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Sample records for pure lipid bilayers

  1. Structure of lipid bilayers

    PubMed Central

    Nagle, John F.; Tristram-Nagle, Stephanie

    2009-01-01

    The quantitative experimental uncertainty in the structure of fully hydrated, biologically relevant, fluid (Lα) phase lipid bilayers has been too large to provide a firm base for applications or for comparison with simulations. Many structural methods are reviewed including modern liquid crystallography of lipid bilayers that deals with the fully developed undulation fluctuations that occur in the Lα phase. These fluctuations degrade the higher order diffraction data in a way that, if unrecognized, leads to erroneous conclusions regarding bilayer structure. Diffraction measurements at high instrumental resolution provide a measure of these fluctuations. In addition to providing better structural determination, this opens a new window on interactions between bilayers, so the experimental determination of interbilayer interaction parameters is reviewed briefly. We introduce a new structural correction based on fluctuations that has not been included in any previous studies. Updated measurements, such as for the area compressibility modulus, are used to provide adjustments to many of the literature values of structural quantities. Since the gel (Lβ′) phase is valuable as a stepping stone for obtaining fluid phase results, a brief review is given of the lower temperature phases. The uncertainty in structural results for lipid bilayers is being reduced and best current values are provided for bilayers of five lipids. PMID:11063882

  2. Immobilized lipid-bilayer materials

    DOEpatents

    Sasaki, Darryl Y.; Loy, Douglas A.; Yamanaka, Stacey A.

    2000-01-01

    A method for preparing encapsulated lipid-bilayer materials in a silica matrix comprising preparing a silica sol, mixing a lipid-bilayer material in the silica sol and allowing the mixture to gel to form the encapsulated lipid-bilayer material. The mild processing conditions allow quantitative entrapment of pre-formed lipid-bilayer materials without modification to the material's spectral characteristics. The method allows for the immobilization of lipid membranes to surfaces. The encapsulated lipid-bilayer materials perform as sensitive optical sensors for the detection of analytes such as heavy metal ions and can be used as drug delivery systems and as separation devices.

  3. Cholesterol's location in lipid bilayers.

    PubMed

    Marquardt, Drew; Kučerka, Norbert; Wassall, Stephen R; Harroun, Thad A; Katsaras, John

    2016-09-01

    It is well known that cholesterol modifies the physical properties of lipid bilayers. For example, the much studied liquid-ordered Lo phase contains rapidly diffusing lipids with their acyl chains in the all trans configuration, similar to gel phase bilayers. Moreover, the Lo phase is commonly associated with cholesterol-enriched lipid rafts, which are thought to serve as platforms for signaling proteins in the plasma membrane. Cholesterol's location in lipid bilayers has been studied extensively, and it has been shown - at least in some bilayers - to align differently from its canonical upright orientation, where its hydroxyl group is in the vicinity of the lipid-water interface. In this article we review recent works describing cholesterol's location in different model membrane systems with emphasis on results obtained from scattering, spectroscopic and molecular dynamics studies. PMID:27056099

  4. Cholesterol's location in lipid bilayers

    DOE PAGESBeta

    Marquardt, Drew; Kučerka, Norbert; Wassall, Stephen R.; Harroun, Thad A.; Katsaras, John

    2016-04-04

    It is well known that cholesterol modifies the physical properties of lipid bilayers. For example, the much studied liquid-ordered Lo phase contains rapidly diffusing lipids with their acyl chains in the all trans configuration, similar to gel phase bilayers. Moreover, the Lo phase is commonly associated with cholesterol-enriched lipid rafts, which are thought to serve as platforms for signaling proteins in the plasma membrane. Cholesterol's location in lipid bilayers has been studied extensively, and it has been shown – at least in some bilayers – to align differently from its canonical upright orientation, where its hydroxyl group is in themore » vicinity of the lipid–water interface. In this study we review recent works describing cholesterol's location in different model membrane systems with emphasis on results obtained from scattering, spectroscopic and molecular dynamics studies.« less

  5. Lipid bilayers on nano-templates

    DOEpatents

    Noy, Aleksandr; Artyukhin, Alexander B.; Bakajin, Olgica; Stoeve, Pieter

    2009-08-04

    A lipid bilayer on a nano-template comprising a nanotube or nanowire and a lipid bilayer around the nanotube or nanowire. One embodiment provides a method of fabricating a lipid bilayer on a nano-template comprising the steps of providing a nanotube or nanowire and forming a lipid bilayer around the polymer cushion. One embodiment provides a protein pore in the lipid bilayer. In one embodiment the protein pore is sensitive to specific agents

  6. Investigating the Structure of Multicomponent Gel-Phase Lipid Bilayers.

    PubMed

    Hartkamp, Remco; Moore, Timothy C; Iacovella, Christopher R; Thompson, Michael A; Bulsara, Pallav A; Moore, David J; McCabe, Clare

    2016-08-23

    Single- and multicomponent lipid bilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC), 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC), isostearyl isostearate, and heptadecanoyl heptadecanoate in the gel phase are studied via molecular dynamics simulations. It is shown that the structural properties of multicomponent bilayers can deviate strongly from the structures of their single-component counterparts. Specifically, the lipid mixtures are shown to adopt a compact packing by offsetting the positioning depths at which different lipid species are located in the bilayer. This packing mechanism affects the area per lipid, the bilayer height, and the chain tilt angles and has important consequences for other bilayer properties, such as interfacial hydrogen bonding and bilayer permeability. In particular, the simulations suggest that bilayers containing isostearyl isostearate or heptadecanoyl heptadecanoate are less permeable than pure 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine or DSPC bilayers. Furthermore, hydrogen-bond analysis shows that the residence times of lipid-water hydrogen bonds depend strongly on the bilayer composition, with longer residence times for bilayers that have a higher DSPC content. The findings illustrate and explain the fundamental differences between the properties of single- and multicomponent bilayers. PMID:27558724

  7. Multiscale Modeling of Heterogeneous Lipid Bilayers

    NASA Astrophysics Data System (ADS)

    Faller, Roland; Bennun-Serrano, Sandra; Dickey, Allison

    2005-03-01

    The first line of defense for a cell against intrusive molecules is the membrane which must be resilient to prevent unwanted molecules from passing through as a change in the intracellular ion balance could be detrimental. Experimentally, it has been shown that as chain length and concentration of alcohols near a membrane increase, the area per lipid expands, increasing the likelihood of permeation. Additionally, there is evidence for pattern formation in cell membranes due to the presence of various lipids. These patterns or rafts are believed to play important roles in cell signaling. Here, we use MD to study the interactions between alcohols and pure lipid bilayers as well as pattern formation in mixed membranes using atomistic and coarse-grained models. We characterize the effect of alcohol chain-length and concentration on the lipid bilayer through area per head group, order parameter, and density profile. We also examine the effects of lipid-alcohol interactions on membrane curvature with the CG model and find satisfactory system representation. We use a mixture of DLPC and DSPC as model system for phase separation. Different concentrations and temperatures are used to reproduce phase transitions. We obtain agreement with experiments for area per lipid head group and deuterium order parameter. At high DSPC concentrations phase separation into a gel and liquid state is found. Simulations confirm that increasing DLPC concentrations lower the transition temperature.

  8. Cholesterol Perturbs Lipid Bilayers Nonuniversally

    SciTech Connect

    Pan Jianjun; Mills, Thalia T.; Tristram-Nagle, Stephanie; Nagle, John F.

    2008-05-16

    Cholesterol is well known to modulate the physical properties of biomembranes. Using modern x-ray scattering methods, we have studied the effects of cholesterol on the bending modulus K{sub C}, the thickness D{sub HH}, and the orientational order parameter S{sub xray} of lipid bilayers. We find that the effects are different for at least three classes of phospholipids characterized by different numbers of saturated hydrocarbon chains. Most strikingly, cholesterol strongly increases K{sub C} when both chains of the phospholipid are fully saturated but not at all when there are two monounsaturated chains.

  9. Lipid mobility in supported lipid bilayers by single molecule tracking

    NASA Astrophysics Data System (ADS)

    Kohram, Maryam; Shi, Xiaojun; Smith, Adam

    2015-03-01

    Phospholipid bilayers are the main component of cell membranes and their interaction with biomolecules in their immediate environment is critical for cellular functions. These interactions include the binding of polycationic polymers to lipid bilayers which affects many cell membrane events. As an alternative method of studying live cell membranes, we assemble a supported lipid bilayer and investigate its binding with polycationic polymers in vitro by fluorescently labeling the molecules of the supported lipid bilayer and tracking their mobility. In this work, we use single molecule tracking total internal reflection fluorescence microscopy (TIRF) to study phosphatidylinositol phosphate (PIP) lipids with and without an adsorbed polycationic polymer, quaternized polyvinylpyridine (QPVP). Individual molecular trajectories are obtained from the experiment, and a Brownian diffusion model is used to determine diffusion coefficients through mean square displacements. Our results indicate a smaller diffusion coefficient for the supported lipid bilayers in the presence of QPVP in comparison to its absence, revealing that their binding causes a decrease in lateral mobility.

  10. Lipid domains in supported lipid bilayer for atomic force microscopy.

    PubMed

    Lin, Wan-Chen; Blanchette, Craig D; Ratto, Timothy V; Longo, Marjorie L

    2007-01-01

    Phase-separated supported lipid bilayers have been widely used to study the phase behavior of multicomponent lipid mixtures. One of the primary advantages of using supported lipid bilayers is that the two-dimensional platform of this model membrane system readily allows lipid-phase separation to be characterized by high-resolution imaging techniques such as atomic force microscopy (AFM). In addition, when supported lipid bilayers have been functionalized with a specific ligand, protein-membrane interactions can also be imaged and characterized through AFM. It has been recently demonstrated that when the technique of vesicle fusion is used to prepare supported lipid bilayers, the thermal history of the vesicles before deposition and the supported lipid bilayers after formation will have significant effects on the final phase-separated domain structures. In this chapter, three methods of vesicle preparations as well as three deposition conditions will be presented. Also, the techniques and strategies of using AFM to image multicomponent phase-separated supported lipid bilayers and protein binding will be discussed. PMID:17951756

  11. Lipid Bilayers Covalently Anchored to Carbon Nanotubes

    PubMed Central

    Dayani, Yasaman; Malmstadt, Noah

    2012-01-01

    The unique physical and electrical properties of carbon nanotubes make them an exciting material for applications in various fields such as bioelectronics and biosensing. Due to the poor water solubility of carbon nanotubes, functionalization for such applications has been a challenge. Of particular need are functionalization methods for integrating carbon nanotubes with biomolecules and constructing novel hybrid nanostructures for bionanoelectronic applications. We present a novel method for the fabrication of dispersible, biocompatible carbon nanotube-based materials. Multi-walled carbon nanotubes (MWCNTs) are covalently modified with primary amine-bearing phospholipids in a carbodiimide-activated reaction. These modified carbon nanotubes have good dispersibility in nonpolar solvents. Fourier transform infrared (FTIR) spectroscopy shows peaks attributable to the formation of amide bonds between lipids and the nanotube surface. Simple sonication of lipid-modified nanotubes with other lipid molecules leads to the formation of a uniform lipid bilayer coating the nanotubes. These bilayer-coated nanotubes are highly dispersible and stable in aqueous solution. Confocal fluorescence microscopy shows labeled lipids on the surface of bilayer-modified nanotubes. Transmission electron microscopy (TEM) shows the morphology of dispersed bilayer-coated MWCNTs. Fluorescence quenching of lipid-coated MWCNTs confirms the bilayer configuration of the lipids on the nanotube surface and fluorescence anisotropy measurements show that the bilayer is fluid above the gel-to-liquid transition temperature. The membrane protein α-hemolysin spontaneously inserts into the MWCNT-supported bilayer, confirming the biomimetic membrane structure. These biomimetic nanostructures are a promising platform for the integration of carbon nanotube-based materials with biomolecules. PMID:22568448

  12. Alcohol's Effects on Lipid Bilayer Properties

    PubMed Central

    Ingólfsson, Helgi I.; Andersen, Olaf S.

    2011-01-01

    Alcohols are known modulators of lipid bilayer properties. Their biological effects have long been attributed to their bilayer-modifying effects, but alcohols can also alter protein function through direct protein interactions. This raises the question: Do alcohol's biological actions result predominantly from direct protein-alcohol interactions or from general changes in the membrane properties? The efficacy of alcohols of various chain lengths tends to exhibit a so-called cutoff effect (i.e., increasing potency with increased chain length, which that eventually levels off). The cutoff varies depending on the assay, and numerous mechanisms have been proposed such as: limited size of the alcohol-protein interaction site, limited alcohol solubility, and a chain-length-dependent lipid bilayer-alcohol interaction. To address these issues, we determined the bilayer-modifying potency of 27 aliphatic alcohols using a gramicidin-based fluorescence assay. All of the alcohols tested (with chain lengths of 1–16 carbons) alter the bilayer properties, as sensed by a bilayer-spanning channel. The bilayer-modifying potency of the short-chain alcohols scales linearly with their bilayer partitioning; the potency tapers off at higher chain lengths, and eventually changes sign for the longest-chain alcohols, demonstrating an alcohol cutoff effect in a system that has no alcohol-binding pocket. PMID:21843475

  13. Supported lipid bilayer/carbon nanotube hybrids

    NASA Astrophysics Data System (ADS)

    Zhou, Xinjian; Moran-Mirabal, Jose M.; Craighead, Harold G.; McEuen, Paul L.

    2007-03-01

    Carbon nanotube transistors combine molecular-scale dimensions with excellent electronic properties, offering unique opportunities for chemical and biological sensing. Here, we form supported lipid bilayers over single-walled carbon nanotube transistors. We first study the physical properties of the nanotube/supported lipid bilayer structure using fluorescence techniques. Whereas lipid molecules can diffuse freely across the nanotube, a membrane-bound protein (tetanus toxin) sees the nanotube as a barrier. Moreover, the size of the barrier depends on the diameter of the nanotube-with larger nanotubes presenting bigger obstacles to diffusion. We then demonstrate detection of protein binding (streptavidin) to the supported lipid bilayer using the nanotube transistor as a charge sensor. This system can be used as a platform to examine the interactions of single molecules with carbon nanotubes and has many potential applications for the study of molecular recognition and other biological processes occurring at cell membranes.

  14. Bright ion channels and lipid bilayers.

    PubMed

    Szymański, Wiktor; Yilmaz, Duygu; Koçer, Armağan; Feringa, Ben L

    2013-12-17

    If we look at a simple organism such as a zebrafish under a microscope, we would see many cells working in harmony. If we zoomed in, we would observe each unit performing its own tasks in a special aqueous environment isolated from the other units by a lipid bilayer approximately 5 nm thick. These confined units are social: they communicate with one another by sensing and responding to the chemical changes in their environment through receptors and ion channels. These channels control the highly specific and selective passage of ions from one side of the cell to the other and are embedded in lipid bilayers. The movement of ions through ion channels supports excitation and electrical signaling in the nervous system. Ion channels have fascinated scientists not only because of their specificity and selectivity, but also for their functions, the serious consequences when they malfunction, and the other potential applications of these molecules. Light is a useful trigger to control and manipulate ion channels externally. With the many state-of-the-art optical technologies available, light offers a high degree of spatial and temporal control, millisecond precision, and noninvasive intervention and does not change the chemical environment of the system of interest. In this Account, we discuss research toward the dynamic control of lipid bilayer assembly and channel function, particularly the transport across the lipid bilayer-ion channel barrier of cells using light. We first summarize the manipulation of ion channel activity with light to modulate the channel's natural activity. Based on the type of photoswitch employed, we can achieve novel functionalities with these channels, and control neural activity. Then we discuss the recent developments in light-induced transport through lipid bilayers. We focus on three different approaches: the incorporation of photoswitchable copolymers into the lipids, the doping of the lipid bilayer with photosensitive amphiphiles and the

  15. Method of fabricating lipid bilayer membranes on solid supports

    NASA Technical Reports Server (NTRS)

    Cho, Nam-Joon (Inventor); Frank, Curtis W. (Inventor); Glenn, Jeffrey S. (Inventor); Cheong, Kwang Ho (Inventor)

    2012-01-01

    The present invention provides a method of producing a planar lipid bilayer on a solid support. With this method, a solution of lipid vesicles is first deposited on the solid support. Next, the lipid vesicles are destabilized by adding an amphipathic peptide solution to the lipid vesicle solution. This destabilization leads to production of a planar lipid bilayer on the solid support. The present invention also provides a supported planar lipid bilayer, where the planar lipid bilayer is made of naturally occurring lipids and the solid support is made of unmodified gold or titanium oxide. Preferably, the supported planar lipid bilayer is continuous. The planar lipid bilayer may be made of any naturally occurring lipid or mixture of lipids, including, but not limited to phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinsitol, cardiolipin, cholesterol, and sphingomyelin.

  16. Supported Lipid Bilayer/Carbon Nanotube Hybrids

    NASA Astrophysics Data System (ADS)

    Zhou, Xinjian; Moran-Mirabal, Jose; Craighead, Harold; McEuen, Paul

    2007-03-01

    We form supported lipid bilayers on single-walled carbon nanotubes and use this hybrid structure to probe the properties of lipid membranes and their functional constituents. We first demonstrate membrane continuity and lipid diffusion over the nanotube. A membrane-bound tetanus toxin protein, on the other hand, sees the nanotube as a diffusion barrier whose strength depends on the diameter of the nanotube. Finally, we present results on the electrical detection of specific binding of streptavidin to biotinylated lipids with nanotube field effect transistors. Possible techniques to extract dynamic information about the protein binding events will also be discussed.

  17. Cholera toxin interactions with lipid bilayers.

    PubMed

    Tosteson, M T; Tosteson, D C; Rubnitz, J

    1980-01-01

    The purpose of the experiments described in this paper was to assess the binding of cholera toxin to bilayers containing its receptor, the monosialoganglioside, GMl. The assay was based on the fact that GMl confers on the bilayer a negative surface charge. The magnitude of this surface charge was estimated by measuring the electrical conductance (G) of the bilayers exposed to nonactin-K+ under conditions where G is directly proportional to the potassium concentration in the aqueous solutions immediatey adjacent to the membrane surface. When bilayers were formed from mixtures of GMl and glycerolmonooleate (GMO), it was found that the molar ratio of the lipids in the bilayer was the same as that in the membrane forming solution. It was further found that cholera toxin or the binding subunit of the toxin (choleragenoid) bind to GMO bilayers containing GMl (but not to GMO bilayers containing phosphatidyl serine or disialoganglioside GDla). The value of the apparent dissociation constant for the binding of choleragen to its receptor was found to be 10(-11) M, comparable to values found in intact cells. PMID:6933823

  18. Molecular Interactions of Alzheimer Amyloid-β Oligomer with Neutral and Negatively Charged Lipid Bilayers

    PubMed Central

    Yu, Xiang; Wang, Qiuming; Pan, Qingfen; Zhou, Feimeng; Zheng, Jie

    2013-01-01

    Interaction of p3 (Aβ17-42) peptides with cell membrane is crucial for the understanding of amyloid toxicity associated with Alzheimer’s disease (AD). Such p3-membrane interactions are considered to induce the disruption of membrane permeability and integrity, but the exact mechanisms of how p3 aggregates, particularly small p3 oligomers, induce receptor-independent membrane disruption are not yet completely understood. Here, we investigate the adsorption, orientation, and surface interaction of the p3 pentamer with lipid bilayers composed of both pure zwitterionic POPC (palmitoyl-oleyl-phosphatidylcholine) and mixed anionic POPC/POPG (palmitoyl-oleyl-phosphatidylglycerol) (3:1) lipids using explicit-solvent molecular dynamics (MD) simulations. MD simulation results show that the p3 pentamer has much stronger interactions with mixed POPC/POPG lipids than pure POPC lipids, consistent with experimental observation that Aβ adsorption and fibrililation are enhanced on anionic lipid bilayers. Although electrostatic interactions are main attractive forces to drive the p3 to adsorb on the bilayer surface, the adsorption of the p3 pentamer on the lipid bilayer with a preferential C-terminal β-strands facing toward the bilayer surface is a net outcome of different competitions between p3 peptides-lipid bilayer and ions-p3-bilayer interactions. More importantly, Ca2+ ions are found to form ionic bridges to associate negatively charged residues of p3 with anionic headgroups of the lipid bilayer, resulting in Aβ–Ca2+–PO4− complexes. Intensive Ca2+ bound to lipid bilayer and Ca2+ ionic bridges may lead to the alternation of Ca2+ hemostasis responsible for neuronal dysfunction and death. This work provides insights into the mutual structure, dynamics, and interactions of both Aβ peptides and lipid bilayer at the atomic level, which expand our understanding of the complex behavior of amyloid-induced membrane disruption. PMID:23493873

  19. DNA nanostructures interacting with lipid bilayer membranes.

    PubMed

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

    2014-06-17

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

  20. Poration of lipid bilayers by shock-induced nanobubble collapse

    NASA Astrophysics Data System (ADS)

    Choubey, Amit; Vedadi, Mohammad; Nomura, Ken-ichi; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    2011-01-01

    We investigate molecular mechanisms of poration in lipid bilayers due to shock-induced collapse of nanobubbles. Our multimillion-atom molecular dynamics simulations reveal dynamics of nanobubble shrinkage and collapse, leading to the formation and penetration of nanojets into lipid bilayers. The nanojet impact generates shear flow of water on bilayer leaflets and pressure gradients across them, which transiently enhance the bilayer permeability by creating nanopores through which water molecules translocate rapidly across the bilayer. Effects of nanobubble size and temperature on the porosity of lipid bilayers are examined.

  1. Lipid Bilayers: Clusters, Domains and Phases

    PubMed Central

    Ackerman, David G.; Feigenson, Gerald W.

    2015-01-01

    In this chapter we discuss the complex mixing behavior of plasma membrane lipids. To do so, we first introduce the plasma membrane and membrane mixtures often used to model its complexity. We then discuss the nature of lipid phase behavior in bilayers and the distinction between these phases and other manifestations of nonrandom mixing found in one-phase mixtures, such as clusters, micelles, and microemulsions. Finally, we demonstrate the applicability of Gibbs phase diagrams to the study of increasingly complex model membrane systems, with a focus on phase coexistence, morphology and their implications for the cell plasma membrane. PMID:25658342

  2. Lipid peroxidation and water penetration in lipid bilayers: a W-band EPR study.

    PubMed

    Conte, Elena; Megli, Francesco Maria; Khandelia, Himanshu; Jeschke, Gunnar; Bordignon, Enrica

    2013-02-01

    Lipid peroxidation plays a key role in the alteration of cell membrane's properties. Here we used as model systems multilamellar vesicles (MLVs) made of the first two products in the oxidative cascade of linoleoyl lecithin, namely 1-palmitoyl-2-(13-hydroperoxy-9,11-octadecanedienoyl)-lecithin (HpPLPC) and 1-palmitoyl-2-(13-hydroxy-9,11-octadecanedienoyl)-lecithin (OHPLPC), exhibiting a hydroperoxide or a hydroxy group at position 13, respectively. The two oxidized lipids were used either pure or in a 1:1 molar ratio mixture with untreated 1-palmitoyl-2-linoleoyl-lecithin (PLPC). The model membranes were doped with spin-labeled lipids to study bilayer alterations by electron paramagnetic resonance (EPR) spectroscopy. Two different spin-labeled lipids were used, bearing the doxyl ring at position (n) 5 or 16: γ-palmitoyl-β-(n-doxylstearoyl)-lecithin (n-DSPPC) and n-doxylstearic acid (n-DSA). Small changes in the acyl chain order in the sub-polar region and at the methyl-terminal induced by lipid peroxidation were detected by X-band EPR. Concomitantly, the polarity and proticity of the membrane bilayer in those regions were investigated at W band in frozen samples. Analysis of the g(xx) and A(zz) parameters revealed that OHPLPC, but mostly HpPLPC, induced a measurable increase in polarity and H-bonding propensity in the central region of the bilayer. Molecular dynamics simulation performed on 16-DSA in the PLPC-HpPLPC bilayer revealed that water molecules are statistically favored with respect to the hydroperoxide groups to interact with the nitroxide at the methyl-terminal, confirming that the H-bonds experimentally observed are due to increased water penetration in the bilayer. The EPR and MD data on model membranes demonstrate that cell membrane damage by oxidative stress cause alteration of water penetration in the bilayer. PMID:23036933

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

    PubMed

    Morigaki, Kenichi; Kiyosue, Kazuyuki; Taguchi, Takahisa

    2004-08-31

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

  4. Mechanism of alamethicin insertion into lipid bilayers.

    PubMed Central

    He, K; Ludtke, S J; Heller, W T; Huang, H W

    1996-01-01

    Alamethicin adsorbs on the membrane surface at low peptide concentrations. However, above a critical peptide-to-lipid ratio (P/L), a fraction of the peptide molecules insert in the membrane. This critical ratio is lipid dependent. For diphytanoyl phosphatidylcholine it is about 1/40. At even higher concentrations P/L > or = 1/15, all of the alamethicin inserts into the membrane and forms well-defined pores as detected by neutron in-plane scattering. A previous x-ray diffraction measurement showed that alamethicin adsorbed on the surface has the effect of thinning the bilayer in proportion to the peptide concentration. A theoretical study showed that the energy cost of membrane thinning can indeed lead to peptide insertion. This paper extends the previous studies to the high-concentration region P/L > 1/40. X-ray diffraction shows that the bilayer thickness increases with the peptide concentration for P/L > 1/23 as the insertion approaches 100%. The thickness change with the percentage of insertion is consistent with the assumption that the hydrocarbon region of the bilayer matches the hydrophobic region of the inserted peptide. The elastic energy of a lipid bilayer including both adsorption and insertion of peptide is discussed. The Gibbs free energy is calculated as a function of P/L and the percentage of insertion phi in a simplified one-dimensional model. The model exhibits an insertion phase transition in qualitative agreement with the data. We conclude that the membrane deformation energy is the major driving force for the alamethicin insertion transition. Images FIGURE 1 PMID:8913604

  5. Water Permeability of Asymmetric Planar Lipid Bilayers

    PubMed Central

    Krylov, Andrey V.; Pohl, Peter; Zeidel, Mark L.; Hill, Warren G.

    2001-01-01

    To understand how plasma membranes may limit water flux, we have modeled the apical membrane of MDCK type 1 cells. Previous experiments demonstrated that liposomes designed to mimic the inner and outer leaflet of this membrane exhibited 18-fold lower water permeation for outer leaflet lipids than inner leaflet lipids (Hill, W.G., and M.L. Zeidel. 2000. J. Biol. Chem. 275:30176–30185), confirming that the outer leaflet is the primary barrier to permeation. If leaflets in a bilayer resist permeation independently, the following equation estimates single leaflet permeabilities: 1/PAB = 1/PA + 1/PB (Eq. l), where PAB is the permeability of a bilayer composed of leaflets A and B, PA is the permeability of leaflet A, and PB is the permeability of leaflet B. Using for the MDCK leaflet–specific liposomes gives an estimated value for the osmotic water permeability (Pf) of 4.6 × 10−4 cm/s (at 25°C) that correlated well with experimentally measured values in intact cells. We have now constructed both symmetric and asymmetric planar lipid bilayers that model the MDCK apical membrane. Water permeability across these bilayers was monitored in the immediate membrane vicinity using a Na+-sensitive scanning microelectrode and an osmotic gradient induced by addition of urea. The near-membrane concentration distribution of solute was used to calculate the velocity of water flow (Pohl, P., S.M. Saparov, and Y.N. Antonenko. 1997. Biophys. J. 72:1711–1718). At 36°C, Pf was 3.44 ± 0.35 × 10−3 cm/s for symmetrical inner leaflet membranes and 3.40 ± 0.34 × 10−4 cm/s for symmetrical exofacial membranes. From , the estimated permeability of an asymmetric membrane is 6.2 × 10−4 cm/s. Water permeability measured for the asymmetric planar bilayer was 6.7 ± 0.7 × 10−4 cm/s, which is within 10% of the calculated value. Direct experimental measurement of Pf for an asymmetric planar membrane confirms that leaflets in a bilayer offer independent and additive resistances to

  6. 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

  7. Approaches toward functional fluid supported lipid bilayers

    NASA Astrophysics Data System (ADS)

    Weng, Kevin Chun-I.

    Planar supported lipid bilayers (PSLBs) have attracted immense interest for their properties as model cell membranes and for potential applications in biosensors and lab-on-a-chip devices. Our study covers three aspects of the construction, characterization, and application of functional PSLBs. First, a combination of micro-fabrication, the Langmuir-Blodgett (LB) technique, and fusion of extruded small unilamellar vesicle (E-SUVs) in sequence was used to create polymer-cushioned PSLBs in a microarray format. Random lipo-glycocopolymer mixed with L-alpha-phosphatidylcholine (egg PC) was compressed at the air-water interface and transferred onto the photoresist-patterned substrate by the LB technique to achieve spatially directed deposition. Construction of planar bilayers in an aqueous environment was subsequently completed by vesicle fusion. Epifluorescence microscopy, fluorescence recovery after photobleaching (FRAP), and electrophoresis-relaxation were employed to examine the resulting patterns as well as to verify the two-dimensional mobility of the supported membrane systems. This approach could possibly provide a useful route to create functional arrays of polymer-supported lipid bilayers. Second, we report the formation of fluid planar biomembranes on hydrophilic silica aerogels and xerogels. When the aerogel/xerogel was pre-hydrated and then allowed to incubate in egg PC E-SUV solution, lipid bilayers were formed due to the favorable interaction of vesicles with the hydroxyl-abundant silica surface. FRAP was used to determine the lateral diffusivity of membranes on aerogels. Quartz crystal microbalance with dissipation monitoring (QCM-D) was used to monitor the kinetics of the irreversible adsorption and fusion of vesicles into bilayers on xerogel thin films. Finally, we compared the formation of PSLBs with and without incorporation of monosialoganglioside GM1 (GM1) as the antigen for in situ antibody binding. Quantifiable differences were observed in the

  8. Functional One-Dimensional Lipid Bilayers on Carbon Nanotube Templates

    SciTech Connect

    Artyukhin, A; Shestakov, A; Harper, J; Bakajin, O; Stroeve, P; Noy, A

    2004-07-23

    We present one-dimensional (1-D) lipid bilayer structures that integrate carbon nanotubes with a key biological environment-phospholipid membrane. Our structures consist of lipid bilayers wrapped around carbon nanotubes modified with a hydrophilic polymer cushion layer. Despite high bilayer curvature, the lipid membrane maintains its fluidity and can sustain repeated damage-recovery cycles. We also present the first evidence of spontaneous insertion of pore-forming proteins into 1-D lipid bilayers. These structures could lead to the development of new classes of biosensors and bioelectronic devices.

  9. Investigating Hydrophilic Pores in Model Lipid Bilayers using Molecular Simulations: Correlating Bilayer Properties with Pore Formation Thermodynamics

    PubMed Central

    Hu, Yuan; Sinha, Sudipta Kumar

    2015-01-01

    Cell-penetrating and antimicrobial peptides show remarkable ability to translocate across physiological membranes. Along with factors such as electric potential induced-perturbations of membrane structure and surface tension effects, experiments invoke pore-like membrane configurations during the solute transfer process into vesicles and cells. The initiation and formation of pores are associated with a non-trivial free energy cost, thus necessitating consideration of the factors associated with pore formation and attendant free energetics. Due to experimental and modeling challenges related to the long timescales of the translocation process, we use umbrella-sampling molecular dynamics simulations with a lipid-density based order parameter to investigate membrane pore-formation free energy employing Martini coarse-grained models. We investigate structure and thermodynamic features of the pore in 18 lipids spanning a range of head-groups, charge states, acyl chain lengths and saturation. We probe the dependence of pore-formation barriers on area per lipid, lipid bilayer thickness, membrane bending rigidities in three different lipid classes. The pore formation free energy in pure bilayers and peptide translocating scenarios are significantly coupled with bilayer thickness. Thicker bilayers require more reversible work to create pores. Pore formation free energy is higher in peptide-lipid systems relative to the peptide-free lipid systems due to penalties to maintain solvation of charged hydrophilic solutes within the membrane environment. PMID:25614183

  10. Repetitive formation of optically-observable planar lipid bilayers by rotating chambers on a microaperture.

    PubMed

    Tomoike, Fumiaki; Tonooka, Taishi; Osaki, Toshihisa; Takeuchi, Shoji

    2016-07-01

    Optical observation of a planar lipid bilayer is an effective method of lipid bilayer characterization. However, previous methods for optically observable lipid bilayer formation are unsuitable for repetitive formation of lipid bilayers. In this paper, we propose a system that facilitates repetitive formation of horizontal lipid bilayers via mechanical rotation of the rotating part. We show that multiple bilayers can be observed within a short period, and that the electrical and optical characteristics of a bilayer can be analyzed simultaneously. PMID:27256329

  11. Cholesterol-induced modifications in lipid bilayers: a simulation study.

    PubMed Central

    Chiu, S W; Jakobsson, Eric; Mashl, R Jay; Scott, H Larry

    2002-01-01

    We present analysis of new configurational bias Monte Carlo and molecular dynamics simulation data for bilayers of dipalmitoyl phosphatidyl choline and cholesterol for dipalmitoyl phosphatidyl choline:cholesterol ratios of 24:1, 47:3, 11.5:1, 8:1, 7:1, 4:1, 3:1, 2:1, and 1:1, using long molecular dynamics runs and interspersed configurational bias Monte Carlo to ensure equilibration and enhance sampling. In all cases with cholesterol concentrations above 12.5% the area per molecule of the heterogeneous membrane varied linearly with cholesterol fraction. By extrapolation to pure cholesterol, we find the cross-sectional area of cholesterol in these mixtures is approximately 22.3 A(2). From the slope of the area/molecule relationship, we also find that the phospholipid in these mixtures is in a liquid ordered state with an average cross-sectional area per lipid of 50.7 A(2), slightly above the molecular area of a pure phospholipid gel. For lower concentrations of cholesterol, the molecular area rises above the straight line, indicating the "melting" of at least some of the phospholipid into a fluid state. Analysis of the lateral distribution of cholesterol molecules in the leaflets reveals peaks in radial distributions of cholesterols at multiples of approximately 5 A. These peaks grow in size as the simulation progresses, suggesting a tendency for small subunits of one lipid plus one cholesterol, hydrogen bonded together, to act as one composite particle, and perhaps to aggregate with other composites. Our results are consistent with experimentally observed effects of cholesterol, including the condensation effect of cholesterol in phospholipid monolayers and the tendency of cholesterol-rich domains to form in cholesterol-lipid bilayers. We are continuing to analyze this tendency on longer timescales and for larger bilayer patches. PMID:12324406

  12. Self-assembled lipid bilayer materials

    DOEpatents

    Sasaki, Darryl Y.; Waggoner, Tina A.; Last, Julie A.

    2005-11-08

    The present invention is a self-assembling material comprised of stacks of lipid bilayers formed in a columnar structure, where the assembly process is mediated and regulated by chemical recognition events. The material, through the chemical recognition interactions, has a self-regulating system that corrects the radial size of the assembly creating a uniform diameter throughout most of the structure. The materials form and are stable in aqueous solution. These materials are useful as structural elements for the architecture of materials and components in nanotechnology, efficient light harvesting systems for optical sensing, chemical processing centers, and drug delivery vehicles.

  13. Automatable lipid bilayer formation for ion channel studies

    NASA Astrophysics Data System (ADS)

    Poulos, Jason L.; Bang, Hyunwoo; Jeon, Tae-Joon; Schmidt, Jacob J.

    2008-08-01

    Transmembrane proteins and ion channels are important drug targets and have been explored as single molecule sensors. For these proteins to function normally they must be integrated within lipid bilayers; however, the labor and skill required to create artificial lipid bilayers have the limited the possible applications utilizing these proteins. In order to reduce the complexity and cost of lipid bilayer formation and measurement, we have modified a previously published lipid bilayer formation technique using mechanically contacted monolayers so that the process is automatable, requiring minimal operator input. Measurement electronics are integrated with the fluid handling system, greatly reducing the time and operator feedback characteristically required of traditional bilayer experiments. To demonstrate the biological functionality of the resultant bilayers and the system's capabilities as a membrane platform, the ion channel gramicidin A was incorporated and measured with this system.

  14. Solid supported lipid bilayers: From biophysical studies to sensor design

    NASA Astrophysics Data System (ADS)

    Castellana, Edward T.; Cremer, Paul S.

    2006-11-01

    The lipid bilayer is one of the most eloquent and important self-assembled structures in nature. It not only provides a protective container for cells and sub-cellular compartments, but also hosts much of the machinery for cellular communication and transport across the cell membrane. Solid supported lipid bilayers provide an excellent model system for studying the surface chemistry of the cell. Moreover, they are accessible to a wide variety of surface-specific analytical techniques. This makes it possible to investigate processes such as cell signaling, ligand-receptor interactions, enzymatic reactions occurring at the cell surface, as well as pathogen attack. In this review, the following membrane systems are discussed: black lipid membranes, solid supported lipid bilayers, hybrid lipid bilayers, and polymer cushioned lipid bilayers. Examples of how supported lipid membrane technology is interfaced with array based systems by photolithographic patterning, spatial addressing, microcontact printing, and microfluidic patterning are explored. Also, the use of supported lipid bilayers in microfluidic devices for the development of lab-on-a-chip based platforms is examined. Finally, the utility of lipid bilayers in nanotechnology and future directions in this area are discussed.

  15. Electric polarizability of lipid bilayers: The influence of the structure

    NASA Astrophysics Data System (ADS)

    Soussi, J.; Chalopin, Y.

    2015-10-01

    We have calculated the electric polarizability of two types of lipid bilayers, formed by 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2- oleoyl-sn-glycero-3-phosphocholine (POPC) lipids. We demonstrate that despite the very similar chemical structures, the bilayers exhibit dramatically different terahertz infrared (IR) properties. We demonstrate that the chemical structure of the lipids influences the morphology of the bilayers, which in turn impacts their IR responses: interestingly, both structures exhibit a non-uniform absorption. For the case of DPPC, the infrared absorption is mostly driven by the hydrophilic heads, whereas for the POPC lipids, the absorption occurs predominately at the hydrophobic tails.

  16. Detection of bilayer lipid with graphene nanoribbon

    NASA Astrophysics Data System (ADS)

    Akbari, Elnaz; Buntat, Zolkafle; Afroozeh, Abdolkarim; Zeinalinezhad, Alireza; Nilashi, Mehrbakhsh

    2015-09-01

    Single-layer graphene consists of sp 2-bonded carbon atoms arranged in a two-dimensional (2D) hexagonal lattice comprising a thin layer of single carbon atoms. Owing to its special characteristics including electrical, physical, and optical properties, graphene is considered more suitable for sensor applications than other materials. Moreover, it is possible to produce biosensors using electrolyte-gated field-effect transistors based on graphene (GFETs) to identify the alterations in charged lipid membrane properties. This paper illustrates how membrane thickness and electrical charge can result in a monolayer GFET, with emphasis on conductance variation. It is proposed that the thickness and electrical charge of the lipid bilayer are functions of carrier density, and equations relating these suitable control parameters were derived. Adaptive neuro fuzzy inference system (ANFIS) has been incorporated to obtain other model for conductance characteristic. The comparison between the analytical models and ANFIS with the experimental data extracted from previous work show an acceptable agreement. [Figure not available: see fulltext.

  17. Polyunsaturated Fatty Acids in Lipid Bilayers and Tubules

    NASA Astrophysics Data System (ADS)

    Hirst, Linda S.; Yuan, Jing; Pramudya, Yohannes; Nguyen, Lam T.

    2007-03-01

    Omega-3 polyunsaturated fatty acids (PUFAs) are found in a variety of biological membranes and have been implicated with lipid raft formation and possible function, typical molecules include DHA (Docosahexanoic Acid) and AA (Alphalinoleic Acid) which have been the focus of considerable attention in recent years. We are interested in the phase behavior of these molecules in the lipid bilayer. The addition of lipid molecules with polyunsaturated chains has a clear effect on the fluidity and curvature of the membrane and we investigate the effects the addition of polyunsaturated lipids on bilayer structure and tubule formation. Self-assembled cylindrical lipid tubules have attracted considerable attention because of their interesting structures and potential technological applications. Using x-ray diffraction techniques, Atomic Force Microscopy and confocal fluorescence imaging, both symmetric and mixed chain lipids were incorporated into model membranes and the effects on bilayer structure and tubule formation investigated.

  18. Microporous device for local electric recordings on model lipid bilayers

    NASA Astrophysics Data System (ADS)

    Kaufeld, Theresa; Steinem, Claudia; Schmidt, Christoph F.

    2015-01-01

    A powerful approach for characterizing lipid membranes and embedded proteins is the reconstitution of model lipid bilayers. The extreme fragility of 5 nm thick bilayers is a challenge for device design and requires a trade off of stability against accessibility. We here present a microporous lab-on-chip device that allows us to form stable, solvent-free lipid bilayers from giant unilamellar vesicles (GUVs) in a geometry that provides a unique set of access possibilities. The device is constructed around a micro-fabricated silicon chip with clusters of 1 µm-diameter pores and provides optical access to the lipid bilayers for high-NA epifluorescence imaging. At the same time, solvent exchange is possible on both sides of the lipid bilayer. Complete coverage can be achieved with GUVs, so that voltages can be applied across the lipid bilayer and single-channel currents can be measured using external or integrated silver/silver chloride electrodes. We describe the micro-fabrication by standard cleanroom techniques and the characterization of the device by atomic force microscopy, scanning electron microscopy and impedance spectroscopy. In proof-of-concept experiments we demonstrate that the device is capable of low-noise, single-ion-channel recordings. Electronic Supplementary Information (ESI) available: See DOI: 10.1039/b000000x/

  19. Intercalation of small hydrophobic molecules in lipid bilayers containing cholesterol

    SciTech Connect

    Worcester, D.L.; Hamacher, K.; Kaiser, H.; Kulasekere, R.; Torbet, J.

    1994-12-31

    Partitioning of small hydrophobic molecules into lipid bilayers containing cholesterol has been studied using the 2XC diffractometer at the University of Missouri Research Reactor. Locations of the compounds were determined by Fourier difference methods with data from both deuterated and undeuterated compounds introduced into the bilayers from the vapor phase. Data fitting procedures were developed for determining how well the compounds were localized. The compounds were found to be localized in a narrow region at the center of the hydrophobic layer, between the two halves of the bilayer. The structures are therefore intercalated structures with the long axis of the molecules in the plane of the bilayer.

  20. Intercalation of small hydrophobic molecules in lipid bilayers containing cholesterol.

    PubMed

    Worcester, D L; Hamacher, K; Kaiser, H; Kulasekere, R; Torbet, J

    1996-01-01

    Partitioning of small hydrophobic molecules into lipid bilayers containing cholesterol has been studied using the 2XC diffractometer at the University of Missouri Research Reactor. Locations of the compounds were determined by Fourier difference methods with data from both deuterated and undeuterated compounds introduced into the bilayers from the vapor phase. Data fitting procedures were developed for determining how well the compounds were localized. The compounds were found to be localized in a narrow region at the center of the hydrophobic layer, between the two halves of the bilayer. The structures are therefore intercalated structures with the long axis of the molecules in the plane of the bilayer. PMID:9031514

  1. Structural Proton Diffusion along Lipid Bilayers

    PubMed Central

    Serowy, Steffen; Saparov, Sapar M.; Antonenko, Yuri N.; Kozlovsky, Wladas; Hagen, Volker; Pohl, Peter

    2003-01-01

    For H+ transport between protein pumps, lateral diffusion along membrane surfaces represents the most efficient pathway. Along lipid bilayers, we measured a diffusion coefficient of 5.8 × 10−5 cm2 s−1. It is too large to be accounted for by vehicle diffusion, considering proton transport by acid carriers. Such a speed of migration is accomplished only by the Grotthuss mechanism involving the chemical exchange of hydrogen nuclei between hydrogen-bonded water molecules on the membrane surface, and the subsequent reorganization of the hydrogen-bonded network. Reconstitution of H+-binding sites on the membrane surface decreased the velocity of H+ diffusion. In the absence of immobile buffers, structural (Grotthuss) diffusion occurred over a distance of 100 μm as shown by microelectrode aided measurements of the spatial proton distribution in the immediate membrane vicinity and spatially resolved fluorescence measurements of interfacial pH. The efficiency of the anomalously fast lateral diffusion decreased gradually with an increase in mobile buffer concentration suggesting that structural diffusion is physiologically important for distances of ∼10 nm. PMID:12547784

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

    PubMed Central

    Needham, D; Nunn, R S

    1990-01-01

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

  3. 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

  4. An engineered dimeric protein pore that spans adjacent lipid bilayers

    PubMed Central

    Mantri, Shiksha; Sapra, K. Tanuj; Cheley, Stephen; Sharp, Thomas H.; Bayley, Hagan

    2013-01-01

    The bottom-up construction of artificial tissues is an underexplored area of synthetic biology. An important challenge is communication between constituent compartments of the engineered tissue and between the engineered tissue and additional compartments, including extracellular fluids, further engineered tissue and living cells. Here we present a dimeric transmembrane pore that can span two adjacent lipid bilayers and thereby allow aqueous compartments to communicate. Two heptameric staphylococcal α-hemolysin (αHL) pores were covalently linked in an aligned cap-to-cap orientation. The structure of the dimer, (α7)2, was confirmed by biochemical analysis, transmission electron microscopy (TEM) and single-channel electrical recording. We show that one of two β barrels of (α7)2 can insert into the lipid bilayer of a small unilamellar vesicle, while the other spans a planar lipid bilayer. (α7)2 pores spanning two bilayers were also observed by TEM. PMID:23591892

  5. 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

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

    PubMed

    Andersson, Jakob; Köper, Ingo

    2016-01-01

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

  7. Interactions between lipid bilayers and inorganic material surfaces

    NASA Astrophysics Data System (ADS)

    Mager, Morgan Douglas

    Because of their unique biological and material properties, lipid bilayers have been extensively studied for use in biosensor and drug delivery applications. In the past, these systems have mostly taken the form of bulk solutions. More recently, researchers have integrated bilayers with chip-based architectures to take advantage of advanced optical, scanning probe and electronic characterization. These applications typically involve the creation of hybrid devices with inorganic and bilayer components, both of which affect the final device performance. In particular, the properties of supported lipid bilayers (SLBs) are known to depend on the substrate chemistry and topography as well as the lipid used. In spite of the large body of work involving these systems, there is still much that remains unknown about the formation and ultimate structure of the interface between these very different materials. One outstanding question in the study of SLBs is the role that the bilayer deposition method plays in determining the bilayer properties. In this work, we have developed a new method for forming and patterning lipid bilayers: bubble collapse deposition (BCD). This method is similar to an in situ version of Langmuir-Blodgett deposition, and offers unique possibilities for the fabrication of lipid-based devices. Briefly, a lipid monolayer is "inked" onto the surface of an air bubble. This bubble is then brought down on a solid support and the air is withdrawn. This withdrawal of air shrinks the bubble, which causes the monolayer to fold over on itself and redeposit on the surface as a bilayer. With BCD, we have demonstrated the first SLB formation on alumina using uncharged lipids. Using this system, we have measured a previously unobserved enhanced hydrodynamic coupling at the alumina surface. We have also used BCD to produce a hybrid lipid-gated chemical delivery device with potentially sub-cellular spatial resolution. Because of the unique material properties of the

  8. Effects of Amyloid β-Peptides on the Lysis Tension of Lipid Bilayer Vesicles Containing Oxysterols

    PubMed Central

    Kim, Dennis H.; Frangos, John A.

    2008-01-01

    Amyloid β-peptides (Aβ) applied directly from solution to model lipid membranes produced dramatic changes in the material properties of the bilayer when certain oxysterols were present in the bilayer. These effects were dependent on both lipid and peptide composition, and occurred at peptide concentrations as low as 100 nM. Using micropipette manipulation of giant unilamellar vesicles, we directly measured the lysis tension of lipid bilayers of various compositions. The glycerophospholipid 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) constituted the main lipid component at 70 mol %. The remaining 30 mol % was composed of the following pure or mixed sterols: cholesterol (CHOL), 7-ketocholesterol (KETO), or 7β-hydroxycholesterol (OHCHOL). SOPC/CHOL bilayers did not exhibit significant changes in mechanical properties after exposure to either Aβ(1–42) or Aβ(1–40). Partial substitution of CHOL with KETO (5 mol %), however, caused a drastic reduction of the lysis tension after exposure to Aβ(1–42) but not to Aβ(1–40). Partial substitution of CHOL with OHCHOL (5 mol %) caused a drastic reduction of the lysis tension after exposure to Aβ(1–40) and to Aβ(1–42). We attribute these effects to the reduction in intermolecular cohesive interactions caused by the presence of the second dipole of oxysterols, which reduces the energetic barrier for Aβ insertion into the bilayer. PMID:18390616

  9. Micropatterned, multicomponent supported lipid bilayers for cellular systems.

    PubMed

    Dutta, Debjit; Kam, Lance C

    2014-01-01

    Lipid bilayer membranes are a central structural feature of living cells, providing a wide range of functions including partitioning of organelles, mediating cell interaction with the environment, and modulating intracellular signaling processes. By capturing the fluidity of the natural membranes in a reductionist in vitro model, substrate supported lipid bilayers have emerged as a compelling model system for these structures. Furthermore, the ability to control the composition and mobility of this system at micro- and nanoscales inspired several new routes of biological and biotechnological investigation. Here, we describe key methods used to create multicomponent lipid bilayers, discuss design considerations important to making these systems, and demonstrate this process in the specific context of understanding juxtacrine cell signaling. Different fabrication techniques were combined to first pattern a surface with barriers to lipid diffusion and then spatially control the exposure of this surface to lipid vesicles, leading to local formation of bilayers of different composition. This multicomponent system was used as a platform for to mimic the natural organization of T cells and antigen presenting cells by presenting ligands to the T cell receptor and lymphocyte function-associated antigen-1 that are tethered to separate, closely juxtaposed regions of bilayer. Other technologies like using photochemical polymerization of lipids to pattern bilayers have also been discussed. The information gathered from evaluating membrane interactions in patterned lipid bilayers may lead to the development of membrane-based biomedical devices for conducting novel cell-based assays and potentially high-throughput drug screens targeting membranes or membrane-associated components. PMID:24484657

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

    PubMed

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

    2016-03-22

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

  11. Coupled Diffusion in Lipid Bilayers upon Close Approach

    PubMed Central

    2015-01-01

    Biomembrane interfaces create regions of slowed water dynamics in their vicinity. When two lipid bilayers come together, this effect is further accentuated, and the associated slowdown can affect the dynamics of larger-scale processes such as membrane fusion. We have used molecular dynamics simulations to examine how lipid and water dynamics are affected as two lipid bilayers approach each other. These two interacting fluid systems, lipid and water, both slow and become coupled when the lipid membranes are separated by a thin water layer. We show in particular that the water dynamics become glassy, and diffusion of lipids in the apposed leaflets becomes coupled across the water layer, while the “outer” leaflets remain unaffected. This dynamic coupling between bilayers appears mediated by lipid–water–lipid hydrogen bonding, as it occurs at bilayer separations where water–lipid hydrogen bonds become more common than water–water hydrogen bonds. We further show that such coupling occurs in simulations of vesicle–vesicle fusion prior to the fusion event itself. Such altered dynamics at membrane–membrane interfaces may both stabilize the interfacial contact and slow fusion stalk formation within the interface region. PMID:25535654

  12. Formation and Characterization of Supported Lipid Bilayers Composed of Hydrogenated and Deuterated Escherichia coli Lipids

    PubMed Central

    Lind, Tania Kjellerup; Wacklin, Hanna; Schiller, Jürgen; Moulin, Martine; Haertlein, Michael; Pomorski, Thomas Günther; Cárdenas, Marité

    2015-01-01

    Supported lipid bilayers are widely used for sensing and deciphering biomolecular interactions with model cell membranes. In this paper, we present a method to form supported lipid bilayers from total lipid extracts of Escherichia coli by vesicle fusion. We show the validity of this method for different types of extracts including those from deuterated biomass using a combination of complementary surface sensitive techniques; quartz crystal microbalance, neutron reflection and atomic force microscopy. We find that the head group composition of the deuterated and the hydrogenated lipid extracts is similar (approximately 75% phosphatidylethanolamine, 13% phosphatidylglycerol and 12% cardiolipin) and that both samples can be used to reconstitute high-coverage supported lipid bilayers with a total thickness of 41 ± 3 Å, common for fluid membranes. The formation of supported lipid bilayers composed of natural extracts of Escherichia coli allow for following biomolecular interactions, thus advancing the field towards bacterial-specific membrane biomimics. PMID:26658241

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

    PubMed Central

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

    2014-01-01

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

  14. Formation and Characterization of Supported Lipid Bilayers Composed of Hydrogenated and Deuterated Escherichia coli Lipids.

    PubMed

    Lind, Tania Kjellerup; Wacklin, Hanna; Schiller, Jürgen; Moulin, Martine; Haertlein, Michael; Pomorski, Thomas Günther; Cárdenas, Marité

    2015-01-01

    Supported lipid bilayers are widely used for sensing and deciphering biomolecular interactions with model cell membranes. In this paper, we present a method to form supported lipid bilayers from total lipid extracts of Escherichia coli by vesicle fusion. We show the validity of this method for different types of extracts including those from deuterated biomass using a combination of complementary surface sensitive techniques; quartz crystal microbalance, neutron reflection and atomic force microscopy. We find that the head group composition of the deuterated and the hydrogenated lipid extracts is similar (approximately 75% phosphatidylethanolamine, 13% phosphatidylglycerol and 12% cardiolipin) and that both samples can be used to reconstitute high-coverage supported lipid bilayers with a total thickness of 41 ± 3 Å, common for fluid membranes. The formation of supported lipid bilayers composed of natural extracts of Escherichia coli allow for following biomolecular interactions, thus advancing the field towards bacterial-specific membrane biomimics. PMID:26658241

  15. Binding Orientations and Lipid Interactions of Human Amylin at Zwitterionic and Anionic Lipid Bilayers

    PubMed Central

    Qian, Zhenyu; Jia, Yan; Wei, Guanghong

    2016-01-01

    Increasing evidence suggests that the interaction of human islet amyloid polypeptide (hIAPP) with lipids may facilitate hIAPP aggregation and cause the death of pancreatic islet β-cells. However, the detailed hIAPP-membrane interactions and the influences of lipid compositions are unclear. In this study, as a first step to understand the mechanism of membrane-mediated hIAPP aggregation, we investigate the binding behaviors of hIAPP monomer at zwitterionic palmitoyloleoyl-phosphatidylcholine (POPC) bilayer by performing atomistic molecular dynamics simulations. The results are compared with those of hIAPP at anionic palmitoyloleoyl-phosphatidylglycerol (POPG) bilayers. We find that the adsorption of hIAPP to POPC bilayer is mainly initiated from the C-terminal region and the peptide adopts a helical structure with multiple binding orientations, while the adsorption to POPG bilayer is mostly initiated from the N-terminal region and hIAPP displays one preferential binding orientation, with its hydrophobic residues exposed to water. hIAPP monomer inserts into POPC lipid bilayers more readily than into POPG bilayers. Peptide-lipid interaction analyses show that the different binding features of hIAPP at POPC and POPG bilayers are attributed to different magnitudes of electrostatic and hydrogen-bonding interactions with lipids. This study provides mechanistic insights into the different interaction behaviors of hIAPP with zwitterionic and anionic lipid bilayers. PMID:26649316

  16. Biophysical implications of lipid bilayer rheometry for mechanosensitive channels.

    PubMed

    Bavi, Navid; Nakayama, Yoshitaka; Bavi, Omid; Cox, Charles D; Qin, Qing-Hua; Martinac, Boris

    2014-09-23

    The lipid bilayer plays a crucial role in gating of mechanosensitive (MS) channels. Hence it is imperative to elucidate the rheological properties of lipid membranes. Herein we introduce a framework to characterize the mechanical properties of lipid bilayers by combining micropipette aspiration (MA) with theoretical modeling. Our results reveal that excised liposome patch fluorometry is superior to traditional cell-attached MA for measuring the intrinsic mechanical properties of lipid bilayers. The computational results also indicate that unlike the uniform bilayer tension estimated by Laplace's law, bilayer tension is not uniform across the membrane patch area. Instead, the highest tension is seen at the apex of the patch and the lowest tension is encountered near the pipette wall. More importantly, there is only a negligible difference between the stress profiles of the outer and inner monolayers in the cell-attached configuration, whereas a substantial difference (∼30%) is observed in the excised configuration. Our results have far-reaching consequences for the biophysical studies of MS channels and ion channels in general, using the patch-clamp technique, and begin to unravel the difference in activity seen between MS channels in different experimental paradigms. PMID:25201991

  17. Octyl-beta-D-glucopyranoside partitioning into lipid bilayers: thermodynamics of binding and structural changes of the bilayer.

    PubMed Central

    Wenk, M R; Alt, T; Seelig, A; Seelig, J

    1997-01-01

    until the disordering of the chains reaches a critical limit. The perturbing effect of OG is thus different from that of another nonionic detergent, octaethyleneglycol mono-n-dodecylether (C12E8), which produces a general disordering at all levels of the lipid bilayer. The OG-POPC interaction was also investigated with POPC monolayers, using a Langmuir trough. In the absence of lipid, the measurement of the Gibbs adsorption isotherm for pure OG solutions yielded an OG surface area of AS = 51 +/- 3 A2. On the other hand, the insertion area AI of OG in a POPC monolayer was determined by a monolayer expansion technique as AI = 58 +/- 10 A2. The similar area requirements with AS approximately AI indicate an almost complete insertion of OG into the lipid monolayer. The OG partition constant for a POPC monolayer at 32 mN/m was Kp approximately 320 M-1 and thus was larger than that for a POPC bilayer. Images FIGURE 8 PMID:9083676

  18. Irregular bilayer structure in vesicles prepared from Halobacterium cutirubrum lipids

    NASA Technical Reports Server (NTRS)

    Lanyi, J. K.

    1974-01-01

    Fluorescent probes were used to study the structure of the cell envelope of Halobacterium cutirubrum, and, in particular, to explore the effect of the heterogeneity of the lipids in this organism on the structure of the bilayers. The fluorescence polarization of perylene was followed in vesicles of unfractionated lipids and polar lipids as a function of temperature in 3.4 M solutions of NaCl, NaNO3, and KSCN, and it was found that vesicles of unfractionated lipids were more perturbed by chaotropic agents than polar lipids. The dependence of the relaxation times of perylene on temperature was studied in cell envelopes and in vesicles prepared from polar lipids, unfractionated lipids, and mixtures of polar and neutral lipids.

  19. Partition, orientation and mobility of ubiquinones in a lipid bilayer.

    PubMed

    Galassi, Vanesa Viviana; Arantes, Guilherme Menegon

    2015-12-01

    Ubiquinone is the universal mobile charge carrier involved in biological electron transfer processes. Its redox properties and biological function depend on the molecular partition and lateral diffusion over biological membranes. However, ubiquinone localization and dynamics within lipid bilayers are long debated and still uncertain. Here we present molecular dynamics simulations of several ubiquinone homologs with variable isoprenoid tail lengths complexed to phosphatidylcholine bilayers. Initially, a new force-field parametrization for ubiquinone is derived from and compared to high level quantum chemical data. Free energy profiles for ubiquinone insertion in the lipid bilayer are obtained with the new force-field. The profiles allow for the determination of the equilibrium location of ubiquinone in the membrane as well as for the validation of the simulation model by direct comparison with experimental partition coefficients. A detailed analysis of structural properties and interactions shows that the ubiquinone polar head group is localized at the water-bilayer interface at the same depth of the lipid glycerol groups and oriented normal to the membrane plane. Both the localization and orientation of ubiquinone head groups do not change significantly when increasing the number of isoprenoid units. The isoprenoid tail is extended and packed with the lipid acyl chains. For ubiquinones with long tails, the terminal isoprenoid units have high flexibility. Calculated ubiquinone diffusion coefficients are similar to that found for the phosphatidylcholine lipid. These results may have further implications for the mechanisms of ubiquinone transport and binding to respiratory and photosynthetic protein complexes. PMID:26255075

  20. Interface-mediation of lipid bilayer organization and dynamics.

    PubMed

    Mize, Hannah E; Blanchard, G J

    2016-06-22

    We report on the morphology and dynamics of planar supported lipid bilayer structures as a function of pH and ionic strength of the aqueous overlayer. Supported lipid bilayers composed of three components (phosphocholine, sphingomyelin and cholesterol) are known to exhibit phase segregation, with the characteristic domain sizes dependent on the amount and identity of each constituent, and the composition of the aqueous overlayer in contact with the bilayer. We report on fluorescence anisotropy decay imaging measurements of a rhodamine chromophore tethered to the headgroup of a phosphoethanolamine, where anisotropy decay images were acquired as a function of solution overlayer pH and ionic strength. The data reveal a two-component anisotropy decay under all conditions, with the faster time constant being largely independent of pH and ionic strength and the slower component depending on pH and ionic strength in different manners. For liposomes of the same composition, a single exponential anisotropy decay was seen. We interpret this difference in terms of bilayer curvature and support surface-bilayer interactions, and the pH and ionic strength dependencies in terms of ionic screening and protonation in the bilayer headgroup region. PMID:27295126

  1. Rigidification of neutral lipid bilayers in the presence of salts.

    PubMed

    Pabst, Georg; Hodzic, Aden; Strancar, Janez; Danner, Sabine; Rappolt, Michael; Laggner, Peter

    2007-10-15

    We studied the influence of sodium and calcium chloride on the global and local membrane properties of fluid palmitoyl-oleoyl phosphatidylcholine bilayers, applying synchrotron small-angle x-ray diffraction, spin-labeling electron paramagnetic resonance spectroscopy, and differential scanning calorimetry, as well as simultaneous density and acoustic measurements. The salt concentration was varied over a wide range from 0 to 5 M. We found that NaCl leads to a continuous swelling of the bilayers, whereas the behavior of the bilayer separation dW in the presence of CaCl2 is more complex, showing an initial large dW value, which decreased upon further addition of salt and finally increased again in the high concentration regime. This can be understood by a change of balance between electrostatic and van der Waals interactions. We were further able to show that both salts lead to a significant increase of order within the lipid bilayer, leading to a decrease of bilayer elasticity and shift of main phase transition temperature. This effect is more pronounced for Ca2+, and occurs mainly in the high salt-concentration regime. Thus, we were able to reconcile previous controversies between molecular dynamics simulations and x-ray diffraction experiments regarding the effect of salts on neutral lipid bilayers. PMID:17586572

  2. Super-resolution microscopy of lipid bilayer phases.

    PubMed

    Kuo, Chinkuei; Hochstrasser, Robin M

    2011-04-01

    Sub-diffraction optical imaging with nanometer resolution of lipid phase-separated regions is reported. Merocyanine 540, a probe whose fluorescence is sensitive to the lipid phase, is combined with super-resolution imaging to distinguish the liquid- and gel-phase nanoscale domains of lipid bilayers supported on glass. The monomer-dimer equilibrium of MC540 in membranes is deemed responsible for the population difference of single-molecule fluorescence bursts in the different phase regions. The extension of this method to other binary or ternary lipid models or natural systems provides a promising new super-resolution strategy. PMID:21405121

  3. Lipid Interactions and Organization in Complex Bilayer Membranes.

    PubMed

    Engberg, Oskar; Yasuda, Tomokazu; Hautala, Victor; Matsumori, Nobuaki; Nyholm, Thomas K M; Murata, Michio; Slotte, J Peter

    2016-04-12

    Bilayer lipids influence the lateral structure of the membranes, but the relationship between lipid properties and the lateral structure formed is not always understood. Model membrane studies on bilayers containing cholesterol and various phospholipids (PLs) suggest that high and low temperature melting PLs may segregate, especially in the presence of cholesterol. The effect of different PL headgroups on lateral structure of bilayers is also not clear. Here, we have examined the formation of lateral heterogeneity in increasingly complex (up to five-component) multilamellar bilayers. We have used time-resolved fluorescence spectroscopy with domain-selective fluorescent probes (PL-conjugated trans-parinaric acid), and (2)H NMR spectroscopy with site or perdeuterated PLs. We have measured changes in bilayer order using such domain-selective probes both as a function of temperature and composition. Our results from time-resolved fluorescence and (2)H NMR showed that in ternary bilayers, acyl chain order and thermostability in sphingomyelin-rich domains were not affected to any greater extent by the headgroup structure of the monounsaturated PLs (phosphatidylcholine, phosphatidylethanolamine, or phosphatidylserine) in the bilayer. In the complex five-component bilayers, we could not detect major differences between the different monounsaturated PLs regarding cholesterol-induced ordering. However, cholesterol clearly influenced deuterated N-palmitoyl sphingomyelin differently than the other deuterated PLs, suggesting that cholesterol favored N-palmitoyl sphingomyelin over the other PLs. Taken together, both the fluorescence spectroscopy and (2)H NMR data suggest that the complex five-component membranes displayed lateral heterogeneity, at least in the lower temperature regimen examined. PMID:27074681

  4. Investigation of the elastic properties of a lipid bilayer by fluorescence interferometry

    NASA Astrophysics Data System (ADS)

    Gui, Dong; Lin, Hsiang-Ku; Noruzifar, Ehsan; Pryadko, Leonid; Zandi, Roya; Mohideen, Umar

    2012-02-01

    Freestanding curved lipid bilayers were formed on micron diameter wells fabricated on a silicon chip. The height profile of the lipid bilayers was measured using fluorescence interference contrast microscopy. Dark and bright rings resulted from the interference of emission from the fluorophores in the lipid bilayers with the same light reflected from the bottom surface of the well. By changing the osmotic pressure difference across the bilayers, the relationship between the pressure and the membrane curvature was studied. By using Helfrich theory, the surface tension of the bilayer was extracted. The influence of detergents and antibiotics on the elastic property of lipid bilayers was also investigated.

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

    PubMed

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

    2013-07-01

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

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

    PubMed

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

    2013-08-14

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

  7. 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.

  8. The Effects of Polyunsaturated Lipid Components on bilayer Structure

    NASA Astrophysics Data System (ADS)

    Pramudya, Y.; Kiss, A.; Nguyen, Lam T.; Yuan, J.; Hirst, Linda S.

    2007-03-01

    Polyunsaturated fatty acids (PUFAs), such as DHA (Docosahexanoic Acid) and AA (Alphalinoleic Acid) have been the focus of much research attention in recent years, due to their apparent health benefits and effects on cell physiology. They are found in a variety of biological membranes and have been implicated with lipid raft formation and possible function, particularly in the retinal rod cells and the central nervous system. In this work lipid bilayer structure has been investigated in lipid mixtures, incorporating polyunsaturated fatty acid moieties. The structural effects of increasing concentrations of both symmetric and asymmetric PUFA materials on the bilayer structure are investigated via synchrotron x-ray diffraction on solution samples. We observe bilayer spacings to increase with the percentage of unsaturated fatty acid lipid in the membrane, whilst the degree of ordering significantly decreases. In fact above 20% of fatty acid, well defined bilayers are no longer observed to form. Evidence of phase separation can be clearly seen from these x-ray results and in combination with AFM measurements.

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

    PubMed Central

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

    2009-01-01

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

  10. Structural studies of lipid-protein interactions on cushioned bilayers

    NASA Astrophysics Data System (ADS)

    Ghosh, S. K.; Mukhopadhyay, M. K.; Ma, Y.; Lopez, I.; Bera, S.; Lurio, L. B.; Chakrabarti, A.; Kim, J. E.; Sanyal, M. K.; Sinha, S. K.

    2013-03-01

    Biological membranes are heterogeneous and dynamical organizations of lipids and proteins, which perform functions fundamental to cell survival. Lipid-protein interactions control these functions by influencing folding and stability of integral or peripheral membrane proteins. Further, the incorporation or adsorption of these proteins into the membrane can in turn influence the lipid bilayer properties. In spite of some progress in understanding this process, a detailed structural analysis is lacking. Towards a better understanding of this interaction, we have performed an advanced interface sensitive scattering experiment using synchrotron x-rays. To accurately mimic the biological membranes with their natural thermal fluctuations and in-plane mobility of lipid molecules, polymer cushioned lipid bilayers have been used. This study shows that the adsorption of peripheral membrane proteinspectrindepends on the lipid headgroups, exhibiting different types of binding to phosphatidylcholine (PC) and phosphatidylethanolamie (PE). Further, the interaction of outer membrane protein A (OMP-A), an integral membrane protein is sensitive to the thermodynamic phase of the lipids. A detailed physical modeling of the lipid-protein interactions is under way.

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

    PubMed

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

    2015-01-01

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

  12. Multi-scale modeling of ternary-component lipid bilayers

    NASA Astrophysics Data System (ADS)

    Tumaneng, Paul

    The connection between membrane inhomogeneity and the structural basis of lipid rafts has sparked interest in the lateral organization of model lipid bilayers of two and three components. In an effort to investigate lateral organization in mixed bilayers, a self-consistent mean-field theoretical model is presented and applied to two important three-component bilayer mixtures. The model utilizes molecular dynamics simulations to estimate interaction parameters and to construct chain conformation libraries for utilization in a statistical mechanical treatment. The first application is to dipalmitoylphosphatidylcholine (DOPC) - stearoyl sphingomyelin (SSM) - cholesterol mixtures. The compositional dependence of lateral organization in these mixtures is mapped onto a ternary plot. It is found that at some concentration ratios the bilayers separate spatially into regions of higher and lower chain order coinciding with areas enriched with SSM and DOPC respectively. In the second application, ternary mixtures of palmitoyloleoylphosphatidylcholine (POPC) - palmitoyl sphingomyelin (PSM) - cholesterol are investigated. Again, results are organized onto a ternary plot. To examine the effect of the asymmetric chain structure of POPC on bilayer lateral inhomogeneity, POPC-POPC interactions with and without angular dependence are considered. Results are compared with experimental data and with results from the DOPC - SSM - cholesterol mixtures.

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

    PubMed

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

    2016-06-01

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

  14. TARP phosphorylation regulates synaptic AMPA receptors through lipid bilayers

    PubMed Central

    Sumioka, Akio; Yan, Dan; Tomita, Susumu

    2010-01-01

    Summary Neurons use neurotransmitters to communicate across synapses, constructing neural circuits in the brain. AMPA-type glutamate receptors are the predominant excitatory neurotransmitter receptors mediating fast synaptic transmission. AMPA receptors localize at synapses by forming protein complexes with transmembrane AMPA receptor regulatory proteins (TARPs) and PSD-95-like MAGUKs. Among the three classes of ionotropic glutamate receptors (AMPA-, NMDA, kainate-type), AMPA receptor activity is most regulatable by neuronal activity to adjust synaptic strength. Here, we mutated the prototypical TARP, stargazin, and found that TARP phosphorylation regulates synaptic AMPA receptor activity in vivo. We also found that stargazin interacts with negatively-charged lipid bilayers in its phosphorylation dependent manner, and that the lipid interaction inhibited stargazin binding to PSD-95. Cationic lipids dissociated stargazin from lipid bilayers and enhanced synaptic AMPA receptor activity in a stargazin phosphorylation-dependent manner. Thus, TARP phosphorylation plays a critical role in regulating AMPA receptor-mediated synaptic transmission via a lipid bilayer interaction. PMID:20547132

  15. Collective Lipid Bilayer Dynamics Excited by Surface Acoustic Waves

    NASA Astrophysics Data System (ADS)

    Reusch, T.; Schülein, F. J. R.; Nicolas, J. D.; Osterhoff, M.; Beerlink, A.; Krenner, H. J.; Müller, M.; Wixforth, A.; Salditt, T.

    2014-09-01

    We use standing surface acoustic waves to induce coherent phonons in model lipid multilayers deposited on a piezoelectric surface. Probing the structure by phase-controlled stroboscopic x-ray pulses we find that the internal lipid bilayer electron density profile oscillates in response to the externally driven motion of the lipid film. The structural response to the well-controlled motion is a strong indication that bilayer structure and membrane fluctuations are intrinsically coupled, even though these structural changes are averaged out in equilibrium and time integrating measurements. Here the effects are revealed by a timing scheme with temporal resolution on the picosecond scale in combination with the sub-nm spatial resolution, enabled by high brilliance synchrotron x-ray reflectivity.

  16. Lipid Bilayer Membrane-Triggered Presynaptic Vesicle Assembly

    PubMed Central

    2009-01-01

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

  17. Dynamics and instabilities of lipid bilayer membrane shapes

    PubMed Central

    Shi, Zheng; Baumgart, Tobias

    2014-01-01

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

  18. Atomistic Simulations of Pore Formation and Closure in Lipid Bilayers

    PubMed Central

    Bennett, W. F. Drew; Sapay, Nicolas; Tieleman, D. Peter

    2014-01-01

    Cellular membranes separate distinct aqueous compartments, but can be breached by transient hydrophilic pores. A large energetic cost prevents pore formation, which is largely dependent on the composition and structure of the lipid bilayer. The softness of bilayers and the disordered structure of pores make their characterization difficult. We use molecular-dynamics simulations with atomistic detail to study the thermodynamics, kinetics, and mechanism of pore formation and closure in DLPC, DMPC, and DPPC bilayers, with pore formation free energies of 17, 45, and 78 kJ/mol, respectively. By using atomistic computer simulations, we are able to determine not only the free energy for pore formation, but also the enthalpy and entropy, which yields what is believed to be significant new insights in the molecular driving forces behind membrane defects. The free energy cost for pore formation is due to a large unfavorable entropic contribution and a favorable change in enthalpy. Changes in hydrogen bonding patterns occur, with increased lipid-water interactions, and fewer water-water hydrogen bonds, but the total number of overall hydrogen bonds is constant. Equilibrium pore formation is directly observed in the thin DLPC lipid bilayer. Multiple long timescale simulations of pore closure are used to predict pore lifetimes. Our results are important for biological applications, including the activity of antimicrobial peptides and a better understanding of membrane protein folding, and improve our understanding of the fundamental physicochemical nature of membranes. PMID:24411253

  19. Naratriptan aggregation in lipid bilayers: perspectives from molecular dynamics simulations.

    PubMed

    Wood, Irene; Pickholz, Mónica

    2016-09-01

    In order to understand the interaction between naratriptan and a fully hydrated bilayer of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidyl-choline (POPC), we carried out molecular dynamics simulations. The simulations were performed considering neutral and protonated ionization states, starting from different initial conditions. At physiological pH, the protonated state of naratriptan is predominant. It is expected that neutral compounds could have larger membrane partition than charged compounds. However, for the specific case of triptans, it is difficult to study neutral species in membranes experimentally, making computer simulations an interesting tool. When the naratriptan molecules were originally placed in water, they partitioned between the bilayer/water interface and water phase, as has been described for similar compounds. From this condition, the drugs displayed low access to the hydrophobic environment, with no significant effects on bilayer organization. The molecules anchored in the interface, due mainly to the barrier function of the polar and oriented lipid heads. On the other hand, when placed inside the bilayer, both neutral and protonated naratriptan showed self-aggregation in the lipid tail environment. In particular, the protonated species exhibited a pore-like structure, dragging water through this environment. Graphical Abstract Different behaviour of Naratriptan and Sumatriptan, when the drugs were originally placed in the lipid core. PMID:27558798

  20. Dynamics and instabilities of lipid bilayer membrane shapes.

    PubMed

    Shi, Zheng; Baumgart, Tobias

    2014-06-01

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

  1. Strong influence of periodic boundary conditions on lateral diffusion in lipid bilayer membranes.

    PubMed

    Camley, Brian A; Lerner, Michael G; Pastor, Richard W; Brown, Frank L H

    2015-12-28

    The Saffman-Delbrück hydrodynamic model for lipid-bilayer membranes is modified to account for the periodic boundary conditions commonly imposed in molecular simulations. Predicted lateral diffusion coefficients for membrane-embedded solid bodies are sensitive to box shape and converge slowly to the limit of infinite box size, raising serious doubts for the prospects of using detailed simulations to accurately predict membrane-protein diffusivities and related transport properties. Estimates for the relative error associated with periodic boundary artifacts are 50% and higher for fully atomistic models in currently feasible simulation boxes. MARTINI simulations of LacY membrane protein diffusion and LacY dimer diffusion in DPPC membranes and lipid diffusion in pure DPPC bilayers support the underlying hydrodynamic model. PMID:26723598

  2. Strong influence of periodic boundary conditions on lateral diffusion in lipid bilayer membranes

    SciTech Connect

    Camley, Brian A.; Lerner, Michael G.; Pastor, Richard W.; Brown, Frank L. H.

    2015-12-28

    The Saffman-Delbrück hydrodynamic model for lipid-bilayer membranes is modified to account for the periodic boundary conditions commonly imposed in molecular simulations. Predicted lateral diffusion coefficients for membrane-embedded solid bodies are sensitive to box shape and converge slowly to the limit of infinite box size, raising serious doubts for the prospects of using detailed simulations to accurately predict membrane-protein diffusivities and related transport properties. Estimates for the relative error associated with periodic boundary artifacts are 50% and higher for fully atomistic models in currently feasible simulation boxes. MARTINI simulations of LacY membrane protein diffusion and LacY dimer diffusion in DPPC membranes and lipid diffusion in pure DPPC bilayers support the underlying hydrodynamic model.

  3. Strong influence of periodic boundary conditions on lateral diffusion in lipid bilayer membranes

    NASA Astrophysics Data System (ADS)

    Camley, Brian A.; Lerner, Michael G.; Pastor, Richard W.; Brown, Frank L. H.

    2015-12-01

    The Saffman-Delbrück hydrodynamic model for lipid-bilayer membranes is modified to account for the periodic boundary conditions commonly imposed in molecular simulations. Predicted lateral diffusion coefficients for membrane-embedded solid bodies are sensitive to box shape and converge slowly to the limit of infinite box size, raising serious doubts for the prospects of using detailed simulations to accurately predict membrane-protein diffusivities and related transport properties. Estimates for the relative error associated with periodic boundary artifacts are 50% and higher for fully atomistic models in currently feasible simulation boxes. MARTINI simulations of LacY membrane protein diffusion and LacY dimer diffusion in DPPC membranes and lipid diffusion in pure DPPC bilayers support the underlying hydrodynamic model.

  4. How antimicrobial peptides disrupt lipid bilayers?

    NASA Astrophysics Data System (ADS)

    Sengupta, Durba

    2011-03-01

    The molecular basis for the activity of cyclic and linear antimicrobial peptides is analysed. We performed multi-scale molecular dynamics simulations and biophysical measurements to probe the interaction of antimicrobial peptides with model membranes. Two linear antimicrobial peptides, magainin and melittin and a cyclic one, BPC194 have been studied. We test different models to determine the generic and specific forces that lead to bilayer disruption. We probe whether interfacial stress or local membrane perturbation is more likely to lead to the porated state. We further analyse the reasons that determine specificity and increase of activity in antimicrobial peptides. The results provide detailed insight in the mode of action of antimicrobial peptides.

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

    PubMed

    Qian, Shuo; Heller, William T

    2015-10-01

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

  6. The effect of compatible solute ectoines on the structural organization of lipid monolayer and bilayer membranes.

    PubMed

    Harishchandra, Rakesh Kumar; Wulff, Stephanie; Lentzen, Georg; Neuhaus, Thorsten; Galla, Hans-Joachim

    2010-08-01

    Compatible solutes are small organic osmolytes responsible for osmotic balance and at the same time compatible with the cellular metabolism. Here, we have investigated the effect of the compatible solutes, ectoine and hydroxyectoine, on the fluid-rigid domain structure of lipid monolayer and bilayer membranes. Mainly saturated dipalmitoyl-phosphatidylcholine membranes exhibiting a clear le/lc phase transition were used. Fluorescence microscopy showed that ectoines added to the aqueous subphase expand and fluidize the lipid monolayers especially at surface pressures below 30mN/m. The domain structure at the le/lc phase transition is sensitively modified leading to smaller but more numerous domains in the presence of ectoines. Hydroxyectoine was more efficient than ectoine. These results are explained by the replacement theory assuming that the ectoines are likely to be expelled from the membrane surface thus favoring the hydration of the lipid membrane. This effect reduces the line tension, which is the interfacial energy at the domain edges leading to reduced domain sizes and increased number of rigid domains. Isotherms of negatively charged phosphatidylglycerol membranes show a similar expansion, while unsaturated lipids are less affected. Mixed phosphatidylcholine/phosphatidylglycerol membranes exhibit the same effect on the line tension increasing the tendency for a phase separation. This could be shown also in bilayer vesicles, where the compatible solutes have only a minor effect on the lipid main phase transition in pure DPPC membranes but reduce the extent of the pretransition. In mixed DPPC/DPPG bilayer membranes ectoines cause a phase separation leading to the enrichment of expanded DPPC domains. In conclusion, our study gives for the first time evidence that ectoines have an effect on lipid membranes increasing the hydration of the surface and thus increasing the mobility of the lipid head groups and fluidizing the lipid layer accordingly. This increased

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

    PubMed

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

    2015-09-15

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

  8. Permeability of acetic acid across gel and liquid-crystalline lipid bilayers conforms to free-surface-area theory.

    PubMed Central

    Xiang, T X; Anderson, B D

    1997-01-01

    Solubility-diffusion theory, which treats the lipid bilayer membrane as a bulk lipid solvent into which permeants must partition and diffuse across, fails to account for the effects of lipid bilayer chain order on the permeability coefficient of any given permeant. This study addresses the scaling factor that must be applied to predictions from solubility-diffusion theory to correct for chain ordering. The effects of bilayer chemical composition, temperature, and phase structure on the permeability coefficient (Pm) of acetic acid were investigated in large unilamellar vesicles by a combined method of NMR line broadening and dynamic light scattering. Permeability values were obtained in distearoylphosphatidylcholine, dipalmitoylphosphatidylcholine, dimyristoylphosphatidylcholine, and dilauroylphosphatidylcholine bilayers, and their mixtures with cholesterol, at various temperatures both above and below the gel-->liquid-crystalline phase transition temperatures (Tm). A new scaling factor, the permeability decrement f, is introduced to account for the decrease in permeability coefficient from that predicted by solubility-diffusion theory owing to chain ordering in lipid bilayers. Values of f were obtained by division of the observed Pm by the permeability coefficient predicted from a bulk solubility-diffusion model. In liquid-crystalline phases, a strong correlation (r = 0.94) between f and the normalized surface density sigma was obtained: in f = 5.3 - 10.6 sigma. Activation energies (Ea) for the permeability of acetic acid decreased with decreasing phospholipid chain length and correlated with the sensitivity of chain ordering to temperature, [symbol: see text] sigma/[symbol: see text](1/T), as chain length was varied. Pm values decreased abruptly at temperatures below the main phase transition temperatures in pure dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine bilayers (30-60-fold) and below the pretransition in dipalmitoylphosphatidylcholine

  9. Phase separation of lipid microdomains controlled by polymerized lipid bilayer matrices.

    PubMed

    Okazaki, Takashi; Tatsu, Yoshiro; Morigaki, Kenichi

    2010-03-16

    We developed a micropatterned model biological membrane on a solid substrate that can induce phase separation of lipid microdomains in a designed geometry. Micropatterned lipid bilayers were generated by the photolithographic polymerization of a diacetylene phospholipid, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DiynePC). By changing the UV dose for the photopolymerization, we could modulate the coverage of the surface by the polymeric bilayer domains. After removing nonpolymerized DiynePC, natural phospholipid membranes were incorporated into the micropatterned polymeric bilayer matrix by a self-assembly process (vesicle fusion). As we incorporated a ternary lipid mixture of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), sphingomyelin (SM), and cholesterol (Chol) (1:1:1), liquid ordered domains (Lo: rich in SM and Chol) were accumulated in the polymer free regions, whereas liquid disordered domains (Ld: rich in DOPC) preferentially participated into the partially polymeric bilayer regions. It was postulated that Ld domains preferentially came in contact with the polymeric bilayer boundaries because of their lower elastic moduli and a smaller thickness mismatch at the boundary. The effect of polymeric bilayer matrix to hinder the size growth of Lo domains should also be playing an important role. The controlled phase separation should open new possibilities to locally concentrate membrane proteins and other nanometer-sized materials on the substrate by associating them with the lipid microdomains. PMID:20020734

  10. Manipulating lipid bilayer material properties using biologically active amphipathic molecules

    NASA Astrophysics Data System (ADS)

    Ashrafuzzaman, Md; Lampson, M. A.; Greathouse, D. V.; Koeppe, R. E., II; Andersen, O. S.

    2006-07-01

    Lipid bilayers are elastic bodies with properties that can be manipulated/controlled by the adsorption of amphipathic molecules. The resulting changes in bilayer elasticity have been shown to regulate integral membrane protein function. To further understand the amphiphile-induced modulation of bilayer material properties (thickness, intrinsic monolayer curvature and elastic moduli), we examined how an enantiomeric pair of viral anti-fusion peptides (AFPs)—Z-Gly-D-Phe and Z-Gly-Phe, where Z denotes a benzyloxycarbonyl group, as well as Z-Phe-Tyr and Z-D-Phe-Phe-Gly—alters the function of enantiomeric pairs of gramicidin channels of different lengths in planar bilayers. For both short and long channels, the channel lifetimes and appearance frequencies increase as linear functions of the aqueous AFP concentration, with no apparent effect on the single-channel conductance. These changes in channel function do not depend on the chirality of the channels or the AFPs. At pH 7.0, the relative changes in channel lifetimes do not vary when the channel length is varied, indicating that these compounds exert their effects primarily by causing a positive-going change in the intrinsic monolayer curvature. At pH 4.0, the AFPs are more potent than at pH 7.0 and have greater effects on the shorter channels, indicating that these compounds now change the bilayer elastic moduli. When AFPs of different anti-fusion potencies are compared, the rank order of the anti-fusion activity and the channel-modifying activity is similar, but the relative changes in anti-fusion potency are larger than the changes in channel-modifying activity. We conclude that gramicidin channels are useful as molecular force transducers to probe the influence of small amphiphiles upon lipid bilayer material properties.

  11. Melittin-induced cholesterol reorganization in lipid bilayer membranes

    SciTech Connect

    Qian, Shuo; Heller, William T.

    2015-06-12

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

  12. Melittin-induced cholesterol reorganization in lipid bilayer membranes

    DOE PAGESBeta

    Qian, Shuo; Heller, William T.

    2015-06-12

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

  13. Dynamic and mechanical properties of supported lipid bilayers.

    PubMed

    Wu, Hsing-Lun; Tsao, Heng-Kwong; Sheng, Yu-Jane

    2016-04-21

    Supported lipid bilayers (SLBs) offer an excellent model system for investigating the physico-chemical properties of the cell membrane. In this work, dynamic and mechanical properties of SLBs are explored by dissipative particle dynamics simulations for lipids with different architectures (chain length, kink, and asymmetry associated with lipid tails). It is found that the lateral diffusivity (Dx) and flip-flop rate (FF) grow with increasing temperature in both gel and liquid phases and can be described by an Arrhenius-like expression. Three regimes can be clearly identified for symmetric and asymmetric saturated lipids but only two regimes are observed for kinked lipids. Both Dx and FF grow with decreasing tail length and increasing number of kinks. The stretching (KA) and apparent bending (KB) moduli exhibit concave upward curves with temperature and the minima are attained at Tm. In general, the minima of KA and KB decrease with the chain length and increase with number of kinks. The typical relation among the bending modulus, area stretching modulus, and bilayer thickness is still followed, KB = βKAh(2) and β is much smaller in the gel phase. The dynamic and mechanical properties of lipids with asymmetric tails are found to situate between their symmetric counterparts. PMID:27389237

  14. Dynamic and mechanical properties of supported lipid bilayers

    NASA Astrophysics Data System (ADS)

    Wu, Hsing-Lun; Tsao, Heng-Kwong; Sheng, Yu-Jane

    2016-04-01

    Supported lipid bilayers (SLBs) offer an excellent model system for investigating the physico-chemical properties of the cell membrane. In this work, dynamic and mechanical properties of SLBs are explored by dissipative particle dynamics simulations for lipids with different architectures (chain length, kink, and asymmetry associated with lipid tails). It is found that the lateral diffusivity (Dx) and flip-flop rate (FF) grow with increasing temperature in both gel and liquid phases and can be described by an Arrhenius-like expression. Three regimes can be clearly identified for symmetric and asymmetric saturated lipids but only two regimes are observed for kinked lipids. Both Dx and FF grow with decreasing tail length and increasing number of kinks. The stretching (KA) and apparent bending (KB) moduli exhibit concave upward curves with temperature and the minima are attained at Tm. In general, the minima of KA and KB decrease with the chain length and increase with number of kinks. The typical relation among the bending modulus, area stretching modulus, and bilayer thickness is still followed, KB = βKAh2 and β is much smaller in the gel phase. The dynamic and mechanical properties of lipids with asymmetric tails are found to situate between their symmetric counterparts.

  15. Formation of solid-supported lipid bilayers: an integrated view.

    PubMed

    Richter, Ralf P; Bérat, Rémi; Brisson, Alain R

    2006-04-11

    Supported lipid bilayers (SLBs) are popular models of cell membranes with potential bio-technological applications. A qualitative understanding of the process of SLB formation after exposure of small lipid vesicles to a hydrophilic support is now emerging. Recent studies have revealed a stunning variety of effects that can take place during this self-organization process. The ensemble of results in our group has revealed unprecedented insight into intermediates of the SLB-formation process and has helped to identify a number of parameters that are determinant for the lipid deposition on solid supports. The pathway of lipid deposition can be tuned by electrostatic interactions and by the presence of calcium. We emphasize the importance of the solid support in the SLB-formation process. Our results suggest that the molecular-level interaction between lipids and the solid support needs to be considered explicitly, to understand the rupture of vesicles and the formation of SLBs as well as to predict the properties of the resulting SLB. The impact of the SLB-formation process on the quality and the physical properties of the resulting SLB as well as implications for other types of surface-confined lipid bilayers are discussed. PMID:16584220

  16. Molecular Dynamics Simulations of Hydrophilic Pores in Lipid Bilayers

    PubMed Central

    Leontiadou, Hari; Mark, Alan E.; Marrink, Siewert J.

    2004-01-01

    Hydrophilic pores are formed in peptide free lipid bilayers under mechanical stress. It has been proposed that the transport of ionic species across such membranes is largely determined by the existence of such meta-stable hydrophilic pores. To study the properties of these structures and understand the mechanism by which pore expansion leads to membrane rupture, a series of molecular dynamics simulations of a dipalmitoylphosphatidylcholine (DPPC) bilayer have been conducted. The system was simulated in two different states; first, as a bilayer containing a meta-stable pore and second, as an equilibrated bilayer without a pore. Surface tension in both cases was applied to study the formation and stability of hydrophilic pores inside the bilayers. It is observed that below a critical threshold tension of ∼38 mN/m the pores are stabilized. The minimum radius at which a pore can be stabilized is 0.7 nm. Based on the critical threshold tension the line tension of the bilayer was estimated to be ∼3 × 10−11 N, in good agreement with experimental measurements. The flux of water molecules through these stabilized pores was analyzed, and the structure and size of the pores characterized. When the lateral pressure exceeds the threshold tension, the pores become unstable and start to expand causing the rupture of the membrane. In the simulations the mechanical threshold tension necessary to cause rupture of the membrane on a nanosecond timescale is much higher in the case of the equilibrated bilayers, as compared with membranes containing preexisting pores. PMID:15041656

  17. Hydrophobic Coupling of Lipid Bilayer Energetics to Channel Function

    PubMed Central

    Goforth, Robyn L.; Chi, Aung K.; Greathouse, Denise V.; Providence, Lyndon L.; Koeppe, Roger E.; Andersen, Olaf S.

    2003-01-01

    The hydrophobic coupling between membrane-spanning proteins and the lipid bilayer core causes the bilayer thickness to vary locally as proteins and other “defects” are embedded in the bilayer. These bilayer deformations incur an energetic cost that, in principle, could couple membrane proteins to each other, causing them to associate in the plane of the membrane and thereby coupling them functionally. We demonstrate the existence of such bilayer-mediated coupling at the single-molecule level using single-barreled as well as double-barreled gramicidin channels in which two gramicidin subunits are covalently linked by a water-soluble, flexible linker. When a covalently attached pair of gramicidin subunits associates with a second attached pair to form a double-barreled channel, the lifetime of both channels in the assembly increases from hundreds of milliseconds to a hundred seconds—and the conductance of each channel in the side-by-side pair is almost 10% higher than the conductance of the corresponding single-barreled channels. The double-barreled channels are stabilized some 100,000-fold relative to their single-barreled counterparts. This stabilization arises from: first, the local increase in monomer concentration around a single-barreled channel formed by two covalently linked gramicidins, which increases the rate of double-barreled channel formation; and second, from the increased lifetime of the double-barreled channels. The latter result suggests that the two barrels of the construct associate laterally. The underlying cause for this lateral association most likely is the bilayer deformation energy associated with channel formation. More generally, the results suggest that the mechanical properties of the host bilayer may cause the kinetics of membrane protein conformational transitions to depend on the conformational states of the neighboring proteins. PMID:12719487

  18. Mechanical properties of lipid bilayers and regulation of mechanosensitive function

    PubMed Central

    Balleza, Daniel

    2012-01-01

    Material properties of lipid bilayers, including thickness, intrinsic curvature and compressibility regulate the function of mechanosensitive (MS) channels. This regulation is dependent on phospholipid composition, lateral packing and organization within the membrane. Therefore, a more complete framework to understand the functioning of MS channels requires insights into bilayer structure, thermodynamics and phospholipid structure, as well as lipid-protein interactions. Phospholipids and MS channels interact with each other mainly through electrostatic forces and hydrophobic matching, which are also crucial for antimicrobial peptides. They are excellent models for studying the formation and stabilization of membrane pores. Importantly, they perform equivalent responses as MS channels: (1) tilting in response to tension and (2) dissipation of osmotic gradients. Lessons learned from pore forming peptides could enrich our knowledge of mechanisms of action and evolution of these channels. Here, the current state of the art is presented and general principles of membrane regulation of mechanosensitive function are discussed. PMID:22790280

  19. Supported Lipid Bilayer Technology for the Study of Cellular Interfaces

    PubMed Central

    Crites, Travis J.; Maddox, Michael; Padhan, Kartika; Muller, James; Eigsti, Calvin; Varma, Rajat

    2015-01-01

    Glass-supported lipid bilayers presenting freely diffusing proteins have served as a powerful tool for studying cell-cell interfaces, in particular, T cell–antigen presenting cell (APC) interactions, using optical microscopy. Here we expand upon existing protocols and describe the preparation of liposomes by an extrusion method, and describe how this system can be used to study immune synapse formation by Jurkat cells. We also present a method for forming such lipid bilayers on silica beads for the study of signaling responses by population methods, such as western blotting, flow cytometry, and gene-expression analysis. Finally, we describe how to design and prepare transmembrane-anchored protein-laden liposomes, following expression in suspension CHO (CHOs) cells, a mammalian expression system alternative to insect and bacterial cell lines, which do not produce mammalian glycosylation patterns. Such transmembrane-anchored proteins may have many novel applications in cell biology and immunology. PMID:26331983

  20. 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.

  1. Monolayer curvature stabilizes nanoscale raft domains in mixed lipid bilayers

    PubMed Central

    Meinhardt, Sebastian; Vink, Richard L. C.; Schmid, Friederike

    2013-01-01

    According to the lipid raft hypothesis, biological lipid membranes are laterally heterogeneous and filled with nanoscale ordered “raft” domains, which are believed to play an important role for the organization of proteins in membranes. However, the mechanisms stabilizing such small rafts are not clear, and even their existence is sometimes questioned. Here, we report the observation of raft-like structures in a coarse-grained molecular model for multicomponent lipid bilayers. On small scales, our membranes demix into a liquid ordered (lo) phase and a liquid disordered (ld) phase. On large scales, phase separation is suppressed and gives way to a microemulsion-type state that contains nanometer-sized lo domains in an ld environment. Furthermore, we introduce a mechanism that generates rafts of finite size by a coupling between monolayer curvature and local composition. We show that mismatch between the spontaneous curvatures of monolayers in the lo and ld phases induces elastic interactions, which reduce the line tension between the lo and ld phases and can stabilize raft domains with a characteristic size of the order of a few nanometers. Our findings suggest that rafts in multicomponent bilayers might be closely related to the modulated ripple phase in one-component bilayers. PMID:23487780

  2. Interaction of Daptomycin with Lipid Bilayers: A Lipid Extracting Effect

    PubMed Central

    2015-01-01

    Daptomycin is the first approved member of a new structural class of antibiotics, the cyclic lipopeptides. The peptide interacts with the lipid matrix of cell membranes, inducing permeability of the membrane to ions, but its molecular mechanism has been a puzzle. Unlike the ubiquitous membrane-acting host-defense antimicrobial peptides, daptomycin does not induce pores in the cell membranes. Thus, how it affects the permeability of a membrane to ions is not clear. We studied its interaction with giant unilamellar vesicles (GUVs) and discovered a lipid-extracting phenomenon that correlates with the direct action of daptomycin on bacterial membranes observed in a recent fluorescence microscopy study. Lipid extraction occurred only when the GUV lipid composition included phosphatidylglycerol and in the presence of Ca2+ ions, the same condition found to be necessary for daptomycin to be effective against bacteria. Furthermore, it occurred only when the peptide/lipid ratio exceeded a threshold value, which could be the basis of the minimal inhibitory concentration of daptomycin. In this first publication on the lipid extracting effect, we characterize its dependence on ions and lipid compositions. We also discuss possibilities for connecting the lipid extracting effect to the antibacterial activity of daptomycin. PMID:25093761

  3. Volatile anesthetics inhibit sodium channels without altering bulk lipid bilayer properties

    PubMed Central

    Sanford, R. Lea; Lee, William; Schultz, Margaret F.; Ingólfsson, Helgi I.

    2014-01-01

    Although general anesthetics are clinically important and widely used, their molecular mechanisms of action remain poorly understood. Volatile anesthetics such as isoflurane (ISO) are thought to alter neuronal function by depressing excitatory and facilitating inhibitory neurotransmission through direct interactions with specific protein targets, including voltage-gated sodium channels (Nav). Many anesthetics alter lipid bilayer properties, suggesting that ion channel function might also be altered indirectly through effects on the lipid bilayer. We compared the effects of ISO and of a series of fluorobenzene (FB) model volatile anesthetics on Nav function and lipid bilayer properties. We examined the effects of these agents on Nav in neuronal cells using whole-cell electrophysiology, and on lipid bilayer properties using a gramicidin-based fluorescence assay, which is a functional assay for detecting changes in lipid bilayer properties sensed by a bilayer-spanning ion channel. At clinically relevant concentrations (defined by the minimum alveolar concentration), both the FBs and ISO produced prepulse-dependent inhibition of Nav and shifted the voltage dependence of inactivation toward more hyperpolarized potentials without affecting lipid bilayer properties, as sensed by gramicidin channels. Only at supra-anesthetic (toxic) concentrations did ISO alter lipid bilayer properties. These results suggest that clinically relevant concentrations of volatile anesthetics alter Nav function through direct interactions with the channel protein with little, if any, contribution from changes in bulk lipid bilayer properties. Our findings further suggest that changes in lipid bilayer properties are not involved in clinical anesthesia. PMID:25385786

  4. The Interaction of Melittin with Dimyristoyl Phosphatidylcholine-Dimyristoyl Phosphatidylserine Lipid Bilayer Membranes

    DOE PAGESBeta

    Rai, Durgesh K.; Qian, Shuo; Heller, William T.

    2016-08-13

    We report that membrane-active peptides (MAPs), which interact directly with the lipid bilayer of a cell and include toxins and host defense peptides, display lipid composition-dependent activity. Phosphatidylserine (PS) lipids are anionic lipids that are found throughout the cellular membranes of most eukaryotic organisms where they serve as both a functional component and as a precursor to phosphatidylethanolamine lipids. The inner leaflet of the plasma membrane contains more PS than the outer one, and the asymmetry is actively maintained. Here, the impact of the MAP melittin on the structure of lipid bilayer vesicles made of a mixture of phosphatidylcholine andmore » phosphatidylserine was studied. Small-angle neutron scattering of the MAP associated with selectively deuterium-labeled lipid bilayer vesicles revealed how the thickness and lipid composition of phosphatidylserine-containing vesicles change in response to melittin. The peptide thickens the lipid bilayer for concentrations up to P/L = 1/500, but membrane thinning results when P/L = 1/200. The thickness transition is accompanied by a large change in the distribution of DMPS between the leaflets of the bilayer. The change in composition is driven by electrostatic interactions, while the change in bilayer thickness is driven by changes in the interaction of the peptide with the headgroup region of the lipid bilayer. Lastly, the results provide new information about lipid-specific interactions that take place in mixed composition lipid bilayer membranes.« less

  5. A comparison of DMPC- and DLPE-based lipid bilayers.

    PubMed Central

    Damodaran, K V; Merz, K M

    1994-01-01

    A 250 ps molecular dynamics simulation of the dimyristoylphosphatidylcholine (DMPC)-based lipid bilayer, including explicit water molecules, is reported. The solvent environment of the head groups and other structural properties of the bilayer have been analyzed and compared with experimental results as well as our previous simulation of the dilauroylphosphatidylethanolamine (DLPE)-based bilayer. From this comparison we find that the solvent structure around the DMPC head group (clathrate shell) is significantly different than that around the DLPE head group (typical hydrogen bonding interactions). We have modeled the probable relationship between the different solvent environments around the R-N(CH3)3+ (DMPC) and R-NH3+ (DLPE) head groups and the different interlammelar distances in these systems by performing potential of mean force (PMF) simulations on two N(CH3)4+ and NH4+ ions in water. From the PMF simulations it appears that the differences in the hydration of the DMPC and DLPE head groups is not responsible for the differences in the hydration force observed for these systems. We also find that the orientational polarization of DLPE and DMPC is similar, which suggests that solvent polarization is not responsible for the differences in the hydration repulsion behavior observed in these systems. We also examined the order parameters for DMPC and found them to be in reasonable agreement with experiment. Given the different characteristics of the DLPE and DMPC head groups, we suggest an explanation of the differences in the interlammellar spacings of bilayers composed of these like-charged lipids. From our DLPE simulations we find that the R-NH3+ head groups can interact with the nonesterified oxygens of the phosphate group in an intraleaflet or an interleaflet manner. For the latter a "cross link" between two leaflets can be formed, which causes a stabilization of the interlamellar spacings at fairly short distances. Moreover, due to the strong intraleaflet

  6. Extension of the GLYCAM06 Biomolecular Force Field to Lipids, Lipid Bilayers and Glycolipids.

    PubMed

    Tessier, Matthew B; Demarco, Mari L; Yongye, Austin B; Woods, Robert J

    2008-01-01

    GLYCAM06 is a generalisable biomolecular force field that is extendible to diverse molecular classes in the spirit of a small-molecule force field. Here we report parameters for lipids, lipid bilayers and glycolipids for use with GLYCAM06. Only three lipid-specific atom types have been introduced, in keeping with the general philosophy of transferable parameter development. Bond stretching, angle bending, and torsional force constants were derived by fitting to quantum mechanical data for a collection of minimal molecular fragments and related small molecules. Partial atomic charges were computed by fitting to ensemble-averaged quantum-computed molecular electrostatic potentials.In addition to reproducing quantum mechanical internal rotational energies and experimental valence geometries for an array of small molecules, condensed-phase simulations employing the new parameters are shown to reproduce the bulk physical properties of a DMPC lipid bilayer. The new parameters allow for molecular dynamics simulations of complex systems containing lipids, lipid bilayers, glycolipids, and carbohydrates, using an internally consistent force field. By combining the AMBER parameters for proteins with the GLYCAM06 parameters, it is also possible to simulate protein-lipid complexes and proteins in biologically relevant membrane-like environments. PMID:22247593

  7. Lipid headgroups mediate organization and dynamics in bilayers

    NASA Astrophysics Data System (ADS)

    Greenough, Kelly P.; Blanchard, G. J.

    2009-01-01

    We report on the fluorescence lifetime and anisotropy decay dynamics of the tethered chromophore NBD in unilamellar vesicles comprised of phosphoglycerol and phosphocholine lipids with C 12 and C 18 saturated acyl chains, with or without cholesterol and/or sphingomyelin. For the phosphocholine vesicles, we use the chromophore 2-(12-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)dodecanoyl-1-hexadecanoyl- sn-glycero-3-phosphocholine (NBD-PC), and for the phosphoglycerol vesicles, we use the chromophore 2-(12-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)dodecanoyl-1-hexadecanoyl- sn-glycero-3-[phospho- rac-(1-glycerol)] (NBD-PG). The addition of cholesterol and/or sphingomyelin to the PC vesicles restricts the chromophore environment, in agreement with the known rigidizing effect of cholesterol on PC membranes. The PG systems do not exhibit an analogous effect with the addition of cholesterol and/or sphingomyelin. The motional freedom of the NBD chromophore is, in general, more restricted in the PC bilayers than it is in the PG bilayers, and we understand this behavior in the context of the role of the lipid headgroups in mediating bilayer organization.

  8. Voltage-dependent capacitance in lipid bilayers made from monolayers.

    PubMed

    Alvarez, O; Latorre, R

    1978-01-01

    Electrocompression has been measured in lipid bilayers made by apposition of two monolayers. The capacitance C(V), as a function of membrane potential, V, was found to be well described by C(V) = C(O) [1 + alpha(V + delta psi)2] where C(O) is the capacitance at V = O, alpha is the fractional increase in capacitance per square volt, and delta psi is the surface potential difference. In lipid bilayers made from monolayers alpha has a value of 0.02 V-2, which is ca. 500-fold smaller than the value found in solvent containing membranes. In asymmetric bilayers made of one neutral and one negatively charged monolayer, delta psi values were found to be those expected from independent measurements of surface charge density. If the fractional increase in capacitance found here is a good approximation to that of biological membranes, nonlinear capacitative charge displacement derived from electrostriction is expected to be less than 1% of the total gating charge displacement found in squid axons. PMID:620076

  9. Electrowetting on dielectric-based microfluidics for integrated lipid bilayer formation and measurement

    NASA Astrophysics Data System (ADS)

    Poulos, Jason L.; Nelson, Wyatt C.; Jeon, Tae-Joon; Kim, Chang-Jin ``Cj''; Schmidt, Jacob J.

    2009-07-01

    We present a microfluidic platform for the formation and electrical measurement of lipid bilayer membranes. Using electrowetting on dielectric (EWOD), two or more aqueous droplets surrounded by a lipid-containing organic phase were manipulated into contact to form a lipid bilayer at their interface. Thin-film Ag/AgCl electrodes integrated into the device enabled electrical measurement of membrane formation and the incorporation of gramicidin channels of two bilayers in parallel.

  10. Positively charged supported lipid bilayer formation on gold surfaces for neuronal cell culture.

    PubMed

    Choi, Sung-Eun; Greben, Kyrylo; Wördenweber, Roger; Offenhäusser, Andreas

    2016-06-01

    Supported lipid bilayers are widely used as cell membrane models and sensor platforms, but the usage on gold surface needs additional surface modification or optimized experimental conditions. In this work, the authors show lipid bilayer formation on plasma activated gold surfaces in physiological conditions without any other modification if at least 30% positively charged lipids are present. Details of bilayer formation from small unilamellar vesicles were monitored using quartz crystal microbalance with dissipation in both basic and acidic environment. The authors also confirmed that this positively charged bilayer system can sustain primary cortical neuron growth and lipid transfer. This method will provide simple means to construct biomimetic interface on gold electrodes. PMID:27052005

  11. Formation and finite element analysis of tethered bilayer lipid structures.

    PubMed

    Kwak, Kwang Joo; Valincius, Gintaras; Liao, Wei-Ching; Hu, Xin; Wen, Xuejin; Lee, Andrew; Yu, Bo; Vanderah, David J; Lu, Wu; Lee, L James

    2010-12-01

    Rapid solvent exchange of an ethanolic solution of diphytanoyl phosphatidylcholine (DPhyPC) in the presence of a mixed self-assembled monolayer (SAM) [thiolipid/β-mercaptoethanol (βME) (3/7 mol/mol) on Au] shows a transition from densely packed tethered bilayer lipid membranes [(dp)tBLMs], to loosely packed tethered bilayer lipid membranes [(lp)tBLMs], and tethered bilayer liposome nanoparticles (tBLNs) with decreasing DPhyPC concentration. The tethered lipidic constructs in the aqueous medium were analyzed by atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). Finite element analysis (FEA) was applied to interpret spectral EIS features without referring to equivalent circuit modeling. Using structural data obtained earlier from neutron reflectometry and dielectric constants of lipid bilayers, we reproduced experimentally observed features of the electrochemical impedance (EI) spectra of complex surface constructs involving small pinhole defects, large membrane-free patches, and bound liposomes. We demonstrated by FEA that highly insulating (dp)tBLMs with low-defect density exhibit EI spectra in the shape of a perfect semicircle with or without low-frequency upward "tails" in the Cole-Cole representation. Such EI spectra were observed at DPhyPC concentrations of >5 × 10(-3) mol L(-1). While AFM was not able to visualize very small lateral defects in such films, EI spectra unambiguously signaled their presence by increased low frequency "tails". Using FEA we demonstrate that films with large diameter visible defects (>25 nm by AFM) produce EI spectral features consisting of two semicircles of comparable size. Such films were typically obtained at DPhyPC concentrations of <5 × 10(-3) mol L(-1). At DPhyPC concentrations of <1.0 × 10(-3) mol L(-1) the planar bilayer structures were replaced by ellipsoidal liposomes with diameters ranging from 50 to 500 nm as observed in AFM images. Despite the distinct surface morphology change, the EI

  12. Lipid bilayer elasticity measurements in giant liposomes in contact with a solubilizing surfactant.

    PubMed

    Ménager, Christine; Guemghar, Dihya; Perzynski, Régine; Lesieur, Sylviane; Cabuil, Valérie

    2008-05-01

    A new method to probe the modification of the elasticity of phospholipid bilayers is presented. The purpose here concerns the action of a solubilizing surfactant on a vesicle bilayer. This method is based on the measure of the under-field elongation of giant magnetic-fluid-loaded liposomes. The addition of the nonionic surfactant octyl-beta-d-glucopyranoside (OG) to vesicles at sublytic levels increases the elasticity of the membrane, as shown by the value of the bending modulus K(b), which decreases. K(b) measured around 20 kT for a pure 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayer indeed reaches a few kT in the case of the mixed OG-DOPC bilayer. The purpose and interest of this study are to allow the determination of the membrane bending modulus before and after the addition of OG on the same magnetic liposome. Moreover, the experimental conditions used in this work allow the control of lipid and surfactant molar fractions in the mixed aggregates. Then, optical microscopy observation can be performed on samples in well-defined regions of the OG-phospholipid state diagram. PMID:18363418

  13. Lipid Bilayers: The Effect of Force Field on Ordering and Dynamics.

    PubMed

    Poger, David; Mark, Alan E

    2012-11-13

    The sensitivity of the structure and dynamics of a fully hydrated pure bilayer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in molecular dynamics simulations to changes in force-field and simulation parameters has been assessed. Three related force fields (the Gromos 54A7 force field, a Gromos 53A6-derived parameter set and a variant of the Berger parameters) in combination with either particle-mesh Ewald (PME) or a reaction field (RF) were compared. Structural properties such as the area per lipid, carbon-deuterium order parameters, electron density profile and bilayer thicknesses, are reproduced by all the parameter sets within the uncertainty of the available experimental data. However, there are clear differences in the ordering of the glycerol backbone and choline headgroup, and the orientation of the headgroup dipole. In some cases, the degree of ordering was reminiscent of a liquid-ordered phase. It is also shown that, although the lateral diffusion of the lipids in the plane of the bilayer is often used to validate lipid force fields, because of the uncertainty in the experimental measurements and the fact that the lateral diffusion is dependent on the choice of the simulation conditions, it should not be employed as a measure of quality. Finally, the simulations show that the effect of small changes in force-field parameters on the structure and dynamics of a bilayer is more significant than the treatment of the long-range electrostatic interactions using RF or PME. Overall, the Gromos 54A7 best reproduced the range of experimental data examined. PMID:26605633

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

    PubMed

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

    2010-07-01

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

  15. Assembly of RNA nanostructures on supported lipid bilayers

    PubMed Central

    Dabkowska, Aleksandra P.; Michanek, Agnes; Jaeger, Luc; Rabe, Michael; Chworos, Arkadiusz; Höök, Fredrik; Nylander, Tommy; Sparr, Emma

    2014-01-01

    The assembly of nucleic acid nanostructures with controlled size and shape has large impact in the fields of nanotechnology, nanomedicine and synthetic biology. The directed arrangement of nanostructures at interfaces is important for many applications. In spite of this, the use of laterally mobile lipid bilayers to control RNA three-dimensional nanostructure formation on surfaces remains largely unexplored. Here, we direct the self-assembly of RNA building blocks into three-dimensional structures of RNA on fluid lipid bilayers composed of cationic 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or mixtures of zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) and cationic sphingosine. We demonstrate the stepwise supramolecular assembly of discrete building blocks through specific and selective RNA-RNA interactions, based on results from quartz crystal microbalance with dissipation (QCM-D), ellipsometry, fluorescence recovery after photobleaching (FRAP) and total internal reflection fluorescence microscopy (TIRF) experiments. The assembly can be controlled to give a densely packed single layer of RNA polyhedrons at the fluid lipid bilayer surface. We show that assembly of the 3D structure can be modulated by sequence specific interactions, surface charge and changes in the salt composition and concentration. In addition, the tertiary structure of the RNA polyhedron can be controllably switched from an extended structure to one that is dense and compact. The versatile approach to building up three-dimensional structures of RNA does not require modification of the surface or the RNA molecules, and can be used as a bottom-up means of nanofabrication of functionalized bio-mimicking surfaces. PMID:25417592

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

    PubMed

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

    2016-04-01

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

  17. Lipid Bilayer Vesicle Dynamics in AC Electric Fields

    NASA Astrophysics Data System (ADS)

    McConnell, Lane; Vlahovska, Petia; Miksis, Michael

    2014-11-01

    Vesicles are closed, fluid-filled lipid bilayers which are mechanically similar to biological cells and which undergo shape transitions in the presence of electric fields. Here we model the vesicle membrane as an infinitely thin, capacitive, area-incompressible interface with the surrounding fluids acting as charge-advecting leaky dielectrics. We then implement the boundary integral method to numerically investigate the dynamics of a vesicle in various AC electric field profiles. Our numerical results are then compared with recent small deformation theory and experimental data. We also note our observation of a new theoretical vesicle behavior that has yet to be observed experimentally.

  18. Lipid bilayer array for simultaneous recording of ion channel activities

    NASA Astrophysics Data System (ADS)

    Hirano-Iwata, Ayumi; Nasu, Tomohiro; Oshima, Azusa; Kimura, Yasuo; Niwano, Michio

    2012-07-01

    This paper describes an array of stable and reduced-solvent bilayer lipid membranes (BLMs) formed in microfabricated silicon chips. BLMs were first vertically formed simultaneously and then turned 90° in order to realize a horizontal BLM array. Since the present BLMs are mechanically stable and robust, the BLMs survive this relatively tough process. Typically, a ˜60% yield in simultaneous BLM formation over 9 sites was obtained. Parallel recordings of gramicidin channel activities from different BLMs were demonstrated. The present system has great potential as a platform of BLM-based high throughput drug screening for ion channel proteins.

  19. Molecular sorting of lipids by bacteriorhodopsin in dilauroylphosphatidylcholine/distearoylphosphatidylcholine lipid bilayers.

    PubMed Central

    Dumas, F; Sperotto, M M; Lebrun, M C; Tocanne, J F; Mouritsen, O G

    1997-01-01

    A combined experimental and theoretical study is performed on binary dilauroylphosphatidylcholine/distearoylphosphatidylcholine (DLPC/DSPC) lipid bilayer membranes incorporating bacteriorhodopsin (BR). The system is designed to investigate the possibility that BR, via a hydrophobic matching principle related to the difference in lipid bilayer hydrophobic thickness and protein hydrophobic length, can perform molecular sorting of the lipids at the lipid-protein interface, leading to lipid specificity/selectivity that is controlled solely by physical factors. The study takes advantage of the strongly nonideal mixing behavior of the DLPC/DSPC mixture and the fact that the average lipid acyl-chain length is strongly dependent on temperature, particularly in the main phase transition region. The experiments are based on fluorescence energy transfer techniques using specifically designed lipid analogs that can probe the lipid-protein interface. The theoretical calculations exploit a microscopic molecular interaction model that embodies the hydrophobic matching as a key parameter. At low temperatures, in the gel-gel coexistence region, experimental and theoretical data consistently indicate that BR is associated with the short-chain lipid DLPC. At moderate temperatures, in the fluid-gel coexistence region, BR remains in the fluid phase, which is mainly composed of short-chain lipid DLPC, but is enriched at the interface between the fluid and gel domains. At high temperatures, in the fluid phase, BR stays in the mixed lipid phase, and the theoretical data suggest a preference of the protein for the long-chain DSPC molecules at the expense of the short-chain DLPC molecules. The combined results of the experiments and the calculations provide evidence that a molecular sorting principle is active because of hydrophobic matching and that BR exhibits physical lipid selectivity. The results are discussed in the general context of membrane organization and compartmentalization and

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

    PubMed

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

    2013-05-01

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

  1. Kinematics, material symmetry, and energy densities for lipid bilayers with spontaneous curvature

    PubMed Central

    Maleki, Mohsen; Seguin, Brian; Fried, Eliot

    2013-01-01

    Continuum mechanical tools are used to describe the deformation, energy density, and material symmetry of a lipid bilayer with spontaneous curvature. In contrast to conventional approaches in which lipid bilayers are modeled by material surfaces, here we rely on a three-dimensional approach in which a lipid bilayer is modeling by a shell-like body with finite thickness. In this setting, the interface between the leaflets of a lipid bilayer is assumed to coincide with the mid-surface of the corresponding shell-like body. The three-dimensional deformation gradient is found to involve the curvature tensors of the mid-surface in the spontaneous and the deformed states, the deformation gradient of the mid-surface, and the transverse deformation. Attention is also given to the coherency of the leaflets and to the area compatibility of closed lipid bilayers (i.e., vesicles). A hyperelastic constitutive theory for lipid bilayers in the liquid phase is developed. In combination, the requirements of frame-indifference and material symmetry yield a representation for the energy density of a lipid bilayer. This representation shows that three scalar invariants suffice to describe the constitutive response of a lipid bilayer exhibiting in-plane fluidity and transverse isotropy. In addition to exploring the geometrical and physical properties of these invariants, fundamental constitutively-associated kinematical quantities are emphasized. On this basis, the effect on the energy density of assuming that the lipid bilayer is incompressible is considered. Lastly, a dimension reduction argument is used to extract an areal energy density per unit area from the three-dimensional energy density. This step explains the origin of spontaneous curvature in the areal energy density. Importantly, along with a standard contribution associated with the natural curvature of lipid bilayer, our analysis indicates that constitutive asymmetry between the leaflets of the lipid bilayer gives rise to

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

    PubMed Central

    Pink, David A.; Chapman, Dennis

    1979-01-01

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

  3. Anisotropic metal growth on phospholipid nanodiscs via lipid bilayer expansion

    NASA Astrophysics Data System (ADS)

    Oertel, Jana; Keller, Adrian; Prinz, Julia; Schreiber, Benjamin; Hübner, René; Kerbusch, Jochen; Bald, Ilko; Fahmy, Karim

    2016-05-01

    Self-assembling biomolecules provide attractive templates for the preparation of metallic nanostructures. However, the intuitive transfer of the “outer shape” of the assembled macromolecules to the final metallic particle depends on the intermolecular forces among the biomolecules which compete with interactions between template molecules and the metal during metallization. The shape of the bio-template may thus be more dynamic than generally assumed. Here, we have studied the metallization of phospholipid nanodiscs which are discoidal particles of ~10 nm diameter containing a lipid bilayer ~5 nm thick. Using negatively charged lipids, electrostatic adsorption of amine-coated Au nanoparticles was achieved and followed by electroless gold deposition. Whereas Au nanoparticle adsorption preserves the shape of the bio-template, metallization proceeds via invasion of Au into the hydrophobic core of the nanodisc. Thereby, the lipidic phase induces a lateral growth that increases the diameter but not the original thickness of the template. Infrared spectroscopy reveals lipid expansion and suggests the existence of internal gaps in the metallized nanodiscs, which is confirmed by surface-enhanced Raman scattering from the encapsulated lipids. Interference of metallic growth with non-covalent interactions can thus become itself a shape-determining factor in the metallization of particularly soft and structurally anisotropic biomaterials.

  4. Anisotropic metal growth on phospholipid nanodiscs via lipid bilayer expansion

    PubMed Central

    Oertel, Jana; Keller, Adrian; Prinz, Julia; Schreiber, Benjamin; Hübner, René; Kerbusch, Jochen; Bald, Ilko; Fahmy, Karim

    2016-01-01

    Self-assembling biomolecules provide attractive templates for the preparation of metallic nanostructures. However, the intuitive transfer of the “outer shape” of the assembled macromolecules to the final metallic particle depends on the intermolecular forces among the biomolecules which compete with interactions between template molecules and the metal during metallization. The shape of the bio-template may thus be more dynamic than generally assumed. Here, we have studied the metallization of phospholipid nanodiscs which are discoidal particles of ~10 nm diameter containing a lipid bilayer ~5 nm thick. Using negatively charged lipids, electrostatic adsorption of amine-coated Au nanoparticles was achieved and followed by electroless gold deposition. Whereas Au nanoparticle adsorption preserves the shape of the bio-template, metallization proceeds via invasion of Au into the hydrophobic core of the nanodisc. Thereby, the lipidic phase induces a lateral growth that increases the diameter but not the original thickness of the template. Infrared spectroscopy reveals lipid expansion and suggests the existence of internal gaps in the metallized nanodiscs, which is confirmed by surface-enhanced Raman scattering from the encapsulated lipids. Interference of metallic growth with non-covalent interactions can thus become itself a shape-determining factor in the metallization of particularly soft and structurally anisotropic biomaterials. PMID:27216789

  5. Anisotropic metal growth on phospholipid nanodiscs via lipid bilayer expansion.

    PubMed

    Oertel, Jana; Keller, Adrian; Prinz, Julia; Schreiber, Benjamin; Hübner, René; Kerbusch, Jochen; Bald, Ilko; Fahmy, Karim

    2016-01-01

    Self-assembling biomolecules provide attractive templates for the preparation of metallic nanostructures. However, the intuitive transfer of the "outer shape" of the assembled macromolecules to the final metallic particle depends on the intermolecular forces among the biomolecules which compete with interactions between template molecules and the metal during metallization. The shape of the bio-template may thus be more dynamic than generally assumed. Here, we have studied the metallization of phospholipid nanodiscs which are discoidal particles of ~10 nm diameter containing a lipid bilayer ~5 nm thick. Using negatively charged lipids, electrostatic adsorption of amine-coated Au nanoparticles was achieved and followed by electroless gold deposition. Whereas Au nanoparticle adsorption preserves the shape of the bio-template, metallization proceeds via invasion of Au into the hydrophobic core of the nanodisc. Thereby, the lipidic phase induces a lateral growth that increases the diameter but not the original thickness of the template. Infrared spectroscopy reveals lipid expansion and suggests the existence of internal gaps in the metallized nanodiscs, which is confirmed by surface-enhanced Raman scattering from the encapsulated lipids. Interference of metallic growth with non-covalent interactions can thus become itself a shape-determining factor in the metallization of particularly soft and structurally anisotropic biomaterials. PMID:27216789

  6. Microporous device for local electric recordings on lipid bilayers

    NASA Astrophysics Data System (ADS)

    Kaufeld, Theresa; Battle, Christopher; Weichbrodt, Conrad; Steinem, Claudia; Schmidt, Christoph

    2012-02-01

    Many methods for artificial membrane formation are available. We focus on the reconstitution of lipid bilayers on porous substrates combining the stability of solid supports and the accessibility of both sides of the bilayer of the classical BLM which is necessary for low noise electric experiments. Most commercially available porous substrates however are not suitable for electric experiments or a combination of several measuring techniques. Therefore, we designed a microporous substrate, which meets several demands: We wanted to have the possibility to perform multiple experiments in one, so we chose to divide the device into several individually addressable arrays of pores with separate electrolyte compartments and integrated electronic connections. Also, to perform electrical and fluorescence experiments at the same time, we designed a PDMS sample chamber so that the substrate is accessible to a microscope objective. By having separated electrolyte compartments, we are also able to exchange solutions or introduce chemicals throughout the experiment. Bilayer formation can be probed by impedance spectroscopy and fluorescence microscopy. The function of inserted ion channels can be measured by current recordings.

  7. Phase and surface properties of lipid bilayers containing neoglycolipids.

    PubMed

    Luzardo, M C; Bernik, D L; Pazos, I F; Figueroa, S; Lanio, M E; Vérez, V; Disalvo, E A

    1999-03-01

    The physical properties conferred to DPPC bilayers by including neoglycolipids composed by two different trisaccharides: mannose-mannose-mannose (3M) and glucose-mannose-glucose (GMG) attached to a cholesterol (cho) and a distearylglycerol (diC18) lipid moiety by a spacer were evaluated by means of the measurement of the electrokinetic potential and interfacial fluorescent probes. The phase properties measured with diphenylhexatriene (DPH) were correlated with the surface properties measured with merocyanine 540, dansyl, and Laurdan probes. The results show that the surface properties of large unilamellar vesicles depend on the sugar exposure to the water phase and also on the hydrocarbon moiety by which it is anchored to the bilayer. The combination of the cholesterol moiety with the saccharide attenuates the cooperativity decrease induced by the cholesterol moiety without the sugar portion. The neoglycolipid GMG-diC18 promotes opposite effects affecting slightly the cooperativity at the hydrocarbon core of DPPC and displacing the phase transition temperature to higher values. The presence of neoglycolipid with diC18 introduces defects in the packing at the interface of the membrane in the gel state. It is concluded that a relatively low proportion of neoglycolipids affects significantly the interfacial properties of DPPC bilayers in large unilamellar vesicles in the absence of changes at the membrane bulk at 25 degrees C. PMID:10049501

  8. Minimal radius of curvature of lipid bilayers in the gel phase state corresponds to the dimension of biomembrane structures "caveolae".

    PubMed

    Meyer, H W; Westermann, M; Stumpf, M; Richter, W; Ulrich, A S; Hoischen, C

    1998-12-01

    Caveolae are membrane invaginations with a radius of curvature in the range of 40 nm for the bulb; 10-15 nm is the minimal radius for lipid bilayers in the liquid-crystalline Lalpha (liquid-disordered: ld) phase state. A minimal radius of 20-30 nm could be detected for the gel phase state by analysis of convex-concave bilayer deformations. Circular protrusions with a diameter in the range of only about 40 nm are closed by a flat lid, and those with diameters of 60 nm or more are closed by hemispherical caps. These structures are found primarily in phosphatidylcholine/sterol mixtures, where the gel phase state "liquid ordered" (lo) has been introduced. As a further example the mixture of dimyristoylphosphatidylcholine (DMPC) with an unusual sterol (diflucortolon-21-valerat) is presented. In the usual hydration at temperatures above the phase transition the deformation requires an incubation at 4 degrees C for several weeks or months to form. Using a low temperature hydration procedure (at 4 degrees C), surprisingly bilayers of pure DMPC and DPPC (dipalmitoylphosphatidylcholine) are found to deform in the same convex-concave manner, and this takes place within hours and days. The dependence on hydration protocol is also observed for formation of a sponge-like bilayer network with 30-35 nm radius of curvature in brain sphingomyelin and its mixtures with cholesterol. Caveolae are microdomains enriched in cholesterol and sphingomyelin and are simultaneously discussed to be in the lo state. Direct evidence by investigation of bilayers formed by the lipids isolated from caveolae is still lacking, but structures similar to caveolae which are in the gel phase state (very probably the lo state) are also formed by lipids extracted from bacterial membranes. A further analogy exists because both natural lipid mixtures (brain sphingomyelin and bacterial lipids) transform during heating from the curved bilayer structures into microvesicles above the phase transition

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

    PubMed

    Kaufman, Yair; Berman, Amir; Freger, Viatcheslav

    2010-05-18

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

  10. Conducting polymer supported bilayer lipid membrane reconstituted with alamethicin

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Salinas, Sergio; Baba Sundaresan, Vishnu

    2011-09-01

    Ionic electroactive polymers and bioderived materials have been independently demonstrated as actuators, sensors and energy harvesting devices. In an electroactive polymer, the applied electric field between the cathode and anode drives ion transport between the electrodes, impregnated electrolyte and the bulk of the polymer to generate force and displacement. Similarly, in a bioderived material an input stimulus (electrical, chemoelectrical or chemical) applied across the protein in a bilayer lipid membrane (BLM) displaces ions across the membrane barrier and enables sensing and actuation functions. This paper presents a novel architecture for a device that integrates the ionic function of an electroactive polymer and a bioderived material into a thin-film laminated device combining their unique advantages. A conducting polymer (PPy(DBS)) is used as the electroactive polymer and alamethicin-bound bilayer lipid membrane is used as the bioderived material in the thin-film laminated device. Owing to the configuration of the laminated device, the protein regulates the ionic concentration in the conducting polymer and regulates the electrochemical doping/undoping process in the polymer. By electrically connecting the conducting polymer across its thickness, this arrangement provides a mechanism external to the polymer besides electrical field that can control the electrical, mechanical and/or optical properties of the conducting polymer. This paper also presents the fabrication and characterization of the integrated ionic device and presents a template for the development of a novel category of electroactive ionic devices.

  11. Assembly of RNA nanostructures on supported lipid bilayers

    NASA Astrophysics Data System (ADS)

    Dabkowska, Aleksandra P.; Michanek, Agnes; Jaeger, Luc; Rabe, Michael; Chworos, Arkadiusz; Höök, Fredrik; Nylander, Tommy; Sparr, Emma

    2014-12-01

    The assembly of nucleic acid nanostructures with controlled size and shape has large impact in the fields of nanotechnology, nanomedicine and synthetic biology. The directed arrangement of nano-structures at interfaces is important for many applications. In spite of this, the use of laterally mobile lipid bilayers to control RNA three-dimensional nanostructure formation on surfaces remains largely unexplored. Here, we direct the self-assembly of RNA building blocks into three-dimensional structures of RNA on fluid lipid bilayers composed of cationic 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or mixtures of zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) and cationic sphingosine. We demonstrate the stepwise supramolecular assembly of discrete building blocks through specific and selective RNA-RNA interactions, based on results from quartz crystal microbalance with dissipation (QCM-D), ellipsometry, fluorescence recovery after photobleaching (FRAP) and total internal reflection fluorescence microscopy (TIRF) experiments. The assembly can be controlled to give a densely packed single layer of RNA polyhedrons at the fluid lipid bilayer surface. We show that assembly of the 3D structure can be modulated by sequence specific interactions, surface charge and changes in the salt composition and concentration. In addition, the tertiary structure of the RNA polyhedron can be controllably switched from an extended structure to one that is dense and compact. The versatile approach to building up three-dimensional structures of RNA does not require modification of the surface or the RNA molecules, and can be used as a bottom-up means of nanofabrication of functionalized bio-mimicking surfaces.The assembly of nucleic acid nanostructures with controlled size and shape has large impact in the fields of nanotechnology, nanomedicine and synthetic biology. The directed arrangement of nano-structures at interfaces is important for many applications. In spite of

  12. Interaction of Ionic Liquids with a Lipid Bilayer: A Biophysical Study of Ionic Liquid Cytotoxicity.

    PubMed

    Jing, Benxin; Lan, Nan; Qiu, Jie; Zhu, Yingxi

    2016-03-17

    Ionic liquids (ILs) have been widely considered and used as "green solvents" for more than two decades. However, their ecotoxicity results have contradicted this view, as ILs, particularly hydrophobic ones, are reported to exhibit high toxicity. Yet the origin of their toxicology remains unclear. In this work, we have investigated the interaction of amphiphilic ILs with a lipid bilayer as a model cell membrane to understand their cytotoxicity at a molecular level. By employing fluorescence imaging and light and X-ray scattering techniques, we have found that amphiphilic ILs could disrupt the lipid bilayer by IL insertion, end-capping the hydrophobic edge of the lipid bilayer, and eventually disintegrating the lipid bilayer at high IL concentration. The insertion of ILs to cause the swelling of the lipid bilayer shows strong dependence on the hydrophobicity of IL cationic alky chain and anions and is strongly correlated with the reported IL cytotoxicity. PMID:26910537

  13. Theoretical studies of lipid bilayer electroporation using molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Levine, Zachary Alan

    Computer simulations of physical, chemical, and biological systems have improved tremendously over the past five decades. From simple studies of liquid argon in the 1960s to fully atomistic simulations of entire viruses in the past few years, recent advances in high-performance computing have continuously enabled simulations to bridge the gap between scientific theory and experiment. Molecular dynamics simulations in particular have allowed for the direct observation of spatial and temporal events which are at present inaccessible to experiments. For this dissertation I employ all-atom molecular dynamics simulations to study the transient, electric field-induced poration (or electroporation) of phospholipid bilayers at MV/m electric fields. Phospholipid bilayers are the dominant constituents of cell membranes and act as both a barrier and gatekeeper to the cell interior. This makes their structural integrity and susceptibility to external perturbations an important topic for study, especially as the density of electromagnetic radiation in our environment is increasing steadily. The primary goal of this dissertation is to understand the specific physical and biological mechanisms which facilitate electroporation, and to connect our simulated observations to experiments with live cells and to continuum models which seek to describe the underlying biological processes of electroporation. In Chapter 1 I begin with a brief introduction to phospholipids and phospholipid bilayers, followed by an extensive overview of electroporation and atomistic molecular dynamics simulations. The following chapters will then focus on peer-reviewed and published work we performed, or on existing projects which are currently being prepared for submission. Chapter 2 looks at how external electric fields affect both oxidized and unoxidized lipid bilayers as a function of oxidation concentration and oxidized lipid type. Oxidative damage to cell membranes represents a physiologically relevant

  14. Permeability of lipid bilayers to amino acids and phosphate

    NASA Technical Reports Server (NTRS)

    Chakrabarti, A. C.; Deamer, D. W.

    1992-01-01

    Permeability coefficients for amino acid classes, including neutral, polar, hydrophobic, and charged species, were measured and compared with values for other ionic solutes such as phosphate. The rates of efflux of glycine, lysine, phenylalanine, serine and tryptophan were determined after they were passively entrapped in large unilamellar vesicles (LUVs) composed of egg phosphatidylcholine (EPC) or dimyristoylphosphatidylcholine (DMPC). The following permeability coefficients were obtained for: glycine, 5.7 x 10(-12) cm s-1 (EPC), 2.0 x 10(-11) cm s-1 (DMPC); serine, 5.5 x 10(-12) cm s-1 (EPC), 1.6 x 10(-11) cm s-1 (DMPC); lysine, 5.1 x 10(-12) cm s-1 (EPC), 1.9 x 10(-11) cm s-1 (DMPC); tryptophan, 4.1 x 10(-10) cm s-1 (EPC); and phenylalanine, 2.5 x 10(-10) cm s-1 (EPC). Decreasing lipid chain length increased permeability slightly, while variations in pH had only minor effects on the permeability coefficients of the amino acids tested. Phosphate permeability was in the range of 10(-12)-10(-13) cm s-1 depending on the pH of the medium. The values for the polar and charged amino acids were surprisingly similar to those previously measured for monovalent cations such as sodium and potassium, which are in the range of 10(-12)-10(-13) cm s-1, depending on conditions and the lipid species used. This observation suggests that the permeation rates for the neutral, polar and charged amino acids are controlled by bilayer fluctuations and transient defects, rather than partition coefficients and Born energy barriers. The results are relevant to the permeation of certain peptides into lipid bilayers during protein translocation and membrane biogenesis.

  15. Tethered or adsorbed supported lipid bilayers in nanotubes characterized by deuterium magic angle spinning NMR spectroscopy.

    PubMed

    Wattraint, Olivier; Warschawski, Dror E; Sarazin, Catherine

    2005-04-12

    2H solid-state NMR experiments were performed under magic angle spinning on lipid bilayers oriented into nanotubes arrays, as a new method to assess the geometrical arrangement of the lipids. Orientational information is obtained from the intensities of the spinning sidebands. The lipid bilayers are formed by fusion of small unilamellar vesicles of DMPC-d54 inside a nanoporous anodic aluminum oxide, either by direct adsorption on the support or by tethering through a streptavidin/biotin linker. The results support that the quality of the lipid bilayers alignment is clearly in favor of the tethering rather than an adsorbed strategy. PMID:15807556

  16. Multi-Stacked Supported Lipid Bilayer Micropatterning through Polymer Stencil Lift-Off.

    PubMed

    Zhu, Yujie; Negmi, Ahmed; Moran-Mirabal, Jose

    2015-01-01

    Complex multi-lamellar structures play a critical role in biological systems, where they are present as lamellar bodies, and as part of biological assemblies that control energy transduction processes. Multi-lamellar lipid layers not only provide interesting systems for fundamental research on membrane structure and bilayer-associated polypeptides, but can also serve as components in bioinspired materials or devices. Although the ability to pattern stacked lipid bilayers at the micron scale is of importance for these purposes, limited work has been done in developing such patterning techniques. Here, we present a simple and direct approach to pattern stacked supported lipid bilayers (SLBs) using polymer stencil lift-off and the electrostatic interactions between cationic and anionic lipids. Both homogeneous and phase-segregated stacked SLB patterns were produced, demonstrating that the stacked lipid bilayers retain lateral diffusivity. We demonstrate patterned SLB stacks of up to four bilayers, where fluorescence resonance energy transfer (FRET) and quenching was used to probe the interactions between lipid bilayers. Furthermore, the study of lipid phase behaviour showed that gel phase domains align between adjacent layers. The proposed stacked SLB pattern platform provides a robust model for studying lipid behaviour with a controlled number of bilayers, and an attractive means towards building functional bioinspired materials or devices. PMID:26343733

  17. Multi-Stacked Supported Lipid Bilayer Micropatterning through Polymer Stencil Lift-Off

    PubMed Central

    Zhu, Yujie; Negmi, Ahmed; Moran-Mirabal, Jose

    2015-01-01

    Complex multi-lamellar structures play a critical role in biological systems, where they are present as lamellar bodies, and as part of biological assemblies that control energy transduction processes. Multi-lamellar lipid layers not only provide interesting systems for fundamental research on membrane structure and bilayer-associated polypeptides, but can also serve as components in bioinspired materials or devices. Although the ability to pattern stacked lipid bilayers at the micron scale is of importance for these purposes, limited work has been done in developing such patterning techniques. Here, we present a simple and direct approach to pattern stacked supported lipid bilayers (SLBs) using polymer stencil lift-off and the electrostatic interactions between cationic and anionic lipids. Both homogeneous and phase-segregated stacked SLB patterns were produced, demonstrating that the stacked lipid bilayers retain lateral diffusivity. We demonstrate patterned SLB stacks of up to four bilayers, where fluorescence resonance energy transfer (FRET) and quenching was used to probe the interactions between lipid bilayers. Furthermore, the study of lipid phase behaviour showed that gel phase domains align between adjacent layers. The proposed stacked SLB pattern platform provides a robust model for studying lipid behaviour with a controlled number of bilayers, and an attractive means towards building functional bioinspired materials or devices. PMID:26343733

  18. Corrugation of Phase-Separated Lipid Bilayers Supported by Nanoporous Silica Xerogel Surfaces

    SciTech Connect

    Goksu, E I; Nellis, B A; Lin, W; Satcher Jr., J H; Groves, J T; Risbud, S H; Longo, M L

    2008-10-30

    Lipid bilayers supported by substrates with nanometer-scale surface corrugations holds interest in understanding both nanoparticle-membrane interactions and the challenges of constructing models of cell membranes on surfaces with desirable properties, e.g. porosity. Here, we successfully form a two-phase (gel-fluid) lipid bilayer supported by nanoporous silica xerogel. Surface topology, diffusion, and lipid density in comparison to mica-supported lipid bilayers were characterized by AFM, FRAP, FCS, and quantitative fluorescence microscopy, respectively. We found that the two-phase lipid bilayer follows the xerogel surface contours. The corrugation imparted on the lipid bilayer results in a lipid density that is twice that on a flat mica surface. In direct agreement with the doubling of actual bilayer area in a projected area, we find that the lateral diffusion coefficient (D) of lipids on xerogel ({approx}1.7 {micro}m{sup 2}/s) is predictably lower than on mica ({approx}4.1 {micro}m{sup 2}/s) by both FRAP and FCS techniques. Furthermore, the gel-phase domains on xerogel compared to mica were larger and less numerous. Overall, our results suggest the presence of a relatively defect-free continuous two-phase bilayer that penetrates approximately midway into the first layer of {approx}50 nm xerogel beads.

  19. Volatile anesthetics inhibit sodium channels without altering bulk lipid bilayer properties.

    PubMed

    Herold, Karl F; Sanford, R Lea; Lee, William; Schultz, Margaret F; Ingólfsson, Helgi I; Andersen, Olaf S; Hemmings, Hugh C

    2014-12-01

    Although general anesthetics are clinically important and widely used, their molecular mechanisms of action remain poorly understood. Volatile anesthetics such as isoflurane (ISO) are thought to alter neuronal function by depressing excitatory and facilitating inhibitory neurotransmission through direct interactions with specific protein targets, including voltage-gated sodium channels (Na(v)). Many anesthetics alter lipid bilayer properties, suggesting that ion channel function might also be altered indirectly through effects on the lipid bilayer. We compared the effects of ISO and of a series of fluorobenzene (FB) model volatile anesthetics on Na(v) function and lipid bilayer properties. We examined the effects of these agents on Na(v) in neuronal cells using whole-cell electrophysiology, and on lipid bilayer properties using a gramicidin-based fluorescence assay, which is a functional assay for detecting changes in lipid bilayer properties sensed by a bilayer-spanning ion channel. At clinically relevant concentrations (defined by the minimum alveolar concentration), both the FBs and ISO produced prepulse-dependent inhibition of Na(v) and shifted the voltage dependence of inactivation toward more hyperpolarized potentials without affecting lipid bilayer properties, as sensed by gramicidin channels. Only at supra-anesthetic (toxic) concentrations did ISO alter lipid bilayer properties. These results suggest that clinically relevant concentrations of volatile anesthetics alter Na(v) function through direct interactions with the channel protein with little, if any, contribution from changes in bulk lipid bilayer properties. Our findings further suggest that changes in lipid bilayer properties are not involved in clinical anesthesia. PMID:25385786

  20. Phase separation in lipid bilayers triggered by low pH

    SciTech Connect

    Suresh, Swetha; Edwardson, J. Michael

    2010-09-03

    Research highlights: {yields} Lipid bilayers have been imaged by atomic force microscopy (AFM). {yields} At pH 5 phase separation occurs in lipid bilayers containing mixed acyl chains. {yields} Phase separation does not occur when lipids have only unsaturated chains. {yields} Phase separation might drive protein clustering during endocytosis. -- Abstract: Endocytosis involves the capture of membrane from the cell surface in the form of vesicles, which become rapidly acidified to about pH 5. Here we show using atomic force microscopy (AFM) imaging that this degree of acidification triggers phase separation in lipid bilayers containing mixed acyl chains (e.g. palmitoyl/oleoyl) or complex mixtures (e.g. total brain extract) but not in bilayers containing only lipids with unsaturated chains (e.g. dioleoyl). Since mixed-chain lipids are major constituents of the outer leaflet of the plasma membrane, the type of phase separation reported here might support protein clustering and signaling during endocytosis.

  1. The Alzheimer's disease Aβ peptide binds to the anionic DMPS lipid bilayer.

    PubMed

    Lockhart, Christopher; Klimov, Dmitri K

    2016-06-01

    We have applied isobaric-isothermal replica exchange molecular dynamics (REMD) and the all-atom explicit water model to study binding of Aβ10-40 peptide to the anionic DMPS bilayer. To provide comparison with a zwitterionic bilayer, we used our previous REMD simulations probing binding of the same peptide to the DMPC bilayer. Using two sets of simulations, we comparatively analyzed the equilibrium Aβ conformational ensemble, peptide-bilayer interactions, and changes in the bilayer structure induced by Aβ binding. Our results are six-fold. (1) Binding to the DMPS bilayer triggers the formation of stable helix in the Aβ C-terminal, although the helix-inducing effect caused by DMPS lipids is weaker than that of DMPC. (2) Compared to the DMPC-bound Aβ monomer, the anionic bilayer weakens intrapeptide interactions, particularly, formed by charged amino acids. (3) Binding of Aβ peptide to the DMPS bilayer is primarily governed by electrostatic interactions between charged amino acids and charged lipid groups. In contrast, these interactions play minor role in Aβ binding to the DMPC bilayer. (4) Aβ peptide generally resides on the DMPS bilayer surface causing relatively minor bilayer thinning. The opposite scenario applies to Aβ binding to the DMPC bilayer. (5) In contrast to DMPC simulations, Aβ largely expels anionic lipids from its binding "footprint" forming a ring of charged amino acids mixed with charged lipid groups around the peptide. (6) Aβ binding disorders proximal DMPS lipids more strongly than their DMPC counterparts. Our simulations show that Aβ monomers fail to perturb anionic or zwitterionic bilayers across both leaflets. PMID:26947182

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

    PubMed

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

    2016-01-01

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

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

    PubMed Central

    Wang, C C; Bruner, L J

    1978-01-01

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

  4. Bridging microscopic and mesoscopic simulations of lipid bilayers.

    PubMed Central

    Ayton, Gary; Voth, Gregory A

    2002-01-01

    A lipid bilayer is modeled using a mesoscopic model designed to bridge atomistic bilayer simulations with macro-scale continuum-level simulation. Key material properties obtained from detailed atomistic-level simulations are used to parameterize the meso-scale model. The fundamental length and time scale of the meso-scale simulation are at least an order of magnitude beyond that used at the atomistic level. Dissipative particle dynamics cast in a new membrane formulation provides the simulation methodology. A meso-scale representation of a dimyristoylphosphatidylcholine membrane is examined in the high and low surface tension regimes. At high surface tensions, the calculated modulus is found to be slightly less than the atomistically determined value. This result agrees with the theoretical prediction that high-strain thermal undulations still persist, which have the effect of reducing the value of the atomistically determined modulus. Zero surface tension simulations indicate the presence of strong thermal undulatory modes, whereas the undulation spectrum and the calculated bending modulus are in excellent agreement with theoretical predictions and experiment. PMID:12496103

  5. Morphogenesis of protrusions from confined lipid bilayers mediated by mechanics

    NASA Astrophysics Data System (ADS)

    Arroyo, Marino; Staykova, Margarita; Rahimi, Mohammad; Stone, Howard A.

    2012-02-01

    Biological membranes adopt a wide range of shapes that structure and give functionality to cells, compartmentalizing the cytosol, forming organelles, or regulating their area. The formation, stabilization, and remodeling of these structures is generally attributed to localized forces or to biochemical processes (insertion of proteins, active compositional regulation). Noting that in the crowded intra and extra-cellular environments membranes are highly constrained, we explore to what extent can mechanics explain the shape of protrusions out of confined membranes. For this purpose, we developed an in-vitro system coupling a lipid bilayer to the strain-controlled deformation of an elastic sheet (Staykova et al, PNAS 108, 2011). We show that upon contracting the elastic support, tubular or spherical protrusions grow out of the adhered membrane, which can be reversibly controlled with strain and osmolarity without resorting to localized forces or chemical alterations of the bilayer. The morphologies produced by our minimal system are ubiquitous in cells, suggesting mechanics may be a simple and generic organizing principle. We can understand most of our observations in terms of a phase diagram accounting for elasticity, adhesion, and the limited amount of area and volume available.

  6. Wetting and freezing of water on supported bilayer lipid membranes

    NASA Astrophysics Data System (ADS)

    Buck, Zachary; Miskowiec, Andrew; Brown, Mia; Kaiser, Helmut; King, Gavin; Jiji, Renee; Cooley, Jason; Taub, Haskell; Hansen, Flemming; Tyagi, Madhusudan; Diallo, Souleymane; Mamontov, Eugene; Herwig, Kenneth

    2014-03-01

    Temperature-dependent elastic incoherent neutron scattering shows qualitatively different behavior for water associated with single bilayers of the charge-neutral DMPC (dimyristoylphosphocholine) lipid than for the anionic DMPG (dimyristoylphosphoglycerol) bilayer supported on an SiO2-coated silicon substrate. For the neutral DMPC membrane, the membrane-associated water shows a step-like freezing transition somewhat below the bulk freezing point followed by a continuous freezing behavior and, on heating, a step-like melting transition at the bulk melting point of 273 K. In contrast, water near the anionic DMPG membrane shows only continuous freezing that extends to much lower temperatures than for DMPC and continuous melting that is complete well below the bulk melting point. We suggest that these results may be explained by a film-like water structure in the DMPG case owing to the hydrophilic nature of the membrane surface, while most of the water in the DMPC system is bulk-like and dewets from this more hydrophobic membrane surface. Supported by NSF Grant Nos. DMR-0944772 and DGE-1069091.

  7. A quantitative coarse-grain model for lipid bilayers.

    PubMed

    Orsi, Mario; Haubertin, David Y; Sanderson, Wendy E; Essex, Jonathan W

    2008-01-24

    A simplified particle-based computer model for hydrated phospholipid bilayers has been developed and applied to quantitatively predict the major physical features of fluid-phase biomembranes. Compared with available coarse-grain methods, three novel aspects are introduced. First, the main electrostatic features of the system are incorporated explicitly via charges and dipoles. Second, water is accurately (yet efficiently) described, on an individual level, by the soft sticky dipole model. Third, hydrocarbon tails are modeled using the anisotropic Gay-Berne potential. Simulations are conducted by rigid-body molecular dynamics. Our technique proves 2 orders of magnitude less demanding of computational resources than traditional atomic-level methodology. Self-assembled bilayers quantitatively reproduce experimental observables such as electron density, compressibility moduli, dipole potential, lipid diffusion, and water permeability. The lateral pressure profile has been calculated, along with the elastic curvature constants of the Helfrich expression for the membrane bending energy; results are consistent with experimental estimates and atomic-level simulation data. Several of the results presented have been obtained for the first time using a coarse-grain method. Our model is also directly compatible with atomic-level force fields, allowing mixed systems to be simulated in a multiscale fashion. PMID:18085766

  8. 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.

  9. Silica xerogel/aerogel-supported lipid bilayers: consequences of surface corrugation.

    PubMed

    Goksu, Emel I; Hoopes, Matthew I; Nellis, Barbara A; Xing, Chenyue; Faller, Roland; Frank, Curtis W; Risbud, Subhash H; Satcher, Joe H; Longo, Marjorie L

    2010-04-01

    The objective of this paper was to review our recent investigations of silica xerogel and aerogel-supported lipid bilayers. These systems provide a format to observe relationships between substrate curvature and supported lipid bilayer formation, lipid dynamics, and lipid mixtures phase behavior and partitioning. Sensitive surface techniques such as quartz crystal microbalance and atomic force microscopy are readily applied to these systems. To inform current and future investigations, we review the experimental literature involving the impact of curvature on lipid dynamics, lipid and phase-separated lipid domain localization, and membrane-substrate conformations and we review our molecular dynamics simulations of supported lipid bilayers with the atomistic and molecular information they provide. PMID:19766590

  10. New optical method for measuring the bending elasticity of lipid bilayers

    NASA Astrophysics Data System (ADS)

    Minetti, C.; Vitkova, V.; Dubois, F.; Bivas, I.

    2016-02-01

    The knowledge of the elasticity of lipid bilayer structures is fundamental for new developments in biophysics, pharmacology and biomedical research. Lipid vesicles are readily prepared in laboratory conditions and employed for studying the physical properties of lipid membranes. The thermal fluctuation analysis of the shape of lipid vesicles (or flicker spectroscopy) is one of the experimental methods widely used for the measurement of the bending modulus of lipid bilayers. We present direct phase measurements performed on dilute vesicular suspensions by means of a new optical method exploiting holographic microscopy. For the bending constant of phosphatidylcholine bilayers we report the value of 23kBT in agreement with values previously measured by micropipette aspiration, electrodeformation and flicker spectroscopy of giant lipid vesicles. The application of this novel approach for the evaluation of the bending elasticity of lipid membranes opens the way to future developments in the phase measurements on lipid vesicles for the evaluation of their mechanical constants.

  11. Simulated microgravity impacts the plant plasmalemma lipid bilayer

    NASA Astrophysics Data System (ADS)

    Nedukha, Olena; Berkovich, Yuliy A.; Vorobyeva, Tamara; Grakhov, Volodimir; Klimenko, Elena; Zhupanov, Ivan; Jadko, Sergiy

    Biological membranes, especially the plasmalemma, and their properties and functions can be considered one of the most sensitive indicators of gravity interaction or alteration of gravity, respectively. Studies on the molecular basis of cellular signal perception and transduction are very important in order to understand signal responses at the cellular and organism level. The plasmalemma lipid bilayer is the boundary between the cell internal and external environment and mediates communication between them. Therefore, we studied the content and composition of lipids, saturated and unsaturated fatty acids, sterols, and microviscosity in the plasmalemma isolated from pea seedling roots and epicotyls grown in the stationary conditions and under slow horizontal clinorotation. In addition, lipid peroxidation intensity of intact roots was also identified. The plasmalemma fraction was isolated by the two-phase aquatic-polymer system optimized for pea using a centrifuge Optima L-90K. Lipid bilayer components were determined by using highly effective liquid chromatography with a system Angilent 1100 (Germany). Spontaneous chemiluminescence intensity was measured with a chemiluminometer ChLMTS-01. The obtained data showed that plasmalemma investigated parameters are sensitive to clinorotation, namely: increasing or decreasing the different lipids content, among which, phospho- and glycolipids were dominated, as well as changes in the content of saturated and unsaturated fatty acids and sterols. A degree of plasmalemma sensitivity to clinorotation was higher for the root plasmalemma than epicocotyl ones. This distinguish may be naturally explained by the differences in the structure, cell types, growth, and specific functions of a root and an epicotyl, those are the most complicated in roots. An index of unsaturation under clinorotation was similar to that in the stationary conditions as a result of the certain balance between changes in the content of saturated and

  12. Nanoscale imaging reveals laterally expanding antimicrobial pores in lipid bilayers

    PubMed Central

    Rakowska, Paulina D.; Jiang, Haibo; Ray, Santanu; Pyne, Alice; Lamarre, Baptiste; Carr, Matthew; Judge, Peter J.; Ravi, Jascindra; M. Gerling, Ulla I.; Koksch, Beate; Martyna, Glenn J.; Hoogenboom, Bart W.; Watts, Anthony; Crain, Jason; Grovenor, Chris R. M.; Ryadnov, Maxim G.

    2013-01-01

    Antimicrobial peptides are postulated to disrupt microbial phospholipid membranes. The prevailing molecular model is based on the formation of stable or transient pores although the direct observation of the fundamental processes is lacking. By combining rational peptide design with topographical (atomic force microscopy) and chemical (nanoscale secondary ion mass spectrometry) imaging on the same samples, we show that pores formed by antimicrobial peptides in supported lipid bilayers are not necessarily limited to a particular diameter, nor they are transient, but can expand laterally at the nano-to-micrometer scale to the point of complete membrane disintegration. The results offer a mechanistic basis for membrane poration as a generic physicochemical process of cooperative and continuous peptide recruitment in the available phospholipid matrix. PMID:23671080

  13. Nanoscale imaging reveals laterally expanding antimicrobial pores in lipid bilayers.

    PubMed

    Rakowska, Paulina D; Jiang, Haibo; Ray, Santanu; Pyne, Alice; Lamarre, Baptiste; Carr, Matthew; Judge, Peter J; Ravi, Jascindra; Gerling, Ulla I M; Koksch, Beate; Martyna, Glenn J; Hoogenboom, Bart W; Watts, Anthony; Crain, Jason; Grovenor, Chris R M; Ryadnov, Maxim G

    2013-05-28

    Antimicrobial peptides are postulated to disrupt microbial phospholipid membranes. The prevailing molecular model is based on the formation of stable or transient pores although the direct observation of the fundamental processes is lacking. By combining rational peptide design with topographical (atomic force microscopy) and chemical (nanoscale secondary ion mass spectrometry) imaging on the same samples, we show that pores formed by antimicrobial peptides in supported lipid bilayers are not necessarily limited to a particular diameter, nor they are transient, but can expand laterally at the nano-to-micrometer scale to the point of complete membrane disintegration. The results offer a mechanistic basis for membrane poration as a generic physicochemical process of cooperative and continuous peptide recruitment in the available phospholipid matrix. PMID:23671080

  14. Small iminium ions block gramicidin channels in lipid bilayers.

    PubMed Central

    Hemsley, G; Busath, D

    1991-01-01

    Guanidinium and acetamidinium, when added to the bathing solution in concentrations of approximately 0.1M, cause brief blocks in the single channel potassium currents from channels formed in planar lipid bilayers by gramicidin A. Single channel lifetimes are not affected indicating that the channel structure is not modified by the blockers. Guanidinium block durations and interblock times are approximately exponential in distribution. Block frequencies increase with guanidinium concentration whereas block durations are unaffected. Increases in membrane potential cause an increase in block frequency as expected for a positively charged blocker but a decrease in block duration suggesting that the block is relieved when the blocker passes through the channel. At low pH, urea, formamide, and acetamide cause similar blocks suggesting that the protonated species of these molecules also block. Arginine and several amines do not block. This indicates that only iminium ions which are small enough to enter the channel can cause blocks in gramicidin channels. PMID:1712240

  15. Porous Nanoparticle Supported Lipid Bilayers (Protocells) as Delivery Vehicles

    PubMed Central

    Liu, Juewen; Stace-Naughton, Alison; Jiang, Xingmao; Brinker, C. Jeffrey

    2009-01-01

    Mixing liposomes with hydrophilic particles will induce fusion of the liposome onto the particle surface. Such supported bilayers have been extensively studied as a model for the cell membrane, while its application in drug delivery has not been pursued. In this communication, we report the use of phospholipids to achieve synergistic loading and encapsulating of a fluorescent dye (calcein) in mesoporous silica nanoparticles, and its delivery into mammalian cells. We found that cationic lipid DOTAP provides the highest calcein loading with the concentration inside silica ∼110× higher than that in the solution under experimental conditions. Compared to some other nanoparticle systems, protocells provide a simple construct for loading, sealing, delivering and releasing, and should serve as a useful system in nanomedicine. PMID:19173660

  16. Porous nanoparticle supported lipid bilayers (protocells) as delivery vehicles.

    PubMed

    Liu, Juewen; Stace-Naughton, Alison; Jiang, Xingmao; Brinker, C Jeffrey

    2009-02-01

    Mixing liposomes with hydrophilic particles induces fusion of the liposome onto the particle surface. Such supported bilayers have been studied extensively as models of the cell membrane, while their applications in drug delivery have not been pursued. In this communication, we report liposome fusion on mesoporous particles as a synergistic means to simultaneously load and seal cargo within the porous core. We find fusion of a cationic lipid (DOTAP) on an anionic silica particle loads an anionic fluorescent dye (calcein) into the particle to a concentration exceeding 100x that in the surrounding medium. The loaded "protocell" particles are taken up efficiently by Chinese hamster ovary cells, where, due to a reduced pH within endosomal compartments, calcein is effectively released. Compared to some other nanoparticle systems, protocells provide a simple construct for cargo loading, sealing, delivery, and release. They promise to serve as useful vectors in nanomedicine. PMID:19173660

  17. Kinetics of Domains Registration in Multicomponent Lipid Bilayer Membranes

    PubMed Central

    Sornbundit, Kan; Modchang, Charin; Triampo, Wannapong; Triampo, Darapond; Nuttavut, Narin; Sunil Kumar, P.B; Laradji, Mohamed

    2014-01-01

    The kinetics of registration of lipid domains in the apposing leaflets of symmetric bilayer membranes is investigated via systematic dissipative particle dynamics simulations. The decay of the distance between the centres of mass of the domains in the apposing leaflets is almost linear during early stages, and then becomes exponential during late times. The time scales of both linear and exponential decays are found to increase with decreasing the strength of interleaflet coupling. The ratio between the time scales of the exponential and linear regimes decreases with increasing the domain size, implying that the decay of the distance between the domains centres of mass is essentially linear for large domains. These numerical results are largely in agreement with the recent theoretical predictions of Han and Haataja [Soft Matter (2013) 9:2120-2124]. We also found that the domains become elongated during the registration process. PMID:25090030

  18. Screening and plasmons in pure and disordered single- and bilayer black phosphorus

    NASA Astrophysics Data System (ADS)

    Jin, Fengping; Roldán, Rafael; Katsnelson, Mikhail I.; Yuan, Shengjun

    2015-09-01

    We study collective plasmon excitations and screening of pure and disordered single- and bilayer black phosphorus (BP) beyond the low energy continuum approximation. The dynamical polarizability of phosphorene is computed using a tight-binding model that properly accounts for the band structure in a wide energy range. Electron-electron interaction is considered within the random phase approximation. Damping of the plasmon modes due to different kinds of disorder, such as resonant scatterers and long-range disorder potentials, is analyzed. We further show that an electric field applied perpendicular to bilayer phosphorene can be used to tune the dispersion of the plasmon modes. For sufficiently large electric field, the bilayer BP enters in a topological phase with a characteristic plasmon spectrum, which is gaped in the armchair direction.

  19. Polymerized lipid bilayers on a solid substrate: morphologies and obstruction of lateral diffusion.

    PubMed

    Okazaki, Takashi; Inaba, Takehiko; Tatsu, Yoshiro; Tero, Ryugo; Urisu, Tsuneo; Morigaki, Kenichi

    2009-01-01

    Substrate supported planar lipid bilayers (SPBs) are versatile models of the biological membrane in biophysical studies and biomedical applications. We previously developed a methodology for generating SPBs composed of polymeric and fluid phospholipid bilayers by using a photopolymerizable diacetylene phospholipid (DiynePC). Polymeric bilayers could be generated with micropatterns by conventional photolithography, and the degree of polymerization could be controlled by modulating UV irradiation doses. After removing nonreacted monomers, fluid lipid membranes could be integrated with polymeric bilayers. Herein, we report on a quantitative study of the morphology of polymeric bilayer domains and their obstruction toward lateral diffusion of membrane-associated molecules. Atomic force microscopy (AFM) observations revealed that polymerized DiynePC bilayers were formed as nanometer-sized domains. The ratio of polymeric and fluid bilayers could be modulated quantitatively by changing the UV irradiation dose for photopolymerization. Lateral diffusion coefficients of lipid molecules in fluid bilayers were measured by fluorescence recovery after photobleaching (FRAP) and correlated with the amount of polymeric bilayer domains on the substrate. Controlled domain structures, lipid compositions, and lateral mobility in the model membranes should allow us to fabricate model membranes that mimic complex features of biological membranes with well-defined structures and physicochemical properties. PMID:19067577

  20. Dynamics, Surface Electrostatics and Phase Properties of Nanoscale Curved Lipid Bilayers

    NASA Astrophysics Data System (ADS)

    Koolivand, Amir

    Surface electrostatic potential of a lipid bilayer governs many vital functions of living cells. Several classes of proteins are known of exhibiting strong binding preferences to curved lipid bilayer surfaces. In this project we employed electron paramagnetic resonance (EPR) of a recently introduced phospholipid (IMTSL-PTE) bearing a pH-sensitive nitroxide covalently attached to the lipid head group to measure the surface electrostatics of the lipid membrane and nanopore-confined lipid bilayers as a function of the bilayer curvature. The pKa of the ionizable group of this lipid-based spin probe is reporting on the bilayer surface electrostatics potential by changes in the EPR spectra. Specifically, both rotational dynamics and magnetic parameters of the nitroxide are affected by the probe protonation. Effect of curvature on the surface electrostatic potential and dynamics of lipid bilayer was studied for POPG and DMPG unilamellar vesicles (ULVs). It was found that the magnitude of the negative surface electrostatic potential increased upon decrease in the vesicle diameter for the bilayers in the fluid phase; however, no significant changes were observed for DMPG ULVs in a gel phase. We speculate that biologically relevant fluid bilayer phase allows for a larger variability in the lipid packing density in the lipid polar head group region than a more ordered gel phase and it is likely that the lipid flip-flop is responsible for pH equilibration of IMTSL-PTE. The kinetic EPR study of nitroxide reduction showed that the rate of flip-flop is in the order of 10-5 s-1. The flip-flop rate constant increases when vesicle size deceases. Oxygen permeability measured by X-ban EPR decreases in higher curved vesicles---an observation that is consistent with a tighter packing in smaller vesicles. Partitioning of a small nitroxide molecule TEMPO into ULVs was measured by X-band (9 GHz) and W-band (95 GHz) EPR spectroscopy. The partitioning coefficient of this probe in the lipid

  1. High Resistivity Lipid Bilayers Assembled on Polyelectrolyte Multilayer Cushions: An Impedance Study.

    PubMed

    Diamanti, Eleftheria; Gregurec, Danijela; Rodríguez-Presa, María José; Gervasi, Claudio A; Azzaroni, Omar; Moya, Sergio E

    2016-06-28

    Supported membranes on top of polymer cushions are interesting models of biomembranes as cell membranes are supported on a polymer network of proteins and sugars. In this work lipid vesicles formed by a mixture of 30% 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 70% 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS) are assembled on top of a polyelectrolyte multilayer (PEM) cushion of poly(allylamine hydrochloride) (PAH) and poly(styrene sodium sulfonate) (PSS). The assembly results in the formation of a bilayer on top of the PEM as proven by means of the quartz crystal microbalance with dissipation technique (QCM-D) and by cryo-transmission electron microscopy (cryo-TEM). The electrical properties of the bilayer are studied by electrochemical impedance spectroscopy (EIS). The bilayer supported on the PEMs shows a high resistance, on the order of 10(7) Ω cm(2), which is indicative of a continuous, dense bilayer. Such resistance is comparable with the resistance of black lipid membranes. This is the first time that such values are obtained for lipid bilayers supported on PEMs. The assembly of polyelectrolytes on top of a lipid bilayer decreases the resistance of the bilayer up to 2 orders of magnitude. The assembly of the polyelectrolytes on the lipids induces defects or pores in the bilayer which in turn prompts a decrease in the measured resistance. PMID:27267089

  2. Analytical investigation of bilayer lipid biosensor based on graphene.

    PubMed

    Akbari, Elnaz; Buntat, Zolkafle; Shahraki, Elmira; Parvaz, Ramtin; Kiani, Mohammad Javad

    2016-01-01

    Graphene is another allotrope of carbon with two-dimensional monolayer honeycomb. Owing to its special characteristics including electrical, physical and optical properties, graphene is known as a more suitable candidate compared to other materials to be used in the sensor application. It is possible, moreover, to use biosensor by using electrolyte-gated field effect transistor based on graphene (GFET) to identify the alterations in charged lipid membrane properties. The current article aims to show how thickness and charges of a membrane electric can result in a monolayer graphene-based GFET while the emphasis is on the conductance variation. It is proposed that the thickness and electric charge of the lipid bilayer (LLP and QLP) are functions of carrier density, and to find the equation relating these suitable control parameters are introduced. Artificial neural network algorithm as well as support vector regression has also been incorporated to obtain other models for conductance characteristic. The results comparison between analytical models, artificial neural network and support vector regression with the experimental data extracted from previous work show an acceptable agreement. PMID:26024896

  3. The Influence of Lipid Bilayer Physicochemical Properties on Gramicidin A Conformer Preferences.

    PubMed

    Patrick, John W; Gamez, Roberto C; Russell, David H

    2016-04-26

    The conformational preferences adopted by gramicidin A (GA) dimers inserted into phospholipid bilayers are reported as a function of the bilayer cholesterol content, temperature, and incubation time. Through use of vesicle capture-freeze drying methodology, GA dimers were captured in lipid bilayers and the conformational preferences of the complex were analyzed using ion mobility-mass spectrometry. Perturbations that affect the physicochemical interactions in the lipid bilayer such as cholesterol incorporation, temperature, and incubation time directly alter the conformer preferences of the complex. Regardless of bilayer cholesterol concentration, the antiparallel double helix (ADH) conformation was observed to be most abundant for GA dimers in bilayers composed of lipids with 12 to 22 carbon acyl chains. Incorporation of cholesterol into lipid bilayers yields increased bilayer thickness and rigidity, and an increased abundance of parallel double helix (PDH) and single-stranded head-to-head (SSHH) dimers were observed. Bilayers prepared using 1,2-dilauroyl-sn-glycero-3-phosphocholine, a lipid with 12 carbon acyl chains, yielded a nascent conformer that decreased in abundance as a function of bilayer cholesterol content. High resolution ion mobility-mass spectrometry data revealed two peaks in the ADH region suggesting that ADH populations are composed of two distinct conformers. The conformer preferences of GA dimers from 1,2-distearoyl-sn-glycero-3-phosphocholine bilayers were significantly different for samples incubated at 4°C vs. 60°C; increased cholesterol content yielded more PDH and SSHH at 60°C. The addition of cholesterol as well as incubating samples of 1,2-distearoyl-sn-glycero-3-phosphocholine at 60°C for 24-72 h yielded an increase in PDH and SSHH abundance. PMID:27119642

  4. Lateral diffusivity of lipid analogue excimeric probes in dimyristoylphosphatidylcholine bilayers.

    PubMed Central

    Sassaroli, M; Vauhkonen, M; Perry, D; Eisinger, J

    1990-01-01

    The lateral mobility of pyrenyl phospholipid probes in dimyristoylphosphatidylcholine (DMPC) vesicles was determined from the dependence of the pyrene monomeric and excimeric fluorescence yields on the molar probe ratio. The analysis of the experimental data makes use of the milling crowd model for two-dimensional diffusivity and the computer simulated random walks of probes in an array of lipids. The fluorescence yields for 1-palmitoyl-2-(1'-pyrenedecanoyl)phosphatidylcholine (py10PC) in DMPC bilayers are well fitted by the model both below and above the fluid-gel phase transition temperature (Tc) and permit the evaluation of the probe diffusion rate (f), which is the frequency with which probes take random steps of length L, the host membrane lipid-lipid spacing. The lateral diffusion coefficient is then obtained from the relationship D = fL2/4. In passing through the fluid-gel phase transition of DMPC (Tc = 24 degrees C), the lateral mobility of py10PC determined in this way decrease only moderately, while D measured by fluorescence photobleaching recovery (FPR) experiments is lowered by two or more orders of magnitude in gel phase. This difference in gel phase diffusivities is discussed and considered to be related either to (a) the diffusion length in FPR experiments being about a micrometer or over 100 times greater than that of excimeric probes (approximately 1 nm), or (b) to nonrandomicity in the distribution of the pyrenyl probes in gel phase DMPC. At 35 degrees C, in fluid DMPC vesicles, the diffusion rate is f = 1.8 x 10(8) s-1, corresponding to D = 29 microns2 s-1, which is about three times larger than the value obtained in FPR experiments. The activation energy for lateral diffusion in fluid DMPC was determined to be 8.0 kcal/mol. PMID:2317550

  5. Formation, Stability, and Mobility of One-Dimensional Lipid Bilayer on High Curvature Substrates

    SciTech Connect

    Huang, J; Martinez, J; Artyukhin, A; Sirbuly, D; Wang, Y; Ju, J W; Stroeve, P; Noy, A

    2007-03-23

    Curved lipid membranes are ubiquitous in living systems and play an important role in many biological processes. To understand how curvature and lipid composition affect membrane formation and fluidity we have assembled and studied mixed 1,2-Dioleoyl-sn-Glycero-3-Phosphocholine (DOPC) and 1,2-Dioleoyl-sn-Glycero-3-Phosphoethanolamine (DOPE) supported lipid bilayers on amorphous silicon nanowires with controlled diameters ranging from 20 nm to 200 nm. Addition of cone-shaped DOPE molecules to cylindrical DOPC molecules promotes vesicle fusion and bilayer formation on smaller diameter nanowires. Our experiments demonstrate that nanowire-supported bilayers are mobile, exhibit fast recovery after photobleaching, and have low concentration of defects. Lipid diffusion coefficients in these high-curvature tubular membranes are comparable to the values reported for flat supported bilayers and increase with decreasing nanowire diameter.

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

    PubMed

    Elliott, J T; Prestwich, G D

    2000-01-01

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

  7. Localized surface plasmon microscopy of submicron domain structures of mixed lipid bilayers

    PubMed Central

    Watanabe, Koyo; Miyazaki, Ryosuke; Terakado, Goro; Okazaki, Takashi; Morigaki, Kenichi; Kano, Hiroshi

    2012-01-01

    We propose scanning localized surface plasmon microscopy of mixed lipid bilayers with submicron domain structures. Our observation technique, which employs localized surface plasmons excited on a flat metal surface as a sensing probe, provides non-label and non-contact imaging with the spatial resolution of ∼ 170 nm. We experimentally show that submicron domain structures of mixed lipid bilayers can be observed. A detailed analysis finds that the domains are classified into two groups. PMID:23024897

  8. Hydrodynamic Forces on Macromolecules Protruding from Lipid Bilayers Due to External Liquid Flows.

    PubMed

    Jönsson, Peter; Jönsson, Bengt

    2015-11-24

    It has previously been observed that an externally applied hydrodynamic shear flow above a fluid lipid bilayer can change the local concentration of macromolecules that are associated with the lipid bilayer. The external liquid flow results in a hydrodynamic force on molecules protruding from the lipid bilayer, causing them to move in the direction of the flow. However, there has been no quantitative study about the magnitude of these forces. We here use finite element simulations to investigate how the magnitude of the external hydrodynamic forces varies with the size and shape of the studied macromolecule. The simulations show that the hydrodynamic force is proportional to the effective hydrodynamic area of the studied molecule, Ahydro, multiplied by the mean hydrodynamic shear stress acting on the membrane surface, σhydro. The parameter Ahydro depends on the size and shape of the studied macromolecule above the lipid bilayer and scales with the cross-sectional area of the molecule. We also investigate how hydrodynamic shielding from other surrounding macromolecules decreases Ahydro when the surface coverage of the shielding macromolecules increases. Experiments where the protein streptavidin is anchored to a supported lipid bilayer on the floor of a microfluidic channel were finally performed at three different surface concentrations, Φ = 1%, 6%, and 10%, where the protein is being moved relative to the lipid bilayer by a liquid flow through the channel. From photobleaching measurements of fluorescently labeled streptavidin we found the experimental drift data to be within good accuracy of the simulated results, less than 12% difference, indicating the validity of the results obtained from the simulations. In addition to giving a deeper insight into how a liquid flow can affect membrane-associated molecules in a lipid bilayer, we also see an interesting potential of using hydrodynamic flow experiments together with the obtained results to study the size and

  9. A phenomenological model of the solvent-assisted lipid bilayer formation method.

    PubMed

    Gillissen, Jurriaan J J; Tabaei, Seyed R; Cho, Nam-Joon

    2016-09-21

    The recently introduced solvent-assisted lipid bilayer (SALB) formation method allows one to efficiently fabricate planar, lipid bilayers on solid supports and can be used for various applications. It involves the introduction of an aqueous buffer into a mixture of lipid and alcohol, which is incubated on a solid support. The associated phase changes in the ternary bulk system are accompanied by the formation of a lipid bilayer at the solid-liquid interface. While the phase behavior of the ternary bulk system is well understood, the mechanism of bilayer assembly at the solid-liquid interface remains to be elucidated, including whether the adsorption process is limited by diffusion of the lipid in the bulk or by lipid binding kinetics onto the surface. Such factors strongly influence the success of bilayer formation as they pertain to operating conditions, such as lipid concentration, solvent exchange rate and chamber dimensions, and are hence of critical importance for SALB fabrication strategies. Herein, we extend an earlier proposed phenomenological kinetic model of the SALB formation process, based on a volume-averaged treatment of the solvent mixing process. By comparing the model to quartz crystal microbalance with dissipation monitoring (QCM-D) experimental data, we conclude that SALB formation is limited by diffusion of suspended lipid aggregates, with a hydrodynamic radius, that is consistent with aggregate size measurements in the literature. This agreement validates the proposed model to serve as the basis for optimizing conditions for SALB formation. PMID:27530868

  10. Direct measurement of DNA-mediated adhesion between lipid bilayers.

    PubMed

    Shimobayashi, S F; Mognetti, B M; Parolini, L; Orsi, D; Cicuta, P; Di Michele, L

    2015-06-28

    Multivalent interactions between deformable mesoscopic units are ubiquitous in biology, where membrane macromolecules mediate the interactions between neighbouring living cells and between cells and solid substrates. Lately, analogous artificial materials have been synthesised by functionalising the outer surface of compliant Brownian units, for example emulsion droplets and lipid vesicles, with selective linkers, in particular short DNA sequences. This development extended the range of applicability of DNA as a selective glue, originally applied to solid nano and colloidal particles. On very deformable lipid vesicles, the coupling between statistical effects of multivalent interactions and mechanical deformation of the membranes gives rise to complex emergent behaviours, as we recently contributed to demonstrate [Parolini et al., Nat. Commun., 2015, 6, 5948]. Several aspects of the complex phenomenology observed in these systems still lack a quantitative experimental characterisation and a fundamental understanding. Here we focus on the DNA-mediated multivalent interactions of a single liposome adhering to a flat supported bilayer. This simplified geometry enables the estimate of the membrane tension induced by the DNA-mediated adhesive forces acting on the liposome. Our experimental investigation is completed by morphological measurements and the characterisation of the DNA-melting transition, probed by in situ Förster Resonant Energy Transfer spectroscopy. Experimental results are compared with the predictions of an analytical theory that couples the deformation of the vesicle to a full description of the statistical mechanics of mobile linkers. With at most one fitting parameter, our theory is capable of semi-quantitatively matching experimental data, confirming the quality of the underlying assumptions. PMID:25989828

  11. Acyl chain composition and coexisting fluid phases in lipid bilayers

    NASA Astrophysics Data System (ADS)

    Gu, Yongwen; Bradley, Miranda; Mitchell, Drake

    2011-10-01

    At room temperature phospholipid bilayers enriched in sphingolipids and cholesterol may form a solid phase as well as two coexisting fluid phases. These are the standard fluid phase, or the liquid-disordered phase, ld, and the liquid-ordered phase, lo, which is commonly associated with lipid rafts. Ternary mixtures of palmitoyl-oleoyl-phosphocholine (POPC; 16:0,18:1 PC), sphingomyelin (SPM), and cholesterol (Chol) form coexisting lo, ld and solid phases over a wide range of molar ratios. We are examining the ability of two fluorescent probes to detect these 2 phases: NBD linked to di-16:0 PE which partitions strongly into the lo phase and NBD linked to di-18:1 PE which partitions strongly into the ld phase. We are also examining the effect of the highly polyunsaturated phospholipid stearoyl-docosahexanoyl-phosphocholine (SDPC; 18:0, 22:6 PC) on the ternary phase diagram of POPC/SPM/Chol with particular focus on the functionally important lo/ld coexistence region. We report on the fluorescence lifetime and anisotropy decay dynamics of these two fluorescent probes.

  12. Strange kinetics of bulk-mediated diffusion on lipid bilayers.

    PubMed

    Krapf, Diego; Campagnola, Grace; Nepal, Kanti; Peersen, Olve B

    2016-05-14

    Diffusion at solid-liquid interfaces is crucial in many technological and biophysical processes. Although its behavior seems to be deceivingly simple, recent studies showing passive superdiffusive transport suggest that diffusion on surfaces may hide rich complexities. In particular, bulk-mediated diffusion occurs when molecules are transiently released from the surface to perform three-dimensional excursions into the liquid bulk. This phenomenon bears the dichotomy where a molecule always return to the surface but the mean jump length is infinite. Such behavior is associated with a breakdown of the central limit theorem and weak ergodicity breaking. Here, we use single-particle tracking to study the statistics of bulk-mediated diffusion on a supported lipid bilayer. We find that the time-averaged mean square displacement (MSD) of individual trajectories, the archetypal measure in diffusion processes, does not converge to the ensemble MSD but it remains a random variable, even in the long observation-time limit. The distribution of time averages is shown to agree with a Lévy flight model. Our results also unravel intriguing anomalies in the statistics of displacements. The time-averaged MSD is shown to depend on experimental time and investigations of fractional moments show a scaling 〈|r(t)|(q)〉∼t(qν(q)) with non-linear exponents, i.e. ν(q) ≠ const. This type of behavior is termed strong anomalous diffusion and is rare among experimental observations. PMID:27095275

  13. Pressure effects on the equilibrium configurations of bilayer lipid membranes

    NASA Astrophysics Data System (ADS)

    DeVita, Raffaella; Stewart, Iain W.; Leo, Donald J.

    2007-10-01

    Planar bilayer lipid membranes (BLMs) are currently employed to construct many bio-inspired material systems and structures. In order to characterize the pressure effects on the equilibrium configurations of these biological membranes, a novel continuum model is proposed. The BLM is assumed to be a two-layer smectic A liquid crystal. The mean orientation of the amphiphilic molecules comprising the membrane is postulated to be perpendicular to the layers and each layer is idealized as a two-dimensional liquid. Moreover, the BLM is modeled as a simply supported plate undergoing small deformations. It is subjected to a pressure load that acts perpendicularly to the layers. The equilibrium equations and boundary conditions are derived from the bulk elastic energy for smectic A liquid crystals as described by de Gennes and Prost (1993 The Physics of Liquid Crystals 2nd edn (Oxford Science Publications)) by using variational methods. The resulting fourth-order linear partial differential equation is solved by employing cylindrical functions and the series solution is proved to be convergent. The solution is numerically computed for values of the model parameters that are reported in the literature. This paper is dedicated to the memory of our colleagues, Professors Kevin P Granata and Liviu Librescv, who lost their lives during the sensless tragedy on 16 April, 2007 at Virginia Tech.

  14. Detergent interaction with tethered bilayer lipid membranes for protein reconstitution

    NASA Astrophysics Data System (ADS)

    Broccio, Matteo; Zan Goh, Haw; Loesche, Mathias

    2009-03-01

    Tethered bilayer lipid membranes (tBLMs) are self-assembled biomimetic structures in which the membrane is separated from a solid substrate by a nm-thick hydrated submembrane space. These model systems are being used in binding studies of peripheral proteins and exotoxins. Here we aim at their application for the reconstitution of water-insoluble integral membrane proteins. As an alternative to fusion of preformed proteoliposomes we study the direct reconstitution of such proteins for applications in biosensing and pharmaceutical screening. For reconstitution, highly insulating tBLMs (R˜10^5-10^6 φ) were temporarily incubated with a detergent to screen for conditions that keep the detergent-saturated membranestable and ready to incorporate detergent-solubilized proteins. We assess the electrical characteristics, i.e. specific resistance and capacitance, by means of electrochemical impedance spectroscopy (EIS) under timed incubation with decylmaltoside and dodecylmaltoside detergents in a regime around their critical micelle concentration, 1.8 mM and 0.17 mM respectively and demonstrate the restoration of the tBLM upon detergent removal. Thereby a range of concentration and incubation times was identified, that represents optimal conditions for the subsequent membrane protein reconstitution.

  15. Coarse-grain molecular dynamics simulations of diblock copolymer surfactants interacting with a lipid bilayer

    NASA Astrophysics Data System (ADS)

    Srinivas, Goundla; Klein, Michael L.

    2004-01-01

    The interaction of surfactant diblock poly(ethylene oxide)-poly(ethylethylene) copolymers (PEO-PEE) with a lipid bilayer of dimyristoylphosphatidylcholine has been studied by means of coarse-grain molecular dynamics simulations. The effect of the surfactants on the lipid bilayer was studied over a wide range of diblock copolymer concentrations. The simulations show that the hydrophilic PEO chains adopt different structures at low and high concentrations. In particular, the computed density profiles reveal that the PEO chains extend over a longer range from the bilayer surface, with increasing copolymer concentration. The simulated density profiles are in agreement with the scaling law predictions.

  16. An Ising-like model for monolayer-monolayer coupling in lipid bilayers

    NASA Astrophysics Data System (ADS)

    Sornbundit, Kan; Modchang, Charin; Nuttavut, Narin; Ngamsaad, Waipot; Triampo, Darapond; Triampo, Wannapong

    2013-07-01

    We have proposed the Ising bilayer model to study the domain growth dynamics in lipid bilayers. Interactions within and between layers are adopted from recent experimental and theoretical data. We investigate the effects of the mismatch area on the domain coarsening dynamics in both symmetric and asymmetric lipid bilayers. To explore domain coarsening, we used the Monte Carlo (MC) method with a standard Kawasaki dynamics to simulate the systems. The results show that domains on both layers grow following a power-law and that the domains grow slower when the mismatch areas are increased.

  17. Shaped Apertures in Photoresist Films Enhance the Lifetime and Mechanical Stability of Suspended Lipid Bilayers

    PubMed Central

    Kalsi, Sumit; Powl, Andrew M.; Wallace, B.A.; Morgan, Hywel; de Planque, Maurits R.R.

    2014-01-01

    Planar lipid bilayers suspended in apertures provide a controlled environment for ion channel studies. However, short lifetimes and poor mechanical stability of suspended bilayers limit the experimental throughput of bilayer electrophysiology experiments. Although bilayers are more stable in smaller apertures, ion channel incorporation through vesicle fusion with the suspended bilayer becomes increasingly difficult. In an alternative bilayer stabilization approach, we have developed shaped apertures in SU8 photoresist that have tapered sidewalls and a minimum diameter between 60 and 100 μm. Bilayers formed at the thin tip of these shaped apertures, either with the painting or the folding method, display drastically increased lifetimes, typically >20 h, and mechanical stability, being able to withstand extensive perturbation of the buffer solution. Single-channel electrical recordings of the peptide alamethicin and of the proteoliposome-delivered potassium channel KcsA demonstrate channel conductance with low noise, made possible by the small capacitance of the 50 μm thick SU8 septum, which is only thinned around the aperture, and unimpeded proteoliposome fusion, enabled by the large aperture diameter. We anticipate that these shaped apertures with micrometer edge thickness can substantially enhance the throughput of channel characterization by bilayer lipid membrane electrophysiology, especially in combination with automated parallel bilayer platforms. PMID:24739164

  18. Single DNA molecules on freestanding and supported cationic lipid bilayers: diverse conformational dynamics controlled by the local bilayer properties

    NASA Astrophysics Data System (ADS)

    Herold, Christoph; Schwille, Petra; Petrov, Eugene P.

    2016-02-01

    We present experimental results on the interaction of DNA macromolecules with cationic lipid membranes with different properties, including freestanding membranes in the fluid and gel state, and supported lipid membranes in the fluid state and under conditions of fluid-gel phase coexistence. We observe diverse conformational dynamics of membrane-bound DNA molecules controlled by the local properties of the lipid bilayer. In case of fluid-state freestanding lipid membranes, the behaviour of DNA on the membrane is controlled by the membrane charge density: whereas DNA bound to weakly charged membranes predominantly behaves as a 2D random coil, an increase in the membrane charge density leads to membrane-driven irreversible DNA collapse and formation of subresolution-sized DNA globules. On the other hand, electrostatic binding of DNA macromolecules to gel-state freestanding membranes leads to completely arrested diffusion and conformational dynamics of membrane-adsorbed DNA. A drastically different picture is observed in case of DNA interaction with supported cationic lipid bilayers: When the supported bilayer is in the fluid state, membrane-bound DNA molecules undergo 2D translational Brownian motion and conformational fluctuations, irrespectively of the charge density of the supported bilayer. At the same time, when the supported cationic membrane shows fluid-gel phase coexistence, membrane-bound DNA molecules are strongly attracted to micrometre-sized gel-phase domains enriched with the cationic lipid, which results in 2D compaction of the membrane-bound macromolecules. This DNA compaction, however, is fully reversible, and disappears as soon as the membrane is heated above the fluid-gel coexistence. We also discuss possible biological implications of our experimental findings.

  19. Regulation of channel function due to physical energetic coupling with a lipid bilayer

    SciTech Connect

    Ashrafuzzaman, Md.; Tseng, C.-Y.; Tuszynski, J.A.

    2014-03-07

    Highlights: • Lipid membrane regulation of membrane protein functions has been addressed. • Energetics behind ion channel-membrane coupling phenomena has been investigated. • Charge based interactions stabilize peptide–lipid complex. • Screened Coulomb interaction model explains the energetics. • Van der Waals and electrostatic forces drive peptides and lipids to close proximity. - Abstract: Regulation of membrane protein functions due to hydrophobic coupling with a lipid bilayer has been investigated. An energy formula describing interactions between lipid bilayer and integral ion channels with different structures, which is based on the screened Coulomb interaction approximation, has been developed. Here the interaction energy is represented as being due to charge-based interactions between channel and lipid bilayer. The hydrophobic bilayer thickness channel length mismatch is found to induce channel destabilization exponentially while negative lipid curvature linearly. Experimental parameters related to channel dynamics are consistent with theoretical predictions. To measure comparable energy parameters directly in the system and to elucidate the mechanism at an atomistic level we performed molecular dynamics (MD) simulations of the ion channel forming peptide–lipid complexes. MD simulations indicate that peptides and lipids experience electrostatic and van der Waals interactions for short period 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 (in ion channel) and lipids (in lipid bilayer) due to mainly their charge properties. The results of in silico MD studies taken together with experimental observable parameters and theoretical energetic predictions suggest that the peptides induce ion channels inside lipid membranes due to peptide–lipid physical interactions

  20. Lipid Asymmetry in DLPC/DSPC-Supported Lipid Bilayers: A Combined AFM and Fluorescence Microscopy Study

    PubMed Central

    Lin, Wan-Chen; Blanchette, Craig D.; Ratto, Timothy V.; Longo, Marjorie L.

    2006-01-01

    A fundamental attribute of cell membranes is transmembrane asymmetry, specifically the formation of ordered phase domains in one leaflet that are compositionally different from the opposing leaflet of the bilayer. Using model membrane systems, many previous studies have demonstrated the formation of ordered phase domains that display complete transmembrane symmetry; but there have been few reports on the more biologically relevant asymmetric membrane structures. Here we report on a combined atomic force microscopy and fluorescence microscopy study whereby we observe three different states of transmembrane symmetry in phase-separated supported lipid bilayers formed by vesicle fusion. We find that if the leaflets differ in gel-phase area fraction, then the smaller domains in one leaflet are in registry with the larger domains in the other leaflet and the system is dynamic. In a presumed lipid flip-flop process similar to Ostwald ripening, the smaller domains in one leaflet erode away whereas the large domains in the other leaflet grow until complete compositional asymmetry is reached and remains stable. We have quantified this evolution and determined that the lipid flip-flop event happens most frequently at the interface between symmetric and asymmetric DSPC domains. If both leaflets have identical area fraction of gel-phase, gel-phase domains are in registry and are static in comparison to the first state. The stability of these three DSPC domain distributions, the degree of registry observed, and the domain immobility have biological significance with regards to maintenance of lipid asymmetry in living cell membranes, communication between inner leaflet and outer leaflet, membrane adhesion, and raft mobility. PMID:16214871

  1. 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

  2. Ordered stacking of F-actin layers and mixed lipid bilayers: a columnar liquid crystal.

    PubMed

    Caillé, A; Artzner, F; Amblard, F

    2013-01-25

    In this Letter, we show how the grooved helical structure of actin microfilaments (F-actin) interacting with mixed fluid lipid bilayers leads to handedness-independent 1D lipid bilayer undulations coupled to longitudinal in-plane ordering of the microfilaments. This longitudinal ordering is forced by the emerging in-plane compression and curvature energy terms of the straight 1D bilayer undulation wave fronts. Thereby, adjacent helices are set into registry along their long axis in their monolayer and π shifted between adjacent monolayers. An ordered composite multilamellar structure emerges by alternate stacking of these lipid bilayers and monolayers of F-actin. This two-dimensionally ordered system has the symmetries of a centered rectangular columnar liquid crystal, the straight 1D wave fronts playing the role of the classical molecular columns. PMID:25166203

  3. Low levels of lipid oxidation radically increase the passive permeability of lipid bilayers.

    PubMed

    Runas, Kristina A; Malmstadt, Noah

    2015-01-21

    Oxidation of unsaturated lipids in cellular membranes has been shown to cause severe membrane damage and potentially cell death. The presence of oxidized lipid species in the membrane is known to cause changes in membrane properties, such as decreased fluidity. This study uses giant unilamellar vesicles (GUVs) to measure passive transport across membranes containing defined concentrations of oxidized lipid species. GUVs consisting of a saturated phospholipid, an unsaturated phospholipid, and cholesterol were used as model membranes. By replacing defined amounts of the unsaturated lipid with a corresponding oxidized product, the oxidation process could be mimicked, yielding vesicles of varying oxidized lipid concentration. Oxidized lipid concentration was varied from 0 mol% to 18 mol% of the total lipid concentration. Passive transport of PEG12-NBD, an uncharged fluorescent molecule, was measured using a microfluidic trap to capture the GUVs and spinning disk confocal microscopy (SDCM) to track the transport of a fluorescent species in the equatorial plane of each GUV. Membrane permeability was determined by fitting the resulting concentration profiles to a finite difference model of diffusion and permeation around and through the membrane. Experiments showed three permeability regimes. Without oxidation, transport was slow, with a measured permeability on the order of 1.5 × 10(-6) cm s(-1). At 2.5-10% oxidized species permeation was fast (1.5 × 10(-5) cm s(-1)). Above 12.5% oxidized species, the bilayer was disrupted by the formation of pore defects. As passive transport is an important mechanism for drug delivery, understanding the relationship between oxidation and permeation could provide insight into the pharmaceutical characteristics of tissues with oxidative damage. PMID:25415555

  4. Formation of supported lipid bilayers on silica: relation to lipid phase transition temperature and liposome size.

    PubMed

    Jing, Yujia; Trefna, Hana; Persson, Mikael; Kasemo, Bengt; Svedhem, Sofia

    2014-01-01

    DPPC liposomes ranging from 90 nm to 160 nm in diameter were prepared and used for studies of the formation of supported lipid membranes on silica (SiO2) at temperatures below and above the gel to liquid-crystalline phase transition temperature (Tm = 41 °C), and by applying temperature gradients through Tm. The main method was the quartz crystal microbalance with dissipation (QCM-D) technique. It was found that liposomes smaller than 100 nm spontaneously rupture on the silica surface when deposited at a temperature above Tm and at a critical surface coverage, following a well-established pathway. In contrast, DPPC liposomes larger than 160 nm do not rupture on the surface when adsorbed at 22 °C or at 50 °C. However, when liposomes of this size are first adsorbed at 22 °C and at a high enough surface coverage, after which they are subject to a constant temperature gradient up to 50 °C, they rupture and fuse to a bilayer, a process that is initiated around Tm. The results are discussed and interpreted considering a combination of effects derived from liposome-surface and liposome-liposome interactions, different softness/stiffness and shape of liposomes below and above Tm, the dynamics and thermal activation of the bilayers occurring around Tm and (for liposomes containing 33% of NaCl) osmotic pressure. These findings are valuable both for preparation of supported lipid bilayer cell membrane mimics and for designing temperature-responsive material coatings. PMID:24651504

  5. A nanohybrid membrane with lipid bilayer-like properties utilized as a conductimetric saccharin sensor.

    PubMed

    Chalkias, Nikolaos G; Giannelis, Emmanuel P

    2007-10-31

    Since their introduction, artificial lipid bilayer membranes were used in a wide array of applications, such as sensors, biocompatible materials and study-models of the cell's outer boundary. Here, we present a nanohybrid membrane using an inorganic host and amphiphilic organic molecules with lipid bilayer-like properties. The stability of the presented mimetic membrane is significantly improved when compared to existing methods. The nanohybrid membrane exhibited two thermotropic phases corresponding to the L(alpha) and L(beta) phases that lipid bilayer membranes are known to adopt. Integration of cholesterol molecules into the nanohybrid membrane lead to the same qualitative effects as in lipid bilayers, including expansion of the bilayer spacing and decrease of the L(alpha) to L(beta) transition enthalpy. To further illustrate the similarities of the synthesized membrane with a lipid bilayer, the ability of the nanohybrid membrane to function as saccharin conductimetric sensor was evaluated. The lower limit of detection of the sensor was 6 microM and the linear range of response was from 20 to 400 microM. PMID:17548189

  6. Storable droplet interface lipid bilayers for cell-free ion channel studies.

    PubMed

    Jung, Sung-Ho; Choi, Sangbaek; Kim, Young-Rok; Jeon, Tae-Joon

    2012-01-01

    An artificially created lipid bilayer is an important platform in studying ion channels and engineered biosensor applications. However, a lipid bilayer created using conventional techniques is fragile and short-lived, and the measurement of ion channels requires expertise and laborious procedures, precluding practical applications. Here, we demonstrate a storable droplet lipid bilayer precursor frozen with ion channels, resulting in a droplet interface bilayer upon thawing. A small vial with an aqueous droplet in organic solution was flash frozen in -80 °C methanol immediately after an aqueous droplet was introduced into the organic solution and gravity draws the droplet down to the interface upon thawing. A lipid bilayer created along the interface using this method had giga-ohm resistance and typical specific capacitance values. The noise level of this system is favorably comparable to the conventional system. The subsequent incorporation of ion channels, alpha-hemolysin and gramicidin A, showed typical conductance values consistent with those in previous literatures. This novel system to create a lipid bilayer as a whole can be automated from its manufacture to use and indefinitely stored when frozen. As a result, ion channel measurements can be carried out in any place, increasing the accessibility of ion channel studies as well as a number of applications, such as biosensors, ion channel drug screening, and biophysical studies. PMID:21909672

  7. Cationic Cell-Penetrating Peptide Binds to Planar Lipid Bilayers Containing Negatively Charged Lipids but does not Induce Conductive Pores

    PubMed Central

    Gurnev, Philip A.; Yang, Sung-Tae; Melikov, Kamran C.; Chernomordik, Leonid V.; Bezrukov, Sergey M.

    2013-01-01

    Using a cation-selective gramicidin A channel as a sensor of the membrane surface charge, we studied interactions of oligoarginine peptide R9C, a prototype cationic cell-penetrating peptide (CPP), with planar lipid membranes. We have found that R9C sorption to the membrane depends strongly on its lipid composition from virtually nonexistent for membranes made of uncharged lipids to very pronounced for membranes containing negatively charged lipids, with charge overcompensation at R9C concentrations exceeding 1 μM. The sorption was reversible as it was removed by addition of polyanionic dextran sulfate to the membrane bathing solution. No membrane poration activity of R9C (as would be manifested by increased bilayer conductance) was detected in the charged or neutral membranes, including those with asymmetric negative/neutral and negative/positive lipid leaflets. We conclude that interaction of R9C with planar lipid bilayers does not involve pore formation in all studied lipid combinations up to 20 μM peptide concentration. However, R9C induces leakage of negatively charged but not neutral liposomes in a process that involves lipid mixing between liposomes. Our findings suggest that direct traversing of CPPs through the uncharged outer leaflet of the plasma membrane bilayer is unlikely and that permeabilization necessarily involves both anionic lipids and CPP-dependent fusion between opposing membranes. PMID:23663836

  8. 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.

  9. Micropatterned fluid lipid bilayer arrays created using a continuous flow microspotter.

    PubMed

    Smith, Kathryn A; Gale, Bruce K; Conboy, John C

    2008-11-01

    We have developed a new method for creating micropatterned lipid bilayer arrays (MLBAs) using a 3D microfluidic system. An array of fluid lipid membranes was patterned onto a glass substrate using a Continuous Flow Microspotter. Fluorescence microscopy experiments were used to verify the formation of a bilayer structure on the glass substrate. Fluorescence recovery after photobleaching experiments demonstrated the bilayers' fluidity was maintained while being individually corralled on the substrate. The reproducibility of bilayer formation within an array was demonstrated by the linear response of membrane fluorescence versus mol % rhodamine functionalized lipids incorporated into the vesicles prior to fusion to the surface. The highly customizable nature of the MLBAs was demonstrated utilizing three different fluorescently labeled lipids to generate a multiple component lipid array. Finally, the cholera toxin B/ganglioside GM 1, antidinitrophenyl (DNP) antibody/DNP, and NeutrAvidin/biotin protein-ligand systems were used to model multiple protein-ligand binding on the MLBAs. The multicomponent patterned bilayers were functionalized with GM 1, DNP, and biotin lipids, and binding curves was generated by recording surface fluorescence versus increasing concentration of membrane bound ligands. PMID:18841940

  10. Micropatterned Fluid Lipid Bilayer Arrays Created Using a Continuous Flow Microspotter

    PubMed Central

    Smith, Kathryn A.; Gale, Bruce K.; Conboy, John C.

    2010-01-01

    We have developed a new method for creating micropatterned lipid bilayer arrays (MLBAs) using a 3D microfluidic system. An array of fluid lipid membranes was patterned onto a glass substrate using a Continuous Flow Microspotter™ (CFM). Fluorescence microscopy experiments were used to verify the formation of a bilayer structure on the glass substrate. Fluorescence recovery after photobleaching (FRAP) experiments demonstrated the bilayers fluidity was maintained while being individually corralled on the substrate. The reproducibility of bilayer formation within an array was demonstrated by the linear response of membrane fluorescence versus mol % rhodamine functionalized lipids incorporated into the vesicles prior to fusion to the surface. The highly customizable nature of the MLBAs was demonstrated utilizing three different fluorescently labeled lipids to generate a multiple component lipid array. Finally, the cholera toxin B (CTB)/ganglioside GM1, anti-dinitrophenyl (DNP) antibody/DNP and NeutrAvidin/biotin protein-ligand systems were used to model multiple protein-ligand binding on the MLBAs. The multi-component patterned bilayers were functionalized with GM1, DNP and biotin lipids and binding curves was generated by recording surface fluorescence versus increasing concentration of membrane bound ligands. PMID:18841940

  11. Shape dynamics, lipid hydrodynamics, and the complex viscoelasticity of bilayer membranes [corrected].

    PubMed

    Rahimi, Mohammad; Arroyo, Marino

    2012-07-01

    Biological membranes are continuously brought out of equilibrium, as they shape organelles, package and transport cargo, or respond to external actions. Even the dynamics of plain lipid membranes in experimental model systems are very complex due to the tight interplay between the bilayer architecture, the shape dynamics, and the rearrangement of the lipid molecules. We formulate and numerically implement a continuum model of the shape dynamics and lipid hydrodynamics, which describes the bilayer by its midsurface and by a lipid density field for each monolayer. The viscoelastic response of bilayers is determined by the stretching and curvature elasticity, and by the inter-monolayer friction and the membrane interfacial shear viscosity. While the bilayer equilibria are well understood theoretically, dynamical calculations have relied on simplified continuum approaches of uncertain transferability, or on molecular simulations reaching very limited length and time scales. Our approach incorporates the main physics, is fully nonlinear, does not assume predefined shapes, and can access a wide range of time and length scales. We validate it with the well understood tether extension. We investigate the tubular lipid transport between cells, the dynamics of bud absorption by a planar membrane, and the fate of a localized lipid density asymmetry in vesicles. These axisymmetric examples bear biological relevance and highlight the diversity of dynamical regimes that bilayers can experience. PMID:23005476

  12. Effect of methyl-branched fatty acids on the structure of lipid bilayers.

    PubMed

    Poger, David; Caron, Bertrand; Mark, Alan E

    2014-12-01

    Methyl-branched fatty acids are widespread in prokaryotic membranes. Although anteiso and iso branching (that is on the antepenultimate and penultimate carbons) and the presence of multiple methyl branches in the phytanoyl chain are known to modify the thermotropic behavior and enhance the fluidity of lipid bilayers, little is known about the effect of methyl branching on the structure of lipid bilayers. In this study, molecular dynamics simulations are used to examine systematically the impact of one or more methyl branches at different positions along the sn-1 palmitoyl chain on the structural properties of a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayer. It is found that methyl branching reduces lipid condensation, decreases the bilayer thickness, and lowers chain ordering. Branching also results in the formation of kinks at the branching point, thereby enhancing the fluidity of lipid bilayers. Furthermore, this effect varies in a methyl-position-dependent fashion. In the case of polymethylated chains, the simulations suggest that if the gap between the methyl groups is sufficient (two or three carbons), the effects of the methyl branches are additive and equivalent to the combined effect of the corresponding monomethyl-branched lipids. PMID:25380125

  13. Mechanics of lipid bilayer junctions affecting the size of a connecting lipid nanotube

    NASA Astrophysics Data System (ADS)

    Karlsson, Roger; Kurczy, Michael; Grzhibovskis, Richards; Adams, Kelly L.; Ewing, Andrew G.; Cans, Ann-Sofie; Voinova, Marina V.

    2011-06-01

    In this study we report a physical analysis of the membrane mechanics affecting the size of the highly curved region of a lipid nanotube (LNT) that is either connected between a lipid bilayer vesicle and the tip of a glass microinjection pipette (tube-only) or between a lipid bilayer vesicle and a vesicle that is attached to the tip of a glass microinjection pipette (two-vesicle). For the tube-only configuration (TOC), a micropipette is used to pull a LNT into the interior of a surface-immobilized vesicle, where the length of the tube L is determined by the distance of the micropipette to the vesicle wall. For the two-vesicle configuration (TVC), a small vesicle is inflated at the tip of the micropipette tip and the length of the tube L is in this case determined by the distance between the two interconnected vesicles. An electrochemical method monitoring diffusion of electroactive molecules through the nanotube has been used to determine the radius of the nanotube R as a function of nanotube length L for the two configurations. The data show that the LNT connected in the TVC constricts to a smaller radius in comparison to the tube-only mode and that tube radius shrinks at shorter tube lengths. To explain these electrochemical data, we developed a theoretical model taking into account the free energy of the membrane regions of the vesicles, the LNT and the high curvature junctions. In particular, this model allows us to estimate the surface tension coefficients from R( L) measurements.

  14. Lipid asymmetry in DLPC/DSPC supported lipid bilayers, a combined AFM and fluorescence microscopy study

    SciTech Connect

    Lin, W; Blanchette, C D; Ratto, T V; Longo, M L

    2005-06-20

    A fundamental attribute of cell membranes is transmembrane asymmetry, specifically the formation of ordered phase domains in one leaflet that are compositionally different from the opposing leaflet of the bilayer. Using model membrane systems, many previous studies have demonstrated the formation of ordered phase domains that display complete transmembrane symmetry but there have been few reports on the more biologically relevant asymmetric membrane structures. Here we report on a combined atomic force microscopy (AFM) and fluorescence microscopy study whereby we observe three different states of transmembrane symmetry in phase-separated supported bilayers formed by vesicle fusion. We find that if the leaflets differ in gel-phase area fraction, then the smaller domains in one leaflet are in registry with the larger domains in the other leaflet and the system is dynamic. In a presumed lipid flip-flop process similar to Ostwald Ripening, the smaller domains in one leaflet erode away while the large domains in the other leaflet grow until complete compositional asymmetry is reached and remains stable. We have quantified this evolution and determined that the lipid flip-flop event happens most frequently at the interface between symmetric and asymmetric DSPC domains. If both leaflets have nearly identical area fraction of gel-phase, gel-phase domains are in registry and are static in comparison to the first state. The stability of these three DSPC domain distributions, the degree of registry observed, and the domain immobility have direct biological significance with regards to maintenance of lipid asymmetry in living cell membranes, communication between inner leaflet and outer leaflet, membrane adhesion, and raft mobility.

  15. Semiconductor particles in bilayer lipid membranes. Formation, characterization, and photoelectrochemistry

    SciTech Connect

    Zhao, X.K.; Baral, S.B.; Rolandi, R.; Fendler, J.H.

    1988-02-17

    Bilayer lipid membranes (BLMs) have been formed from bovine brain phosphatidylserine (PS), glyceryl monooleate (GMO), and a ploymerizable surfactant, (n-C/sub 15/H/sub 31/CO/sub 2/(CH/sub 2/))/sub 2/N/sup +/(CH/sub 3/)CH/sub 2/C/sub 6/H/sub 4/CH==CH/sub 2/Cl/sup -/(STYRS). These BLMs were then used to provide matrices for the in situ generation of microcrystalline CdS, CuS, Cu/sub 2/S, PbS, ZnS, HgS, and In/sub 2/S/sub 3/. Semiconductors were formed by injecting appropriate metal ion precursors and H/sub 2/S into the bathing solutions on opposite sides of the BLM. Their presence was established by voltage-dependent capacitance measurements, absorption spectroscopy, and optical microscopy. Subsequent to the injection of H/sub 2/S, the first observable change was the appearance of fairly uniform white dots on the black film. These dots rapidly moved around and grew in size, forming islands that then merged with themselves and with a second generation of dots, which ultimately led to a continuous film that continued to grow in thickness. Film formation and growth were monitored by simultaneous optical thickness and capacitance measurements. These data were treated in terms of an equivalent R-C circuit and allowed for the assessment of the semiconductor penetration depth into the BLM. This value for a GMO-BLM-supported In/sub 2/S/sub 3/ film was determined to be 24 A. Bandgap excitation, by nanosecond-pulsed or continuous illumination of the BLM-supported semiconductor film, led to observable photoelectric effects. Visible light (lambda > 350 nm) excitation into STYRS-BLM-supported CdS led to polymerization of the styrene moiety of STYRS. BLM-supported semiconductors remained stable for days.

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

    PubMed

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

    1984-08-01

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

  17. Real-time detection of lipid bilayer assembly and detergent-initiated solubilization using optical cavities

    NASA Astrophysics Data System (ADS)

    Sun, V.; Armani, A. M.

    2015-02-01

    The cellular membrane governs numerous fundamental biological processes. Therefore, developing a comprehensive understanding of its structure and function is critical. However, its inherent biological complexity gives rise to numerous inter-dependent physical phenomena. In an attempt to develop a model, two different experimental approaches are being pursued in parallel: performing single cell experiments (top down) and using biomimetic structures (bottom up), such as lipid bilayers. One challenge in many of these experiments is the reliance on fluorescent probes for detection which can create confounds in this already complex system. In the present work, a label-free detection method based on an optical resonant cavity is used to detect one of the fundamental physical phenomena in the system: assembly and solubilization of the lipid bilayer. The evanescent field of the cavity strongly interacts with the lipid bilayer, enabling the detection of the bilayer behavior in real-time. Two independent detection mechanisms confirm the formation and detergent-assisted solubilization of the lipid bilayers: (1) a refractive index change and (2) a material loss change. Both mechanisms can be monitored in parallel, on the same device, thus allowing for cross-confirmation of the results. To verify the proposed method, we have detected the formation of self-assembled phosphatidylcholine lipid bilayers from small unilamellar vesicles on the device surface in real-time. Subsequently, we exposed the bilayers to two different detergents (non-ionic Triton X-100 and anionic sodium dodecyl sulfate) to initiate solubilization, and this process was also detected in real-time. After the bilayer solubilization, the device returned to its initial state, exhibiting minimal hysteresis. The experimental wash-off was also collected and analyzed using dynamic light scattering.

  18. Diffusion studies on permeable nitroxyl spin probes through bilayer lipid membranes: A low frequency ESR study

    SciTech Connect

    Meenakumari, V.; Benial, A. Milton Franklin; Utsumi, Hideo; Ichikawa, Kazuhiro; Yamada, Ken-ichi; Hyodo, Fuminori; Jawahar, A.

    2015-06-24

    Electron spin resonance (ESR) studies were carried out for permeable 2mM {sup 14}N-labeled deutrated 3 Methoxy carbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (MC-PROXYL) in pure water and 1mM, 2mM, 3mM, 4mM concentration of 14N-labeled deutrated MC-PROXYL in 400mM concentration of liposomal solution by using a 300 MHz ESR spectrometer. The ESR parameters such as linewidth, hyperfine coupling constant, g-factor, partition parameter and permeability were reported for these samples. The line broadening was observed for the nitroxyl spin probe in the liposomal solution. The line broadening indicates that the high viscous nature of the liposomal solution. The partition parameter and permeability values indicate the maximum diffusion of nitroxyl spin probes in the bilayer lipid membranes at 2 mM concentration of nitroxyl radical. This study illustrates that ESR can be used to differentiate between the intra and extra- membrane water by loading the liposome vesicles with a lipid-permeable nitroxyl spin probe. From the ESR results, the spin probe concentration was optimized as 2mM in liposomal solution for ESR phantom studies/imaging, invivo and invitro experiments.

  19. Diffusion studies on permeable nitroxyl spin probes through bilayer lipid membranes: A low frequency ESR study

    NASA Astrophysics Data System (ADS)

    Meenakumari, V.; Utsumi, Hideo; Ichikawa, Kazuhiro; Yamada, Ken-ichi; Hyodo, Fuminori; Jawahar, A.; Benial, A. Milton Franklin

    2015-06-01

    Electron spin resonance (ESR) studies were carried out for permeable 2mM 14N-labeled deutrated 3 Methoxy carbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (MC-PROXYL) in pure water and 1mM, 2mM, 3mM, 4mM concentration of 14N-labeled deutrated MC-PROXYL in 400mM concentration of liposomal solution by using a 300 MHz ESR spectrometer. The ESR parameters such as linewidth, hyperfine coupling constant, g-factor, partition parameter and permeability were reported for these samples. The line broadening was observed for the nitroxyl spin probe in the liposomal solution. The line broadening indicates that the high viscous nature of the liposomal solution. The partition parameter and permeability values indicate the maximum diffusion of nitroxyl spin probes in the bilayer lipid membranes at 2 mM concentration of nitroxyl radical. This study illustrates that ESR can be used to differentiate between the intra and extra- membrane water by loading the liposome vesicles with a lipid-permeable nitroxyl spin probe. From the ESR results, the spin probe concentration was optimized as 2mM in liposomal solution for ESR phantom studies/imaging, invivo and invitro experiments.

  20. Structure of Carbon Nanotube Porins in Lipid Bilayers: An in Situ Small-Angle X-ray Scattering (SAXS) Study.

    PubMed

    Tran, Ich C; Tunuguntla, Ramya H; Kim, Kyunghoon; Lee, Jonathan R I; Willey, Trevor M; Weiss, Thomas M; Noy, Aleksandr; van Buuren, Tony

    2016-07-13

    Carbon nanotube porins (CNTPs), small segments of carbon nanotubes capable of forming defined pores in lipid membranes, are important future components for bionanoelectronic devices as they could provide a robust analog of biological membrane channels. In order to control the incorporation of these CNT channels into lipid bilayers, it is important to understand the structure of the CNTPs before and after insertion into the lipid bilayer as well as the impact of such insertion on the bilayer structure. Here we employed a noninvasive in situ probe, small-angle X-ray scattering, to study the integration of CNT porins into dioleoylphosphatidylcholine bilayers. Our results show that CNTPs in solution are stabilized by a monolayer of lipid molecules wrapped around their outer surface. We also demonstrate that insertion of CNTPs into the lipid bilayer results in decreased bilayer thickness with the magnitude of this effect increasing with the concentration of CNTPs. PMID:27322135

  1. Lipid bilayer-assisted release of an enediyne antibiotic from neocarzinostatin chromoprotein.

    PubMed

    Hariharan, Parameswaran; Sudhahar, Christopher Gunasekaran; Chou, Shan-Ho; Chin, Der-Hang

    2010-09-01

    The nine-membered enediyne class has drawn extensive interest because of extremely high antitumor potency and intricate interactions with its carrier protein. While the drug-induced DNA cleavage reactions have been mostly elucidated, the critical release-transport process of the labile enediyne molecule in cellular environment remained obscure. Using neocarzinostatin chromoprotein as a model, we demonstrated a lipid bilayer-assisted release mechanism. The in vitro enediyne release rate under aqueous conditions was found to be too slow to account for its efficient DNA cleavage action. Via the presence of lipid bilayers, chaotropic agents, or organic solvents, we found the release was substantially enhanced. The increased rate was linearly dependent on the lipid bilayer concentration and the dielectric value of the binary organic solvent mixtures. While lipid bilayers provided a low surrounding dielectricity to assist in drug release, there were no major conformational changes in the apo and holo forms of the carrier protein. In addition, the lifespan of the released enediyne chromophore was markedly extended through partitioning of the chromophore in the hydrophobic bilayer phase, and the lipid bilayer-stabilized enediyne chromophore significantly enhanced DNA cleavage in vitro. Collectively, we depicted how a lipid bilayer membrane efficiently enhanced dissociation of the enediyne chromophore through a hydrophobic sensing release mechanism and then acted as a protector of the released enediyne molecule until its delivery to the target DNA. The proposed membrane-assisted antibiotic release-transport model might signify a new dimension to our understanding of the modus operandi of the antitumor enediyne drugs. PMID:20712297

  2. Erythrocyte Membrane Model with Explicit Description of the Lipid Bilayer and the Spectrin Network

    PubMed Central

    Li, He; Lykotrafitis, George

    2014-01-01

    The membrane of the red blood cell (RBC) consists of spectrin tetramers connected at actin junctional complexes, forming a two-dimensional (2D) sixfold triangular network anchored to the lipid bilayer. Better understanding of the erythrocyte mechanics in hereditary blood disorders such as spherocytosis, elliptocytosis, and especially, sickle cell disease requires the development of a detailed membrane model. In this study, we introduce a mesoscale implicit-solvent coarse-grained molecular dynamics (CGMD) model of the erythrocyte membrane that explicitly describes the phospholipid bilayer and the cytoskeleton, by extending a previously developed two-component RBC membrane model. We show that the proposed model represents RBC membrane with the appropriate bending stiffness and shear modulus. The timescale and self-consistency of the model are established by comparing our results with experimentally measured viscosity and thermal fluctuations of the RBC membrane. Furthermore, we measure the pressure exerted by the cytoskeleton on the lipid bilayer. We find that defects at the anchoring points of the cytoskeleton to the lipid bilayer (as in spherocytes) cause a reduction in the pressure compared with an intact membrane, whereas defects in the dimer-dimer association of a spectrin filament (as in elliptocytes) cause an even larger decrease in the pressure. We conjecture that this finding may explain why the experimentally measured diffusion coefficients of band-3 proteins are higher in elliptocytes than in spherocytes, and higher than in normal RBCs. Finally, we study the effects that possible attractive forces between the spectrin filaments and the lipid bilayer have on the pressure applied on the lipid bilayer by the filaments. We discover that the attractive forces cause an increase in the pressure as they diminish the effect of membrane protein defects. As this finding contradicts with experimental results, we conclude that the attractive forces are moderate and do

  3. Cholesterol behavior in asymmetric lipid bilayers: insights from molecular dynamics simulations.

    PubMed

    Yesylevskyy, Semen O; Demchenko, Alexander P

    2015-01-01

    Asymmetric lipid composition of the cell membranes plays an important role in the multitude of important biological functions. Much less is known, however, about the distribution and dynamics of cholesterol in asymmetric biological membranes. In this work we show how this issue could be addressed computationally by molecular dynamics simulations. The influence of the lipid head group charge, acyl chain saturation, spontaneous membrane curvature and the surface tension of the membrane on cholesterol distribution in asymmetric lipid bilayers is investigated. Four asymmetric bilayers containing DOPC, DOPS, DSPC, or DSPS lipids, were simulated on the time scale extended to tens of microseconds. We show that cholesterol strongly prefers anionic lipids to neutral and saturated lipid tails to unsaturated with distribution ratio ~0.4-0.6. Multiple flip-flop transitions of cholesterol were observed directly and their mean times range from 350 to 2,000 ns. It was shown that the distribution of cholesterol in the asymmetric bilayer depends not only on the type of lipids but also on the local membrane curvature and the surface tension. The geometric shape of spontaneously curved asymmetric bilayer changes dramatically in the presence of cholesterol. The membrane curvature becomes less homogeneous with large patches of flattened regions interleaved by rather sharp bends. PMID:25331142

  4. Disturb or Stabilize? A Molecular Dynamics Study of the Effects of Resorcinolic Lipids on Phospholipid Bilayers

    PubMed Central

    Siwko, Magdalena E.; de Vries, Alex H.; Mark, Alan E.; Kozubek, Arkadiusz; Marrink, Siewert J.

    2009-01-01

    Abstract Resorcinolic lipids, or resorcinols, are commonly found in plant membranes. They consist of a substituted benzene ring forming the hydrophilic lipid head, attached to an alkyl chain forming the hydrophobic tail. Experimental results show alternative effects of resorcinols on lipid membranes. Depending on whether they are added to lipid solutions before or after the formation of the liposomes, they either stabilize or destabilize these liposomes. Here we use atomistic molecular dynamics simulations to elucidate the molecular nature of this dual effect. Systems composed of either one of three resorcinol homologs, differing in the alkyl tail length, interacting with dimyristoylphosphatidylcholine lipid bilayers were studied. It is shown that resorcinols preincorporated into bilayers induce order within the lipid acyl chains, decrease the hydration of the lipid headgroups, and make the bilayers less permeable to water. In contrast, simulations in which the resorcinols are incorporated from the aqueous solution into a preformed phospholipid bilayer induce local disruption, leading to either transient pore formation or even complete rupture of the membrane. In line with the experimental data, our simulations thus demonstrate that resorcinols can either disturb or stabilize the membrane structure, and offer a detailed view of the underlying molecular mechanism. PMID:19383459

  5. One-Photon Lithography for High-Quality Lipid Bilayer Micropatterns.

    PubMed

    Sánchez, M Florencia; Dodes Traian, Martín M; Levi, Valeria; Carrer, Dolores C

    2015-11-01

    A relevant question in cell biology with broad implications in biomedicine is how the organization and dynamics of interacting membranes modulate signaling cascades that involve cell-cell contact. The functionalization of surfaces with supported lipid bilayers containing tethered proteins is a particularly useful method to present ligands with membrane-like mobility to cells. Here, we present a method to generate micrometer-sized patches of lipid bilayers decorated with proteins. The method uses an economic microcontact printing technique based on one-photon lithography that can be easily implemented in a commercial laser scanning microscope. We verified that both proteins and lipids freely diffuse within the patterned bilayer, as assessed by z-scan fluorescence correlation spectroscopy and fluorescence recovery after photobleaching. These results suggest that the supported lipid bilayer patterns constitute an optimal system to explore processes involving direct interactions between cells. We also illustrate possible applications of this method by exploring the interaction of cells expressing the Fas receptor and patterns of lipid bilayers containing an agonist antibody against Fas. PMID:26452154

  6. The Lipid Bilayer Provides a Site for Cortisone Crystallization at High Cortisone Concentrations.

    PubMed

    Alsop, Richard J; Khondker, Adree; Hub, Jochen S; Rheinstädter, Maikel C

    2016-01-01

    Cortisone is an injected anti-inflammatory drug that can cause painful side effects known as "steroid flares" which are caused by cortisone crystallizing at the injection site. We used molecular dynamics simulations and X-ray diffraction to study the interaction of cortisone with model lipid membranes made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at drug concentrations from 0 mol% to 50 mol%. Cortisone was found to partition in the lipid bilayer and locate in the hydrophilic to hydrophobic interface of the membranes. Cortisone strongly affects the integrity of the membrane, as quantified by a decreased membrane thickness, increased area per lipid, and decreased lipid tail order parameters. At cortisone concentrations of more than 20 mol%, signals from crystallized cortisone were observed. These crystallites are embedded in the bilayers and orient with the membranes. While the cortisone molecules align parallel to the bilayers at low concentrations, they start to penetrate the hydrophobic core at higher concentrations. Trans-membrane crystallites start to nucleate when the membrane thickness has decreased such that cortisone molecules in the different leaflets can find partners from the opposite leaflet resulting in a non-zero density of cortisone molecules in the bilayer center. We suggest that the lipid bilayer provides a site for cortisone crystallization. PMID:26936102

  7. The Lipid Bilayer Provides a Site for Cortisone Crystallization at High Cortisone Concentrations

    PubMed Central

    Alsop, Richard J.; Khondker, Adree; Hub, Jochen S.; Rheinstädter, Maikel C.

    2016-01-01

    Cortisone is an injected anti-inflammatory drug that can cause painful side effects known as “steroid flares” which are caused by cortisone crystallizing at the injection site. We used molecular dynamics simulations and X-ray diffraction to study the interaction of cortisone with model lipid membranes made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at drug concentrations from 0 mol% to 50 mol%. Cortisone was found to partition in the lipid bilayer and locate in the hydrophilic to hydrophobic interface of the membranes. Cortisone strongly affects the integrity of the membrane, as quantified by a decreased membrane thickness, increased area per lipid, and decreased lipid tail order parameters. At cortisone concentrations of more than 20 mol%, signals from crystallized cortisone were observed. These crystallites are embedded in the bilayers and orient with the membranes. While the cortisone molecules align parallel to the bilayers at low concentrations, they start to penetrate the hydrophobic core at higher concentrations. Trans-membrane crystallites start to nucleate when the membrane thickness has decreased such that cortisone molecules in the different leaflets can find partners from the opposite leaflet resulting in a non-zero density of cortisone molecules in the bilayer center. We suggest that the lipid bilayer provides a site for cortisone crystallization. PMID:26936102

  8. Mechanism of ionophoric transport of indium-111 cations through a lipid bilayer membrane

    SciTech Connect

    Choi, H.O.; Hwang, K.J.

    1987-01-01

    The use of mobile ionophores to facilitate the transport of /sup 111/In through a lipid bilayer membrane has broad applications in liposome technology and cell labeling. However, the mechanism of such ionophore-mediated transport of /sup 111/In through a lipid bilayer membrane is not completely clear. The present report describes the correlations of the behaviors of ionophoric loading of /sup 111/In into liposomes with the lipophilicity and the indium-binding affinity of three ionophores, namely, 8-hydroxyquinoline, acetylacetone, and tropolone. Our results suggest that the mechanism of the ionophoric transport of /sup 111/In through a lipid bilayer membrane involves the rapid exchange of /sup 111/In cations among the ionophores in both the aqueous solution and the lipid bilayer. Furthermore, the effectiveness of an ionophore in facilitating the transport of /sup 111/In from the external aqueous compartment to the entrapped nitrilotriacetic acid depends not only on the lipophilicity of the (/sup 111/In)ionophore complex, but also on the lipophilicity of the free ionophore itself and the competition of /sup 111/In between nitrilotriacetic acid inside the inner aqueous compartment of the liposome and the ionophore imbedded in the lipid bilayer membrane of the liposome.

  9. Main phase transitions in supported lipid single-bilayer.

    PubMed

    Charrier, A; Thibaudau, F

    2005-08-01

    We have studied the phase transitions of a phospholipidic single-bilayer supported on a mica substrate by real-time temperature-controlled atomic force microscopy. We show the existence of two phase transitions in this bilayer that we attribute to two gel (L(beta))/fluid (L(alpha)) transitions, corresponding to the independent melting of each leaflet of the bilayer. The ratio of each phase with temperature and the large broadening of the transitions' widths have been interpreted through a basic thermodynamic framework in which the surface tension varies during the transitions. The experimental data can be fit with such a model using known thermodynamic parameters. PMID:15879467

  10. A droplet microfluidic system for sequential generation of lipid bilayers and transmembrane electrical recordings.

    PubMed

    Czekalska, Magdalena A; Kaminski, Tomasz S; Jakiela, Slawomir; Tanuj Sapra, K; Bayley, Hagan; Garstecki, Piotr

    2015-01-21

    This paper demonstrates a microfluidic system that automates i) formation of a lipid bilayer at the interface between a pair of nanoliter-sized aqueous droplets in oil, ii) exchange of one droplet of the pair to form a new bilayer, and iii) current measurements on single proteins. A new microfluidic architecture is introduced - a set of traps designed to localize the droplets with respect to each other and with respect to the recording electrodes. The system allows for automated execution of experimental protocols by active control of the flow on chip with the use of simple external valves. Formation of stable artificial lipid bilayers, incorporation of α-hemolysin into the bilayers and electrical measurements of ionic transport through the protein pore are demonstrated. PMID:25412368

  11. The role of inertia and coarse-graining on the transverse modes of lipid bilayers

    NASA Astrophysics Data System (ADS)

    Hömberg, M.; Müller, M.

    2012-03-01

    We determine the transverse dispersion relations of a lipid bilayer by generalizing the Seifert-Langer theory to include the bilayer's inertia and its surface tension. Thereby we extend the applicability of the original theory to computer simulations of lipid bilayers with and without solvent, as well as to simulations with and without momentum conservation. We calculate the asymptotic dispersion relations and identify conditions under which propagating modes occur. The theory is compared with simulations of a coarse-grained, solvent-free model, where we extract the transverse dispersion relations by fitting the intermediate scattering function of bilayer undulations. An estimate of the intermonolayer friction is obtained and compared with the result of a Green-Kubo relation.

  12. Bilayer properties of hydroxytyrosol- and tyrosol-phosphatidylcholine lipids

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Tyrosol and hydroxytyrosol are the phytochemicals abundantly found in olive oil. Transphosphatidylation of tyrosol and hydroxytyrosol with dioleoylphosphocholine resulted in phospholipids with antioxidant properties. The ability of these phyto-phospholipids to form liposomes and supported bilayers w...

  13. Molecular Dynamics of a Water-Lipid Bilayer Interface

    NASA Technical Reports Server (NTRS)

    Wilson, Michael A.; Pohorille, Andrew

    1994-01-01

    We present results of molecular dynamics simulations of a glycerol 1-monooleate bilayer in water. The total length of analyzed trajectories is 5ns. The calculated width of the bilayer agrees well with the experimentally measured value. The interior of the membrane is in a highly disordered fluid state. Atomic density profile, orientational and conformational distribution functions, and order parameters indicate that disorder increases toward the center of the bilayer. Analysis of out-of-plane thermal fluctuations of the bilayer surfaces occurring at the time scale of the present calculations reveals that the distribution of modes agrees with predictions of the capillary wave model. Fluctuations of both bilayer surfaces are uncorrelated, yielding Gaussian distribution of instantaneous widths of the membrane. Fluctuations of the width produce transient thinning defects in the bilayer which occasionally span almost half of the membrane. The leading mechanism of these fluctuations is the orientational and conformational motion of head groups rather than vertical motion of the whole molecules. Water considerably penetrates the head group region of the bilayer but not its hydrocarbon core. The total net excess dipole moment of the interfacial water points toward the aqueous phase, but the water polarization profile is non-monotonic. Both water and head groups significantly contribute to the surface potential across the interface. The calculated sign of the surface potential is in agreement with that from experimental measurements, but the value is markedly overestimated. The structural and electrical properties of the water-bilayer system are discussed in relation to membrane functions, in particular transport of ions and nonelectrolytes across membranes.

  14. Bilayer Asymmetry Influences Integrin Sequestering in Raft-Mimicking Lipid Mixtures

    PubMed Central

    Hussain, Noor F.; Siegel, Amanda P.; Ge, Yifan; Jordan, Rainer; Naumann, Christoph A.

    2013-01-01

    There is growing recognition that lipid heterogeneities in cellular membranes play an important role in the distribution and functionality of membrane proteins. However, the detection and characterization of such heterogeneities at the cellular level remains challenging. Here we report on the poorly understood relationship between lipid bilayer asymmetry and membrane protein sequestering in raft-mimicking model membrane mixtures using a powerful experimental platform comprised of confocal spectroscopy XY-scan and photon-counting histogram analyses. This experimental approach is utilized to probe the domain-specific sequestering and oligomerization state of αvβ3 and α5β1 integrins in bilayers, which contain coexisting liquid-disordered/liquid-ordered (ld/lo) phase regions exclusively in the top leaflet of the bilayer (bottom leaflet contains ld phase). Comparison with previously reported integrin sequestering data in bilayer-spanning lo-ld phase separations demonstrates that bilayer asymmetry has a profound influence on αvβ3 and α5β1 sequestering behavior. For example, both integrins sequester preferentially to the lo phase in asymmetric bilayers, but to the ld phase in their symmetric counterparts. Furthermore, our data show that bilayer asymmetry significantly influences the role of native ligands in integrin sequestering. PMID:23708361

  15. Thermal, dynamic and structural properties of drug AT1 antagonist olmesartan in lipid bilayers.

    PubMed

    Ntountaniotis, Dimitrios; Mali, Gregor; Grdadolnik, Simona Golic; Halabalaki, Maria; Maria, Halabalaki; Skaltsounis, Alexios-Leandros; Potamitis, Constantinos; Siapi, Eleni; Chatzigeorgiou, Petros; Rappolt, Michael; Mavromoustakos, Thomas

    2011-12-01

    It is proposed that AT1 antagonists (ARBs) exert their biological action by inserting into the lipid membrane and then diffuse to the active site of AT1 receptor. Thus, lipid bilayers are expected to be actively involved and play a critical role in drug action. For this reason, the thermal, dynamic and structural effects of olmesartan alone and together with cholesterol were studied using differential scanning calorimetry (DSC), 13C magic-angle spinning (MAS) nuclear magnetic resonance (NMR), cross-polarization (CP) MAS NMR, and Raman spectroscopy as well as small- and wide angle X-ray scattering (SAXS and WAXS) on dipalmitoyl-phosphatidylcholine (DPPC) multilamellar vesicles. 13C CP/MAS spectra provided direct evidence for the incorporation of olmesartan and cholesterol in lipid bilayers. Raman and X-ray data revealed how both molecules modify the bilayer's properties. Olmesartan locates itself at the head-group region and upper segment of the lipid bilayers as 13C CP/MAS spectra show that its presence causes significant chemical shift changes mainly in the A ring of the steroidal part of cholesterol. The influence of olmesartan on DPPC/cholesterol bilayers is less pronounced. Although, olmesartan and cholesterol are residing at the same region of the lipid bilayers, due to their different sizes, display distinct impacts on the bilayer's properties. Cholesterol broadens significantly the main transition, abolishes the pre-transition, and decreases the membrane fluidity above the main transition. Olmesartan is the only so far studied ARB that increases the gauche:trans ratio in the liquid crystalline phase. These significant differences of olmesartan may in part explain its distinct pharmacological profile. PMID:21843501

  16. Linking lipid architecture to bilayer structure and mechanics using self-consistent field modelling

    NASA Astrophysics Data System (ADS)

    Pera, H.; Kleijn, J. M.; Leermakers, F. A. M.

    2014-02-01

    To understand how lipid architecture determines the lipid bilayer structure and its mechanics, we implement a molecularly detailed model that uses the self-consistent field theory. This numerical model accurately predicts parameters such as Helfrichs mean and Gaussian bending modulus kc and bar{k} and the preferred monolayer curvature J_0^m, and also delivers structural membrane properties like the core thickness, and head group position and orientation. We studied how these mechanical parameters vary with system variations, such as lipid tail length, membrane composition, and those parameters that control the lipid tail and head group solvent quality. For the membrane composition, negatively charged phosphatidylglycerol (PG) or zwitterionic, phosphatidylcholine (PC), and -ethanolamine (PE) lipids were used. In line with experimental findings, we find that the values of kc and the area compression modulus kA are always positive. They respond similarly to parameters that affect the core thickness, but differently to parameters that affect the head group properties. We found that the trends for bar{k} and J_0^m can be rationalised by the concept of Israelachivili's surfactant packing parameter, and that both bar{k} and J_0^m change sign with relevant parameter changes. Although typically bar{k}<0, membranes can form stable cubic phases when the Gaussian bending modulus becomes positive, which occurs with membranes composed of PC lipids with long tails. Similarly, negative monolayer curvatures appear when a small head group such as PE is combined with long lipid tails, which hints towards the stability of inverse hexagonal phases at the cost of the bilayer topology. To prevent the destabilisation of bilayers, PG lipids can be mixed into these PC or PE lipid membranes. Progressive loading of bilayers with PG lipids lead to highly charged membranes, resulting in J_0^m ≫ 0, especially at low ionic strengths. We anticipate that these changes lead to unstable membranes

  17. High Density Arrays of Sub-Micron Spherical Supported Lipid Bilayers

    PubMed Central

    Wittenberg, Nathan J.; Johnson, Timothy W.; Oh, Sang-Hyun

    2012-01-01

    Lipid bilayer membranes found in nature are heterogeneous mixtures of lipids and proteins. Model systems, such as supported lipid bilayers (SLBs) are often employed to simplify experimental systems while mimicking the properties of natural lipid bilayers. Here we demonstrate a new method to form SLB arrays by first forming spherical supported lipid bilayers (SSLBs) on sub-micron-diameter SiO2 beads. The SSLBs are then arrayed into microwells using a simple physical assembly method that requires no chemical modification of the substrate, nor modification of the lipid membrane with recognition moieties. The resulting arrays have sub-micron SSLBs with 3 μm periodicity where > 75 % of the microwells are occupied by an individual SSLB. Because the arrays have high density, fluorescence from > 1000 discrete SSLBs can be acquired with a single image capture. We show that 2-component random arrays can be formed and we also use the arrays to determine the equilibrium dissociation constant for cholera toxin binding to ganglioside GM1. SSLB arrays are robust and are stable for at least one week in buffer. PMID:22967217

  18. Component and state separation in DMPC/DSPC lipid bilayers: a Monte Carlo simulation study.

    PubMed Central

    Michonova-Alexova, Ekaterina I; Sugár, István P

    2002-01-01

    In this paper a two-state, two-component, Ising-type model is used to simulate the lateral distribution of the components and gel/fluid state acyl chains in dimyristoylphosphatidylcholine/distearoylphosphatidylcholine (DMPC/DSPC) lipid bilayers. The same model has been successful in calculating the excess heat capacity curves, the fluorescence recovery after photobleaching (FRAP) threshold temperatures, the most frequent center-to-center distances between DSPC clusters, and the fractal dimensions of gel clusters (Sugar, I. P., T. E. Thompson, and R. L. Biltonen, 1999. Biophys. J. 76:2099-2110). Depending on the temperature and mole fraction the population of the cluster size is either homogeneous or inhomogeneous. In the inhomogeneous population the size of the largest cluster scales with the size of the system, while the rest of the clusters remain small with increasing system size. In a homogeneous population, however, every cluster remains small with increasing system size. For both compositional and fluid/gel state clusters, threshold temperatures-the so-called percolation threshold temperatures-are determined where change in the type of the population takes place. At a given mole fraction, the number of percolation threshold temperatures can be 0, 1, 2, or 3. By plotting these percolation threshold temperatures on the temperature/mole fraction plane, the diagrams of component and state separation of DMPC/DSPC bilayers are constructed. In agreement with the small-angle neutron scattering measurements, the component separation diagram shows nonrandom lateral distribution of the components not only in the gel-fluid mixed phase region, but also in the pure gel and pure fluid regions. A combined diagram of component and state separation is constructed to characterize the lateral distribution of lipid components and gel/fluid state acyl chains in DMPC/DSPC mixtures. While theoretical phase diagrams of two component mixtures can be constructed only in the case of

  19. Semihydrophobic nanoparticle-induced disruption of supported lipid bilayers: specific ion effect.

    PubMed

    Jing, Benxin; Abot, Rosary C T; Zhu, Yingxi

    2014-11-20

    The interaction of nanoparticles with cell membranes is critical to understand and control the structural change and molecular transport of cell membranes for medicines and medical diagnostics, in which hydrophobic interaction is often involved. We examine the specific ion effect on the interaction of semihydrophobic nanoparticle with zwitterionic phospholipid bilayer in aqueous media added with different types of salts. Specifically, we compare the effect of different anions or cations on the adsorption of carboxyl-functionalized polystyrene nanoparticle on supported lipid bilayer and its induced bilayer disruption. By adding different anions at the same ionic concentration to the nanoparticle-lipid bilayer interface, we observe that the growth rate of nanoparticle-induced lipid-poor regions follows the exact Hofmeister anion order of CH3COO(-) > Cl(-) > NO3(-) ≫ SCN(-), suggesting the regulated hydrophobic interaction by anions. In contrast, the specific cation effect on nanoparticle-induced disruption rate of lipid bilayer does not follow the Hofmeister cation order and instead exhibits a trend of Cs(+) ∼ Rb(+) > Na(+) ≫ N(CH3)4(+). It is suggested that the effect of specific ions can be exploited as a simple and efficient approach to modify the nanoparticles-biomembrane interactions with the implication from drug delivery to nontoxic nanomaterial design. PMID:25337793

  20. A Hybrid Model for Erythrocyte Membrane: A Single Unit of Protein Network Coupled with Lipid Bilayer

    PubMed Central

    Zhu, Qiang; Vera, Carlos; Asaro, Robert J.; Sche, Paul; Sung, L. Amy

    2007-01-01

    To investigate the nanomechanics of the erythrocyte membrane we developed a hybrid model that couples the actin-spectrin network to the lipid bilayer. This model features a Fourier space Brownian dynamics model of the bilayer, a Brownian dynamics model of the actin protofilament, and a modified wormlike-chain model of the spectrin (including a cable-dynamics model to predict the oscillation in tension). This model enables us to predict the nanomechanics of single or multiple units of the protein network, the lipid bilayer, and the effect of their interactions. The present work is focused on the attitude of the actin protofilament at the equilibrium states coupled with the elevations of the lipid bilayer through their primary linkage at the suspension complex in deformations. Two different actin-spectrin junctions are considered at the junctional complex. With a point-attachment junction, large pitch angles and bifurcation of yaw angles are predicted. Thermal fluctuations at bifurcation may lead to mode-switching, which may affect the network and the physiological performance of the membrane. In contrast, with a wrap-around junction, pitch angles remain small, and the occurrence of bifurcation is greatly reduced. These simulations suggest the importance of three-dimensional molecular junctions and the lipid bilayer/protein network coupling on cell membrane mechanics. PMID:17449663

  1. Importance of phospholipid bilayer integrity in the analysis of protein–lipid interactions

    SciTech Connect

    Drücker, Patrick; Gerke, Volker; Galla, Hans-Joachim

    2014-10-10

    Highlights: • We show long-term mechanical stabilization of solid supported bilayers. • Bilayer integrity is essential for the investigation of protein–lipid interactions. • Protein adsorption to a bilayer containing defects causes membrane destruction. - Abstract: The integrity of supported phospholipid bilayer membranes is of crucial importance for the investigation of lipid–protein interactions. Therefore we recorded the formation of supported membranes on SiO{sub 2} and mica by quartz crystal microbalance and controlled the integrity by atomic force microscopy. This study aims to analyze how membrane defects affect protein–lipid interactions. The experiments focused on a lipid mixture of POPC/DOPC/Chol/POPS/PI(4,5)P{sub 2} (37:20:20:20:3) and the binding of the peripheral membrane associated protein annexin A2. We found that formation of a continuous undisturbed bilayer is an indispensable precondition for a reliable determination and quantification of lipid–protein-interactions. If membrane defects were present, protein adsorption causes membrane disruption and lipid detachment on a support thus leading to false determination of binding constants. Our results obtained for PI(4,5)P{sub 2} and cholesterol containing supported membranes yield new knowledge to construct functional surfaces that may cover nanoporous substrates, form free standing membranes or may be used for lab-on-a-chip applications.

  2. Sampling errors in free energy simulations of small molecules in lipid bilayers.

    PubMed

    Neale, Chris; Pomès, Régis

    2016-10-01

    Free energy simulations are a powerful tool for evaluating the interactions of molecular solutes with lipid bilayers as mimetics of cellular membranes. However, these simulations are frequently hindered by systematic sampling errors. This review highlights recent progress in computing free energy profiles for inserting molecular solutes into lipid bilayers. Particular emphasis is placed on a systematic analysis of the free energy profiles, identifying the sources of sampling errors that reduce computational efficiency, and highlighting methodological advances that may alleviate sampling deficiencies. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg. PMID:26952019

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  4. Study of supported bilayer lipid membranes for use in chemo-electric energy conversion via active proton transport

    NASA Astrophysics Data System (ADS)

    Sarles, Stephen A.; Sundaresan, Vishnu B.; Leo, Donald J.

    2007-09-01

    Bilayer lipid membranes (BLMs) have been studied extensively due to functional and structural similarities to cell membranes, fostering research to understand ion-channel protein functions, measure bilayer mechanical properties, and identify self-assembly mechanisms. BLMs have traditionally been formed across single pores in substrates such as PTFE (Teflon). The incorporation of ion-channel proteins into the lipid bilayer enables the selective transfer of ions and fluid through the BLM. Processes of this nature have led to the measurement of ion current flowing across the lipid membrane and have been used to develop sensors that signal the presence of a particular reactant (glucose, urea, penicillin), improve drug recognition in cells, and develop materials capable of creating chemical energy from light. Recent research at Virginia Tech has shown that the incorporation of proton transporters in a supported BLM formed across an array of pores can convert chemical energy available in the adenosine triphosphate (ATP) into electricity. Experimental results from this work show that the system-named Biocell-is capable of developing 2µW/cm2 of membrane area with 15μl of ATPase. Efforts to increase the power output and conversion efficiency of this process while moving toward a packaged device present a unique engineering problem. The bilayer, as host to the active proton transporters, must therefore be formed evenly across a porous substrate, remain stable and yet fluid-like for protein interaction, and exhibit a large seal resistance. This article presents the ongoing work to characterize the Biocell using impedance analysis. Electrical impedance spectroscopy (EIS) is used to study the effect of adding ATPase proteins to POPS:POPE bilayer lipid membranes and correlate structural changes evident in the impedance data to the energy-conversion capability of various partial and whole Biocell assemblies. The specific membrane resistance of a pure BLM drops from 40-120k

  5. Using Micropatterned Lipid Bilayer Arrays to Measure the Effect of Membrane Composition on Merocyanine 540 Binding

    PubMed Central

    Smith, Kathryn A.; Conboy, John C.

    2011-01-01

    The lipophilic dye merocyanine 540 (MC540) was used to model small molecule-membrane interactions using micropatterned lipid bilayer arrays (MLBAs) prepared using a 3D Continuous Flow Microspotter (CFM). Fluorescence microscopy was used to monitor MC540 binding to fifteen different bilayer compositions simultaneously. MC540 fluorescence was two times greater for bilayers composed of liquid-crystalline (l.c.) phase lipids (1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)) compared to bilayers in the gel phase (1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)). The effect cholesterol (CHO) had on MC540 binding to the membrane was found to be dependent on the lipid component; cholesterol decreased MC540 bindingin DMPC, DPPC and DSPC bilayers while having little to no effect on the remaining l.c. phase lipids. MC540 fluorescence was also lowered when 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (sodium salt) (DOPS) was incorporated into DOPC bilayers. The increase in the surface charge density appears to decrease the occurrence of highly fluorescent monomers and increase the formation of weakly fluorescent dimers via electrostatic repulsion. This paper demonstrates that MLBAs are a useful tool for preparing high density reproducible bilayer arrays to study small molecule-membrane interactions in a high-throughput manner. PMID:21376014

  6. Interaction of Human Chloride Intracellular Channel Protein 1 (CLIC1) with Lipid Bilayers: A Fluorescence Study.

    PubMed

    Hare, Joanna E; Goodchild, Sophia C; Breit, Samuel N; Curmi, Paul M G; Brown, Louise J

    2016-07-12

    Chloride intracellular channel protein 1 (CLIC1) is very unusual as it adopts a soluble glutathione S-transferase-like canonical fold but can also autoinsert into lipid bilayers to form an ion channel. The conversion between these forms involves a large, but reversible, structural rearrangement of the CLIC1 module. The only identified environmental triggers controlling the metamorphic transition of CLIC1 are pH and oxidation. Until now, there have been no high-resolution structural data available for the CLIC1 integral membrane state, and consequently, a limited understanding of how CLIC1 unfolds and refolds across the bilayer to form a membrane protein with ion channel activity exists. Here we show that fluorescence spectroscopy can be used to establish the interaction and position of CLIC1 in a lipid bilayer. Our method employs a fluorescence energy transfer (FRET) approach between CLIC1 and a dansyl-labeled lipid analogue to probe the CLIC1-lipid interface. Under oxidizing conditions, a strong FRET signal between the single tryptophan residue of CLIC1 (Trp35) and the dansyl-lipid analogue was detected. When considering the proportion of CLIC1 interacting with the lipid bilayer, as estimated by fluorescence quenching experiments, the FRET distance between Trp35 and the dansyl moiety on the membrane surface was determined to be ∼15 Å. This FRET-detected interaction provides direct structural evidence that CLIC1 associates with membranes. The results presented support the current model of an oxidation-driven interaction of CLIC1 with lipid bilayers and also propose a membrane anchoring role for Trp35. PMID:27299171

  7. Covalent attachment of functionalized lipid bilayers to planar waveguides for measuring protein binding to biomimetic membranes.

    PubMed Central

    Heyse, S.; Vogel, H.; Sänger, M.; Sigrist, H.

    1995-01-01

    A new method is presented for measuring sensitively the interactions between ligands and their membrane-bound receptors in situ using integrated optics, thus avoiding the need for additional labels. Phospholipid bilayers were attached covalently to waveguides by a novel protocol, which can in principle be used with any glass-like surface. In a first step, phospholipids carrying head-group thiols were covalently immobilized onto SiO2-TiO2 waveguide surfaces. This was accomplished by acylation of aminated waveguides with the heterobifunctional crosslinker N-succinimidyl-3-maleimidopropionate, followed by the formation of thioethers between the surface-grafted maleimides and the synthetic thiolipids. The surface-attached thiolipids served as hydrophobic templates and anchors for the deposition of a complete lipid bilayer either by fusion of lipid vesicles or by lipid self-assembly from mixed lipid/detergent micelles. The step-by-step lipid bilayer formation on the waveguide surface was monitored in situ by an integrated optics technique, allowing the simultaneous determination of optical thickness and one of the two refractive indices of the adsorbed organic layers. Surface coverages of 50-60% were calculated for thiolipid layers. Subsequent deposition of POPC resulted in an overall lipid layer thickness of 45-50 A, which corresponds to the thickness of a fluid bilayer membrane. Specific recognition reactions occurring at cell membrane surfaces were modeled by the incorporation of lipid-anchored receptor molecules into the supported bilayer membranes. (1) The outer POPC layer was doped with biotinylated phosphatidylethanolamine. Subsequent specific binding of streptavidin was optically monitored. (2) A lipopeptide was incorporated in the outer POPC monolayer. Membrane binding of monoclonal antibodies, which were directed against the peptide moiety of the lipopeptide, was optically detected. The specific antibody binding correlated well with the lipopepitde

  8. Partitioning of long-chain alcohols into lipid bilayers: implications for mechanisms of general anesthesia.

    PubMed Central

    Franks, N P; Lieb, W R

    1986-01-01

    Alcohols act as anesthetics only up to a certain chain length, beyond which their biological activity disappears. Although the molecular nature of general anesthetic target sites remains unknown, presently available data support the hypothesis that this "cutoff" in anesthetic activity could be due to a corresponding cutoff in the absorption of long-chain alcohols into lipid-bilayer portions of nerve membranes. To test this hypothesis, we have developed an extremely sensitive biological assay, based on inhibition of the light-emitting firefly luciferase reaction, which is capable of measuring lipid-bilayer/buffer partition coefficients K for very lipid soluble compounds. Contrary to the hypothesis and reported data, we find a strictly linear increase in log(K) as the chain length increases [delta(delta G0)CH2 = - 3.63 kJ/mol] for the primary alcohols from decanol to pentadecanol, with no hint of a cutoff. The fact that alcohols continue to partition into lipid bilayers long after their biological activity has ceased is consistent with the view that the primary target sites in general anesthesia are proteins rather than the lipid-bilayer portions of nerve membranes. PMID:3460084

  9. Fluid Phase Lipid Areas and Bilayer Thicknesses of Commonly Used Phosphatidylcholines as a Function of Temperature

    SciTech Connect

    Kucerka, Norbert; Nieh, Mu-Ping; Katsaras, John

    2011-01-01

    The structural parameters of fluid phase bilayers composed of phosphatidylcholines with fully saturated, mixed, and branched fatty acid chains, at several temperatures, have been determined by simultaneously analyzing small-angle neutron and X-ray scattering data. Bilayer parameters, such as area per lipid and overall bilayer thickness have been obtained in conjunction with intrabilayer structural parameters (e.g. hydrocarbon region thickness). The results have allowed us to assess the effect of temperature and hydrocarbon chain composition on bilayer structure. For example, we found that for all lipids there is, not surprisingly, an increase in fatty acid chain trans-gauche isomerization with increasing temperature. Moreover, this increase in trans-gauche isomerization scales with fatty acid chain length in mixed chain lipids. However, in the case of lipids with saturated fatty acid chains, trans-gauche isomerization is increasingly tempered by attractive chain-chain van der Waals interactions with increasing chain length. Finally, our results confirm a strong dependence of lipid chain dynamics as a function of double bond position along fatty acid chains.

  10. 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

  11. Layer-by-Layer Assembly of Supported Lipid Bilayer Poly-L-Lysine Multilayers.

    PubMed

    Heath, George R; Li, Mengqiu; Polignano, Isabelle L; Richens, Joanna L; Catucci, Gianluca; O'Shea, Paul; Sadeghi, Sheila J; Gilardi, Gianfranco; Butt, Julea N; Jeuken, Lars J C

    2016-01-11

    Multilayer lipid membranes perform many important functions in biology, such as electrical isolation (myelination of axons), increased surface area for biocatalytic purposes (thylakoid grana and mitochondrial cristae), and sequential processing (golgi cisternae). Here we develop a simple layer-by-layer methodology to form lipid multilayers via vesicle rupture onto existing supported lipid bilayers (SLBs) using poly l-lysine (PLL) as an electrostatic polymer linker. The assembly process was monitored at the macroscale by quartz crystal microbalance with dissipation (QCM-D) and the nanoscale by atomic force microscopy (AFM) for up to six lipid bilayers. By varying buffer pH and PLL chain length, we show that longer chains (≥300 kDa) at pH 9.0 form thicker polymer supported multilayers, while at low pH and shorter length PLL, we create close packed layers (average lipid bilayers separations of 2.8 and 0.8 nm, respectively). Fluorescence recovery after photobleaching (FRAP) and AFM were used to show that the diffusion of lipid and three different membrane proteins in the multilayered membranes has little dependence on lipid stack number or separation between membranes. These approaches provide a straightforward route to creating the complex membrane structures that are found throughout nature, allowing possible applications in areas such as energy production and biosensing while developing our understanding of the biological processes at play. PMID:26642374

  12. Swing motion as a diffusion mechanism of lipid bilayers in a gel phase.

    PubMed

    Oh, Younghoon; Kim, Jeongmin; Yethiraj, Arun; Sung, Bong June

    2016-01-01

    Lipid bilayers are a model system for studying the properties of cell membranes. For lipid bilayers of a single lipid component, there is a phase transition from a fluid phase to a gel phase as the temperature is decreased. The dynamic behavior of lipids in the gel phase is interesting: some models show dynamic heterogeneity with a large disparity in timescales between fast and slow molecules, and a spatial segregation of the slow molecules. In this paper we study the dynamics of coarse-grained models of lipid bilayers using the dry Martini, Lennard-Jones Martini, polarizable Martini, and BMW models. All four models show similar dynamical behaviors in the gel phase although the transition temperature is model-dependent. We find that the primary mode of transport in the gel phase is a hopping of the lipid molecules. Hopping is seen in both the translational and rotational dynamics, which are correlated, i.e., the lipid molecules display a swing-like motion in the gel phase. PMID:26871103

  13. Swing motion as a diffusion mechanism of lipid bilayers in a gel phase

    NASA Astrophysics Data System (ADS)

    Oh, Younghoon; Kim, Jeongmin; Yethiraj, Arun; Sung, Bong June

    2016-01-01

    Lipid bilayers are a model system for studying the properties of cell membranes. For lipid bilayers of a single lipid component, there is a phase transition from a fluid phase to a gel phase as the temperature is decreased. The dynamic behavior of lipids in the gel phase is interesting: some models show dynamic heterogeneity with a large disparity in timescales between fast and slow molecules, and a spatial segregation of the slow molecules. In this paper we study the dynamics of coarse-grained models of lipid bilayers using the dry Martini, Lennard-Jones Martini, polarizable Martini, and BMW models. All four models show similar dynamical behaviors in the gel phase although the transition temperature is model-dependent. We find that the primary mode of transport in the gel phase is a hopping of the lipid molecules. Hopping is seen in both the translational and rotational dynamics, which are correlated, i.e., the lipid molecules display a swing-like motion in the gel phase.

  14. Organization and dynamics of pyrene and pyrene lipids in intact lipid bilayers. Photo-induced charge transfer processes.

    PubMed Central

    Barenholz, Y; Cohen, T; Korenstein, R; Ottolenghi, M

    1991-01-01

    The dynamics of fluorescence quenching and the organization of a series of pyrene derivatives anchored in various depths in bilayers of phosphatidylcholine small unilamellar vesicles was studied and compared with their behavior in homogeneous solvent systems. The studies include characterization of the environmental polarity of the pyrene fluorophore based on its vibronic peaks, as well as the interaction with three collisional quenchers: the two membrane-soluble quenchers, diethylaniline and bromobenzene, and the water soluble quencher potassium iodide. The system of diethylaniline-pyrene derivatives in the membrane of phosphatidylcholine vesicles was characterized in detail. The diethylaniline partition coefficient between the lipid bilayers and the buffer is approximately 5,800. Up to a diethylaniline/phospholipid mole ratio of 1:3 the perturbation to membrane structure is minimal so that all photophysical studies were performed below this mole ratio. The quenching reaction, in all cases, was shown to take place in the lipid bilayer interior and the relative quenching efficiencies of the various probe molecules was used to provide information on the distribution of both fluorescent probes and quencher molecules in the lipid bilayer. The quenching efficiency by diethylaniline in the lipid bilayer was found to be essentially independent on the length of the methylene chain of the pyrene moiety. These findings suggest that the quenching process, being a diffusion controlled reaction, is determined by the mobility of the diethylaniline quencher (with an effective diffusion coefficient D approximately 10(-7) cm2 s-1) which appears to be homogeneously distributed throughout the lipid bilayer. The pulsed laser photolysis products of the charge-transfer quenching reaction were examined. No exciplex (excited-complex) formation was observed and the yield of the separated radical ions was shown to be tenfold smaller than in homogenous polar solutions. The decay of the

  15. Aqueous-filled polymer microcavity arrays: versatile & stable lipid bilayer platforms offering high lateral mobility to incorporated membrane proteins.

    PubMed

    Basit, Hajra; Gaul, Vinnie; Maher, Sean; Forster, Robert J; Keyes, Tia E

    2015-05-01

    A key prerequisite in an ideal supported lipid bilayer based cell membrane model is that the mobility of both the lipid matrix and its components are unhindered by the underlying support. This is not trivial and with the exception of liposomes, many of even the most advanced approaches, although accomplishing lipid mobility, fail to achieve complete mobility of incorporated membrane proteins. This is addressed in a novel platform comprising lipid bilayers assembled over buffer-filled, arrays of spherical cap microcavities formed from microsphere template polydimethoxysilane. Prior to bilayer assembly the PDMS is rendered hydrophilic by plasma treatment and the lipid bilayer prepared using Langmuir Blodgett assembly followed by liposome/proteoliposome fusion. Fluorescence Lifetime Correlation Spectroscopy confirmed the pore suspended lipid bilayer exhibits diffusion coefficients comparable to free-standing vesicles in solution. The bilayer modified arrays are highly reproducible and stable over days. As the bilayers are suspended over deep aqueous reservoirs, reconstituted membrane proteins experience an aqueous interface at both membrane interfaces and attain full lateral mobility. Their utility as membrane protein platforms was exemplified in two case studies with proteins of different dimensions in their extracellular and cytoplasmic domains reconstituted into DOPC lipid bilayers; Glycophorin A, and Integrin αIIbβ3. In both cases, the proteins exhibited 100% mobility with high lateral diffusion coefficients. PMID:25798456

  16. Myelin basic protein and myelin protein 2 act synergistically to cause stacking of lipid bilayers.

    PubMed

    Suresh, Swetha; Wang, Chaozhan; Nanekar, Rahul; Kursula, Petri; Edwardson, J Michael

    2010-04-27

    Saltatory conduction of nerve impulses along axonal membranes depends on the presence of a multilayered membrane, myelin, that wraps around the axon. Myelin basic protein (MBP) and myelin protein 2 (P2) are intimately involved in the generation of the myelin sheath. They are also implicated in a number of neurological diseases, including autoimmune diseases of both the central and peripheral nervous systems. Here, we have used atomic force microsopy (AFM) to study the effects of MBP and P2 on lipid bilayers. MBP in association with a mica substrate appeared unstructured, and tended to coat the mica surface in the form of a monolayer. In contrast, P2 appeared as discrete particles, with molecular volumes consistent with the formation of both monomers and dimers. Either MBP or P2, at micromolar concentrations, caused stacking of brain lipid bilayers. This stacking effect was significantly potentiated when both proteins were added together. Bilayers composed of phosphatidylcholine (PC) and phosphatidylserine (PS) were stacked by MBP, provided that cholesterol was also present; in contrast, P2 did not stack PC/PS/cholesterol bilayers. Hence, the bilayer stacking effects of the two proteins have different lipid requirements. PMID:20334434

  17. A Molecular Rotor that Measures Dynamic Changes of Lipid Bilayer Viscosity Caused by Oxidative Stress.

    PubMed

    Vyšniauskas, Aurimas; Qurashi, Maryam; Kuimova, Marina K

    2016-09-01

    Oxidation of cellular structures is typically an undesirable process that can be a hallmark of certain diseases. On the other hand, photooxidation is a necessary step of photodynamic therapy (PDT), a cancer treatment causing cell death upon light irradiation. Here, the effect of photooxidation on the microscopic viscosity of model lipid bilayers constructed of 1,2-dioleoyl-sn-glycero-3-phosphocholine has been studied. A molecular rotor has been employed that displays a viscosity-dependent fluorescence lifetime as a quantitative probe of the bilayer's viscosity. Thus, spatially-resolved viscosity maps of lipid photooxidation in giant unilamellar vesicles (GUVs) were obtained, testing the effect of the positioning of the oxidant relative to the rotor in the bilayer. It was found that PDT has a strong impact on viscoelastic properties of lipid bilayers, which 'travels' through the bilayer to areas that have not been irradiated directly. A dramatic difference in viscoelastic properties of oxidized GUVs by Type I (electron transfer) and Type II (singlet oxygen-based) photosensitisers was also detected. PMID:27487026

  18. Soft lithographic patterning of supported lipid bilayers onto a surface and inside microfluidic channels.

    PubMed

    Kim, Pilnam; Lee, Sang Eun; Jung, Ho Sup; Lee, Hea Yeon; Kawai, Tomoji; Suh, Kahp Y

    2006-01-01

    We present simple soft lithographic methods for patterning supported lipid bilayer (SLB) membranes onto a surface and inside microfluidic channels. Micropatterns of polyethylene glycol (PEG)-based polymers were fabricated on glass substrates by microcontact printing or capillary moulding. The patterned PEG surfaces have shown 97 +/- 0.5% reduction in lipid adsorption onto two dimensional surfaces and 95 +/- 1.2% reduction inside microfluidic channels in comparison to glass control. Atomic force microscopy measurements indicated that the deposition of lipid vesicles led to the formation of SLB membranes by vesicle fusion due to hydrophilic interactions with the exposed substrate. Furthermore, the functionality of the patterned SLBs was tested by measuring the binding interactions between biotin (ligand)-labeled lipid bilayer and streptavidin (receptor). SLB arrays were fabricated with spatial resolution down to approximately 500 nm on flat substrate and approximately 1 microm inside microfluidic channels, respectively. PMID:16372069

  19. Molecular dynamics simulations of Oxprenolol and Propranolol in a DPPC lipid bilayer.

    PubMed

    Azizi, Khaled; Koli, Mokhtar Ganjali

    2016-03-01

    Extensive microscopic molecular dynamics simulations have been performed to study the effects of tow β-blocker drugs (Propranolol, Oxprenolol) on fully hydrated dipalmitoylphosphatidylcholine (DPPC) in the fluid phase at 323K. Simulation of 4 systems containing varying concentrations of drugs was carried out. For the purpose of comparison, a fully hydrated DPPC bilayer without drugs was also studied at the same level of simulation technique which has been done on 4 other systems. The length of each simulation was 100ns. The effects of concentrations of both drugs were analyzed on lipid bilayer properties, such as electrostatic potential, order parameter, diffusion coefficients, and hydrogen bond formation, etc. Penetration of water in the bilayer system was also investigated using radial distribution function analysis. Efficacy of varying concentrations of both drugs has no significant effect on P-N vector. Consistent with experimental results, by increasing the concentration of Propranolol, the thickness of the bilayer was increased. PMID:26851866

  20. Insertion mechanism and stability of boron nitride nanotubes in lipid bilayers.

    PubMed

    Thomas, Michael; Enciso, Marta; Hilder, Tamsyn A

    2015-04-16

    We provide insight into the interaction of boron nitride nanotubes (BNNTs) with cell membranes to better understand their improved biocompatibility compared to carbon nanotubes (CNTs). Contrary to CNTs, no computational studies exist investigating the insertion mechanism and stability of BNNTs in membranes. Our molecular dynamics simulations demonstrate that BNNTs are spontaneously attracted to lipid bilayers and are stable once inserted. They insert via a lipid-mediated, passive insertion mechanism. BNNTs demonstrate similar characteristics to more biocompatible functionalized CNTs. PMID:25800058

  1. Molecular Delivery into a Lipid Bilayer with a Single Shock Waves Using Molecular Dynamic Simulation

    NASA Astrophysics Data System (ADS)

    Koshiyama, Kenichiro; Kodama, Tetsuya; Hamblin, Michael R.; Doukas, Apostolos G.; Yano, Takeru; Fujikawa, Shigeo

    2005-03-01

    Cell permeabilization by shock waves may have application in gene therapy and anticancer drug delivery. In the present study we performed direct molecular dynamic (MD) simulation of the interaction of a single shock wave with a cell membrane to investigate the mechanism of the cell permeabilization. The shock wave was characterized by an impulse that was expressed with a velocity determined by the change in the momentum. The cell membrane was designed as a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer placed between two layers of water molecules. The MD simulation determined the relationship between water penetration into the bilayer, the order parameter, the fluidity of each lipid molecule, and the intensity of impulse. These structural changes in the bilayer may be an important factor in the use of shock waves to produce transient membrane permeability.

  2. Lipid-bilayer-assisted two-dimensional self-assembly of DNA origami nanostructures

    NASA Astrophysics Data System (ADS)

    Suzuki, Yuki; Endo, Masayuki; Sugiyama, Hiroshi

    2015-08-01

    Self-assembly is a ubiquitous approach to the design and fabrication of novel supermolecular architectures. Here we report a strategy termed `lipid-bilayer-assisted self-assembly' that is used to assemble DNA origami nanostructures into two-dimensional lattices. DNA origami structures are electrostatically adsorbed onto a mica-supported zwitterionic lipid bilayer in the presence of divalent cations. We demonstrate that the bilayer-adsorbed origami units are mobile on the surface and self-assembled into large micrometre-sized lattices in their lateral dimensions. Using high-speed atomic force microscopy imaging, a variety of dynamic processes involved in the formation of the lattice, such as fusion, reorganization and defect filling, are successfully visualized. The surface modifiability of the assembled lattice is also demonstrated by in situ decoration with streptavidin molecules. Our approach provides a new strategy for preparing versatile scaffolds for nanofabrication and paves the way for organizing functional nanodevices in a micrometer space.

  3. Hydrodynamic coupling of particle inclusions embedded in curved lipid bilayer membranes.

    PubMed

    Sigurdsson, Jon Karl; Atzberger, Paul J

    2016-08-10

    We develop theory and computational methods to investigate particle inclusions embedded within curved lipid bilayer membranes. We consider the case of spherical lipid vesicles where inclusion particles are coupled through (i) intramembrane hydrodynamics, (ii) traction stresses with the external and trapped solvent fluid, and (iii) intermonolayer slip between the two leaflets of the bilayer. We investigate relative to flat membranes how the membrane curvature and topology augment hydrodynamic responses. We show how both the translational and rotational mobility of protein inclusions are effected by the membrane curvature, ratio of intramembrane viscosity to solvent viscosity, and intermonolayer slip. For general investigations of many-particle dynamics, we also discuss how our approaches can be used to treat the collective diffusion and hydrodynamic coupling within spherical bilayers. PMID:27373277

  4. Critical density fluctuations in lipid bilayers detected by fluorescence lifetime heterogeneity.

    PubMed Central

    Ruggiero, A; Hudson, B

    1989-01-01

    The heterogeneity of the decay of the fluorescence of transparinaric acid in single-component lipid bilayers at temperatures above their gel/liquid crystalline phase transition is shown to be due to the presence of regions of higher local density and higher acyl chain order than the predominant fluid regions. This conclusion is based on selective excitation behavior and the observation of time-resolved fluorescence anisotropies that increase at long times. The fractional amplitude of the long lifetime component of the fluorescence shows a temperature variation that conforms to conventional descriptions of critical behavior. The critical exponent extracted from this variation is 1.1, close to the value of 1.0 that describes ultrasonic data. We therefore conclude that liquid crystalline lipid bilayers exhibit critical behavior with significant density and order fluctuations. This behavior must be taken into account in the interpretation of fluorescence and other spectroscopic measurements of the properties of bilayers. PMID:2765649

  5. Interactions of ibuprofen with hybrid lipid bilayers probed by complementary surface-enhanced vibrational spectroscopies

    PubMed Central

    Levin, Carly S.; Kundu, Janardan; Janesko, Benjamin G.; Scuseria, Gustavo E.; Raphael, Robert M.; Halas, Naomi J.

    2016-01-01

    The incorporation of small molecules into lipid bilayers is a process of biological importance and clinical relevance that can change the material properties of cell membranes and cause deleterious side effects for certain drugs. Here we report the direct observation, using surface enhanced Raman and IR spectroscopies (SERS, SEIRA), of the insertion of ibuprofen molecules into hybrid lipid bilayers. The alkanethiol-phospholipid hybrid bilayers were formed onto gold nanoshells by self-assembly, where the underlying nanoshell substrates provided the necessary enhancements for SERS and SEIRA. The spectroscopic data reveal specific interactions between ibuprofen and phospholipid moieties and indicate that the overall hydrophobicity of ibuprofen plays an important role in its intercalation in these membrane mimics. PMID:18942873

  6. A Simplified Sum-Frequency Vibrational Imaging Setup Used for Imaging Lipid Bilayer Arrays

    PubMed Central

    Smith, Kathryn A.; Conboy, John C.

    2012-01-01

    Given the complexity of cell membranes, there is a need for an analytical technique which can explore the physical properties of lipid membranes in a high-throughput and noninvasive manner. A simplified sum-frequency vibrational imaging (SFVI) setup has been developed and characterized using asymmetrically prepared 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC):1,2-distearoyl(d70)-sn-glycero-3-phosphocholine (DSPC-d70) lipid bilayer arrays. Exploiting the vibrational selectivity and inherent symmetry constraints of sum-frequency generation, SFVI was successfully used to probe the transition temperature of a patterned DSPC:DSPC-d70 lipid bilayer array. SFVI was also used to study the phase behavior in a multi-component micropatterned lipid bilayer array (MLBA) prepared using three different binary lipid mixtures (1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC):DSPC, DOPC:1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC:DSPC). This paper demonstrates that a simplified SFVI setup provides the necessary chemical imaging capabilities with the spatial resolution, sensitivity and field of view required for exploring lipid membrane properties in a high-throughput array based assay. PMID:22947074

  7. Continuity of Monolayer-Bilayer Junctions for Localization of Lipid Raft Microdomains in Model Membranes.

    PubMed

    Ryu, Yong-Sang; Wittenberg, Nathan J; Suh, Jeng-Hun; Lee, Sang-Wook; Sohn, Youngjoo; Oh, Sang-Hyun; Parikh, Atul N; Lee, Sin-Doo

    2016-01-01

    We show that the selective localization of cholesterol-rich domains and associated ganglioside receptors prefer to occur in the monolayer across continuous monolayer-bilayer junctions (MBJs) in supported lipid membranes. For the MBJs, glass substrates were patterned with poly(dimethylsiloxane) (PDMS) oligomers by thermally-assisted contact printing, leaving behind 3 nm-thick PDMS patterns. The hydrophobicity of the transferred PDMS patterns was precisely tuned by the stamping temperature. Lipid monolayers were formed on the PDMS patterned surface while lipid bilayers were on the bare glass surface. Due to the continuity of the lipid membranes over the MBJs, essentially free diffusion of lipids was allowed between the monolayer on the PDMS surface and the upper leaflet of the bilayer on the glass substrate. The preferential localization of sphingomyelin, ganglioside GM1 and cholesterol in the monolayer region enabled to develop raft microdomains through coarsening of nanorafts. Our methodology provides a simple and effective scheme of non-disruptive manipulation of the chemical landscape associated with lipid phase separations, which leads to more sophisticated applications in biosensors and as cell culture substrates. PMID:27230411

  8. A simplified sum-frequency vibrational imaging setup used for imaging lipid bilayer arrays.

    PubMed

    Smith, Kathryn A; Conboy, John C

    2012-10-01

    Given the complexity of cell membranes, there is a need for an analytical technique which can explore the physical properties of lipid membranes in a high-throughput and noninvasive manner. A simplified sum-frequency vibrational imaging (SFVI) setup has been developed and characterized using asymmetrically prepared 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC):1,2-distearoyl(d70)-sn-glycero-3-phosphocholine (DSPC-d(70)) lipid bilayer arrays. Exploiting the vibrational selectivity and inherent symmetry constraints of sum-frequency generation, SFVI was successfully used to probe the transition temperature of a patterned DSPC:DSPC-d(70) lipid bilayer array. SFVI was also used to study the phase behavior in a multicomponent micropatterned lipid bilayer array (MLBA) prepared using three different binary lipid mixtures (1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC):DSPC, DOPC:1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC:DSPC). This paper demonstrates that a simplified SFVI setup provides the necessary chemical imaging capabilities with the spatial resolution, sensitivity, and field of view required for exploring lipid membrane properties in a high-throughput array based assay. PMID:22947074

  9. Continuity of monolayer-bilayer junctions for localization of lipid raft microdomains in model membranes

    DOE PAGESBeta

    Ryu, Yong -Sang; Wittenberg, Nathan J.; Suh, Jeng -Hun; Lee, Sang -Wook; Sohn, Youngjoo; Oh, Sang -Hyun; Parikh, Atul N.; Lee, Sin -Doo

    2016-05-27

    We show that the selective localization of cholesterol-rich domains and associated ganglioside receptors prefer to occur in the monolayer across continuous monolayer-bilayer junctions (MBJs) in supported lipid membranes. For the MBJs, glass substrates were patterned with poly(dimethylsiloxane) (PDMS) oligomers by thermally-assisted contact printing, leaving behind 3 nm-thick PDMS patterns. The hydrophobicity of the transferred PDMS patterns was precisely tuned by the stamping temperature. Lipid monolayers were formed on the PDMS patterned surface while lipid bilayers were on the bare glass surface. Due to the continuity of the lipid membranes over the MBJs, essentially free diffusion of lipids was allowed betweenmore » the monolayer on the PDMS surface and the upper leaflet of the bilayer on the glass substrate. The preferential localization of sphingomyelin, ganglioside GM1 and cholesterol in the monolayer region enabled to develop raft microdomains through coarsening of nanorafts. Furthermore, our methodology provides a simple and effective scheme of non-disruptive manipulation of the chemical landscape associated with lipid phase separations, which leads to more sophisticated applications in biosensors and as cell culture substrates.« less

  10. Folding of β-barrel membrane proteins in lipid bilayers - Unassisted and assisted folding and insertion.

    PubMed

    Kleinschmidt, Jörg H

    2015-09-01

    In cells, β-barrel membrane proteins are transported in unfolded form to an outer membrane into which they fold and insert. Model systems have been established to investigate the mechanisms of insertion and folding of these versatile proteins into detergent micelles, lipid bilayers and even synthetic amphipathic polymers. In these experiments, insertion into lipid membranes is initiated from unfolded forms that do not display residual β-sheet secondary structure. These studies therefore have allowed the investigation of membrane protein folding and insertion in great detail. Folding of β-barrel membrane proteins into lipid bilayers has been monitored from unfolded forms by dilution of chaotropic denaturants that keep the protein unfolded as well as from unfolded forms present in complexes with molecular chaperones from cells. This review is aimed to provide an overview of the principles and mechanisms observed for the folding of β-barrel transmembrane proteins into lipid bilayers, the importance of lipid-protein interactions and the function of molecular chaperones and folding assistants. This article is part of a Special Issue entitled: Lipid-protein interactions. PMID:25983306