all with known structural parameters. Using this new method, the structural perturbation of the conformal annular lipids in close proximity to the embedded protein in a lipid/protein system will also be presented.

  11. 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

  12. Molecular Dynamics Simulations of Model Trans-Membrane Peptides in Lipid Bilayers: A Systematic Investigation of Hydrophobic Mismatch

    PubMed Central

    Kandasamy, Senthil K.; Larson, Ronald G.

    2006-01-01

    Hydrophobic mismatch, which is the difference between the hydrophobic length of trans-membrane segments of a protein and the hydrophobic width of the surrounding lipid bilayer, is known to play a role in membrane protein function. We have performed molecular dynamics simulations of trans-membrane KALP peptides (sequence: GKK(LA)nLKKA) in phospholipid bilayers to investigate hydrophobic mismatch alleviation mechanisms. By varying systematically the length of the peptide (KALP15, KALP19, KALP23, KALP27, and KALP31) and the lipid hydrophobic length (DLPC, DMPC, and DPPC), a wide range of mismatch conditions were studied. Simulations of durations of 50–200 ns show that under positive mismatch, the system alleviates the mismatch predominantly by tilting the peptide and to a smaller extent by increased lipid ordering in the immediate vicinity of the peptide. Under negative mismatch, alleviation takes place by a combination of local bilayer bending and the snorkeling of the lysine residues of the peptide. Simulations performed at a higher peptide/lipid molar ratio (1:25) reveal slower dynamics of both the peptide and lipid relative to those at a lower peptide/lipid ratio (1:128). The lysine residues have favorable interactions with specific oxygen atoms of the phospholipid headgroups, indicating the preferred localization of these residues at the lipid/water interface. PMID:16428278

  13. Molecular dynamics simulations of model trans-membrane peptides in lipid bilayers: a systematic investigation of hydrophobic mismatch.

    PubMed

    Kandasamy, Senthil K; Larson, Ronald G

    2006-04-01

    Hydrophobic mismatch, which is the difference between the hydrophobic length of trans-membrane segments of a protein and the hydrophobic width of the surrounding lipid bilayer, is known to play a role in membrane protein function. We have performed molecular dynamics simulations of trans-membrane KALP peptides (sequence: GKK(LA)nLKKA) in phospholipid bilayers to investigate hydrophobic mismatch alleviation mechanisms. By varying systematically the length of the peptide (KALP15, KALP19, KALP23, KALP27, and KALP31) and the lipid hydrophobic length (DLPC, DMPC, and DPPC), a wide range of mismatch conditions were studied. Simulations of durations of 50-200 ns show that under positive mismatch, the system alleviates the mismatch predominantly by tilting the peptide and to a smaller extent by increased lipid ordering in the immediate vicinity of the peptide. Under negative mismatch, alleviation takes place by a combination of local bilayer bending and the snorkeling of the lysine residues of the peptide. Simulations performed at a higher peptide/lipid molar ratio (1:25) reveal slower dynamics of both the peptide and lipid relative to those at a lower peptide/lipid ratio (1:128). The lysine residues have favorable interactions with specific oxygen atoms of the phospholipid headgroups, indicating the preferred localization of these residues at the lipid/water interface.

  14. FT-IR Investigations Into The Fluidity Of Lipopolysaccharide And Lipid A Membrane Systems

    NASA Astrophysics Data System (ADS)

    Brandenburg, K.; Seydel, U.

    1989-12-01

    Lipopolysaccharides (LPS) are the major amphiphilic components of the outer membrane of Gram-negative bacteria. They are composed of a poly- or oligosaccharide portion being covalently linked to a lipid moiety called lipid A. LPS are also called endotoxins because of their ability to induce harmful effects in organisms. However, they also exhibit beneficial ('adjuvant') activity for example by stimulating the immune system and inducing the production of e.g. the tumor necrosis factor and interleukin 1. The mechanisms leading to a stimulation of the cells of the immune system should mainly be governed by the fluidity and/or the supramolecular structure of the LPS and lipid A assemblies interacting with the cell membrane. In this contribution we report on FT-IR measurements of the fluidity of various LPS and of some lipid A's, and on the influence of the concentration of divalent cations, pH and water content on this parameter. The LPS differ in the headgroup conformation/composition, i.e in the length of the sugar moiety. The lipid A's show variation in their acylation patterns.

  15. Investigating the Biosynthesis of Membrane-spanning Lipids Using Model Strains of Acidobacteria

    NASA Astrophysics Data System (ADS)

    Bradley, A. S.; Chubiz, L. M.

    2016-12-01

    Glycerol dialkyl glycerol tetraethers (GDGTs), deriving from the membrane-spanning lipids of microbes, are detected in a wide range of environments including marine and lacustrine waters, sediments, and in terrestrial soils. In sediments and soils, ratios of various GDGT structures form the basis of the TEX86 proxy based on isoprenoidal GDGTs derived from archaea, and the MBT/CBT proxy based on bacterial-derived branched GDGTs (brGDGTs), which is influenced by both temperature and pH. While the relationships of the proxy values to environmental variables have been empirically calibrated, much uncertainty remains in understanding genetic and physiological factors that affect the production of these lipid structures by microbes. In this study we compare two model bacterial strains - Edaphobacter aggregans WGB-1 , which has been previously demonstrated to produce brGDGTs (Damsté et al 2011) and Edaphobacter modestus JBG-1 (a non-brGDGT producer) to gain traction into understanding brGDGT production. We have sequenced each genome, facilitating comparisons that can be used to computationally generate hypotheses for genes involved in brGDGT biosynthesis. We will also report the results of initial experiments conducted to understand how the lipid profiles of each strain vary as a function of growth phase. Through a combination of genetic approaches and physiolotical experiments, we aim to bring new understanding to brGDGTs and how proxies derived from these lipids relate to environmental variables. Damsté et al. 2011 AEM 77: 4147

  16. Membrane Organization and Lipid Rafts

    PubMed Central

    Simons, Kai; Sampaio, Julio L.

    2011-01-01

    Cell membranes are composed of a lipid bilayer, containing proteins that span the bilayer and/or interact with the lipids on either side of the two leaflets. Although recent advances in lipid analytics show that membranes in eukaryotic cells contain hundreds of different lipid species, the function of this lipid diversity remains enigmatic. The basic structure of cell membranes is the lipid bilayer, composed of two apposing leaflets, forming a two-dimensional liquid with fascinating properties designed to perform the functions cells require. To coordinate these functions, the bilayer has evolved the propensity to segregate its constituents laterally. This capability is based on dynamic liquid–liquid immiscibility and underlies the raft concept of membrane subcompartmentalization. This principle combines the potential for sphingolipid-cholesterol self-assembly with protein specificity to focus and regulate membrane bioactivity. Here we will review the emerging principles of membrane architecture with special emphasis on lipid organization and domain formation. PMID:21628426

  17. An investigation of the effect of membrane curvature on transmembrane-domain dependent protein sorting in lipid bilayers

    PubMed Central

    Fossati, Matteo; Goud, Bruno; Borgese, Nica; Manneville, Jean-Baptiste

    2014-01-01

    Sorting of membrane proteins within the secretory pathway of eukaryotic cells is a complex process involving discrete sorting signals as well as physico-chemical properties of the transmembrane domain (TMD). Previous work demonstrated that tail-anchored (TA) protein sorting at the interface between the Endoplasmic Reticulum (ER) and the Golgi complex is exquisitely dependent on the length and hydrophobicity of the transmembrane domain, and suggested that an imbalance between TMD length and bilayer thickness (hydrophobic mismatch) could drive long TMD-containing proteins into curved membrane domains, including ER exit sites, with consequent export of the mismatched protein out of the ER. Here, we tested a possible role of curvature in TMD-dependent sorting in a model system consisting of Giant Unilamellar Vesicles (GUVs) from which narrow membrane tubes were pulled by micromanipulation. Fluorescent TA proteins differing in TMD length were incorporated into GUVs of uniform lipid composition or made of total ER lipids, and TMD-dependent sorting and diffusion, as well as the bending rigidity of bilayers made of microsomal lipids, were investigated. Long and short TMD-containing constructs were inserted with similar orientation, diffused equally rapidly in GUVs and in tubes pulled from GUVs, and no difference in their final distribution between planar and curved regions was detected. These results indicate that curvature alone is not sufficient to drive TMD-dependent sorting at the ER-Golgi interface, and set the basis for the investigation of the additional factors that must be required. PMID:25210649

  18. An investigation of the effect of membrane curvature on transmembrane-domain dependent protein sorting in lipid bilayers.

    PubMed

    Fossati, Matteo; Goud, Bruno; Borgese, Nica; Manneville, Jean-Baptiste

    2014-01-01

    Sorting of membrane proteins within the secretory pathway of eukaryotic cells is a complex process involving discrete sorting signals as well as physico-chemical properties of the transmembrane domain (TMD). Previous work demonstrated that tail-anchored (TA) protein sorting at the interface between the Endoplasmic Reticulum (ER) and the Golgi complex is exquisitely dependent on the length and hydrophobicity of the transmembrane domain, and suggested that an imbalance between TMD length and bilayer thickness (hydrophobic mismatch) could drive long TMD-containing proteins into curved membrane domains, including ER exit sites, with consequent export of the mismatched protein out of the ER. Here, we tested a possible role of curvature in TMD-dependent sorting in a model system consisting of Giant Unilamellar Vesicles (GUVs) from which narrow membrane tubes were pulled by micromanipulation. Fluorescent TA proteins differing in TMD length were incorporated into GUVs of uniform lipid composition or made of total ER lipids, and TMD-dependent sorting and diffusion, as well as the bending rigidity of bilayers made of microsomal lipids, were investigated. Long and short TMD-containing constructs were inserted with similar orientation, diffused equally rapidly in GUVs and in tubes pulled from GUVs, and no difference in their final distribution between planar and curved regions was detected. These results indicate that curvature alone is not sufficient to drive TMD-dependent sorting at the ER-Golgi interface, and set the basis for the investigation of the additional factors that must be required.

  19. Investigation of the interaction of dimethyl sulfoxide with lipid membranes by small-angle neutron scattering

    SciTech Connect

    Gorshkova, J. E. Gordeliy, V. I.

    2007-05-15

    The influence of dimethyl sulfoxide (CH{sub 3}){sub 2}SO (DMSO) on the structure of membranes of 1,2-dimiristoyl-sn-glycero-3-phosphatidylcholine (DMPC) in an excess of a water-DMSO solvent is investigated over a wide range of DMSO molar concentrations 0.0 {<=} X{sub DMSO} {<=} 1.0 at temperatures T = 12.5 and 55 deg. C. The dependences of the repeat distance d of multilamellar membranes and the thickness d{sub b} of single vesicles on the molar concentration X{sub DMSO} in the L{sub {beta}}{sub '} gel and L{sub {alpha}} liquid-crystalline phases are determined by small-angle neutron scattering. The intermembrane distance d{sub s} is determined from the repeat distance d and the membrane thickness d{sub b}. It is shown that an increase in the molar concentration X{sub DMSO} leads to a considerable decrease in the intermembrane distance and that, at X{sub DMSO} = 0.4, the neighboring membranes are virtually in steric contact with each other. The use of the deuterated phospholipid (DMSO-D6) and the contrast variation method makes it possible, for the first time, to determine the number of DMSO molecules strongly bound to the membrane.

  20. Investigation of molecular mechanisms of action of chelating drugs on protein-lipid model membranes by X-ray fluorescence

    SciTech Connect

    Novikova, N. N.; Zheludeva, S. I.; Koval'chuk, M. V.; Stepina, N. D.; Erko, A. I.; Yur'eva, E. A.

    2009-12-15

    Protein-lipid films based on the enzyme alkaline phosphatase were subjected to the action of chelating drugs, which are used for accelerating the removal of heavy metals from the human body, and the elemental composition of the resulting films was investigated. Total-reflection X-ray fluorescence measurements were performed at the Berlin Electron Storage Ring Company for Synchrotron Radiation (BESSY) in Germany. A comparative estimation of the protective effect of four drugs (EDTA, succimer, xydiphone, and mediphon) on membrane-bound enzymes damaged by lead ions was made. The changes in the elemental composition of the protein-lipid films caused by high doses of chelating drugs were investigated. It was shown that state-of-the-art X-ray techniques can, in principle, be used to develop new methods for the in vitro evaluation of the efficiency of drugs, providing differential data on their actions.

  1. Using patterned supported lipid membranes to investigate the role of receptor organization in intercellular signaling

    PubMed Central

    Nair, Pradeep M; Salaita, Khalid; Petit, Rebecca S; Groves, Jay T

    2014-01-01

    physical inputs, both internal and external to a cell, can directly alter the spatial organization of cell surface receptors and their associated functions. Here we describe a protocol that combines solid-state nanolithography and supported lipid membrane techniques to trigger and manipulate specific receptors on the surface of living cells and to develop an understanding of the interplay between spatial organization and receptor function. While existing protein-patterning techniques are capable of presenting cells with well-defined clusters of protein, this protocol uniquely allows for the control of the spatial organization of laterally fluid receptor-ligand complex at an intermembrane junction. a combination of immunofluorescence and single-cell microscopy methods and complementary biochemical analyses are used to characterize receptor signaling pathways and cell functions. the protocol requires 2–5 d to complete depending on the parameters to be studied. In principle, this protocol is widely applicable to eukaryotic cells and herein is specifically developed to study the role of physical organization and translocation of the EphA2 receptor tyrosine kinase across a library of model breast cancer cell lines. PMID:21455188

  2. Experimental Investigations of Direct and Converse Flexoelectric Effect in Bilayer Lipid Membranes.

    NASA Astrophysics Data System (ADS)

    Todorov, Angelio Todorov

    Flexoelectric coefficients (direct and converse), electric properties (capacitance and resistivity) and mechanical properties (thickness and elastic coefficients) have been determined for bilayer lipid membranes (BLMs) prepared from egg yolk lecithin (EYL), glycerol monoleate (GMO), phosphatidyl choline (PC) and phosphatidyl serine (PS) as a function of frequency, pH and surface charge modifiers. Direct flexoelectric effect manifested itself in the development of microvolt range a.c. potential (U_{f}) upon subjecting one side of a BLM to an oscillating hydrostatic pressure, in the 100-1000 Hz range. Operationally, the flexoelectric coefficient (f) is expressed by the ratio between U_{f} and the change of curvature (c) which accompanied the flexing of the membrane. Membrane curvature was determined by means of either the electric method (capacitance microphone effect) or by the newly developed method of stroboscopic interferometry. Real-time stroboscopic interferometry coupled with simultaneous electric measurements, provided a direct method for the determination of f. Two different frequency regimes of f were recognized. At low frequencies (<300 Hz), associated with free mobility of the surfactant, f-values of 24.1 times 10^{-19} and 0.87 times 10^ {-19} Coulombs were obtained for PC and GMO BLMs. At high frequencies (>300 Hz), associated with blocked mobility of the surfactant, f-values of 16.5 times 10^ {-19} and 0.30 times 10^{-19} Coulombs were obtained for PC and GMO BLMs. The theoretically calculated value for the GMO BLM oscillating at high frequency (0.12 times 10^{-19 } Coulombs) agreed well with that determined experimentally (0.3 times 10 ^{-19} Coulombs). For charged bovine brain PS BLM the observed flexocoefficient was f = 4.0 times 10^{ -18} Coulombs. Converse flexoelectric effect manifested itself in voltage-induced BLM curvature. Observations were carried out on uranyl acetate (UA) stabilized PS BLM under a.c. excitation. Frequency dependence of f

  3. Lysosomal degradation of membrane lipids.

    PubMed

    Kolter, Thomas; Sandhoff, Konrad

    2010-05-03

    The constitutive degradation of membrane components takes place in the acidic compartments of a cell, the endosomes and lysosomes. Sites of lipid degradation are intralysosomal membranes that are formed in endosomes, where the lipid composition is adjusted for degradation. Cholesterol is sorted out of the inner membranes, their content in bis(monoacylglycero)phosphate increases, and, most likely, sphingomyelin is degraded to ceramide. Together with endosomal and lysosomal lipid-binding proteins, the Niemann-Pick disease, type C2-protein, the GM2-activator, and the saposins sap-A, -B, -C, and -D, a suitable membrane lipid composition is required for degradation of complex lipids by hydrolytic enzymes. Copyright 2009 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

  4. Lipids and Membrane Lateral Organization

    PubMed Central

    Sonnino, Sandro; Prinetti, Alessandro

    2010-01-01

    Shortly after the elucidation of the very basic structure and properties of cellular membranes, it became evident that cellular membranes are highly organized structures with multiple and multi-dimensional levels of order. Very early observations suggested that the lipid components of biological membranes might be active players in the creation of these levels of order. In the late 1980s, several different and diverse experimental pieces of evidence coalesced together giving rise to the lipid raft hypothesis. Lipid rafts became enormously (and, in the opinion of these authors, sometimes acritically) popular, surprisingly not just within the lipidologist community (who is supposed to be naturally sensitive to the fascination of lipid rafts). Today, a PubMed search using the key word “lipid rafts” returned a list of 3767 papers, including 690 reviews (as a term of comparison, searching over the same time span for a very hot lipid-related key word, “ceramide” returned 6187 hits with 799 reviews), and a tremendous number of different cellular functions have been described as “lipid raft-dependent.” However, a clear consensus definition of lipid raft has been proposed only in recent times, and the basic properties, the ruling forces, and even the existence of lipid rafts in living cells has been recently matter of intense debate. The scenario that is gradually emerging from the controversies elicited by the lipid raft hypothesis emphasizes multiple roles for membrane lipids in determining membrane order, that encompass their tendency to phase separation but are clearly not limited to this. In this review, we would like to re-focus the attention of the readers on the importance of lipids in organizing the fine structure of cellular membranes. PMID:21423393

  5. Dynamics of multicomponent lipid membranes

    NASA Astrophysics Data System (ADS)

    Camley, Brian Andrew

    We present theoretical and computational descriptions of the dynamics of multicomponent lipid bilayer membranes. These systems are both model systems for "lipid rafts" in cell membranes and interesting physical examples of quasi-two-dimensional fluids. Our chief tool is a continuum simulation that uses a phase field to track the composition of the membrane, and solves the hydrodynamic equations exactly using the appropriate Green's function (Oseen tensor) for the membrane. We apply this simulation to describe the diffusion of domains in phase-separated membranes, the dynamics of domain flickering, and the process of phase separation in lipid membranes. We then derive an analytical theory to describe domain flickering that is consistent with our simulation results, and use this to analyze experimental measurements of membrane domains. Through this method, we measure the membrane viscosity solely from fluorescence microscopy measurements. We study phase separation in quasi-two-dimensional membranes in depth with both simulations and scaling theory, and classify the different scaling regimes and morphologies, which differ from pure two-dimensional fluids. Our results may explain previous inconsistent measurements of the dynamical scaling exponent for phase separation in membranes. We also extend our theory beyond the simplest model, including the possibility that the membrane will be viscoelastic, as well as considering the inertia of the membrane and the fluid surrounding the membrane.

  6. 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

  7. Electronic polymers in lipid membranes.

    PubMed

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

    2015-06-10

    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.

  8. Lipid Polymorphisms and Membrane Shape

    PubMed Central

    Frolov, Vadim A.; Shnyrova, Anna V.; Zimmerberg, Joshua

    2011-01-01

    Morphological plasticity of biological membrane is critical for cellular life, as cells need to quickly rearrange their membranes. Yet, these rearrangements are constrained in two ways. First, membrane transformations may not lead to undesirable mixing of, or leakage from, the participating cellular compartments. Second, membrane systems should be metastable at large length scales, ensuring the correct function of the particular organelle and its turnover during cellular division. Lipids, through their ability to exist with many shapes (polymorphism), provide an adequate construction material for cellular membranes. They can self-assemble into shells that are very flexible, albeit hardly stretchable, which allows for their far-reaching morphological and topological behaviors. In this article, we will discuss the importance of lipid polymorphisms in the shaping of membranes and its role in controlling cellular membrane morphology. PMID:21646378

  9. A Raman spectroscopic investigation of the lipid state in acetylcholine receptor-rich membranes from Torpedo marmorata.

    PubMed Central

    Aslanian, D; Négrerie, M

    1985-01-01

    The lipid state in acetylcholine receptor (AcChR)-rich membranes purified from electric organ of Torpedo marmorata was studied in the temperature interval from 0 degrees C to 35 degrees C using the (C-H) stretching and (C-C) skeletal optical vibrations. The Raman spectra of AcChR-rich membranes, recorded immediately after preparation of the samples, indicate that the lipids are in a predominant triclinic crystalline lattice and do not undergo a phase transition when the temperature increases up to 35 degrees C. However, the polar groups of the lipids appear subject to temperature-induced variations. After extraction of 43-kd and other non-receptor proteins, spectra indicate an order-disorder phase transition of lipids at approximately 21 degrees C. This transition appears less cooperative than the transition of the membrane lipid extract. The role of the proteins in preservation of the crystalline state of lipids in AcChR-rich membranes is discussed. PMID:4018037

  10. Ethanol perturbs lipid organization in models of stratum corneum membranes: An investigation combining differential scanning calorimetry, infrared and (2)H NMR spectroscopy.

    PubMed

    Kwak, Sungjong; Brief, Elana; Langlais, Denis; Kitson, Neil; Lafleur, Michel; Thewalt, Jenifer

    2012-05-01

    Ethanol is used in a variety of topical products. It is known to enhance the permeability of the skin by altering the ability of the stratum corneum (SC) intercellular membranes to form an effective barrier. In addition, ethanol and other alcohols are key components of antiseptic gels currently used for hand wash. Using infrared and deuterium NMR spectroscopy as well as calorimetry, we have investigated the effect of ethanol on a model membrane composed of lipids representing the three classes of SC lipids, an equimolar mixture of N-palmitoylsphingosine (ceramide), palmitic acid and cholesterol. Ethanol is found to influence the membrane in a dose dependent manner, disrupting packing and increasing lipid motion at low concentrations and selectively extracting lipids at moderate concentrations.

  11. 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.

  12. Interactions of the baicalin and baicalein with bilayer lipid membranes investigated by cyclic voltammetry and UV-Vis spectroscopy.

    PubMed

    Zhang, Ying; Wang, Xuejing; Wang, Lei; Yu, Miao; Han, Xiaojun

    2014-02-01

    The baicalin and baicalein are the major flavonoids found in Radix Scutellariae, an essential herb in traditional Chinese medicine for thousands of years. The interactions of the baicalin and baicalein with lipid bilayer membranes were studied using cyclic voltammetry and UV-Vis spectroscopy. The thickness d of supported bilayer lipid membranes was calculated as d=4.59(±0.36) nm using AC impedance spectroscopy. The baicalein interacted with egg PC bilayer membranes in a dose-dependent manner. The responses of K3Fe(CN)6 on lipid bilayer membrane modified Pt electrode linearly increased in a concentration range of baicalein from 6.25μM to 25μM with a detection limit of 0.1μM and current-concentration sensitivity of 0.11(±0.01) μA/μM, and then reached a plateau from 25μM to 50μM. However the baicalin showed much weaker interactions with egg PC bilayer membranes. UV-Vis spectroscopy also confirmed that the baicalein could interact with egg PC membranes noticeably, but the interaction of baicalin with membranes was hard to be detected. The results provide useful information on understanding the mechanism of action of Radix Scutellariae in vivo.

  13. Mechanics of Lipid Bilayer Membranes

    NASA Astrophysics Data System (ADS)

    Powers, Thomas R.

    All cells have membranes. The plasma membrane encapsulates the cell's interior, acting as a barrier against the outside world. In cells with nuclei (eukaryotic cells), membranes also form internal compartments (organelles) which carry out specialized tasks, such as protein modification and sorting in the case of the Golgi apparatus, and ATP production in the case of mitochondria. The main components of membranes are lipids and proteins. The proteins can be channels, carriers, receptors, catalysts, signaling molecules, or structural elements, and typically contribute a substantial fraction of the total membrane dry weight. The equilibrium properties of pure lipid membranes are relatively well-understood, and will be the main focus of this article. The framework of elasticity theory and statistical mechanics that we will develop will serve as the foundation for understanding biological phenomena such as the nonequilibrium behavior of membranes laden with ion pumps, the role of membrane elasticity in ion channel gating, and the dynamics of vesicle fission and fusion. Understanding the mechanics of lipid membranes is also important for drug encapsulation and delivery.

  14. Interactions of Lipidic Cubic Phase Nanoparticles with Lipid Membranes.

    PubMed

    Jabłonowska, Elżbieta; Nazaruk, Ewa; Matyszewska, Dorota; Speziale, Chiara; Mezzenga, Raffaele; Landau, Ehud M; Bilewicz, Renata

    2016-09-20

    The interactions of liquid-crystalline monoolein (GMO) cubic phase nanoparticles with various model lipid membranes spread at the air-solution interface by the Langmuir technique were investigated. Cubosomes have attracted attention as potential biocompatible drug delivery systems, and thus understanding their mode of interaction with membranes is of special interest. Cubosomes spreading at the air-water interface as well as interactions with a monolayer of 1, 2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) compressed to different surface pressures were studied by monitoring surface pressure-time dependencies at constant area. Progressive incorporation of the nanoparticles was shown to lead to mixed monolayer formation. The concentration of cubosomes influenced the mechanism of incorporation, as well as the fluidity and permeability of the resulting lipid membranes. Brewster angle microscopy images reflected the dependence of the monolayer structure on the cubosomes presence in the subphase. A parameter Csat was introduced to indicate the point of saturation of the lipid membrane with the cubosomal material. This parameter was found to depend on the surface pressure showing that the cubosomes disintegrate in prolonged contact with the membrane, filling available voids in the lipid membrane. At highest surface pressures when the layer is most compact, the penetration of cubosomal material is not possible and only some exchange with the membrane lipid becomes the route of including GMO into the layer. Finally, comparative studies of the interactions between lipids with various headgroup charges with cubosomes suggest that at high surface pressure an exchange of lipid component between the monolayer and the cubosome in its intact form may occur.

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

    PubMed

    Sani, Marc-Antoine; Separovic, Frances

    2016-06-21

    The structure-function relationship for a family of antimicrobial peptides (AMPs) from the skin of Australian tree frogs is discussed and compared with that of peptide toxins from bee and Australian scorpion venoms. Although these membrane-active peptides induce a similar cellular fate by disrupting the lipid bilayer integrity, their lytic activity is achieved via different modes of action, which are investigated in relation to amino acid sequence, secondary structure, and membrane lipid composition. In order to better understand what structural features govern the interaction between peptides and lipid membranes, cell-penetrating peptides (CPPs), which translocate through the membrane without compromising its integrity, are also discussed. AMPs possess membrane lytic activities that are naturally designed to target the cellular membrane of pathogens or competitors. They are extremely diverse in amino acid composition and often show specificity against a particular strain of microbe. Since our antibiotic arsenal is declining precariously in the face of the rise in multiantibiotic resistance, AMPs increasingly are seen as a promising alternative. In an effort to understand their molecular mechanism, biophysical studies of a myriad of AMPs have been reported, yet no unifying mechanism has emerged, rendering difficult the rational design of drug leads. Similarly, a wide variety of cytotoxic peptides are found in venoms, the best known being melittin, yet again, predicting their activity based on a particular amino acid composition or secondary structure remains elusive. A common feature of these membrane-active peptides is their preference for the lipid environment. Indeed, they are mainly unstructured in solution and, in the presence of lipid membranes, quickly adsorb onto the surface, change their secondary structure, eventually insert into the hydrophobic core of the membrane bilayer, and finally disrupt the bilayer integrity. These steps define the molecular

  16. 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

  17. Investigation into Formation of Lipid Hydroperoxides from Membrane Lipids in Escherichia coli O157:H7 following Exposure to Hot Water.

    PubMed

    Cálix-Lara, Thelma F; Kirsch, Katie R; Hardin, Margaret D; Castillo, Alejandro; Smith, Stephen B; Taylor, Thomas M

    2015-06-01

    Although studies have shown antimicrobial treatments consisting of hot water sprays alone or paired with lactic acid rinses are effective for reducing Escherichia coli O157:H7 loads on beef carcass surfaces, the mechanisms by which these interventions inactivate bacterial pathogens are still poorly understood. It was hypothesized that E. coli O157:H7 exposure to hot water in vitro at rising temperatures for longer time periods would result in increasing deterioration of bacterial outer membrane lipids, sensitizing the pathogen to subsequent lactic acid application. Cocktails of E. coli O157:H7 strains were subjected to hot water at 25 (control) 65, 75, or 85 °C incrementally up to 60 s, after which surviving cells were enumerated by plating. Formation of lipid hydroperoxides from bacterial membranes and cytoplasmic accumulation of L-lactic acid was quantified spectrophotometrically. Inactivation of E. coli O157:H7 proceeded in a hot water exposure duration- and temperature-dependent manner, with populations being reduced to nondetectable numbers following heating of cells in 85 °C water for 30 and 60 s (P < 0.05). Lipid hydroperoxide formation was not observed to be dependent upon increasing water temperature or exposure period. The data suggest that hot water application prior to organic acid application may function to increase the sensitivity of E. coli O157:H7 cells by degrading membrane lipids.

  18. TOPICAL REVIEW: The microcalorimetry of lipid membranes

    NASA Astrophysics Data System (ADS)

    Heerklotz, Heiko

    2004-04-01

    Insight into the forces governing a system is essential for understanding its behaviour and function. Calorimetric investigations provide a wealth of information that is not, or is hardly, available by other methods. This paper reviews calorimetric approaches and assays for the study of lipid vesicles (liposomes) and biological membranes. With respect to the instrumentation, differential scanning calorimetry (DSC), pressure perturbation calorimetry (PPC), isothermal titration calorimetry (ITC) and water sorption calorimetry are considered. Applications of these techniques to lipid systems include the measurement of thermodynamic parameters and a detailed characterization of the thermotropic, barotropic, and lyotropic phase behaviour. The membrane binding or partitioning of solutes (proteins, peptides, drugs, surfactants, ions, etc) can also be quantified. Many calorimetric assays are available for studying the effect of proteins and other additives on membranes, characterizing non-ideal mixing, domain formation, stability, curvature strain, permeability, solubilization, and fusion. Studies of membrane proteins in lipid environments elucidate lipid-protein interactions in membranes. The systems are described in terms of enthalpic and entropic forces, equilibrium constants, heat capacities, partial volume changes etc, shedding light also on the stability of structures and the molecular origin and mechanism of structural changes.

  19. Fluid and Resistive Tethered Lipid Membranes on Nanoporous Substrates.

    PubMed

    Gupta, Gautam; Staggs, Kyle; Mohite, Aditya D; Baldwin, Jon K; Iyer, Srinivas; Mukundan, Rangachary; Misra, Amit; Antoniou, Antonia; Dattelbaum, Andrew M

    2015-10-08

    Cell membranes perform important biological roles including compartmentalization, signaling, and transport of nutrients. Supported lipid membranes mimic the behavior of cell membranes and are an important model tool for studying membrane properties in a controlled laboratory environment. Lipid membranes may be supported on solid substrates; however, protein and lipid interactions with the substrate typically result in their denaturation. In this report, we demonstrate the formation of intact lipid membranes tethered on nanoporous metal thin films obtained via a dealloying process. Uniform lipid membranes were formed when the surface defect density of the nanoporous metal film was significantly reduced through a two-step dealloying process reported here. We show that the tethered lipid membranes on nanoporous metal substrates maintain both fluidity and electrical resistivity, which are key attributes to naturally occurring lipid membranes. The lipid assemblies supported on nanoporous metals provide a new platform for investigating lipid membrane properties, and potentially membrane proteins, for numerous applications including next generation biosensor platforms, targeted drug-delivery, and energy harvesting devices.

  20. Lipid membrane domains in the brain.

    PubMed

    Aureli, Massimo; Grassi, Sara; Prioni, Simona; Sonnino, Sandro; Prinetti, Alessandro

    2015-08-01

    The brain is characterized by the presence of cell types with very different functional specialization, but with the common trait of a very high complexity of structures originated by their plasma membranes. Brain cells bear evident membrane polarization with the creation of different morphological and functional subcompartments, whose formation, stabilization and function require a very high level of lateral order within the membrane. In other words, the membrane specialization of brain cells implies the presence of distinct membrane domains. The brain is the organ with the highest enrichment in lipids like cholesterol, glycosphingolipids, and the most recently discovered brain membrane lipid, phosphatidylglucoside, whose collective behavior strongly favors segregation within the membrane leading to the formation of lipid-driven membrane domains. Lipid-driven membrane domains function as dynamic platforms for signal transduction, protein processing, and membrane turnover. Essential events involved in the development and in the maintenance of the functional integrity of the brain depend on the organization of lipid-driven membrane domains, and alterations in lipid homeostasis, leading to deranged lipid-driven membrane organization, are common in several major brain diseases. In this review, we summarize the forces behind the formation of lipid membrane domains and their biological roles in different brain cells. This article is part of a Special Issue entitled Brain Lipids.

  1. Theoretical and simulation study of lipid membranes

    NASA Astrophysics Data System (ADS)

    Khelashvili, George

    It has been established that a proper functioning of biological lipid membranes is in large part due to cholesterol's ability to regulate fluidity of a lipid bilayer. In particular, a growing body of evidence suggested that cholesterol participates in the formation of cholesterol- and sphingolipid-enriched phase-separated domains known as "rafts" in the plasma and other membranes of animal cells. Rafts have been identified as important membrane structural components in signal transduction, protein transport and sorting of membrane components. At a molecular level, the detailed, localized behavior of lipid-cholesterol bilayers is unclear. In order to better understand how cholesterols function in lipid membranes it is desirable to built theoretical models. The goal of the present research is to model lipid-cholesterol bilayers on the different length and timescales. In the first part of the work, mixtures of sphingomyelin (SM) lipid and cholesterol at different temperatures and cholesterol concentrations were investigated using Molecular Dynamics and Monte-Carlo simulation techniques. The objective was to study the properties of cholesterol- and SM-enriched raft-like domains at the atomic level. The simulations revealed that, addition of 31% cholesterol induced intermediate degree of organization in the model SM-cholesterol bilayers at temperatures below and above the main phase transition temperature of pure SM bilayer. This intermediate state of fluidity may be necessary for the binding of proteins and other molecules that associate with raft domains. In the second part of the work, dynamical self-consistent mean-field model based on atomistic simulations was developed to investigate phase properties of lipid-cholesterol bilayers on the length and timescales currently unreachable with traditional atomistic level simulation methods. This new technique allows studying systems consisting of 104 or more number of molecules, on microsecond timescales. The model was

  2. Changes in lipid density induce membrane curvature.

    PubMed

    de Jesus, Armando J; Kastelowitz, Noah; Yin, Hang

    2013-09-07

    Highly curved bilayer lipid membranes make up the shell of many intra- and extracellular compartments, including organelles and vesicles. Using all-atom molecular dynamics simulations, we show that increasing the density of lipids in the bilayer membrane can induce the membrane to form a curved shape.

  3. Polymer Diffusion in Lipid Membranes

    NASA Astrophysics Data System (ADS)

    Prasad, Ashok

    2005-03-01

    Motivated by experiments on fluorescently labeled DNA molecules on a supported lipid bilayer, we have examined theoretically diffusion of polymers in two dimensions. The key experimental finding we focus on is the scaling of the diffusion constant of the center of mass, D˜1/N. This implies that no effective hydrodynamic coupling exists between the diffusing DNA segments in the membrane. We construct our theoretical model using the phenomenological hydrodynamic model of supported membranes proposed by Evans and Sackmann. Our model is based on the pre-averaged Oseen tensor, and is similar to the model of Komura and Seki, but elaborated and extended to take explicit account of self-avoidance. We find that the 1/N scaling of D can be understood as a consequence of membrane hydrodynamics in the presence of a supporting surface. Further experimental consequences of the model, in particular the diffusion constant for DNA in free standing membranes, will also be discussed. This work was supported by the NSF through grants DMR-9984471 and DMR-0403997. JK is a Cottrell Scholar of Research Corporation.

  4. Lipid-protein interactions in DHPC micelles containing the integral membrane protein OmpX investigated by NMR spectroscopy.

    PubMed

    Fernández, César; Hilty, Christian; Wider, Gerhard; Wüthrich, Kurt

    2002-10-15

    Intermolecular nuclear Overhauser effects (NOEs) between the integral outer membrane protein OmpX from Escherichia coli and dihexanoylphosphatidylcholine (DHPC) provided a detailed description of protein-detergent interactions. The NOEs were measured in 3D (15)N- and (13)C-resolved [(1)H,(1)H]-NOESY spectra recorded with selectively methyl-protonated and otherwise uniformly (2)H,(13)C,(15)N-labeled OmpX in micelles of DHPC at natural isotope abundance. In these mixed micelles the NMR structure of OmpX consists of an eight-stranded antiparallel beta-barrel. The OmpX surface area covered with intermolecular NOEs to the DHPC hydrophobic tails forms a continuous cylinder jacket of approximately 28 A in height, which is centered about the middle of the long axis through the beta-barrel. In addition, some intermolecular NOEs with methyl groups of the DHPC polar head were identified along both boundaries of this cylinder jacket. The experimental data suggest that the hydrophobic surface areas of OmpX are covered with a monolayer of DHPC molecules, which appears to mimic quite faithfully the embedding of the beta-barrel in a double-layer lipid membrane.

  5. Membrane fusion in vesicles of oligomerizable lipids.

    PubMed Central

    Ravoo, B J; Weringa, W D; Engberts, J B

    1999-01-01

    Membrane fusion has been examined in a model system of small unilamellar vesicles of synthetic lipids that can be oligomerized through the lipid headgroups. The oligomerization can be induced either in both bilayer leaflets or in the inner leaflet exclusively. Oligomerization leads to denser lipid headgroup packing, with concomitant reduction of lipid lateral diffusion and membrane permeability. As evidenced by lipid mixing assays, electron microscopy, and light scattering, calcium-induced fusion of the bilayer vesicles is strongly retarded and inhibited by oligomerization. Remarkably, oligomerization of only the inner leaflet of the bilayer is already sufficient to affect fusion. The efficiency of inhibition and retardation of fusion critically depend on the relative amount of oligomeric lipid present, on the concentration of calcium ions, and on temperature. Implications for the mechanism of bilayer membrane fusion are discussed in terms of lipid lateral diffusion and membrane curvature effects. PMID:9876149

  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. [Germ cell membrane lipids in spermatogenesis].

    PubMed

    Wang, Ting; Shi, Xiao; Quan, Song

    2016-05-01

    Spermatogenesis is a complex developmental process in which a diploid progenitor germ cell transforms into highly specialized spermatozoa. During spermatogenesis, membrane remodeling takes place, and cell membrane permeability and liquidity undergo phase-specific changes, which are all associated with the alteration of membrane lipids. Lipids are important components of the germ cell membrane, whose volume and ratio fluctuate in different phases of spermatogenesis. Abnormal lipid metabolism can cause spermatogenic dysfunction and consequently male infertility. Germ cell membrane lipids are mainly composed of cholesterol, phospholipids and glycolipids, which play critical roles in cell adhesion and signal transduction during spermatogenesis. An insight into the correlation of membrane lipids with spermatogenesis helps us to better understand the mechanisms of spermatogenesis and provide new approaches to the diagnosis and treatment of male infertility.

  8. Pore formation in lipid membranes by alamethicin.

    PubMed Central

    Fringeli, U P; Fringeli, M

    1979-01-01

    The conformation of the linear peptide antibiotic alamethicin in dipalmitoyl phosphatidylcholine multilayers was investigated in the absence of an electric field by means of infrared attenuated total reflection spectroscopy. Alamethicin was found to be incorporated into the lipid membrane not only in the dry state but also in an aqueous environment. Its molecular conformation, however, changed from a helix when dry to an extended chain when aqueous. The extended chain aggregated to di- and multimers spanning the lipid bilayer. The equilibrium concentration of alamethicin in the surrounding water was 90 nM, which is in the range of concentrations used in black film experiments. The corresponding molar ratio of lipid to peptide was 80:1. Concerning the molecular mechanism of electric field-induced pore formation, one has to conclude that the dipole model proposed by several authors is very unlikely because it is based on the assumption that the major part of alamethicin is adsorbed on the membrane surface, from which small amounts flip into the membrane under the influence of an electric field. An alternative mechanism is proposed, based on a field-induced conformational change of the peptide from the extended state to a helix. This transition is favored by the resulting dipole moment of the alamethicin helix. PMID:291045

  9. Lipid-lipid and lipid-drug interactions in biological membranes

    NASA Astrophysics Data System (ADS)

    Martynowycz, Michael W.

    Interactions between lipids and drug molecules in biological membranes help govern proper biological function in organisms. The mechanisms responsible for hydrophobic drug permeation remain elusive. Many small molecule drugs are hydrophobic. These drugs inhibit proteins in the cellular interior. The rise of antibiotic resistance in bacteria is thought to be caused by mutations in protein structure, changing drug kinetics to favor growth. However, small molecule drugs have been shown to have different mechanisms depending in the structure of the lipid membrane of the target cell. Biological membranes are investigated using Langmuir monolayers at the air-liquid interface. These offer the highest level of control in the mimetic system and allow them to be investigated using complementary techniques. Langmuir isotherms and insertion assays are used to determine the area occupied by each lipid in the membrane and the change in area caused by the introduction of a drug molecule, respectively. Specular X-ray reflectivity is used to determine the electron density of the monolayer, and grazing incidence X-ray diffraction is used to determine the in-plane order of the monolayer. These methods determine the affinity of the drug and the mechanism of action. Studies are presented on hydrophobic drugs with mammalian membrane mimics using warfarin along with modified analogues, called superwarfarins. Data shows that toxicity of these modified drugs are modulated by the membrane cholesterol content in cells; explaining several previously unexplained effects of the drugs. Membrane mimics of bacteria are investigated along with their interactions with a hydrophobic antibiotic, novobiocin. Data suggests that permeation of the drug is mediated by modifications to the membrane lipids, and completely ceases translocation under certain circumstances. Circumventing deficiencies in small, hydrophobic drugs is approached by using biologically mimetic oligomers. Peptoids, mimetic of host

  10. Characterization of lipid domains in erythrocyte membranes.

    PubMed

    Rodgers, W; Glaser, M

    1991-02-15

    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.

  11. Control of lipid membrane stability by cholesterol content.

    PubMed Central

    Raffy, S; Teissié, J

    1999-01-01

    Cholesterol has a concentration-dependent effect on membrane organization. It is able to control the membrane permeability by inducing conformational ordering of the lipid chains. A systematic investigation of lipid bilayer permeability is described in the present work. It takes advantage of the transmembrane potential difference modulation induced in vesicles when an external electric field is applied. The magnitude of this modulation is under the control of the membrane electrical permeability. When brought to a critical value by the external field, the membrane potential difference induces a new membrane organization. The membrane is then permeable and prone to solubilized membrane protein back-insertion. This is obtained for an external field strength, which depends on membrane native permeability. This approach was used to study the cholesterol effect on phosphatidylcholine bilayers. Studies have been performed with lipids in gel and in fluid states. When cholesterol is present, it does not affect electropermeabilization and electroinsertion in lipids in the fluid state. When lipids are in the gel state, cholesterol has a dose-dependent effect. When present at 6% (mol/mol), cholesterol prevents electropermeabilization and electroinsertion. When cholesterol is present at more than 12%, electropermeabilization and electroinsertion are obtained under milder field conditions. This is tentatively explained by a cholesterol-induced alteration of the hydrophobic barrier of the bilayer core. Our results indicate that lipid membrane permeability is affected by the cholesterol content. PMID:10096902

  12. DMSO Induces Dehydration near Lipid Membrane Surfaces

    PubMed Central

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

    2015-01-01

    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

  13. 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.

  14. Artificial Lipid Membranes: Past, Present, and Future.

    PubMed

    Siontorou, Christina G; Nikoleli, Georgia-Paraskevi; Nikolelis, Dimitrios P; Karapetis, Stefanos K

    2017-07-26

    The multifaceted role of biological membranes prompted early the development of artificial lipid-based models with a primary view of reconstituting the natural functions in vitro so as to study and exploit chemoreception for sensor engineering. Over the years, a fair amount of knowledge on the artificial lipid membranes, as both, suspended or supported lipid films and liposomes, has been disseminated and has helped to diversify and expand initial scopes. Artificial lipid membranes can be constructed by several methods, stabilized by various means, functionalized in a variety of ways, experimented upon intensively, and broadly utilized in sensor development, drug testing, drug discovery or as molecular tools and research probes for elucidating the mechanics and the mechanisms of biological membranes. This paper reviews the state-of-the-art, discusses the diversity of applications, and presents future perspectives. The newly-introduced field of artificial cells further broadens the applicability of artificial membranes in studying the evolution of life.

  15. Finite element modeling of lipid bilayer membranes

    NASA Astrophysics Data System (ADS)

    Feng, Feng; Klug, William S.

    2006-12-01

    A numerical simulation framework is presented for the study of biological membranes composed of lipid bilayers based on the finite element method. The classic model for these membranes employs a two-dimensional-fluid-like elastic constitutive law which is sensitive to curvature, and subjects vesicles to physically imposed constraints on surface area and volume. This model is implemented numerically via the use of C1-conforming triangular Loop subdivision finite elements. The validity of the framework is tested by computing equilibrium shapes from previously-determined axisymmetric shape-phase diagram of lipid bilayer vesicles with homogeneous material properties. Some of the benefits and challenges of finite element modeling of lipid bilayer systems are discussed, and it is indicated how this framework is natural for future investigation of biologically realistic bilayer structures involving nonaxisymmetric geometries, binding and adhesive interactions, heterogeneous mechanical properties, cytoskeletal interactions, and complex loading arrangements. These biologically relevant features have important consequences for the shape mechanics of nonidealized vesicles and cells, and their study requires not simply advances in theory, but also advances in numerical simulation techniques, such as those presented here.

  16. Alamethicin aggregation in lipid membranes

    PubMed Central

    Pan, Jianjun; Tristram-Nagle, Stephanie; Nagle, John F.

    2009-01-01

    X-ray scattering features induced by aggregates of alamethicin (Alm) were obtained in oriented stacks of model membranes of DOPC(diC18:1PC) and diC22:1PC. The first feature obtained near full hydration was Bragg rod in-plane scattering near 0.11 Å-1 in DOPC and near 0.08 Å-1 in diC22:1PC at 1:10 Alm:lipid ratio. This feature is interpreted as bundles consisting of N Alm monomers in a barrel-stave configuration surrounding a water pore. Fitting the scattering data to previously published MD simulations indicates that the number N of peptides per bundle is N=6 in DOPC and N≥9 in diC22:1PC. The larger bundle size in diC22:1PC is explained by hydrophobic mismatch of Alm with the thicker bilayer. A second diffuse scattering peak located at qr≈0.7 Å-1 is obtained for both DOPC and diC22:1PC at several peptide concentrations. Theoretical calculations indicate that this peak can not be caused by the Alm bundle structure. Instead, we interpret it as due to two-dimensional hexagonally packed clusters in equilibrium with Alm bundles. As the relative humidity was reduced, interactions between Alm in neighboring bilayers produced more peaks with three dimensional crystallographic character that do not index with the conventional hexagonal space groups. PMID:19789905

  17. Membrane Structure: Lipid-Protein Interactions in Microsomal Membranes*

    PubMed Central

    Trump, Benjamin F.; Duttera, Sue M.; Byrne, William L.; Arstila, Antti U.

    1970-01-01

    The relationships of phospholipid to membrane structure and function were examined in hepatic microsomes. Findings indicate that normal microsomal membrane structure is dependent on lipid-protein interactions and that it correlates closely with glucose-6-phosphatase activity. Modification of most phospholipid with phospholipase-C is associated with widening of the membrane which can be reversed following readdition of phospholipid. Images PMID:4317915

  18. 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

  19. Biosynthesis of archaeal membrane ether lipids.

    PubMed

    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.

  20. Human milk fat globules: polar lipid composition and in situ structural investigations revealing the heterogeneous distribution of proteins and the lateral segregation of sphingomyelin in the biological membrane.

    PubMed

    Lopez, Christelle; Ménard, Olivia

    2011-03-01

    Although human milk fat globules (MFG) are of primary importance since they are the exclusive lipid delivery carriers in the gastrointestinal tract of breast-fed infants, they remain the poorly understood aspect of milk. The objectives of this study were to investigate these unique colloidal assemblies and their interfacial properties, i.e. composition and structure of their biological membrane. In mature breast milk, MFG have a mean diameter of 4-5 microm, a surface area of about 2m(2)/g fat and an apparent zeta potential ζ=-6.7 ± 0.5 mV at 37°C. Human MFG contain 3-4mg polar lipids/g fat as quantified by HPLC/ELSD. The main polar lipids are sphingomyelin (SM; 36-45%, w/w), phosphatidylcholine (19-23%, w/w) and phosphatidylethanolamine (10-15%, w/w). In situ structural investigations of human MFG have been performed using light and confocal microscopy with adapted fluorescent probes, i.e. Nile Red, the extrinsic phospholipid Rh-DOPE, Fast Green and the lectin WGA-488. This study revealed a spatial heterogeneity in the human milk fat globule membrane (MFGM), with the lateral segregation of SM in liquid-ordered phase domains of various shapes and sizes surrounded by a liquid-disordered phase composed of the glycerophospholipids in which the proteins are dispersed. The glycocalyx formed by glycoproteins and cytoplasmic remnents have also been characterised around human MFG. A new model for the structure of the human MFGM is proposed and discussed. The unique composition and lateral organisation of the human MFGM components could be of metabolic significance and have health impact for the infants that need to be further explored.

  1. Liquid immiscibility in model bilayer lipid membranes

    NASA Astrophysics Data System (ADS)

    Veatch, Sarah L.

    There is growing evidence that cell plasma membranes are laterally organized into "raft" regions in which particular lipids and proteins are concentrated. These domains have sub-micron dimensions and have been implicated in vital cell functions. Similar liquid domains are observed in model bilayer membrane mixtures that mimick cellular lipid compositions. In model membranes, domains can be large (microns) and can readily form in the absence of proteins. This thesis presents studies of liquid immiscibility in model membrane systems using two experimental methods. By fluorescence microscopy, this thesis documents that miscibility transitions occur in a wide variety of ternary lipid mixtures containing high melting temperature (saturated) lipids, low melting temperature (usually unsaturated) lipids, and cholesterol. I have constructed detailed miscibility phase diagrams for three separate ternary lipid mixtures (DOPC/DPPC/Chol, DOPC/PSM/Chol, and POPC/PSM/Chol). Phase separation is also observed in membranes of lipids extracted from human erythrocytes. NMR experiments probe lipid order and verify the coexistence of a saturated lipid and cholesterol rich liquid ordered (Lo) phase with a more disordered, unsaturated lipid rich liquid crystalline (Lalpha) phase at low temperatures. These experiments also find multiple thermodynamic transitions and lipid organization on different length-scales. This complexity is revealed because fluorescence microscopy and NMR probe lipid order at different length-scales (>1mum vs. ˜100nm). NMR detects small domains (˜80nm) at temperatures just below the miscibility transition, even though micron-scale domains are observed by fluorescent microscopy. NMR does detect large-scale ("100nm) demixing, but at a lower temperature. In addition, it has long been known that >10nm length-scale structure is present in many lipid mixtures containing cholesterol and at least one additional lipid species, though it is shown here that only a subset of

  2. Membrane domains and the "lipid raft" concept.

    PubMed

    Sonnino, S; Prinetti, A

    2013-01-01

    The bulk structure of biological membranes consists of a bilayer of amphipathic lipids. According to the fluid mosaic model proposed by Singer and Nicholson, the glycerophospholipid bilayer is a two-dimensional fluid construct that allows the lateral movement of membrane components. Different types of lateral interactions among membrane components can take place, giving rise to multiple levels of lateral order that lead to highly organized structures. Early observations suggested that some of the lipid components of biological membranes may play active roles in the creation of these levels of order. In the late 1980s, a diverse series of experimental findings collectively gave rise to the lipid raft hypothesis. Lipid rafts were originally defined as membrane domains, i.e., ordered structures created as a consequence of the lateral segregation of sphingolipids and differing from the surrounding membrane in their molecular composition and properties. This definition was subsequently modified to introduce the notion that lipid rafts correspond to membrane areas stabilized by the presence of cholesterol within a liquid-ordered phase. During the past two decades, the concept of lipid rafts has become extremely popular among cell biologists, and these structures have been suggested to be involved in a great variety of cellular functions and biological events. During the same period, however, some groups presented experimental evidence that appeared to contradict the basic tenets that underlie the lipid raft concept. The concept is currently being re-defined, with greater consistency regarding the true nature and role of lipid rafts. In this article we will review the concepts, criticisms, and the novel confirmatory findings relating to the lipid raft hypothesis.

  3. Sorting of Lipids and Proteins in Membrane Curvature Gradients

    PubMed Central

    Tian, A.; Baumgart, T.

    2009-01-01

    The sorting of lipids and proteins in cellular trafficking pathways is a process of central importance in maintaining compartmentalization in eukaryotic cells. However, the mechanisms behind these sorting phenomena are currently far from being understood. Among several mechanistic suggestions, membrane curvature has been invoked as a means to segregate lipids and proteins in cellular sorting centers. To assess this hypothesis, we investigate the sorting of lipid analog dye trace components between highly curved tubular membranes and essentially flat membranes of giant unilamellar vesicles. Our experimental findings indicate that intracellular lipid sorting, contrary to frequent assumptions, is unlikely to occur by lipids fitting into membrane regions of appropriate curvature. This observation is explained in the framework of statistical mechanical lattice models that show that entropy, rather than curvature energy, dominates lipid distribution in the absence of strongly preferential lateral intermolecular interactions. Combined with previous findings of curvature induced phase segregation, we conclude that lipid cooperativity is required to enable efficient sorting. In contrast to lipid analog dyes, the peripheral membrane binding protein Cholera toxin subunit B is effectively curvature-sorted. The sorting of Cholera toxin subunit B is rationalized by statistical models. We discuss the implications of our findings for intracellular sorting mechanisms. PMID:19348750

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

    PubMed Central

    Li, Dianfan; Lee, Jean; Caffrey, Martin

    2011-01-01

    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. PMID:21743796

  5. 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.

  6. 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.

  7. 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

  8. Unconventional membrane lipid biosynthesis in Xanthomonas campestris.

    PubMed

    Aktas, Meriyem; Narberhaus, Franz

    2015-09-01

    All bacteria are surrounded by at least one bilayer membrane mainly composed of phospholipids (PLs). Biosynthesis of the most abundant PLs phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and cardiolipin (CL) is well understood in model bacteria such as Escherichia coli. It recently emerged, however, that the diversity of bacterial membrane lipids is huge and that not yet explored biosynthesis pathways exist, even for the common PLs. A good example is the plant pathogen Xanthomonas campestris pv. campestris. It contains PE, PG and CL as major lipids and small amounts of the N-methylated PE derivatives monomethyl PE and phosphatidylcholine (PC = trimethylated PE). Xanthomonas campestris uses a repertoire of canonical and non-canonical enzymes for the synthesis of its membrane lipids. In this minireview, we briefly recapitulate standard pathways and integrate three recently discovered pathways into the overall picture of bacterial membrane biosynthesis.

  9. 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.

  10. Orchestration of membrane receptor signaling by membrane lipids.

    PubMed

    Arish, Mohd; Husein, Atahar; Kashif, Mohammad; Sandhu, Padmani; Hasnain, Seyed E; Akhter, Yusuf; Rub, Abdur

    2015-06-01

    Receptors on cell membrane bind to their respective ligands and transduce intracellular signals resulting in variety of effector functions. Membrane lipid composition determines the receptor signaling behavior, as the receptors assume different conformation to suit the biochemical milieu in its immediate vicinity in the membrane. Accordingly, these accommodate different signaling intermediates that dictate the course of intracellular signaling and the resulting effectors functions. In this review we provide an overview of how membrane lipids modulate membrane-properties, membrane-receptor functions and their significance in the host-pathogen interaction. Copyright © 2015 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM). All rights reserved.

  11. Targeting Membrane Lipid a Potential Cancer Cure?

    PubMed

    Tan, Loh Teng-Hern; Chan, Kok-Gan; Pusparajah, Priyia; Lee, Wai-Leng; Chuah, Lay-Hong; Khan, Tahir Mehmood; Lee, Learn-Han; Goh, Bey-Hing

    2017-01-01

    Cancer mortality and morbidity is projected to increase significantly over the next few decades. Current chemotherapeutic strategies have significant limitations, and there is great interest in seeking novel therapies which are capable of specifically targeting cancer cells. Given that fundamental differences exist between the cellular membranes of healthy cells and tumor cells, novel therapies based on targeting membrane lipids in cancer cells is a promising approach that deserves attention in the field of anticancer drug development. Phosphatidylethanolamine (PE), a lipid membrane component which exists only in the inner leaflet of cell membrane under normal circumstances, has increased surface representation on the outer membrane of tumor cells with disrupted membrane asymmetry. PE thus represents a potential chemotherapeutic target as the higher exposure of PE on the membrane surface of cancer cells. This feature as well as a high degree of expression of PE on endothelial cells in tumor vasculature, makes PE an attractive molecular target for future cancer interventions. There have already been several small molecules and membrane-active peptides identified which bind specifically to the PE molecules on the cancer cell membrane, subsequently inducing membrane disruption leading to cell lysis. This approach opens up a new front in the battle against cancer, and is of particular interest as it may be a strategy that may be prove effective against tumors that respond poorly to current chemotherapeutic agents. We aim to highlight the evidence suggesting that PE is a strong candidate to be explored as a potential molecular target for membrane targeted novel anticancer therapy.

  12. 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

  13. 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.

  14. Biotechnology Applications of Tethered Lipid Bilayer Membranes

    PubMed Central

    Jackman, Joshua A.; Knoll, Wolfgang; Cho, Nam-Joon

    2012-01-01

    The importance of cell membranes in biological systems has prompted the development of model membrane platforms that recapitulate fundamental aspects of membrane biology, especially the lipid bilayer environment. Tethered lipid bilayers represent one of the most promising classes of model membranes and are based on the immobilization of a planar lipid bilayer on a solid support that enables characterization by a wide range of surface-sensitive analytical techniques. Moreover, as the result of molecular engineering inspired by biology, tethered bilayers are increasingly able to mimic fundamental properties of natural cell membranes, including fluidity, electrical sealing and hosting transmembrane proteins. At the same time, new methods have been employed to improve the durability of tethered bilayers, with shelf-lives now reaching the order of weeks and months. Taken together, the capabilities of tethered lipid bilayers have opened the door to biotechnology applications in healthcare, environmental monitoring and energy storage. In this review, several examples of such applications are presented. Beyond the particulars of each example, the focus of this review is on the emerging design and characterization strategies that made these applications possible. By drawing connections between these strategies and promising research results, future opportunities for tethered lipid bilayers within the biotechnology field are discussed.

  15. Single-molecule investigation of the interactions between reconstituted planar lipid membranes and an analogue of the HP(2-20) antimicrobial peptide

    SciTech Connect

    Mereuta, Loredana; Luchian, Tudor Park, Yoonkyung; Hahm, Kyung-Soo

    2008-09-05

    In this study, we employed electrophysiology experiments carried out at the single-molecule level to study the mechanism of action of the HPA3 peptide, an analogue of the linear antimicrobial peptide, HP(2-20), isolated from the N-terminal region of the Helicobacter pylori ribosomal protein. Amplitude analysis of currents fluctuations induced by HPA3 peptide at various potentials in zwitterionic lipid membranes reveal the existence of reproducible conductive states in the stochastic behavior of such events, which directly supports the existence of transmembrane pores induced the peptide. From our data recorded both at the single-pore and macroscopic levels, we propose that the HPA3 pore formation is electrophoretically facilitated by trans-negative transmembrane potentials, and HPA3 peptides translocate into the trans monolayers after forming the pores. We present evidence according to which the decrease in the membrane dipole potential of a reconstituted lipid membranes leads to an augmentation of the membrane activity of HPA3 peptides, and propose that a lower electric dipole field of the interfacial region of the membrane caused by phloretin facilitates the surface-bound HPA3 peptides to break free from one leaflet of the membrane, insert into the membrane and contribute to pore formation spanning the entire thickness of the membrane.

  16. Single-molecule investigation of the interactions between reconstituted planar lipid membranes and an analogue of the HP(2-20) antimicrobial peptide.

    PubMed

    Mereuta, Loredana; Luchian, Tudor; Park, Yoonkyung; Hahm, Kyung-Soo

    2008-09-05

    In this study, we employed electrophysiology experiments carried out at the single-molecule level to study the mechanism of action of the HPA3 peptide, an analogue of the linear antimicrobial peptide, HP(2-20), isolated from the N-terminal region of the Helicobacter pylori ribosomal protein. Amplitude analysis of currents fluctuations induced by HPA3 peptide at various potentials in zwitterionic lipid membranes reveal the existence of reproducible conductive states in the stochastic behavior of such events, which directly supports the existence of transmembrane pores induced the peptide. From our data recorded both at the single-pore and macroscopic levels, we propose that the HPA3 pore formation is electrophoretically facilitated by trans-negative transmembrane potentials, and HPA3 peptides translocate into the trans monolayers after forming the pores. We present evidence according to which the decrease in the membrane dipole potential of a reconstituted lipid membranes leads to an augmentation of the membrane activity of HPA3 peptides, and propose that a lower electric dipole field of the interfacial region of the membrane caused by phloretin facilitates the surface-bound HPA3 peptides to break free from one leaflet of the membrane, insert into the membrane and contribute to pore formation spanning the entire thickness of the membrane.

  17. Probing the Lipid Membrane Dipole Potential by Atomic Force Microscopy

    PubMed Central

    Yang, Yi; Mayer, Kathryn M.; Wickremasinghe, Nissanka S.; Hafner, Jason H.

    2008-01-01

    The electrostatic properties of biological membranes can be described by three parameters: the transmembrane potential, the membrane surface potential, and the membrane dipole potential. The first two are well characterized in terms of their magnitudes and biological effects. The dipole potential, however, is not well characterized. Various methods to measure the membrane dipole potential indirectly yield different values, and there is not even agreement on the source of the membrane dipole moment. This ambiguity impedes investigations into the biological effects of the membrane dipole moment, which should be substantial considering the large interfacial fields with which it is associated. Electrostatic analysis of phosphatidylcholine lipid membranes with the atomic force microscope reveals a repulsive force between the negatively charged probe tips and the zwitterionic lipids. This unexpected interaction has been analyzed quantitatively to reveal that the repulsion is due to a weak external field created by the internal membrane dipole potential. The analysis yields a dipole moment of 1.5 Debye per lipid with a dipole potential of +275 mV for supported phosphatidylcholine membranes. This new ability to quantitatively measure the membrane dipole moment in a noninvasive manner with nanometer scale spatial resolution will be useful in identifying the biological effects of the dipole potential. PMID:18805919

  18. Membrane-spanning lipids for an uncompromised monitoring of membrane fusion and intermembrane lipid transfer

    PubMed Central

    Schwarzmann, Günter; Breiden, Bernadette; Sandhoff, Konrad

    2015-01-01

    A Förster resonance energy transfer-based fusion and transfer assay was developed to study, in model membranes, protein-mediated membrane fusion and intermembrane lipid transfer of fluorescent sphingolipid analogs. For this assay, it became necessary to apply labeled reporter molecules that are resistant to spontaneous as well as protein-mediated intermembrane transfer. The novelty of this assay is the use of nonextractable fluorescent membrane-spanning bipolar lipids. Starting from the tetraether lipid caldarchaeol, we synthesized fluorescent analogs with fluorophores at both polar ends. In addition, we synthesized radioactive glycosylated caldarchaeols. These labeled lipids were shown to stretch through bilayer membranes rather than to loop within a single lipid layer of liposomes. More important, the membrane-spanning lipids (MSLs) in contrast to phosphoglycerides proved to be nonextractable by proteins. We could show that the GM2 activator protein (GM2AP) is promiscuous with respect to glycero- and sphingolipid transfer. Saposin (Sap) B also transferred sphingolipids albeit with kinetics different from GM2AP. In addition, we could unambiguously show that the recombinant activator protein Sap C x His6 induced membrane fusion rather than intermembrane lipid transfer. These findings showed that these novel MSLs, in contrast with fluorescent phosphoglycerolipids, are well suited for an uncompromised monitoring of membrane fusion and intermembrane lipid transfer. PMID:26269359

  19. Membrane-spanning lipids for an uncompromised monitoring of membrane fusion and intermembrane lipid transfer.

    PubMed

    Schwarzmann, Günter; Breiden, Bernadette; Sandhoff, Konrad

    2015-10-01

    A Förster resonance energy transfer-based fusion and transfer assay was developed to study, in model membranes, protein-mediated membrane fusion and intermembrane lipid transfer of fluorescent sphingolipid analogs. For this assay, it became necessary to apply labeled reporter molecules that are resistant to spontaneous as well as protein-mediated intermembrane transfer. The novelty of this assay is the use of nonextractable fluorescent membrane-spanning bipolar lipids. Starting from the tetraether lipid caldarchaeol, we synthesized fluorescent analogs with fluorophores at both polar ends. In addition, we synthesized radioactive glycosylated caldarchaeols. These labeled lipids were shown to stretch through bilayer membranes rather than to loop within a single lipid layer of liposomes. More important, the membrane-spanning lipids (MSLs) in contrast to phosphoglycerides proved to be nonextractable by proteins. We could show that the GM2 activator protein (GM2AP) is promiscuous with respect to glycero- and sphingolipid transfer. Saposin (Sap) B also transferred sphingolipids albeit with kinetics different from GM2AP. In addition, we could unambiguously show that the recombinant activator protein Sap C x His6 induced membrane fusion rather than intermembrane lipid transfer. These findings showed that these novel MSLs, in contrast with fluorescent phosphoglycerolipids, are well suited for an uncompromised monitoring of membrane fusion and intermembrane lipid transfer.

  20. Electrophysiology investigation of Trichogin GA IV activity in planar lipid membranes reveals ion channels of well-defined size.

    PubMed

    Iftemi, Sorana; De Zotti, Marta; Formaggio, Fernando; Toniolo, Claudio; Stella, Lorenzo; Luchian, Tudor

    2014-07-01

    Trichogin GA IV, an antimicrobial peptaibol, exerts its function by augmenting membrane permeability, but the molecular aspects of its pore-forming mechanism are still debated. Several lines of evidence indicate a 'barrel-stave' channel structure, similar to that of alamethicin, but the length of a trichogin helix is too short to span a normal bilayer. Herein, we present electrophysiology measurements in planar bilayers, showing that trichogin does form channels of a well-defined size (R=4.2⋅10(9)  Ω; corresponding at least to a trimeric aggregate) that span the membrane and allow ion diffusion, but do not exhibit voltage-dependent rectification, unlike those of alamethicin. Copyright © 2014 Verlag Helvetica Chimica Acta AG, Zürich.

  1. The physics of stratum corneum lipid membranes

    PubMed Central

    Das, Chinmay

    2016-01-01

    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

  2. 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.

  3. Spontaneous insertion of lipopolysaccharide into lipid membranes from aqueous solution.

    PubMed

    Alam, Jahangir Md; Yamazaki, Masahito

    2011-02-01

    Lipopolysaccharide (LPS), one of the main components of outer membranes of Gram-negative bacteria, consists of a hydrophobic lipid (lipid A) with six hydrocarbon chains and a large hydrophilic polysaccharide chain. LPS plays endotoxic roles and can stimulate macrophages and B cells. To elucidate the mechanism of the interaction of LPS with various cell membranes, it is important to investigate the interaction of wild type LPS in a buffer with lipid membranes. In this report we investigated the interaction of low concentrations of LPS in a buffer with giant unilamellar vesicles (GUVs) of dioleoylphosphatidylcholine (DOPC) membrane in the liquid-crystalline (L(α)) phase and sphingomyelin (SM)/cholesterol(chol) (molar ration; 6/4) membrane in the liquid-ordered (lo) phase. We found that low concentrations (less than critical micelle concentration) of LPS in aqueous solution induced the shape changes such as the transformation from a prolate to a two-spheres-connected by a very narrow neck in the DOPC-GUVs and also in the SM/chol (6/4)-GUVs above their threshold concentrations. The analysis of the shape changes of the GUVs indicates that the monomers of LPS can insert spontaneously into the external monolayer of the lipid membranes of these GUVs from the aqueous solution. Moreover, higher concentrations of LPS induced the vesicle fission of SM/chol(6/4)-GUVs above its higher threshold concentration. The vesicle fission of GUVs is similar to those induced by single long chain amphiphiles such as lysophosphatidylcholine. On the basis of these results, we discuss the interaction of wild type LPS with lipid membranes and cell membranes. These results suggest that LPS molecules can insert spontaneously into the external monolayer of the plasma membranes composed of the L(α) phase-membrane and the microdomain in the lo phase. Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.

  4. Perfluorooctanoic acid rigidifies a model lipid membrane

    NASA Astrophysics Data System (ADS)

    Brüning, B.; Farago, B.

    2014-04-01

    We report a combined dynamic light scattering and neutron spin-echo (NSE) study on vesicles composed of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine under the influence of varying amounts of perfluorooctanoic acid. We study local lipid bilayer undulations using NSE on time scales up to 200 ns. Similar to the effect evoked by cholesterol, we attribute the observed lipid bilayer stiffening to a condensing effect of the perfluorinated compound on the membrane.

  5. Ionic Permeability of Thin Lipid Membranes

    PubMed Central

    Gutknecht, John; Tosteson, D. C.

    1970-01-01

    Ultrathin (black) lipid membranes were made from sheep red cell lipids dissolved in n-decane. The presence of aliphatic alcohols in the aqueous solutions bathing these membranes produced reversible changes in the ionic permeability, but not the osomotic permeability. Heptanol (8 mM), for example, caused the membrane resistance (Rm) to decrease from >108 to about 105 ohm-cm2 and caused a marked increase in the permeability to cations, especially potassium. In terms of ionic transference numbers, deduced from measurements of the membrane potential at zero current, Tcat/TCl increased from about 6 to 21 and TK/TNa increased from about 3 to 21. The addition of long-chain (C8ndash;C10) alcohols to the lipid solutions from which membranes were made produced similar effects on the ionic permeability. A plot of log Rm vs. log alcohol concentration was linear over the range of maximum change in Rm, and the slope was -3 to -5 for C2 through C7 alcohols, suggesting that a complex of several alcohol molecules is responsible for the increase in ionic permeability. Membrane permselectivity changed from cationic to anionic when thorium or ferric iron (10-4 M) was present in the aqueous phase or when a secondary amine (Amberlite LA-2) was added to the lipid solutions from which membranes were made. When membranes containing the secondary amine were exposed to heptanol, Rm became very low (103–104 ohm-cm2) and the membranes became perfectly anion-selective, developing chloride diffusion potentials up to 150 mv. PMID:5535355

  6. 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.

  7. 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.

  8. Formation and Stability of Lipid Membrane Nanotubes.

    PubMed

    Bahrami, Amir Houshang; Hummer, Gerhard

    2017-09-26

    Lipid membrane nanotubes are abundant in living cells, even though tubules are energetically less stable than sheet-like structures. According to membrane elastic theory, the tubular endoplasmic reticulum (ER), with its high area-to-volume ratio, appears to be particularly unstable. We explore how tubular membrane structures can nevertheless be induced and why they persist. In Monte Carlo simulations of a fluid-elastic membrane model subject to thermal fluctuations and without constraints on symmetry, we find that a steady increase in the area-to-volume ratio readily induces tubular structures. In simulations mimicking the ER wrapped around the cell nucleus, tubules emerge naturally as the membrane area increases. Once formed, a high energy barrier separates tubules from the thermodynamically favored sheet-like membrane structures. Remarkably, this barrier persists even at large area-to-volume ratios, protecting tubules against shape transformations despite enormous driving forces toward sheet-like structures. Molecular dynamics simulations of a molecular membrane model confirm the metastability of tubular structures. Volume reduction by osmotic regulation and membrane area growth by lipid production and by fusion of small vesicles emerge as powerful factors in the induction and stabilization of tubular membrane structures.

  9. Microparticle Assembly Pathways on Lipid Membranes

    NASA Astrophysics Data System (ADS)

    van der Wel, Casper; Heinrich, Doris; Kraft, Daniela J.

    2017-09-01

    Understanding interactions between microparticles and lipid membranes is of increasing importance, especially for unraveling the influence of microplastics on our health and environment. Here, we study how a short-ranged adhesive force between microparticles and model lipid membranes causes membrane-mediated particle assembly. Using confocal microscopy, we observe the initial particle attachment to the membrane, then particle wrapping, and in rare cases spontaneous membrane tubulation. In the attached state, we measure that the particle mobility decreases by 26%. If multiple particles adhere to the same vesicle, their initial single-particle state determines their interactions and subsequent assembly pathways: 1) attached particles only aggregate when small adhesive vesicles are present in solution, 2) wrapped particles reversibly attract one another by membrane deformation, and 3) a combination of wrapped and attached particles form membrane-mediated dimers, which further assemble into a variety of complex structures. The experimental observation of distinct assembly pathways induced only by a short ranged membrane-particle adhesion, shows that a cellular cytoskeleton or other active components are not required for microparticle aggregation. We suggest that this membrane-mediated microparticle aggregation is a reason behind reported long retention times of polymer microparticles in organisms.

  10. 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

  11. Photoinduced Fusion of Lipid Bilayer Membranes.

    PubMed

    Suzuki, Yui; Nagai, Ken H; Zinchenko, Anatoly; Hamada, Tsutomu

    2017-03-14

    We have developed a novel system for photocontrol of the fusion of lipid vesicles through the use of a photosensitive surfactant containing an azobenzene moiety (AzoTAB). Real-time microscopic observations clarified a change in both the surface area and internal volume of vesicles during fusion. We also determined the optimal cholesterol concentrations and temperature for inducing fusion. The mechanism of fusion can be attributed to a change in membrane tension, which is caused by the solubilization of lipids through the isomerization of AzoTAB. We used a micropipet technique to estimate membrane tension and discuss the mechanism of fusion in terms of membrane elastic energy. The obtained results regarding this novel photoinduced fusion could lead to a better understanding of the mechanism of membrane fusion in living cells and may also see wider applications, such as in drug delivery and biomimetic material design.

  12. The membrane lipids of Halobacterium halobium

    PubMed Central

    Marshall, Carolyn L.; Brown, A. D.

    1968-01-01

    The lipid content of the cell membrane of Halobacterium halobium increased from about 15% to 21% during exponential growth of the organism. Total lipid phosphorus more than doubled during the growth cycle. The mixture of membrane lipids from stationary-phase organisms was similar to lipid mixtures from whole cells of other halobacteria inasmuch as 80% of the lipid phosphorus occurred in a diether analogue of phosphatidylglycerophosphate and an additional 7·5% occurred in the ether analogue of phosphatidylglycerol. The lipid mixture was more complex than those reported for other halophils, however, 12 components being recognized in the acetone-insoluble fraction and 17 in the acetone-soluble fraction. There were major changes in the proportions of some minor components of the acetone-insoluble fraction during a growth cycle. Three nitrogenous lipids were recognized in the acetone-insoluble fraction, but all were present in relatively low proportion. One, which was not a phospholipid, contained a bound peptide. Of the 17 acetonesoluble compounds, 15 were pigments. The major carotenoids were α- and β-bacteriorubrin. The carotenoid pigments occurred at maximal concentration after 6–7 days' growth. ImagesFig. 2. PMID:5701674

  13. Inducing morphological changes in lipid bilayer membranes with microfabricated substrates

    NASA Astrophysics Data System (ADS)

    Liu, Fangjie; Collins, Liam F.; Ashkar, Rana; Heberle, Frederick A.; Srijanto, Bernadeta R.; Collier, C. Patrick

    2016-11-01

    Lateral organization of lipids and proteins into distinct domains and anchoring to a cytoskeleton are two important strategies employed by biological membranes to carry out many cellular functions. However, these interactions are difficult to emulate with model systems. Here we use the physical architecture of substrates consisting of arrays of micropillars to systematically control the behavior of supported lipid bilayers - an important step in engineering model lipid membrane systems with well-defined functionalities. Competition between attractive interactions of supported lipid bilayers with the underlying substrate versus the energy cost associated with membrane bending at pillar edges can be systematically investigated as functions of pillar height and pitch, chemical functionalization of the microstructured substrate, and the type of unilamellar vesicles used for assembling the supported bilayer. Confocal fluorescent imaging and AFM measurements highlight correlations that exist between topological and mechanical properties of lipid bilayers and lateral lipid mobility in these confined environments. This study provides a baseline for future investigations into lipid domain reorganization on structured solid surfaces and scaffolds for cell growth.

  14. 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.

  15. Ionic transport in lipid bilayer membranes.

    PubMed Central

    Bordi, F; Cametti, C; Naglieri, A

    1998-01-01

    The current-voltage relationships of model bilayer membranes have been measured in various phospholipid systems, under the influence of both a gradient of potential and an ionic concentration, in order to describe the ion translocation through hydrated transient defects (water channels) across the bilayer formed because of lipid structure fluctuations and induced by temperature. The results have been analyzed in the light of a statistical rate theory for the transport process across a lipid bilayer, recently proposed by Skinner et al. (1993). In order to take into account the observed I-V curves and in particular the deviation from an ohmic behavior observed at high potential values, the original model has been modified, and a new version has been proposed by introducing an additional kinetic process. In this way, a very good agreement with the experimental values has been obtained for all of the systems we have investigated (dimyristoylphosphatidyl ethanolamine bilayers and mixed systems composed by dimyristoylphosphatidyl ethanolamine/dimyristoylphosphatidylcholine mixtures and dimyristoylphosphatidyl ethanolamine/phosphatidic acid dipalmitoyl mixtures). The rate constants governing the reactions at the bilayer interfaces have been evaluated for K+ and Cl- ions, as a function of temperature, from 5 to 35 degrees C and bulk ionic concentrations from 0.02 to 0.2 M. Finally, a comparison between the original model of Skinner and the modified version is presented, and the advantages of this new formulation are briefly discussed. PMID:9512032

  16. Super-resolution optical microscopy of lipid plasma membrane dynamics.

    PubMed

    Eggeling, Christian

    2015-01-01

    Plasma membrane dynamics are an important ruler of cellular activity, particularly through the interaction and diffusion dynamics of membrane-embedded proteins and lipids. FCS (fluorescence correlation spectroscopy) on an optical (confocal) microscope is a popular tool for investigating such dynamics. Unfortunately, its full applicability is constrained by the limited spatial resolution of a conventional optical microscope. The present chapter depicts the combination of optical super-resolution STED (stimulated emission depletion) microscopy with FCS, and why it is an important tool for investigating molecular membrane dynamics in living cells. Compared with conventional FCS, the STED-FCS approach demonstrates an improved possibility to distinguish free from anomalous molecular diffusion, and thus to give new insights into lipid-protein interactions and the traditional lipid 'raft' theory.

  17. 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

  18. 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.

  19. Self-segregation of myelin membrane lipids in model membranes.

    PubMed

    Yurlova, Larisa; Kahya, Nicoletta; Aggarwal, Shweta; Kaiser, Hermann-Josef; Chiantia, Salvatore; Bakhti, Mostafa; Pewzner-Jung, Yael; Ben-David, Oshrit; Futerman, Anthony H; Brügger, Britta; Simons, Mikael

    2011-12-07

    Rapid conduction of nerve impulses requires coating of axons by myelin sheaths, which are multilamellar, lipid-rich membranes produced by oligodendrocytes in the central nervous system. To act as an insulator, myelin has to form a stable and firm membrane structure. In this study, we have analyzed the biophysical properties of myelin membranes prepared from wild-type mice and from mouse mutants that are unable to form stable myelin. Using C-Laurdan and fluorescence correlation spectroscopy, we find that lipids are tightly organized and highly ordered in myelin isolated from wild-type mice, but not from shiverer and ceramide synthase 2 null mice. Furthermore, only myelin lipids from wild-type mice laterally segregate into physically distinct lipid phases in giant unilamellar vesicles in a process that requires very long chain glycosphingolipids. Taken together, our findings suggest that oligodendrocytes exploit the potential of lipids to self-segregate to generate a highly ordered membrane for electrical insulation of axons. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  20. Bacterial membrane lipids: diversity in structures and pathways.

    PubMed

    Sohlenkamp, Christian; Geiger, Otto

    2016-01-01

    For many decades, Escherichia coli was the main model organism for the study of bacterial membrane lipids. The results obtained served as a blueprint for membrane lipid biochemistry, but it is clear now that there is no such thing as a typical bacterial membrane lipid composition. Different bacterial species display different membrane compositions and even the membrane composition of cells belonging to a single species is not constant, but depends on the environmental conditions to which the cells are exposed. Bacterial membranes present a large diversity of amphiphilic lipids, including the common phospholipids phosphatidylglycerol, phosphatidylethanolamine and cardiolipin, the less frequent phospholipids phosphatidylcholine, and phosphatidylinositol and a variety of other membrane lipids, such as for example ornithine lipids, glycolipids, sphingolipids or hopanoids among others. In this review, we give an overview about the membrane lipid structures known in bacteria, the different metabolic pathways involved in their formation, and the distribution of membrane lipids and metabolic pathways across taxonomical groups.

  1. 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

  2. Interaction of tau protein with model lipid membranes induces tau structural compaction and membrane disruption

    PubMed Central

    Jones, Emmalee M.; Dubey, Manish; Camp, Phillip J.; Vernon, Briana C.; Biernat, Jacek; Mandelkow, Eckhard; Majewski, Jaroslaw; Chi, Eva Y.

    2012-01-01

    The misfolding and aggregation of the intrinsically disordered, microtubule-associated tau protein into neurofibrillary tangles is implicated in the pathogenesis of Alzheimer's disease. However, the mechanisms of tau aggregation and toxicity remain unknown. Recent work has shown that lipid membrane can induce tau aggregation and that membrane permeabilization may serve as a pathway by which protein aggregates exert toxicity, suggesting that the plasma membrane may play dual roles in tau pathology. This prompted our investigation to assess tau's propensity to interact with membranes and to elucidate the mutually disruptive structural perturbations the interactions induce in both tau and the membrane. We show that although highly charged and soluble, the full-length tau (hTau40) is also highly surface active, selectively inserts into anionic DMPG lipid monolayers and induces membrane morphological changes. To resolve molecular-scale structural details of hTau40 associated with lipid membranes, X-ray and neutron scattering techniques are utilized. X-ray reflectivity indicates hTau40's presence underneath a DMPG monolayer and penetration into the lipid headgroups and tailgroups, whereas grazing incidence X-ray diffraction shows that hTau40 insertion disrupts lipid packing. Moreover, both air/water and DMPG lipid membrane interfaces induce the disordered hTau40 to partially adopt a more compact conformation with density similar to that of a folded protein. Neutron reflectivity shows that tau completely disrupts supported DMPG bilayers while leaving the neutral DPPC bilayer intact. Our results show that hTau40's strong interaction with anionic lipids induces tau structural compaction and membrane disruption, suggesting possible membrane-based mechanisms of tau aggregation and toxicity in neurodegenerative diseases. PMID:22401494

  3. Noble gases in pure lipid membranes.

    PubMed

    Sierra-Valdez, F J; Ruiz-Suárez, J C

    2013-03-21

    The mechanism of how a noble gas modifies the excitability of nerve cells and how such excitability can be recovered under hyperbaric pressure remains unclear. Here we present a calorimetric study where the melting point depression of pure lipid membranes induced by noble gases and its recovery with a hydrostatic pressure is addressed. A correlation is found between the electric polarizability (α) of these gases and their effect on the melting transition of the membranes. These results concur with other findings to support the idea that general anesthesia only depends on the ability of a certain atom or molecule to increase the general disorder of the membrane.

  4. Targeting Membrane Lipid a Potential Cancer Cure?

    PubMed Central

    Tan, Loh Teng-Hern; Chan, Kok-Gan; Pusparajah, Priyia; Lee, Wai-Leng; Chuah, Lay-Hong; Khan, Tahir Mehmood; Lee, Learn-Han; Goh, Bey-Hing

    2017-01-01

    Cancer mortality and morbidity is projected to increase significantly over the next few decades. Current chemotherapeutic strategies have significant limitations, and there is great interest in seeking novel therapies which are capable of specifically targeting cancer cells. Given that fundamental differences exist between the cellular membranes of healthy cells and tumor cells, novel therapies based on targeting membrane lipids in cancer cells is a promising approach that deserves attention in the field of anticancer drug development. Phosphatidylethanolamine (PE), a lipid membrane component which exists only in the inner leaflet of cell membrane under normal circumstances, has increased surface representation on the outer membrane of tumor cells with disrupted membrane asymmetry. PE thus represents a potential chemotherapeutic target as the higher exposure of PE on the membrane surface of cancer cells. This feature as well as a high degree of expression of PE on endothelial cells in tumor vasculature, makes PE an attractive molecular target for future cancer interventions. There have already been several small molecules and membrane-active peptides identified which bind specifically to the PE molecules on the cancer cell membrane, subsequently inducing membrane disruption leading to cell lysis. This approach opens up a new front in the battle against cancer, and is of particular interest as it may be a strategy that may be prove effective against tumors that respond poorly to current chemotherapeutic agents. We aim to highlight the evidence suggesting that PE is a strong candidate to be explored as a potential molecular target for membrane targeted novel anticancer therapy. PMID:28167913

  5. 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

  6. Self-assembled tethered bimolecular lipid membranes.

    PubMed

    Sinner, Eva-Kathrin; Ritz, Sandra; Naumann, Renate; Schiller, Stefan; Knoll, Wolfgang

    2009-01-01

    This chapter describes some of the strategies developed in our group for designing, constructing and structurally and functionally characterizing tethered bimolecular lipid membranes (tBLM). We introduce this platform as a novel model membrane system that complements the existing ones, for example, Langmuir monolayers, vesicular liposomal dispersions and bimolecular ("black") lipid membranes. Moreover, it offers the additional advantage of allowing for studies of the influence of membrane structure and order on the function of integral proteins, for example, on how the composition and organization of lipids in a mixed membrane influence the ion translocation activity of integral channel proteins. The first strategy that we introduce concerns the preparation of tethered monolayers by the self-assembly of telechelics. Their molecular architecture with a headgroup, a spacer unit (the "tether") and the amphiphile that mimics the lipid molecule allows them to bind specifically to the solid support thus forming the proximal layer of the final architecture. After fusion of vesicles that could contain reconstituted proteins from a liposomal dispersion in contact to this monolayer the tethered bimolecular lipid membrane is obtained. This can then be characterized by a broad range of surface analytical techniques, including surface plasmon spectroscopies, the quartz crystal microbalance, fluorescence and IR spectroscopies, and electrochemical techniques, to mention a few. It is shown that this concept allows for the construction of tethered lipid bilayers with outstanding electrical properties including resistivities in excess of 10 MOmega cm2. A modified strategy uses the assembly of peptides as spacers that couple covalently via their engineered sulfhydryl or lipoic acid groups at the N-terminus to the employed gold substrate, while their C-terminus is being activated afterward for the coupling of, for example, dimyristoylphosphatidylethanol amine (DMPE) lipid molecules

  7. Interaction pathways between soft lipid nanodiscs and plasma membranes: A molecular modeling study.

    PubMed

    Li, Shixin; Luo, Zhen; Xu, Yan; Ren, Hao; Deng, Li; Zhang, Xianren; Huang, Fang; Yue, Tongtao

    2017-10-01

    Lipid nanodisc, a model membrane platform originally synthesized for study of membrane proteins, has recently been used as the carrier to deliver amphiphilic drugs into target tumor cells. However, the central question of how cells interact with such emerging nanomaterials remains unclear and deserves our research for both improving the delivery efficiency and reducing the side effect. In this work, a binary lipid nanodisc is designed as the minimum model to investigate its interactions with plasma membranes by using the dissipative particle dynamics method. Three typical interaction pathways, including the membrane attachment with lipid domain exchange of nanodiscs, the partial membrane wrapping with nanodisc vesiculation, and the receptor-mediated endocytosis, are discovered. For the first pathway, the boundary normal lipids acting as ligands diffuse along the nanodisc rim to gather at the membrane interface, repelling the central bola lipids to reach a stable membrane attachment. If bola lipids are positioned at the periphery and act as ligands, they diffuse to form a large aggregate being wrapped by the membrane, leaving the normal lipids exposed on the membrane exterior by assembling into a vesicle. Finally, by setting both central normal lipids and boundary bola lipids as ligands, the receptor-mediated endocytosis occurs via both deformation and self-rotation of the nanodiscs. All above pathways for soft lipid nanodiscs are quite different from those for rigid nanoparticles, which may provide useful guidelines for design of soft lipid nanodiscs in widespread biomedical applications. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. 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.

  9. 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.

  10. Anionic lipids and the maintenance of membrane electrostatics in eukaryotes

    PubMed Central

    Platre, Matthieu Pierre

    2017-01-01

    ABSTRACT A wide range of signaling processes occurs at the cell surface through the reversible association of proteins from the cytosol to the plasma membrane. Some low abundant lipids are enriched at the membrane of specific compartments and thereby contribute to the identity of cell organelles by acting as biochemical landmarks. Lipids also influence membrane biophysical properties, which emerge as an important feature in specifying cellular territories. Such parameters are crucial for signal transduction and include lipid packing, membrane curvature and electrostatics. In particular, membrane electrostatics specifies the identity of the plasma membrane inner leaflet. Membrane surface charges are carried by anionic phospholipids, however the exact nature of the lipid(s) that powers the plasma membrane electrostatic field varies among eukaryotes and has been hotly debated during the last decade. Herein, we discuss the role of anionic lipids in setting up plasma membrane electrostatics and we compare similarities and differences that were found in different eukaryotic cells. PMID:28102755

  11. Atomic force microscopy of model lipid membranes.

    PubMed

    Morandat, Sandrine; Azouzi, Slim; Beauvais, Estelle; Mastouri, Amira; El Kirat, Karim

    2013-02-01

    Supported lipid bilayers (SLBs) are biomimetic model systems that are now widely used to address the biophysical and biochemical properties of biological membranes. Two main methods are usually employed to form SLBs: the transfer of two successive monolayers by Langmuir-Blodgett or Langmuir-Schaefer techniques, and the fusion of preformed lipid vesicles. The transfer of lipid films on flat solid substrates offers the possibility to apply a wide range of surface analytical techniques that are very sensitive. Among them, atomic force microscopy (AFM) has opened new opportunities for determining the nanoscale organization of SLBs under physiological conditions. In this review, we first focus on the different protocols generally employed to prepare SLBs. Then, we describe AFM studies on the nanoscale lateral organization and mechanical properties of SLBs. Lastly, we survey recent developments in the AFM monitoring of bilayer alteration, remodeling, or digestion, by incubation with exogenous agents such as drugs, proteins, peptides, and nanoparticles.

  12. 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

  13. 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.

  14. Cholesterol effect on the dipole potential of lipid membranes.

    PubMed

    Starke-Peterkovic, Thomas; Turner, Nigel; Vitha, Mark F; Waller, Mark P; Hibbs, David E; Clarke, Ronald J

    2006-06-01

    The effect of cholesterol removal by methyl-beta-cyclodextrin on the dipole potential, psi(d), of membrane vesicles composed of natural membrane lipids extracted from the kidney and brain of eight vertebrate species was investigated using the voltage-sensitive fluorescent probe di-8-ANEPPS. Cyclodextrin treatment reduced cholesterol levels by on average 80% and this was associated with an average reduction in psi(d) of 50 mV. Measurements of the effect of a range of cholesterol derivatives on the psi(d) of DMPC lipid vesicles showed that the magnitude of the effect correlated with the component of the sterol's dipole moment perpendicular to the membrane surface. The changes in psi(d) observed could not be accounted for solely by the electric field originating from the sterols' dipole moments. Additional factors must arise from sterol-induced changes in lipid packing, which changes the density of dipoles in the membrane, and changes in water penetration into the membrane, which changes the effective dielectric constant of the interfacial region. In DMPC membranes, the cholesterol-induced change in psi(d) was biphasic, i.e., a maximum in psi(d) was observed at approximately 35-45 mol %, after which psi(d) started to decrease. We suggest that this could be associated with a maximum in the strength of DMPC-cholesterol intermolecular forces at this composition.

  15. Importance of the hexagonal lipid phase in biological membrane organization

    PubMed Central

    Jouhet, Juliette

    2013-01-01

    Domains are present in every natural membrane. They are characterized by a distinctive protein and/or lipid composition. Their size is highly variable from the nano- to the micrometer scale. The domains confer specific properties to the membrane leading to original structure and function. The determinants leading to domain organization are therefore important but remain obscure. This review presents how the ability of lipids to organize into hexagonal II or lamellar phases can promote particular local structures within membranes. Since biological membranes are composed of a mixture of lipids, each with distinctive biophysical properties, lateral and transversal sorting of lipids can promote creation of domains inside the membrane through local modulation of the lipid phase. Lipid biophysical properties have been characterized for long based on in vitro analyses using non-natural lipid molecules; their re-examinations using natural lipids might open interesting perspectives on membrane architecture occurring in vivo in various cellular and physiological contexts. PMID:24348497

  16. Modeling Membrane Deformations and Lipid Demixing upon Protein-Membrane Interaction: The BAR Dimer Adsorption

    PubMed Central

    Khelashvili, George; Harries, Daniel; Weinstein, Harel

    2009-01-01

    We use a self-consistent mean-field theory, designed to investigate membrane reshaping and lipid demixing upon interaction with proteins, to explore BAR domains interacting with large patches of lipid membranes of heterogeneous compositions. The computational model includes contributions to the system free energy from electrostatic interactions and elastic energies of the membrane, as well as salt and lipid mixing entropies. The results from our simulation of a single adsorbing Amphiphysin BAR dimer indicate that it is capable of stabilizing a significantly curved membrane. However, we predict that such deformations will occur only for membrane patches that have the inherent propensity for high curvature, reflected in the tendency to create local distortions that closely match the curvature of the BAR dimer itself. Such favorable preconditioning for BAR-membrane interaction may be the result of perturbations such as local lipid demixing induced by the interaction, or of a prior insertion of the BAR domain's amphiphatic N-helix. From our simulations it appears that local segregation of charged lipids under the influence of the BAR dimer cannot produce high enough asymmetry between bilayer leaflets to induce significant bending. In the absence of additional energy contributions that favor membrane asymmetry, the membrane will remain nearly flat upon single BAR dimer adsorption, relative to the undulation expected from thermal fluctuations. Thus, we conclude that the N-helix insertions have a critical mechanistic role in the local perturbation and curving of the membrane, which is then stabilized by the electrostatic interaction with the BAR dimer. We discuss how these results can be used to estimate the tendency of BARs to bend membranes in terms of a spatially nonisotropic spontaneous curvature. PMID:19751667

  17. 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.

  18. Influence of membrane lipid composition on flavonoid-membrane interactions: Implications on their biological activity.

    PubMed

    Selvaraj, Stalin; Krishnaswamy, Sridharan; Devashya, Venkappayya; Sethuraman, Swaminathan; Krishnan, Uma Maheswari

    2015-04-01

    The membrane interactions and localization of flavonoids play a vital role in altering membrane-mediated cell signaling cascades as well as influence the pharmacological activities such as anti-tumour, anti-microbial and anti-oxidant properties of flavonoids. Various techniques have been used to investigate the membrane interaction of flavonoids. These include partition coefficient, fluorescence anisotropy, differential scanning calorimetry, NMR spectroscopy, electrophysiological methods and molecular dynamics simulations. Each technique will provide specific information about either alteration of membrane fluidity or localization of flavonoids within the lipid bilayer. Apart from the diverse techniques employed, the concentrations of flavonoids and lipid membrane composition employed in various studies reported in literature also are different and together these variables contribute to diverse findings that sometimes contradict each other. This review highlights different techniques employed to investigate the membrane interaction of flavonoids with special emphasis on erythrocyte model membrane systems and their significance in understanding the nature and extent of flavonoid-membrane interactions. We also attempt to correlate the membrane localization and alteration in membrane fluidity with the biological activities of flavonoids such as anti-oxidant, anti-cancer and anti-microbial properties.

  19. 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.

  20. Molecular dynamics study of bipolar tetraether lipid membranes.

    PubMed

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

    2005-11-01

    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.

  1. Effect of Amphotericin B antibiotic on the properties of model lipid membrane

    NASA Astrophysics Data System (ADS)

    Kiryakova, S.; Dencheva-Zarkova, M.; Genova, J.

    2014-12-01

    Model membranes formed from natural and synthetic lipids are an interesting object for scientific investigations due to their similarity to biological cell membrane and their simple structure with controlled composition and properties. Amphotericin B is an important polyene antifungal antibiotic, used for treatment of systemic fungal infections. It is known from the literature that the studied antibiotic has a substantial effect on the transmembrane ionic channel structures. When applied to the lipid membranes it has the tendency to create pores and in this way to affect the structure and the properties of the membrane lipid bilayer. In this work the thermally induced shape fluctuations of giant quasi-spherical liposomes have been used to study the influence of polyene antibiotic amphotericin B on the elastic properties of model lipid membranes. It have been shown experimentally that the presence of 3 mol % of AmB in the lipid membrane reduces the bending elasticity of the lipid membrane for both studied cases: pure SOPC membrane and mixed SOPC-Cholesterol membrane. Interaction of the amphotericin B with bilayer lipid membranes containing channels have been studied in this work. Model membranes were self-assembled using the patch-clamp and tip-dip patch clamp technique. We have found that amphotericin B is an ionophore and reduces the resistance of the lipid bilayer.

  2. Preparation of Artificial Plasma Membrane Mimicking Vesicles with Lipid Asymmetry

    PubMed Central

    Lin, Qingqing; London, Erwin

    2014-01-01

    Lipid asymmetry, the difference in lipid distribution across the lipid bilayer, is one of the most important features of eukaryotic cellular membranes. However, commonly used model membrane vesicles cannot provide control of lipid distribution between inner and outer leaflets. We recently developed methods to prepare asymmetric model membrane vesicles, but facile incorporation of a highly controlled level of cholesterol was not possible. In this study, using hydroxypropyl-α-cyclodextrin based lipid exchange, a simple method was devised to prepare large unilamellar model membrane vesicles that closely resemble mammalian plasma membranes in terms of their lipid composition and asymmetry (sphingomyelin (SM) and/or phosphatidylcholine (PC) outside/phosphatidylethanolamine (PE) and phosphatidylserine (PS) inside), and in which cholesterol content can be readily varied between 0 and 50 mol%. We call these model membranes “artificial plasma membrane mimicking” (“PMm”) vesicles. Asymmetry was confirmed by both chemical labeling and measurement of the amount of externally-exposed anionic lipid. These vesicles should be superior and more realistic model membranes for studies of lipid-lipid and lipid-protein interaction in a lipid environment that resembles that of mammalian plasma membranes. PMID:24489974

  3. Preparation of artificial plasma membrane mimicking vesicles with lipid asymmetry.

    PubMed

    Lin, Qingqing; London, Erwin

    2014-01-01

    Lipid asymmetry, the difference in lipid distribution across the lipid bilayer, is one of the most important features of eukaryotic cellular membranes. However, commonly used model membrane vesicles cannot provide control of lipid distribution between inner and outer leaflets. We recently developed methods to prepare asymmetric model membrane vesicles, but facile incorporation of a highly controlled level of cholesterol was not possible. In this study, using hydroxypropyl-α-cyclodextrin based lipid exchange, a simple method was devised to prepare large unilamellar model membrane vesicles that closely resemble mammalian plasma membranes in terms of their lipid composition and asymmetry (sphingomyelin (SM) and/or phosphatidylcholine (PC) outside/phosphatidylethanolamine (PE) and phosphatidylserine (PS) inside), and in which cholesterol content can be readily varied between 0 and 50 mol%. We call these model membranes "artificial plasma membrane mimicking" ("PMm") vesicles. Asymmetry was confirmed by both chemical labeling and measurement of the amount of externally-exposed anionic lipid. These vesicles should be superior and more realistic model membranes for studies of lipid-lipid and lipid-protein interaction in a lipid environment that resembles that of mammalian plasma membranes.

  4. 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.

  5. On the interaction between fluoxetine and lipid membranes: Effect of the lipid composition.

    PubMed

    Pham, Vy T; Nguyen, Trinh Q; Dao, Uyen P N; Nguyen, Trang T

    2017-09-20

    Molecular interaction between the antidepressant fluoxetine and lipid bilayers was investigated in order to provide insights into the drug's incorporation to lipid membranes. In particular, the effects of lipid's unsaturation degree and cholesterol content on the partitioning of fluoxetine into large unilamellar vesicles (LUVs) comprised of unsaturated 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and saturated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) were evaluated using second derivative spectrophotometry and Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). It was found that fluoxetine partitioned to a greater extent into the liquid-crystalline DOPC LUVs than into the solid-gel DPPC LUVs. The lipid physical state dependence of drug partitioning was verified by increasing the temperature in which the partition coefficient of fluoxetine significantly increased upon the change of the lipid phase from solid-gel to liquid-crystalline. The incorporation of 28mol% cholesterol into the LUVs exerted a significant influence on the drug partitioning into both DOPC and DPPC LUVs. The ATR-FTIR study revealed that fluoxetine perturbed the conformation of DOPC more strongly than that of DPPC due to the cis-double bonds in the lipid acyl chains. Fluoxetine possibly bound to the carbonyl moiety of the lipids through the hydrogen bonding formation while displaced some water molecules surrounding the PO2(-) regions of the lipid head groups. Cholesterol, however, could lessen the interaction between fluoxetine and the carbonyl groups of both DOPC and DPPC LUVs. These findings provided a better understanding of the role of lipid structure and cholesterol on the interaction between fluoxetine and lipid membranes, shedding more light into the drug's therapeutic action. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. Three-Phase Coexistence in Lipid Membranes.

    PubMed

    Aufderhorst-Roberts, Anders; Chandra, Udayan; Connell, Simon D

    2017-01-24

    Phospholipid ternary systems are useful model systems for understanding lipid-lipid interactions and their influence on biological properties such as cell signaling and protein translocation. Despite extensive studies, there are still open questions relating to membrane phase behavior, particularly relating to a proposed state of three-phase coexistence, due to the difficulty in clearly distinguishing the three phases. We look in and around the region of the phase diagram where three phases are expected and use a combination of different atomic force microscopy (AFM) modes to present the first images of three coexisting lipid phases in biomimetic cell lipid membranes. Domains form through either nucleation or spinodal decomposition dependent upon composition, with some exhibiting both mechanisms in different domains simultaneously. Slow cooling rates are necessary to sufficiently separate mixtures with high proportions of lo and lβ phase. We probe domain heights and mechanical properties and demonstrate that the gel (lβ) domains have unusually low structural integrity in the three-phase region. This finding supports the hypothesis of a "disordered gel" state that has been proposed from NMR studies of similar systems, where the addition of small amounts of cholesterol was shown to disrupt the regular packing of the lβ state. We use NMR data from the literature on chain disorder in different mixtures and estimate an expected step height that is in excellent agreement with the AFM data. Alternatively, the disordered solid phase observed here and in the wider literature could be explained by the lβ phase being out of equilibrium, in a surface kinetically trapped state. This view is supported by the observation of unusual growth of nucleated domains, which we term "tree-ring growth," reflecting compositional heterogeneity in large disordered lβ phase domains.

  7. 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.

  8. 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

  9. A sliding selectivity scale for lipid binding to membrane proteins

    PubMed Central

    Landreh, Michael; Marty, Michael T.; Gault, Joseph; Robinson, Carol V.

    2017-01-01

    Biological membranes form barriers that are essential for cellular integrity and compartmentalisation. Proteins that reside in the membrane have co-evolved with their hydrophobic lipid environment which serves as a solvent for proteins with very diverse requirements. As a result, membrane protein-lipid interactions range from completely non-selective to highly discriminating. Mass spectrometry (MS), in combination with X-ray crystallography and molecular dynamics simulations, enables us to monitor how lipids interact with intact membrane protein complexes and assess their effects on structure and dynamics. Recent studies illustrate the ability to differentiate specific lipid binding, preferential interactions with lipid subsets, and nonselective annular contacts. In this review, we consider the biological implications of different lipid-binding scenarios and propose that binding occurs on a sliding selectivity scale, in line with the view of biological membranes as facilitators of dynamic protein and lipid organization. PMID:27155089

  10. Imaging of blood plasma coagulation at supported lipid membranes.

    PubMed

    Faxälv, Lars; Hume, Jasmin; Kasemo, Bengt; Svedhem, Sofia

    2011-12-15

    The blood coagulation system relies on lipid membrane constituents to act as regulators of the coagulation process upon vascular trauma, and in particular the 2D configuration of the lipid membranes is known to efficiently catalyze enzymatic activity of blood coagulation factors. This work demonstrates a new application of a recently developed methodology to study blood coagulation at lipid membrane interfaces with the use of imaging technology. Lipid membranes with varied net charges were formed on silica supports by systematically using different combinations of lipids where neutral phosphocholine (PC) lipids were mixed with phospholipids having either positively charged ethylphosphocholine (EPC), or negatively charged phosphatidylserine (PS) headgroups. Coagulation imaging demonstrated that negatively charged SiO(2) and membrane surfaces exposing PS (obtained from liposomes containing 30% of PS) had coagulation times which were significantly shorter than those for plain PC membranes and EPC exposing membrane surfaces (obtained from liposomes containing 30% of EPC). Coagulation times decreased non-linearly with increasing negative surface charge for lipid membranes. A threshold value for shorter coagulation times was observed below a PS content of ∼6%. We conclude that the lipid membranes on solid support studied with the imaging setup as presented in this study offers a flexible and non-expensive solution for coagulation studies at biological membranes. It will be interesting to extend the present study towards examining coagulation on more complex lipid-based model systems. Copyright © 2011 Elsevier Inc. All rights reserved.

  11. Do membrane lipids modify the ouabain-sensitivity of cardiac (Na,K)ATPase?

    PubMed

    Hegyvary, C; Chigurupati, R; Mahoney, D

    1981-02-01

    We investigated whether membrane lipids can alter the affinity of cardiac (Na,K)ATPase (ATP phosphohydrolase, EC 3.6.1.6) for ouabain. We recombined partially (80-95%) delipidated membrane proteins from a digitalis-sensitive species (dog) with membrane lipids from a relatively digitalis-insensitive species (rat) or vice versa, and estimated the affinity of (Na,K)ATPase for ouabain in these hybrid membranes by measuring the half-maximal inhibitory concentration (I50). Delipidation reduced the enzyme activity by 90-95%, but 40-60% of the original activity could be restored with lipids from the same or from the other species and distribution of [14C]phosphatidylcholine showed complete mixing between the native and foreign lipids. In these hybrid cardiac membranes affinity (I50) for ouabain was determined by the origin of the (Na,K)ATPase protein and was not modified by the change in membrane lipids.

  12. Hydrostatic pressure decreases membrane fluidity and lipid desaturase expression in chondrocyte progenitor cells.

    PubMed

    Montagne, Kevin; Uchiyama, Hiroki; Furukawa, Katsuko S; Ushida, Takashi

    2014-01-22

    Membrane biomechanical properties are critical in modulating nutrient and metabolite exchange as well as signal transduction. Biological membranes are predominantly composed of lipids, cholesterol and proteins, and their fluidity is tightly regulated by cholesterol and lipid desaturases. To determine whether such membrane fluidity regulation occurred in mammalian cells under pressure, we investigated the effects of pressure on membrane lipid order of mouse chondrogenic ATDC5 cells and desaturase gene expression. Hydrostatic pressure linearly increased membrane lipid packing and simultaneously repressed lipid desaturase gene expression. We also showed that cholesterol mimicked and cholesterol depletion reversed those effects, suggesting that desaturase gene expression was controlled by the membrane physical state itself. This study demonstrates a new effect of hydrostatic pressure on mammalian cells and may help to identify the molecular mechanisms involved in hydrostatic pressure sensing in chondrocytes.

  13. Tuning Membrane Thickness Fluctuations in Model Lipid Bilayers

    PubMed Central

    Ashkar, Rana; Nagao, Michihiro; Butler, Paul D.; Woodka, Andrea C.; Sen, Mani K.; Koga, Tadanori

    2015-01-01

    Membrane thickness fluctuations have been associated with a variety of critical membrane phenomena, such as cellular exchange, pore formation, and protein binding, which are intimately related to cell functionality and effective pharmaceuticals. Therefore, understanding how these fluctuations are controlled can remarkably impact medical applications involving selective macromolecule binding and efficient cellular drug intake. Interestingly, previous reports on single-component bilayers show almost identical thickness fluctuation patterns for all investigated lipid tail-lengths, with similar temperature-independent membrane thickness fluctuation amplitude in the fluid phase and a rapid suppression of fluctuations upon transition to the gel phase. Presumably, in vivo functions require a tunability of these parameters, suggesting that more complex model systems are necessary. In this study, we explore lipid tail-length mismatch as a regulator for membrane fluctuations. Unilamellar vesicles of an equimolar mixture of dimyristoylphosphatidylcholine and distearoylphosphatidylcholine molecules, with different tail-lengths and melting transition temperatures, are used as a model system for this next level of complexity. Indeed, this binary system exhibits a significant response of membrane dynamics to thermal variations. The system also suggests a decoupling of the amplitude and the relaxation time of the membrane thickness fluctuations, implying a potential for independent control of these two key parameters. PMID:26153707

  14. Bipolar tetraether lipids: chain flexibility and membrane polarity gradients from spin-label electron spin resonance.

    PubMed

    Bartucci, R; Gambacorta, A; Gliozzi, A; Marsh, D; Sportelli, L

    2005-11-15

    Membranes of thermophilic Archaea are composed of unique tetraether lipids in which C40, saturated, methyl-branched biphytanyl chains are linked at both ends to polar groups. In this paper, membranes composed of bipolar lipids P2 extracted from the acidothermophile archaeon Sulfolobus solfataricus are studied. The biophysical basis for the membrane formation and thermal stability is investigated by using electron spin resonance (ESR) of spin-labeled lipids. Spectral anisotropy and isotropic hyperfine couplings are used to determine the chain flexibility and polarity gradients, respectively. For comparison, similar measurements have been carried out on aqueous dispersions of diacyl reference lipid dipalmitoyl phosphatidylcholine and also of diphytanoyl phosphatidylcholine, which has methyl-branched chains. At a given temperature, the bolaform lipid chains are more ordered and less flexible than in normal bilayer membranes. Only at elevated temperatures (80 degrees C) does the flexibility of the chain environment in tetraether lipid assemblies approach that of fluid bilayer membranes. The height of the hydrophobic barrier formed by a monolayer of archaebacterial lipids is similar to that in conventional fluid bilayer membranes, and the permeability barrier width is comparable to that formed by a bilayer of C16 lipid chains. At a mole ratio of 1:2, the tetraether P2 lipids mix well with dipalmitoyl phosphatidylcholine lipids and stabilize conventional bilayer membranes. The biological as well as the biotechnological relevance of the results is discussed.

  15. Efficient replacement of plasma membrane outer leaflet phospholipids and sphingolipids in cells with exogenous lipids.

    PubMed

    Li, Guangtao; Kim, JiHyun; Huang, Zhen; St Clair, Johnna R; Brown, Deborah A; London, Erwin

    2016-12-06

    Our understanding of membranes and membrane lipid function has lagged far behind that of nucleic acids and proteins, largely because it is difficult to manipulate cellular membrane lipid composition. To help solve this problem, we show that methyl-α-cyclodextrin (MαCD)-catalyzed lipid exchange can be used to maximally replace the sphingolipids and phospholipids in the outer leaflet of the plasma membrane of living mammalian cells with exogenous lipids, including unnatural lipids. In addition, lipid exchange experiments revealed that 70-80% of cell sphingomyelin resided in the plasma membrane outer leaflet; the asymmetry of metabolically active cells was similar to that previously defined for erythrocytes, as judged by outer leaflet lipid composition; and plasma membrane outer leaflet phosphatidylcholine had a significantly lower level of unsaturation than phosphatidylcholine in the remainder of the cell. The data also provided a rough estimate for the total cellular lipids residing in the plasma membrane (about half). In addition to such lipidomics applications, the exchange method should have wide potential for investigations of lipid function and modification of cellular behavior by modification of lipids.

  16. Efficient replacement of plasma membrane outer leaflet phospholipids and sphingolipids in cells with exogenous lipids

    PubMed Central

    Kim, JiHyun; Huang, Zhen; St. Clair, Johnna R.; Brown, Deborah A.; London, Erwin

    2016-01-01

    Our understanding of membranes and membrane lipid function has lagged far behind that of nucleic acids and proteins, largely because it is difficult to manipulate cellular membrane lipid composition. To help solve this problem, we show that methyl-α-cyclodextrin (MαCD)-catalyzed lipid exchange can be used to maximally replace the sphingolipids and phospholipids in the outer leaflet of the plasma membrane of living mammalian cells with exogenous lipids, including unnatural lipids. In addition, lipid exchange experiments revealed that 70–80% of cell sphingomyelin resided in the plasma membrane outer leaflet; the asymmetry of metabolically active cells was similar to that previously defined for erythrocytes, as judged by outer leaflet lipid composition; and plasma membrane outer leaflet phosphatidylcholine had a significantly lower level of unsaturation than phosphatidylcholine in the remainder of the cell. The data also provided a rough estimate for the total cellular lipids residing in the plasma membrane (about half). In addition to such lipidomics applications, the exchange method should have wide potential for investigations of lipid function and modification of cellular behavior by modification of lipids. PMID:27872310

  17. 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

  18. Reconstitution of a Kv Channel into Lipid Membranes for Structural and Functional Studies

    PubMed Central

    Shi, Liang; Jiang, Qiu-Xing

    2013-01-01

    To study the lipid-protein interaction in a reductionistic fashion, it is necessary to incorporate the membrane proteins into membranes of well-defined lipid composition. We are studying the lipid-dependent gating effects in a prototype voltage-gated potassium (Kv) channel, and have worked out detailed procedures to reconstitute the channels into different membrane systems. Our reconstitution procedures take consideration of both detergent-induced fusion of vesicles and the fusion of protein/detergent micelles with the lipid/detergent mixed micelles as well as the importance of reaching an equilibrium distribution of lipids among the protein/detergent/lipid and the detergent/lipid mixed micelles. Our data suggested that the insertion of the channels in the lipid vesicles is relatively random in orientations, and the reconstitution efficiency is so high that no detectable protein aggregates were seen in fractionation experiments. We have utilized the reconstituted channels to determine the conformational states of the channels in different lipids, record electrical activities of a small number of channels incorporated in planar lipid bilayers, screen for conformation-specific ligands from a phage-displayed peptide library, and support the growth of 2D crystals of the channels in membranes. The reconstitution procedures described here may be adapted for studying other membrane proteins in lipid bilayers, especially for the investigation of the lipid effects on the eukaryotic voltage-gated ion channels. PMID:23892292

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

    PubMed

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

    2016-04-14

    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 10(8)-10(9) 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 ⋅ 10(8) V m(-1)) when in the fluid phase with a monovalent counter-ion and ∼1.4 V (∼2.8 ⋅ 10(8) 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

  20. 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

  1. Supported lipid bilayers as models for studying membrane domains.

    PubMed

    Kiessling, Volker; Yang, Sung-Tae; Tamm, Lukas K

    2015-01-01

    Supported lipid bilayers have been in use for over 30 years. They have been employed to study the structure, composition, and dynamics of lipid bilayer phases, the binding and distribution of soluble, integral, and lipidated proteins in membranes, membrane fusion, and interactions of membranes with elements of the cytoskeleton. This review focuses on the unique ability of supported lipid bilayers to study liquid-ordered and liquid-disordered domains in membranes. We highlight methods to produce asymmetric lipid bilayers with lipid compositions that mimic those of the extracellular and cytoplasmic leaflets of cell membranes and the functional reconstitution of membrane proteins into such systems. Questions related to interleaflet domain coupling and membrane protein activation have been addressed and answered using advanced reconstitution and imaging procedures in symmetric and asymmetric supported membranes with and without coexisting lipid phase domains. Previously controversial topics regarding anomalous and anisotropic diffusion in membranes have been resolved by using supported membrane approaches showing that the propensity of certain lipid compositions to form "rafts" are important but overlaid with "picket-fence" interactions that are imposed by a subtended cytoskeletal network.

  2. [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.

  3. [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.

  4. 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)

  5. 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)

  6. [Depth-dependent investigation of the apolar zone of lipid membranes using a series of fluorescent probes, Me4-BODIPY-8-labeled phosphatidylcholines].

    PubMed

    Omel'kov, A V; Pavlova, Iu B; Boldyrev, I A; Molotkovskiĭ, Iu G

    2007-01-01

    A series of lipid probes, phosphatidylcholines labeled with Me4-BODIPY-8 (4,4-difluoro-1,3,5,7- tetramethyl-4-bora-3a,4a-diaza-s-indacen-8-yl) fluorophore attached to the end of an acyl residue at different distances from the polar head, were used as depth-dependent probes for the apolar zone of model membrane systems, large unilamellar vesicles (LUVs). Data on the anisotropy of probe fluorescence demonstrated different mobility profiles for the fluorophore microenvironment in LUVs of different composition at various temperatures, which indicates a high sensitivity of these probes as tools for studying membrane systems. An interesting anomaly was observed for LUVs from dimiristoylphosphatidylcholine (DMPC) or from a DMPC-cholesterol mixture: the anisotropy of the fluorophore located near the bilayer center is larger than that of the fluorophore located further from the center; i.e., the mobility of the microenvironment is lower in the first case. This anomaly is supposed to result from the penetration of the unlabeled long chain of the probes into the opposite bilayer leaflet. Such a possibility should be taken into account in constructing fluorescent probes and interpreting the results.

  7. Lipid dependence of diadinoxanthin solubilization and de-epoxidation in artificial membrane systems resembling the lipid composition of the natural thylakoid membrane.

    PubMed

    Goss, Reimund; Latowski, Dariusz; Grzyb, Joanna; Vieler, Astrid; Lohr, Martin; Wilhelm, Christian; Strzalka, Kazimierz

    2007-01-01

    In the present study, the solubility and enzymatic de-epoxidation of diadinoxanthin (Ddx) was investigated in three different artificial membrane systems: (1) Unilamellar liposomes composed of different concentrations of the bilayer forming lipid phosphatidylcholine (PC) and the inverted hexagonal phase (H(II) phase) forming lipid monogalactosyldiacylglycerol (MGDG), (2) liposomes composed of PC and the H(II) phase forming lipid phosphatidylethanolamine (PE), and (3) an artificial membrane system composed of digalactosyldiacylglycerol (DGDG) and MGDG, which resembles the lipid composition of the natural thylakoid membrane. Our results show that Ddx de-epoxidation strongly depends on the concentration of the inverted hexagonal phase forming lipids MGDG or PE in the liposomes composed of PC or DGDG, thus indicating that the presence of inverted hexagonal structures is essential for Ddx de-epoxidation. The difference observed for the solubilization of Ddx in H(II) phase forming lipids compared with bilayer forming lipids indicates that Ddx is not equally distributed in the liposomes composed of different concentrations of bilayer versus non-bilayer lipids. In artificial membranes with a high percentage of bilayer lipids, a large part of Ddx is located in the membrane bilayer. In membranes composed of equal proportions of bilayer and H(II) phase forming lipids, the majority of the Ddx molecules is located in the inverted hexagonal structures. The significance of the pigment distribution and the three-dimensional structure of the H(II) phase for the de-epoxidation reaction is discussed, and a possible scenario for the lipid dependence of Ddx (and violaxanthin) de-epoxidation in the native thylakoid membrane is proposed.

  8. Aspirin inhibits formation of cholesterol rafts in fluid lipid membranes.

    PubMed

    Alsop, Richard J; Toppozini, Laura; Marquardt, Drew; Kučerka, Norbert; Harroun, Thad A; Rheinstädter, Maikel C

    2015-03-01

    Aspirin and other non-steroidal anti-inflammatory drugs have a high affinity for phospholipid membranes, altering their structure and biophysical properties. Aspirin has been shown to partition into the lipid head groups, thereby increasing membrane fluidity. Cholesterol is another well known mediator of membrane fluidity, in turn increasing membrane stiffness. As well, cholesterol is believed to distribute unevenly within lipid membranes leading to the formation of lipid rafts or plaques. In many studies, aspirin has increased positive outcomes for patients with high cholesterol. We are interested if these effects may be, at least partially, the result of a non-specific interaction between aspirin and cholesterol in lipid membranes. We have studied the effect of aspirin on the organization of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) membranes containing cholesterol. Through Langmuir-Blodgett experiments we show that aspirin increases the area per lipid and decreases compressibility at 32.5 mol% cholesterol, leading to a significant increase of fluidity of the membranes. Differential scanning calorimetry provides evidence for the formation of meta-stable structures in the presence of aspirin. The molecular organization of lipids, cholesterol and aspirin was studied using neutron diffraction. While the formation of rafts has been reported in binary DPPC/cholesterol membranes, aspirin was found to locally disrupt membrane organization and lead to the frustration of raft formation. Our results suggest that aspirin is able to directly oppose the formation of cholesterol structures through non-specific interactions with lipid membranes.

  9. Lipid exchange between membranes: effects of membrane surface charge, composition, and curvature.

    PubMed

    Zhu, Tao; Jiang, Zhongying; Ma, Yuqiang

    2012-09-01

    Intermembrane lipid exchange is critical to membrane functions and pharmaceutical applications. The exchange process is not fully understood and it is explored by quartz crystal microbalance with dissipation monitor method in this research. It is found that intermembrane lipid exchange is accelerated with the decrease of vesicle size and the increase of charge and liquid crystalline lipid composition ratio. Vesicle adsorption rate, membrane lateral pressure gradient, and lipid lateral diffusion coefficient are inferred to be critical in deciding the lipid exchange kinetics between membranes. Besides that, the membrane contact situation during lipid exchange is also studied. The maximum total membrane contact area is found to increase with the decrease of vesicle size, charged and liquid crystalline lipid composition ratio. A competition mechanism between the vesicle adsorption rate and the intermembrane lipid exchange rate was proposed to control the maximum total membrane contact area.

  10. Analysis of membrane lipid biogenesis pathways using yeast genetics.

    PubMed

    Gsell, Martina; Daum, Günther

    2013-01-01

    The yeast Saccharomyces cerevisiae has become a valuable eukaryotic model organism to study biochemical and cellular processes at a molecular basis. A common strategy for such studies is the use of single and multiple mutants constructed by genetic manipulation which are compromised in individual enzymatic steps or certain metabolic pathways. Here, we describe selected examples of yeast research on phospholipid metabolism with emphasis on our own work dealing with investigations of phosphatidylethanolamine synthesis. Such studies start with the selection and construction of appropriate mutants and lead to phenotype analysis, lipid profiling, enzymatic analysis, and in vivo experiments. Comparing results obtained with wild-type and mutant strains allows us to understand the role of gene products and metabolic processes in more detail. Such studies are valuable not only for contributing to our knowledge of the complex network of lipid metabolism, but also of effects of lipids on structure and function of cellular membranes.

  11. 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.

  12. Lipids: architects and regulators of membrane dynamics and trafficking.

    PubMed

    Moreau, Patrick

    2007-05-01

    We have recently shown that an inhibition of sterol synthesis by fenpropimorph leads to an accumulation of sterol precursors, hydroxypalmitic acid-containing glucosylceramides and detergent resistant membranes in the Golgi bodies instead of the plasma membrane, suggesting that the individual molecules or the microdomains were blocked in the Golgi. These results and others from several eukaryotic models link lipid metabolism with membrane morphodynamics that are involved in membrane trafficking. Focus has been expanded to other lipid families, and numerous evidences are given showing lipids and lipid-modifying enzymes as key regulators of membrane homeostasis which can strongly regulate membrane morphodynamics and therefore trafficking. Beside protein-based machineries, lipid-based machineries are also shown as crucial regulatory forces involved in protein transport and sorting.

  13. Membrane humidity control investigation

    NASA Technical Reports Server (NTRS)

    Elam, J.; Ruder, J.; Strumpf, H.

    1974-01-01

    The basic performance data on a hollow fiber membrane unit that removes water from a breathing gas loop by diffusion is presented. Using available permeability data for cellulose acetate, a preliminary design was made of a dehumidifier unit that would meet the problem statement.

  14. The role of ceramide chain length distribution on the barrier properties of the skin lipid membranes.

    PubMed

    Mojumdar, E H; Kariman, Z; van Kerckhove, L; Gooris, G S; Bouwstra, J A

    2014-10-01

    The skin barrier function is provided by the stratum corneum (SC). The lipids in the SC are composed of three lipid classes: ceramides (CERs), cholesterol (CHOL) and free fatty acids (FFAs) which form two crystalline lamellar structures. In the present study, we investigate the effect of CER chain length distribution on the barrier properties of model lipid membranes mimicking the lipid composition and organization of SC. The membranes were prepared with either isolated pig CERs (PCERs) or synthetic CERs. While PCERs have a wide chain length distribution, the synthetic CERs are quite uniform in chain length. The barrier properties were examined by means of permeation studies using hydrocortisone as a model drug. Our studies revealed a reduced barrier in lipid membranes prepared with PCERs compared to synthetic CERs. Additional studies revealed that a wider chain length distribution of PCERs results in an enhanced hexagonal packing and increased conformational disordering of the lipid tails compared to synthetic CERs, while the lamellar phases did not change. This demonstrates that the chain length distribution affects the lipid barrier by reducing the lipid ordering and density within the lipid lamellae. In subsequent studies, the effect of increased levels of FFAs or CERs with a long acyl chain in the PCERs membranes was also studied. These changes in lipid composition enhanced the level of orthorhombic packing, reduced the conformational disordering and increased the barrier of the lipid membranes. In conclusion, the CER chain length distribution is an important key factor for maintaining a proper barrier.

  15. Engineering lipid structure for recognition of the liquid ordered membrane phase

    SciTech Connect

    Bordovsky, Stefan S.; Wong, Christopher S.; Bachand, George D.; Stachowiak, Jeanne C.; Sasaki, Darryl Y.

    2016-08-26

    The selective partitioning of lipid components in phase-separated membranes is essential for domain formation involved in cellular processes. Identifying and tracking the movement of lipids in cellular systems would be improved if we understood how to achieve selective affinity between fluorophore-labeled lipids and membrane assemblies. Furthermore, we investigated the structure and chemistry of membrane lipids to evaluate lipid designs that partition to the liquid ordered (Lo) phase. A range of fluorophores at the headgroup position and lengths of PEG spacer between the lipid backbone and fluorophore were examined. On a lipid body with saturated palmityl or palmitoyl tails, we found that although the lipid tails can direct selective partitioning to the Lo phase through favorable packing interactions, headgroup hydrophobicity can override the partitioning behavior and direct the lipid to the disordered membrane phase (Ld). The PEG spacer can serve as a buffer to mute headgroup–membrane interactions and thus improve Lo phase partitioning, but its effect is limited with strongly hydrophobic fluorophore headgroups. We present a series of lipid designs leading to the development of novel fluorescently labeled lipids with selective affinity for the Lo phase.

  16. Engineering lipid structure for recognition of the liquid ordered membrane phase

    DOE PAGES

    Bordovsky, Stefan S.; Wong, Christopher S.; Bachand, George D.; ...

    2016-08-26

    The selective partitioning of lipid components in phase-separated membranes is essential for domain formation involved in cellular processes. Identifying and tracking the movement of lipids in cellular systems would be improved if we understood how to achieve selective affinity between fluorophore-labeled lipids and membrane assemblies. Furthermore, we investigated the structure and chemistry of membrane lipids to evaluate lipid designs that partition to the liquid ordered (Lo) phase. A range of fluorophores at the headgroup position and lengths of PEG spacer between the lipid backbone and fluorophore were examined. On a lipid body with saturated palmityl or palmitoyl tails, we foundmore » that although the lipid tails can direct selective partitioning to the Lo phase through favorable packing interactions, headgroup hydrophobicity can override the partitioning behavior and direct the lipid to the disordered membrane phase (Ld). The PEG spacer can serve as a buffer to mute headgroup–membrane interactions and thus improve Lo phase partitioning, but its effect is limited with strongly hydrophobic fluorophore headgroups. We present a series of lipid designs leading to the development of novel fluorescently labeled lipids with selective affinity for the Lo phase.« less

  17. Engineering lipid structure for recognition of the liquid ordered membrane phase

    SciTech Connect

    Bordovsky, Stefan S.; Wong, Christopher S.; Bachand, George D.; Stachowiak, Jeanne C.; Sasaki, Darryl Y.

    2016-08-26

    The selective partitioning of lipid components in phase-separated membranes is essential for domain formation involved in cellular processes. Identifying and tracking the movement of lipids in cellular systems would be improved if we understood how to achieve selective affinity between fluorophore-labeled lipids and membrane assemblies. Furthermore, we investigated the structure and chemistry of membrane lipids to evaluate lipid designs that partition to the liquid ordered (Lo) phase. A range of fluorophores at the headgroup position and lengths of PEG spacer between the lipid backbone and fluorophore were examined. On a lipid body with saturated palmityl or palmitoyl tails, we found that although the lipid tails can direct selective partitioning to the Lo phase through favorable packing interactions, headgroup hydrophobicity can override the partitioning behavior and direct the lipid to the disordered membrane phase (Ld). The PEG spacer can serve as a buffer to mute headgroup–membrane interactions and thus improve Lo phase partitioning, but its effect is limited with strongly hydrophobic fluorophore headgroups. We present a series of lipid designs leading to the development of novel fluorescently labeled lipids with selective affinity for the Lo phase.

  18. The Lantibiotic Nisin Induces Lipid II Aggregation, Causing Membrane Instability and Vesicle Budding

    PubMed Central

    Scherer, Katharina M.; Spille, Jan-Hendrik; Sahl, Hans-Georg; Grein, Fabian; Kubitscheck, Ulrich

    2015-01-01

    The antimicrobial peptide nisin exerts its activity by a unique dual mechanism. It permeates the cell membranes of Gram-positive bacteria by binding to the cell wall precursor Lipid II and inhibits cell wall synthesis. Binding of nisin to Lipid II induces the formation of large nisin-Lipid II aggregates in the membrane of bacteria as well as in Lipid II-doped model membranes. Mechanistic details of the aggregation process and its impact on membrane permeation are still unresolved. In our experiments, we found that fluorescently labeled nisin bound very inhomogeneously to bacterial membranes as a consequence of the strong aggregation due to Lipid II binding. A correlation between cell membrane damage and nisin aggregation was observed in vivo. To further investigate the aggregation process of Lipid II and nisin, we assessed its dynamics by single-molecule microscopy of fluorescently labeled Lipid II molecules in giant unilamellar vesicles using light-sheet illumination. We observed a continuous reduction of Lipid II mobility due to a steady growth of nisin-Lipid II aggregates as a function of time and nisin concentration. From the measured diffusion constants of Lipid II, we estimated that the largest aggregates contained tens of thousands of Lipid II molecules. Furthermore, we observed that the formation of large nisin-Lipid II aggregates induced vesicle budding in giant unilamellar vesicles. Thus, we propose a membrane permeation mechanism that is dependent on the continuous growth of nisin-Lipid II aggregation and probably involves curvature effects on the membrane. PMID:25762323

  19. Tarantula Toxins Interact with Voltage Sensors within Lipid Membranes

    PubMed Central

    Milescu, Mirela; Vobecky, Jan; Roh, Soung H.; Kim, Sung H.; Jung, Hoi J.; Kim, Jae Il; Swartz, Kenton J.

    2007-01-01

    Voltage-activated ion channels are essential for electrical signaling, yet the mechanism of voltage sensing remains under intense investigation. The voltage-sensor paddle is a crucial structural motif in voltage-activated potassium (Kv) channels that has been proposed to move at the protein–lipid interface in response to changes in membrane voltage. Here we explore whether tarantula toxins like hanatoxin and SGTx1 inhibit Kv channels by interacting with paddle motifs within the membrane. We find that these toxins can partition into membranes under physiologically relevant conditions, but that the toxin–membrane interaction is not sufficient to inhibit Kv channels. From mutagenesis studies we identify regions of the toxin involved in binding to the paddle motif, and those important for interacting with membranes. Modification of membranes with sphingomyelinase D dramatically alters the stability of the toxin–channel complex, suggesting that tarantula toxins interact with paddle motifs within the membrane and that they are sensitive detectors of lipid–channel interactions. PMID:17938232

  20. 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

  1. 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

  2. Brain membrane lipids in major depression and anxiety disorders.

    PubMed

    Müller, Christian P; Reichel, Martin; Mühle, Christiane; Rhein, Cosima; Gulbins, Erich; Kornhuber, Johannes

    2015-08-01

    Major depression and anxiety disorders have high prevalence rates and are frequently comorbid. The neurobiological bases for these disorders are not fully understood, and available treatments are not always effective. Current models assume that dysfunctions in neuronal proteins and peptide activities are the primary causes of these disorders. Brain lipids determine the localization and function of proteins in the cell membrane and in doing so regulate synaptic throughput in neurons. Lipids may also leave the membrane as transmitters and relay signals from the membrane to intracellular compartments or to other cells. Here we review how membrane lipids, which play roles in the membrane's function as a barrier and a signaling medium for classical transmitter signaling, contribute to depression and anxiety disorders and how this role may provide targets for lipid-based treatment approaches. Preclinical findings have suggested a crucial role for the membrane-forming n-3 polyunsaturated fatty acids, glycerolipids, glycerophospholipids, and sphingolipids in the induction of depression- and anxiety-related behaviors. These polyunsaturated fatty acids also offer new treatment options such as targeted dietary supplementation or pharmacological interference with lipid-regulating enzymes. While clinical trials support this view, effective lipid-based therapies may need more individualized approaches. Altogether, accumulating evidence suggests a crucial role for membrane lipids in the pathogenesis of depression and anxiety disorders; these lipids could be exploited for improved prevention and treatment. This article is part of a Special Issue entitled Brain Lipids.

  3. Critical point fluctuations in supported lipid membranes.

    PubMed

    Connell, Simon D; Heath, George; Olmsted, Peter D; Kisil, Anastasia

    2013-01-01

    In this paper, we demonstrate that it is possible to observe many aspects of critical phenomena in supported lipid bilayers using atomic force microscopy (AFM) with the aid of stable and precise temperature control. The regions of criticality were determined by accurately measuring and calculating phase diagrams for the 2 phase L(d)-L(o) region, and tracking how it moves with temperature, then increasing the sampling density around the estimated critical regions. Compositional fluctuations were observed above the critical temperature (T(c)) and characterised using a spatial correlation function. From this analysis, the phase transition was found to be most closely described by the 2D Ising model, showing it is a critical transition. Below T(c) roughening of the domain boundaries occurred due to the reduction in line tension close to the critical point. Smaller scale density fluctuations were also detected just below T(c). At T(c), we believe we have observed fluctuations on length scales greater than 10 microm. The region of critically fluctuating 10-100 nm nanodomains has been found to extend a considerable distance above T(c) to temperatures within the biological range, and seem to be an ideal candidate for the actual structure of lipid rafts in cell membranes. Although evidence for this idea has recently emerged, this is the first direct evidence for nanoscale domains in the critical region.

  4. Nonlinear Poisson-Boltzmann model of charged lipid membranes: Accounting for the presence of zwitterionic lipids

    NASA Astrophysics Data System (ADS)

    Mengistu, Demmelash H.; May, Sylvio

    2008-09-01

    The nonlinear Poisson-Boltzmann model is used to derive analytical expressions for the free energies of both mixed anionic-zwitterionic and mixed cationic-zwitterionic lipid membranes as function of the mole fraction of charged lipids. Accounting explicitly for the electrostatic properties of the zwitterionic lipid species affects the free energy of anionic and cationic membranes in a qualitatively different way: That of an anionic membrane changes monotonously as a function of the mole fraction of charged lipids, whereas it passes through a pronounced minimum for a cationic membrane.

  5. Oriented Membrane Protein Reconstitution into Tethered Lipid Membranes for AFM Force Spectroscopy.

    PubMed

    Bronder, Anna M; Bieker, Adeline; Elter, Shantha; Etzkorn, Manuel; Häussinger, Dieter; Oesterhelt, Filipp

    2016-11-01

    Membrane proteins act as a central interface between the extracellular environment and the intracellular response and as such represent one of the most important classes of drug targets. The characterization of the molecular properties of integral membrane proteins, such as topology and interdomain interaction, is key to a fundamental understanding of their function. Atomic force microscopy (AFM) and force spectroscopy have the intrinsic capabilities of investigating these properties in a near-native setting. However, atomic force spectroscopy of membrane proteins is traditionally carried out in a crystalline setup. Alternatively, model membrane systems, such as tethered bilayer membranes, have been developed for surface-dependent techniques. While these setups can provide a more native environment, data analysis may be complicated by the normally found statistical orientation of the reconstituted protein in the model membrane. We have developed a model membrane system that enables the study of membrane proteins in a defined orientation by single-molecule force spectroscopy. Our approach is demonstrated using cell-free expressed bacteriorhodopsin coupled to a quartz glass surface in a defined orientation through a protein anchor and reconstituted inside an artificial membrane system. This approach offers an effective way to study membrane proteins in a planar lipid bilayer. It can be easily transferred to all membrane proteins that possess a suitable tag and can be reconstituted into a lipid bilayer. In this respect, we anticipate that this technique may contribute important information on structure, topology, and intra- and intermolecular interactions of other seven-transmembrane helical receptors. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  6. Membrane proteins, lipids and detergents: not just a soap opera.

    PubMed

    Seddon, Annela M; Curnow, Paul; Booth, Paula J

    2004-11-03

    Studying membrane proteins represents a major challenge in protein biochemistry, with one of the major difficulties being the problems encountered when working outside the natural lipid environment. In vitro studies such as crystallization are reliant on the successful solubilization or reconstitution of membrane proteins, which generally involves the careful selection of solubilizing detergents and mixed lipid/detergent systems. This review will concentrate on the methods currently available for efficient reconstitution and solubilization of membrane proteins through the use of detergent micelles, mixed lipid/detergent micelles and bicelles or liposomes. We focus on the relevant molecular properties of the detergents and lipids that aid understanding of these processes. A significant barrier to membrane protein research is retaining the stability and function of the protein during solubilization, reconstitution and crystallization. We highlight some of the lessons learnt from studies of membrane protein folding in vitro and give an overview of the role that lipids can play in stabilizing the proteins.

  7. Monoolein lipid phases as incorporation and enrichment materials for membrane protein crystallization.

    SciTech Connect

    Wallace, E.; Dranow, D.; Laible, P. D.; Christensen, J.; Nollert, P.

    2011-01-01

    The crystallization of membrane proteins in amphiphile-rich materials such as lipidic cubic phases is an established methodology in many structural biology laboratories. The standard procedure employed with this methodology requires the generation of a highly viscous lipidic material by mixing lipid, for instance monoolein, with a solution of the detergent solubilized membrane protein. This preparation is often carried out with specialized mixing tools that allow handling of the highly viscous materials while minimizing dead volume to save precious membrane protein sample. The processes that occur during the initial mixing of the lipid with the membrane protein are not well understood. Here we show that the formation of the lipidic phases and the incorporation of the membrane protein into such materials can be separated experimentally. Specifically, we have investigated the effect of different initial monoolein-based lipid phase states on the crystallization behavior of the colored photosynthetic reaction center from Rhodobacter sphaeroides. We find that the detergent solubilized photosynthetic reaction center spontaneously inserts into and concentrates in the lipid matrix without any mixing, and that the initial lipid material phase state is irrelevant for productive crystallization. A substantial in-situ enrichment of the membrane protein to concentration levels that are otherwise unobtainable occurs in a thin layer on the surface of the lipidic material. These results have important practical applications and hence we suggest a simplified protocol for membrane protein crystallization within amphiphile rich materials, eliminating any specialized mixing tools to prepare crystallization experiments within lipidic cubic phases. Furthermore, by virtue of sampling a membrane protein concentration gradient within a single crystallization experiment, this crystallization technique is more robust and increases the efficiency of identifying productive crystallization

  8. Monoolein Lipid Phases as Incorporation and Enrichment Materials for Membrane Protein Crystallization

    PubMed Central

    Wallace, Ellen; Dranow, David; Laible, Philip D.; Christensen, Jeff; Nollert, Peter

    2011-01-01

    The crystallization of membrane proteins in amphiphile-rich materials such as lipidic cubic phases is an established methodology in many structural biology laboratories. The standard procedure employed with this methodology requires the generation of a highly viscous lipidic material by mixing lipid, for instance monoolein, with a solution of the detergent solubilized membrane protein. This preparation is often carried out with specialized mixing tools that allow handling of the highly viscous materials while minimizing dead volume to save precious membrane protein sample. The processes that occur during the initial mixing of the lipid with the membrane protein are not well understood. Here we show that the formation of the lipidic phases and the incorporation of the membrane protein into such materials can be separated experimentally. Specifically, we have investigated the effect of different initial monoolein-based lipid phase states on the crystallization behavior of the colored photosynthetic reaction center from Rhodobacter sphaeroides. We find that the detergent solubilized photosynthetic reaction center spontaneously inserts into and concentrates in the lipid matrix without any mixing, and that the initial lipid material phase state is irrelevant for productive crystallization. A substantial in-situ enrichment of the membrane protein to concentration levels that are otherwise unobtainable occurs in a thin layer on the surface of the lipidic material. These results have important practical applications and hence we suggest a simplified protocol for membrane protein crystallization within amphiphile rich materials, eliminating any specialized mixing tools to prepare crystallization experiments within lipidic cubic phases. Furthermore, by virtue of sampling a membrane protein concentration gradient within a single crystallization experiment, this crystallization technique is more robust and increases the efficiency of identifying productive crystallization

  9. 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.

  10. Biophysical interactions with model lipid membranes: applications in drug discovery and drug delivery

    PubMed Central

    Peetla, Chiranjeevi; Stine, Andrew; Labhasetwar, Vinod

    2009-01-01

    The transport of drugs or drug delivery systems across the cell membrane is a complex biological process, often difficult to understand because of its dynamic nature. In this regard, model lipid membranes, which mimic many aspects of cell-membrane lipids, have been very useful in helping investigators to discern the roles of lipids in cellular interactions. One can use drug-lipid interactions to predict pharmacokinetic properties of drugs, such as their transport, biodistribution, accumulation, and hence efficacy. These interactions can also be used to study the mechanisms of transport, based on the structure and hydrophilicity/hydrophobicity of drug molecules. In recent years, model lipid membranes have also been explored to understand their mechanisms of interactions with peptides, polymers, and nanocarriers. These interaction studies can be used to design and develop efficient drug delivery systems. Changes in the lipid composition of cells and tissue in certain disease conditions may alter biophysical interactions, which could be explored to develop target-specific drugs and drug delivery systems. In this review, we discuss different model membranes, drug-lipid interactions and their significance, studies of model membrane interactions with nanocarriers, and how biophysical interaction studies with lipid model membranes could play an important role in drug discovery and drug delivery. PMID:19432455

  11. Membrane Lipid Screen to Identify Molecular Targets of Biomolecules.

    PubMed

    Jimah, John R; Schlesinger, Paul H; Tolia, Niraj H

    2017-08-05

    Proteins that bind to and disrupt cell membranes may target specific phospholipids. Here we describe a protocol to identify the lipid targets of proteins and biomolecules. First, we describe a screen to identify lipids in membranes that are specifically bound by the biomolecule of interest. Second, we describe a method for determining if the presence of these lipids within membranes is necessary for membrane disruption. The methods described here were used to determine that the malaria vaccine candidate CelTOS disrupts cell membranes by specifically targeting phosphatidic acid (Jimah et al., 2016). This protocol has a companion protocol: 'Liposome disruption assay to examine lytic properties of biomolecules' which can be applied to examine the ability of the biomolecule to disrupt membranes composed of the lipid target identified by following this protocol (Jimah et al., 2017).

  12. 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

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

    PubMed

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

    2014-06-01

    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 as 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 on 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. Copyright © 2014. Published by Elsevier B.V.

  14. Curvature forces in membrane lipid-protein interactions.

    PubMed

    Brown, Michael F

    2012-12-11

    Membrane biochemists are becoming increasingly aware of the role of lipid-protein interactions in diverse cellular functions. This review describes how conformational changes in membrane proteins, involving folding, stability, and membrane shape transitions, potentially involve elastic remodeling of the lipid bilayer. Evidence suggests that membrane lipids affect proteins through interactions of a relatively long-range nature, extending beyond a single annulus of next-neighbor boundary lipids. It is assumed the distance scale of the forces is large compared to the molecular range of action. Application of the theory of elasticity to flexible soft surfaces derives from classical physics and explains the polymorphism of both detergents and membrane phospholipids. A flexible surface model (FSM) describes the balance of curvature and hydrophobic forces in lipid-protein interactions. Chemically nonspecific properties of the lipid bilayer modulate the conformational energetics of membrane proteins. The new biomembrane model challenges the standard model (the fluid mosaic model) found in biochemistry texts. The idea of a curvature force field based on data first introduced for rhodopsin gives a bridge between theory and experiment. Influences of bilayer thickness, nonlamellar-forming lipids, detergents, and osmotic stress are all explained by the FSM. An increased awareness of curvature forces suggests that research will accelerate as structural biology becomes more closely entwined with the physical chemistry of lipids in explaining membrane structure and function.

  15. Curvature Forces in Membrane Lipid-Protein Interactions

    PubMed Central

    Brown, Michael F.

    2012-01-01

    Membrane biochemists are becoming increasingly aware of the role of lipid-protein interactions in diverse cellular functions. This review describes how conformational changes of membrane proteins—involving folding, stability, and membrane shape transitions—potentially involve elastic remodeling of the lipid bilayer. Evidence suggests that membrane lipids affect proteins through interactions of a relatively long-range nature, extending beyond a single annulus of next-neighbor boundary lipids. It is assumed the distance scale of the forces is large compared to the molecular range of action. Application of the theory of elasticity to flexible soft surfaces derives from classical physics, and explains the polymorphism of both detergents and membrane phospholipids. A flexible surface model (FSM) describes the balance of curvature and hydrophobic forces in lipid-protein interactions. Chemically nonspecific properties of the lipid bilayer modulate the conformational energetics of membrane proteins. The new biomembrane model challenges the standard model (the fluid mosaic model) found in biochemistry texts. The idea of a curvature force field based on data first introduced for rhodopsin gives a bridge between theory and experiment. Influences of bilayer thickness, nonlamellar-forming lipids, detergents, and osmotic stress are all explained by the FSM. An increased awareness of curvature forces suggests that research will accelerate as structural biology becomes more closely entwined with the physical chemistry of lipids in explaining membrane structure and function. PMID:23163284

  16. Thermal Adaptation of the Archaeal and Bacterial Lipid Membranes

    PubMed Central

    Koga, Yosuke

    2012-01-01

    The physiological characteristics that distinguish archaeal and bacterial lipids, as well as those that define thermophilic lipids, are discussed from three points of view that (1) the role of the chemical stability of lipids in the heat tolerance of thermophilic organisms: (2) the relevance of the increase in the proportion of certain lipids as the growth temperature increases: (3) the lipid bilayer membrane properties that enable membranes to function at high temperatures. It is concluded that no single, chemically stable lipid by itself was responsible for the adaptation of surviving at high temperatures. Lipid membranes that function effectively require the two properties of a high permeability barrier and a liquid crystalline state. Archaeal membranes realize these two properties throughout the whole biological temperature range by means of their isoprenoid chains. Bacterial membranes meet these requirements only at or just above the phase-transition temperature, and therefore their fatty acid composition must be elaborately regulated. A recent hypothesis sketched a scenario of the evolution of lipids in which the “lipid divide” emerged concomitantly with the differentiation of archaea and bacteria. The two modes of thermal adaptation were established concurrently with the “lipid divide.” PMID:22927779

  17. 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.

  18. The Interaction of Polyene Antibiotics with Thin Lipid Membranes

    PubMed Central

    Andreoli, Thomas E.; Monahan, Marcia

    1968-01-01

    Optically black, thin lipid membranes prepared from sheep erythrocyte lipids have a high dc resistance (Rm ≅ 108 ohm-cm2) when the bathing solutions contain NaCl or KCl. The ionic transference numbers (Ti) indicate that these membranes are cation-selective (TNa ≅ 0.85; TCl ≅ 0.15). These electrical properties are independent of the cholesterol content of the lipid solutions from which the membranes are formed. Nystatin, and probably amphotericin B, are cyclic polyene antibiotics containing ≈36 ring atoms and a free amino and carboxyl group. When the lipid solutions used to form membranes contained equimolar amounts of cholesterol and phospholipid, these antibiotics reduced Rm to ≈102 ohm-cm2; concomitantly, TCl became ≅0.92. The slope of the line relating log Rm and log antibiotic concentration was ≅4.5. Neither nystatin (2 x 10-5 M) nor amphotericin B (2 x 10-7 M) had any effect on membrane stability. The antibiotics had no effect on Rm or membrane permselectivity when the lipids used to form membranes were cholesterol-depleted. Filipin (10-5 M), an uncharged polyene with 28 ring atoms, produced striking membrane instability, but did not affect Rm or membrane ionic selectivity. These data suggest that amphotericin B or nystatin may interact with membrane-bound sterols to produce multimolecular complexes which greatly enhance the permeability of such membranes for anions (Cl-, acetate), and, to a lesser degree, cations (Na+, K+, Li+). PMID:5672005

  19. The influence of membrane lipid structure on plasma membrane Ca2+ -ATPase activity.

    PubMed

    Tang, Daxin; Dean, William L; Borchman, Douglas; Paterson, Christopher A

    2006-03-01

    Lipid composition and Ca(2+)-ATPase activity both change with age and disease in many tissues. We explored relationships between lipid composition/structure and plasma membrane Ca(2+)-ATPase (PMCA) activity. PMCA was purified from human erythrocytes and was reconstituted into liposomes prepared from human ocular lens membrane lipids and synthetic lipids. Lens lipids were used in this study as a model for naturally ordered lipids, but the influence of lens lipids on PMCA function is especially relevant to the lens since calcium homeostasis is vital to lens clarity. Compared to fiber cell lipids, epithelial lipids exhibited an ordered to disordered phase transition temperature that was 12 degrees C lower. Reconstitution of PMCA into lipids was essential for maximal activity. PMCA activity was two to three times higher when the surrounding phosphatidylcholine molecules contained acyl chains that were ordered (stiff) compared to disordered (fluid) acyl chains. In a completely ordered lipid hydrocarbon chain environment, PMCA associates more strongly with the acidic lipid phosphatidylserine in comparison to phosphatidylcholine. PMCA associates much more strongly with phosphatidylcholine containing disordered hydrocarbon chains than ordered hydrocarbon chains. PMCA activity is influenced by membrane lipid composition and structure. The naturally high degree of lipid order in plasma membranes such as those found in the human lens may serve to support PMCA activity. The absence of PMCA activity in the cortical region of human lenses is apparently not due to a different lipid environment. Changes in lipid composition such as those observed with age or disease could potentially influence PMCA function.

  20. Probing Peptide and Protein Insertion in a Biomimetic S-Layer Supported Lipid Membrane Platform

    PubMed Central

    Damiati, Samar; Schrems, Angelika; Sinner, Eva-Kathrin; Sleytr, Uwe B.; Schuster, Bernhard

    2015-01-01

    The most important aspect of synthetic lipid membrane architectures is their ability to study functional membrane-active peptides and membrane proteins in an environment close to nature. Here, we report on the generation and performance of a biomimetic platform, the S-layer supported lipid membrane (SsLM), to investigate the structural and electrical characteristics of the membrane-active peptide gramicidin and the transmembrane protein α-hemolysin in real-time using a quartz crystal microbalance with dissipation monitoring in combination with electrochemical impedance spectroscopy. A shift in membrane resistance is caused by the interaction of α-hemolysin and gramicidin with SsLMs, even if only an attachment onto, or functional channels through the lipid membrane, respectively, are formed. Moreover, the obtained results did not indicate the formation of functional α-hemolysin pores, but evidence for functional incorporation of gramicidin into this biomimetic architecture is provided. PMID:25633104

  1. Elucidating how bamboo salt interacts with supported lipid membranes: influence of alkalinity on membrane fluidity.

    PubMed

    Jeong, Jong Hee; Choi, Jae-Hyeok; Kim, Min Chul; Park, Jae Hyeon; Herrin, Jason Scott; Kim, Seung Hyun; Lee, Haiwon; Cho, Nam-Joon

    2015-07-01

    Bamboo salt is a traditional medicine produced from sea salt. It is widely used in Oriental medicine and is an alkalizing agent with reported antiinflammatory, antimicrobial and chemotherapeutic properties. Notwithstanding, linking specific molecular mechanisms with these properties has been challenging to establish in biological systems. In part, this issue may be related to bamboo salt eliciting nonspecific effects on components found within these systems. Herein, we investigated the effects of bamboo salt solution on supported lipid bilayers as a model system to characterize the interaction between lipid membranes and bamboo salt. The atomic composition of unprocessed and processed bamboo salts was first analyzed by mass spectrometry, and we identified several elements that have not been previously reported in other bamboo salt preparations. The alkalinity of hydrated samples was also measured and determined to be between pH 10 and 11 for bamboo salts. The effect of processed bamboo salt solutions on the fluidic properties of a supported lipid bilayer on glass was next investigated by fluorescence recovery after photobleaching (FRAP) analysis. It was demonstrated that, with increasing ionic strength of the bamboo salt solution, the fluidity of a lipid bilayer increased. On the contrary, increasing the ionic strength of near-neutral buffer solutions with sodium chloride salt diminished fluidity. To reconcile these two observations, we identified that solution alkalinity is critical for the effects of bamboo salt on membrane fluidity, as confirmed using three additional commercial bamboo salt preparations. Extended-DLVO model calculations support that the effects of bamboo salt on lipid membranes are due to the alkalinity imparting a stronger hydration force. Collectively, the results of this work demonstrate that processing of bamboo salt strongly affects its atomic composition and that the alkalinity of bamboo salt solutions contributes to its effect on membrane

  2. Membranes: a meeting point for lipids, proteins and therapies.

    PubMed

    Escribá, Pablo V; González-Ros, José M; Goñi, Félix M; Kinnunen, Paavo K J; Vigh, Lászlo; Sánchez-Magraner, Lissete; Fernández, Asia M; Busquets, Xavier; Horváth, Ibolya; Barceló-Coblijn, Gwendolyn

    2008-06-01

    Membranes constitute a meeting point for lipids and proteins. Not only do they define the entity of cells and cytosolic organelles but they also display a wide variety of important functions previously ascribed to the activity of proteins alone. Indeed, lipids have commonly been considered a mere support for the transient or permanent association of membrane proteins, while acting as a selective cell/organelle barrier. However, mounting evidence demonstrates that lipids themselves regulate the location and activity of many membrane proteins, as well as defining membrane microdomains that serve as spatio-temporal platforms for interacting signalling proteins. Membrane lipids are crucial in the fission and fusion of lipid bilayers and they also act as sensors to control environmental or physiological conditions. Lipids and lipid structures participate directly as messengers or regulators of signal transduction. Moreover, their alteration has been associated with the development of numerous diseases. Proteins can interact with membranes through lipid co-/post-translational modifications, and electrostatic and hydrophobic interactions, van der Waals forces and hydrogen bonding are all involved in the associations among membrane proteins and lipids. The present study reviews these interactions from the molecular and biomedical point of view, and the effects of their modulation on the physiological activity of cells, the aetiology of human diseases and the design of clinical drugs. In fact, the influence of lipids on protein function is reflected in the possibility to use these molecular species as targets for therapies against cancer, obesity, neurodegenerative disorders, cardiovascular pathologies and other diseases, using a new approach called membrane-lipid therapy.

  3. Membranes: a meeting point for lipids, proteins and therapies

    PubMed Central

    Escribá, Pablo V; González-Ros, José M; Goñi, Félix M; Kinnunen, Paavo K J; Vigh, Lászlo; Sánchez-Magraner, Lissete; Fernández, Asia M; Busquets, Xavier; Horváth, Ibolya; Barceló-Coblijn, Gwendolyn

    2008-01-01

    Abstract Membranes constitute a meeting point for lipids and proteins. Not only do they define the entity of cells and cytosolic organelles but they also display a wide variety of important functions previously ascribed to the activity of proteins alone. Indeed, lipids have commonly been considered a mere support for the transient or permanent association of membrane proteins, while acting as a selective cell/organelle barrier. However, mounting evidence demonstrates that lipids themselves regulate the location and activity of many membrane proteins, as well as defining membrane microdomains that serve as spatio-temporal platforms for interacting signalling proteins. Membrane lipids are crucial in the fission and fusion of lipid bilayers and they also act as sensors to control environmental or physiological conditions. Lipids and lipid structures participate directly as messengers or regulators of signal transduction. Moreover, their alteration has been associated with the development of numerous diseases. Proteins can interact with membranes through lipid co-/post-translational modifications, and electrostatic and hydrophobic interactions, van der Waals forces and hydrogen bonding are all involved in the associations among membrane proteins and lipids. The present study reviews these interactions from the molecular and biomedical point of view, and the effects of their modulation on the physiological activity of cells, the aetiology of human diseases and the design of clinical drugs. In fact, the influence of lipids on protein function is reflected in the possibility to use these molecular species as targets for therapies against cancer, obesity, neurodegenerative disorders, cardiovascular pathologies and other diseases, using a new approach called membrane-lipid therapy. PMID:18266954

  4. Investigation by focused laser beam scanning of the photoelectric activity of bacteriorhodopsin-containing lipid bilayers.

    PubMed Central

    Dancsházy, Z; Ormos, P; Drachev, L A; Skulachev, V P

    1978-01-01

    The photoelectric activity of different parts of lipid bilayer containing bacteriorhodopsin was investigated by moving a small actinic light spot across the Plateau-Gibbs border and the bimolecular part of this reconstituted model membrane. The results give direct evidence that bacteriorhodopsin incorporated into the bimolecular region of the lipid membrane is responsible for the photoelectric activity of this system. A technique for scanning the photoelectric activity of a modified bimolecular lipid membrane is described in detail. PMID:728523

  5. Lipid membrane-assisted condensation and assembly of amphiphilic Janus particles

    SciTech Connect

    Chambers, Mariah; Mallory, Stewart Anthony; Malone, Heather; Gao, Yuan; Anthony, Stephen M.; Yi, Yi; Cacciuto, Angelo; Yu, Yan

    2016-01-01

    Amphiphilic Janus particles self-assemble into complex metastructures, but little is known about how their assembly might be modified by weak interactions with a nearby biological membrane surface. Here, we report an integrated experimental and molecular dynamics simulation study to investigate the self-assembly of amphiphilic Janus particles on a lipid membrane. We created an experimental system in which Janus particles are allowed to self-assemble in the same medium where zwitterionic lipids form giant unilamellar vesicles (GUVs). Janus particles spontaneously concentrated on the inner leaflet of the GUVs. They exhibited biased orientation and heterogeneous rotational dynamics as revealed by single particle rotational tracking. The combined experimental and simulation results show that Janus particles concentrate on the lipid membranes due to weak particle–lipid attraction, whereas the biased orientation of particles is driven predominantly by inter-particle interactions. Furthermore, this study demonstrates the potential of using lipid membranes to influence the self-assembly of Janus particles.

  6. A study on the interaction of nanoparticles with lipid membranes and their influence on membrane fluidity

    NASA Astrophysics Data System (ADS)

    Santhosh, P. B.; Penič, S.; Genova, J.; Iglič, A.; Kralj-Iglič, V.; Ulrih, N. P.

    2012-12-01

    In recent years, liposomes encapsulated with nanoparticles have found enormous scopes in various biomedical fields such as drug design, transport, imaging, targeted delivery and therapy. These applications require a clear understanding about the interaction of nanoparticles with cell membranes. The present work aims to investigate the effect of encapsulation of uncharged and positively charged nanoparticles in three different types of lipids such as1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC),1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine and1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine(SOPC-POPS) mixture and archaeal lipids. Through the temperature dependent fluorescence anisotropy measurements, we have found that the entrapment of nanoparticles in the bilayer has decreased the lipid transition temperature and increased the membrane fluidity of all three types of lipid vesicles. The results were more predominant in SOPC-POPS mixture because of high density encapsulation of nanoparticles in the vesicles due to electrostatic interaction between negatively charged membrane and positively charged iron oxide nanoparticles.

  7. Measuring lipid packing of model and cellular membranes with environment sensitive probes.

    PubMed

    Sezgin, Erdinc; Sadowski, Tomasz; Simons, Kai

    2014-07-15

    The extent of lipid packing is one of the key physicochemical features of biological membranes and is involved in many membrane processes. Polarity sensitive fluorescent probes are commonly used tools to measure membrane lipid packing in both artificial and biological membranes. In this paper, we have systematically compared eight different probes to measure membrane lipid ordering. We investigated how these probes behave in small unilamellar liposomes, phase-separated giant unilamellar vesicles, cell-derived giant plasma membrane vesicles, and live cells. We have tested the order sensitivity of a variety of measurable parameters, including generalized polarization, peak shift, or intensity shift. We also investigated internalization and photostability of the probes to assess probe potential for time-lapse live cell imaging. These results provide a catalogue of properties to facilitate the choice of probe according to need.

  8. Photon correlation spectroscopy of bilayer lipid membranes.

    PubMed Central

    Crilly, J F; Earnshaw, J C

    1983-01-01

    Light scattering by thermal fluctuations on simple monoglyceride bilayer membranes has been used to investigate the viscoelastic properties of these structures. Spectroscopic analysis of these fluctuations (capillary waves) permits the nonperturbative measurement of the interfacial tension and a shear interfacial viscosity acting normal to the membrane plane. The methods were established by studies of solvent and nonsolvent bilayers of glycerol monooleate (GMO). Changes in the tension of GMO/n-decane membranes induced by altering the composition of the parent solution were detected and quantified. In a test of the reliability of the technique controlled variations of the viscosity of the aqueous bathing solution were accurately monitored. The technique was applied to solvent-free bilayers formed from dispersions of GMO in squalane. The lower tensions observed attested to the comparative absence of solvent in such bilayers. In contrast to the solvent case, the solvent-free membranes exhibited a significant transverse shear viscosity, indicative of the enhanced intermolecular interactions within the bilayer. PMID:6838962

  9. Isolation and analysis of membrane lipids and lipid rafts in common carp (Cyprinus carpio L.).

    PubMed

    Brogden, Graham; Propsting, Marcus; Adamek, Mikolaj; Naim, Hassan Y; Steinhagen, Dieter

    2014-03-01

    Cell membranes act as an interface between the interior of the cell and the exterior environment and facilitate a range of essential functions including cell signalling, cell structure, nutrient uptake and protection. It is composed of a lipid bilayer with integrated proteins, and the inner leaflet of the lipid bilayer comprises of liquid ordered (Lo) and liquid disordered (Ld) domains. Lo microdomains, also named as lipid rafts are enriched in cholesterol, sphingomyelin and certain types of proteins, which facilitate cell signalling and nutrient uptake. Lipid rafts have been extensively researched in mammals and the presence of functional lipid rafts was recently demonstrated in goldfish, but there is currently very little knowledge about their composition and function in fish. Therefore a protocol was established for the analysis of lipid rafts and membranous lipids in common carp (Cyprinus carpio L.) tissues. Twelve lipids were identified and analysed in the Ld domain of the membrane with the most predominant lipids found in all tissues being; triglycerides, cholesterol, phosphoethanolamine and phosphatidylcholine. Four lipids were identified in lipid rafts in all tissues analysed, triglycerides (33-62%) always found in the highest concentration followed by cholesterol (24-32%), phosphatidylcholine and sphingomyelin. Isolation of lipid rafts was confirmed by identifying the presence of the lipid raft associated protein flotillin, present at higher concentrations in the detergent resistant fraction. The data provided here build a lipid library of important carp tissues as a baseline for further studies into virus entry, protein trafficking or environmental stress analysis.

  10. Conformations of double-headed, triple-tailed phospholipid oxidation lipid products in model membranes.

    PubMed

    Hermetter, Albin; Kopec, Wojciech; Khandelia, Himanshu

    2013-08-01

    Products of phospholipid oxidation can produce lipids with a carbonyl moiety at the end of a shortened lipid acyl tail, such as 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC). The carbonyl tail of POVPC can covalently bond to the free tertiary amine of a phosphatidylethanolamine lipid in a Schiff base reaction to form a conjugate lipid (SCH) with two head groups, and three acyl tails. We investigate the conformations and properties of this unique class of adduct lipids using molecular dynamics simulations, and show that their insertion into lipid bilayers of POPC increases the average cross-sectional area per lipid and decreases bilayer thickness. Significant increase in acyl tail fluidity is only observed at 25% SCH concentration. The SCH occupies a larger area per lipid than expected for a lipid with three acyl tails, owing to the interfacial location of the long spacer between the two head groups of the SCH. Schiff base formation of lipids can alter the concentration, homeostasis and localizations of phosphatidylserine and phosphatidylethanol lipids in membranes, and can therefore influence several membrane-associated processes including fusion and budding. The current work provides the first detailed structural model of this unique new class of lipids that may have important roles to play in modulating membrane properties and cell physiology. Copyright © 2013 Elsevier B.V. All rights reserved.

  11. Influence of squalene on lipid particle/droplet and membrane organization in the yeast Saccharomyces cerevisiae

    PubMed Central

    Spanova, Miroslava; Zweytick, Dagmar; Lohner, Karl; Klug, Lisa; Leitner, Erich; Hermetter, Albin; Daum, Günther

    2012-01-01

    In a previous study (Spanova et al., 2010, J. Biol. Chem., 285, 6127–6133) we demonstrated that squalene, an intermediate of sterol biosynthesis, accumulates in yeast strains bearing a deletion of the HEM1 gene. In such strains, the vast majority of squalene is stored in lipid particles/droplets together with triacylglycerols and steryl esters. In mutants lacking the ability to form lipid particles, however, substantial amounts of squalene accumulate in organelle membranes. In the present study, we investigated the effect of squalene on biophysical properties of lipid particles and biological membranes and compared these results to artificial membranes. Our experiments showed that squalene together with triacylglycerols forms the fluid core of lipid particles surrounded by only a few steryl ester shells which transform into a fluid phase below growth temperature. In the hem1∆ deletion mutant a slight disordering effect on steryl esters was observed indicated by loss of the high temperature transition. Also in biological membranes from the hem1∆ mutant strain the effect of squalene per se is difficult to pinpoint because multiple effects such as levels of sterols and unsaturated fatty acids contribute to physical membrane properties. Fluorescence spectroscopic studies using endoplasmic reticulum, plasma membrane and artificial membranes revealed that it is not the absolute squalene level in membranes but rather the squalene to sterol ratio which mainly affects membrane fluidity/rigidity. In a fluid membrane environment squalene induces rigidity of the membrane, whereas in rigid membranes there is almost no additive effect of squalene. In summary, our results demonstrate that squalene (i) can be well accommodated in yeast lipid particles and organelle membranes without causing deleterious effects; and (ii) although not being a typical membrane lipid may be regarded as a mild modulator of biophysical membrane properties. PMID:22342273

  12. Influence of squalene on lipid particle/droplet and membrane organization in the yeast Saccharomyces cerevisiae.

    PubMed

    Spanova, Miroslava; Zweytick, Dagmar; Lohner, Karl; Klug, Lisa; Leitner, Erich; Hermetter, Albin; Daum, Günther

    2012-04-01

    In a previous study (Spanova et al., 2010, J. Biol. Chem., 285, 6127-6133) we demonstrated that squalene, an intermediate of sterol biosynthesis, accumulates in yeast strains bearing a deletion of the HEM1 gene. In such strains, the vast majority of squalene is stored in lipid particles/droplets together with triacylglycerols and steryl esters. In mutants lacking the ability to form lipid particles, however, substantial amounts of squalene accumulate in organelle membranes. In the present study, we investigated the effect of squalene on biophysical properties of lipid particles and biological membranes and compared these results to artificial membranes. Our experiments showed that squalene together with triacylglycerols forms the fluid core of lipid particles surrounded by only a few steryl ester shells which transform into a fluid phase below growth temperature. In the hem1∆ deletion mutant a slight disordering effect on steryl esters was observed indicated by loss of the high temperature transition. Also in biological membranes from the hem1∆ mutant strain the effect of squalene per se is difficult to pinpoint because multiple effects such as levels of sterols and unsaturated fatty acids contribute to physical membrane properties. Fluorescence spectroscopic studies using endoplasmic reticulum, plasma membrane and artificial membranes revealed that it is not the absolute squalene level in membranes but rather the squalene to sterol ratio which mainly affects membrane fluidity/rigidity. In a fluid membrane environment squalene induces rigidity of the membrane, whereas in rigid membranes there is almost no additive effect of squalene. In summary, our results demonstrate that squalene (i) can be well accommodated in yeast lipid particles and organelle membranes without causing deleterious effects; and (ii) although not being a typical membrane lipid may be regarded as a mild modulator of biophysical membrane properties. Copyright © 2012 Elsevier B.V. All

  13. Lipid Clustering Correlates with Membrane Curvature as Revealed by Molecular Simulations of Complex Lipid Bilayers

    PubMed Central

    Koldsø, Heidi; Shorthouse, David; Hélie, Jean; Sansom, Mark S. P.

    2014-01-01

    Cell membranes are complex multicomponent systems, which are highly heterogeneous in the lipid distribution and composition. To date, most molecular simulations have focussed on relatively simple lipid compositions, helping to inform our understanding of in vitro experimental studies. Here we describe on simulations of complex asymmetric plasma membrane model, which contains seven different lipids species including the glycolipid GM3 in the outer leaflet and the anionic lipid, phosphatidylinositol 4,5-bisphophate (PIP2), in the inner leaflet. Plasma membrane models consisting of 1500 lipids and resembling the in vivo composition were constructed and simulations were run for 5 µs. In these simulations the most striking feature was the formation of nano-clusters of GM3 within the outer leaflet. In simulations of protein interactions within a plasma membrane model, GM3, PIP2, and cholesterol all formed favorable interactions with the model α-helical protein. A larger scale simulation of a model plasma membrane containing 6000 lipid molecules revealed correlations between curvature of the bilayer surface and clustering of lipid molecules. In particular, the concave (when viewed from the extracellular side) regions of the bilayer surface were locally enriched in GM3. In summary, these simulations explore the nanoscale dynamics of model bilayers which mimic the in vivo lipid composition of mammalian plasma membranes, revealing emergent nanoscale membrane organization which may be coupled both to fluctuations in local membrane geometry and to interactions with proteins. PMID:25340788

  14. Lipid clustering correlates with membrane curvature as revealed by molecular simulations of complex lipid bilayers.

    PubMed

    Koldsø, Heidi; Shorthouse, David; Hélie, Jean; Sansom, Mark S P

    2014-10-01

    Cell membranes are complex multicomponent systems, which are highly heterogeneous in the lipid distribution and composition. To date, most molecular simulations have focussed on relatively simple lipid compositions, helping to inform our understanding of in vitro experimental studies. Here we describe on simulations of complex asymmetric plasma membrane model, which contains seven different lipids species including the glycolipid GM3 in the outer leaflet and the anionic lipid, phosphatidylinositol 4,5-bisphophate (PIP2), in the inner leaflet. Plasma membrane models consisting of 1500 lipids and resembling the in vivo composition were constructed and simulations were run for 5 µs. In these simulations the most striking feature was the formation of nano-clusters of GM3 within the outer leaflet. In simulations of protein interactions within a plasma membrane model, GM3, PIP2, and cholesterol all formed favorable interactions with the model α-helical protein. A larger scale simulation of a model plasma membrane containing 6000 lipid molecules revealed correlations between curvature of the bilayer surface and clustering of lipid molecules. In particular, the concave (when viewed from the extracellular side) regions of the bilayer surface were locally enriched in GM3. In summary, these simulations explore the nanoscale dynamics of model bilayers which mimic the in vivo lipid composition of mammalian plasma membranes, revealing emergent nanoscale membrane organization which may be coupled both to fluctuations in local membrane geometry and to interactions with proteins.

  15. The superlattice model of lateral organization of membranes and its implications on membrane lipid homeostasis.

    PubMed

    Somerharju, Pentti; Virtanen, Jorma A; Cheng, Kwan H; Hermansson, Martin

    2009-01-01

    Most biological membranes are extremely complex structures consisting of hundreds of different lipid and protein molecules. According to the famous fluid-mosaic model lipids and many proteins are free to diffuse very rapidly in the plane of the membrane. While such fast diffusion implies that different membrane lipids would be laterally randomly distributed, accumulating evidence indicates that in model and natural membranes the lipid components tend to adopt regular (superlattice-like) distributions. The superlattice model, put forward based on such evidence, is intriguing because it predicts that 1) there is a limited number of allowed compositions representing local minima in membrane free energy and 2) those energy minima could provide set-points for enzymes regulating membrane lipid compositions. Furthermore, the existence of a discrete number of allowed compositions could help to maintain organelle identity in the face of rapid inter-organelle membrane traffic.

  16. Effects of dimethyl sulfoxide on lipid membrane electroporation.

    PubMed

    Fernández, M Laura; Reigada, Ramon

    2014-08-07

    Pores can be generated in lipid membranes by the application of an external electric field or by the addition of particular chemicals such as dimethyl sulfoxide (DMSO). Molecular dynamics (MD) has been shown to be a useful tool for unveiling many aspects of pore formation in lipid membranes in both situations. By means of MD simulations, we address the formation of electropores in cholesterol-containing lipid bilayers under the influence of DMSO. We show how a combination of physical and chemical mechanisms leads to more favorable conditions for generating membrane pores and, in particular, how the addition of DMSO to the medium significantly reduces the minimum electric field required to electroporate a lipid membrane. The strong alteration of membrane transversal properties and the energetic stabilization of the hydrophobic pore stage by DMSO provide the physicochemical mechanisms that explain this effect.

  17. Rat liver mitochondrial membrane characteristics and mitochondrial functions are more profoundly altered by dietary lipid quantity than by dietary lipid quality: effect of different nutritional lipid patterns.

    PubMed

    Aoun, Manar; Feillet-Coudray, Christine; Fouret, Gilles; Chabi, Béatrice; Crouzier, David; Ferreri, Carla; Chatgilialoglu, Chryssostomos; Wrutniak-Cabello, Chantal; Cristol, Jean Paul; Carbonneau, Marie-Annette; Coudray, Charles

    2012-03-01

    Dietary lipids are known to affect the composition of the biological membrane and functions that are involved in cell death and survival. The mitochondrial respiratory chain enzymes are membrane protein complexes whose function depends on the composition and fluidity of the mitochondrial membrane lipid. The present study aimed at investigating the impact of different nutritional patterns of dietary lipids on liver mitochondrial functions. A total of forty-eight Wistar male rats were divided into six groups and fed for 12 weeks with a basal diet, lard diet or fish oil diet, containing either 50 or 300 g lipid/kg. The 30 % lipid intake increased liver NEFA, TAG and cholesterol levels, increased mitochondrial NEFA and TAG, and decreased phospholipid (PL) levels. SFA, PUFA and unsaturation index (UI) increased, whereas MUFA and trans-fatty acids (FA) decreased in the mitochondrial membrane PL in 30 % fat diet-fed rats compared with 5 % lipid diet-fed rats. PL UI increased with fish oil diet v. basal and lard-rich diets, and PL trans-FA increased with lard diet v. basal and fish oil diets. The 30 % lipid diet intake increased mitochondrial membrane potential, membrane fluidity, mitochondrial respiration and complex V activity, and decreased complex III and IV activities. With regard to lipid quality effects, β-oxidation decreased with the intake of basal or fish oil diets compared with that of the lard diet. The intake of a fish oil diet decreased complex III and IV activities compared with both the basal and lard diets. In conclusion, the characteristics and mitochondrial functions of the rat liver mitochondrial membrane are more profoundly altered by the quantity of dietary lipid than by its quality, which may have profound impacts on the pathogenesis and development of non-alcoholic fatty liver disease.

  18. Dynamic sorting of lipids and proteins in membrane tubes with a moving phase boundary

    PubMed Central

    Heinrich, Michael; Tian, Aiwei; Esposito, Cinzia; Baumgart, Tobias

    2010-01-01

    Cellular organelle membranes maintain their integrity, global shape, and composition despite vigorous exchange among compartments of lipids and proteins during trafficking and signaling. Organelle homeostasis involves dynamic molecular sorting mechanisms that are far from being understood. In contrast, equilibrium thermodynamics of membrane mixing and sorting, particularly the phase behavior of binary and ternary model membrane mixtures and its coupling to membrane mechanics, is relatively well characterized. Elucidating the continuous turnover of live cell membranes, however, calls for experimental and theoretical membrane models enabling manipulation and investigation of directional mass transport. Here we introduce the phenomenon of curvature-induced domain nucleation and growth in membrane mixtures with fluid phase coexistence. Membrane domains were consistently observed to nucleate precisely at the junction between a strongly curved cylindrical (tube) membrane and a pipette-aspirated giant unilamellar vesicle. This experimental geometry mimics intracellular sorting compartments, because they often show tubular-vesicular membrane regions. Nucleated domains at tube necks were observed to present diffusion barriers to the transport of lipids and proteins. We find that curvature-nucleated domains grow with characteristic parabolic time dependence that is strongly curvature-dependent. We derive an analytical model that reflects the observed growth dynamics. Numerically calculated membrane shapes furthermore allow us to elucidate mechanical details underlying curvature-dependent directed lipid transport. Our observations suggest a novel dynamic membrane sorting principle that may contribute to intracellular protein and lipid sorting and trafficking. PMID:20368457

  19. Lipid trafficking at endoplasmic reticulum-chloroplast membrane contact sites.

    PubMed

    Block, Maryse A; Jouhet, Juliette

    2015-08-01

    Glycerolipid synthesis in plant cells is characterized by an intense trafficking of lipids between the endoplasmic reticulum (ER) and chloroplasts. Initially, fatty acids are synthesized within chloroplasts and are exported to the ER where they are used to build up phospholipids and triacylglycerol. Ultimately, derivatives of these phospholipids return to chloroplasts to form galactolipids, monogalactosyldiacylglycerol and digalactosyldiacylglycerol, the main and essential lipids of photosynthetic membranes. Lipid trafficking was proposed to transit through membrane contact sites (MCSs) connecting both organelles. Here, we review recent insights into ER-chloroplast MCSs and lipid trafficking between chloroplasts and the ER.

  20. Thermodynamics of sodium dodecyl sulfate partitioning into lipid membranes.

    PubMed

    Tan, Anmin; Ziegler, André; Steinbauer, Bernhard; Seelig, Joachim

    2002-09-01

    The partition equilibria of sodium dodecyl sulfate (SDS) and lithium dodecyl sulfate between water and bilayer membranes were investigated with isothermal titration calorimetry and spectroscopic methods (light scattering, (31)P-nuclear magnetic resonance) in the temperature range of 28 degrees C to 56 degrees C. The partitioning of the dodecyl sulfate anion (DS(-)) into the bilayer membrane is energetically favored by an exothermic partition enthalpy of Delta H(O)(D) = -6.0 kcal/mol at 28 degrees C. This is in contrast to nonionic detergents where Delta H(O)(D) is usually positive. The partition enthalpy decreases linearly with increasing temperature and the molar heat capacity is Delta C(O)(P) = -50 +/- 3 cal mol(-1) K(-1). The partition isotherm is nonlinear if the bound detergent is plotted versus the free detergent concentration in bulk solution. This is caused by the electrostatic repulsion between the DS(-) ions inserted into the membrane and those free in solution near the membrane surface. The surface concentration of DS(-) immediately above the plane of binding was hence calculated with the Gouy-Chapman theory, and a strictly linear relationship was obtained between the surface concentration and the extent of DS(-) partitioning. The surface partition constant K describes the chemical equilibrium in the absence of electrostatic effects. For the SDS-membrane equilibrium K was found to be 1.2 x 10(4) M(-1) to 6 x 10(4) M(-1) for the various systems and conditions investigated, very similar to data available for nonionic detergents of the same chain length. The membrane-micelle phase diagram was also studied. Complete membrane solubilization requires a ratio of 2.2 mol SDS bound per mole of total lipid at 56 degrees C. The corresponding equilibrium concentration of SDS free in solution is C (sat)(D,F) approximately 1.7 mM and is slightly below the critical micelles concentration (CMC) = 2.1 mM (at 56 degrees C and 0.11 M buffer). Membrane saturation occurs at

  1. The Effect of Lidocaine · HCl on the Fluidity of Native and Model Membrane Lipid Bilayers

    PubMed Central

    Park, Jun-Seop; Jung, Tae-Sang; Noh, Yang-Ho; Kim, Woo-Sung; Park, Won-Ick; Kim, Young-Soo; Chung, In-Kyo; Sohn, Uy Dong; Bae, Soo-Kyung

    2012-01-01

    The purpose of this study is to investigated the mechanism of pharmacological action of local anesthetic and provide the basic information about the development of new effective local anesthetics. Fluorescent probe techniques were used to evaluate the effect of lidocaine·HCl on the physical properties (transbilayer asymmetric lateral and rotational mobility, annular lipid fluidity and protein distribution) of synaptosomal plasma membrane vesicles (SPMV) isolated from bovine cerebral cortex, and liposomes of total lipids (SPMVTL) and phospholipids (SPMVPL) extracted from the SPMV. An experimental procedure was used based on selective quenching of 1,3-di(1-pyrenyl)propane (Py-3-Py) and 1,6-diphenyl-1,3,5-hexatriene (DPH) by trinitrophenyl groups, and radiationless energy transfer from the tryptophans of membrane proteins to Py-3-Py. Lidocaine·HCl increased the bulk lateral and rotational mobility of neuronal and model membrane lipid bilayes, and had a greater fluidizing effect on the inner monolayer than the outer monolayer. Lidocaine·HCl increased annular lipid fluidity in SPMV lipid bilayers. It also caused membrane proteins to cluster. The most important finding of this study is that there is far greater increase in annular lipid fluidity than that in lateral and rotational mobilities by lidocaine·HCl. Lidocaine·HCl alters the stereo or dynamics of the proteins in the lipid bilayers by combining with lipids, especially with the annular lipids. In conclusion, the present data suggest that lidocaine, in addition to its direct interaction with proteins, concurrently interacts with membrane lipids, fluidizing the membrane, and thus inducing conformational changes of proteins known to be intimately associated with membrane lipid. PMID:23269904

  2. Nucleic acid-lipid membrane interactions studied by DSC.

    PubMed

    Giatrellis, Sarantis; Nounesis, George

    2011-01-01

    The interactions of nucleic acids with lipid membranes are of great importance for biological mechanisms as well as for biotechnological applications in gene delivery and drug carriers. The optimization of liposomal vectors for clinical use is absolutely dependent upon the formation mechanisms, the morphology, and the molecular organization of the lipoplexes, that is, the complexes of lipid membranes with DNA. Differential scanning calorimetry (DSC) has emerged as an efficient and relatively easy-to-operate experimental technique that can straightforwardly provide data related to the thermodynamics and the kinetics of the DNA-lipid complexation and especially to the lipid organization and phase transitions within the membrane. In this review, we summarize DSC studies considering nucleic acid-membrane systems, accentuating DSC capabilities, and data analysis. Published work involving cationic, anionic, and zwitterionic lipids as well as lipid mixtures interacting with RNA and DNA of different sizes and conformations are included. It is shown that despite limitations, issues such as DNA- or RNA-induced phase separation and microdomain lipid segregation, liposomal aggregation and fusion, alterations of the lipid long-range molecular order, as well as membrane-induced structural changes of the nucleic acids can be efficiently treated by systematic high-sensitivity DSC studies.

  3. Membrane Lipid Co-Aggregation with α-Synuclein Fibrils

    PubMed Central

    Topgaard, Daniel; Linse, Sara; Sparr, Emma

    2013-01-01

    Amyloid deposits from several human diseases have been found to contain membrane lipids. Co-aggregation of lipids and amyloid proteins in amyloid aggregates, and the related extraction of lipids from cellular membranes, can influence structure and function in both the membrane and the formed amyloid deposit. Co-aggregation can therefore have important implications for the pathological consequences of amyloid formation. Still, very little is known about the mechanism behind co-aggregation and molecular structure in the formed aggregates. To address this, we study in vitro co-aggregation by incubating phospholipid model membranes with the Parkinson’s disease-associated protein, α-synuclein, in monomeric form. After aggregation, we find spontaneous uptake of phospholipids from anionic model membranes into the amyloid fibrils. Phospholipid quantification, polarization transfer solid-state NMR and cryo-TEM together reveal co-aggregation of phospholipids and α-synuclein in a saturable manner with a strong dependence on lipid composition. At low lipid to protein ratios, there is a close association of phospholipids to the fibril structure, which is apparent from reduced phospholipid mobility and morphological changes in fibril bundling. At higher lipid to protein ratios, additional vesicles adsorb along the fibrils. While interactions between lipids and amyloid-protein are generally discussed within the perspective of different protein species adsorbing to and perturbing the lipid membrane, the current work reveals amyloid formation in the presence of lipids as a co-aggregation process. The interaction leads to the formation of lipid-protein co-aggregates with distinct structure, dynamics and morphology compared to assemblies formed by either lipid or protein alone. PMID:24146972

  4. Electro-Optical Imaging Microscopy of Dye-Doped Artificial Lipidic Membranes

    PubMed Central

    Hajj, Bassam; De Reguardati, Sophie; Hugonin, Loïc; Le Pioufle, Bruno; Osaki, Toshihisa; Suzuki, Hiroaki; Takeuchi, Shoji; Mojzisova, Halina; Chauvat, Dominique; Zyss, Joseph

    2009-01-01

    Artificial lipidic bilayers are widely used as a model for the lipid matrix in biological cell membranes. We use the Pockels electro-optical effect to investigate the properties of an artificial lipidic membrane doped with nonlinear molecules in the outer layer. We report here what is believed to be the first electro-optical Pockels signal and image from such a membrane. The electro-optical dephasing distribution within the membrane is imaged and the signal is shown to be linear as a function of the applied voltage. A theoretical analysis taking into account the statistical orientation distribution of the inserted dye molecules allows us to estimate the doped membrane nonlinearity. Ongoing extensions of this work to living cell membranes are discussed. PMID:19948120

  5. 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.

  6. Plasma membrane organization and function: moving past lipid rafts.

    PubMed

    Kraft, Mary L

    2013-09-01

    "Lipid raft" is the name given to the tiny, dynamic, and ordered domains of cholesterol and sphingolipids that are hypothesized to exist in the plasma membranes of eukaryotic cells. According to the lipid raft hypothesis, these cholesterol- and sphingolipid-enriched domains modulate the protein-protein interactions that are essential for cellular function. Indeed, many studies have shown that cellular levels of cholesterol and sphingolipids influence plasma membrane organization, cell signaling, and other important biological processes. Despite 15 years of research and the application of highly advanced imaging techniques, data that unambiguously demonstrate the existence of lipid rafts in mammalian cells are still lacking. This Perspective summarizes the results that challenge the lipid raft hypothesis and discusses alternative hypothetical models of plasma membrane organization and lipid-mediated cellular function.

  7. 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. Copyright © 2015 Elsevier B.V. All rights reserved.

  8. 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

  9. 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.

  10. Electroporation of archaeal lipid membranes using MD simulations.

    PubMed

    Polak, Andraž; Tarek, Mounir; Tomšič, Matija; Valant, Janez; Ulrih, Nataša Poklar; Jamnik, Andrej; Kramar, Peter; Miklavčič, Damijan

    2014-12-01

    Molecular dynamics (MD) simulations were used to investigate the electroporation of archaeal lipid bilayers when subjected to high transmembrane voltages induced by a charge imbalance, mimicking therefore millisecond electric pulse experiments. The structural characteristics of the bilayer, a 9:91 mol% 2,3-di-O-sesterterpanyl-sn-glicerol-1-phospho-myo-inositol (AI) and 2,3-di-O-sesterterpanyl-sn-glicerol-1-phospho-1'(2'-O-α-D-glucosyl)-myo-inositol (AGI) were compared to small angle X-ray scattering data. A rather good agreement of the electron density profiles at temperatures of 298 and 343 K was found assessing therefore the validity of the protocols and force fields used in simulations. Compared to dipalmitoyl-phosphatidylcholine (DPPC), the electroporation threshold for the bilayer was found to increase from ~2 V to 4.3 V at 323 K, and to 5.2 V at 298 K. Comparing the electroporation thresholds of the archaeal lipids to those of simple diphytanoyl-phosphatidylcholine (DPhPC) bilayers (2.5 V at 323 K) allowed one to trace back the stability of the membranes to the structure of their lipid head groups. Addition of DPPC in amounts of 50 mol% to the archaeal lipid bilayers decreases their stability and lowers the electroporation thresholds to 3.8 V and 4.1 V at respectively 323 and 298 K. The present study therefore shows how membrane compositions can be selected to cover a wide range of responses to electric stimuli. This provides new routes for the design of liposomes that can be efficiently used as drug delivery carriers, as the selection of their composition allows one to tune in their electroporation threshold for subsequent release of their load.

  11. Structural elucidation of the interaction between neurodegenerative disease-related tau protein with model lipid membranes

    NASA Astrophysics Data System (ADS)

    Jones, Emmalee M.

    A protein's sequence of amino acids determines how it folds. That folded structure is linked to protein function, and misfolding to dysfunction. Protein misfolding and aggregation into beta-sheet rich fibrillar aggregates is connected with over 20 neurodegenerative diseases, including Alzheimer's disease (AD). AD is characterized in part by misfolding, aggregation and deposition of the microtubule associated tau protein into neurofibrillary tangles (NFTs). However, two questions remain: What is tau's fibrillization mechanism, and what is tau's cytotoxicity mechanism? Tau is prone to heterogeneous interactions, including with lipid membranes. Lipids have been found in NFTs, anionic lipid vesicles induced aggregation of the microtubule binding domain of tau, and other protein aggregates induced ion permeability in cells. This evidence prompted our investigation of tau's interaction with model lipid membranes to elucidate the structural perturbations those interactions induced in tau protein and in the membrane. We show that although tau is highly charged and soluble, it is highly surface active and preferentially interacts with anionic membranes. To resolve molecular-scale structural details of tau and model membranes, we utilized X-ray and neutron scattering techniques. X-ray reflectivity indicated tau aggregated at air/water and anionic lipid membrane interfaces and penetrated into membranes. More significantly, membrane interfaces induced tau protein to partially adopt a more compact conformation with density similar to folded protein and ordered structure characteristic of beta-sheet formation. This suggests possible membrane-based mechanisms of tau aggregation. Membrane morphological changes were seen using fluorescence microscopy, and X-ray scattering techniques showed tau completely disrupts anionic membranes, suggesting an aggregate-based cytotoxicity mechanism. Further investigation of protein constructs and a "hyperphosphorylation" disease mimic helped

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

    PubMed Central

    Allison, Timothy M.; Ulmschneider, Martin B.; Degiacomi, Matteo T.; Baldwin, Andrew J.; Robinson, Carol V.

    2014-01-01

    Previous studies have established that the folding, structure and function of membrane proteins are influenced by their lipid environments1-7 and that lipids can bind to specific sites, for example in potassium channels8. Fundamental questions remain however regarding the extent of membrane protein selectivity toward lipids. Here we report a mass spectrometry (MS) approach designed to determine the selectivity of lipid binding to membrane protein complexes. We investigate the mechanosensitive channel of large conductance (MscL), aquaporin Z (AqpZ), and the ammonia channel (AmtB) using ion mobility MS (IM-MS), which reports gas-phase collision cross sections. We demonstrate that folded conformations of membrane protein complexes can exist in the gas-phase. By resolving lipid-bound states we then rank bound lipids based on their ability to resist gas phase unfolding and thereby stabilize membrane protein structure. Results show that lipids bind non-selectively and with high avidity to MscL, all imparting comparable stability, the highest-ranking lipid however is phosphatidylinositol phosphate, in line with its proposed functional role in mechanosensation9. AqpZ is also stabilized by many lipids with cardiolipin imparting the most significant resistance to unfolding. Subsequently, through functional assays, we discover that cardiolipin modulates AqpZ function. Analogous experiments identify AmtB as being highly selective for phosphatidylglycerol prompting us to obtain an X-ray structure in this lipid membrane-like environment. The 2.3Å resolution structure, when compared with others obtained without lipid bound, reveals distinct conformational changes that reposition AmtB residues to interact with the lipid bilayer. Overall our results demonstrate that resistance to unfolding correlates with specific lipid-binding events enabling distinction of lipids that merely bind from those that modulate membrane protein structure and/or function. We anticipate that these

  13. The role of interfacial lipids in stabilizing membrane protein oligomers.

    PubMed

    Gupta, Kallol; Donlan, Joseph A C; Hopper, Jonathan T S; Uzdavinys, Povilas; Landreh, Michael; Struwe, Weston B; Drew, David; Baldwin, Andrew J; Stansfeld, Phillip J; Robinson, Carol V

    2017-01-19

    Oligomerization of membrane proteins in response to lipid binding has a critical role in many cell-signalling pathways but is often difficult to define or predict. Here we report the development of a mass spectrometry platform to determine simultaneously the presence of interfacial lipids and oligomeric stability and to uncover how lipids act as key regulators of membrane-protein association. Evaluation of oligomeric strength for a dataset of 125 α-helical oligomeric membrane proteins reveals an absence of interfacial lipids in the mass spectra of 12 membrane proteins with high oligomeric stability. For the bacterial homologue of the eukaryotic biogenic transporters (LeuT, one of the proteins with the lowest oligomeric stability), we found a precise cohort of lipids within the dimer interface. Delipidation, mutation of lipid-binding sites or expression in cardiolipin-deficient Escherichia coli abrogated dimer formation. Molecular dynamics simulation revealed that cardiolipin acts as a bidentate ligand, bridging across subunits. Subsequently, we show that for the Vibrio splendidus sugar transporter SemiSWEET, another protein with low oligomeric stability, cardiolipin shifts the equilibrium from monomer to functional dimer. We hypothesized that lipids are essential for dimerization of the Na(+)/H(+) antiporter NhaA from E. coli, which has the lowest oligomeric strength, but not for the substantially more stable homologous Thermus thermophilus protein NapA. We found that lipid binding is obligatory for dimerization of NhaA, whereas NapA has adapted to form an interface that is stable without lipids. Overall, by correlating interfacial strength with the presence of interfacial lipids, we provide a rationale for understanding the role of lipids in both transient and stable interactions within a range of α-helical membrane proteins, including G-protein-coupled receptors.

  14. 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.

  15. The role of interfacial lipids in stabilising membrane protein oligomers

    PubMed Central

    Uzdavinys, Povilas; Landreh, Michael; Struwe, Weston B.; Drew, David; Baldwin, Andrew J.; Stansfeld, Phillip J.; Robinson, Carol V.

    2017-01-01

    Oligomerisation of membrane proteins in response to lipid binding plays a critical role in many cell-signaling pathways 1 but is often difficult to define 2 or predict 3. Here we develop a mass spectrometry platform to determine simultaneously presence of interfacial lipids and oligomeric stability and discover how lipids act as key regulators of membrane protein association. Evaluation of oligomeric strength for a dataset of 125 α-helical oligomeric membrane proteins revealed an absence of interfacial lipids in the mass spectra of 12 membrane proteins with high oligomeric stability. For the bacterial homologue of the eukaryotic biogenic transporters (LeuT) 4 one of the proteins with the lowest oligomeric stability, we found a precise cohort of lipids within the dimer interface. Delipidation, mutation of lipid binding sites or expression in cardiolipin (CDL) deficient Escherichia coli, abrogated dimer formation. Molecular dynamics simulation revealed that CDL acts as a bidentate ligand bridging across subunits. Subsequently, we show that for the sugar transporter SemiSWEET from Vibrio splendidus 5, another protein with low oligomeric stability, cardiolipin shifts the equilibrium from monomer to functional dimer. We hypothesised that lipids would be essential for dimerisation of the Na+/H+ antiporter NhaA from E. coli, which has the lowest oligomeric strength, but not for substantially more stable, homologous NapA from Thermus thermophilus. We found that lipid binding is obligatory for dimerisation of NhaA, whereas NapA has adapted to form an interface that is stable without lipids. Overall, by correlating interfacial strength with the presence of interfacial lipids we provide a rationale for understanding the role of lipids in both transient and stable interactions within a range of α-helical membrane proteins, including GPCRs. PMID:28077870

  16. Molecular Dynamics Simulation Reveals Unique Interplays Between a Tarantula Toxin and Lipid Membranes.

    PubMed

    Wu, Lei; Xie, Si-Si; Meng, Er; Li, Wen-Ying; Liu, Long; Zhang, Dong-Yi

    2017-06-01

    Tarantula toxins compose an important class of spider toxins that target ion channels, and some are known to interact with lipid membranes. In this study, we focus on a tarantula toxin, Jingzhaotoxin-III (JZTx-III) that specifically targets the cardiac voltage-gated sodium channel Na[Formula: see text]1.5 and is suspected to be able to interact with lipid membranes. Here, we use an all-atom model and long-term molecular dynamics simulations to investigate the interactions between JZTx-III and lipid membranes of different compositions. Trajectory analyses show that JZTx-III has no substantial interaction with the neutral 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipids, but binds to membranes containing negatively charged 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (POPG). The most intriguing observations in our simulation are the different interactions between the toxin and the membrane in the mixed and pure POPG membrane systems. The POPC/POPG mixed membrane undergoes a phase transition to a rippled phase upon binding of the toxin, while the pure POPG membrane has no apparent change. Moreover, the binding of JZTx-III to both of the mixture and the pure POPG membrane systems induce small conformational changes. The sequence alignment shows that JZTx-III may not partition into the lipid bilayer due to the mutations of a C-terminal hydrophobic residue and some charged residues that affect toxin orientation. Taken together, JZTx-III and lipid membranes have unique effects on each other that may facilitate the specific binding of JZTx-III to Na[Formula: see text]1.5. This computational study also enriches our understanding of the potential complex interactions between spider toxins and lipid membranes.

  17. Chemotherapy drugs form ion pores in membranes due to physical interactions with lipids.

    PubMed

    Ashrafuzzaman, Mohammad; Tseng, Chih-Yuan; Duszyk, Marek; Tuszynski, Jack A

    2012-12-01

    We demonstrate the effects on membrane of the tubulin-binding chemotherapy drugs: thiocolchicoside and taxol. Electrophysiology recordings across lipid membranes in aqueous phases containing drugs were used to investigate the drug effects on membrane conductance. Molecular dynamics simulation of the chemotherapy drug-lipid complexes was used to elucidate the mechanism at an atomistic level. Both drugs are observed to induce stable ion-flowing pores across membranes. Discrete pore current-time plots exhibit triangular conductance events in contrast to rectangular ones found for ion channels. Molecular dynamics simulations indicate that drugs and lipids experience electrostatic and van der Waals interactions for short periods of time when found within each other's proximity. The energies from these two interactions are found to be similar to the energies derived theoretically using the screened Coulomb and the van der Waals interactions between peptides and lipids due to mainly their charge properties while forming peptide-induced ion channels in lipid bilayers. Experimental and in silico studies together suggest that the chemotherapy drugs induce ion pores inside lipid membranes due to drug-lipid physical interactions. The findings reveal cytotoxic effects of drugs on the cell membrane, which may aid in novel drug development for treatment of cancer and other diseases.

  18. Direct evidence of vinculin tail-lipid membrane interaction in beta-sheet conformation.

    PubMed

    Diez, Gerold; List, Felix; Smith, James; Ziegler, Wolfgang H; Goldmann, Wolfgang H

    2008-08-15

    The focal adhesion protein vinculin (1066 residues) plays an important role in cell adhesion and migration. The interaction between vinculin and lipid membranes is necessary to ensure these processes. There are three putative lipid-membrane interaction sites located at the vinculin tail domain two that form amphipathic alpha-helices (residues 935-978 and 1020-1040) and one that remains unstructured (residues 1052-1066) during crystallization. In this work, the structural and biochemical properties of the last 21 residues of the vinculin tail domain were investigated. Differential scanning calorimetry was performed in the presence of lipid vesicles consisting of dimyristoyl-L-alpha-phosphatidylcholine and dimyristoyl-L-alpha-phosphatidylglycerol at various molar ratios. The results demonstrate that this peptide inserts into lipid vesicle membranes. Examining the secondary structure of this peptide by molecular dynamics simulations and circular dichroism spectroscopy, we show that it adopts an antiparallel beta sheet backbone geometry that could ensure the association with lipid vesicles.

  19. Capacities of membrane lipids to accumulate neutral organic chemicals.

    PubMed

    Endo, Satoshi; Escher, Beate I; Goss, Kai-Uwe

    2011-07-15

    Lipids have been considered as the predominant components for bioaccumulation of organic chemicals. However, differences in accumulation properties between different types of lipid (e.g., storage and membrane lipids) have rarely been considered. Moreover, in view of toxic effects on organisms, chemical accumulation specifically in biological membranes is of particular importance. In this review article, partition coefficients of 240 neutral organic compounds between liposomes (phospholipid membrane vesicles) and water (K(lipw)), reported in the literature or measured additionally for this work, were evaluated. Values of log K(lipw) and log K(ow) (octanol-water partition coefficients) differ by 0.4 on average. Polyparameter linear free energy relationships (PP-LFERs) can describe the log K(lipw) data even better (standard deviations = 0.28-0.31) than the log K(ow) model. Recent experimental data for highly hydrophobic compounds fit well to the PP-LFERs and do not indicate the existence of a previously postulated "hydrophobicity cutoff". Predictive approaches based only on the molecular structure (KOWWIN, SPARC, COSMOthermX, COSMOmic) were also evaluated for K(lipw) prediction. The PP-LFERs revealed that partition coefficients into membrane lipids can be two log units higher than those into storage lipids for H-bond donor compounds, suggesting that distinguishing between the two lipids is necessary to account for the bioaccumulation of these compounds, and that tissues rich in membrane lipids (e.g., kidneys, liver) instead of fat tissue can be the primary phase for accumulation.

  20. Interaction of poloxamine block copolymers with lipid membranes: Role of copolymer structure and membrane cholesterol content.

    PubMed

    Sandez-Macho, Isabel; Casas, Matilde; Lage, Emilio V; Rial-Hermida, M Isabel; Concheiro, Angel; Alvarez-Lorenzo, Carmen

    2015-09-01

    Interactions of X-shaped poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers with cell membranes were investigated recording the π-A isotherms of monolayer systems of dipalmitoylphosphatidylcholine (DPPC):cholesterol 100:0; 80:20 and 60:40 mol ratio and evaluating the capability of the copolymers to trigger haemolysis or to protect from haemolytic agents. Four varieties of poloxamine (Tetronic 904, 908, 1107 and 1307) were chosen in order to cover a wide range of EO and PO units contents and molecular weights, and compared to a variety of poloxamer (Pluronic P85). The π-A isotherms revealed that the greater the content in cholesterol, the stronger the interaction of the block copolymers with the lipids monolayer. The interactions were particularly relevant at low pressures and low lipid proportions, mimicking the conditions of damaged membranes. Relatively hydrophobic copolymers bearing short PEO blocks (e.g., T904 and P85) intercalated among the lipids expanding the surface area (ΔGexc) but not effectively sealing the pores. These varieties showed haemolytic behavior. Oppositely, highly hydrophilic copolymers bearing long PEO blocks (e.g., T908, T1107 and T1307) caused membrane contraction and outer leaflet sealing due to strong interactions of PEO with cholesterol and diamine core with phospholipids. These later varieties were not haemolytic and exerted a certain protective effect against spontaneous haemolysis for both intact erythrocytes and cholesterol-depleted erythrocytes.

  1. Lipid rafts and detergent-resistant membranes in epithelial keratinocytes.

    PubMed

    McGuinn, Kathleen P; Mahoney, Mỹ G

    2014-01-01

    Our understanding of the plasma membrane has markedly increased since Singer and Nicolson proposed the fluid mosaic model in 1972. While their revolutionary theory of the lipid bilayer remains largely valid, it is now known that lipids and proteins are not randomly dispersed throughout the plasma membrane but instead may be organized within membrane microdomains, commonly referred to as lipid rafts. Lipid rafts are highly dynamic, detergent resistant, and enriched with both cholesterol and glycosphingolipids. The two main types are flotillin-rich planar lipid rafts and caveolin-rich caveolae. It is proposed that flotillin and caveolin proteins regulate cell communication by compartmentalizing and interacting with signal transduction proteins within their respective lipid microdomains. Consequently, membrane rafts play an important role in vital cellular functions including migration, invasion, and signaling; thus, alterations in their microenvironment can initiate signaling pathways that affect cellular function and behavior. Therefore, the identification of lipid rafts and their associated proteins is integral to the study of transmembrane signaling. Here, we review the current standard protocols and biochemical approaches used to isolate and define raft proteins from epithelial cells and tissues. Furthermore, in Section 3 of this chapter, detailed protocols are offered for isolating lipid rafts by subjection to detergent and sucrose density centrifugation, as well as an approach for selectively isolating caveolae. Methods to manipulate rafts with treatments such as methyl-β-cyclodextrin and flotillin III are also described.

  2. Adhesion and hemifusion of cytoplasmic myelin lipid membranes are highly dependent on the lipid composition

    PubMed Central

    Banquy, Xavier; Kristiansen, Kai; Lee, Dong Woog; Israelachvili, Jacob N.

    2012-01-01

    We report the effects of calcium ions on the adhesion and hemifusion mechanisms of model supported myelin lipid bilayer membranes of differing lipid composition. As in our previous studies [1, 2], the lipid compositions used mimic “healthy” and “diseased-like” (experimental autoimmune encephalomyelitis, EAE) membranes. Our results show that the interaction forces as a function of membrane separation distance are well described by a generic model that also (and in particular) includes the hydrophobic interaction arising from the hydrophobically exposed (interior) parts of the bilayers. The model is able to capture the mechanical instability that triggers the onset of the hemifusion event, and highlights the primary role of the hydrophobic interaction in membrane fusion. The effects of lipid composition on the fusion mechanism, and the adhesion forces between myelin lipid bilayers, can be summarized as follow: in calcium-free buffer, healthy membranes do not present any signs of adhesion or hemifusion, while diseased membranes hemifuse easily. Addition of 2 mM calcium favors adhesion and hemifusion of the membranes independently of their composition, but the mechanisms involved in the two processes were different: healthy bilayers systematically presented stronger adhesion forces and lower energy barriers to fusion compared to diseased bilayers. These results are of particular relevance for understanding lesion development (demyelination, swelling, vacuolization and/or vesiculation) in myelin associated diseases such as multiple sclerosis and its relationship to lipid domain formation in myelin membranes. PMID:22047743

  3. Lipid flow through fusion pores connecting membranes of different tensions.

    PubMed

    Chizmadzhev, Y A; Kumenko, D A; Kuzmin, P I; Chernomordik, L V; Zimmerberg, J; Cohen, F S

    1999-06-01

    When two membranes fuse, their components mix; this is usually described as a purely diffusional process. However, if the membranes are under different tensions, the material will spread predominantly by convection. We use standard fluid mechanics to rigorously calculate the steady-state convective flux of lipids. A fusion pore is modeled as a toroid shape, connecting two planar membranes. Each of the membrane monolayers is considered separately as incompressible viscous media with the same shear viscosity, etas. The two monolayers interact by sliding past each other, described by an intermonolayer viscosity, etar. Combining a continuity equation with an equation that balances the work provided by the tension difference, Deltasigma, against the energy dissipated by flow in the viscous membrane, yields expressions for lipid velocity, upsilon, and area of lipid flux, Phi. These expressions for upsilon and Phi depend on Deltasigma, etas, etar, and geometrical aspects of a toroidal pore, but the general features of the theory hold for any fusion pore that has a roughly hourglass shape. These expressions are readily applicable to data from any experiments that monitor movement of lipid dye between fused membranes under different tensions. Lipid velocity increases nonlinearly from a small value for small pore radii, rp, to a saturating value at large rp. As a result of velocity saturation, the flux increases linearly with pore radius for large pores. The calculated lipid flux is in agreement with available experimental data for both large and transient fusion pores.

  4. Lipid flow through fusion pores connecting membranes of different tensions.

    PubMed Central

    Chizmadzhev, Y A; Kumenko, D A; Kuzmin, P I; Chernomordik, L V; Zimmerberg, J; Cohen, F S

    1999-01-01

    When two membranes fuse, their components mix; this is usually described as a purely diffusional process. However, if the membranes are under different tensions, the material will spread predominantly by convection. We use standard fluid mechanics to rigorously calculate the steady-state convective flux of lipids. A fusion pore is modeled as a toroid shape, connecting two planar membranes. Each of the membrane monolayers is considered separately as incompressible viscous media with the same shear viscosity, etas. The two monolayers interact by sliding past each other, described by an intermonolayer viscosity, etar. Combining a continuity equation with an equation that balances the work provided by the tension difference, Deltasigma, against the energy dissipated by flow in the viscous membrane, yields expressions for lipid velocity, upsilon, and area of lipid flux, Phi. These expressions for upsilon and Phi depend on Deltasigma, etas, etar, and geometrical aspects of a toroidal pore, but the general features of the theory hold for any fusion pore that has a roughly hourglass shape. These expressions are readily applicable to data from any experiments that monitor movement of lipid dye between fused membranes under different tensions. Lipid velocity increases nonlinearly from a small value for small pore radii, rp, to a saturating value at large rp. As a result of velocity saturation, the flux increases linearly with pore radius for large pores. The calculated lipid flux is in agreement with available experimental data for both large and transient fusion pores. PMID:10354423

  5. Simulations of simple linoleic acid-containing lipid membranes and models for the soybean plasma membranes

    NASA Astrophysics Data System (ADS)

    Zhuang, Xiaohong; Ou, Anna; Klauda, Jeffery B.

    2017-06-01

    The all-atom CHARMM36 lipid force field (C36FF) has been tested with saturated, monounsaturated, and polyunsaturated lipids; however, it has not been validated against the 18:2 linoleoyl lipids with an unsaturated sn-1 chain. The linoleoyl lipids are common in plants and the main component of the soybean membrane. The lipid composition of soybean plasma membranes has been thoroughly characterized with experimental studies. However, there is comparatively less work done with computational modeling. Our molecular dynamics (MD) simulation results show that the pure linoleoyl lipids, 1-stearoyl-2-linoleoyl-sn-glycero-3-phosphocholine (18:0/18:2) and 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (di-18:2), agree very well with the experiments, which demonstrates the accuracy of the C36FF for the computational study of soybean membranes. Based on the experimental composition, the soybean hypocotyl and root plasma membrane models are developed with each containing seven or eight types of linoleoyl phospholipids and two types of sterols (sitosterol and stigmasterol). MD simulations are performed to characterize soybean membranes, and the hydrogen bonds and clustering results demonstrate that the lipids prefer to interact with the lipids of the same/similar tail unsaturation. All the results suggest that these two soybean membrane models can be used as a basis for further research in soybean and higher plant membranes involving membrane-associated proteins.

  6. Simulations of simple linoleic acid-containing lipid membranes and models for the soybean plasma membranes.

    PubMed

    Zhuang, Xiaohong; Ou, Anna; Klauda, Jeffery B

    2017-06-07

    The all-atom CHARMM36 lipid force field (C36FF) has been tested with saturated, monounsaturated, and polyunsaturated lipids; however, it has not been validated against the 18:2 linoleoyl lipids with an unsaturated sn-1 chain. The linoleoyl lipids are common in plants and the main component of the soybean membrane. The lipid composition of soybean plasma membranes has been thoroughly characterized with experimental studies. However, there is comparatively less work done with computational modeling. Our molecular dynamics (MD) simulation results show that the pure linoleoyl lipids, 1-stearoyl-2-linoleoyl-sn-glycero-3-phosphocholine (18:0/18:2) and 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (di-18:2), agree very well with the experiments, which demonstrates the accuracy of the C36FF for the computational study of soybean membranes. Based on the experimental composition, the soybean hypocotyl and root plasma membrane models are developed with each containing seven or eight types of linoleoyl phospholipids and two types of sterols (sitosterol and stigmasterol). MD simulations are performed to characterize soybean membranes, and the hydrogen bonds and clustering results demonstrate that the lipids prefer to interact with the lipids of the same/similar tail unsaturation. All the results suggest that these two soybean membrane models can be used as a basis for further research in soybean and higher plant membranes involving membrane-associated proteins.

  7. Lipids and topological rules governing membrane protein assembly☆

    PubMed Central

    Bogdanov, Mikhail; Dowhan, William; Vitrac, Heidi

    2014-01-01

    Membrane protein folding and topogenesis are tuned to a given lipid profile since lipids and proteins have co-evolved to follow a set of interdependent rules governing final protein topological organization. Transmembrane domain (TMD) topology is determined via a dynamic process in which topogenic signals in the nascent protein are recognized and interpreted initially by the translocon followed by a given lipid profile in accordance with the Positive Inside Rule. The net zero charged phospholipid phosphatidylethanolamine and other neutral lipids dampen the translocation potential of negatively charged residues in favor of the cytoplasmic retention potential of positively charged residues (Charge Balance Rule). This explains why positively charged residues are more potent topological signals than negatively charged residues. Dynamic changes in orientation of TMDs during or after membrane insertion are attributed to non-sequential cooperative and collective lipid–protein charge interactions as well as long-term interactions within a protein. The proportion of dual topological conformers of a membrane protein varies in a dose responsive manner with changes in the membrane lipid composition not only in vivo but also in vitro and therefore is determined by the membrane lipid composition. Switching between two opposite TMD topologies can occur in either direction in vivo and also in liposomes (designated as fliposomes) independent of any other cellular factors. Such lipid-dependent post-insertional reversibility of TMD orientation indicates a thermodynamically driven process that can occur at any time and in any cell membrane driven by changes in the lipid composition. This dynamic view of protein topological organization influenced by the lipid environment reveals previously unrecognized possibilities for cellular regulation and understanding of disease states resulting from mis-folded proteins. This article is part of a Special Issue entitled: Protein Trafficking

  8. Do local anesthetics interact preferentially with membrane lipid rafts? Comparative interactivities with raft-like membranes.

    PubMed

    Tsuchiya, Hironori; Ueno, Takahiro; Mizogami, Maki; Takakura, Ko

    2010-08-01

    Membranous lipid bilayers have been reconsidered as the site of action of local anesthetics (LAs). Recent understanding of biomembranes indicates the existence of lipid raft microdomains enriched in cholesterol and sphingolipids as potential platforms for channels and receptors. Based on the hypothesis that LAs may interact preferentially with lipid rafts over non-raft membranes, we compared their effects on raft model membranes and cardiolipin-containing biomimetic membranes. Liposomes were prepared with phospholipids, sphingomyelin, cerebroside, and cholesterol to have compositions corresponding to lipid rafts and cardiomyocyte mitochondrial membranes. After reacting LAs (50-200 microM) with the membrane preparations, their interactivities were determined by measuring fluorescence polarization with 1,6-diphenyl-1,3,5-hexatriene. Although bupivacaine and lidocaine acted on different raft-like liquid-ordered membranes to reduce polarization values, their effects on biomimetic less ordered membranes were much greater. LAs interacted with biomimetic membranes with the potency being R(+)-bupivacaine > racemic bupivacaine > S(-)-bupivacaine > ropivacaine > lidocaine > prilocaine, which is consistent with the rank order of pharmacotoxicological potency. However, raft model membranes showed neither structure-dependence nor stereoselectivity. The relevance of membrane lipid rafts to LAs is questionable at least in their effects on raft-like liquid-ordered membranes.

  9. Reduction in lateral lipid mobility of lipid bilayer membrane by atmospheric pressure plasma irradiation

    NASA Astrophysics Data System (ADS)

    Suda, Yoshiyuki; Tero, Ryugo; Yamashita, Ryuma; Yusa, Kota; Takikawa, Hirofumi

    2016-03-01

    Plasma medicine is an emerging research field in which various applications of electrical discharge, especially in the form of nonequilibrium plasma at atmospheric pressure, are examined, for example, the application of plasma to biological targets for various purposes such as selective killing of tumor cells and blood stanching. We have focused on the behavior of an artificial cell membrane system at the solid-liquid interface. To evaluate the lateral lipid mobility, we measured the diffusion coefficient of the supported lipid bilayer (SLB) composed of dioleoylphosphatidylcholine with fluorescence recovery after photobleaching by confocal laser scanning microscopy. It was found that the diffusion coefficient was decreased by plasma irradiation and that the diffusion coefficient decreasing rate proceeded with increasing plasma power. We investigated the effects of stimulation with an equilibrium chemical, H2O2, on the SLB and confirmed that the diffusion coefficient did not change at least up to a H2O2 concentration of 5 mM. These results indicate that transient active species generated by plasma play critical roles in the reduction in SLB fluidity. The effects of the two generated major oxidized lipid species, hydroxyl- or hydroperoxy-phosphatidylcholine (PC) and acyl-chain-truncated PCs terminated with aldehyde or carboxyl group, on lateral lipid mobility are discussed.

  10. Single Lipid Molecule Dynamics on Supported Lipid Bilayers with Membrane Curvature

    PubMed Central

    Cheney, Philip P.; Weisgerber, Alan W.; Feuerbach, Alec M.; Knowles, Michelle K.

    2017-01-01

    The plasma membrane is a highly compartmentalized, dynamic material and this organization is essential for a wide variety of cellular processes. Nanoscale domains allow proteins to organize for cell signaling, endo- and exocytosis, and other essential processes. Even in the absence of proteins, lipids have the ability to organize into domains as a result of a variety of chemical and physical interactions. One feature of membranes that affects lipid domain formation is membrane curvature. To directly test the role of curvature in lipid sorting, we measured the accumulation of two similar lipids, 1,2-Dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DHPE) and hexadecanoic acid (HDA), using a supported lipid bilayer that was assembled over a nanopatterned surface to obtain regions of membrane curvature. Both lipids studied contain 16 carbon, saturated tails and a head group tag for fluorescence microscopy measurements. The accumulation of lipids at curvatures ranging from 28 nm to 55 nm radii was measured and fluorescein labeled DHPE accumulated more than fluorescein labeled HDA at regions of membrane curvature. We then tested whether single biotinylated DHPE molecules sense curvature using single particle tracking methods. Similar to groups of fluorescein labeled DHPE accumulating at curvature, the dynamics of single molecules of biotinylated DHPE was also affected by membrane curvature and highly confined motion was observed. PMID:28294967

  11. 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.

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

    PubMed Central

    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.

    2013-01-01

    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. PMID:23947891

  13. Mechanisms of membrane deformation by lipid-binding domains.

    PubMed

    Itoh, Toshiki; Takenawa, Tadaomi

    2009-09-01

    Among an increasing number of lipid-binding domains, a group that not only binds to membrane lipids but also changes the shape of the membrane has been found. These domains are characterized by their strong ability to transform globular liposomes as well as flat plasma membranes into elongated membrane tubules both in vitro and in vivo. Biochemical studies on the structures of these proteins have revealed the importance of the amphipathic helix, which potentially intercalates into the lipid bilayer to induce and/or sense membrane curvature. Among such membrane-deforming domains, BAR and F-BAR/EFC domains form crescent-shaped dimers, suggesting a preference for a curved membrane, which is important for curvature sensing. Bioinformatics in combination with structural analyses has been identifying an increasing number of novel families of lipid-binding domains. This review attempts to summarize the evidence obtained by recent studies in order to gain general insights into the roles of membrane-deforming domains in a variety of biological events.

  14. A novel biotinylated lipid raft reporter for electron microscopic imaging of plasma membrane microdomains.

    PubMed

    Krager, Kimberly J; Sarkar, Mitul; Twait, Erik C; Lill, Nancy L; Koland, John G

    2012-10-01

    The submicroscopic spatial organization of cell surface receptors and plasma membrane signaling molecules is readily characterized by electron microscopy (EM) via immunogold labeling of plasma membrane sheets. Although various signaling molecules have been seen to segregate within plasma membrane microdomains, the biochemical identity of these microdomains and the factors affecting their formation are largely unknown. Lipid rafts are envisioned as submicron membrane subdomains of liquid ordered structure with differing lipid and protein constituents that define their specific varieties. To facilitate EM investigation of inner leaflet lipid rafts and the localization of membrane proteins therein, a unique genetically encoded reporter with the dually acylated raft-targeting motif of the Lck kinase was developed. This reporter, designated Lck-BAP-GFP, incorporates green fluorescent protein (GFP) and biotin acceptor peptide (BAP) modules, with the latter allowing its single-step labeling with streptavidin-gold. Lck-BAP-GFP was metabolically biotinylated in mammalian cells, distributed into low-density detergent-resistant membrane fractions, and was readily detected with avidin-based reagents. In EM images of plasma membrane sheets, the streptavidin-gold-labeled reporter was clustered in 20-50 nm microdomains, presumably representative of inner leaflet lipid rafts. The utility of the reporter was demonstrated in an investigation of the potential lipid raft localization of the epidermal growth factor receptor.

  15. A novel biotinylated lipid raft reporter for electron microscopic imaging of plasma membrane microdomains[S

    PubMed Central

    Krager, Kimberly J.; Sarkar, Mitul; Twait, Erik C.; Lill, Nancy L.; Koland, John G.

    2012-01-01

    The submicroscopic spatial organization of cell surface receptors and plasma membrane signaling molecules is readily characterized by electron microscopy (EM) via immunogold labeling of plasma membrane sheets. Although various signaling molecules have been seen to segregate within plasma membrane microdomains, the biochemical identity of these microdomains and the factors affecting their formation are largely unknown. Lipid rafts are envisioned as submicron membrane subdomains of liquid ordered structure with differing lipid and protein constituents that define their specific varieties. To facilitate EM investigation of inner leaflet lipid rafts and the localization of membrane proteins therein, a unique genetically encoded reporter with the dually acylated raft-targeting motif of the Lck kinase was developed. This reporter, designated Lck-BAP-GFP, incorporates green fluorescent protein (GFP) and biotin acceptor peptide (BAP) modules, with the latter allowing its single-step labeling with streptavidin-gold. Lck-BAP-GFP was metabolically biotinylated in mammalian cells, distributed into low-density detergent-resistant membrane fractions, and was readily detected with avidin-based reagents. In EM images of plasma membrane sheets, the streptavidin-gold-labeled reporter was clustered in 20–50 nm microdomains, presumably representative of inner leaflet lipid rafts. The utility of the reporter was demonstrated in an investigation of the potential lipid raft localization of the epidermal growth factor receptor. PMID:22822037

  16. Steady-state compartmentalization of lipid membranes by active proteins.

    PubMed Central

    Sabra, M C; Mouritsen, O G

    1998-01-01

    Using a simple microscopic model of lipid-protein interactions, based on the hydrophobic matching principle, we study some generic aspects of lipid-membrane compartmentalization controlled by a dispersion of active integral membrane proteins. The activity of the proteins is simulated by conformational excitations governed by an external drive, and the deexcitation is controlled by interaction of the protein with its lipid surroundings. In response to the flux of energy into the proteins from the environment and the subsequent dissipation of energy into the lipid bilayer, the lipid-protein assembly reorganizes into a steady-state structure with a typical length scale determined by the strength of the external drive. In the specific case of a mixed dimyristoylphosphatidylcholine-distearoylphosphatidylcholine bilayer in the gel-fluid coexistence region, it is shown explicitly by computer simulation that the activity of an integral membrane protein can lead to a compartmentalization of the lipid-bilayer membrane. The compartmentalization is related to the dynamical process of phase separation and lipid domain formation. PMID:9533687

  17. Interaction of octyl-beta-thioglucopyranoside with lipid membranes.

    PubMed

    Wenk, M R; Seelig, J

    1997-11-01

    Octyl-beta-thioglucopyranoside (octyl thioglucoside, OTG) is a nonionic surfactant used for the purification, reconstitution, and crystallization of membrane proteins. The thermodynamic properties of the OTG-membrane partition equilibrium are not known and have been investigated here with high-sensitivity titration calorimetry. The critical concentration for inducing the bilayer <==> micelle transition was determined as cD* = 7.3 mM by 90 degree light scattering. All thermodynamic studies were performed well below this limit. Sonified, unilamellar lipid vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with and without cholesterol were employed in the titration calorimetry experiments, and the temperature was varied between 28 degrees C and 45 degrees C. Depending on the surfactant concentration in the membrane, the partition enthalpy was found to be exothermic or endothermic, leading to unusual titration patterns. A quantitative interpretation of all titration curves was possible with the following model: 1) The partitioning of OTG into the membrane follows a simple partition law, i.e., Xb = Kc(D,f), where Xb denotes the molar amount of detergent bound per mole of lipid and c(D,f) is the detergent concentration in bulk solution. 2) The partition enthalpy for the transfer of OTG from the aqueous phase to the membrane depends linearly on the mole fraction, R, of detergent in the membrane. All calorimetric OTG titration curves can be characterized quantitatively by using a composition-dependent partition enthalpy of the form deltaHD(R) = -0.08 + 1.7 R (kcal/mol) (at 28 degrees C). At low OTG concentrations (R < or = 0.05) the reaction enthalpy is exothermic; it becomes distinctly endothermic as more and more surfactant is incorporated into the membrane. OTG has a partition constant of 240 M(-1) and is more hydrophobic than its oxygen-containing analog, octyl-beta-D-glucopyranoside (OG). Including a third nonionic amphiphile, octa

  18. Plasma Membrane Lipids and Their Role in Fungal Virulence

    PubMed Central

    Del Poeta, Maurizio

    2016-01-01

    There has been considerable evidence in recent years suggesting that plasma membrane lipids are important regulators of fungal pathogenicity. Various glycolipids have been shown to impart virulent properties in several fungal species, while others have been shown to play a role in host defense. In addition to their role as virulence factors, lipids also contribute to other virulence mechanisms such as drug resistance, biofilm formation, and release of extracellular vesicles. In addition, lipids also affect the mechanical properties of the plasma membrane through the formation of packed microdomains composed mainly of sphingolipids and sterols. Changes in the composition of lipid microdomains has been shown to disrupt the localization of virulence factors and affect fungal pathogenicity. This review gathers evidence on the various roles of plasma membrane lipids in fungal virulence and how lipids might contribute to the different processes that occur during infection and treatment. Insight into the role of lipids in fungal virulence can lead to an improved understanding of the process of fungal pathogenesis and the development of new lipid-mediated therapeutic strategies. PMID:26703191

  19. 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.

  20. Plasma membrane lipids and their role in fungal virulence.

    PubMed

    Rella, Antonella; Farnoud, Amir M; Del Poeta, Maurizio

    2016-01-01

    There has been considerable evidence in recent years suggesting that plasma membrane lipids are important regulators of fungal pathogenicity. Various glycolipids have been shown to impart virulent properties in several fungal species, while others have been shown to play a role in host defense. In addition to their role as virulence factors, lipids also contribute to other virulence mechanisms such as drug resistance, biofilm formation, and release of extracellular vesicles. In addition, lipids also affect the mechanical properties of the plasma membrane through the formation of packed microdomains composed mainly of sphingolipids and sterols. Changes in the composition of lipid microdomains have been shown to disrupt the localization of virulence factors and affect fungal pathogenicity. This review gathers evidence on the various roles of plasma membrane lipids in fungal virulence and how lipids might contribute to the different processes that occur during infection and treatment. Insight into the role of lipids in fungal virulence can lead to an improved understanding of the process of fungal pathogenesis and the development of new lipid-mediated therapeutic strategies. Published by Elsevier Ltd.

  1. Interactions of Lipid Membranes with Fibrillar Protein Aggregates.

    PubMed

    Gorbenko, Galyna; Trusova, Valeriya; Girych, Mykhailo; Adachi, Emi; Mizuguchi, Chiharu; Saito, Hiroyuki

    2015-01-01

    Amyloid fibrils are an intriguing class of protein aggregates with distinct physicochemical, structural and morphological properties. They display peculiar membrane-binding behavior, thus adding complexity to the problem of protein-lipid interactions. The consensus that emerged during the past decade is that amyloid cytotoxicity arises from a continuum of cross-β-sheet assemblies including mature fibrils. Based on literature survey and our own data, in this chapter we address several aspects of fibril-lipid interactions, including (i) the effects of amyloid assemblies on molecular organization of lipid bilayer; (ii) competition between fibrillar and monomeric membrane-associating proteins for binding to the lipid surface; and (iii) the effects of lipids on the structural morphology of fibrillar aggregates. To illustrate some of the processes occurring in fibril-lipid systems, we present and analyze fluorescence data reporting on lipid bilayer interactions with fibrillar lysozyme and with the N-terminal 83-residue fragment of amyloidogenic mutant apolipoprotein A-I, 1-83/G26R/W@8. The results help understand possible mechanisms of interaction and mutual remodeling of amyloid fibers and lipid membranes, which may contribute to amyloid cytotoxicity.

  2. 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.

  3. Procyanidins can interact with Caco-2 cell membrane lipid rafts: involvement of cholesterol.

    PubMed

    Verstraeten, Sandra V; Jaggers, Grayson K; Fraga, Cesar G; Oteiza, Patricia I

    2013-11-01

    Large procyanidins (more than three subunits) are not absorbed at the gastrointestinal tract but could exert local effects through their interactions with membranes. We previously showed that hexameric procyanidins (Hex), although not entering cells, interact with membranes modulating cell signaling and fate. This paper investigated if Hex, as an example of large procyanidins, can selectively interact with lipid rafts which could in part explain its biological actions. This mechanism was studied in both synthetic membranes (liposomes) and Caco-2 cells. Hex promoted Caco-2 cell membrane rigidification and dehydration, effects that were abolished upon cholesterol depletion with methyl-β-cyclodextrin (MCD). Hex prevented lipid raft structure disruption induced by cholesterol depletion/redistribution by MCD or sodium deoxycholate. Supporting the involvement of cholesterol-Hex bonding in Hex interaction with lipid rafts, the absence of cholesterol markedly decreased the capacity of Hex to prevent deoxycholate- and Triton X-100-mediated disruption of lipid raft-like liposomes. Stressing the functional relevance of this interaction, Hex mitigated lipid raft-associated activation of the extracellular signal-regulated kinases (ERK) 1/2. Results support the capacity of a large procyanidin (Hex) to interact with membrane lipid rafts mainly through Hex-cholesterol bondings. Procyanidin-lipid raft interactions can in part explain the capacity of large procyanidins to modulate cell physiology.

  4. Imidazolium-Based Lipid Analogues and Their Interaction with Phosphatidylcholine Membranes.

    PubMed

    Wang, Da; de Jong, Djurre H; Rühling, Andreas; Lesch, Volker; Shimizu, Karina; Wulff, Stephanie; Heuer, Andreas; Glorius, Frank; Galla, Hans-Joachim

    2016-12-06

    4,5-Dialkylated imidazolium lipid salts are a new class of lipid analogues showing distinct biological activities. The potential effects of the imidazolium lipids on artificial lipid membranes and the corresponding membrane interactions was analyzed. Therefore, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) was employed to create an established lipid monolayer model and a bilayer membrane. Mixed monolayers of DPPC and 4,5-dialkylimidazolium lipids differing by their alkyl chain length (C7, C11, and C15) were characterized by surface pressure-area (π-A) isotherms using a Wilhelmy film balance in combination with epifluorescence microscopy. Monolayer hysteresis for binary mixtures was examined by recording triplicate consecutive compression-expansion cycles. The lipid miscibility and membrane stability of DPPC/imidazolium lipids were subsequently evaluated by the excess mean molecular area (ΔA(ex)) and the excess Gibbs free energy (ΔG(ex)) of mixing. Furthermore, the thermotropic behavior of mixed liposomes of DPPC/imidazolium lipids was investigated by differential scanning calorimetry (DSC). The C15-imidazolium lipid (C15-IMe·HI) forms a thermodynamically favored and kinetically reversible Langmuir monolayer with DPPC and exhibits a rigidification effect on both DPPC monolayer and bilayer structures at low molar fractions (X ≤ 0.3). However, the incorporation of the C11-imidazolium lipid (C11-IMe·HI) causes the formation of an unstable and irreversible Langmuir-Gibbs monolayer with DPPC and disordered DPPC liposomes. The C7-imidazolium lipid (C7-IMe·HI) displays negligible membrane activity. To better understand these results on a molecular level, all-atom molecular dynamics (MD) simulations were performed. The simulations yield two opposing molecular mechanisms governing the different behavior of the three imidazolium lipids: a lateral ordering effect and a free volume/stretching effect. Overall, our study provides the first evidence that the membrane

  5. Autonomous buckling of micrometer-sized lipid-protein membrane patches constructed by Dictyostelium discoideum.

    PubMed

    Takahashi, Kei; Toyota, Taro

    2015-01-01

    The cytosol of amoeba cells controls the membrane deformation during their motion in vivo. To investigate such ability of the cytosol of amoeba cell, Dictyostelium discoideum (Dictyostelium), in vitro, we used lipids extracted from Dictyostelium and commercially available phospholipids, and prepared substrate-supported lipid membrane patches on the micrometer scale by spin coating. We found that the spin coater holder, which has pores (pore size = 3.1 mm) of negative pressure to hold the cover glass induced the concave surface of the cover glass. The membrane lipid patches were formed at each position in the vicinity of the holder pores and their sizes were in the range of 2.7 to 3.2 × 10(4) μm(2). After addition of the cytosol extracted from Dictyostelium to the lipid membrane patches, through time-lapse observation with a confocal laser scanning fluorescence microscope, we observed an autonomous buckling of the Dictyostelium lipid patches and localized behaviours of proteins found within. The current method serves as the novel technique for the preparation of film patches in which the positions of patches are controlled by the holder pores without fabricating, modifying, and arranging the chemical properties of the solution components of lipids. The findings imply that lipid-binding proteins in the cytosol were adsorbed and accumulated within the Dictyostelium lipid patches, inducing the transformation of the cell-sized patch.

  6. Edelfosine and miltefosine effects on lipid raft properties: membrane biophysics in cell death by antitumor lipids.

    PubMed

    Castro, Bruno M; Fedorov, Aleksander; Hornillos, Valentin; Delgado, Javier; Acuña, A Ulises; Mollinedo, Faustino; Prieto, Manuel

    2013-07-03

    Edelfosine (1-O-octadecyl-2-O-methyl-sn-glycero-phosphocholine) and miltefosine (hexadecylphosphocholine) are synthetic alkylphospholipids (ALPs) that are reported to selectively accumulate in tumor cell membranes, inducing Fas clustering and activation on lipid rafts, triggering apoptosis. However, the exact mechanism by which these lipids elicit these events is still not fully understood. Recent studies propose that their mode of action might be related with alterations of lipid rafts biophysical properties caused by these lipid drugs. To achieve a clear understanding of this mechanism, we studied the effects of pharmacologically relevant amounts of edelfosine and miltefosine in the properties of model and cellular membranes. The influence of these molecules on membrane order, lateral organization, and lipid rafts molar fraction and size were studied by steady-state and time-resolved fluorescence methods, Förster resonance energy transfer (FRET), confocal and fluorescence lifetime imaging microscopy (FLIM). We found that the global membrane and lipid rafts biophysical properties of both model and cellular membranes were not significantly affected by both the ALPs. Nonetheless, in model membranes, a mild increase in membrane fluidity induced by both alkyl lipids was detected, although this effect was more noticeable for edelfosine than miltefosine. This absence of drastic alterations shows for the first time that ALPs mode of action is unlikely to be directly linked to alterations of lipid rafts biophysical properties caused by these drugs. The biological implications of this result are discussed in the context of ALPs effects on lipid metabolism, mitochondria homeostasis modulation, and their relationship with tumor cell death.

  7. Mechano-capacitive properties of polarized membranes and the application to conductance measurements of lipid membrane patches

    NASA Astrophysics Data System (ADS)

    Zecchi, Karis A.; Mosgaard, Lars D.; Heimburg, Thomas

    2017-01-01

    Biological membranes are capacitors that can be charged by applying an electric field across the membrane. The charges on the capacitor exert a force on the membrane that leads to electrostriction, i.e., a thinning of the membrane. This effect is especially strong close to chain melting transitions. A consequence is voltage induced pore formation in the lipid membrane. Since the force is quadratic in voltage, negative and positive voltages have an identical influence on the physics of symmetric membranes. This is not the case for a membrane with an asymmetry leading to a permanent electric polarization. Positive and negative voltages of identical magnitude lead to different physical properties. Such an asymmetry can originate from a lipid composition that is different on the two monolayers of the membrane, or from membrane curvature. The latter effect is called flexoelectricity. It was investigated in detail by A.G. Petrov in the recent decades. As a consequence of permanent polarization, the membrane capacitor is discharged at a voltage different from zero. This leads to interesting electrical phenomena such as outward or inward rectification of membrane permeability. The changes in current-voltage relationships are consistent with the known magnitude of the flexoelectric effect.

  8. Differential Interaction of Synthetic Glycolipids with Biomimetic Plasma Membrane Lipids Correlates with the Plant Biological Response.

    PubMed

    Nasir, Mehmet Nail; Lins, Laurence; Crowet, Jean-Marc; Ongena, Marc; Dorey, Stephan; Dhondt-Cordelier, Sandrine; Clément, Christophe; Bouquillon, Sandrine; Haudrechy, Arnaud; Sarazin, Catherine; Fauconnier, Marie-Laure; Nott, Katherine; Deleu, Magali

    2017-09-26

    Natural and synthetic amphiphilic molecules including lipopeptides, lipopolysaccharides, and glycolipids are able to induce defense mechanisms in plants. In the present work, the perception of two synthetic C14 rhamnolipids, namely, Alk-RL and Ac-RL, differing only at the level of the lipid tail terminal group have been investigated using biological and biophysical approaches. We showed that Alk-RL induces a stronger early signaling response in tobacco cell suspensions than does Ac-RL. The interactions of both synthetic RLs with simplified biomimetic membranes were further analyzed using experimental and in silico approaches. Our results indicate that the interactions of Alk-RL and Ac-RL with lipids were different in terms of insertion and molecular responses and were dependent on the lipid composition of model membranes. A more favorable insertion of Alk-RL than Ac-RL into lipid membranes is observed. Alk-RL forms more stable molecular assemblies than Ac-RL with phospholipids and sterols. At the molecular level, the presence of sterols tends to increase the RLs' interaction with lipid bilayers, with a fluidizing effect on the alkyl chains. Taken together, our findings suggest that the perception of these synthetic RLs at the membrane level could be related to a lipid-driven process depending on the organization of the membrane and the orientation of the RLs within the membrane and is correlated with the induction of early signaling responses in tobacco cells.

  9. Lipid binding and membrane penetration of polymyxin B derivatives studied in a biomimetic vesicle system.

    PubMed Central

    Katz, Marina; Tsubery, Haim; Kolusheva, Sofiya; Shames, Alex; Fridkin, Mati; Jelinek, Raz

    2003-01-01

    Understanding membrane interactions and cell-wall permeation of Gram-negative bacteria is of great importance, owing to increasing bacterial resistance to existing drugs and therapeutic treatments. Here we use biomimetic lipid vesicles to analyse membrane association and penetration by synthetic derivatives of polymyxin B (PMB), a potent naturally occurring antibacterial cyclic peptide. The PMB analogues studied were PMB nonapeptide (PMBN), in which the hydrophobic alkyl residue was cleaved, PMBN diastereomer containing D-instead of L-amino acids within the cyclic ring (dPMBN) and PMBN where the hydrophobic alkyl chain was replaced with an Ala6 repeat (Ala6-PMBN). Peptide binding measurements, colorimetric transitions induced within the vesicles, fluorescence quenching experiments and ESR spectroscopy were applied to investigate the structural parameters underlying the different membrane-permeation profiles and biological activities of the analogues. The experiments point to the role of negatively charged lipids in membrane binding and confirm the prominence of lipopolisaccharide (LPS) in promoting membrane association and penetration by the peptides. Examination of the lipid interactions of the PMB derivatives shows that the cyclic moiety of PMB is not only implicated in lipid attachment and LPS binding, but also affects penetration into the inner bilayer core. The addition of the Ala6 peptide moiety, however, does not significantly promote peptide insertion into the hydrophobic lipid environment. The data also indicate that the extent of penetration into the lipid bilayer is not related to the overall affinity of the peptides to the membrane. PMID:12848621

  10. Homeostatic restitution of cell membranes. Nuclear membrane lipid biogenesis and transport of protein from cytosol to intranuclear spaces.

    PubMed

    Slomiany, Amalia; Grabska, Maria; Slomiany, Bronislaw L

    2006-08-30

    Our studies on homeostatic restitution of cellular and subcellular membranes showed that vesicular intracellular transport is engaged in systematic and coordinated replacement of lipids and proteins in the membranes of the secretory, non-dividing epithelial cells (Slomiany et al., J. Physiol. Pharmacol. 2004; 55: 837-860). In this report, we present evidence on the homeostatic restitution of lipids in the biomembranes that constitute nuclear envelopes. We investigated nuclear membranes lipid synthesis by employing purified intact nuclei (IN), the outer nuclear membrane (ONM), the inner nuclear membrane (INM) and the cell cytosol (CC). In contrast to Endoplasmic Reticulum (ER) which in the presence of CC generates new biomembrane that forms ER vesicles transporting ER products to Golgi, the IN, ONM and INM are not producing transport vesicles. Instead, the newly synthesized lipids remain in the nuclear membranes. The membranes (INM, ONM) of IN incubated with CC become enriched with newly synthesized phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylinositol phosphates (PIPs) and phosphatidic acid (PA). The incubation of separated ONM and INM with CC also enriched the membranes with IN specific lipids identified above. Moreover, the incubation of IN or its membranes with CC afforded retention of numerous CC proteins on the nuclear membrane. Here, we concentrated on 30kDa CC protein that displayed affinity to nuclear membrane PIP2. The 30kDa CC protein bound to PIP2 of IN, INM, and ONM. With IN, initially the PIP2-30kDa CC protein complex was detected on ONM, after 30-120 min of incubation, was found on INM and in nuclear contents. At the same time when the 30 kDa protein was released from INM and found in nuclear contents, the PIP2 of INM and ONM became undetectable, while the lipid extract from the membrane displaced from IN contained labeled PI only. Since ONM is an uninterrupted continuum of ER and INM, we speculate that the synthesis of the lipids

  11. Lipid domains in model membranes: a brief historical perspective.

    PubMed

    Mouritsen, Ole G; Bagatolli, Luis A

    2015-01-01

    All biological membranes consist of a complex composite of macromolecules and macromolecular assemblies, of which the fluid lipid-bilayer component is a core element with regard to cell encapsulation and barrier properties. The fluid lipid bilayer also supports the functional machinery of receptors, channels and pumps that are associated with the membrane. This bilayer is stabilized by weak physical and colloidal forces, and its nature is that of a self-assembled system of amphiphiles in water. Being only approximately 5 nm in thickness and still encapsulating a cell that is three orders of magnitude larger in diameter, the lipid bilayer as a material has very unusual physical properties, both in terms of structure and dynamics. Although the lipid bilayer is a fluid, it has a distinct and structured trans-bilayer profile, and in the plane of the bilayer the various molecular components, viz different lipid species and membrane proteins, have the capacity to organize laterally in terms of differentiated domains on different length and time scales. These elements of small-scale structure and order are crucial for the functioning of the membrane. It has turned out to be difficult to quantitatively study the small-scale structure of biological membranes. A major part of the insight into membrane micro- and nano-domains and the concepts used to describe them have hence come from studies of simple lipid bilayers as models of membranes, by use of a wide range of theoretical, experimental and simulational approaches. Many questions remain to be answered as to which extent the result from model studies can carry over to real biological membranes.

  12. Coupling between pore formation and phase separation in charged lipid membranes

    NASA Astrophysics Data System (ADS)

    Himeno, Hiroki; Ito, Hiroaki; Higuchi, Yuji; Hamada, Tsutomu; Shimokawa, Naofumi; Takagi, Masahiro

    2015-12-01

    We investigated the effect of charge on the membrane morphology of giant unilamellar vesicles (GUVs) composed of various mixtures containing charged lipids. We observed the membrane morphologies by fluorescent and confocal laser microscopy in lipid mixtures consisting of a neutral unsaturated lipid [dioleoylphosphatidylcholine (DOPC)], a neutral saturated lipid [dipalmitoylphosphatidylcholine (DPPC)], a charged unsaturated lipid [dioleoylphosphatidylglycerol (DOP G(-)) ], a charged saturated lipid [dipalmitoylphosphatidylglycerol (DPP G(-)) ], and cholesterol (Chol). In binary mixtures of neutral DOPC-DPPC and charged DOPC -DPP G(-) , spherical vesicles were formed. On the other hand, pore formation was often observed with GUVs consisting of DOP G(-) and DPPC. In a DPPC-DPPG(-) -Chol ternary mixture, pore-formed vesicles were also frequently observed. The percentage of pore-formed vesicles increased with the DPP G(-) concentration. Moreover, when the head group charges of charged lipids were screened by the addition of salt, pore-formed vesicles were suppressed in both the binary and ternary charged lipid mixtures. We discuss the mechanisms of pore formation in charged lipid mixtures and the relationship between phase separation and the membrane morphology. Finally, we reproduce the results seen in experimental systems by using coarse-grained molecular dynamics simulations.

  13. Lateral mobility of plasma membrane lipids in dividing Xenopus eggs.

    PubMed

    Tetteroo, P A; Bluemink, J G; Dictus, W J; van Zoelen, E J; de Laat, S W

    1984-07-01

    The lateral mobility of plasma membrane lipids was analyzed during first cleavage of Xenopus laevis eggs by fluorescence photobleaching recovery (FPR) measurements, using the lipid analogs 5-(N-hexadecanoyl)aminofluorescein ("HEDAF") and 5-(N-tetradecanoyl)aminofluorescein ("TEDAF") as probes. The preexisting plasma membrane of the animal side showed an inhomogeneous, dotted fluorescence pattern after labeling and the lateral mobility of both probes used was below the detection limits of the FPR method (D much less than 10(-10) cm2/sec). In contrast, the preexisting plasma membrane of the vegetal side exhibited homogeneous fluorescence and the lateral diffusion coefficient of both probes used was relatively high (HEDAF, D = 2.8 X 10(-8) cm2/sec; TEDAF, D = 2.4 X 10(-8) cm2/sec). In the cleaving egg visible transfer of HEDAF or TEDAF from prelabeled plasma membrane to the new membrane in the furrow did not occur, even on the vegetal side. Upon labeling during cleavage, however, the new membrane was uniformly labeled and both probes were mobile, as in the vegetal preexisting plasma membrane. These data show that the membrane of the dividing Xenopus egg comprises three macrodomains: (i) the animal preexisting plasma membrane; (ii) the vegetal preexisting plasma membrane; (iii) the new furrow membrane.

  14. Properties of Membranes Derived from the Total Lipids Extracted from the Human Lens Cortex and Nucleus

    PubMed Central

    Mainali, Laxman; Raguz, Marija; O’Brien, William J.; Subczynski, Witold K.

    2013-01-01

    Human lens lipid membranes prepared using a rapid solvent exchange method from the total lipids extracted from the clear lens cortex and nucleus of 41- to 60-year-old donors were investigated using electron paramagnetic resonance spin-labeling. Profiles of the phospholipid alkyl-chain order, fluidity, oxygen transport parameter, and hydrophobicity were assessed across coexisting membrane domains. Membranes prepared from the lens cortex and nucleus were found to contain two distinct lipid environments, the bulk phospholipid-cholesterol domain and the cholesterol bilayer domain (CBD). The alkyl chains of phospholipids were strongly ordered at all depths, indicating that the amplitude of the wobbling motion of alkyl chains was small. However, profiles of the membrane fluidity, which explicitly contain time (expressed as the spin-lattice relaxation rate) and depend on the rotational motion of spin labels, show relatively high fluidity of alkyl chains close to the membrane center. Profiles of the oxygen transport parameter and hydrophobicity have a rectangular shape and also indicate a high fluidity and hydrophobicity of the membrane center. The amount of CBD was greater in nuclear membranes than in cortical membranes. The presence of the CBD in lens lipid membranes, which at 37°C showed a permeability coefficient for oxygen about 60% smaller than across a water layer of the same thickness, would be expected to raise the barrier for oxygen transport across the fiber cell membrane. Properties of human membranes are compared with those obtained for membranes made of lipids extracted from cortex and nucleus of porcine and bovine eye lenses. PMID:23438364

  15. Equilibrium microphase separation in the two-leaflet model of lipid membranes

    NASA Astrophysics Data System (ADS)

    Reigada, Ramon; Mikhailov, Alexander S.

    2016-01-01

    Because of the coupling between local lipid composition and the thickness of the membrane, microphase separation in two-component lipid membranes can take place; such effects may underlie the formation of equilibrium nanoscale rafts. Using a kinetic description, this phenomenon is analytically and numerically investigated. The phase diagram is constructed through the stability analysis for linearized kinetic equations, and conditions for microphase separation are discussed. Simulations of the full kinetic model reveal the development of equilibrium membrane nanostructures with various morphologies from the initial uniform state.

  16. 3D-Membrane Stacks on Supported Membranes Composed of Diatom Lipids Induced by Long-Chain Polyamines.

    PubMed

    Gräb, Oliver; Abacilar, Maryna; Daus, Fabian; Geyer, Armin; Steinem, Claudia

    2016-10-04

    Long-chain polyamines (LCPAs) are intimately involved in the biomineralization process of diatoms taking place in silica deposition vesicles being acidic compartments surrounded by a lipid bilayer. Here, we addressed the question whether and how LCPAs interact with lipid membranes composed of glycerophospholipids and glyceroglycolipids mimicking the membranes of diatoms and higher plants. Solid supported lipid bilayers and monolayers containing the three major components that are unique in diatoms and higher plants, i.e., monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), and sulfoquinovosyldiacylglycerol (SQDG), were prepared by spreading small unilamellar vesicles. The integrity of the membranes was investigated by fluorescence microscopy and atomic force microscopy showing continuous flat bilayers and monolayers with small protrusions on top of the membrane. The addition of a synthetic polyamine composed of 13 amine groups separated by a propyl spacer (C3N13) results in flat but three-dimensional membrane stacks within minutes. The membrane stacks are connected with the underlying membrane as verified by fluorescence recovery after photobleaching experiments. Membrane stack formation was found to be independent of the lipid composition; i.e., neither glyceroglycolipids nor negatively charged lipids were required. However, the formation process was strongly dependent on the chain length of the polyamine. Whereas short polyamines such as the naturally occurring spermidine, spermine, and the synthetic polyamines C3N4 and C3N5 do not induce stack formation, those containing seven and more amine groups (C3N7, C3N13, and C3N18) do form membrane stacks. The observed stack formation might have implications for the stability and expansion of the silica deposition vesicle during valve and girdle band formation in diatoms.

  17. Effect of electrostatic interaction between fluoxetine and lipid membranes on the partitioning of fluoxetine investigated using second derivative spectrophotometry and FTIR.

    PubMed

    Do, Tien T T; Dao, Uyen P N; Bui, Huong T; Nguyen, Trang T

    2017-10-01

    The interaction between a drug molecule and lipid bilayers is highly important regarding the pharmaceutical activity of the drug. In this study, the interaction of fluoxetine, a well-known selective serotonin reuptake inhibitor antidepressant and lipid bilayers composed of 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) was studied from the aspect of electrostatics using second derivative spectrophotometry and Fourier transform infrared spectroscopy (FTIR) in order to provide insights into the drug behavior. Changing pH from 7.4 to 9.5 to increases the neutral state of fluoxetine, the partitioning of fluoxetine into the zwitterionic DPPC large unilamellar vesicles (LUVs) was increased whereas it was reduced into the negatively charged DPPG LUVs. Fluoxetine was found to exhibit a disordering effect on the acyl chains of DPPC and DPPG bilayers upon its partitioning. In addition, increasing concentration of NaCl lessened the binding of fluoxetine into DPPG bilayers due to the reduction in electrostatic attraction between positively charged fluoxetine and negatively charged DPPG LUVs. In addition, the FTIR study revealed that increasing the NaCl concentration could trigger the shift to higher frequency of the CH2 stretching as well as the notable blue shift in the PO2(-) regions of DPPG, indicating that fluoxetine had deeper penetration into DPPG LUVs. The differences in the NaCl concentration showed a negligible effect on the incorporation of fluoxetine into the zwitterionic DPPC LUVs. In summary, the electrostatic interaction plays an important role on the partitioning of a cationic amphiphilic SSIR drug into the lipid bilayers and the drug partitioning induces the lipids' conformational change. These imply a possible influence on the drug pharmacology. Copyright © 2017 Elsevier B.V. All rights reserved.

  18. Interactions of the anticancer drug tamoxifen with lipid membranes

    DOE PAGES

    Khadka, Nawal K.; Cheng, Xiaolin; Ho, Chian Sing; ...

    2015-05-19

    Interactions of the hydrophobic anticancer drug tamoxifen (TAM) with lipid model membranes were studied using calcein-encapsulated vesicle leakage, attenuated total reflection Fourier transform infrared (FTIR) spectroscopy, small-angle neutron scattering (SANS), atomic force microscopy (AFM) based force spectroscopy, and all-atom molecular dynamics (MD) simulations. The addition of TAM enhances membrane permeability, inducing calcein to translocate from the interior to the exterior of lipid vesicles. A large decrease in the FTIR absorption band’s magnitude was observed in the hydrocarbon chain region, suggesting suppressed bond vibrational dynamics. Bilayer thickening was determined from SANS data. Force spectroscopy measurements indicate that the lipid bilayer areamore » compressibility modulus KA is increased by a large amount after the incorporation of TAM. MD simulations show that TAM decreases the lipid area and increases chain order parameters. Moreover, orientational and positional analyses show that TAM exhibits a highly dynamic conformation within the lipid bilayer. Lastly, our detailed experimental and computational studies of TAM interacting with model lipid membranes shed new light on membrane modulation by TAM.« less

  19. 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.

  20. Interactions of the Anticancer Drug Tamoxifen with Lipid Membranes

    PubMed Central

    Khadka, Nawal K.; Cheng, Xiaolin; Ho, Chian Sing; Katsaras, John; Pan, Jianjun

    2015-01-01

    Interactions of the hydrophobic anticancer drug tamoxifen (TAM) with lipid model membranes were studied using calcein-encapsulated vesicle leakage, attenuated total reflection Fourier transform infrared (FTIR) spectroscopy, small-angle neutron scattering (SANS), atomic force microscopy (AFM) based force spectroscopy, and all-atom molecular dynamics (MD) simulations. The addition of TAM enhances membrane permeability, inducing calcein to translocate from the interior to the exterior of lipid vesicles. A large decrease in the FTIR absorption band’s magnitude was observed in the hydrocarbon chain region, suggesting suppressed bond vibrational dynamics. Bilayer thickening was determined from SANS data. Force spectroscopy measurements indicate that the lipid bilayer area compressibility modulus KA is increased by a large amount after the incorporation of TAM. MD simulations show that TAM decreases the lipid area and increases chain order parameters. Moreover, orientational and positional analyses show that TAM exhibits a highly dynamic conformation within the lipid bilayer. Our detailed experimental and computational studies of TAM interacting with model lipid membranes shed new light on membrane modulation by TAM. PMID:25992727

  1. Ceramides in the skin lipid membranes: length matters.

    PubMed

    Skolová, Barbora; Janůšová, Barbora; Zbytovská, Jarmila; Gooris, Gert; Bouwstra, Joke; Slepička, Petr; Berka, Pavel; Roh, Jaroslav; Palát, Karel; Hrabálek, Alexandr; Vávrová, Kateřina

    2013-12-17

    Ceramides are essential constituents of the skin barrier that allow humans to live on dry land. Reduced levels of ceramides have been associated with skin diseases, e.g., atopic dermatitis. However, the structural requirements and mechanisms of action of ceramides are not fully understood. Here, we report the effects of ceramide acyl chain length on the permeabilities and biophysics of lipid membranes composed of ceramides (or free sphingosine), fatty acids, cholesterol, and cholesterol sulfate. Short-chain ceramides increased the permeability of the lipid membranes compared to a long-chain ceramide with maxima at 4-6 carbons in the acyl. By a combination of differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, Langmuir monolayers, and atomic force microscopy, we found that the reason for this effect in short ceramides was a lower proportion of tight orthorhombic packing and phase separation of continuous short ceramide-enriched domains with shorter lamellar periodicity compared to native long ceramides. Thus, long acyl chains in ceramides are essential for the formation of tightly packed impermeable lipid lamellae. Moreover, the model skin lipid membranes are a valuable tool to study the relationships between the lipid structure and composition, lipid organization, and the membrane permeability.

  2. Melittin-induced cholesterol reorganization in lipid bilayer membranes

    DOE PAGES

    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

  3. Membrane dynamics as seen by fourier transform infrared spectroscopy in a cyanobacterium, Synechocystis PCC 6803. The effects of lipid unsaturation and the protein-to-lipid ratio.

    PubMed

    Szalontai, B; Nishiyama, Y; Gombos, Z; Murata, N

    2000-12-20

    The roles of lipid unsaturation and lipid-protein interactions in maintaining the physiologically required membrane dynamics were investigated in a cyanobacterium strain, Synechocystis PCC 6803. The specific effects of lipid unsaturation on the membrane structure were addressed by the use of desaturase-deficient (desA(-)/desD(-)) mutant cells (which contain only oleic acid as unsaturated fatty acid species) of Synechocystis PCC 6803. The dynamic properties of the membranes were determined from the temperature dependence of the symmetric CH(2) stretching vibration frequency, which is indicative of the lipid fatty acyl chain disorder. It was found that a similar membrane dynamics is maintained at any growth temperature, in both the wild-type and the mutant cell membranes, with the exception of mutant cells grown at the lower physiological temperature limit. It seems that in the physiological temperature range the desaturase system of the cells can modulate the level of lipid desaturation sufficiently to maintain similar membrane dynamics. Below the range of normal growth temperatures, however, the extent of lipid disorder was always higher in the thylakoid than in the cytoplasmic membranes prepared from the same cells. This difference was attributed to the considerable difference in protein-to-lipid ratio in the two kinds of membranes, as determined from the ratio of the intensities of the protein amide I band and the lipid ester C&z.dbnd6;O vibration. The contributions to the membrane dynamics of an ab ovo present 'structural' lipid disorder due to the protein-lipid interactions and of a thermally induced 'dynamic' lipid disorder could be distinguished.

  4. 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

  5. A theoretical formalism for aggregation of peroxidized lipids and plasma membrane stability during photolysis.

    PubMed Central

    Busch, N A; Yarmush, M L; Toner, M

    1998-01-01

    The objective of this investigation was to examine, from a theoretical perspective, the mechanism underlying the lysis of plasma membranes by photoinduced, chemically mediated damage such as is found in photolysis. Toward this end, a model is presented which relates the membrane lifetime to the thermodynamic parameters of the membrane components based upon the kinetic theory of aggregate formation. The formalism includes a standard birth/death process for the formation of damaged membrane components (i.e., peroxidized lipids) as well as a terminating condensation process for the formation of aggregates of peroxidized plasma membrane lipids. Our theory predicts that 1) the membrane lifetime is inversely correlated with predicted rate of membrane damage; 2) an upper limit on the duration of membrane damage exists, above which the mean and variance of the membrane lifetime is independent of further membrane damage; and 3) both the mean and variance of the time of membrane lifetime distribution are correlated with the number of sites that may be damaged to form a single membrane defect. The model provides a framework to optimize the lysis of cell membranes by photodynamic therapy. PMID:9826616

  6. Spectral Imaging to Measure Heterogeneity in Membrane Lipid Packing

    PubMed Central

    Sezgin, Erdinc; Waithe, Dominic; Bernardino de la Serna, Jorge; Eggeling, Christian

    2015-01-01

    Physicochemical properties of the plasma membrane have been shown to play an important role in cellular functionality. Among those properties, the molecular order of the lipids, or the lipid packing, is of high importance. Changes in lipid packing are believed to compartmentalize cellular signaling by initiating coalescence and conformational changes of proteins. A common way to infer membrane lipid packing is by using membrane-embedded polarity-sensitive dyes, whose emission spectrum is dependent on the molecular order of the immediate membrane environment. Here, we report on an improved determination of such spectral shifts in the emission spectrum of the polarity-sensitive dyes. This improvement is based on the use of spectral imaging on a scanning confocal fluorescence microscope in combination with an improved analysis, which considers the whole emission spectrum instead of just single wavelength ranges. Using this approach and the polarity-sensitive dyes C-Laurdan or Di-4-ANEPPDHQ, we were able to image—with high accuracy—minute differences in the lipid packing of model and cellular membranes. PMID:25755090

  7. Digital holographic microscopy of phase separation in multicomponent lipid membranes

    NASA Astrophysics Data System (ADS)

    Farzam Rad, Vahideh; Moradi, Ali-Reza; Darudi, Ahmad; Tayebi, Lobat

    2016-12-01

    Lateral in-homogeneities in lipid compositions cause microdomains formation and change in the physical properties of biological membranes. With the presence of cholesterol and mixed species of lipids, phospholipid membranes segregate into lateral domains of liquid-ordered and liquid-disordered phases. Coupling of two-dimensional intralayer phase separations and interlayer liquid-crystalline ordering in multicomponent membranes has been previously demonstrated. By the use of digital holographic microscopy (DHMicroscopy), we quantitatively analyzed the volumetric dynamical behavior of such membranes. The specimens are lipid mixtures composed of sphingomyelin, cholesterol, and unsaturated phospholipid, 1,2-dioleoyl-sn-glycero-3-phosphocholine. DHMicroscopy in a transmission mode is an effective tool for quantitative visualization of phase objects. By deriving the associated phase changes, three-dimensional information on the morphology variation of lipid stacks at arbitrary time scales is obtained. Moreover, the thickness distribution of the object at demanded axial planes can be obtained by numerical focusing. Our results show that the volume evolution of lipid domains follows approximately the same universal growth law of previously reported area evolution. However, the thickness of the domains does not alter significantly by time; therefore, the volume evolution is mostly attributed to the changes in area dynamics. These results might be useful in the field of membrane-based functional materials.

  8. Laurdan fluorescence senses mechanical strain in the lipid bilayer membrane.

    PubMed

    Zhang, Yan-Liang; Frangos, John A; Chachisvilis, Mirianas

    2006-09-01

    The precise molecular mechanisms by which cells transduce a mechanical stimulus into an intracellular biochemical response have not yet been established. Here, we show for the first time that the fluorescence emission of an environment-sensitive membrane probe Laurdan is modulated by mechanical strain of the lipid bilayer membrane. We have measured fluorescence emission of Laurdan in phospholipid vesicles of 30, 50, and 100 nm diameter to show that osmotically induced membrane tension leads to an increase in polarity (hydration depth) of the phospholipid bilayer interior. Our data indicate that the general polarization of Laurdan emission is linearly dependent on membrane tension. We also show that higher membrane curvature leads to higher hydration levels. We anticipate that the proposed method will facilitate future studies of mechanically induced changes in physical properties of lipid bilayer environment both in vitro and in vivo.

  9. Kinetic and thermodynamic aspects of lipid translocation in biological membranes.

    PubMed Central

    Frickenhaus, S; Heinrich, R

    1999-01-01

    A theoretical analysis of the lipid translocation in cellular bilayer membranes is presented. We focus on an integrative model of active and passive transport processes determining the asymmetrical distribution of the major lipid components between the monolayers. The active translocation of the aminophospholipids phosphatidylserine and phosphatidylethanolamine is mathematically described by kinetic equations resulting from a realistic ATP-dependent transport mechanism. Concerning the passive transport of the aminophospholipids as well as of phosphatidylcholine, sphingomyelin, and cholesterol, two different approaches are used. The first treatment makes use of thermodynamic flux-force relationships. Relevant forces are transversal concentration differences of the lipids as well as differences in the mechanical states of the monolayers due to lateral compressions. Both forces, originating primarily from the operation of an aminophospholipid translocase, are expressed as functions of the lipid compositions of the two monolayers. In the case of mechanical forces, lipid-specific parameters such as different molecular surface areas and compression force constants are taken into account. Using invariance principles, it is shown how the phenomenological coefficients depend on the total lipid amounts. In a second approach, passive transport is analyzed in terms of kinetic mechanisms of carrier-mediated translocation, where mechanical effects are incorporated into the translocation rate constants. The thermodynamic as well as the kinetic approach are applied to simulate the time-dependent redistribution of the lipid components in human red blood cells. In the thermodynamic model the steady-state asymmetrical lipid distribution of erythrocyte membranes is simulated well under certain parameter restrictions: 1) the time scales of uncoupled passive transbilayer movement must be different among the lipid species; 2) positive cross-couplings of the passive lipid fluxes are

  10. Measuring the composition-curvature coupling in binary lipid membranes by computer simulations

    SciTech Connect

    Barragán Vidal, I. A. Müller, M.; Rosetti, C. M.; Pastorino, C.

    2014-11-21

    The coupling between local composition fluctuations in binary lipid membranes and curvature affects the lateral membrane structure. We propose an efficient method to compute the composition-curvature coupling in molecular simulations and apply it to two coarse-grained membrane models—a minimal, implicit-solvent model and the MARTINI model. Both the weak-curvature behavior that is typical for thermal fluctuations of planar bilayer membranes as well as the strong-curvature regime corresponding to narrow cylindrical membrane tubes are studied by molecular dynamics simulation. The simulation results are analyzed by using a phenomenological model of the thermodynamics of curved, mixed bilayer membranes that accounts for the change of the monolayer area upon bending. Additionally the role of thermodynamic characteristics such as the incompatibility between the two lipid species and asymmetry of composition are investigated.

  11. Measuring the composition-curvature coupling in binary lipid membranes by computer simulations.

    PubMed

    Barragán Vidal, I A; Rosetti, C M; Pastorino, C; Müller, M

    2014-11-21

    The coupling between local composition fluctuations in binary lipid membranes and curvature affects the lateral membrane structure. We propose an efficient method to compute the composition-curvature coupling in molecular simulations and apply it to two coarse-grained membrane models-a minimal, implicit-solvent model and the MARTINI model. Both the weak-curvature behavior that is typical for thermal fluctuations of planar bilayer membranes as well as the strong-curvature regime corresponding to narrow cylindrical membrane tubes are studied by molecular dynamics simulation. The simulation results are analyzed by using a phenomenological model of the thermodynamics of curved, mixed bilayer membranes that accounts for the change of the monolayer area upon bending. Additionally the role of thermodynamic characteristics such as the incompatibility between the two lipid species and asymmetry of composition are investigated.

  12. The unique lipid composition of gecko (Gekko Gekko) photoreceptor outer segment membranes.

    PubMed

    Yuan, C; Chen, H; Anderson, R E; Kuwata, O; Ebrey, T G

    1998-08-01

    This study investigated the lipid and fatty acid composition of gecko photoreceptor outer segment membranes which contain the P521 cone-type pigment. The lipids of gecko photoreceptor outer segment membranes were first extracted and separated by thin layer chromatography (TLC) and then analyzed by gas chromatography (GC). Our results show that gecko photoreceptor outer segment membranes contain less phosphatidylethanolamine (PE) and more phosphatidylcholine (PC) and phosphatidylserine (PS) compared with those of bovine and frog. The content of the polyunsaturated fatty acid, docosahexaenoic acid (DHA), in PC and PS is also the highest yet reported (55 and 63%, respectively). These lipid differences may provide some insight into the specific lipid requirements of cone-type pigments.

  13. Lipid nanotechnologies for structural studies of membrane-associated proteins.

    PubMed

    Stoilova-McPhie, Svetla; Grushin, Kirill; Dalm, Daniela; Miller, Jaimy

    2014-11-01

    We present a methodology of lipid nanotubes (LNT) and nanodisks technologies optimized in our laboratory for structural studies of membrane-associated proteins at close to physiological conditions. The application of these lipid nanotechnologies for structure determination by cryo-electron microscopy (cryo-EM) is fundamental for understanding and modulating their function. The LNTs in our studies are single bilayer galactosylceramide based nanotubes of ∼20 nm inner diameter and a few microns in length, that self-assemble in aqueous solutions. The lipid nanodisks (NDs) are self-assembled discoid lipid bilayers of ∼10 nm diameter, which are stabilized in aqueous solutions by a belt of amphipathic helical scaffold proteins. By combining LNT and ND technologies, we can examine structurally how the membrane curvature and lipid composition modulates the function of the membrane-associated proteins. As proof of principle, we have engineered these lipid nanotechnologies to mimic the activated platelet's phosphtaidylserine rich membrane and have successfully assembled functional membrane-bound coagulation factor VIII in vitro for structure determination by cryo-EM. The macromolecular organization of the proteins bound to ND and LNT are further defined by fitting the known atomic structures within the calculated three-dimensional maps. The combination of LNT and ND technologies offers a means to control the design and assembly of a wide range of functional membrane-associated proteins and complexes for structural studies by cryo-EM. The presented results confirm the suitability of the developed methodology for studying the functional structure of membrane-associated proteins, such as the coagulation factors, at a close to physiological environment. © 2014 Wiley Periodicals, Inc.

  14. Membranes as programmable matter: modulating physical-chemical behavior in lipid ensembles derived from archaea and eukaryotes

    NASA Astrophysics Data System (ADS)

    Gilmore, Sean Fitzpatrick

    Lipid membranes are of general interest to the scientific community due to their roles as cellular membranes, and because of their interesting material properties, such as tendencies to self-assemble into two- and three-dimensional structures. Further, there is interest in using lipid membranes as a self-assembling template or substrate for other materials, such as membrane proteins. The work presented here explores the physical-chemical interactions in and around artificial lipid membranes. In the first two chapters, lipid membranes are investigated as a form of programmable matter that responds to environmental changes. These responses manifest as two- and three-dimensional reorganization. In the subsequent chapters, the lipids of an extremophilic archaeon are examined in synthetic configurations to 1) identify how ensembles of lipids originating from organisms of different domains on the tree of life may behave in similar ways, and 2) to examine how the lipids of a desiccation-tolerant organism may be used to create robust lipid (bilayer) membranes that do not rely on liquid water to retain their structure. These collected findings expand how living membranes may be modulated or reorganized in vivo, and also suggest new ways to create programmable lipid-based materials.

  15. Electrophoretic separation method for membrane pore-forming proteins in multilayer lipid membranes.

    PubMed

    Okamoto, Yukihiro; Tsujimoto, Yusuke; Umakoshi, Hiroshi

    2016-03-01

    In this paper, we report on a novel electrophoretic separation and analysis method for membrane pore-forming proteins in multilayer lipid membranes (MLMs) in order to overcome the problems related to current separation and analysis methods of membrane proteins, and to obtain a high-performance separation method on the basis of specific properties of the lipid membranes. We constructed MLMs, and subsequently characterized membrane pore-forming protein behavior in MLMs. Through the use of these MLMs, we were able to successfully separate and analyze membrane pore-forming proteins in MLMs. To the best of our knowledge, this research is the first example of membrane pore-forming protein separation in lipid membranes. Our method can be expected to be applied for the separation and analysis of other membrane proteins including intrinsic membrane proteins and to result in high-performance by utilizing the specific properties of lipid membranes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. 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.

  17. DNA Release from Lipoplexes by Anionic Lipids: Correlation with Lipid Mesomorphism, Interfacial Curvature, and Membrane Fusion

    PubMed Central

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

    2004-01-01

    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. PMID:15298910

  18. Cytoskeletal pinning controls phase separation in multicomponent lipid membranes.

    PubMed

    Arumugam, Senthil; Petrov, Eugene P; Schwille, Petra

    2015-03-10

    We study the effect of a minimal cytoskeletal network formed on the surface of giant unilamellar vesicles by the prokaryotic tubulin homolog, FtsZ, on phase separation in freestanding lipid membranes. FtsZ has been modified to interact with the membrane through a membrane targeting sequence from the prokaryotic protein MinD. FtsZ with the attached membrane targeting sequence efficiently forms a highly interconnected network on membranes with a concentration-dependent mesh size, much similar to the eukaryotic cytoskeletal network underlying the plasma membrane. Using giant unilamellar vesicles formed from a quaternary lipid mixture, we demonstrate that the artificial membrane-associated cytoskeleton, on the one hand, suppresses large-scale phase separation below the phase transition temperature, and, on the other hand, preserves phase separation above the transition temperature. Our experimental observations support the ideas put forward in our previous simulation study: In particular, the picket fence effect on phase separation may explain why micrometer-scale membrane domains are observed in isolated, cytoskeleton-free giant plasma membrane vesicles, but not in intact cell membranes. The experimentally observed suppression of large-scale phase separation much below the transition temperatures also serves as an argument in favor of the cryoprotective role of the cytoskeleton. Copyright © 2015 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  19. EDTA-induced membrane fluidization and destabilization: biophysical studies on artificial lipid membranes.

    PubMed

    Prachayasittikul, Virapong; Isarankura-Na-Ayudhya, Chartchalerm; Tantimongcolwat, Tanawut; Nantasenamat, Chanin; Galla, Hans-Joachim

    2007-11-01

    The molecular mechanism of ethylenediaminetetraacetic acid (EDTA)-induced membrane destabilization has been studied using a combination of four biophysical techniques on artificial lipid membranes. Data from Langmuir film balance and epifluorescence microscopy revealed the fluidization and expansion effect of EDTA on phase behavior of monolayers of either 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or mixtures of DPPC and metal-chelating lipids, such as N(alpha),N(alpha)-Bis[carboxymethyl]-N(epsilon)-[(dioctadecylamino)succinyl]-L-lysine or 1,2-dioleoyl-sn-glycero-3-[N-(5-amino-1-carboxypentyl iminodiacetic acid) succinyl]. A plausible explanation could be drawn from the electrostatic interaction between negatively charged groups of EDTA and the positively charged choline head group of DPPC. Intercalation of EDTA into the lipid membrane induced membrane curvature as elucidated by atomic force microscopy. Growth in size and shape of the membrane protrusion was found to be time-dependent upon exposure to EDTA. Further loss of material from the lipid membrane surface was monitored in real time using a quartz crystal microbalance. This indicates membrane restabilization by exclusion of the protrusions from the surface. Loss of lipid components facilitates membrane instability, leading to membrane permeabilization and lysis.

  20. Effect of Membrane Tension on the Electric Field and Dipole Potential of Lipid Bilayer Membrane

    PubMed Central

    Warshaviak, Dora Toledo; Muellner, Michael J.; Chachisvilis, Mirianas

    2011-01-01

    The dipole potential of lipid bilayer membrane controls the difference in permeability of the membrane to oppositely charged ions. We have combined molecular dynamics (MD) simulations and experimental studies to determine changes in electric field and electrostatic potential of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid bilayer in response to applied membrane tension. MD simulations based on CHARMM36 force field showed that electrostatic potential of DOPC bilayer decreases by ~45 mV in the physiologically relevant range of membrane tension values (0 to 15 dyn/cm). The electrostatic field exhibits a peak (~0.8×109 V/m) near the water/lipid interface which shifts by 0.9 Å towards the bilayer center at 15 dyn/cm. Maximum membrane tension of 15 dyn/cm caused 6.4% increase in area per lipid, 4.7% decrease in bilayer thickness and 1.4% increase in the volume of the bilayer. Dipole-potential sensitive fluorescent probes were used to detect membrane tension induced changes in DOPC vesicles exposed to osmotic stress. Experiments confirmed that dipole potential of DOPC bilayer decreases at higher membrane tensions. These results are suggestive of a potentially new mechanosensing mechanism by which mechanically induced structural changes in the lipid bilayer membrane could modulate the function of membrane proteins by altering electrostatic interactions and energetics of protein conformational states. PMID:21722624

  1. Penetration of Cell Membranes and Synthetic Lipid Bilayers by Nanoprobes

    PubMed Central

    Angle, Matthew R.; Wang, Andrew; Thomas, Aman; Schaefer, Andreas T.; Melosh, Nicholas A.

    2014-01-01

    Nanoscale devices have been proposed as tools for measuring and controlling intracellular activity by providing electrical and/or chemical access to the cytosol. Unfortunately, nanostructures with diameters of 50–500 nm do not readily penetrate the cell membrane, and rationally optimizing nanoprobes for cell penetration requires real-time characterization methods that are capable of following the process of membrane penetration with nanometer resolution. Although extensive work has examined the rupture of supported synthetic lipid bilayers, little is known about the applicability of these model systems to living cell membranes with complex lipid compositions, cytoskeletal attachment, and membrane proteins. Here, we describe atomic force microscopy (AFM) membrane penetration experiments in two parallel systems: live HEK293 cells and stacks of synthetic lipid bilayers. By using the same probes in both systems, we were able to clearly identify membrane penetration in synthetic bilayers and compare these events with putative membrane penetration events in cells. We examined membrane penetration forces for three tip geometries and 18 chemical modifications of the probe surface, and in all cases the median forces required to penetrate cellular and synthetic lipid bilayers with nanoprobes were greater than 1 nN. The penetration force was sensitive to the probe's sharpness, but not its surface chemistry, and the force did not depend on cell surface or cytoskeletal properties, with cells and lipid stacks yielding similar forces. This systematic assessment of penetration under various mechanical and chemical conditions provides insights into nanoprobe-cell interactions and informs the design of future intracellular nanoprobes. PMID:25418094

  2. Randomization of membrane lipids in relation to transport system assembly in Escherichia coli.

    PubMed

    Thilo, L; Overath, P

    1976-01-27

    The distribution of newly synthesized lipid molecules in the pre-existing lipid phase of the membrane was studied in whole cells of the fatty acid requiring Escheria coli strain K1062. The fluorescence probe N-phenyl-1-naphthylamine revealed reversible lipid phase transitions in cells supplemented with cis-delta9-octadecenoate (transition temperature Tt = 14 degrees C; width of the transition deltaT = 13 degrees C) or trans-delta9-hexadecenoate (Tt = 27 degrees C; deltaT = 7 degrees C). Cells were first grown in the presence of cis-delta9-octadecenoate at 37 degrees C and subsequently for various periods in the presence of trans-delta9-hexadecenoate at 37 or 22 degrees C, i.e. above or below the transition of the newly formed lipids. Reproducible phase transitions with single, well-defined Tt values between 14 and 27 degrees C were observed under both conditions. Beta-Galactoside transport induced in a similar experiment before or during a change in the fatty acid composition showed a single change in activation energy at a temperature close to the lipid transition temperature, Tt. Starvation of cis-delta9-octadecenoate-supplemented cells for this fatty acid led to a gradual rise in the transition temperature, due to an increase in the percentage of saturated acyl chains in the membrane lipids. It is concluded that under all conditions investigated a mixed lipid phase composed of newly synthesized and pre-existing lipid molecules is formed in the membrane. Since conserved domains of newly synthesized lipids surrounding simultaneously formed transport proteins could not be demonstrated, the results do not support a membrane assembly mechanism proposed by N. Tsukagoshi and C. F. Fox [(1973), Biochemistry 12, 2822-2829]. It rather appears that newly formed lipid molecules are continuously released from their sites of synthesis into the lipid matrix by a rapid diffusion-controlled process.

  3. Plant lipid environment and membrane enzymes: the case of the plasma membrane H+-ATPase.

    PubMed

    Morales-Cedillo, Francisco; González-Solís, Ariadna; Gutiérrez-Angoa, Lizbeth; Cano-Ramírez, Dora Luz; Gavilanes-Ruiz, Marina

    2015-04-01

    Several lipid classes constitute the universal matrix of the biological membranes. With their amphipathic nature, lipids not only build the continuous barrier that confers identity to every cell and organelle, but they are also active actors that modulate the activity of the proteins immersed in the lipid bilayer. The plasma membrane H(+)-ATPase, an enzyme from plant cells, is an excellent example of a transmembrane protein whose activity is influenced by the hydrophilic compartments at both sides of the membrane and by the hydrophobic domains of the lipid bilayer. As a result, an extensive documentation of the effect of numerous amphiphiles in the enzyme activity can be found. Detergents, membrane glycerolipids, and sterols can produce activation or inhibition of the enzyme activity. In some cases, these effects are associated with the lipids of the membrane bulk, but in others, a direct interaction of the lipid with the protein is involved. This review gives an account of reports related to the action of the membrane lipids on the H(+)-ATPase activity.

  4. Lipid Bilayer Vesicles with Numbers of Membrane-Linking Pores

    NASA Astrophysics Data System (ADS)

    Ken-ichirou Akashi,; Hidetake Miyata,

    2010-06-01

    We report that phospholipid membranes spontaneously formed in aqueous medium giant unilamellar vesicles (GUVs) possessing many membranous wormhole-like structures (membrane-linking pores, MLPs). By phase contract microscopy and confocal fluorescence microscopy, the structures of the MLPs, consisting of lipid bilayer, were resolvable, and a variety of vesicular shapes having many MLPs (a high genus topology) were found. These vesicles were stable but easily deformed by micromanipulation with a microneedle. We also observed the size reduction of the MLPs with the increase in membrane tension, which was qualitatively consistent with a prediction from a simple dynamical model.

  5. Lipid membranes in external electric fields: kinetics of large pore formation causing rupture.

    PubMed

    Winterhalter, Mathias

    2014-06-01

    About 40 years ago, Helfrich introduced an elastic model to explain shapes and shape transitions of cells (Z Naturforsch C, 1973; 28:693). This seminal article stimulated numerous theoretical as well as experimental investigations and created new research fields. In particular, the predictive power of his approach was demonstrated in a large variety of lipid model system. Here in this review, we focus on the development with respect to planar lipid membranes in external electric fields. Stimulated by the early work of Helfrich on electric field forces acting on liposomes, we extended his early approach to understand the kinetics of lipid membrane rupture. First, we revisit the main forces determining the kinetics of membrane rupture followed by an overview on various experiments. Knowledge on the kinetics of defect formation may help to design stable membranes or serve for novel mechanism for controlled release.

  6. Structure of spin-coated lipid films and domain formation in supported membranes formed by hydration.

    PubMed

    Simonsen, Adam Cohen; Bagatolli, Luis A

    2004-10-26

    An atomic force and fluorescence microscopy investigation of the structure of spin-coated lipid films is presented. In the surface of the dry film, lipids are found to orient in a conformation where acyl chains are pointing outward while laterally the individual layers of the multilamellar film exhibit a dewetting pattern similar to what is found in polymer thin films. Hydration of the film in liquid water promotes detachment of bilayers from the surface while a single membrane remains on the mica substrate. This supported membrane is highly uniform and defect-free as compared to supported membranes prepared by conventional methods. It is further demonstrated that supported membranes of binary lipid mixtures prepared by this method exhibit gel-fluid domain coexistence in accordance with expectations from the phase diagrams.

  7. Probing protein-lipid interactions by FRET between membrane fluorophores

    NASA Astrophysics Data System (ADS)

    Trusova, Valeriya M.; Gorbenko, Galyna P.; Deligeorgiev, Todor; Gadjev, Nikolai

    2016-09-01

    Förster resonance energy transfer (FRET) is a powerful fluorescence technique that has found numerous applications in medicine and biology. One area where FRET proved to be especially informative involves the intermolecular interactions in biological membranes. The present study was focused on developing and verifying a Monte-Carlo approach to analyzing the results of FRET between the membrane-bound fluorophores. This approach was employed to quantify FRET from benzanthrone dye ABM to squaraine dye SQ-1 in the model protein-lipid system containing a polycationic globular protein lysozyme and negatively charged lipid vesicles composed of phosphatidylcholine and phosphatidylglycerol. It was found that acceptor redistribution between the lipid bilayer and protein binding sites resulted in the decrease of FRET efficiency. Quantification of this effect in terms of the proposed methodology yielded both structural and binding parameters of lysozyme-lipid complexes.

  8. 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

  9. 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.

  10. Phosphoinositides, Major Actors in Membrane Trafficking and Lipid Signaling Pathways

    PubMed Central

    De Craene, Johan-Owen; Bertazzi, Dimitri L.; Bär, Séverine; Friant, Sylvie

    2017-01-01

    Phosphoinositides are lipids involved in the vesicular transport of proteins and lipids between the different compartments of eukaryotic cells. They act by recruiting and/or activating effector proteins and thus are involved in regulating various cellular functions, such as vesicular budding, membrane fusion and cytoskeleton dynamics. Although detected in small concentrations in membranes, their role is essential to cell function, since imbalance in their concentrations is a hallmark of many cancers. Their synthesis involves phosphorylating/dephosphorylating positions D3, D4 and/or D5 of their inositol ring by specific lipid kinases and phosphatases. This process is tightly regulated and specific to the different intracellular membranes. Most enzymes involved in phosphoinositide synthesis are conserved between yeast and human, and their loss of function leads to severe diseases (cancer, myopathy, neuropathy and ciliopathy). PMID:28294977

  11. Molecular mechanisms of protein and lipid targeting to ciliary membranes

    PubMed Central

    Emmer, Brian T.; Maric, Danijela; Engman, David M.

    2010-01-01

    Cilia are specialized surface regions of eukaryotic cells that serve a variety of functions, ranging from motility to sensation and to regulation of cell growth and differentiation. The discovery that a number of human diseases, collectively known as ciliopathies, result from defective cilium function has expanded interest in these structures. Among the many properties of cilia, motility and intraflagellar transport have been most extensively studied. The latter is the process by which multiprotein complexes associate with microtubule motors to transport structural subunits along the axoneme to and from the ciliary tip. By contrast, the mechanisms by which membrane proteins and lipids are specifically targeted to the cilium are still largely unknown. In this Commentary, we review the current knowledge of protein and lipid targeting to ciliary membranes and outline important issues for future study. We also integrate this information into a proposed model of how the cell specifically targets proteins and lipids to the specialized membrane of this unique organelle. PMID:20145001

  12. 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

  13. Novel probes for visualizing reactive oxygen species in lipid membranes

    NASA Astrophysics Data System (ADS)

    Krumova, Katerina; Cosa, Gonzalo

    2010-04-01

    This work describes the rationale behind the preparation of fluorescent probes for imaging lipid peroxyl radicals within membranes of living cells (fluorescent lipophilic antioxidants). The new probes are based on BODIPY dyes tethered to phenol moieties. We discuss the spectroscopic properties of these novel probes, specifically the BODIPY-α-tocopherol analogue B-TOH, and present a molecular level explanation, based on photoinduced electron transfer, that accounts for the significant emission enhancement that the probe BTOH experiences upon reaction with peroxyl free radicals. In addition to the spectroscopy results in homogeneous media, we also describe studies performed in model lipid membranes which show that the sensitivity of BTOH towards lipid peroxyl radicals is somewhat reduced when the probe is membrane embedded. Solutions to increase the sensitivity of the free radical probes are discussed based on the redox potential of BODIPY dyes.

  14. 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

  15. Evidence for condensed complexes of cholesterol in lipid membranes

    NASA Astrophysics Data System (ADS)

    Ratajczak, Maria K.

    Although cholesterol is a predominant lipid in the eukaryotic plasma membrane, its interactions with other lipids are still not well understood. Insights into the nature of lipid assembly can be gained from examining lipid-cholesterol interaction using model systems. A key observation was the discovery of liquid-liquid phase diagrams with two critical points in the binary mixtures of cholesterol and lipids. The shape of the phase diagrams can be explained by a thermodynamic model of "condensed complexes". In our quest to characterize cholesterol-lipid interactions, we determined phase diagrams of cholesterol and phospholipids that point to the existence of condensed complexes. This complex formation hypothesis was further supported by experiments involving cholesterol removal by cyclodextrin, grazing x-ray diffraction and x-ray reflectivity studies and isothermal calorimetry. Our study aimed at establishing a correlation (or the lack of) between domain formation and complex formation, as well as determining the mode of cholesterol association with different lipids based on their structural and physical properties. We established a displacement assay by which we were able to probe cholesterol-lipid interactions by perturbing them in the presence of an intercalator that competes with cholesterol for association with lipids. Our data support the condensed complex model between cholesterol and lipids, and cholesterol when complexed with lipids shows low activity whereas free, uncomplexed cholesterol exhibits high activity. We were successful in modulating cholesterol activity by varying the level of intercalator while keeping the cholesterol content fixed. In this thesis, not only have we shown that cholesterol can be displaced by intercalators in model systems, we have further established that such displacement can take place in membranes of live cell.

  16. Ionic channels and nerve membrane lipids. Cholesterol-tetrodotoxin interaction.

    PubMed

    Villegas, R; Barnola, F V; Camejo, G

    1970-04-01

    Experiments were carried out to investigate possible interactions of tetrodotoxin (TTX) with lipid molecules isolated from nerve fiber plasma membranes of the squid Dosidicus gigas. TTX has a highly selective ability to block the channel normally used by Na(+) to cross the axolemma during nervous impulse conduction. In order to investigate the interaction each lipid sample was spread on 5 x 10(-7)M TTX and TTX-free 0.15 M NaCl solutions adjusted to pH 7.4 with 7 x 10(-3)M phosphate buffer. The surface pressure-area diagrams of the lipid monolayers revealed that TTX interacts only with cholesterol. The expansion of the cholesterol monolayers at 5 x 10(-7)M TTX was 2 A(2)/molecule at zero pressure for the experiments at 20 degrees C and 2.5 A(2)/molecule for those at 25 degrees C. Similar results were obtained in KCl subphases. The apparent dissociation constant of the cholesterol-TTX complex calculated from dose-response experiments is 2.6 x 10(-7)M. Experiments at pH 10.1 revealed that the zwitter ionic form of TTX is less active. Experiments with cholesterol derivatives (cholesteryl acetate, cholesterol methyl ether, cholestanol, and cholestanyl acetate) indicate that for the interaction with TTX a partial negatively charged group at C-3 and a double bond between C-5 and C-6 on the steroid nucleus are required. Tetrodonic acid, a biologically inactive derivative of TTX, does not interact with cholesterol. The results lead us to propose that cholesterol is part of the Na(+) channel.

  17. PE and PS Lipids Synergistically Enhance Membrane Poration by a Peptide with Anticancer Properties

    PubMed Central

    Leite, Natália Bueno; Aufderhorst-Roberts, Anders; Palma, Mario Sergio; Connell, Simon D.; Neto, João Ruggiero; Beales, Paul A.

    2015-01-01

    Polybia-MP1 (MP1) is a bioactive host-defense peptide with known anticancer properties. Its activity is attributed to excess serine (phosphatidylserine (PS)) on the outer leaflet of cancer cells. Recently, higher quantities of phosphatidylethanolamine (PE) were also found at these cells’ surface. We investigate the interaction of MP1 with model membranes in the presence and absence of POPS (PS) and DOPE (PE) to understand the role of lipid composition in MP1’s anticancer characteristics. Indeed we find that PS lipids significantly enhance the bound concentration of peptide on the membrane by a factor of 7–8. However, through a combination of membrane permeability assays and imaging techniques we find that PE significantly increases the susceptibility of the membrane to disruption by these peptides and causes an order-of-magnitude increase in membrane permeability by facilitating the formation of larger transmembrane pores. Significantly, atomic-force microscopy imaging reveals differences in the pore formation mechanism with and without the presence of PE. Therefore, PS and PE lipids synergistically combine to enhance membrane poration by MP1, implying that the combined enrichment of both these lipids in the outer leaflet of cancer cells is highly significant for MP1’s anticancer action. These mechanistic insights could aid development of novel chemotherapeutics that target pathological changes in the lipid composition of cancerous cells. PMID:26331251

  18. PE and PS Lipids Synergistically Enhance Membrane Poration by a Peptide with Anticancer Properties.

    PubMed

    Leite, Natália Bueno; Aufderhorst-Roberts, Anders; Palma, Mario Sergio; Connell, Simon D; Ruggiero Neto, João; Beales, Paul A

    2015-09-01

    Polybia-MP1 (MP1) is a bioactive host-defense peptide with known anticancer properties. Its activity is attributed to excess serine (phosphatidylserine (PS)) on the outer leaflet of cancer cells. Recently, higher quantities of phosphatidylethanolamine (PE) were also found at these cells' surface. We investigate the interaction of MP1 with model membranes in the presence and absence of POPS (PS) and DOPE (PE) to understand the role of lipid composition in MP1's anticancer characteristics. Indeed we find that PS lipids significantly enhance the bound concentration of peptide on the membrane by a factor of 7-8. However, through a combination of membrane permeability assays and imaging techniques we find that PE significantly increases the susceptibility of the membrane to disruption by these peptides and causes an order-of-magnitude increase in membrane permeability by facilitating the formation of larger transmembrane pores. Significantly, atomic-force microscopy imaging reveals differences in the pore formation mechanism with and without the presence of PE. Therefore, PS and PE lipids synergistically combine to enhance membrane poration by MP1, implying that the combined enrichment of both these lipids in the outer leaflet of cancer cells is highly significant for MP1's anticancer action. These mechanistic insights could aid development of novel chemotherapeutics that target pathological changes in the lipid composition of cancerous cells.

  19. A method for detergent-free isolation of membrane proteins in their local lipid environment.

    PubMed

    Lee, Sarah C; Knowles, Tim J; Postis, Vincent L G; Jamshad, Mohammed; Parslow, Rosemary A; Lin, Yu-Pin; Goldman, Adrian; Sridhar, Pooja; Overduin, Michael; Muench, Stephen P; Dafforn, Timothy R

    2016-07-01

    Despite the great importance of membrane proteins, structural and functional studies of these proteins present major challenges. A significant hurdle is the extraction of the functional protein from its natural lipid membrane. Traditionally achieved with detergents, purification procedures can be costly and time consuming. A critical flaw with detergent approaches is the removal of the protein from the native lipid environment required to maintain functionally stable protein. This protocol describes the preparation of styrene maleic acid (SMA) co-polymer to extract membrane proteins from prokaryotic and eukaryotic expression systems. Successful isolation of membrane proteins into SMA lipid particles (SMALPs) allows the proteins to remain with native lipid, surrounded by SMA. We detail procedures for obtaining 25 g of SMA (4 d); explain the preparation of protein-containing SMALPs using membranes isolated from Escherichia coli (2 d) and control protein-free SMALPS using E. coli polar lipid extract (1-2 h); investigate SMALP protein purity by SDS-PAGE analysis and estimate protein concentration (4 h); and detail biophysical methods such as circular dichroism (CD) spectroscopy and sedimentation velocity analytical ultracentrifugation (svAUC) to undertake initial structural studies to characterize SMALPs (∼2 d). Together, these methods provide a practical tool kit for those wanting to use SMALPs to study membrane proteins.

  20. Lipid signalling dynamics at the β-cell plasma membrane.

    PubMed

    Wuttke, Anne

    2015-04-01

    Pancreatic β-cells are clustered in islets of Langerhans and secrete insulin in response to increased concentrations of circulating glucose. Insulin in turn acts on liver, muscle and fat tissue to store energy and normalize the blood glucose level. Inappropriate insulin release may lead to impaired glucose tolerance and diabetes. In addition to glucose, other nutrients, neural stimuli and hormonal stimuli control insulin secretion. Many of these signals are perceived at the plasma membrane, which is also the site where insulin granules undergo exocytosis. Therefore, it is not surprising that membrane lipids play an important role in the regulation of insulin secretion. β-cells release insulin in a pulsatile fashion. Signalling lipids integrate the nutrient and neurohormonal inputs to fine-tune, shape and co-ordinate the pulsatility. An important group of signalling lipids are phosphoinositides and their downstream messengers. This MiniReview will discuss new insights into lipid signalling dynamics in β-cells obtained from live-cell imaging experiments with fluorescent translocation biosensors. The plasma membrane concentration of several phosphoinositides and of their downstream messengers changes rapidly upon nutrient or neurohormonal stimulation. Glucose induces the most complex spatio-temporal patterns, typically involving oscillations of messenger concentrations, which sometimes are locally restricted. The tightly controlled levels of lipid messengers can mediate specific binding of downstream effectors to the plasma membrane, contributing to the appropriate regulation of insulin secretion. © 2014 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society).

  1. Lamellar biogels: Fluid-membrane-based hydrogels containing polymer lipids

    SciTech Connect

    Warriner, H.E.; Idziak, S.H.J.; Slack, N.L.

    1996-02-16

    A class of lamellar biological hydrogels comprised of fluid membranes of lipids and surfactants with small amounts of low molecular weight poly(ethylene glycol)-derived polymer pipids (PEG-lipids) were studied by x-ray diffraction, polarized light microscopy, and rheometry. In contrast to isotropic hydrogels of polymer networks, these membrane-based birefringent liquid crystalline biogels, labeled L{sub {alpha},g,} form the gel phase when water is added to the liquid-like lamellar L{sub {alpha}} phase, which reenters a liquid-like mixed phase upon further dilution. Furthermore, gels with larger water content require less PEG-lipid to remain stable. Although concentrated ({approx}50 weight percent) mixtures of free PEG (molecular weight, 5000) and water do not gel, gelatin does occur in mixtures containing as little as 0.5 weight percent PEG lipid. A defining signature of the L{sub {alpha}, g} regime as it sets in from the fluid lamellar L{sub {alpha}} phase is the proliferation of layer-dislocation-type defects, which are stabilized by the segregation of PEG-lipids to the defect regions of high membrane curvature that connect the membranes. 32 refs., 5 figs.

  2. Membrane Lipid Metabolism in Germinating Castor Bean Endosperm 1

    PubMed Central

    Donaldson, Robert P.

    1976-01-01

    Castor bean (Ricinus communis L. var. Hale) endosperms, excised after 2 days germination at 30 C, were incubated 5 min to 8 hr with 14C-acetate and 3H-glycerol. Homogenates were fractionated by sucrose gradient centrifugation. Organelles found to be active in lipid synthesis were the lipid bodies and the endoplasmic reticulum. The products of incorporation in the lipid bodies were 3H-diglycerides containing 14C-fatty acids of more than 20 carbons. In contrast, the endoplasmic reticulum produced 3H-phospholipids as well as 3H-diglycerides rich in 14C-linoleate. The phospholipids synthesized and their acyl contents were of the types known to be the major components of organelle membranes in this tissue. Phospholipids and diglycerides containing 14C and 3H were found in the glyoxysomes and mitochondria subsequent to their appearance in the endoplasmic reticulum. The results show that germinating castor bean endosperm synthesizes membrane lipids de novo from acetate rather than reutilizing stored lipid components directly. It is also apparent that the endoplasmic reticulum is responsible for several steps in membrane lipid production. PMID:16659516

  3. The interaction of local anesthetics with lipid membranes.

    PubMed

    Zapata-Morin, Patricio A; Sierra-Valdez, F J; Ruiz-Suárez, J C

    2014-09-01

    Molecular Dynamic Simulations are performed to evaluate the interaction of lidocaine, procaine and tetracaine with a lipid membrane. The main interest is to evaluate the structural changes produced by these local anesthetics in the bilayers. Penetration trajectories, interaction energies, entropy changes and an order parameter are calculated to quantify the destabilization of the lipid configurations. We show that such structural parameters give important information to understand how anesthetic agents influence the structure of plasma membranes. Graphic processing units (GPUs) are used in our simulations. Copyright © 2014 Elsevier Inc. All rights reserved.

  4. Two-Phase Contiguous Supported Lipid Bilayer Model for Membrane Rafts via Polymer Blotting and Stenciling.

    PubMed

    Richards, Mark J; Daniel, Susan

    2017-02-07

    The supported lipid bilayer has been portrayed as a useful model of the cell membrane compatible with many biophysical tools and techniques that demonstrate its appeal in learning about the basic features of the plasma membrane. However, some of its potential has yet to be realized, particularly in the area of bilayer patterning and phase/composition heterogeneity. In this work, we generate contiguous bilayer patterns as a model system that captures the general features of membrane domains and lipid rafts. Micropatterned polymer templates of two types are investigated for generating patterned bilayer formation: polymer blotting and polymer lift-off stenciling. While these approaches have been used previously to create bilayer arrays by corralling bilayers patches with various types of boundaries impenetrable to bilayer diffusion, unique to the methods presented here, there are no physical barriers to diffusion. In this work, interfaces between contiguous lipid phases define the pattern shapes, with continuity between them allowing transfer of membrane-bound biomolecules between the phases. We examine effectors of membrane domain stability including temperature and cholesterol content to investigate domain dynamics. Contiguous patterning of supported bilayers as a model of lipid rafts expands the application of the SLB to an area with current appeal and brings with it a useful toolset for characterization and analysis. These combined tools should be helpful to researchers investigating lipid raft dynamics and function and biomolecule partitioning studies. Additionally, this patterning technique may be useful for applications such as bioseparations that exploit differences in lipid phase partitioning or creation of membranes that bind species like viruses preferentially at lipid phase boundaries, to name a few.

  5. Thermodynamics and mechanics of membrane curvature generation and sensing by proteins and lipids.

    PubMed

    Baumgart, Tobias; Capraro, Benjamin R; Zhu, Chen; Das, Sovan L

    2011-01-01

    Research investigating lipid membrane curvature generation and sensing is a rapidly developing frontier in membrane physical chemistry and biophysics. The fast recent progress is based on the discovery of a plethora of proteins involved in coupling membrane shape to cellular membrane function, the design of new quantitative experimental techniques to study aspects of membrane curvature, and the development of analytical theories and simulation techniques that allow a mechanistic interpretation of quantitative measurements. The present review first provides an overview of important classes of membrane proteins for which function is coupled to membrane curvature. We then survey several mechanisms that are assumed to underlie membrane curvature sensing and generation. Finally, we discuss relatively simple thermodynamic/mechanical models that allow quantitative interpretation of experimental observations.

  6. Thermodynamics and Mechanics of Membrane Curvature Generation and Sensing by Proteins and Lipids

    PubMed Central

    Baumgart, Tobias; Capraro, Benjamin R.; Zhu, Chen; Das, Sovan L.

    2014-01-01

    Research investigating lipid membrane curvature generation and sensing is a rapidly developing frontier in membrane physical chemistry and biophysics. The fast recent progress is based on the discovery of a plethora of proteins involved in coupling membrane shape to cellular membrane function, the design of new quantitative experimental techniques to study aspects of membrane curvature, and the development of analytical theories and simulation techniques that allow a mechanistic interpretation of quantitative measurements. The present review first provides an overview of important classes of membrane proteins for which function is coupled to membrane curvature. We then survey several mechanisms that are assumed to underlie membrane curvature sensing and generation. Finally, we discuss relatively simple thermodynamic/mechanical models that allow quantitative interpretation of experimental observations. PMID:21219150

  7. 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

  8. Dissipative dynamics of fluid lipid membranes enriched in cholesterol.

    PubMed

    Arriaga, Laura R; Rodríguez-García, Ruddi; Moleiro, Lara H; Prévost, Sylvain; López-Montero, Iván; Hellweg, Thomas; Monroy, Francisco

    2017-09-01

    Cholesterol is an intriguing component of fluid lipid membranes: It makes them stiffer but also more fluid. Despite the enormous biological significance of this complex dynamical behavior, which blends aspects of membrane elasticity with viscous friction, their mechanical bases remain however poorly understood. Here, we show that the incorporation of physiologically relevant contents of cholesterol in model fluid membranes produces a fourfold increase in the membrane bending modulus. However, the increase in the compression rigidity that we measure is only twofold; this indicates that cholesterol increases coupling between the two membrane leaflets. In addition, we show that although cholesterol makes each membrane leaflet more fluid, it increases the friction between the membrane leaflets. This dissipative dynamics causes opposite but advantageous effects over different membrane motions: It allows the membrane to rearrange quickly in the lateral dimension, and to simultaneously dissipate out-of-plane stresses through friction between the two membrane leaflets. Moreover, our results provide a clear correlation between coupling and friction of membrane leaflets. Furthermore, we show that these rigid membranes are optimal to resist slow deformations with minimum energy dissipation; their optimized stability might be exploited to design soft technological microsystems with an encoded mechanics, vesicles or capsules for instance, useful beyond classical applications as model biophysical systems. Copyright © 2017 Elsevier B.V. All rights reserved.

  9. Fatty Acids from Membrane Lipids Become Incorporated into Lipid Bodies during Myxococcus xanthus Differentiation

    PubMed Central

    Bhat, Swapna; Boynton, Tye O.; Pham, Dan; Shimkets, Lawrence J.

    2014-01-01

    Myxococcus xanthus responds to amino acid limitation by producing fruiting bodies containing dormant spores. During development, cells produce triacylglycerides in lipid bodies that become consumed during spore maturation. As the cells are starved to induce development, the production of triglycerides represents a counterintuitive metabolic switch. In this paper, lipid bodies were quantified in wild-type strain DK1622 and 33 developmental mutants at the cellular level by measuring the cross sectional area of the cell stained with the lipophilic dye Nile red. We provide five lines of evidence that triacylglycerides are derived from membrane phospholipids as cells shorten in length and then differentiate into myxospores. First, in wild type cells, lipid bodies appear early in development and their size increases concurrent with an 87% decline in membrane surface area. Second, developmental mutants blocked at different stages of shortening and differentiation accumulated lipid bodies proportionate with their cell length with a Pearson's correlation coefficient of 0.76. Third, peripheral rods, developing cells that do not produce lipid bodies, fail to shorten. Fourth, genes for fatty acid synthesis are down-regulated while genes for fatty acid degradation are up regulated. Finally, direct movement of fatty acids from membrane lipids in growing cells to lipid bodies in developing cells was observed by pulse labeling cells with palmitate. Recycling of lipids released by Programmed Cell Death appears not to be necessary for lipid body production as a fadL mutant was defective in fatty acid uptake but proficient in lipid body production. The lipid body regulon involves many developmental genes that are not specifically involved in fatty acid synthesis or degradation. MazF RNA interferase and its target, enhancer-binding protein Nla6, appear to negatively regulate cell shortening and TAG accumulation whereas most cell-cell signals activate these processes. PMID:24906161

  10. 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

  11. 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.

  12. Hybrid lipids increase nanoscale fluctuation lifetimes in mixed membranes.

    PubMed

    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.

  13. The Influence of Natural Lipid Asymmetry upon the Conformation of a Membrane-inserted Protein (Perfringolysin O)*

    PubMed Central

    Lin, Qingqing; London, Erwin

    2014-01-01

    Eukaryotic membrane proteins generally reside in membrane bilayers that have lipid asymmetry. However, in vitro studies of the impact of lipids upon membrane proteins are generally carried out in model membrane vesicles that lack lipid asymmetry. Our recently developed method to prepare lipid vesicles with asymmetry similar to that in plasma membranes and with controlled amounts of cholesterol was used to investigate the influence of lipid composition and lipid asymmetry upon the conformational behavior of the pore-forming, cholesterol-dependent cytolysin perfringolysin O (PFO). PFO conformational behavior in asymmetric vesicles was found to be distinct both from that in symmetric vesicles with the same lipid composition as the asymmetric vesicles and from that in vesicles containing either only the inner leaflet lipids from the asymmetric vesicles or only the outer leaflet lipids from the asymmetric vesicles. The presence of phosphatidylcholine in the outer leaflet increased the cholesterol concentration required to induce PFO binding, whereas phosphatidylethanolamine and phosphatidylserine in the inner leaflet of asymmetric vesicles stabilized the formation of a novel deeply inserted conformation that does not form pores, even though it contains transmembrane segments. This conformation may represent an important intermediate stage in PFO pore formation. These studies show that lipid asymmetry can strongly influence the behavior of membrane-inserted proteins. PMID:24398685

  14. Evidence of pores and thinned lipid bilayers induced in oriented lipid membranes interacting with the antimicrobial peptides, magainin-2 and aurein-3.3.

    PubMed

    Kim, Chul; Spano, Justin; Park, Eun-Kyung; Wi, Sungsool

    2009-07-01

    Dynamic structures of supramolecular lipid assemblies, such as toroidal pores and thinned bilayers induced in oriented lipid membranes, which are interacting with membrane-acting antimicrobial peptides (AMPs), magainin-2 and aurein-3.3, were explored by 31P and 2H solid-state NMR (ssNMR) spectroscopy. Various types of phospholipid systems, such as POPC-d31, POPC-d31/POPG, and POPC-d31/cholesterol, were investigated to understand the membrane disruption mechanisms of magainin-2 and aurein-3.3 peptides at various peptide-to-lipid (P:L) ratios. The experimental lineshapes of anisotropic 31P and 2H ssNMR spectra measured on these peptide-lipid systems were simulated reasonably well by assuming the presence of supramolecular lipid assemblies, such as toroidal pores and thinned bilayers, in membranes. Furthermore, the observed decrease in the anisotropic frequency span of either 31P or 2H ssNMR spectra of oriented lipid bilayers, particularly when anionic POPG lipids are interacting with AMPs at high P:L ratios, can directly be explained by a thinned membrane surface model with fast lateral diffusive motions of lipids. The spectral analysis protocol we developed enables extraction of the lateral diffusion coefficients of lipids distributed on the curved surfaces of pores and thinned bilayers on a few nanometers scale.

  15. Stabilization of Lipid Membranes With Dendritic Polymers

    DTIC Science & Technology

    2004-12-01

    monolayer coverage was possible using the spin - coating procedure for concentrations of 10-5 w/w dendrimers in solution or lower. Higher coverages...The fluorescence intensity increased as coverage time before spin coating increased and as the dendrimer solution concentration increased (Fig...enhanced the adsorption of lipids to the substrate. Figure 7: Fluorescence intensity as a function of the PAMAM concentration used in the spin

  16. Coupling of lipid membrane elasticity and in-plane dynamics

    NASA Astrophysics Data System (ADS)

    Tsang, Kuan-Yu; Lai, Yei-Chen; Chiang, Yun-Wei; Chen, Yi-Fan

    2017-07-01

    Biomembranes exhibit liquid and solid features concomitantly with their in-plane fluidity and elasticity tightly regulated by cells. Here, we present experimental evidence supporting the existence of the dynamics-elasticity correlations for lipid membranes and propose a mechanism involving molecular packing densities to explain them. This paper thereby unifies, at the molecular level, the aspects of the continuum mechanics long used to model the two membrane features. This ultimately may elucidate the universal physical principles governing the cellular phenomena involving biomembranes.

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

    PubMed Central

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

    2015-01-01

    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. PMID:27877825

  18. 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.

  19. Membrane fluidity is a driving force for recoverin myristoyl immobilization in zwitterionic lipids.

    PubMed

    Potvin-Fournier, Kim; Valois-Paillard, Geneviève; Lefèvre, Thierry; Cantin, Line; Salesse, Christian; Auger, Michèle

    2017-09-02

    Recoverin is the only protein for which the phenomenon of calcium-myristoyl switch has been demonstrated without ambiguity. It is located in rod disk membranes where the highest content in polyunsaturated lipid acyl chains can be found. However, although essential to better understand the inactivation of the phototransduction process, the role of membrane fluidity on recoverin recruitment is unclear. We have therefore investigated the immobilization of the recoverin myristoyl moiety in the presence of phosphocholine bilayers using (2)H solid-state NMR spectroscopy. Several lipids with different acyl chains were selected to investigate model membranes characterized by different fluidity. Immobilization of the recoverin myristoyl moiety was successfully observed but only in the presence of calcium and in specific lipid disordered states, showing that an optimal fluidity is required for recoverin immobilization. Copyright © 2017 Elsevier Inc. All rights reserved.

  20. Plasma membrane lipid diffusion and composition of Sea urchin egg membranes vary with ocean temperature

    PubMed Central

    Weaver, Frances E.; Shaikh, Saame Raza; Edidin, Michael

    2008-01-01

    A diverse and complex array of lipids plays a vital role in structuring and organizing cell membranes. However, the details of lipid requirements for global membrane organization are poorly understood. One obstacle to this understanding is the difficulty of accurately manipulating the lipid composition of commonly studied mammalian cells. In contrast, the lipid composition of cells of ectotherms changes with changes in environmental temperatures. Thus, comparison of lipid probe diffusion in cells from animals living at different temperatures, together with biochemical analysis, can be used toward understanding membrane organization. We used two dialkyindocarbocyanine iodide (DiI) probes, of differing chain length, to probe lipid organization in terms of their lateral diffusion in eggs of the sea urchin Strongylocentrotus purpuratus. The lateral diffusion of our probes changed in urchins developing in the year of an “El Niño” weather event, which raised the ocean temperature by several degrees, suggesting alterations in membrane domain composition and structure. Indeed the changes in lateral diffusion were correlated with lower levels of unsaturated fatty acids and cholesterol in animals of the “El Niño” year than in animals of the preceding or following years. We found similar trends comparing DiI diffusion in membranes of eggs from 15 °C waters with those from 10°C. Our findings establish a new approach for manipulating and studying membrane organization. PMID:17986387

  1. Plasma membrane lipid diffusion and composition of sea urchin egg membranes vary with ocean temperature.

    PubMed

    Weaver, Frances E; Shaikh, Saame Raza; Edidin, Michael

    2008-01-01

    A diverse and complex array of lipids plays a vital role in structuring and organizing cell membranes. However, the details of lipid requirements for global membrane organization are poorly understood. One obstacle to this understanding is the difficulty of accurately manipulating the lipid composition of commonly studied mammalian cells. In contrast, the lipid composition of cells of ectotherms changes with changes in environmental temperatures. Thus, comparison of lipid probe diffusion in cells from animals living at different temperatures, together with biochemical analysis, can be used toward understanding membrane organization. We used two dialkyindocarbocyanine iodide (DiI) probes, of differing chain length, to probe lipid organization in terms of their lateral diffusion in eggs of the sea urchin Strongylocentrotus purpuratus. The lateral diffusion of our probes changed in urchins developing in the year of an "El Niño" weather event, which raised the ocean temperature by several degrees, suggesting alterations in membrane domain composition and structure. Indeed the changes in lateral diffusion were correlated with lower levels of unsaturated fatty acids and cholesterol in animals of the "El Niño" year than in animals of the preceding or following years. We found similar trends comparing DiI diffusion in membranes of eggs from 15 degrees C waters with those from 10 degrees C. Our findings establish a new approach for manipulating and studying membrane organization.

  2. Effect of Gold Nanoparticle on Structure and Fluidity of Lipid Membrane

    PubMed Central

    Mhashal, Anil R.; Roy, Sudip

    2014-01-01

    This paper deals with the effect of different size gold nanoparticles on the fluidity of lipid membrane at different regions of the bilayer. To investigate this, we have considered significantly large bilayer leaflets and incorporated only one nanoparticle each time, which was subjected to all atomistic molecular dynamics simulations. We have observed that, lipid molecules located near to the gold nanoparticle interact directly with it, which results in deformation of lipid structure and slower dynamics of lipid molecules. However, lipid molecules far away from the interaction site of the nanoparticle get perturbed, which gives rise to increase in local ordering of the lipid domains and decrease in fluidity. The bilayer thickness and area per head group in this region also get altered. Similar trend, but with different magnitude is also observed when different size nanoparticle interact with the bilayer. PMID:25469786

  3. 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

  4. Interaction of pristine and functionalized carbon nanotubes with lipid membranes.

    PubMed

    Baoukina, Svetlana; Monticelli, Luca; Tieleman, D Peter

    2013-10-10

    Carbon nanotubes are widely used in a growing number of applications. Their interactions with biological materials, cell membranes in particular, is of interest in applications including drug delivery and for understanding the toxicity of carbon nanotubes. We use extensive molecular dynamics simulations with the MARTINI model to study the interactions of model nanotubes of different thickness, length, and patterns of chemical modification with model membranes. In addition, we characterize the interactions of small bundles of carbon nanotubes with membrane models. Short pristine carbon nanotubes readily insert into membranes and adopt an orientation parallel to the plane of the membrane in the center of the membrane. Larger aggregates and functionalized nanotubes exhibit a range of possible interactions. The distribution and orientation of carbon nanotubes can be controlled by functionalizing the nanotubes. Free energy calculations provide thermodynamic insight into the preferred orientations of different nanotubes and quantify structural defects in the lipid matrix.

  5. 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.

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

    PubMed

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

    2016-03-04

    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.

  7. Raman Imaging in Cell Membranes, Lipid-Rich Organelles, and Lipid Bilayers.

    PubMed

    Syed, Aleem; Smith, Emily A

    2017-06-12

    Raman-based optical imaging is a promising analytical tool for noninvasive, label-free chemical imaging of lipid bilayers and cellular membranes. Imaging using spontaneous Raman scattering suffers from a low intensity that hinders its use in some cellular applications. However, developments in coherent Raman imaging, surface-enhanced Raman imaging, and tip-enhanced Raman imaging have enabled video-rate imaging, excellent detection limits, and nanometer spatial resolution, respectively. After a brief introduction to these commonly used Raman imaging techniques for cell membrane studies, this review discusses selected applications of these modalities for chemical imaging of membrane proteins and lipids. Finally, recent developments in chemical tags for Raman imaging and their applications in the analysis of selected cell membrane components are summarized. Ongoing developments toward improving the temporal and spatial resolution of Raman imaging and small-molecule tags with strong Raman scattering cross sections continue to expand the utility of Raman imaging for diverse cell membrane studies.

  8. Pore spanning lipid bilayers on silanised nanoporous alumina membranes

    NASA Astrophysics Data System (ADS)

    Md Jani, Abdul M.; Zhou, Jinwen; Nussio, Matthew R.; Losic, Dusan; Shapter, Joe G.; Voelcker, Nicolas H.

    2008-12-01

    The preparation of bilayer lipid membranes (BLMs) on solid surfaces is important for many studies probing various important biological phenomena including the cell barrier properties, ion-channels, biosensing, drug discovery and protein/ligand interactions. In this work we present new membrane platforms based on suspended BLMs on nanoporous anodic aluminium oxide (AAO) membranes. AAO membranes were prepared by electrochemical anodisation of aluminium foil in 0.3 M oxalic acid using a custom-built etching cell and applying voltage of 40 V, at 1oC. AAO membranes with controlled diameter of pores from 30 - 40 nm (top of membrane) and 60 -70 nm (bottom of membrane) were fabricated. Pore dimensions have been confirmed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). AAO membranes were chemically functionalised with 3-aminopropyltriethoxysilane (APTES). Confirmation of the APTES attachment to the AAO membrane was achieved by means of infrared spectroscopy, X-ray photoelectron spectroscopy and contact angle measurements. The Fourier transform infrared (FTIR) spectra of functionalised membranes show several peaks from 2800 to 3000 cm-1 which were assigned to symmetric and antisymmetric CH2 bands. XPS data of the membrane showed a distinct increase in C1s (285 eV), N1s (402 eV) and Si2p (102 eV) peaks after silanisation. The water contact angle of the functionalised membrane was 80o as compared to 20o for the untreated membrane. The formation of BLMs comprising dioleoyl-phosphatidylserine (DOPS) on APTESmodified AAO membranes was carried using the vesicle spreading technique. AFM imaging and force spectroscopy was used to characterise the structural and nanomechanical properties of the suspended membrane. This technique also confirmed the stability of bilayers on the nanoporous alumina support for several days. Fabricated suspended BLMs on nanoporous AAO hold promise for the construction of biomimetic membrane architectures with embedded

  9. Effect of anesthetics on bending elasticity of lipid membranes

    NASA Astrophysics Data System (ADS)

    Yi, Zheng; Michihiro, Nagao; Bossev, Dobrin

    2008-03-01

    Change in physical and chemical properties of bio-membranes is of great interest for understanding the mechanism of anesthetic action on membranes. Hypothetically the anesthetic alters the lipid membrane structure (promoting pore formation across membranes or at least switching transmembrane channels) and therefore the biophysical properties of the membrane. We have used neutron spin echo (NSE) spectroscopy to study the effect of anesthetic molecule, lidocaine, on the bending elasticity (BE) of lipid membranes. BE of lipid bilayers made of (1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine) DMPC and 1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine (DPPC) have been measured at different temperatures and different in the fluid (Lα) phase. Using Zilman-Granek theory the BE were obtained from the decay of the NSE intermediate scattering function. We have found that in the presence of lidocaine the BE of DMPC and DPPC bilayers increases. The results were correlated with those from differential scanning calorimetry. Increase in the lidocaine concentration leads to decrease in the liquid/crystalline transition temperature.

  10. Interaction of aspirin (acetylsalicylic acid) with lipid membranes.

    PubMed

    Barrett, Matthew A; Zheng, Songbo; Roshankar, Golnaz; Alsop, Richard J; Belanger, Randy K R; Huynh, Chris; Kučerka, Norbert; Rheinstädter, Maikel C

    2012-01-01

    We studied the interaction of Aspirin (acetylsalicylic acid) with lipid membranes using x-ray diffraction for bilayers containing up to 50 mol% of aspirin. From 2D x-ray intensity maps that cover large areas of reciprocal space we determined the position of the ASA molecules in the phospholipid bilayers and the molecular arrangement of the molecules in the plane of the membranes. We present direct experimental evidence that ASA molecules participate in saturated lipid bilayers of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) and preferably reside in the head group region of the membrane. Up to 50 mol% ASA molecules can be dissolved in this type of bilayer before the lateral membrane organization is disturbed and the membranes are found to form an ordered, 2D crystal-like structure. Furthermore, ASA and cholesterol were found to co-exist in saturated lipid bilayers, with the ASA molecules residing in the head group region and the cholesterol molecules participating in the hydrophobic membrane core.

  11. Preserved transmembrane protein mobility in polymer-supported lipid bilayers derived from cell membranes.

    PubMed

    Pace, Hudson; Simonsson Nyström, Lisa; Gunnarsson, Anders; Eck, Elizabeth; Monson, Christopher; Geschwindner, Stefan; Snijder, Arjan; Höök, Fredrik

    2015-09-15

    Supported lipid bilayers (SLBs) have contributed invaluable information about the physiochemical properties of cell membranes, but their compositional simplicity often limits the level of knowledge that can be gained about the structure and function of transmembrane proteins in their native environment. Herein, we demonstrate a generic protocol for producing polymer-supported lipid bilayers on glass surfaces that contain essentially all naturally occurring cell-membrane components of a cell line while still retaining transmembrane protein mobility and activity. This was achieved by merging vesicles made from synthetic lipids (PEGylated lipids and POPC lipids) with native cell-membrane vesicles to generate hybrid vesicles which readily rupture into a continuous polymer-supported lipid bilayer. To investigate the properties of these complex hybrid SLBs and particularly the behavior of their integral membrane-proteins, we used total internal reflection fluorescence imaging to study a transmembrane protease, β-secretase 1 (BACE1), whose ectoplasmic and cytoplasmic domains could both be specifically targeted with fluorescent reporters. By selectively probing the two different orientations of BACE1 in the resulting hybrid SLBs, the role of the PEG-cushion on transmembrane protein lateral mobility was investigated. The results reveal the necessity of having the PEGylated lipids present during vesicle adsorption to prevent immobilization of transmembrane proteins with protruding domains. The proteolytic activity of BACE1 was unadulterated by the sonication process used to merge the synthetic and native membrane vesicles; importantly it was also conserved in the SLB. The presented strategy could thus serve both fundamental studies of membrane biophysics and the production of surface-based bioanalytical sensor platforms.

  12. Proteomic Profiling of Detergent Resistant Membranes (Lipid Rafts) of Prostasomes.

    PubMed

    Dubois, Louise; Ronquist, Karl K Göran; Ek, Bo; Ronquist, Gunnar; Larsson, Anders

    2015-11-01

    Prostasomes are exosomes derived from prostate epithelial cells through exocytosis by multivesicular bodies. Prostasomes have a bilayered membrane and readily interact with sperm. The membrane lipid composition is unusual with a high contribution of sphingomyelin at the expense of phosphatidylcholine and saturated and monounsaturated fatty acids are dominant. Lipid rafts are liquid-ordered domains that are more tightly packed than the surrounding nonraft phase of the bilayer. Lipid rafts are proposed to be highly dynamic, submicroscopic assemblies that float freely within the liquid disordered membrane bilayer and some proteins preferentially partition into the ordered raft domains. We asked the question whether lipid rafts do exist in prostasomes and, if so, which proteins might be associated with them. Prostasomes of density range 1.13-1.19g/ml were subjected to density gradient ultracentrifugation in sucrose fabricated by phosphate buffered saline (PBS) containing 1% Triton X-100 with capacity for banding at 1.10 g/ml, i.e. the classical density of lipid rafts. Prepared prostasomal lipid rafts (by gradient ultracentrifugation) were analyzed by mass spectrometry. The clearly visible band on top of 1.10g/ml sucrose in the Triton X-100 containing gradient was subjected to liquid chromatography-tandem MS and more than 370 lipid raft associated proteins were identified. Several of them were involved in intraluminal vesicle formation, e.g. tetraspanins, ESCRTs, and Ras-related proteins. This is the first comprehensive liquid chromatography-tandem MS profiling of proteins in lipid rafts derived from exosomes. Data are available via ProteomeXchange with identifier PXD002163.

  13. Reduced Lateral Mobility of Lipids and Proteins in Crowded Membranes

    PubMed Central

    Goose, Joseph E.; Sansom, Mark S. P.

    2013-01-01

    Coarse-grained molecular dynamics simulations of the E. coli outer membrane proteins FhuA, LamB, NanC, OmpA and OmpF in a POPE/POPG (3∶1) bilayer were performed to characterise the diffusive nature of each component of the membrane. At small observation times (<10 ns) particle vibrations dominate phospholipid diffusion elevating the calculated values from the longer time-scale bulk value (>50 ns) of 8.5×10−7 cm2 s−1. The phospholipid diffusion around each protein was found to vary based on distance from protein. An asymmetry in the diffusion of annular lipids in the inner and outer leaflets was observed and correlated with an asymmetry in charged residues in the vicinity of the inner and outer leaflet head-groups. Protein rotational and translational diffusion were also found to vary with observation time and were inversely correlated with the radius of gyration of the protein in the plane of the bilayer. As the concentration of protein within the bilayer was increased, the overall mobility of the membrane decreased reflected in reduced lipid diffusion coefficients for both lipid and protein components. The increase in protein concentration also resulted in a decrease in the anomalous diffusion exponent α of the lipid. Formation of extended clusters and networks of proteins led to compartmentalisation of lipids in extreme cases. PMID:23592975

  14. 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.

  15. Phase separation in model lipid membranes: physics and biophysics

    NASA Astrophysics Data System (ADS)

    Gordon, Vernita; Beales, Paul; Deserno, Markus; Andrew, Caroline; Zhao, Zhijun; Egelhaaf, Stefan; Poon, Wilson

    2007-03-01

    Lipids are biological amphiphiles that, in aqueous solution, self-assemble into a variety of structures, including bilayer membranes that form hollow vesicles. In membranes with two or more constituents, lipids are well-mixed when the temperature is sufficiently high. As the temperature is lowered, systems undergo ordering transitions, membranes phase-separate laterally, and the resulting domains pattern vesicles. Here we demonstrate different aspects of this patterning that are important both for basic science and for their technological potentials: the packings of lipids in ordered-phase domains determine the domains' morphologies and inclusivities; adherent regions of membranes favour the growth of ordered-phase domains; rapid phase separation forms many small stripe domains that pattern vesicles with a `baseball' texture. These phenomena demonstrate basic physics and also have strong potential for exploitation to achieve vesicles with controllable patterns and properties. Lipid structures such as vesicles are attractive candidates for such technological development because they are intrinsicly biocompatible and because technologies using liposomes for controlled delivery and release are already widespread and under active development.

  16. Interaction of articaine hydrochloride with prokaryotic membrane lipids.

    PubMed

    Lygre, Henning; Moe, Grete; Nerdal, Willy; Holmsen, Holm

    2009-01-01

    Local anesthetics are the most commonly used drugs in dentistry, with a wide range of effects, including antimicrobial activity. High antimicrobial effects have recently been reported on oral microbes from articaine hydrochloride, revealed by the minimum inhibitory concentration and minimal bactericidal concentration. Additionally, articaine has recently been used as an alkaline component in endodontic materials with a proposed antibacterial activity. However, the detailed mechanisms of action have not been discussed. We determined the Langmuir surface pressure/molecular area isotherms of prokaryotic lipid monolayers, as well as the phospholipid phase transitions, by employing differential scanning calorimetry on unilamellar prokaryotic liposomes (bilayers). Articaine hydrochloride was found to interact with the prokaryotic membrane lipids in both monolayers and bilayers. An increase of the phospholipid molecular area of acidic glycerophospholipids as well as a decrease in phase transition temperature and enthalpy were found with increasing articaine hydrochloride concentration. The thermodynamic changes by adding articaine hydrochloride to prokaryotic membrane lipids are potentially related to the effects observed from antimicrobial peptides resulting from membrane insertion, aggregate composition, pore formation, and lysis. Interaction of articaine hydrochloride with prokaryotic membrane lipids is indicated. Hence, further research is necessary to gain insight into where these compounds exert their effects at the molecular level.

  17. Micrometer-Scale Membrane Transition of Supported Lipid Bilayer Membrane Reconstituted with Cytosol of Dictyostelium discoideum

    PubMed Central

    Takahashi, Kei; Toyota, Taro

    2017-01-01

    Background: The transformation of the supported lipid bilayer (SLB) membrane by extracted cytosol from living resources, has recently drawn much attention. It enables us to address the question of whether the purified phospholipid SLB membrane, including lipids related to amoeba locomotion, which was discussed in many previous studies, exhibits membrane deformation in the presence of cytosol extracted from amoeba; Methods: In this report, a method for reconstituting a supported lipid bilayer (SLB) membrane, composed of purified phospholipids and cytosol extracted from Dictyostelium discoideum, is described. This technique is a new reconstitution method combining the artificial constitution of membranes with the reconstitution using animate cytosol (without precise purification at a molecular level), contributing to membrane deformation analysis; Results: The morphology transition of a SLB membrane composed of phosphatidylcholines, after the addition of cytosolic extract, was traced using a confocal laser scanning fluorescence microscope. As a result, pore formation in the SLB membrane was observed and phosphatidylinositides incorporated into the SLB membrane tended to suppress pore formation and expansion; Conclusions: The current findings imply that phosphatidylinositides have the potential to control cytoplasm activity and bind to a phosphoinositide-containing SLB membrane. PMID:28272354

  18. Micrometer-Scale Membrane Transition of Supported Lipid Bilayer Membrane Reconstituted with Cytosol of Dictyostelium discoideum.

    PubMed

    Takahashi, Kei; Toyota, Taro

    2017-03-07

    The transformation of the supported lipid bilayer (SLB) membrane by extracted cytosol from living resources, has recently drawn much attention. It enables us to address the question of whether the purified phospholipid SLB membrane, including lipids related to amoeba locomotion, which was discussed in many previous studies, exhibits membrane deformation in the presence of cytosol extracted from amoeba; Methods: In this report, a method for reconstituting a supported lipid bilayer (SLB) membrane, composed of purified phospholipids and cytosol extracted from Dictyostelium discoideum, is described. This technique is a new reconstitution method combining the artificial constitution of membranes with the reconstitution using animate cytosol (without precise purification at a molecular level), contributing to membrane deformation analysis; Results: The morphology transition of a SLB membrane composed of phosphatidylcholines, after the addition of cytosolic extract, was traced using a confocal laser scanning fluorescence microscope. As a result, pore formation in the SLB membrane was observed and phosphatidylinositides incorporated into the SLB membrane tended to suppress pore formation and expansion; Conclusions: The current findings imply that phosphatidylinositides have the potential to control cytoplasm activity and bind to a phosphoinositide-containing SLB membrane.

  19. Membrane lipid rafts disturbance in the response of rat skeletal muscle to short-term disuse.

    PubMed

    Petrov, Alexey M; Kravtsova, Violetta V; Matchkov, Vladimir V; Vasiliev, Alexander N; Zefirov, Andrey L; Chibalin, Alexander V; Heiny, Judith A; Krivoi, Igor I

    2017-03-08

    Marked loss of skeletal muscle mass occurs under various conditions of disuse, but the molecular and cellular mechanisms leading to atrophy are not completely understood. We investigate early molecular events which might play a role in skeletal muscle remodeling during mechanical unloading (disuse). The effects of acute (6 - 12 h) hindlimb suspension on the soleus muscles from adult rats were examined. The integrity of plasma membrane lipid rafts was tested utilizing cholera toxin B subunit, or fluorescent sterols. In addition, resting intracellular Ca(2+) level was analyzed. Acute disuse disturbed the plasma membrane lipid-ordered phase throughout the sarcolemma and was more pronounced in junctional membrane regions. Ouabain (1 µM), which specifically inhibits the Na,K-ATPase α2 isozyme in rodent skeletal muscles, produced similar lipid rafts changes in control muscles, but was ineffective in suspended muscles, which show an initial loss of α2 Na,K-ATPase activity. Lipid rafts were able to recover with cholesterol supplementation, suggesting that disturbance results from cholesterol loss. Repetitive nerve stimulation also restores lipid rafts, specifically in junctional sarcolemma region. Disuse locally lowered the resting intracellular Ca(2+) concentration only near the neuromuscular junction of muscle fibers. Our results provide the evidence to suggest that the ordering of lipid rafts strongly depends on motor nerve input and may involve interactions with the α2 Na,K-ATPase. Lipid rafts disturbance, accompanied by intracellular Ca(2+) dysregulation are among the earliest remodeling events induced by skeletal muscle disuse.

  20. 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

  1. Anesthetic diffusion through lipid membranes depends on the protonation rate.

    PubMed

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

    2014-12-18

    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.

  2. 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.

  3. Lipid-Protein Interactions in Plasma Membranes of Fiber Cells Isolated from the Human Eye Lens

    PubMed Central

    Raguz, Marija; Mainali, Laxman; O’Brien, William J.; Subczynski, Witold K.

    2014-01-01

    The protein content in human lens membranes is extremely high, increases with age, and is higher in the nucleus as compared with the cortex, which should strongly affect the organization and properties of the lipid bilayer portion of intact membranes. To assess these effects, the intact cortical and nuclear fiber cell plasma membranes isolated from human lenses from 41- to 60-year-old donors were studied using electron paramagnetic resonance spin-labeling methods. Results were compared with those obtained for lens lipid membranes prepared from total lipid extracts from human eyes of the same age group [Mainali,L., Raguz, M., O’Brien, W. J., and Subczynski, W. K. (2013) Biochim. Biophys. Acta]. Differences were considered to be mainly due to the effect of membrane proteins. The lipid-bilayer portions of intact membranes were significantly less fluid than lipid bilayers of lens lipid membranes, prepared without proteins. The intact membranes were found to contain three distinct lipid environments termed the bulk lipid domain, boundary lipid domain, and trapped lipid domain. However, the cholesterol bilayer domain, which was detected in cortical and nuclear lens lipid membranes, was not detected in intact membranes. The relative amounts of bulk and trapped lipids were evaluated. The amount of lipids in domains uniquely formed due to the presence of membrane proteins was greater in nuclear membranes than in cortical membranes. Thus, it is evident that the rigidity of nuclear membranes is greater than that of cortical membranes. Also the permeability coefficients for oxygen measured in domains of nuclear membranes were significantly lower than appropriate coefficients measured in cortical membranes. Relationships between the organization of lipids into lipid domains in fiber cells plasma membranes and the organization of membrane proteins are discussed. PMID:24486794

  4. Lipid-protein interactions in plasma membranes of fiber cells isolated from the human eye lens.

    PubMed

    Raguz, Marija; Mainali, Laxman; O'Brien, William J; Subczynski, Witold K

    2014-03-01

    The protein content in human lens membranes is extremely high, increases with age, and is higher in the nucleus as compared with the cortex, which should strongly affect the organization and properties of the lipid bilayer portion of intact membranes. To assess these effects, the intact cortical and nuclear fiber cell plasma membranes isolated from human lenses from 41- to 60-year-old donors were studied using electron paramagnetic resonance spin-labeling methods. Results were compared with those obtained for lens lipid membranes prepared from total lipid extracts from human eyes of the same age group [Mainali, L., Raguz, M., O'Brien, W. J., and Subczynski, W. K. (2013) Biochim. Biophys. Acta]. Differences were considered to be mainly due to the effect of membrane proteins. The lipid-bilayer portions of intact membranes were significantly less fluid than lipid bilayers of lens lipid membranes, prepared without proteins. The intact membranes were found to contain three distinct lipid environments termed the bulk lipid domain, boundary lipid domain, and trapped lipid domain. However, the cholesterol bilayer domain, which was detected in cortical and nuclear lens lipid membranes, was not detected in intact membranes. The relative amounts of bulk and trapped lipids were evaluated. The amount of lipids in domains uniquely formed due to the presence of membrane proteins was greater in nuclear membranes than in cortical membranes. Thus, it is evident that the rigidity of nuclear membranes is greater than that of cortical membranes. Also the permeability coefficients for oxygen measured in domains of nuclear membranes were significantly lower than appropriate coefficients measured in cortical membranes. Relationships between the organization of lipids into lipid domains in fiber cells plasma membranes and the organization of membrane proteins are discussed. Copyright © 2014 Elsevier Ltd. All rights reserved.

  5. Cholesterol drives aβ(1-42) interaction with lipid rafts in model membranes.

    PubMed

    Seghezza, Silvia; Diaspro, Alberto; Canale, Claudio; Dante, Silvia

    2014-11-25

    The molecular mechanism at the basis of the neurodegenerative process related to Alzheimer's disease (AD) is triggered by the local composition of the neural plasma membrane. The role of cholesterol is controversial. In this investigation the interaction of the AD peptide amyloid-beta (1-42) with model membranes containing lipid rafts has been investigated by atomic force microscopy techniques. Supported lipid membranes made of phospholipids/sphingomyelin/cholesterol have been investigated as a function of the molar content of cholesterol, in a range spanning the phase diagram of the lipid system. The administration of amyloid-beta induced a phase reorganization of the lipid domains, when the cholesterol molar fraction was below 5%. At the same time, a mechanical destabilization and an appreciable thinning of the membrane induced by the peptide were detected. The major interaction was observed in the presence of the gel phase Lβ, and was enhanced by a low cholesterol amount. With the appearance of the liquid ordered phase Lo, the effect was hindered. At high cholesterol content (20% mol), no detectable effects in the bilayer morphology or in its mechanical stability were recorded. These findings give new insights on the molecular mechanism of the amyloid/membrane interaction, highlighting the peculiar role of cholesterol.

  6. 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.

  7. Lipid domains control myelin basic protein adsorption and membrane interactions between model myelin lipid bilayers.

    PubMed

    Lee, Dong Woog; Banquy, Xavier; Kristiansen, Kai; Kaufman, Yair; Boggs, Joan M; Israelachvili, Jacob N

    2014-02-25

    The surface forces apparatus and atomic force microscope were used to study the effects of lipid composition and concentrations of myelin basic protein (MBP) on the structure of model lipid bilayers, as well as the interaction forces and adhesion between them. The lipid bilayers had a lipid composition characteristic of the cytoplasmic leaflets of myelin from "normal" (healthy) and "disease-like" [experimental allergic encephalomyelitis (EAE)] animals. They showed significant differences in the adsorption mechanism of MBP. MBP adsorbs on normal bilayers to form a compact film (3-4 nm) with strong intermembrane adhesion (∼0.36 mJ/m(2)), in contrast to its formation of thicker (7-8 nm) swelled films with weaker intermembrane adhesion (∼0.13 mJ/m(2)) on EAE bilayers. MBP preferentially adsorbs to liquid-disordered submicron domains within the lipid membranes, attributed to hydrophobic attractions. These results show a direct connection between the lipid composition of membranes and membrane-protein adsorption mechanisms that affects intermembrane spacing and adhesion and has direct implications for demyelinating diseases.

  8. 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.

  9. Viral rewiring of cellular lipid metabolism to create membranous replication compartments.

    PubMed

    Strating, Jeroen Rpm; van Kuppeveld, Frank Jm

    2017-08-01

    Positive-strand RNA (+RNA) viruses (e.g. poliovirus, hepatitis C virus, dengue virus, SARS-coronavirus) remodel cellular membranes to form so-called viral replication compartments (VRCs), which are the sites where viral RNA genome replication takes place. To induce VRC formation, these viruses extensively rewire lipid metabolism. Disparate viruses have many commonalities as well as disparities in their interactions with the host lipidome and accumulate specific sets of lipids (sterols, glycerophospholipids, sphingolipids) at their VRCs. Recent years have seen an upsurge in studies investigating the role of lipids in +RNA virus replication, in particular of sterols, and uncovered that membrane contact sites and lipid transfer proteins are hijacked by viruses and play pivotal roles in VRC formation. Copyright © 2017 Elsevier Ltd. All rights reserved.

  10. Studies of water diffusion in the vicinity of single-supported lipid membranes

    NASA Astrophysics Data System (ADS)

    Miskowiec, Andrew

    The insertion and function of membrane-embedded proteins is one of the most fundamental challenges facing biological physics today. At its core, addressing these phenomena requires an understanding of the interaction of proteins with the lipid bilayer and its associated water molecules. As such, the study of water dynamics and structure near model lipid bilayers can provide foundational knowledge upon which more detailed understanding of these core issues may be developed. Previous quasielastic neutron scattering measurements on lipid membranes have used samples of large stacks of membranes with an unknown amount of water between layers. This geometry complicates interpretation and renders comparison to molecular dynamics simulations difficult. Instead, this work investigates water dynamics on single-supported bilayers of the model charge-neutral lipid DMPC (dimyristoyl-sn- glycero-3-phosphocholine) and its anionic analogue DMPG (dimyristoyl-sn-glycero- 3-phosphoglycerol). Single bilayers can be more directly compared to molecular dynamics simulations, can be interrogated with Atomic Force Microscopy, and avoid the uncertainty in quantifying the amount of water in samples. A new method for producing the anionic bilayers is developed, which is a variant of the vesicle fusion method. Atomic Force Microscopy is used to characterize the quality of both DMPC and DMPG membranes supported on SiO2-coated silicon substrates. Measuring the bilayer thickness as a function of temperature reveals that the gel-to-fluid phase transition is found to be shifted to significantly higher temperatures for adsorbed lipid bilayers in air compared to free vesicles in solution. The temperature-dependent quasielastic spectra from hydrated DMPC bilayers reveal three types of membrane-associated water. First, a large amount of water difuses similarly to bulk supercooled water and freezes at 265 K. Second, a smaller amount of water closer to the membrane diffuses more slowly than bulk

  11. DNA-Tile Structures Induce Ionic Currents through Lipid Membranes.

    PubMed

    Göpfrich, Kerstin; Zettl, Thomas; Meijering, Anna E C; Hernández-Ainsa, Silvia; Kocabey, Samet; Liedl, Tim; Keyser, Ulrich F

    2015-05-13

    Self-assembled DNA nanostructures have been used to create man-made transmembrane channels in lipid bilayers. Here, we present a DNA-tile structure with a nominal subnanometer channel and cholesterol-tags for membrane anchoring. With an outer diameter of 5 nm and a molecular weight of 45 kDa, the dimensions of our synthetic nanostructure are comparable to biological ion channels. Because of its simple design, the structure self-assembles within a minute, making its creation scalable for applications in biology. Ionic current recordings demonstrate that the tile structures enable ion conduction through lipid bilayers and show gating and voltage-switching behavior. By demonstrating the design of DNA-based membrane channels with openings much smaller than that of the archetypical six-helix bundle, our work showcases their versatility inspired by the rich diversity of natural membrane components.

  12. Shear rheology of lipid monolayers and insights on membrane fluidity

    PubMed Central

    Espinosa, Gabriel; López-Montero, Iván; Monroy, Francisco; Langevin, Dominique

    2011-01-01

    The concept of membrane fluidity usually refers to a high molecular mobility inside the lipid bilayer which enables lateral diffusion of embedded proteins. Fluids have the ability to flow under an applied shear stress whereas solids resist shear deformations. Biological membranes require both properties for their function: high lateral fluidity and structural rigidity. Consequently, an adequate account must include, in addition to viscosity, the possibility for a nonzero shear modulus. This knowledge is still lacking as measurements of membrane shear properties have remained incomplete so far. In the present contribution we report a surface shear rheology study of different lipid monolayers that model distinct biologically relevant situations. The results evidence a large variety of mechanical behavior under lateral shear flow. PMID:21444777

  13. Polyunsaturation in lipid membranes: dynamic properties and lateral pressure profiles.

    PubMed

    Ollila, Samuli; Hyvönen, Marja T; Vattulainen, Ilpo

    2007-03-29

    We elucidate the influence of unsaturation on single-component membrane properties, focusing on their dynamical aspects and lateral pressure profiles across the membrane. To this end, we employ atomistic molecular dynamics simulations to study five different membrane systems with varying degrees of unsaturation, starting from saturated membranes and systematically increasing the level of unsaturation, ending up with a bilayer of phospholipids containing the docosahexaenoic acid. For an increasing level of unsaturation, we find considerable effects on dynamical properties, such as accelerated dynamics of the phosphocholine head groups and glycerol backbones and speeded up rotational dynamics of the lipid molecules. The lateral pressure profile is found to be altered by the degree of unsaturation. For an increasing number of double bonds, the peak in the middle of the bilayer decreases. This is compensated for by changes in the membrane-water interface region in terms of increasing peak heights of the lateral pressure profile. Implications of the findings are briefly discussed.

  14. Artificial black membranes from bipolar lipids of thermophilic Archaebacteria.

    PubMed Central

    Gliozzi, A; Rolandi, R; De Rosa, M; Gambacorta, A

    1982-01-01

    The membrane of thermophilic archaebacteria is characterized by the presence of unusual isoprenoid bipolar lipids. The molecular organization of these lipids is still a matter of study. Important information could come from forming artificial black membranes. Black films can be formed from n-alkane or squalene dispersions of bipolar lipids extracted from the membrane of Caldariella acidophila. Membrane formation occurred only above a critical temperature (approximately 70 degrees C) corresponding to the physiological one. At lower temperatures, special solvent systems (n-alkanes or squalene, butanol and n-alkanes or squalene, butanol chloroform) were required. To characterize the physical parameters of these membranes, conductance and capacitance measurements were performed. Conductance was in the range of 10(-8) - 10(-7) omega -1 cm -2 , where specific capacitance at T = 72 degrees C was Cs = 0.685 +/- 0.004 microF/cm2 and Cs = 0.658 +/- 0.08 microF/cm2, corresponding to a dielectric thickness of 27 and 29 A for squalene and dodecane dispersions, respectively. Capacitance was shown to vary as the square of membrane potential, as usual in lipid bilayers. Values of the proportionality constant alpha have been compared to those of solvent-containing and solvent-free bilayers. The behavior of capacitance as a function of temperature is also shown by lowering temperature; the occurrence of complex structural changes was indicated. All the experimental data suggest that the presence of solvent is very low. Two possible molecular configurations of the films are discussed. PMID:6800415

  15. Dynamical Clustering and the Origin of Raft-like Structures in a Model Lipid Membrane

    NASA Astrophysics Data System (ADS)

    Starr, Francis

    2014-03-01

    We investigate the dynamical heterogeneity of a model single-component lipid membrane using simulations of a coarse-grained representation of lipid molecules. In the liquid-ordered (LO) phase, lipid diffusion is hindered by the transient trapping of molecules by their neighbors, giving rise to two distinct mobility groups: low-mobility lipids which are temporarily ``caged'', and lipids with displacements on the scale of the intermolecular spacing. The lipid molecules within these distinct mobility states cluster, giving rise to transient ``islands'' of enhanced mobility having the size and time scale expected for lipid ``rafts''. These clusters are strikingly similar to the dynamical clusters found in glass-forming fluids, and distinct from phase-separation clusters. Such dynamic heterogeneity is ubiquitous in disordered condensed-phase systems. Thus, we hypothesize that rafts may originate from this universal mechanism, explaining why raft-like regions should arise, regardless of lipid structural or compositional details. This perspective provides a new approach to understand membrane transport.

  16. Distribution of Fullerene Nanoparticles between Water and Solid Supported Lipid Membranes: Thermodynamics and Effects of Membrane Composition on Distribution.

    PubMed

    Ha, Yeonjeong; Katz, Lynn E; Liljestrand, Howard M

    2015-12-15

    The distribution coefficient (Klipw) of fullerene between solid supported lipid membranes (SSLMs) and water was examined using different lipid membrane compositions. Klipw of fullerene was significantly higher with a cationic lipid membrane compared to that with a zwitterionic or anionic lipid membrane, potentially due to the strong interactions between negative fullerene dispersions and positive lipid head groups. The higher Klipw for fullerene distribution to ternary lipid mixture membranes was attributed to an increase in the interfacial surface area of the lipid membrane resulting from phase separation. These results imply that lipid composition can be a critical factor that affects bioconcentration of fullerene. Distribution of fullerene into zwitterionic unsaturated lipid membranes was dominated by the entropy contribution (ΔS) and the process was endothermic (ΔH > 0). This result contrasts the partitioning thermodynamics of highly and moderately hydrophobic chemicals indicating that the lipid-water distribution mechanism of fullerene may be different from that of molecular level chemicals. Potential mechanisms for the distribution of fullerene that may explain these differences include adsorption on the lipid membrane surfaces and partitioning into the center of lipid membranes (i.e., absorption).

  17. Mechanical properties that influence antimicrobial peptide activity in lipid membranes.

    PubMed

    Marín-Medina, Nathaly; Ramírez, Diego Alejandro; Trier, Steve; Leidy, Chad

    2016-12-01

    Antimicrobial peptides are small amphiphilic proteins found in animals and plants as essential components of the innate immune system and whose function is to control bacterial infectious activity. In order to accomplish their function, antimicrobial peptides use different mechanisms of action which have been deeply studied in view of their potential exploitation to treat antibiotic-resistant bacterial infections. One of the main mechanisms of action of these peptides is the disruption of the bacterial membrane through pore formation, which, in some cases, takes place via a monomer to oligomer cooperative transition. Previous studies have shown that lipid composition, and the presence of exogenous components, such as cholesterol in model membranes or carotenoids in bacteria, can affect the potency of distinct antimicrobial peptides. At the same time, considering the membrane as a two-dimensional material, it has been shown that membrane composition defines its mechanical properties which might be relevant in many membrane-related processes. Nevertheless, the correlation between the mechanical properties of the membrane and antimicrobial peptide potency has not been considered according to the importance it deserves. The relevance of these mechanical properties in membrane deformation due to peptide insertion is reviewed here for different types of pores in order to elucidate if indeed membrane composition affects antimicrobial peptide activity by modulation of the mechanical properties of the membrane. This would also provide a better understanding of the mechanisms used by bacteria to overcome antimicrobial peptide activity.

  18. Incorporation of large guest molecules into liposomes via chemical reactions in lipid membranes.

    PubMed

    Tsuchiya, Yuki; Sugikawa, Kouta; Ueda, Masafumi; Ikeda, Atsushi

    2017-02-22

    The incorporation of hydrophobic guest molecules into lipid membranes by the exchange of the guest molecule from a cyclodextrin (CDx) complex to a liposome is limited to guest molecules that can be included in CDxs. To solve this problem, large guest molecules were incorporated into liposomes by chemical reactions of guest molecules in lipid membranes. Stable lipid-membrane-incorporated fullerene derivatives with large substituent(s) were prepared by Diels-Alder reactions in lipid membranes.

  19. Lipid membrane domain formation and alamethicin aggregation studied by calorimetry, sound velocity measurements, and atomic force microscopy.

    PubMed

    Oliynyk, Vitaliy; Jäger, Markus; Heimburg, Thomas; Buckin, Vitaly; Kaatze, Udo

    2008-05-01

    An experimental study of phosphocholine membranes made from one lipid, from mixtures of DPPC and DLPC, and also from lipids and small amounts of alamethicin is presented. We used atomic force microscopy to investigate the spatial organization and structure of lipid domains and also of the defects induced by the peptide. Alamethicin was found to alter the state of lipids in the gel state in a way that domains of fluid lipids are formed close to the defects. Differential calorimetry revealed phase characteristics of the lipid mixtures and the effect of small amounts of alamethicin on the phase behavior. It was also shown that the sound velocity profiles of the membranes suspensions can be well calculated from the heat capacity traces of the samples. This result confirms the correlation between the mechanical properties and the specific heat of membrane systems.

  20. 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.

  1. Targeting proteins to liquid-ordered domains in lipid membranes.

    PubMed

    Stachowiak, Jeanne C; Hayden, Carl C; Sanchez, Mari Angelica A; Wang, Julia; Bunker, Bruce C; Voigt, James A; Sasaki, Darryl Y

    2011-02-15

    We demonstrate the construction of novel protein-lipid assemblies through the design of a lipid-like molecule, DPIDA, endowed with tail-driven affinity for specific lipid membrane phases and head-driven affinity for specific proteins. In studies performed on giant unilamellar vesicles (GUVs) with varying mole fractions of dipalymitoylphosphatidylcholine (DPPC), cholesterol, and diphytanoylphosphatidyl choline (DPhPC), DPIDA selectively partitioned into the more ordered phases, either solid or liquid-ordered (L(o)) depending on membrane composition. Fluorescence imaging established the phase behavior of the resulting quaternary lipid system. Fluorescence correlation spectroscopy confirmed the fluidity of the L(o) phase containing DPIDA. In the presence of CuCl(2), the iminodiacetic acid (IDA) headgroup of DPIDA forms the Cu(II)-IDA complex that exhibits a high affinity for histidine residues. His-tagged proteins were bound specifically to domains enriched in DPIDA, demonstrating the capacity to target protein binding selectively to both solid and L(o) phases. Steric pressure from the crowding of surface-bound proteins transformed the domains into tubules with persistence lengths that depended on the phase state of the lipid domains.

  2. Lipid domains in intact fiber-cell plasma membranes isolated from cortical and nuclear regions of human eye lenses of donors from different age groups.

    PubMed

    Raguz, Marija; Mainali, Laxman; O'Brien, William J; Subczynski, Witold K

    2015-03-01

    The results reported here clearly document changes in the properties and the organization of fiber-cell membrane lipids that occur with age, based on electron paramagnetic resonance (EPR) analysis of lens membranes of clear lenses from donors of age groups from 0 to 20, 21 to 40, and 61 to 80 years. The physical properties, including profiles of the alkyl chain order, fluidity, hydrophobicity, and oxygen transport parameter, were investigated using EPR spin-labeling methods, which also provide an opportunity to discriminate coexisting lipid domains and to evaluate the relative amounts of lipids in these domains. Fiber-cell membranes were found to contain three distinct lipid environments: bulk lipid domain, which appears minimally affected by membrane proteins, and two domains that appear due to the presence of membrane proteins, namely boundary and trapped lipid domains. In nuclear membranes the amount of boundary and trapped phospholipids as well as the amount of cholesterol in trapped lipid domains increased with the donors' age and was greater than that in cortical membranes. The difference between the amounts of lipids in domains uniquely formed due to the presence of membrane proteins in nuclear and cortical membranes increased with the donors' age. It was also shown that cholesterol was to a large degree excluded from trapped lipid domains in cortical membranes. It is evident that the rigidity of nuclear membranes was greater than that of cortical membranes for all age groups. The amount of lipids in domains of low oxygen permeability, mainly in trapped lipid domains, were greater in nuclear than cortical membranes and increased with the age of donors. These results indicate that the nuclear fiber cell plasma membranes were less permeable to oxygen than cortical membranes and become less permeable to oxygen with age. In clear lenses, age-related changes in the lens lipid and protein composition and organization appear to occur in ways that increase fiber

  3. Lipid Domains in Intact Fiber-Cell Plasma Membranes Isolated from Cortical and Nuclear Regions of Human Eye Lenses of Donors from Different Age Groups

    PubMed Central

    Raguz, Marija; Mainali, Laxman; O’Brien, William J.; Subczynski, Witold K.

    2015-01-01

    The results reported here clearly document changes in the properties and the organization of fiber-cell membrane lipids that occur with age, based on electron paramagnetic resonance (EPR) analysis of lens membranes of clear lenses from donors of age groups from 0 to 20, 21 to 40, and 61 to 80 years. The physical properties, including profiles of the alkyl chain order, fluidity, hydrophobicity, and oxygen transport parameter, were investigated using EPR spin-labeling methods, which also provide an opportunity to discriminate coexisting lipid domains and to evaluate the relative amounts of lipids in these domains. Fiber-cell membranes were found to contain three distinct lipid environments: bulk lipid domain, which appears minimally affected by membrane proteins, and two domains that appear due to the presence of membrane proteins, namely boundary and trapped lipid domains. In nuclear membranes the amount of boundary and trapped phospholipids as well as the amount of cholesterol in trapped lipid domains increased with the donors’ age and was greater than that in cortical membranes. The difference between the amounts of lipids in domains uniquely formed due to the presence of membrane proteins in nuclear and cortical membranes increased with the donors’ age. It was also shown that cholesterol was to a large degree excluded from trapped lipid domains in cortical membranes. It is evident that the rigidity of nuclear membranes was greater than that of cortical membranes for all age groups. The amount of lipids in domains of low oxygen permeability, mainly in trapped lipid domains, were greater in nuclear than cortical membranes and increased with the age of donors. These results indicate that the nuclear fiber cell plasma membranes were less permeable to oxygen than cortical membranes and become less permeable to oxygen with age. In clear lenses, age-related changes in the lens lipid and protein composition and organization appear to occur in ways that increase fiber

  4. The influence of solid scaffolds on flat and curved lipid membranes

    NASA Astrophysics Data System (ADS)

    de Jong, D. H.; Heuer, A.

    2017-07-01

    Solid-supported membranes have become a common tool to study lipid membrane properties in a controlled environment. One particular example is the study of membrane curvature and its effect on lipid sorting. Here we simulate solid-supported membranes using the coarse grain molecular dynamics Martini force field. We characterize basic properties of the solid surfaces and lipid membranes deposited on them. Subsequently we construct large, solid ridges and use them to induce curvature in DOPC membranes. We study membrane properties, such as lateral diffusion and tail order parameters, relative to the curved membrane. Finally, we study the effect of the induced curvature on lateral lipid sorting in a ternary lipid membrane. Thus, we obtain comprehensive and microscopic insight into the impact of curvature on a lipid membrane in terms of structure and dynamics.

  5. How sterol tilt regulates properties and organization of lipid membranes and membrane insertions

    PubMed Central

    Khelashvili, George; Harries, Daniel

    2013-01-01

    Serving as a crucial component of mammalian cells, cholesterol critically regulates the functions of biomembranes. This review focuses on a specific property of cholesterol and other sterols: the tilt modulus χ that quantifies the energetic cost of tilting sterol molecules inside the lipid membrane. We show how χ is involved in determining properties of cholesterol-containing membranes, and detail a novel approach to quantify its value from atomistic molecular dynamics (MD) simulations. Specifically, we link χ with other structural, thermodynamic, and mechanical properties of cholesterol-containing lipid membranes, and delineate how this useful parameter can be obtained from the sterol tilt probability distributions derived from relatively small-scale unbiased MD simulations. We demonstrate how the tilt modulus quantitatively describes the aligning field that sterol molecules create inside the phospholipid bilayers, and we relate χ to the bending rigidity of the lipid bilayer through effective tilt and splay energy contributions to the elastic deformations. Moreover, we show how χ can conveniently characterize the “condensing effect” of cholesterol on phospholipids. Finally, we demonstrate the importance of this cholesterol aligning field to the proper folding and interactions of membrane peptides. Given the relative ease of obtaining the tilt modulus from atomistic simulations, we propose that χ can be routinely used to characterize the mechanical properties of sterol/lipid bilayers, and can also serve as a required fitting parameter in multi-scaled simulations of lipid membrane models to relate the different levels of coarse-grained details. PMID:23291283

  6. Membrane protein crystallization in lipidic mesophases: detergent effects.

    PubMed Central

    Ai, X; Caffrey, M

    2000-01-01

    The "cubic phase method" for growing crystals of membrane proteins uses a complex mixture of water, lipid, protein, and other components. The current view is that the cubic phase is integral to the process. Thus additives from whatever source introduce the possibility of destabilizing the phase, thereby compromising the crystallization process. Detergents are used to solubilize membrane proteins and are likely to be ported into the cubic medium with the target protein. Depending on the identity and concentration of the detergent, the cubic phase, which itself is membranous, may be solubilized or destabilized in such a way as to render it unsuitable as a crystal growing system. The nonionic detergent n-dodecyl-beta-D-maltopyranoside is commonly used in membrane protein work. In this study, we evaluate its effect on the cubic mesophase of hydrated monoolein. X-ray diffraction was used for phase identification and mesophase microstructure characterization. The results show that while low levels of the detergent are tolerated, increasing concentrations trigger a cubic-to-lamellar phase transition in a temperature-dependent manner. This finding is rationalized in the context of complementary molecular shapes of the lipid and the detergent and has implications for the mechanism of crystallization in lipidic mesophases as discussed. PMID:10866965

  7. Important roles for membrane lipids in haloarchaeal bioenergetics.

    PubMed

    Kellermann, Matthias Y; Yoshinaga, Marcos Y; Valentine, Raymond C; Wörmer, Lars; Valentine, David L

    2016-11-01

    Recent advances in lipidomic analysis in combination with various physiological experiments set the stage for deciphering the structure-function of haloarchaeal membrane lipids. Here we focused primarily on changes in lipid composition of Haloferax volcanii, but also performed a comparative analysis with four other haloarchaeal species (Halobacterium salinarum, Halorubrum lacusprofundi, Halorubrum sodomense and Haloplanus natans) all representing distinctive cell morphologies and behaviors (i.e., rod shape vs. pleomorphic behavior). Common to all five haloarchaea, our data reveal an extraordinary high level of menaquinone, reaching up to 72% of the total lipids. This ubiquity suggests that menaquinones may function beyond their ordinary role as electron and proton transporter, acting simultaneously as ion permeability barriers and as powerful shield against oxidative stress. In addition, we aimed at understanding the role of cations interacting with the characteristic negatively charged surface of haloarchaeal membranes. We propose for instance that by bridging the negative charges of adjacent anionic phospholipids, Mg(2+) acts as surrogate for cardiolipin, a molecule that is known to control curvature stress of membranes. This study further provides a bioenergetic perspective as to how haloarchaea evolved following oxygenation of Earth's atmosphere. The success of the aerobic lifestyle of haloarchaea includes multiple membrane-based strategies that successfully balance the need for a robust bilayer structure with the need for high rates of electron transport - collectively representing the molecular basis to inhabit hypersaline water bodies around the planet.

  8. Molecular dynamics study of lipid bilayers modeling the plasma membranes of mouse hepatocytes and hepatomas

    NASA Astrophysics Data System (ADS)

    Andoh, Yoshimichi; Aoki, Noriyuki; Okazaki, Susumu

    2016-02-01

    Molecular dynamics (MD) calculations of lipid bilayers modeling the plasma membranes of normal mouse hepatocytes and hepatomas in water have been performed under physiological isothermal-isobaric conditions (310.15 K and 1 atm). The changes in the membrane properties induced by hepatic canceration were investigated and were compared with previous MD calculations included in our previous study of the changes in membrane properties induced by murine thymic canceration. The calculated model membranes for normal hepatocytes and hepatomas comprised 23 and 24 kinds of lipids, respectively. These included phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, sphingomyelin, lysophospholipids, and cholesterol. We referred to previously published experimental values for the mole fraction of the lipids adopted in the present calculations. The calculated structural and dynamic properties of the membranes such as lateral structure, order parameters, lateral self-diffusion constants, and rotational correlation times all showed that hepatic canceration causes plasma membranes to become more ordered laterally and less fluid. Interestingly, this finding contrasts with the less ordered structure and increased fluidity of plasma membranes induced by thymic canceration observed in our previous MD study.

  9. Molecular dynamics study of lipid bilayers modeling the plasma membranes of mouse hepatocytes and hepatomas.

    PubMed

    Andoh, Yoshimichi; Aoki, Noriyuki; Okazaki, Susumu

    2016-02-28

    Molecular dynamics (MD) calculations of lipid bilayers modeling the plasma membranes of normal mouse hepatocytes and hepatomas in water have been performed under physiological isothermal-isobaric conditions (310.15 K and 1 atm). The changes in the membrane properties induced by hepatic canceration were investigated and were compared with previous MD calculations included in our previous study of the changes in membrane properties induced by murine thymic canceration. The calculated model membranes for normal hepatocytes and hepatomas comprised 23 and 24 kinds of lipids, respectively. These included phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, sphingomyelin, lysophospholipids, and cholesterol. We referred to previously published experimental values for the mole fraction of the lipids adopted in the present calculations. The calculated structural and dynamic properties of the membranes such as lateral structure, order parameters, lateral self-diffusion constants, and rotational correlation times all showed that hepatic canceration causes plasma membranes to become more ordered laterally and less fluid. Interestingly, this finding contrasts with the less ordered structure and increased fluidity of plasma membranes induced by thymic canceration observed in our previous MD study.

  10. Buffers affect the bending rigidity of model lipid membranes.

    PubMed

    Bouvrais, Hélène; Duelund, Lars; Ipsen, John H

    2014-01-14

    In biophysical and biochemical studies of lipid bilayers the influence of the used buffer is often ignored or assumed to be negligible on membrane structure, elasticity, or physical properties. However, we here present experimental evidence, through bending rigidity measurements performed on giant vesicles, of a more complex behavior, where the buffering molecules may considerably affect the bending rigidity of phosphatidylcholine bilayers. Furthermore, a synergistic effect on the bending modulus is observed in the presence of both salt and buffer molecules, which serves as a warning to experimentalists in the data interpretation of their studies, since typical lipid bilayer studies contain buffer and ion molecules.

  11. Lipid A binding sites in membranes of macrophage tumor cells

    SciTech Connect

    Hampton, R.Y.; Golenbock, D.T.; Raetz, C.R.

    1988-10-15

    Lipopolysaccharide affects a variety of eukaryotic cells and mammalian organisms. These actions are involved in the pathogenesis of Gram-negative septicemia. Many of the actions of lipopolysaccharide are believed to be caused by its active moiety, lipid A. Our laboratory has previously identified a bioactive lipid A precursor, termed lipid IVA, which can be labeled with 32P of high specific activity and purified. In this work we have used the labeled probe, 4'-32P-lipid IVA, to develop a novel assay for the specific binding of lipid IVA to whole cells. We have also demonstrated its use in a ligand blotting assay of immobilized cellular proteins. Using the whole cell assay, we show that 4'-32P-lipid IVA specifically binds to RAW 264.7 macrophage-like cultured cells. The binding is saturable, is inhibited with excess unlabeled lipid IVA, and is proteinase K-sensitive. It displays cellular and pharmacological specificity. Using the ligand blotting assay, we show that several RAW 264.7 cell proteins can bind 4'-32P-lipid IVA. The two principal binding proteins have Mr values of 31 and 95 kDa, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Fractionation studies indicate that the 31-kDa protein is enriched in the nuclear fraction and may be a histone, whereas the 95-kDa protein is enriched in the membrane fraction. The binding assays that we have developed should lead to a clearer understanding of lipid A/animal cell interactions.

  12. The interaction of polyglutamine peptides with lipid membranes is regulated by flanking sequences associated with huntingtin.

    PubMed

    Burke, Kathleen A; Kauffman, Karlina J; Umbaugh, C Samuel; Frey, Shelli L; Legleiter, Justin

    2013-05-24

    Huntington disease (HD) is caused by an expanded polyglutamine (poly(Q)) repeat near the N terminus of the huntingtin (htt) protein. Expanded poly(Q) facilitates formation of htt aggregates, eventually leading to deposition of cytoplasmic and intranuclear inclusion bodies containing htt. Flanking sequences directly adjacent to the poly(Q) domain, such as the first 17 amino acids on the N terminus (Nt17) and the polyproline (poly(P)) domain on the C-terminal side of the poly(Q) domain, heavily influence aggregation. Additionally, htt interacts with a variety of membraneous structures within the cell, and Nt17 is implicated in lipid binding. To investigate the interaction between htt exon1 and lipid membranes, a combination of in situ atomic force microscopy, Langmuir trough techniques, and vesicle permeability assays were used to directly monitor the interaction of a variety of synthetic poly(Q) peptides with different combinations of flanking sequences (KK-Q35-KK, KK-Q35-P10-KK, Nt17-Q35-KK, and Nt17-Q35-P10-KK) on model membranes and surfaces. Each peptide aggregated on mica, predominately forming extended, fibrillar aggregates. In contrast, poly(Q) peptides that lacked the Nt17 domain did not appreciably aggregate on or insert into lipid membranes. Nt17 facilitated the interaction of peptides with lipid surfaces, whereas the poly(P) region enhanced this interaction. The aggregation of Nt17-Q35-P10-KK on the lipid bilayer closely resembled that of a htt exon1 construct containing 35 repeat glutamines. Collectively, this data suggests that the Nt17 domain plays a critical role in htt binding and aggregation on lipid membranes, and this lipid/htt interaction can be further modulated by the presence of the poly(P) domain.

  13. The Interaction of Polyglutamine Peptides with Lipid Membranes Is Regulated by Flanking Sequences Associated with Huntingtin*

    PubMed Central

    Burke, Kathleen A.; Kauffman, Karlina J.; Umbaugh, C. Samuel; Frey, Shelli L.; Legleiter, Justin

    2013-01-01

    Huntington disease (HD) is caused by an expanded polyglutamine (poly(Q)) repeat near the N terminus of the huntingtin (htt) protein. Expanded poly(Q) facilitates formation of htt aggregates, eventually leading to deposition of cytoplasmic and intranuclear inclusion bodies containing htt. Flanking sequences directly adjacent to the poly(Q) domain, such as the first 17 amino acids on the N terminus (Nt17) and the polyproline (poly(P)) domain on the C-terminal side of the poly(Q) domain, heavily influence aggregation. Additionally, htt interacts with a variety of membraneous structures within the cell, and Nt17 is implicated in lipid binding. To investigate the interaction between htt exon1 and lipid membranes, a combination of in situ atomic force microscopy, Langmuir trough techniques, and vesicle permeability assays were used to directly monitor the interaction of a variety of synthetic poly(Q) peptides with different combinations of flanking sequences (KK-Q35-KK, KK-Q35-P10-KK, Nt17-Q35-KK, and Nt17-Q35-P10-KK) on model membranes and surfaces. Each peptide aggregated on mica, predominately forming extended, fibrillar aggregates. In contrast, poly(Q) peptides that lacked the Nt17 domain did not appreciably aggregate on or insert into lipid membranes. Nt17 facilitated the interaction of peptides with lipid surfaces, whereas the poly(P) region enhanced this interaction. The aggregation of Nt17-Q35-P10-KK on the lipid bilayer closely resembled that of a htt exon1 construct containing 35 repeat glutamines. Collectively, this data suggests that the Nt17 domain plays a critical role in htt binding and aggregation on lipid membranes, and this lipid/htt interaction can be further modulated by the presence of the poly(P) domain. PMID:23572526

  14. Lipid membrane-assisted condensation and assembly of amphiphilic Janus particles

    DOE PAGES

    Chambers, Mariah; Mallory, Stewart Anthony; Malone, Heather; ...

    2016-01-01

    Amphiphilic Janus particles self-assemble into complex metastructures, but little is known about how their assembly might be modified by weak interactions with a nearby biological membrane surface. Here, we report an integrated experimental and molecular dynamics simulation study to investigate the self-assembly of amphiphilic Janus particles on a lipid membrane. We created an experimental system in which Janus particles are allowed to self-assemble in the same medium where zwitterionic lipids form giant unilamellar vesicles (GUVs). Janus particles spontaneously concentrated on the inner leaflet of the GUVs. They exhibited biased orientation and heterogeneous rotational dynamics as revealed by single particle rotationalmore » tracking. The combined experimental and simulation results show that Janus particles concentrate on the lipid membranes due to weak particle–lipid attraction, whereas the biased orientation of particles is driven predominantly by inter-particle interactions. Furthermore, this study demonstrates the potential of using lipid membranes to influence the self-assembly of Janus particles.« less

  15. Influence of membrane surface charge on adsorption of complement proteins onto supported lipid bilayers.

    PubMed

    Yorulmaz, Saziye; Jackman, Joshua A; Hunziker, Walter; Cho, Nam-Joon

    2016-12-01

    The complement system is an important part of the innate immune response, and there is great interest in understanding how complement proteins interact with lipid membrane interfaces, especially in the context of recognizing foreign particulates (e.g., liposomal nanomedicines). Herein, a supported lipid bilayer platform was employed in order to investigate the effect of membrane surface charge (positive, negative, or neutral) on the adsorption of three complement proteins. Quartz crystal microbalance-dissipation (QCM-D) experiments measured the real-time kinetics and total uptake of protein adsorption onto supported lipid bilayers. The results demonstrate that all three proteins exhibit preferential, mainly irreversible adsorption onto negatively charged lipid bilayers, yet there was also significant variation in total uptake and the relative degree of adsorption onto negatively charged bilayers versus neutral and positively charged bilayers. The total uptake was also observed to strongly depend on the bulk protein concentration. Taken together, our findings contribute to a broader understanding of the factors which influence adsorption of complement proteins onto lipid membranes and offer guidance towards the design of synthetic lipid bilayers with immunocompetent features.

  16. Lipids and topological rules of membrane protein assembly: balance between long and short range lipid-protein interactions.

    PubMed

    Vitrac, Heidi; Bogdanov, Mikhail; Heacock, Phil; Dowhan, William

    2011-04-29

    The N-terminal six-transmembrane domain (TM) bundle of lactose permease of Escherichia coli is uniformly inverted when assembled in membranes lacking phosphatidylethanolamine (PE). Inversion is dependent on the net charge of cytoplasmically exposed protein domains containing positive and negative residues, net charge of the membrane surface, and low hydrophobicity of TM VII acting as a molecular hinge between the two halves of lactose permease (Bogdanov, M., Xie, J., Heacock, P., and Dowhan, W. (2008) J. Cell Biol. 182, 925-935). Net neutral lipids suppress the membrane translocation potential of negatively charged amino acids, thus increasing the cytoplasmic retention potential of positively charged amino acids. Herein, TM organization of sucrose permease (CscB) and phenylalanine permease (PheP) as a function of membrane lipid composition was investigated to extend these principles to other proteins. For CscB, topological dependence on PE only becomes evident after a significant increase in the net negative charge of the cytoplasmic surface of the N-terminal TM bundle. High negative charge is required to overcome the thermodynamic block to inversion due to the high hydrophobicity of TM VII. Increasing the positive charge of the cytoplasmic surface of the N-terminal TM hairpin of PheP, which is misoriented in PE-lacking cells, favors native orientation in the absence of PE. PheP and CscB also display co-existing dual topologies dependent on changes in the charge balance between protein domains and the membrane lipids. Therefore, the topology of both permeases is dependent on PE. However, CscB topology is governed by thermodynamic balance between opposing lipid-dependent electrostatic and hydrophobic interactions.

  17. Triglyceride Blisters in Lipid Bilayers: Implications for Lipid Droplet Biogenesis and the Mobile Lipid Signal in Cancer Cell Membranes

    PubMed Central

    Khandelia, Himanshu; Duelund, Lars; Pakkanen, Kirsi I.; Ipsen, John H.

    2010-01-01

    Triglycerides have a limited solubility, around 3%, in phosphatidylcholine lipid bilayers. Using millisecond-scale course grained molecular dynamics simulations, we show that the model lipid bilayer can accommodate a higher concentration of triolein (TO) than earlier anticipated, by sequestering triolein molecules to the bilayer center in the form of a disordered, isotropic, mobile neutral lipid aggregate, at least 17 nm in diameter, which forms spontaneously, and remains stable on at least the microsecond time scale. The results give credence to the hotly debated existence of mobile neutral lipid aggregates of unknown function present in malignant cells, and to the early biogenesis of lipid droplets accommodated between the two leaflets of the endoplasmic reticulum membrane. The TO aggregates give the bilayer a blister-like appearance, and will hinder the formation of multi-lamellar phases in model, and possibly living membranes. The blisters will result in anomalous membrane probe partitioning, which should be accounted for in the interpretation of probe-related measurements. PMID:20877640

  18. 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

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

    DOE PAGES

    Adams, Peter G.; Swingle, Kirstie L.; Paxton, Walter F.; ...

    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

  20. 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.

  1. Phytosphingosine, sphingosine and dihydrosphingosine ceramides in model skin lipid membranes: permeability and biophysics.

    PubMed

    Školová, Barbora; Kováčik, Andrej; Tesař, Ondřej; Opálka, Lukáš; Vávrová, Kateřina

    2017-05-01

    Ceramides based on phytosphingosine, sphingosine and dihydrosphingosine are essential constituents of the skin lipid barrier that protects the body from excessive water loss. The roles of the individual ceramide subclasses in regulating skin permeability and the reasons for C4-hydroxylation of these sphingolipids are not completely understood. We investigated the chain length-dependent effects of dihydroceramides, sphingosine ceramides (with C4-unsaturation) and phytoceramides (with C4-hydroxyl) on the permeability, lipid organization and thermotropic behavior of model stratum corneum lipid membranes composed of ceramide/lignoceric acid/cholesterol/cholesteryl sulfate. Phytoceramides with very long C24 acyl chains increased the permeability of the model lipid membranes compared to dihydroceramides or sphingosine ceramides with the same chain lengths. Either unsaturation or C4-hydroxylation of dihydroceramides induced chain length-dependent increases in membrane permeability. Infrared spectroscopy showed that C4-hydroxylation of the sphingoid base decreased the relative ratio of orthorhombic chain packing in the membrane and lowered the miscibility of C24 phytoceramide with lignoceric acid. The phase separation in phytoceramide membranes was confirmed by X-ray diffraction. In contrast, phytoceramides formed strong hydrogen bonds and highly thermostable domains. Thus, the large heterogeneity in ceramide structures and in their aggregation mechanisms may confer resistance towards the heterogeneous external stressors that are constantly faced by the skin barrier.

  2. The Permeability of Thin Lipid Membranes to Bromide and Bromine

    PubMed Central

    Gutknecht, John; Bruner, L. J.; Tosteson, D. C.

    1972-01-01

    Thin lipid (optically black) membranes were made from sheep red cell lipids dissolved in n-decane. The flux of Br across these membranes was measured by the use of tracer 82Br. The unidirectional flux of Br (in 50–100 mM NaBr) was 1–3 x 10-12 mole/cm2sec. This flux is more than 1000 times the flux predicted from the membrane electrical resistance (>108 ohm-cm2) and the transference number for Br- (0.2–0.3), which was estimated from measurements of the zero current potential difference. The Br flux was not affected by changes in the potential difference imposed across the membrane (±60 mv) or by the ionic strength of the bathing solutions. However, the addition of a reducing agent, sodium thiosulfate (10-3 M), to the NaBr solution bathing the membrane caused a 90% reduction in the Br flux. The inhibiting effect of S2O3= suggests that the Br flux is due chiefly to traces of Br2 in NaBr solutions. As expected, the addition of Br2 to the NaBr solutions greatly stimulated the Br flux. However, at constant Br2 concentration, the Br flux was also stimulated by increasing the Br- concentration, in spite of the fact that the membrane was virtually impermeable to Br-. Finally, the Br flux appeared to saturate at high Br2 concentrations, and the saturation value was roughly proportional to the Br- concentration. These results can be explained by a model which assumes that Br crosses the membrane only as Br2 but that rapid equilibration of Br between Br2 and Br- occurs in the unstirred layers of aqueous solution bathing the two sides of the membrane. A consequence of the model is that Br- "facilitates" the diffusion of Br across the unstirred layers. PMID:5063846

  3. 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.

  4. Molecular dynamics study of lipid bilayers modeling the plasma membranes of normal murine thymocytes and leukemic GRSL cells.

    PubMed

    Andoh, Yoshimichi; Okazaki, Susumu; Ueoka, Ryuichi

    2013-04-01

    Molecular dynamics (MD) calculations for the plasma membranes of normal murine thymocytes and thymus-derived leukemic GRSL cells in water have been performed under physiological isothermal-isobaric conditions (310.15K and 1 atm) to investigate changes in membrane properties induced by canceration. The model membranes used in our calculations for normal and leukemic thymocytes comprised 23 and 25 kinds of lipids, respectively, including phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, sphingomyelin, lysophospholipids, and cholesterol. The mole fractions of the lipids adopted here were based on previously published experimental values. Our calculations clearly showed that the membrane area was increased in leukemic cells, and that the isothermal area compressibility of the leukemic plasma membranes was double that of normal cells. The calculated membranes of leukemic cells were thus considerably bulkier and softer in the lateral direction compared with those of normal cells. The tilt angle of the cholesterol and the conformation of the phospholipid fatty acid tails both showed a lower level of order in leukemic cell membranes compared with normal cell membranes. The lateral radial distribution function of the lipids also showed a more disordered structure in leukemic cell membranes than in normal cell membranes. These observations all show that, for the present thymocytes, the lateral structure of the membrane is considerably disordered by canceration. Furthermore, the calculated lateral self-diffusion coefficient of the lipid molecules in leukemic cell membranes was almost double that in normal cell membranes. The calculated rotational and wobbling autocorrelation functions also indicated that the molecular motion of the lipids was enhanced in leukemic cell membranes. Thus, here we have demonstrated that the membranes of thymocyte leukemic cells are more disordered and more fluid than normal cell membranes. Copyright © 2013

  5. 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.

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

    SciTech Connect

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

    2016-01-15

    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.

  7. Physical aspects of heterogeneities in multi-component lipid membranes.

    PubMed

    Komura, Shigeyuki; Andelman, David

    2014-06-01

    Ever since the raft model for biomembranes has been proposed, the traditional view of biomembranes based on the fluid-mosaic model has been altered. In the raft model, dynamical heterogeneities in multi-component lipid bilayers play an essential role. Focusing on the lateral phase separation of biomembranes and vesicles, we review some of the most relevant research conducted over the last decade. We mainly refer to those experimental works that are based on physical chemistry approach, and to theoretical explanations given in terms of soft matter physics. In the first part, we describe the phase behavior and the conformation of multi-component lipid bilayers. After formulating the hydrodynamics of fluid membranes in the presence of the surrounding solvent, we discuss the domain growth-law and decay rate of concentration fluctuations. Finally, we review several attempts to describe membrane rafts as two-dimensional microemulsion.

  8. Modulation of a membrane lipid lamellar-nonlamellar phase transition by cationic lipids: A measure for transfection efficiency

    SciTech Connect

    Tenchov, Boris G; Wang, Li; Koynova, Rumiana; MacDonald, Robert C

    2010-01-18

    Synthetic cationic lipids can be used as DNA carriers and are regarded to be the most promising non-viral gene carriers. For this investigation, six novel phosphatidylcholine (PC) cationic derivatives with various hydrophobic moieties were synthesized and their transfection efficiencies for human umbilical artery endothelial cells (HUAEC) were determined. Three compounds with relatively short, myristoleoyl or myristelaidoyl 14:1 chains exhibited very high activity, exceeding by {approx}10 times that of the reference cationic derivative dioleoyl ethylPC (EDOPC). Noteworthy, cationic lipids with 14:1 hydrocarbon chains have not been tested as DNA carriers in transfection assays previously. The other three lipids, which contained oleoyl 18:1 and longer chains, exhibited moderate to weak transfection activity. Transfection efficiency was found to correlate strongly with the effect of the cationic lipids on the lamellar-to-inverted hexagonal, L{sub {alpha}} {yields} H{sub II}, phase conversion in dipalmitoleoyl phosphatidylethanolamine dispersions (DPoPE). X-ray diffraction on binary DPoPE/cationic lipid mixtures showed that the superior transfection agents eliminated the direct L{sub {alpha}} {yields} H{sub II} phase transition and promoted formation of an inverted cubic phase between the L{sub {alpha}} and H{sub II} phases. In contrast, moderate and weak transfection agents retained the direct L{sub {alpha}} {yields} H{sub II} transition but shifted to higher temperatures than that of pure DPoPE, and induced cubic phase formation at a later stage. On the basis of current models of lipid membrane fusion, promotion of a cubic phase by the high-efficiency agents may be considered as an indication that their high transfection activity results from enhanced lipoplex fusion with cellular membranes. The distinct, well-expressed correlation established between transfection efficiency of a cationic lipid and the way it modulates nonlamellar phase formation of a membrane lipid

  9. Membrane fluidity and the surface properties of the lipid bilayer: ESR experiment and computer simulation.

    PubMed

    Man, Dariusz; Olchawa, Ryszard; Kubica, Krystian

    2010-09-01

    Penetration of the liposome membranes formed in the gel phase from DPPC (DPPC liposomes) and in the liquid-crystalline phase from egg yolk lecithin (EYL liposomes) by the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) and 16 DOXYL (2-ethyl-2-(15-methoxy-oxopentadecyl)-4,4-dimethyl-3-oxazolidinyloxy) spin probes has been investigated. The penetration process was followed by 120 hours at 24(0)C, using the electron spin resonance (ESR) method. The investigation of the kinetics of the TEMPO probe building into the membranes of both types of liposomes revealed differences appearing 30 minutes after the start of the experiment. The number of TEMPO particles built into the EYL liposome membranes began to clearly rise, aiming asymptotically to a constant value after about 100 minutes, whereas the number of the TEMPO particles built into the DPPC liposome membranes was almost constant in time. The interpretation of the obtained experimental results was enriched with those of computer simulation, following the behavior of the polar heads (dipoles) of the lipid particles forming a lipid layer due to the change in the value of the model parameter, k, determining the mobility of the dipoles. The possibility of the formation of an irregular ordering of the polar part of lipid membranes was proved, which leads to the appearance of spaces filled with of water for k > 0.4. The appearance of these defects enables the penetration of the bilayer by the TEMPO particles. The limited mobility of lipid polar heads (k < 0.2) prevents the appearance of such areas facilitating the penetration of the lipid membrane by alien particles in the gel phase.

  10. Peroxidation of tobacco membrane lipids by the photosensitizing toxin, cercosporin.

    PubMed

    Daub, M E

    1982-06-01

    Cercosporin, a nonspecific toxin from Cercospora species, is a photosensitizing compound which rapidly kills plant cells in the light. Cell death appears to be due to a cercosporin-mediated peroxidation of membrane lipids. Tobacco leaf discs treated with cercosporin showed a large increase in electrolyte leakage 1 to 2 minutes after irradiation with light. All tobacco protoplasts exposed to cercosporin in the light were damaged within 45 minutes. Chloroform:methanol extracts of toxin-treated suspension cultures gave positive reactions for lipid hydroperoxides in the thiobarbituric acid test. Cercosporin-treated leaf discs emitted high concentrations of ethane 12 to 24 hours after incubation in the light. Cercosporin also oxidized solutions of methyl linolenate as determined by the thiobarbituric acid assay and the emission of ethane. alpha-Tocopherol had an inhibitory effect on the cercosporin-mediated lipid peroxidation.

  11. The HIV-1 Nucleocapsid Protein Recruits Negatively Charged Lipids To Ensure Its Optimal Binding to Lipid Membranes

    PubMed Central

    Kempf, Noémie; Postupalenko, Viktoriia; Bora, Saurabh; Didier, Pascal; Arntz, Youri; de Rocquigny, Hugues

    2014-01-01

    ABSTRACT The HIV-1 Gag polyprotein precursor composed of the matrix (MA), capsid (CA), nucleocapsid (NC), and p6 domains orchestrates virus assembly via interactions between MA and the cell plasma membrane (PM) on one hand and NC and the genomic RNA on the other hand. As the Gag precursor can adopt a bent conformation, a potential interaction of the NC domain with the PM cannot be excluded during Gag assembly at the PM. To investigate the possible interaction of NC with lipid membranes in the absence of any interference from the other domains of Gag, we quantitatively characterized by fluorescence spectroscopy the binding of the mature NC protein to large unilamellar vesicles (LUVs) used as membrane models. We found that NC, either in its free form or bound to an oligonucleotide, was binding with high affinity (∼107 M−1) to negatively charged LUVs. The number of NC binding sites, but not the binding constant, was observed to decrease with the percentage of negatively charged lipids in the LUV composition, suggesting that NC and NC/oligonucleotide complexes were able to recruit negatively charged lipids to ensure optimal binding. However, in contrast to MA, NC did not exhibit a preference for phosphatidylinositol-(4,5)-bisphosphate. These results lead us to propose a modified Gag assembly model where the NC domain contributes to the initial binding of the bent form of Gag to the PM. IMPORTANCE The NC protein is a highly conserved nucleic acid binding protein that plays numerous key roles in HIV-1 replication. While accumulating evidence shows that NC either as a mature protein or as a domain of the Gag precursor also interacts with host proteins, only a few data are available on the possible interaction of NC with lipid membranes. Interestingly, during HIV-1 assembly, the Gag precursor is thought to adopt a bent conformation where the NC domain may interact with the plasma membrane. In this context, we quantitatively characterized the binding of NC, as a free

  12. 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.

  13. Simulation of Nanoparticle Permeation through a Lipid Membrane

    PubMed Central

    Fiedler, Steven L.; Violi, Angela

    2010-01-01

    Abstract A metric of nanoparticle toxicity is the passive permeability rate through cellular membranes. To assess the influence of nanoparticle morphology on this process, the permeability of buckyball-sized molecules through a representative lipid bilayer was investigated by molecular-dynamics simulation. When C60 was compared with a prototypical opened C60 molecule and a representative combustion-generated particle, C68H29, the calculated free-energy profiles along the permeation coordinate revealed a sizable variation in form and depth. The orientation of the anisotropic molecules was determined by monitoring the principal axis corresponding to the largest moment of inertia, and free rotation was shown to be hindered in the bilayer interior. Diffusion constant values of the permeant molecules were calculated from a statistical average of seven to 10 trajectories at five locations along the permeation coordinate. A relatively minor variation of the values was observed in the bilayer interior; however, local resistance values spanned up to 24 orders of magnitude from the water layer to the bilayer center, due primarily to its exponential dependence on free energy. The permeability coefficient values calculated for the three similarly sized but structurally distinct nanoparticles showed a significant variance. The use of C60 to represent similarly sized carbonaceous nanoparticles for assessments of toxicity is questioned. PMID:20655842

  14. The membrane-induced structure of melittin is correlated with the fluidity of the lipids.

    PubMed

    Andersson, August; Biverståhl, Henrik; Nordin, Jon; Danielsson, Jens; Lindahl, Emma; Mäler, Lena

    2007-01-01

    The effect of the bee toxin melittin on DMPC dynamics in fast-tumbling bicelles has been investigated. The (13)C R(1) and (13)C-(1)H NOE relaxation parameters for DMPC were used to monitor the effect of melittin and cholesterol on lipid dynamics. It was found that melittin has the largest effect on the DMPC mobility in DMPC/DHPC bicelles, while less effect was observed in cholesterol-doped bicelles, or in bicelles made with CHAPS, indicating that the rigidity of the membrane affects the melittin-membrane interaction. CD spectra were analysed in terms of cooperativity of the alpha-helix to random coil transition in melittin, and these results also indicated similar differences between the bicelles. The study shows that bicelles can be used to investigate lipid dynamics by spin relaxation, and in particular of peptide-induced changes in membrane fluidity.

  15. Investigating cell membrane structure and dynamics with TCSPC-FLIM

    NASA Astrophysics Data System (ADS)

    Le Marois, Alix; Owen, Dylan M.; Suhling, Klaus

    2015-03-01

    We report the use of Time-Correlated Single Photon Counting (TCSPC) in a polarization-resolved Fluorescence Lifetime Imaging (FLIM) setup for the investigation of cell membrane structural and dynamic properties. This technique allows us to study the orientation and mobility of fluorescent membrane dyes, namely di-4-ANEPPDHQ and DiO, in model bilayers of different lipid compositions. Dipole alignment and extent of rotational motion can be linked to membrane order and fluidity. Comparison of the time-resolved anisotropy decays of the two fluorescent dyes suggests that rotational motion of membrane constituents is restricted in liquid-ordered phases, and appears to be limited to the region of aliphatic tails in liquid-disordered phases. In living cells, understanding the membrane structure provides crucial information on its functional properties, such as exo- and endocytosis, cell mobility and signal transduction.

  16. Lipid membrane-mediated attraction between curvature inducing objects

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    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.

  17. Lipid membrane-mediated attraction between curvature inducing objects

    PubMed Central

    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

  18. 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

  19. [The action of week inorganic acids and lower carboxylic acids on the conductivity of bilayer lipid membranes].

    PubMed

    Kilivnik, K E; Khmarskaia, L A; Ksenzhek, O S

    2009-01-01

    The ability of weak inorganic acids (H2S, HCN) and lower carboxylic acids to interact with bilayer lipid membranes, change their conductivity, and act as protonophores has been investigated. The mechanism of changes in BLM conductivity was studied. Factors influencing the interaction of acids with model lipid membranes were determined. Maximum changes in conductivity were observed at pH values equal to the dissociation constants of weak acids and depend on the coefficients of distribution "octanol-water".

  20. Protonation Dynamics on Lipid Nanodiscs: Influence of the Membrane Surface Area and External Buffers.

    PubMed

    Xu, Lei; Öjemyr, Linda Näsvik; Bergstrand, Jan; Brzezinski, Peter; Widengren, Jerker

    2016-05-10

    Lipid membrane surfaces can act as proton-collecting antennae, accelerating proton uptake by membrane-bound proton transporters. We investigated this phenomenon in lipid nanodiscs (NDs) at equilibrium on a local scale, analyzing fluorescence fluctuations of individual pH-sensitive fluorophores at the membrane surface by fluorescence correlation spectroscopy (FCS). The protonation rate of the fluorophores was ∼100-fold higher when located at 9- and 12-nm diameter NDs, compared to when in solution, indicating that the proton-collecting antenna effect is maximal already for a membrane area of ∼60 nm(2). Fluorophore-labeled cytochrome c oxidase displayed a similar increase when reconstituted in 12 nm NDs, but not in 9 nm NDs, i.e., an acceleration of the protonation rate at the surface of cytochrome c oxidase is found when the lipid area surrounding the protein is larger than 80 nm(2), but not when below 30 nm(2). We also investigated the effect of external buffers on the fluorophore proton exchange rates at the ND membrane-water interfaces. With increasing buffer concentrations, the proton exchange rates were found to first decrease and then, at millimolar buffer concentrations, to increase. Monte Carlo simulations, based on a simple kinetic model of the proton exchange at the membrane-water interface, and using rate parameter values determined in our FCS experiments, could reconstruct both the observed membrane-size and the external buffer dependence. The FCS data in combination with the simulations indicate that the local proton diffusion coefficient along a membrane is ∼100 times slower than that observed over submillimeter distances by proton-pulse experiments (Ds ∼ 10(-5)cm(2)/s), and support recent theoretical studies showing that proton diffusion along membrane surfaces is time- and length-scale dependent. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  1. Analytical solution of lipid membrane morphology subjected to boundary forces on the edges of rectangular membranes

    NASA Astrophysics Data System (ADS)

    Belay, T.; Kim, C. I.; Schiavone, P.

    2016-03-01

    We develop a complete analytical solution predicting the deformation of rectangular lipid membranes resulting from boundary forces acting on the perimeter of the membrane. The shape equation describing the equilibrium state of a lipid membrane is taken from the classical Helfrich model. A linearized version of the shape equation describing membrane morphology (within the Monge representation) is obtained via a limit of superposed incremental deformations. We obtain a complete analytical solution by reducing the corresponding problem to a single partial differential equation and by using Fourier series representations for various types of boundary forces. The solution obtained predicts smooth morphological transition over the domain of interest. Finally, we note that the methods used in our analysis are not restricted to the particular type of boundary conditions considered here and can accommodate a wide class of practical and important edge conditions.

  2. Novel tilt-curvature coupling in lipid membranes

    NASA Astrophysics Data System (ADS)

    Terzi, M. Mert; Deserno, Markus

    2017-08-01

    On mesoscopic scales, lipid membranes are well described by continuum theories whose main ingredients are the curvature of a membrane's reference surface and the tilt of its lipid constituents. In particular, Hamm and Kozlov [Eur. Phys. J. E 3, 323 (2000)] have shown how to systematically derive such a tilt-curvature Hamiltonian based on the elementary assumption of a thin fluid elastic sheet experiencing internal lateral pre-stress. Performing a dimensional reduction, they not only derive the basic form of the effective surface Hamiltonian but also express its emergent elastic couplings as trans-membrane moments of lower-level material parameters. In the present paper, we argue, though, that their derivation unfortunately missed a coupling term between curvature and tilt. This term arises because, as one moves along the membrane, the curvature-induced change of transverse distances contributes to the area strain—an effect that was believed to be small but nevertheless ends up contributing at the same (quadratic) order as all other terms in their Hamiltonian. We illustrate the consequences of this amendment by deriving the monolayer and bilayer Euler-Lagrange equations for the tilt, as well as the power spectra of shape, tilt, and director fluctuations. A particularly curious aspect of our new term is that its associated coupling constant is the second moment of the lipid monolayer's lateral stress profile—which within this framework is equal to the monolayer Gaussian curvature modulus, κ¯ m. On the one hand, this implies that many theoretical predictions now contain a parameter that is poorly known (because the Gauss-Bonnet theorem limits access to the integrated Gaussian curvature); on the other hand, the appearance of κ¯ m outside of its Gaussian curvature provenance opens opportunities for measuring it by more conventional means, for instance by monitoring a membrane's undulation spectrum at short scales.

  3. Steric confinement of proteins on lipid membranes can drive curvature and tubulation.

    PubMed

    Stachowiak, Jeanne C; Hayden, Carl C; Sasaki, Darryl Y

    2010-04-27

    Deformation of lipid membranes into curved structures such as buds and tubules is essential to many cellular structures including endocytic pits and filopodia. Binding of specific proteins to lipid membranes has been shown to promote membrane bending during endocytosis and transport vesicle formation. Additionally, specific lipid species are found to colocalize with many curved membrane structures, inspiring ongoing exploration of a variety of roles for lipid domains in membrane bending. However, the specific mechanisms by which lipids and proteins collaborate to induce curvature remain unknown. Here we demonstrate a new mechanism for induction and amplification of lipid membrane curvature that relies on steric confinement of protein binding on membrane surfaces. Using giant lipid vesicles that contain domains with high affinity for his-tagged proteins, we show that protein crowding on lipid domain surfaces creates a protein layer that buckles outward, spontaneously bending the domain into stable buds and tubules. In contrast to previously described bending mechanisms relying on local steric interactions between proteins and lipids (i.e. helix insertion into membranes), this mechanism produces tubules whose dimensions are defined by global parameters: domain size and membrane tension. Our results suggest the intriguing possibility that confining structures, such as lipid domains and protein lattices, can amplify membrane bending by concentrating the steric interactions between bound proteins. This observation highlights a fundamental physical mechanism for initiation and control of membrane bending that may help explain how lipids and proteins collaborate to create the highly curved structures observed in vivo.

  4. Fuel cell ion-exchange membrane investigation

    NASA Technical Reports Server (NTRS)

    Toy, M. S.

    1972-01-01

    The present deficiencies in the fluorocarbon sulfonic acid membrane used as the solid polymer electrolyte in the H2/O2 fuel cell are studied. Considered are: Adhesives selection, elastomeric formulations, scavenger exploration, and membrane characterization. The significant data are interpreted and recommendations are given for both short and long range further investigations in two of the four major areas: membrane adhesives and membrane stabilization.

  5. Spin-label studies on the anchoring and lipid-protein interactions of avidin with N-biotinylphosphatidylethanolamines in lipid bilayer membranes.

    PubMed

    Swamy, M J; Marsh, D

    1997-06-17

    The specific binding of hen egg white avidin to phosphatidylcholine lipid membranes containing spin-labeled N-biotinylphosphatidylethanolamines (biotin-PESLs) was investigated by using ESR spectroscopy. Spin-labeled biotin-PEs were prepared with the nitroxide group at position C-5, C-8, C-10, C-12, or C-14 of the sn-2 chain and were incorporated at 1 mol % in lipid bilayer membranes of dimyristoylphosphatidylcholine. Binding of avidin produced a strong and selective restriction of the biotin-PE lipid mobility at all positions of chain labeling, as shown by the ESR spectra recorded in the fluid lipid phase. The spectral components of the fraction of the biotin-PESLs that were not complexed by avidin indicated that the mobility of the bulk membrane lipids was unperturbed by binding avidin, as demonstrated by difference spectroscopy. Comparison of the positional profiles and temperature dependences of the outer hyperfine splittings from the biotin-PESLs suggests that the C-12 and C-14 positions of the avidin-bound biotin-PEs are in register with the C-5 and C-7/C-6 positions, respectively, of the chains of the bulk membrane lipids. This indicates that the biotin-PEs are partially withdrawn from the membrane, with a vertical displacement of ca. 7-8 A, on complexation with avidin. In addition, the specific lipid-protein interaction with avidin results in a selective reduction in the rates of lipid chain motion, as shown by the increased ESR line widths. These data define the way in which avidin is anchored to lipid membranes containing biotin-PEs.

  6. Anomalous surface diffusion of protons on lipid membranes.

    PubMed

    Wolf, Maarten G; Grubmüller, Helmut; Groenhof, Gerrit

    2014-07-01

    The cellular energy machinery depends on the presence and properties of protons at or in the vicinity of lipid membranes. To asses the energetics and mobility of a proton near a membrane, we simulated an excess proton near a solvated DMPC bilayer at 323 K, using a recently developed method to include the Grotthuss proton shuttling mechanism in classical molecular dynamics simulations. We obtained a proton surface affinity of -13.0 ± 0.5 kJ mol(-1). The proton interacted strongly with both lipid headgroup and linker carbonyl oxygens. Furthermore, the surface diffusion of the proton was anomalous, with a subdiffusive regime over the first few nanoseconds, followed by a superdiffusive regime. The time- and distance dependence of the proton surface diffusion coefficient within these regimes may also resolve discrepancies between previously reported diffusion coefficients. Our simulations show that the proton anomalous surface diffusion originates from restricted diffusion in two different surface-bound states, interrupted by the occasional bulk-mediated long-range surface diffusion. Although only a DMPC membrane was considered in this work, we speculate that the restrictive character of the on-surface diffusion is highly sensitive to the specific membrane conditions, which can alter the relative contributions of the surface and bulk pathways to the overall diffusion process. Finally, we discuss the implications of our findings for the energy machinery.

  7. Anomalous Surface Diffusion of Protons on Lipid Membranes

    PubMed Central

    Wolf, Maarten G.; Grubmüller, Helmut; Groenhof, Gerrit

    2014-01-01

    The cellular energy machinery depends on the presence and properties of protons at or in the vicinity of lipid membranes. To asses the energetics and mobility of a proton near a membrane, we simulated an excess proton near a solvated DMPC bilayer at 323 K, using a recently developed method to include the Grotthuss proton shuttling mechanism in classical molecular dynamics simulations. We obtained a proton surface affinity of −13.0 ± 0.5 kJ mol−1. The proton interacted strongly with both lipid headgroup and linker carbonyl oxygens. Furthermore, the surface diffusion of the proton was anomalous, with a subdiffusive regime over the first few nanoseconds, followed by a superdiffusive regime. The time- and distance dependence of the proton surface diffusion coefficient within these regimes may also resolve discrepancies between previously reported diffusion coefficients. Our simulations show that the proton anomalous surface diffusion originates from restricted diffusion in two different surface-bound states, interrupted by the occasional bulk-mediated long-range surface diffusion. Although only a DMPC membrane was considered in this work, we speculate that the restrictive character of the on-surface diffusion is highly sensitive to the specific membrane conditions, which can alter the relative contributions of the surface and bulk pathways to the overall diffusion process. Finally, we discuss the implications of our findings for the energy machinery. PMID:24988343

  8. Electrical resonance of Amphotericin B channel activity in lipidic membranes

    NASA Astrophysics Data System (ADS)

    Récamier, Karla S.; Ortega-Blake, Iván; Parmananda, P.

    2017-05-01

    In our previous work [J. Membrane Biol. 237, 31 (2010)], we showed the dependence of the time average conductance of Nystatin channels as a function of the applied potential. Specifically, it was observed that greater potential induced enhanced channel activity. This indicates that the supramolecular structure could be stabilized by a large field, possibly by giving a preferential orientation to the monomers. In the present work, we entertain the notion that the process of pore formation in the lipidic membranes has an underlying deterministic component. To verify this hypothesis, experiments were performed under potentio-dynamic conditions, i.e., a square train of pulses of different frequencies (0.05-2 Hz) were applied to a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine membrane having 30 mol. % cholesterol and the presence of 35 μM Amphotericin B. An emergence of a resonant frequency, in the present experiments, is tantamount to observing fingerprints of determinism in the activity of these channels in lipidic membranes.

  9. 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

  10. Analytical and computational studies of compositional lipid microdomains in bilayer membranes

    NASA Astrophysics Data System (ADS)

    Han, Tao

    In this dissertation, we both analytically and computationally investigate several dynamic problems related to compositional lipid microdomains in model bilayer membranes. We utilize continuum diffuse-interface methods as the computational framework, and develop the corresponding sharp interface limit equations to facilitate analytical derivations. The model possesses a complicated coupling structure, which involves not only the thermodynamic and frictional coupling between the two leaflets of the membrane, but also between the membrane itself and the solvent outside. In the compositional domain registration project, we investigate interleaflet thermodynamic and frictional coupling effects on both the recurrence of domain registration and shear flow driven domain de-registration dynamics. Analytical predictions for the approaching speed and threshold flow velocity are provided, accounting for both diffusive and advective transport mechanisms. It is proposed that these results would enable an experimental measurement of the interleaflet coupling strength. In the compositional interface fluctuation relaxation project, we consider the frictional coupling between both the two leaflets and between the membrane and solvent outside. For symmetric membranes, a general dispersion relation between decay rate versus wavenumber is derived. Various factors are incorporated in the analysis, including diffusive and advective lipid transport processes, inertia and viscosity of both membrane and solvent, and finite thickness of solvent. All previously considered scenarios naturally emerge as limiting cases of our more general result, and two new scenarios are obtained as well, which are solvent inertia dominated and membrane viscoelasticity dominated cases, respectively. For asymmetric membranes, a new scaling behavior is derived, due to the interleaflet friction effect. Finally, we explore the phase behaviors in spherical vesicles, under the thermodynamic coupling between membrane

  11. Partitioning of caffeine in lipid bilayers reduces membrane fluidity and increases membrane thickness.

    PubMed

    Khondker, Adree; Dhaliwal, Alexander; Alsop, Richard J; Tang, Jennifer; Backholm, Matilda; Shi, An-Chang; Rheinstädter, Maikel C

    2017-03-08

    Caffeine is a small amphiphilic molecule, which is widely consumed as a stimulant to prevent fatigue, but is also used as a common drug adjuvant in modern medicine. Here, we show that caffeine interacts with unsaturated lipid membranes made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). By combining X-ray diffraction and molecular dynamics simulations, we present evidence that caffeine partitions in lipid membranes and locates at the head group-tail group interface of the bilayers. By attracting water molecules from neighboring lipid molecules, it leads to the formation of "water pockets", i.e., a local increase of water density at this interface. Through this mechanism, caffeine leads to an overall decrease of the gauche defect density in the membranes and an increase of membrane thickness, indicating a loss of membrane fluidity. These non-specific membrane interactions may increase the efficacy of analgesic drugs through changes in the bioavailability and rate of metabolism of these drugs.

  12. Effects of the antimalarial drug primaquine on the dynamic structure of lipid model membranes.

    PubMed

    Basso, Luis G M; Rodrigues, Renata Z; Naal, Rose M Z G; Costa-Filho, Antonio J

    2011-01-01

    Primaquine (PQ) is a potent therapeutic agent used in the treatment of malaria and its mechanism of action still lacks a more detailed understanding at a molecular level. In this context, we used differential scanning calorimetry (DSC), pressure perturbation calorimetry (PPC), and electron spin resonance (ESR) to investigate the effects of PQ on the lipid phase transition, acyl chain dynamics, and on volumetric properties of lipid model membranes. DSC thermograms revealed that PQ stabilizes the fluid phase of the lipid model membranes and interacts mainly with the lipid headgroups. This result was revealed by the great effect on the pretransition of phosphatidylcholines and the destabilization of the inverted hexagonal phase of a phosphatidylethanolamine bilayer. Spin probes located at different positions along the lipid chain were used to monitor different membrane regions. ESR results indicated that PQ is effective in changing the acyl chain ordering and dynamics of the whole chain of dimyristoylphosphatidylcholine (DMPC) phospholipid in the rippled gel phase. The combined ESR and PPC results revealed that the slight DMPC volume changes at the main phase transition induced by the presence of PQ is probably due to a less dense lipid gel phase. At physiological pH, the cationic amphiphilic PQ strongly interacts with the lipid headgroup region of the bilayers, causing considerable disorganization in the hydrophobic core. These results shed light on the molecular mechanism of primaquine-lipid interaction, which may be useful in the understanding of the complex mechanism of action and/or the adverse effects of this antimalarial drug. Copyright © 2010 Elsevier B.V. All rights reserved.

  13. Phosphatidylserine lipids and membrane order precisely regulate the activity of Polybia-MP1 peptide.

    PubMed

    Alvares, Dayane S; Neto, João Ruggiero; Ambroggio, Ernesto E

    2017-03-05

    Polybia-MP1 (IDWKKLLDAAKQIL-NH2) is a lytic peptide from the Brazilian wasp venom with known anti-cancer properties. Previous evidence indicates that phosphatidylserine (PS) lipids are relevant for the lytic activity of MP1. In agreement with this requirement, phosphatidylserine lipids are translocated to the outer leaflet of cells, and are available for MP1 binding, depending on the presence of liquid-ordered domains. Here, we investigated the effect of PS on MP1 activity when this lipid is reconstituted in membranes of giant or large liposomes with different lipid-phase states. By monitoring the membrane and soluble luminal content of giant unilamellar vesicles (GUVs), using fluorescence confocal microscopy, we were able to determine that MP1 has a pore-forming activity at the membrane level. Liquid-ordered domains, which were phase-separated within the membrane of GUVs, influenced the pore-forming activity of MP1. Experiments evaluating the membrane-binding and lytic activity of MP1 on large unilamellar vesicles (LUVs), with the same lipid composition as GUVs, demonstrated that there was synergy between liquid-ordered domains and PS, which enhanced both activities. Based on our findings, we propose that the physicochemical properties of cancer cell membranes, which possess a much higher concentration of PS than normal cells, renders them susceptible to MP1 binding and lytic pore formation. These results can be correlated with MP1's potent and selective anti-cancer activity and pave the way for future research to develop cancer therapies that harness and exploit the properties of MP1.

  14. Ultraviolet- and sunlight-induced lipid peroxidation in liposomal membrane

    SciTech Connect

    Mandal, T.K.; Chatterjee, S.N.

    1980-08-01

    Ultraviolet radiation and sunlight caused lipid peroxidation in the liposomal membrane (as detected by measurement of the oxidation index, A/sub 233//A/sub 215/, and the amount of malondialdehyde formed) and made the membrane leaky (as revealed by the release of the trapped chromate anions). The oxidation index and the formation of malondialdehyde increased linearly with increasing dose of radiation and depended significantly on the dose rate. The effects were smaller in liposomes derived from Vibrio cholerae phospholipid than in those derived from egg lecithin. The effects of the radiation dose and dose rate on hemolysis and peroxidation (MDA formation) of the erythrocyte membrane followed a similar pattern. A direct correlation between the percentage leakage of chromate (Y) and the oxidation index (X) of the liposomal system was obtained as Y = 236.5 x X.

  15. Elasto-plasticity in wrinkled polymerized lipid membranes

    NASA Astrophysics Data System (ADS)

    Chaieb, Sahraoui

    2014-01-01

    Biomembranes shown to behave like elastic sheets, can also suffer plastic deformations. Neutron scattering experiments on partially polymerised wrinkled membranes revealed that when a critical degree of polymerisation is crossed, the wrinkled membranes do not resume their spherical shapes. Instead they remain wrinkled and rigid while their non-polymerised counterparts resume their spherical floppy shapes. The yield stress of these membranes, measured for the first time via the fractal dimension, is intimately related to the degree of polymerisation probably through a 2D disorder that quenches the lateral diffusion of the lipid molecules. This work might shed light on the physical reason behind the irreversible deformation of echinocytes, acanthocytes and malaria infected red blood cells.

  16. 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.

  17. Microfluidic Generation of Lipidic Mesophases for Membrane Protein Crystallization

    SciTech Connect

    Perry, S.; Roberts, G; Tice, J; Gennis, R; Kenis, P

    2009-01-01

    We report on a microfluidic method for the formation of aqueous/lipid mesophases to enable screening of suitable crystallization conditions of membrane proteins from a membrane-like phase in sub-20 nL volumes. This integrated microfluidic chip and the employed mixing strategy address the specific challenges associated with the mixing of fluids of highly different viscosities (here a factor of 30) as well as the non-Newtonian character of the resulting mesophases. The chip requires less than 20 nL of material per condition screened, whereas typically on the order of 10 {micro}L or more is needed for a batch preparation in the present screening methods. We validated our approach with the successful crystallization of the membrane protein bacteriorhodopsin.

  18. Lipid bilayer thickness determines cholesterol's location in model membranes

    DOE PAGES

    Marquardt, Drew; Heberle, Frederick A.; Greathouse, Denise V.; ...

    2016-10-11

    Cholesterol is an essential biomolecule of animal cell membranes, and an important precursor for the biosynthesis of certain hormones and vitamins. It is also thought to play a key role in cell signaling processes associated with functional plasma membrane microdomains (domains enriched in cholesterol), commonly referred to as rafts. In all of these diverse biological phenomena, the transverse location of cholesterol in the membrane is almost certainly an important structural feature. Using a combination of neutron scattering and solid-state 2H NMR, we have determined the location and orientation of cholesterol in phosphatidylcholine (PC) model membranes having fatty acids of differentmore » lengths and degrees of unsaturation. The data establish that cholesterol reorients rapidly about the bilayer normal in all the membranes studied, but is tilted and forced to span the bilayer midplane in the very thin bilayers. The possibility that cholesterol lies flat in the middle of bilayers, including those made from PC lipids containing polyunsaturated fatty acids (PUFAs), is ruled out. Finally, these results support the notion that hydrophobic thickness is the primary determinant of cholesterol's location in membranes.« less

  19. Lipid bilayer thickness determines cholesterol's location in model membranes

    SciTech Connect

    Marquardt, Drew; Heberle, Frederick A.; Greathouse, Denise V.; Koeppe, II, Roger E.; Standaert, Robert F.; Van Oosten, Brad J.; Harroun, Thad A.; Kinnun, Jacob J.; Williams, Justin A.; Wassall, Stephen R.; Katsaras, John

    2016-10-11

    Cholesterol is an essential biomolecule of animal cell membranes, and an important precursor for the biosynthesis of certain hormones and vitamins. It is also thought to play a key role in cell signaling processes associated with functional plasma membrane microdomains (domains enriched in cholesterol), commonly referred to as rafts. In all of these diverse biological phenomena, the transverse location of cholesterol in the membrane is almost certainly an important structural feature. Using a combination of neutron scattering and solid-state 2H NMR, we have determined the location and orientation of cholesterol in phosphatidylcholine (PC) model membranes having fatty acids of different lengths and degrees of unsaturation. The data establish that cholesterol reorients rapidly about the bilayer normal in all the membranes studied, but is tilted and forced to span the bilayer midplane in the very thin bilayers. The possibility that cholesterol lies flat in the middle of bilayers, including those made from PC lipids containing polyunsaturated fatty acids (PUFAs), is ruled out. Finally, these results support the notion that hydrophobic thickness is the primary determinant of cholesterol's location in membranes.

  20. Specific Lipid Binding of Membrane Proteins in Detergent Micelles Characterized by NMR and Molecular Dynamics.

    PubMed

    Zhao, Linlin; Wang, Shuqing; Run, Changqing; OuYang, Bo; Chou, James J

    2016-09-27

    Many membrane proteins bind specifically to lipids as an integral component of their structures. The ability of detergents to support lipid binding is thus an important consideration when solubilizing membrane proteins for structural studies. In particular, the zwitterionic phosphocholine (PC)-based detergents, which have been widely used in solution NMR studies of channels and transporters, are controversial because of their strong solubilization power and thus perceived as more denaturing than nonionic detergents such as the maltosides. Here, we investigate the ability of the mitochondrial ADP/ATP carrier (AAC) to specifically bind cardiolipin, a mitochondrial lipid important for the carrier function, in dodecylphosphocholine (DPC) micelles. We found that in DPC, the AAC specifically binds cardiolipin in a manner consistent with the bound cardiolipins found in the crystal structures of the AAC determined in n-decyl β-d-maltoside. Our results suggest that PC detergent is compatible with specific lipid binding and that PC detergent mixed with the relevant lipid represents a viable solubilization system for NMR studies of membrane proteins.

  1. Structural Diversity of the Membrane Core Lipids of Extreme Halophiles.

    PubMed

    Morita, M; Yamauchi, N; Eguchi, T; Kakinuma, K

    1998-01-01

    The structural diversity of the core lipids of extreme halophiles Haloarcula japonica and Halobacterium halobium was investigated. The most significant difference is that Ha. japonica contains sn-2,3-di-O-phytanylglycerol exclusively as the core lipid, whereas Hb. halobium contains both sn-2,3-di-O-phytanylglycerol and sn-2-O-sesterterpanyl (3,7,11,15,19-pentamethyleicosanyl)-3-O-phytanylglycerol.

  2. Quantitative characterization of the lateral distribution of membrane proteins within the lipid bilayer.

    PubMed Central

    Freire, E; Snyder, B

    1982-01-01

    The dependence of the lateral distribution of membrane proteins on the size, protein/lipoid molar ratio, and the magnitude of the interaction potentials has been investigated by computer modeling protein-lipid distributions with Monte Carlo calculations. These results have allowed us to develop a quantitative characterization of the distribution of membrane proteins and to correlate these distributions with experimental observables. The topological arrangement of protein domains, protein plus annular lipid domains, and free lipid domains is described in terms of radial distribution, pair connectedness, and cluster distribution functions. The radial distribution functions are used to measure the distribution of intermolecular distances between protein molecules, whereas the pair connectedness functions are used to estimate the physical extension of compositional domains. It is shown that, at characteristic protein/lipid molar ratios, previously isolated domains become connected, forming domain networks that extend over the entire membrane surface. These changes in the lateral connectivity of compositional domains are paralleled by changes in the calculated lateral diffusion coefficients and might have important implications for the regulation of diffusion controlled processes within the membrane. PMID:7074188

  3. Partitioning of exogenous delta-tocopherol between the triacylglycerol and membrane lipid fractions of chicken muscle.

    PubMed

    Sigfusson, Halldor; Hultin, Herbert O

    2002-11-20

    The partitioning of exogenous delta-tocopherol, added dissolved in ethanol, between the neutral triacylglycerols and membranes of chicken leg muscles was investigated. The two lipid fractions were separated using differential ultracentrifugation techniques. Triacylglycerols were obtained after high-speed centrifugation of the minced muscle at 130000 g for 30 min. Membranes were collected from a muscle-buffer homogenate (pH 7.5) between 10000 g for 20 min and 130000 g for 30 min. The triacylglycerols collected represented from 15 to 80% of the total triacylglycerols of the minced muscle, the yields increasing with increasing muscle triacylglycerol content. The phospholipids in the isolated membrane fraction represented from 20 to 35% of the total phospholipids of the muscle. At low muscle total lipid contents (3-5%), the added delta-tocopherol was present in approximately the same concentration in both muscle lipid fractions. At higher total lipid contents, achieved by adding exogenous triacylglycerols, the delta-tocopherol concentration in the membranes increased relative to that in the triacylglycerols.

  4. 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

  5. Effect of primycin on monovalent cation transport of erythrocyte membrane and lipid bilayer.

    PubMed

    Blaskó, K; Györgyi, S; Horváth, I

    1979-04-01

    The effects of primycin were investigated on the alkali-cation transport of human erythrocytes and on the electric conduction of bimolecular lipid membranes. In the concentration range of 3.10(-6) approximately 10(-5) M primycin increased the permeability of erythrocytes to alkali-cations according to the sequences Cs+ greater than Rb+ approximately K+ greater than Na+, while the conductance of the negatively charged phosphatidylserine bimolecular lipid membrane increased by 2 approximately 3 orders of magnitude. The resistance-lowering effect of primycin strongly depended on the cationic species applied and a selectivity order Na+ greater than K+ greater than Rb+ greater than Cs+ was found. A possible mechanism of the primycin-membrane interaction is suggested on the basis of experimental data.

  6. Modeling the phase separation in binary lipid membrane under externally imposed oscillatory shear flow.

    PubMed

    Chen, Xiao-Bo; Niu, Li-Sha; Shi, Hui-Ji

    2008-09-01

    By adding external velocity terms, the two-dimensional time-dependent Ginzburg-Landau (TDGL) equations are modified. Based on this, the phase separation in binary lipid membrane under externally imposed oscillatory shear flow is numerically modeled employing the Cell Dynamical System (CDS) approach. Considering shear flows with different frequencies and amplitudes, several aspects of such a phase evolving process are studied. Firstly, visualized results are shown via snapshot figures of the membrane shape. And then, the simulated scattering patterns at typical moments are presented. Furthermore, in order to more quantitatively discuss this phase-separation process, the time growth laws of the characteristic domain sizes in both directions parallel and perpendicular to the flow are investigated for each case. Finally, the peculiar rheological properties of such binary lipid membrane system have been discussed, mainly the normal stress difference and the viscoelastic complex shear moduli.

  7. Area per lipid and cholesterol interactions in membranes from separated local-field (13)C NMR spectroscopy.

    PubMed

    Leftin, Avigdor; Molugu, Trivikram R; Job, Constantin; Beyer, Klaus; Brown, Michael F

    2014-11-18

    Investigations of lipid membranes using NMR spectroscopy generally require isotopic labeling, often precluding structural studies of complex lipid systems. Solid-state (13)C magic-angle spinning NMR spectroscopy at natural isotopic abundance gives site-specific structural information that can aid in the characterization of complex biomembranes. Using the separated local-field experiment DROSS, we resolved (13)C-(1)H residual dipolar couplings that were interpreted with a statistical mean-torque model. Liquid-disordered and liquid-ordered phases were characterized according to membrane thickness and average cross-sectional area per lipid. Knowledge of such structural parameters is vital for molecular dynamics simulations, and provides information about the balance of forces in membrane lipid bilayers. Experiments were conducted with both phosphatidylcholine (dimyristoylphosphatidylcholine (DMPC) and palmitoyloleoylphosphatidylcholine (POPC)) and egg-yolk sphingomyelin (EYSM) lipids, and allowed us to extract segmental order parameters from the (13)C-(1)H residual dipolar couplings. Order parameters were used to calculate membrane structural quantities, including the area per lipid and bilayer thickness. Relative to POPC, EYSM is more ordered in the ld phase and experiences less structural perturbation upon adding 50% cholesterol to form the lo phase. The loss of configurational entropy is smaller for EYSM than for POPC, thus favoring its interaction with cholesterol in raftlike lipid systems. Our studies show that solid-state (13)C NMR spectroscopy is applicable to investigations of complex lipids and makes it possible to obtain structural parameters for biomembrane systems where isotope labeling may be prohibitive.

  8. Distinguishing Bicontinuous Lipid Cubic Phases from Isotropic Membrane Morphologies Using 31P Solid-State NMR Spectroscopy

    PubMed Central

    Yang, Yu; Yao, Hongwei

    2015-01-01

    Nonlamellar lipid membranes are frequently induced by proteins that fuse, bend, and cut membranes. Understanding the mechanism of action of these proteins requires the elucidation of the membrane morphologies that they induce. While hexagonal phases and lamellar phases are readily identified by their characteristic solid-state NMR lineshapes, bicontinuous lipid cubic phases are more difficult to discern, since the static NMR spectra of cubic-phase lipids consist of an isotropic 31P or 2H peak, indistinguishable from the spectra of isotropic membrane morphologies such as micelles and small vesicles. To date, small-angle X-ray scattering is the only method to identify bicontinuous lipid cubic phases. To explore unique NMR signatures of lipid cubic phases, we first describe the orientation distribution of lipid molecules in cubic phases and simulate the static 31P chemical shift lineshapes of oriented cubic-phase membranes in the limit of slow lateral diffusion. We then show that 31P T2 relaxation times differ significantly between isotropic micelles and cubic-phase membranes: the latter exhibit two-orders-of magnitude shorter T2 relaxation times. These differences are explained by the different timescales of lipid lateral diffusion on the cubic-phase surface versus the timescales of micelle tumbling. Using this relaxation NMR approach, we investigated a DOPE membrane containing the transmembrane domain (TMD) of a viral fusion protein. The static 31P spectrum of DOPE shows an isotropic peak, whose T2 relaxation times correspond to that of a cubic phase. Thus, the viral fusion protein TMD induces negative Gaussian curvature, which is an intrinsic characteristic of cubic phases, to the DOPE membrane. This curvature induction has important implications to the mechanism of virus-cell fusion. This study establishes a simple NMR diagnostic probe of lipid cubic phases, which is expected to be useful for studying many protein-induced membrane remodeling phenomena in biology

  9. Chemical and structural investigation of lipid nanoparticles: drug-lipid interaction and molecular distribution

    NASA Astrophysics Data System (ADS)

    Anantachaisilp, Suranan; Meejoo Smith, Siwaporn; Treetong, Alongkot; Pratontep, Sirapat; Puttipipatkhachorn, Satit; Rungsardthong Ruktanonchai, Uracha

    2010-03-01

    Lipid nanoparticles are a promising alternative to existing carriers in chemical or drug delivery systems. A key challenge is to determine how chemicals are incorporated and distributed inside nanoparticles, which assists in controlling chemical retention and release characteristics. This study reports the chemical and structural investigation of γ-oryzanol loading inside a model lipid nanoparticle drug delivery system composed of cetyl palmitate as solid lipid and Miglyol 812® as liquid lipid. The lipid nanoparticles were prepared by high pressure homogenization at varying liquid lipid content, in comparison with the γ-oryzanol free systems. The size of the lipid nanoparticles, as measured by the photon correlation spectroscopy, was found to decrease with increased liquid lipid content from 200 to 160 nm. High-resolution proton nuclear magnetic resonance (1H-NMR) measurements of the medium chain triglyceride of the liquid lipid has confirmed successful incorporation of the liquid lipid in the lipid nanoparticles. Differential scanning calorimetric and powder x-ray diffraction measurements provide complementary results to the 1H-NMR, whereby the crystallinity of the lipid nanoparticles diminishes with an increase in the liquid lipid content. For the distribution of γ-oryzanol inside the lipid nanoparticles, the 1H-NMR revealed that the chemical shifts of the liquid lipid in γ-oryzanol loaded systems were found at rather higher field than those in γ-oryzanol free systems, suggesting incorporation of γ-oryzanol in the liquid lipid. In addition, the phase-separated structure was observed by atomic force microscopy for lipid nanoparticles with 0% liquid lipid, but not for lipid nanoparticles with 5 and 10% liquid lipid. Raman spectroscopic and mapping measurements further revealed preferential incorporation of γ-oryzanol in the liquid part rather than the solid part of in the lipid nanoparticles. Simple models representing the distribution of γ-oryzanol and

  10. β2-Microglobulin Amyloid Fibril-Induced Membrane Disruption Is Enhanced by Endosomal Lipids and Acidic pH

    PubMed Central

    Goodchild, Sophia C.; Sheynis, Tania; Thompson, Rebecca; Tipping, Kevin W.; Xue, Wei-Feng; Ranson, Neil A.; Beales, Paul A.; Hewitt, Eric W.; Radford, Sheena E.

    2014-01-01

    Although the molecular mechanisms underlying the pathology of amyloidoses are not well understood, the interaction between amyloid proteins and cell membranes is thought to play a role in several amyloid diseases. Amyloid fibrils of β2-microglobulin (β2m), associated with dialysis-related amyloidosis (DRA), have been shown to cause disruption of anionic lipid bilayers in vitro. However, the effect of lipid composition and the chemical environment in which β2m-lipid interactions occur have not been investigated previously. Here we examine membrane damage resulting from the interaction of β2m monomers and fibrils with lipid bilayers. Using dye release, tryptophan fluorescence quenching and fluorescence confocal microscopy assays we investigate the effect of anionic lipid composition and pH on the susceptibility of liposomes to fibril-induced membrane damage. We show that β2m fibril-induced membrane disruption is modulated by anionic lipid composition and is enhanced by acidic pH. Most strikingly, the greatest degree of membrane disruption is observed for liposomes containing bis(monoacylglycero)phosphate (BMP) at acidic pH, conditions likely to reflect those encountered in the endocytic pathway. The results suggest that the interaction between β2m fibrils and membranes of endosomal origin may play a role in the molecular mechanism of β2m amyloid-associated osteoarticular tissue destruction in DRA. PMID:25100247

  11. Genetic analysis of Arabidopsis mutants impaired in plastid lipid import reveals a role of membrane lipids in chloroplast division.

    PubMed

    Fan, Jilian; Xu, Changcheng