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Sample records for fluid bilayer membranes

  1. 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

  2. Relaxation dynamics of two-component fluid bilayer membranes.

    PubMed

    Okamoto, Ryuichi; Kanemori, Yuichi; Komura, Shigeyuki; Fournier, Jean-Baptiste

    2016-05-01

    We theoretically investigate the relaxation dynamics of a nearly flat binary lipid bilayer membrane by taking into account the membrane tension, hydrodynamics of the surrounding fluid, inter-monolayer friction and mutual diffusion. Mutual diffusion is the collective irreversible process that leads to homogenization of the density difference between the two lipid species. We find that two relaxation modes associated with the mutual diffusion appear in addition to the three previously discussed relaxation modes reflecting the bending and compression of the membrane. Because of the symmetry, only one of the two diffusive modes is coupled to the bending mode. The two diffusive modes are much slower than the bending and compression modes in the entire realistic wave number range. This means that the long time relaxation behavior is dominated by the mutual diffusion in binary membranes. The two diffusive modes become even slower in the vicinity of the unstable region towards phase separation, while the other modes are almost unchanged. In short time scales, on the other hand, the lipid composition heterogeneity induces in-plane compression and bending of the bilayer. PMID:27145960

  3. Efficient tunable generic model for self-assembling fluid bilayer membranes

    NASA Astrophysics Data System (ADS)

    Deserno, Markus

    2005-03-01

    We present a new model for the simulation of generic lipid bilayers in the mesoscopic regime (between a few nanometers and many tens of nanometers), which is very robust, versatile, and extremely efficient, since it avoids the need for an embedding solvent. Based entirely on simple pair potentials, it features a wide region of unassisted self assembly into fluid bilayers without the need for careful parameter tuning. The resulting membranes display the correct continuum elastic behavior with bending constants in the experimentally relevant range. It can be readily used to study events like bilayer fusion, bilayer melting, lipid mixtures, rafts, and protein-bilayer interactions.

  4. A class of supported membranes: formation of fluid phospholipid bilayers on photonic band gap colloidal crystals.

    PubMed

    Brozell, Adrian M; Muha, Michelle A; Sanii, Babak; Parikh, Atul N

    2006-01-11

    We report the formation of a new class of supported membranes consisting of a fluid phospholipid bilayer coupled directly to a broadly tunable colloidal crystal with a well-defined photonic band gap. For nanoscale colloidal crystals exhibiting a band gap at the optical frequencies, substrate-induced vesicle fusion gives rise to a surface bilayer riding onto the crystal surface. The bilayer is two-dimensionally continuous, spanning multiple beads with lateral mobilities which reflect the coupling between the bilayer topography and the curvature of the supporting colloidal surface. In contrast, the spreading of vesicles on micrometer scale colloidal crystals results in the formation of bilayers wrapping individual colloidal beads. We show that simple UV photolithography of colloidal crystals produces binary patterns of crystal wettabilities, photonic stopbands, and corresponding patterns of lipid mono- and bilayer morphologies. We envisage that these approaches will be exploitable for the development of optical transduction assays and microarrays for many membrane-mediated processes, including transport and receptor-ligand interactions. PMID:16390122

  5. Nonequilibrium patterns of cholesterol-rich chemical heterogenieties within single fluid supported phospholipid bilayer membranes.

    PubMed

    Sapuri-Butti, Annapoorna R; Li, Qijuan; Groves, Jay T; Parikh, Atul N

    2006-06-01

    We have developed a simple method to introduce cholesterol- and sphingomyelin-rich chemical heterogeneities into controlled densities and concentrations within predetermined regions of another distinct fluid phospholipid bilayer supported on a solid substrate. A contiguous primary phase--a fluid POPC bilayer displaying a well-defined array of lipid-free voids (e.g., 20-100 microm squares)--was first prepared on a clean glass surface by microcontact printing under water using a poly(dimethylsiloxane) stamp. The aqueous-phase primary bilayer pattern was subsequently incubated with secondary-phase small unilamellar vesicles composed of independent chemical compositions. Backfilling by comparable vesicles resulted in gradual mixing between the primary- and secondary-phase lipids, effacing the pattern. When the secondary vesicles consisted of phase-separating mixtures of cholesterol, sphingomyelin, and a phospholipid (2:1:1 POPC/sphingomyelin/cholesterol or 1:1:1 DOPC/sphingomyelin/cholesterol), well-defined spatial patterns of fluorescence, chemical compositions, and fluidities emerged. We conjecture that these patterns form because of the differences in the equilibration rates of the secondary liquid-ordered and liquid-disordered phases with the primary fluid POPC phase. The pattern stability depended strongly on the ambient-phase temperature, cholesterol concentration, and miscibility contrast between the two phases. When cholesterol concentration in the secondary vesicles was below 20 mol %, secondary intercalants gradually diffused within the primary POPC bilayer phase, ultimately dissolving the pattern in several minutes and presumably forming a new quasi-equilibrated lipid mixture. These phase domain micropatterns retain some properties of biological rafts including detergent resistance and phase mixing induced by selective cholesterol extraction. These patterns enable direct comparisons of cholesterol- and sphingomyelin-rich phase domains and fluid phospholipid

  6. Bending membranes on demand: fluid phospholipid bilayers on topographically deformable substrates.

    PubMed

    Sanii, Babak; Smith, Andreia Michelle; Butti, Ravichandra; Brozell, Adrian M; Parikh, Atul N

    2008-03-01

    We combine hierarchical surface wrinkling of elastomers with lipid membrane deposition techniques to dynamically template complex three-dimensional topographies onto supported lipid bilayers. The real-time introduction of corresponding nano- to micrometer scale curvatures triggers spatially periodic, elastic bending of the bilayer, accompanied by molecular-level reorganizations. This ability to dynamically impose curvatures on supported bilayers and the ensuing re-equilibration promises fundamental material and biophysical investigations of curvature-dependent, static heterogeneities and dynamic reorganizations pervasive in biological membranes. PMID:18271562

  7. Life, death and membrane bilayers.

    PubMed

    Hulbert, A J

    2003-07-01

    Membrane bilayers are essential elements of life, and the synthesis of the hydrocarbons that make up membrane bilayers may have preceded the appearance of life on Earth. Membrane-associated processes are significant components of metabolism, and the acyl composition of membrane bilayers is associated with metabolic activity in a predictable manner. This has resulted in the "membrane pacemaker" theory of metabolism, which proposes that the relative balance between monounsaturated and long-chain polyunsaturated acyl chains in membrane bilayers is a fundamental determinant of metabolic rate of a species. The omega-3 polyunsaturated docosahexaenoate is an especially important component of membranes in this regard. Whilst it is suggested that the physical properties of membrane polyunsaturates are important with respect to their influence on metabolic rate, it is their chemistry that is important in aging. Membrane acyl composition is related to maximum lifespan in mammals and birds, probably via their role in lipid peroxidation. Calorie restriction modifies acyl composition of membrane bilayers and is associated with decreased membrane lipid peroxidation and lifespan extension. The membrane pacemaker theory of metabolism has given birth to the membrane pacemaker hypothesis of aging, which will require further investigation. PMID:12796449

  8. 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

  9. Interaction of n-octyl β,D-glucopyranoside with giant magnetic-fluid-loaded phosphatidylcholine vesicles: direct visualization of membrane curvature fluctuations as a function of surfactant partitioning between water and lipid bilayer.

    PubMed

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

    2010-10-01

    The present study deals with the morphological modifications of giant dioleoyl phosphatidylcholine vesicles (DOPC GUVs) induced by the nonionic surfactant n-octyl β,D-glucopyranoside at sublytic levels, i.e., in the first steps of the vesicle-to-micelle transition process, when surfactant inserts into the vesicle bilayer without disruption. Experimental conditions were perfected to exactly control the surfactant bilayer composition of the vesicles, in line with former work focused on the mechanical properties of the membrane of magnetic-fluid-loaded DOPC GUVs submitted to a magnetic field. The purpose here was to systematically examine, in the absence of any external mechanical constraint, the dynamics of giant vesicle shape and membrane deformations as a function of surfactant partitioning between the aqueous phase and the lipid membrane, beforehand established by turbidity measurements from small unilamellar vesicles. PMID:20825201

  10. Design of Asymmetric Peptide Bilayer Membranes.

    PubMed

    Li, Sha; Mehta, Anil K; Sidorov, Anton N; Orlando, Thomas M; Jiang, Zhigang; Anthony, Neil R; Lynn, David G

    2016-03-16

    Energetic insights emerging from the structural characterization of peptide cross-β assemblies have enabled the design and construction of robust asymmetric bilayer peptide membranes. Two peptides differing only in their N-terminal residue, phosphotyrosine vs lysine, coassemble as stacks of antiparallel β-sheets with precisely patterned charged lattices stabilizing the bilayer leaflet interface. Either homogeneous or mixed leaflet composition is possible, and both create nanotubes with dense negative external and positive internal solvent exposed surfaces. Cross-seeding peptide solutions with a preassembled peptide nanotube seed leads to domains of different leaflet architecture within single nanotubes. Architectural control over these cross-β assemblies, both across the bilayer membrane and along the nanotube length, provides access to highly ordered asymmetric membranes for the further construction of functional mesoscale assemblies. PMID:26942690

  11. Bilayer membrane interactions with nanofabricated scaffolds

    DOE PAGESBeta

    Collier, C. Patrick

    2015-07-29

    Membrane function is facilitated by lateral organization within the lipid bilayer, including phase-separation of lipids into more ordered domains (lipid rafts) and anchoring of the membrane to a cytoskeleton. These features have proven difficult to reproduce in model membrane systems such as black lipid membranes, unilamellar vesicles and supported bilayers. However, advances in micro/nanofabrication have resulted in more realistic synthetic models of membrane-cytoskeleton interactions that can help uncover the design rules responsible for biological membrane formation and organization. This review will focus on describing micro-/nanostructured scaffolds that can emulate the connections of a cellular membrane to an underlying “cytoskeleton”. Thismore » includes molecular-based scaffolds anchored to a solid substrate through surface chemistry, solid-state supports modified by material deposition, lithography and etching, the creation of micro/nanoporous arrays, integration with microfluidics, and droplet-based bilayers at interfaces. Lastly, model systems such as these are increasing our understanding of structure and organization in cell membranes, and how they result in the emergence of functionality at the nanoscale.« less

  12. Bilayer membrane interactions with nanofabricated scaffolds

    SciTech Connect

    Collier, C. Patrick

    2015-07-29

    Membrane function is facilitated by lateral organization within the lipid bilayer, including phase-separation of lipids into more ordered domains (lipid rafts) and anchoring of the membrane to a cytoskeleton. These features have proven difficult to reproduce in model membrane systems such as black lipid membranes, unilamellar vesicles and supported bilayers. However, advances in micro/nanofabrication have resulted in more realistic synthetic models of membrane-cytoskeleton interactions that can help uncover the design rules responsible for biological membrane formation and organization. This review will focus on describing micro-/nanostructured scaffolds that can emulate the connections of a cellular membrane to an underlying “cytoskeleton”. This includes molecular-based scaffolds anchored to a solid substrate through surface chemistry, solid-state supports modified by material deposition, lithography and etching, the creation of micro/nanoporous arrays, integration with microfluidics, and droplet-based bilayers at interfaces. Lastly, model systems such as these are increasing our understanding of structure and organization in cell membranes, and how they result in the emergence of functionality at the nanoscale.

  13. 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

  14. Line tension of multicomponent bilayer membranes

    NASA Astrophysics Data System (ADS)

    Dehghan, Ashkan; Pastor, Kyle A.; Shi, An-Chang

    2015-02-01

    The line tension or edge energy of bilayer membranes self-assembled from binary amphiphilic molecules is studied using self-consistent-field theory (SCFT). Specifically, solutions of the SCFT equations corresponding to an infinite membrane with a circular pore, or an open membrane, are obtained for a coarse-grained model in which the amphiphilic species and hydrophilic solvents are represented by A B and E D diblock copolymers and C homopolymers, respectively. The edge energy of the membrane is extracted from the free energy of the open membranes. Results for membranes composed of mixtures of symmetric and cone- or inverse cone-shaped amphiphilic molecules with neutral and/or repulsive interactions are obtained and analyzed. It is observed that an increase in the concentration of the cone-shaped species leads to a decrease of the line tension. In contrast, adding inverse cone-shaped copolymers results in an increase of the line tension. Furthermore, the density profile of the copolymers reveals that the line tension is regulated by the distribution of the amphiphiles at the bilayer edge.

  15. Engineering Lipid Bilayer Membranes for Protein Studies

    PubMed Central

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

    2013-01-01

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

  16. Fluctuation and dynamics of a lipid bilayer membrane under an electric field

    NASA Astrophysics Data System (ADS)

    Young, Yuan-Nan; Miksis, Michael; Vlahovska, Petia

    2015-11-01

    Membrane fluctuation and dynamics under an electric field is investigated, and results show that the membrane instability and dynamics depend not only on the mismatch in conductivity and permittivity between the bulk fluids, but also on the membrane charging time. In addition, the (entropic) membrane tension is found to depend on the electric field. Lubrication theory is utilized to examine the nonlinear dynamics of a planar lipid bilayer membrane with and without electrokinetics. Partial support from NSF/DMS 1222550, 1412789.

  17. Bilayer-thickness-mediated interactions between integral membrane proteins.

    PubMed

    Kahraman, Osman; Koch, Peter D; Klug, William S; Haselwandter, Christoph A

    2016-04-01

    Hydrophobic thickness mismatch between integral membrane proteins and the surrounding lipid bilayer can produce lipid bilayer thickness deformations. Experiment and theory have shown that protein-induced lipid bilayer thickness deformations can yield energetically favorable bilayer-mediated interactions between integral membrane proteins, and large-scale organization of integral membrane proteins into protein clusters in cell membranes. Within the continuum elasticity theory of membranes, the energy cost of protein-induced bilayer thickness deformations can be captured by considering compression and expansion of the bilayer hydrophobic core, membrane tension, and bilayer bending, resulting in biharmonic equilibrium equations describing the shape of lipid bilayers for a given set of bilayer-protein boundary conditions. Here we develop a combined analytic and numerical methodology for the solution of the equilibrium elastic equations associated with protein-induced lipid bilayer deformations. Our methodology allows accurate prediction of thickness-mediated protein interactions for arbitrary protein symmetries at arbitrary protein separations and relative orientations. We provide exact analytic solutions for cylindrical integral membrane proteins with constant and varying hydrophobic thickness, and develop perturbative analytic solutions for noncylindrical protein shapes. We complement these analytic solutions, and assess their accuracy, by developing both finite element and finite difference numerical solution schemes. We provide error estimates of our numerical solution schemes and systematically assess their convergence properties. Taken together, the work presented here puts into place an analytic and numerical framework which allows calculation of bilayer-mediated elastic interactions between integral membrane proteins for the complicated protein shapes suggested by structural biology and at the small protein separations most relevant for the crowded membrane

  18. Bilayer-thickness-mediated interactions between integral membrane proteins

    NASA Astrophysics Data System (ADS)

    Kahraman, Osman; Koch, Peter D.; Klug, William S.; Haselwandter, Christoph A.

    2016-04-01

    Hydrophobic thickness mismatch between integral membrane proteins and the surrounding lipid bilayer can produce lipid bilayer thickness deformations. Experiment and theory have shown that protein-induced lipid bilayer thickness deformations can yield energetically favorable bilayer-mediated interactions between integral membrane proteins, and large-scale organization of integral membrane proteins into protein clusters in cell membranes. Within the continuum elasticity theory of membranes, the energy cost of protein-induced bilayer thickness deformations can be captured by considering compression and expansion of the bilayer hydrophobic core, membrane tension, and bilayer bending, resulting in biharmonic equilibrium equations describing the shape of lipid bilayers for a given set of bilayer-protein boundary conditions. Here we develop a combined analytic and numerical methodology for the solution of the equilibrium elastic equations associated with protein-induced lipid bilayer deformations. Our methodology allows accurate prediction of thickness-mediated protein interactions for arbitrary protein symmetries at arbitrary protein separations and relative orientations. We provide exact analytic solutions for cylindrical integral membrane proteins with constant and varying hydrophobic thickness, and develop perturbative analytic solutions for noncylindrical protein shapes. We complement these analytic solutions, and assess their accuracy, by developing both finite element and finite difference numerical solution schemes. We provide error estimates of our numerical solution schemes and systematically assess their convergence properties. Taken together, the work presented here puts into place an analytic and numerical framework which allows calculation of bilayer-mediated elastic interactions between integral membrane proteins for the complicated protein shapes suggested by structural biology and at the small protein separations most relevant for the crowded membrane

  19. Combined influence of cholesterol and synthetic amphiphillic peptides upon bilayer thickness in model membranes.

    PubMed Central

    Nezil, F A; Bloom, M

    1992-01-01

    Deuterium (2H) NMR was used to study bilayer hydrophobic thickness and mechanical properties when cholesterol and/or synthetic amphiphillic polypeptides were added to deuterated POPC lipid bilayer membranes in the liquid-crystalline (fluid) phase. Smoothed acyl chain orientational order profiles were used to calculate bilayer hydrophobic thickness. Addition of 30 mol% cholesterol to POPC at 25 degrees C increased the bilayer thickness from 2.58 to 2.99 nm. The peptides were chosen to span the bilayers with more or less mismatch between the hydrophobic peptide length and membrane hydrophobic thickness. The average thickness of the pure lipid bilayers was significantly perturbed upon addition of peptide only in cases of large mismatch, being increased (decreased) when the peptide hydrophobic length was greater (less) than that of the pure bilayer, consistent with the "mattress" model of protein lipid interactions (Mouritsen, O.G., and M. Bloom. 1984. Biophys. J. 46:141-153). The experimental results were also used to examine the combined influence of the polypeptides and cholesterol on the orientational order profile and thickness expansivity of the membranes. A detailed model for the spatial distribution of POPC and cholesterol molecules in the bilayers was proposed to reconcile the general features of these measurements with micromechanical measurements of area expansivity in closely related systems. Experiments to test the model were proposed. PMID:1600079

  20. Phase transitions in planar bilayer membranes.

    PubMed Central

    White, S H

    1975-01-01

    Temperature-dependent structural changes in planar bilayer membranes formed from glycerol monooleate (GMO) dispersed in various n-alkane solvents (C12-C17) have been studied using precise measurements of specific geometric capacitance (Cg). Cg generally increases as temperature (T) decreases. A change in the slope of Cg(T) occurs between 15 and 18 degrees C for all solvent systems examined. Measurements of the interfacial tension (gamma) of the bulk GMO-alkane dispersions against 0.1 M NaCl show that gamma generally decreases with decreasing temperature. The data can be fitted with two straight lines of different slope which intersect on the average at 17 degrees C. Pagano et al. (1973, Science (Wash. D.C.). 181:557) have shown using calorimetry that GMO has a phase transition at about 15 degrees C. Thus, the changes in Cg and gamma with temperature are likely to result from a GMO phase transition. A second structural change is observed to occur between 5 and 10 degrees C which has not been detected calorimetrically. Calculations of Cg based on various estimates of the hydrocarbon dielectric coefficient (epsilon-b) and/or hydrocarbon thickness (delta-b) leads to models for the structure of the bilayer above and below the phase transition temperature. PMID:1111634

  1. 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

  2. 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

  3. 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

  4. Mechanism of unassisted ion transport across membrane bilayers

    NASA Technical Reports Server (NTRS)

    Wilson, M. A.; Pohorille, A.

    1996-01-01

    To establish how charged species move from water to the nonpolar membrane interior and to determine the energetic and structural effects accompanying this process, we performed molecular dynamics simulations of the transport of Na+ and Cl- across a lipid bilayer located between two water lamellae. The total length of molecular dynamics trajectories generated for each ion was 10 ns. Our simulations demonstrate that permeation of ions into the membrane is accompanied by the formation of deep, asymmetric thinning defects in the bilayer, whereby polar lipid head groups and water penetrate the nonpolar membrane interior. Once the ion crosses the midplane of the bilayer the deformation "switches sides"; the initial defect slowly relaxes, and a defect forms in the outgoing side of the bilayer. As a result, the ion remains well solvated during the process; the total number of oxygen atoms from water and lipid head groups in the first solvation shell remains constant. A similar membrane deformation is formed when the ion is instantaneously inserted into the interior of the bilayer. The formation of defects considerably lowers the free energy barrier to transfer of the ion across the bilayer and, consequently, increases the permeabilities of the membrane to ions, compared to the rigid, planar structure, by approximately 14 orders of magnitude. Our results have implications for drug delivery using liposomes and peptide insertion into membranes.

  5. Fusion and fission of fluid amphiphilic bilayers.

    PubMed

    Gotter, Martin; Strey, Reinhard; Olsson, Ulf; Wennerström, Håkan

    2005-01-01

    The system water-oil (n-decane)-nonionic surfactant (C12E5) forms bilayer phases in a large concentration region, but, for a given oil-to-surfactant ratio, only in a narrow temperature range. In addition to the anisotropic lamellar phase (Lalpha) there is also, at slightly higher temperature, a sponge or L3-phase where the bilayers build up an isotropic structure extending macroscopically in three dimensions. In this phase the bilayer mid-surface has a mean curvature close to zero and a negative Euler characteristic. In this paper we study how the bilayers in the lamellar and the sponge phase respond dynamically to sudden temperature changes. The monolayer spontaneous curvature depends sensitively on temperature and a change of temperature thus provides a driving force for a change in bilayer topology. The equilibration therefore involves kinetic steps of fusion/fission of bilayers. Such dynamic processes have previously been monitored by temperature jump experiments using light scattering in the sponge phase. These experiments revealed an extraordinarily strong dependence of the relaxation time on the bilayer volume fraction phi. At phi < 0.1 the relaxation times are so slow that experiments using deuterium nuclear magnetic resonance (2H-NMR) appear feasible. We here report on the first experiments concerned with the dynamics of the macroscopic phase transition sponge-lamellae by 2H-NMR. We find that the sponge-to-lamellae transition occurs through a nucleation process followed by domain growth involving bilayer fission at domain boundaries. In contrast, the lamellae-to-sponge transformation apparently occurs through a succession of uncorrelated bilayer fusion events. PMID:15715316

  6. Evidence for superlattice arrangements in fluid phosphatidylcholine/phosphatidylethanolamine bilayers.

    PubMed Central

    Cheng, K H; Ruonala, M; Virtanen, J; Somerharju, P

    1997-01-01

    Recently, evidence for cholesterol and phosphatidylcholine (PC) molecules to adapt superlattice arrangements in fluid lipid bilayers has been presented. Whether superlattice arrangements exist in other biologically relevant lipid membranes, such as phosphatidylethanolamine (PE)/PC, is still speculative. In this study, we have examined the physical properties of fluid 1-palmitoyl-2-oleoyl-PC (POPC) and 1-palmitoyl-2-oleoyl-PE (POPE) binary mixtures as a function of the POPE mole fraction (X(PE)) using fluorescence and Fourier transform infrared spectroscopy. At 30 degrees C, i.e., above the Tm of POPE and POPC, deviations, or dips, as well as local data scattering in the excimer-to-monomer fluorescence intensity ratio of intramolecular excimer forming dipyrenylphosphatidylcholine probe in POPE/POPC mixtures were detected at X(PE) approximately 0.04, 0.11, 0.16, 0.26, 0.33, 0.51, 0.66, 0.75, 0.82, 0.91, and 0.94. The above critical values of X(PE) coincide (within +/-0.03) with the critical mole fractions X(HX,PE) or X(R,PE) predicted by a headgroup superlattice model, which assumes that the lipid headgroups form hexagonal or rectangular superlattice, respectively, in the bilayer. Other spectroscopic data, generalized polarization of Laurdan and infrared carbonyl and phosphate stretching frequency, were also collected. Similar agreements between some of the observed critical values of X(PE) from these data and the X(HX,PE) or X(R,PE) values were also found. However, all techniques yielded critical values of X(PE) (e.g., 0.42 and 0.58) that cannot be explained by the present headgroup superlattice model. The effective cross-sectional area of the PE headgroup is smaller than that of the acyl chains. Hence, the relief of "packing frustration" of PE in the presence of PC (larger headgroup than PE) may be one of the major mechanisms in driving the PE and PC components to superlattice-like lateral distributions in the bilayer. We propose that headgroup superlattices may

  7. 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

  8. 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

  9. Viscoelastic changes measured in partially suspended single bilayer membranes.

    PubMed

    Hasan, Imad Younus; Mechler, Adam

    2015-07-21

    For studies involving biomimetic phospholipid membrane systems, such as membrane-protein interactions, it is crucial that the supported membrane is biomimetic in its physical properties as well as in its composition. Two often overlooked aspects of biomimicry are the need for unrestrained lipid mobility, reflected in the viscoelastic properties of the membrane, and sufficient space between the membrane and the support for the insertion of transmembrane proteins. Here we show for a series of DMPC-based membranes that a partially suspended single bilayer membrane can be formed on functionalized gold surface without tethering. These membranes exhibit sufficient freedom of motion to represent the viscoelastic properties of a free lamellar bilayer membrane as demonstrated by determining the phase transition temperatures of these single bilayer membranes from the viscosity change upon chain melting using the dissipation signal of a quartz crystal microbalance (QCM-D). Atomic force microscopy imaging confirmed confluent, smooth membrane coverage of the QCM-D sensor that completely obscured the roughness of the sputtered gold surface. High-force AFM imaging was able to push membrane patches into the valleys of the gold morphology, confirming the inherently suspended nature of the MPA supported membrane. We show that the correlation between frequency and dissipation changes in the QCM-D sensograms is a sensitive indicator of the morphology of the membrane. PMID:26073288

  10. Galactocerebroside-phospholipid interactions in bilayer membranes.

    PubMed Central

    Ruocco, M J; Shipley, G G; Oldfield, E

    1983-01-01

    Differential scanning calorimetry (DSC) and x-ray diffraction have been used to study the interaction of hydrated N-palmitoylgalactosylsphingosine (NPGS) and dipalmitoylphosphatidylcholine (DPPC). For mixtures containing less than 23 mol% NPGS, complete miscibility of NPGS into hydrated DPPC bilayers is observed in both the bilayer gel and liquid-crystal phases. X-ray diffraction data demonstrate insignificant differences in the DPPC-bilayer gel-phase parameters on incorporation of up to 23 mol% NPGS. At greater than 23 mol% NPGS, additional high-temperature transitions occur, indicating phase separation of cerebroside. For these cerebroside concentrations, at 20 degrees C, x-ray diffraction shows two lamellar phases, hydrated DPPC-NPGS gel bilayers (d = 64 A) containing 23 mol% NPGS, and NPGS "crystal" bilayers (d = 55 A). On heating to temperatures greater than 45 degrees C, the mixed DPPC-NPGS bilayer phase undergoes chain melting, and on further increasing the temperature progressively more NPGS is incorporated into the liquid-crystal DPPC-NPGS bilayer phase. At temperatures greater than 82 degrees C (the transition temperature of hydrated NPGS), complete lipid miscibility is observed at all DPPC/NPGS molar ratios. Images FIGURE 4 FIGURE 5 FIGURE 6 PMID:6688367

  11. 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

  12. 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.

  13. 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

  14. 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

  15. 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

  16. Modeling Nanoparticle Wrapping or Translocation in Bilayer Membranes

    PubMed Central

    Curtis, Emily M.; Bahrami, Amir H.; Weikl, Thomas R.; Hall, Carol K.

    2015-01-01

    The spontaneous wrapping of nanoparticles by membranes is of increasing interest as nanoparticles become more prevalent in consumer products and hence more likely to enter the human body. We introduce a simulations-based tool that can be used to visualize the molecular level interaction between nanoparticles and bilayer membranes. By combining LIME, an intermediate resolution, implicit solvent model for phospholipids, with discontinuous molecular dynamics (DMD), we are able to simulate the wrapping or embedding of nanoparticles by 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayer membranes. Simulations of hydrophilic nanoparticles with diameters from 10Å to 250Å show that hydrophilic nanoparticles with diameters greater than 20Å become wrapped while the nanoparticle with a diameter of 10Å does not . Instead this smaller particle became embedded in the bilayer surface where it could interact with the hydrophilic head groups of the lipid molecules. We also investigate the interaction between a DPPC bilayer and hydrophobic nanoparticles with diameters 10Å to 40Å. These nanoparticles do not undergo the wrapping process; instead they directly penetrate the membrane and embed themselves within the inner hydrophobic core of the bilayers. PMID:26260123

  17. 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

  18. 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

  19. 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

  20. Simulations of a Membrane-Anchored Peptide: Structure, Dynamics, and Influence on Bilayer Properties

    PubMed Central

    Jensen, Morten Ø.; Mouritsen, Ole G.; Peters, Günther H.

    2004-01-01

    A three-dimensional structure of a model decapeptide is obtained by performing molecular dynamics simulations of the peptide in explicit water. Interactions between an N-myristoylated form of the folded peptide anchored to dipalmitoylphosphatidylcholine fluid phase lipid membranes are studied at different applied surface tensions by molecular dynamics simulations. The lipid membrane environment influences the conformational space explored by the peptide. The overall secondary structure of the anchored peptide is found to deviate at times from its structure in aqueous solution through reversible conformational transitions. The peptide is, despite the anchor, highly mobile at the membrane surface with the peptide motion along the bilayer normal being integrated into the collective modes of the membrane. Peptide anchoring moderately alters the lateral compressibility of the bilayer by changing the equilibrium area of the membrane. Although membrane anchoring moderately affects the elastic properties of the bilayer, the model peptide studied here exhibits conformational flexibility and our results therefore suggest that peptide acylation is a feasible way to reinforce peptide-membrane interactions whereby, e.g., the lifetime of receptor-ligand interactions can be prolonged. PMID:15189854

  1. Behavior of Bilayer Leaflets in Asymmetric Model Membranes: Atomistic Simulation Studies.

    PubMed

    Tian, Jianhui; Nickels, Jonathan; Katsaras, John; Cheng, Xiaolin

    2016-08-25

    Spatial organization within lipid bilayers is an important feature for a range of biological processes. Leaflet compositional asymmetry and lateral lipid organization are just two of the ways in which membrane structure appears to be more complex than initially postulated by the fluid mosaic model. This raises the question of how the phase behavior in one bilayer leaflet may affect the apposing leaflet and how one begins to construct asymmetric model systems to investigate these interleaflet interactions. Here we report on all-atom molecular dynamics simulations (a total of 4.1 μs) of symmetric and asymmetric bilayer systems composed of liquid-ordered (Lo) or liquid-disordered (Ld) leaflets, based on the nanodomain-forming POPC/DSPC/cholesterol system. We begin by analyzing an asymmetric bilayer with leaflets derived from simulations of symmetric Lo and Ld bilayers. In this system, we observe that the properties of the Lo and Ld leaflets are similar to those of the Lo and Ld leaflets in corresponding symmetric systems. However, it is not obvious that mixing the equilibrium structures of their symmetric counterparts is the most appropriate way to construct asymmetric bilayers nor that these structures will manifest interleaflet couplings that lead to domain registry/antiregistry. We therefore constructed and simulated four additional asymmetric bilayer systems by systematically adding or removing lipids in the Ld leaflet to mimic potential density fluctuations. We find that the number of lipids in the Ld leaflet affects its own properties, as well as those of the apposing Lo leaflet. Collectively, the simulations reveal the presence of weak acyl chain interdigitation across bilayer leaflets, suggesting that interdigitation alone does not contribute significantly to the interleaflet coupling in nonphase-separated bilayers of this chemical composition. However, the properties of both leaflets appear to be sensitive to changes in in-plane lipid packing, possibly

  2. Helix insertion into bilayers and the evolution of membrane proteins

    PubMed Central

    2010-01-01

    Polytopic α-helical membrane proteins cannot spontaneously insert into lipid bilayers without assistance from polytopic α-helical membrane proteins that already reside in the membrane. This raises the question of how these proteins evolved. Our current knowledge of the insertion of α-helices into natural and model membranes is reviewed with the goal of gaining insight into the evolution of membrane proteins. Topics include: translocon-dependent membrane protein insertion, antibiotic peptides and proteins, in vitro insertion of membrane proteins, chaperone-mediated insertion of transmembrane helices, and C-terminal tail-anchored (TA) proteins. Analysis of the E. coli genome reveals several predicted C-terminal TA proteins that may be descendents of proteins involved in pre-cellular membrane protein insertion. Mechanisms of pre-translocon polytopic α-helical membrane protein insertion are discussed. PMID:20039094

  3. Effect of cholesterol on the lateral nanoscale dynamics of fluid membranes

    SciTech Connect

    Armstrong, Clare L; Barrett, M; Heiss, Arno; Salditt, Tim; Katsaras, John; Shi, An-Chang; Rheinstadter, Maikel C

    2012-01-01

    Inelastic neutron scattering was used to study the effect of 5 and 40 mol% cholesterol on the lateral nanoscale dynamics of phospholipid membranes. By measuring the excitation spectrum at several lateral q || values (up to q || = 3 1), complete dispersion curves were determined of gel, fluid and liquid-ordered phase bilayers. The inclusion of cholesterol had a distinct effect on the collective dynamics of the bilayer s hydrocarbon chains; specifically, we observed a pronounced stiffening of the membranes on the nanometer length scale in both gel and fluid bilayers, even though they were experiencing a higher degree of molecular disorder. Also, for the first time we determined the nanoscale dynamics in the high-cholesterol liquid-ordered phase of bilayers containing cholesterol. Namely, this phase appears to be softer than fluid bilayers, but better ordered than bilayers in the gel phase.

  4. 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

  5. Spontaneous curvature of bilayer membranes from molecular simulations: Asymmetric lipid densities and asymmetric adsorption

    NASA Astrophysics Data System (ADS)

    RóŻycki, Bartosz; Lipowsky, Reinhard

    2015-02-01

    Biomimetic and biological membranes consist of molecular bilayers with two leaflets which are typically exposed to different aqueous environments and may differ in their molecular density or composition. Because of these asymmetries, the membranes prefer to curve in a certain manner as quantitatively described by their spontaneous curvature. Here, we study such asymmetric membranes via coarse-grained molecular dynamics simulations. We consider two mechanisms for the generation of spontaneous curvature: (i) different lipid densities within the two leaflets and (ii) leaflets exposed to different concentrations of adsorbing particles. We focus on membranes that experience no mechanical tension and describe two methods to compute the spontaneous curvature. The first method is based on the detailed structure of the bilayer's stress profile which can hardly be measured experimentally. The other method starts from the intuitive view that the bilayer represents a thin fluid film bounded by two interfaces and reduces the complexity of the stress profile to a few membrane parameters that can be measured experimentally. For the case of asymmetric adsorption, we introduce a simulation protocol based on two bilayers separated by two aqueous compartments with different adsorbate concentrations. The adsorption of small particles with a size below 1 nm is shown to generate large spontaneous curvatures up to about 1/(24 nm). Our computational approach is quite general: it can be applied to any molecular model of bilayer membranes and can be extended to other mechanisms for the generation of spontaneous curvatures as provided, e.g., by asymmetric lipid composition or depletion layers of solute molecules.

  6. Local membrane mechanics of pore-spanning bilayers.

    PubMed

    Mey, Ingo; Stephan, Milena; Schmitt, Eva K; Müller, Martin Michael; Ben Amar, Martine; Steinem, Claudia; Janshoff, Andreas

    2009-05-27

    The mechanical behavior of lipid bilayers spanning the pores of highly ordered porous silicon substrates was scrutinized by local indentation experiments as a function of surface functionalization, lipid composition, solvent content, indentation velocity, and pore radius. Solvent-containing nano black lipid membranes (nano-BLMs) as well as solvent-free pore-spanning bilayers were imaged by fluorescence and atomic force microscopy prior to force curve acquisition, which allows distinguishing between membrane-covered and uncovered pores. Force indentation curves on pore-spanning bilayers attached to functionalized hydrophobic porous silicon substrates reveal a predominately linear response that is mainly attributed to prestress in the membranes. This is in agreement with the observation that indentation leads to membrane lysis well below 5% area dilatation. However, membrane bending and lateral tension dominate over prestress and stretching if solvent-free supported membranes obtained from spreading giant liposomes on hydrophilic porous silicon are indented. An elastic regime diagram is presented that readily allows determining the dominant contribution to the mechanical response upon indentation as a function of load and pore radius. PMID:19453196

  7. 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

  8. 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

  9. NMR Structures of Membrane Proteins in Phospholipid Bilayers

    PubMed Central

    Radoicic, Jasmina; Lu, George J.; Opella, Stanley J.

    2014-01-01

    Membrane proteins have always presented technical challenges for structural studies because of their requirement for a lipid environment. Multiple approaches exist including X-ray crystallography and electron microscopy that can give significant insights into their structure and function. However, nuclear magnetic resonance (NMR) is unique in that it offers the possibility of determining the structures of unmodified membrane proteins in their native environment of phospholipid bilayers under physiological conditions. Furthermore, NMR enables the characterization of the structure and dynamics of backbone and side chain sites of the proteins alone and in complexes with both small molecules and other biopolymers. The learning curve has been steep for the field as most initial studies were performed under non-native environments using modified proteins until ultimately progress in both techniques and instrumentation led to the possibility of examining unmodified membrane proteins in phospholipid bilayers under physiological conditions. This review aims to provide an overview of the development and application of NMR to membrane proteins. It highlights some of the most significant structural milestones that have been reached by NMR spectroscopy of membrane proteins; especially those accomplished with the proteins in phospholipid bilayer environments where they function. PMID:25032938

  10. 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

  11. 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

  12. 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

  13. The mechanoelectrical response of droplet interface bilayer membranes.

    PubMed

    Freeman, E C; Najem, J S; Sukharev, S; Philen, M K; Leo, D J

    2016-03-28

    Mechanotransduction and interfacial properties in unsupported liquid biomimetic membranes are explored using the droplet-interface bilayer technique. The fluidic monolayer-membrane system afforded by this technique allows for dynamic control over the membrane dimensions and curvature, which under periodic deformations generates capacitive currents (akin to a Kelvin probe), and permits a detailed electrostatic characterization of the boundary layers as well as observation of flexoelectric effects. Both high and low displacement frequency regimes are examined, and the results show that the mechanoelectric signals generated by the membranes may be linked to the membrane electrostatic structure. In addition, we show that periodic membrane bending in a high-frequency regime generates tension sufficient to activate reconstituted mechanosensitive channels. PMID:26905644

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

    PubMed

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

    2013-07-01

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

  15. Supported Bilayers with Excess Membrane Reservoir: A Template for Reconstituting Membrane Budding and Fission

    PubMed Central

    Pucadyil, Thomas J.; Schmid, Sandra L.

    2010-01-01

    Abstract A complete mechanistic understanding of membrane-localized processes in vesicular transport, such as membrane budding and fission, requires their reconstitution with biochemically-defined components from a biochemically-defined substrate. Supported bilayers formed by vesicle fusion represent an attractive substrate for this purpose. However, conventional supported bilayers lack a sufficient membrane reservoir to recreate membrane budding and fission events. We describe the formation of supported bilayers with excess membrane reservoir (SUPER) templates from the fusion of liposomes containing negatively charged lipids on silica beads under high-ionic-strength conditions. Using a fluorescence microscopy-based assay to monitor early and late stages of supported bilayer formation, we show that an increase in ionic strength leads to an increase in the rates of liposome adsorption and subsequent fusion during formation of supported bilayers. The two rates, however, increase disproportionally, leading to accumulation of excess reservoir with an increase in ionic strength. SUPER templates allow the seamless application of microscopy-based assays to analyze membrane-localized processes together with sedimentation-based assays to isolate vesicular and nonvesicular products released from the membrane. The results presented here emphasize the general utility of these templates for analyzing vesicular and nonvesicular transport processes. PMID:20643070

  16. Molecular dynamics simulation of melittin in a dimyristoylphosphatidylcholine bilayer membrane.

    PubMed Central

    Bernèche, S; Nina, M; Roux, B

    1998-01-01

    Molecular dynamics trajectories of melittin in an explicit dimyristoyl phosphatidylcholine (DMPC) bilayer are generated to study the details of lipid-protein interactions at the microscopic level. Melittin, a small amphipathic peptide found in bee venom, is known to have a pronounced effect on the lysis of membranes. The peptide is initially set parallel to the membrane-solution interfacial region in an alpha-helical conformation with unprotonated N-terminus. Solid-state nuclear magnetic resonance (NMR) and polarized attenuated total internal reflectance Fourier transform infrared (PATIR-FTIR) properties of melittin are calculated from the trajectory to characterize the orientation of the peptide relative to the bilayer. The residue Lys7 located in the hydrophobic moiety of the helix and residues Lys23, Arg24, Gln25, and Gln26 at the C-terminus hydrophilic form hydrogen bonds with water molecules and with the ester carbonyl groups of the lipids, suggesting their important contribution to the stability of the helix in the bilayer. Lipid acyl chains are closely packed around melittin, contributing to the stable association with the membrane. Calculated density profiles and order parameters of the lipid acyl chains averaged over the molecular dynamics trajectory indicate that melittin has effects on both layers of the membrane. The presence of melittin in the upper layer causes a local thinning of the bilayer that favors the penetration of water through the lower layer. The energetic factors involved in the association of melittin at the membrane surface are characterized using an implicit mean-field model in which the membrane and the surrounding solvent are represented as structureless continuum dielectric material. The results obtained by solving the Poisson-Bolztmann equation numerically are in qualitative agreement with the detailed dynamics. The influence of the protonation state of the N-terminus of melittin is examined. After 600 ps, the N-terminus of melittin

  17. 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

  18. 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.

  19. 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

  20. 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

  1. Membrane Protein Mobility and Orientation Preserved in Supported Bilayers Created Directly from Cell Plasma Membrane Blebs.

    PubMed

    Richards, Mark J; Hsia, Chih-Yun; Singh, Rohit R; Haider, Huma; Kumpf, Julia; Kawate, Toshimitsu; Daniel, Susan

    2016-03-29

    Membrane protein interactions with lipids are crucial for their native biological behavior, yet traditional characterization methods are often carried out on purified protein in the absence of lipids. We present a simple method to transfer membrane proteins expressed in mammalian cells to an assay-friendly, cushioned, supported lipid bilayer platform using cell blebs as an intermediate. Cell blebs, expressing either GPI-linked yellow fluorescent proteins or neon-green fused transmembrane P2X2 receptors, were induced to rupture on glass surfaces using PEGylated lipid vesicles, which resulted in planar supported membranes with over 50% mobility for multipass transmembrane proteins and over 90% for GPI-linked proteins. Fluorescent proteins were tracked, and their diffusion in supported bilayers characterized, using single molecule tracking and moment scaling spectrum (MSS) analysis. Diffusion was characterized for individual proteins as either free or confined, revealing details of the local lipid membrane heterogeneity surrounding the protein. A particularly useful result of our bilayer formation process is the protein orientation in the supported planar bilayer. For both the GPI-linked and transmembrane proteins used here, an enzymatic assay revealed that protein orientation in the planar bilayer results in the extracellular domains facing toward the bulk, and that the dominant mode of bleb rupture is via the "parachute" mechanism. Mobility, orientation, and preservation of the native lipid environment of the proteins using cell blebs offers advantages over proteoliposome reconstitution or disrupted cell membrane preparations, which necessarily result in significant scrambling of protein orientation and typically immobilized membrane proteins in SLBs. The bleb-based bilayer platform presented here is an important step toward integrating membrane proteomic studies on chip, especially for future studies aimed at understanding fundamental effects of lipid interactions

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. Proton/hydroxide conductance and permeability through phospholipid bilayer membranes.

    PubMed Central

    Gutknecht, J

    1987-01-01

    Proton/hydroxide (H+/OH-) permeability of phospholipid bilayers is several orders of magnitude higher than alkali or halide ion permeabilities at pH 7. The objective of this study was to determine the mechanism(s) of H+/OH- conductance and permeability through planar phospholipid bilayer membranes. Membranes were formed from decane solutions of bacterial phosphatidylethanolamine, diphytanoyl phosphatidylcholine, or egg phosphatidylcholine plus cholesterol. At pH 7, H+/OH- conductance (GH/OH) ranged from 2 to 6 nS.cm-2, corresponding to H+/OH- "net" permeabilities of (0.4-1.6) X 10(-5) cm.sec-1. GH/OH was inhibited by serum albumin (fatty acid-free), phloretin, and low pH. GH/OH was increased by chlorodecane, long-chain fatty acids, and voltages greater than 80 mV. Water permeability and GH/OH were not correlated. The results suggest that the H+/OH- charge carrier (i) is primarily anionic, (ii) crosses the membrane via nonpolar pathway(s), and (iii) can be removed from the membrane by "washing" with serum albumin. The simplest explanation is that the phospholipids contain weakly acidic contaminants that act as proton carriers at neutral pH. However, at low pH or in the presence of inhibitors, a "background" GH/OH remains that may be due to other mechanisms. PMID:2819878

  7. Nanometric Gap Structure with a Fluid Lipid Bilayer for the Selective Transport and Detection of Biological Molecules.

    PubMed

    Ando, Koji; Tanabe, Masashi; Morigaki, Kenichi

    2016-08-01

    The biological membrane is a natural biosensing platform that can detect specific molecules with extremely high sensitivity. We developed a biosensing methodology by combining a model biological membrane and a nanometer-sized gap structure on a glass substrate. The model membrane comprised lithographically patterned polymeric and fluid lipid bilayers. The polymeric bilayer was bonded to a poly(dimethylsiloxane) (PDMS) sheet by using an adhesion layer with a defined thickness (lipid vesicles). Extruded lipid vesicles having a biotin moiety on the surface were used as the adhesion layer in conjunction with the biotin-streptavidin linkage. A gap structure was formed between the fluid bilayer and PDMS (nanogap junction). The thickness of the gap structure was several tens of nanometers, as determined by the thickness of the adhesion layer. The nanogap junction acted as a sensitive biosensing platform. From a mixture of proteins (cholera toxin and albumin), the target protein (cholera toxin) was selectively transported into the gap by the specific binding to a glycolipid (GM1) in the fluid bilayer and lateral diffusion. The target protein molecules were then detected with an elevated signal-to-noise ratio due to the reduced background noise in the nanometric gap. The combination of selective transport and reduced background noise drastically enhanced the sensitivity toward the target protein. The nanogap junction should have broad biomedical applications by realizing highly selective and sensitive biosensing in samples having diverse coexisting molecules. PMID:27427950

  8. Solute effects on the colloidal and phase behavior of lipid bilayer membranes: ethanol-dipalmitoylphosphatidylcholine mixtures.

    PubMed Central

    Vierl, U; Löbbecke, L; Nagel, N; Cevc, G

    1994-01-01

    By means of the scanning differential calorimetry, x-ray diffractometry, and the dynamic light scattering, we have systematically studied the phase and packing properties of dipalmitoylphosphatidylcholine vesicles or multibilayers in the presence of ethanol. We have also determined the partial ternary phase diagram of such dipalmitoylphosphatidylcholine/water/ethanol mixtures. The directly measured variability of the structural bilayer parameters implies that ethanol binding to the phospholipid bilayers increases the lateral as well as the transverse repulsion between the lipid molecules. This enlarges the hydrocarbon tilt (by up to 23 degrees) and molecular area (by < or = 40%). Ethanol-phospholid association also broadens the interface and, thus, promotes lipid headgroup solvation. This results in excessive swelling (by 130%) of the phosphatidylcholine bilayers in aqueous ethanol solutions. Lateral bilayer expansion, moreover, provokes a successive interdigitation of the hydrocarbon chains in the systems with bulk ethanol concentrations of 0.4-1.2 M. The hydrocarbon packing density as well as the propensity for the formation of lamellar gel phases simultaneously increase. The pretransition temperature of phosphatidylcholine bilayers is more sensitive to the addition of alcohol (initial shift: delta Tp = 22 degrees C/mol) than the subtransition temperature (delta Ts reversible 5 degrees C/mol), whereas the chain-melting phase transition temperature is even less affected (delta Tm = 1.8 degrees C/mol). After an initial decrease of 3 degrees for the bulk ethanol concentrations below 1.2 M, the Tm value increases by 2.5 degrees above this limiting concentration. The gel-phase phosphatidylcholine membranes below Tm are fully interdigitated above this limiting concentration. The chain tilt on the fringe of full chain interdigitation is zero and increases with higher ethanol concentrations. Above Tm, some of the lipid molecules are solubilized by the bound ethanol

  9. 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.

  10. The impact of cell-penetrating peptides on membrane bilayer structure during binding and insertion.

    PubMed

    Hirst, Daniel J; Lee, Tzong-Hsien; Kulkarni, Ketav; Wilce, Jacqueline A; Aguilar, Marie-Isabel

    2016-08-01

    We have studied the effect of penetratin and a truncated analogue on the bilayer structure using dual polarisation interferometry, to simultaneously measure changes in mass per unit area and birefringence (an optical parameter representing bilayer order) with high sensitivity during the binding and dissociation from the membrane. Specifically, we studied penetratin (RQIKIWFQNRRMKWKK), along with a shortened and biotinylated version known as R8K-biotin (RRMKWKKK(Biotin)-NH2). Overall both peptides bound only weakly to the neutral DMPC and POPC bilayers, while much higher binding was observed for the anionic DMPC/DMPG and POPC/POPG. The binding of penetratin to gel-phase DMPC/DMPG was adequately represented by a two-state model, whereas on the fluid-phase POPC/POPG it exhibited a distinctly different binding pattern, best represented by a three-state kinetic model. However, R8K-biotin did not bind well to DMPC/DMPG and showed a more transitory and superficial binding to POPC/POPG. Comparing the modelling results for both peptides binding to POPC/POPG suggests an important role for a securely bound intermediate prior to penetratin insertion and translocation. Overall these results further elucidate the mechanism of penetratin, and provide another example of the significance of the ability of DPI to measure structural changes and the use of kinetic analysis to investigate the stages of peptide-membrane interactions. PMID:27163492

  11. 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

  12. 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

  13. Lateral organization, bilayer asymmetry, and inter-leaflet coupling of biological membranes

    SciTech Connect

    Smith, Jeremy C.; Cheng, Xiaolin; Nickels, Jonathan D.

    2015-07-29

    Understanding of cell membrane organization has evolved significantly from the classic fluid mosaic model. It is now recognized that biological membranes are highly organized structures, with differences in lipid compositions between inner and outer leaflets and in lateral structures within the bilayer plane, known as lipid rafts. These organizing principles are important for protein localization and function as well as cellular signaling. However, the mechanisms and biophysical basis of lipid raft formation, structure, dynamics and function are not clearly understood. One key question, which we focus on in this review, is how lateral organization and leaflet compositional asymmetry are coupled. Detailed information elucidating this question has been sparse because of the small size and transient nature of rafts and the experimental challenges in constructing asymmetric bilayers. Resolving this mystery will require advances in both experimentation and modeling. We discuss here the preparation of model systems along with experimental and computational approaches that have been applied in efforts to address this key question in membrane biology. Furthermore, we seek to place recent and future advances in experimental and computational techniques in context, providing insight into in-plane and transverse organization of biological membranes.

  14. Lateral organization, bilayer asymmetry, and inter-leaflet coupling of biological membranes

    DOE PAGESBeta

    Smith, Jeremy C.; Cheng, Xiaolin; Nickels, Jonathan D.

    2015-07-29

    Understanding of cell membrane organization has evolved significantly from the classic fluid mosaic model. It is now recognized that biological membranes are highly organized structures, with differences in lipid compositions between inner and outer leaflets and in lateral structures within the bilayer plane, known as lipid rafts. These organizing principles are important for protein localization and function as well as cellular signaling. However, the mechanisms and biophysical basis of lipid raft formation, structure, dynamics and function are not clearly understood. One key question, which we focus on in this review, is how lateral organization and leaflet compositional asymmetry are coupled.more » Detailed information elucidating this question has been sparse because of the small size and transient nature of rafts and the experimental challenges in constructing asymmetric bilayers. Resolving this mystery will require advances in both experimentation and modeling. We discuss here the preparation of model systems along with experimental and computational approaches that have been applied in efforts to address this key question in membrane biology. Furthermore, we seek to place recent and future advances in experimental and computational techniques in context, providing insight into in-plane and transverse organization of biological membranes.« less

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

    PubMed

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

    1993-10-01

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

  16. 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

  17. Electrostatics of phosphoinositide bilayer membranes. Theoretical and experimental results.

    PubMed Central

    Langner, M; Cafiso, D; Marcelja, S; McLaughlin, S

    1990-01-01

    We made fluorescence, electron paramagnetic resonance (EPR), electrophoretic mobility, and ionizing electrode measurements to study the effect of the monovalent lipid phosphatidylinositol (PI) and the trivalent lipid phosphatidylinositol 4,5-bisphosphate (PIP2) on the electrostatic potential adjacent to bilayer membranes. When the membranes were formed from mixtures of PI and the zwitterionic lipid phosphatidylcholine (PC), the Gouy-Chapman-Stern (GCS) theory described adequately the dependence of potential on distance (0, 1, 2 nm) from the membrane, mole % negative lipid, and [KCI]. Furthermore, all EPR and fluorescence probes reported identical surface potentials with a PC/PI membrane. With PC/PIP2 membranes, however, the anionic (coion) probes reported less negative potentials than the cationic (counterion) probes; the deviations from the GCS theory were greater for the coions than the counterions. Discreteness-of-charge theories based on the Poisson-Boltzmann equation incorrectly predict that deviations from the GCS theory should be greater for counterions than for coions. We discuss a consistent statistical mechanical theory that takes into account three effects ignored in the GCS theory: the finite size of the ions in the double layer, the electrical interaction between pairs of ions (correlation effects), and the mobile discrete nature of the surface charges. This theory correctly predicts that deviations from GCS theory should be negligible for monovalent lipids, significant for trivalent lipids, and greater for coions than for counterions. PMID:2156577

  18. 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

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

    NASA Astrophysics Data System (ADS)

    Andoh, Yoshimichi; Aoki, Noriyuki; Okazaki, Susumu

    2016-02-01

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

  20. 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.

  1. Multiscale modeling of droplet interface bilayer membrane networks.

    PubMed

    Freeman, Eric C; Farimani, Amir B; Aluru, Narayana R; Philen, Michael K

    2015-11-01

    Droplet interface bilayer (DIB) networks are considered for the development of stimuli-responsive membrane-based materials inspired by cellular mechanics. These DIB networks are often modeled as combinations of electrical circuit analogues, creating complex networks of capacitors and resistors that mimic the biomolecular structures. These empirical models are capable of replicating data from electrophysiology experiments, but these models do not accurately capture the underlying physical phenomena and consequently do not allow for simulations of material functionalities beyond the voltage-clamp or current-clamp conditions. The work presented here provides a more robust description of DIB network behavior through the development of a hierarchical multiscale model, recognizing that the macroscopic network properties are functions of their underlying molecular structure. The result of this research is a modeling methodology based on controlled exchanges across the interfaces of neighboring droplets. This methodology is validated against experimental data, and an extension case is provided to demonstrate possible future applications of droplet interface bilayer networks. PMID:26594262

  2. Properties of ganglioside GM1 in phosphatidylcholine bilayer membranes.

    PubMed

    Reed, R A; Shipley, G G

    1996-03-01

    Gangliosides have been shown to function as cell surface receptors, as well as participating in cell growth, differentiation, and transformation. In spite of their multiple biological functions, relatively little is known about their structure and physical properties in membrane systems. The thermotropic and structural properties of ganglioside GM1 alone and in a binary system with 1,2-dipalmitoyl phosphatidylcholine (DPPC) have been investigated by differential scanning calorimetry (DSC) and x-ray diffraction. By DSC hydrated GM1 undergoes a broad endothermic transition TM = 26 degrees C (delta H = 1.7 kcal/mol GM1). X-ray diffraction below (-2 degrees C) and above (51 degrees C) this transition indicates a micellar structure with changes occurring only in the wide angle region of the diffraction pattern (relatively sharp reflection at 1/4.12 A-1 at -2 degrees C; more diffuse reflection at 1/4.41 A-1 at 51 degrees C). In hydrated binary mixtures with DPPC, incorporation of GM1 (0-30 mol%; zone 1) decreases the enthalpy of the DPPC pretransition at low molar compositions while increasing the TM of both the pre- and main transitions (limiting values, 39 and 44 degrees C, respectively). X-ray diffraction studies indicate the presence of a single bilayer gel phase in zone 1 that can undergo chain melting to an L alpha bilayer phase. A detailed hydration study of GM1 (5.7 mol %)/DPPC indicated a conversion of the DPPC bilayer gel phase to an infinite swelling system in zone 1 due to the presence of the negatively charged sialic acid moiety of GM1. At 30-61 mol % GM1 (zone 2), two calorimetric transitions are observed at 44 and 47 degrees C, suggesting the presence of two phases. The lower transition reflects the bilayer gel --> L alpha transition (zone 1), whereas the upper transition appears to be a consequence of the formation of a nonbilayer, micellar or hexagonal phase, although the structure of this phase has not been defined by x-ray diffraction. At > 61 mol % GM

  3. Enhanced sensitivity of a microfabricated resonator using a graphene-polystyrene bilayer membrane

    SciTech Connect

    Yun, Minhyuk; Lee, Eunho; Cho, Kilwon; Jeon, Sangmin

    2014-08-18

    A graphene layer was synthesized using chemical vapor deposition methods and a polystyrene solution was spin-cast onto the graphene film. The graphene-polystyrene bilayer membrane was attached between the two tines of a microfabricated quartz tuning fork (QTF). The modulus of the graphene-polystyrene bilayer was measured to be twice that of a pristine polystyrene membrane. Exposure of the membrane-coated QTF to ethanol vapor decreased the resonance frequency of the microresonator. The bilayer membrane-coated QTF produced a frequency change that was three times the change obtained using a polystyrene membrane-coated QTF, with a lower degree of degradation in the Q factor. The limit of detection of the bilayer membrane-coated QTF to ethanol vapor was determined to be 20 ppm.

  4. 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

  5. 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.

  6. Neuronal Activation by GPI-Linked Neuroligin-1 Displayed in Synthetic Lipid Bilayer Membranes

    PubMed Central

    Baksh, Michael M.; Groves, Jay T.; Dean, Camin; Pautot, Sophie; DeMaria, Shannon; Isacoff, Ehud

    2006-01-01

    We have characterized, in vitro, interactions between hippocampal neuronal cells and silica microbeads coated with synthetic, fluid, lipid bilayer membranes containing the glycosylphosphatidyl inositol (GPI)-linked extracellular domain of the postsynaptic membrane protein neuroligin-1. These bilayer–neuroligin-1 beads activated neuronal cells to form presynaptic nerve terminals at the point of contact in a manner similar to that observed for live PC12 cells, ectopically expressing the full length neuroligin-1. The synthetic membranes exhibited biological activity at neuroligin-1 densities of ∼1 to 6 proteins/μm2. Polyolycarbonate beads with neuroligin-1 covalently attached to the surface failed to activate neurons despite the fact that neuroligin-1 binding activity is preserved. This implies that a lipid membrane environment is likely to be essential for neuroligin-1 activity. This technique allows the study of isolated proteins in an environment that has physical properties resembling those of a cell surface; proteins can diffuse freely within the membrane, retain their in vivo orientations, and are in a nondenatured state. In addition, the synthetic membrane environment affords control over both lipid and protein composition. This technology is easily implemented and can be applied to a wide variety of cellular studies. PMID:16262338

  7. 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

  8. Fluid transport by active elastic membranes

    NASA Astrophysics Data System (ADS)

    Evans, Arthur A.; Lauga, Eric

    2011-09-01

    A flexible membrane deforming its shape in time can self-propel in a viscous fluid. Alternatively, if the membrane is anchored, its deformation will lead to fluid transport. Past work in this area focused on situations where the deformation kinematics of the membrane were prescribed. Here we consider models where the deformation of the membrane is not prescribed, but instead the membrane is internally forced. Both the time-varying membrane shape and the resulting fluid motion result then from a balance between prescribed internal active stresses, internal passive resistance, and external viscous stresses. We introduce two specific models for such active internal forcing: one where a distribution of active bending moments is prescribed, and one where active inclusions exert normal stresses on the membrane by pumping fluid through it. In each case, we asymptotically calculate the membrane shape and the fluid transport velocities for small forcing amplitudes, and recover our results using scaling analysis.

  9. 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.

  10. Analyzing membrane remodeling and fission using supported bilayers with excess membrane reservoir

    PubMed Central

    Neumann, Sylvia; Pucadyil, Thomas J; Schmid, Sandra L

    2016-01-01

    A complete understanding of the molecular mechanisms governing vesicle formation requires quantitative assays and vesicle reconstitution using purified components. We describe a simple model membrane template for studying protein-mediated membrane remodeling and vesicle formation or fission that is amenable to both quantitative biochemical analysis and real-time imaging by epifluorescence microscopy. Supported bilayers with excess membrane reservoir (SUPER) templates are compositionally well-defined unilamellar membrane systems prepared on 2–5-μm silica beads under conditions that enable incorporation of excess membrane to form a loosely fitting bilayer that can be used to study membrane remodeling and fission. This protocol describes methods for SUPER template formation and characterization, as well as for the qualitative observation and quantitative measurement of vesicle formation and fission via microscopy and a simple sedimentation assay. SUPER templates can be prepared within 60 min. Results from either sedimentation-based or microscopy-based assays can be obtained within an additional 60 min. PMID:23288321

  11. Silica nanoparticles for the oriented encapsulation of membrane proteins into artificial bilayer lipid membranes.

    PubMed

    Schadauer, Florian; Geiss, Andreas F; Srajer, Johannes; Siebenhofer, Bernhard; Frank, Pinar; Reiner-Rozman, Ciril; Ludwig, Bernd; Richter, Oliver-M H; Nowak, Christoph; Naumann, Renate L C

    2015-03-01

    An artificial bilayer lipid membrane system is presented, featuring the oriented encapsulation of membrane proteins in a functionally active form. Nickel nitrilo-triacetic acid-functionalized silica nanoparticles, of a diameter of around 25 nm, are used to attach the proteins via a genetically engineered histidine tag in a uniform orientation. Subsequently, the proteins are reconstituted within a phospholipid bilayer, formed around the particles by in situ dialysis to form so-called proteo-lipobeads (PLBs). With a final size of about 50 nm, the PLBs can be employed for UV/vis spectroscopy studies, particularly of multiredox center proteins, because the effects of light scattering are negligible. As a proof of concept, we use cytochrome c oxidase (CcO) from P. denitrificans with the his tag genetically engineered to subunit I. In this orientation, the P side of CcO is directed to the outside and hence electron transfer can be initiated by reduced cytochrome c (cc). UV/vis measurements are used in order to determine the occupancy by CcO molecules encapsulated in the lipid bilayer as well as the kinetics of electron transfer between CcO and cc. The kinetic data are analyzed in terms of the Michaelis-Menten kinetics showing that the turnover rate of CcO is significantly decreased compared to that of solubilized protein, whereas the binding characteristics are improved. The data demonstrate the suitability of PLBs for functional cell-free bioassays of membrane proteins. PMID:25670233

  12. Particle-based simulations of bilayer membranes: self-assembly, structural analysis, and shock-wave damage

    NASA Astrophysics Data System (ADS)

    Steinhauser, Martin O.; Schindler, Tanja

    2016-08-01

    We report on the results of particle-based, coarse-grained molecular dynamics simulations of amphiphilic lipid molecules in aqueous environment where the membrane structures at equilibrium are subsequently exposed to strong shock waves, and their damage is analyzed. The lipid molecules self-assemble from unbiased random initial configurations to form stable bilayer membranes, including closed vesicles. During self-assembly of lipid molecules, we observe several stages of clustering, starting with many small clusters of lipids, gradually merging together to finally form one single bilayer membrane. We find that the clustering of lipids sensitively depends on the hydrophobic interaction h_c of the lipid tails in our model and on temperature T of the system. The self-assembled bilayer membranes are quantitatively analyzed at equilibrium with respect to their degree of order and their local structure. We also show that—by analyzing the membrane fluctuations and using a linearized theory— we obtain area compression moduli K_A and bending stiffnesses κ_B for our bilayer membranes which are within the experimental range of in vivo and in vitro measurements of biological membranes. We also discuss the density profile and the pair correlation function of our model membranes at equilibrium which has not been done in previous studies of particle-based membrane models. Furthermore, we present a detailed phase diagram of our lipid model that exhibits a sol-gel transition between quasi-solid and fluid domains, and domains where no self-assembly of lipids occurs. In addition, we present in the phase diagram the conditions for temperature T and hydrophobicity h_c of the lipid tails of our model to form closed vesicles. The stable bilayer membranes obtained at equilibrium are then subjected to strong shock waves in a shock tube setup, and we investigate the damage in the membranes due to their interaction with shock waves. Here, we find a transition from self

  13. Effective interactions between fluid membranes

    NASA Astrophysics Data System (ADS)

    Lu, Bing-Sui; Podgornik, Rudolf

    2015-08-01

    A self-consistent theory is proposed for the general problem of interacting undulating fluid membranes subject to the constraint that they do not interpenetrate. We implement the steric constraint via an exact functional integral representation and, through the use of a saddle-point approximation, transform it into a novel effective steric potential. The steric potential is found to consist of two contributions: one generated by zero-mode fluctuations of the membranes and the other by thermal bending fluctuations. For membranes of cross-sectional area S , we find that the bending fluctuation part scales with the intermembrane separation d as d-2 for d ≪√{S } but crosses over to d-4 scaling for d ≫√{S } , whereas the zero-mode part of the steric potential always scales as d-2. For membranes interacting exclusively via the steric potential, we obtain closed-form expressions for the effective interaction potential and for the rms undulation amplitude σ , which becomes small at low temperatures T and/or large bending stiffnesses κ . Moreover, σ scales as d for d ≪√{S } but saturates at √{kBT S /κ } for d ≫√{S } . In addition, using variational Gaussian theory, we apply our self-consistent treatment to study intermembrane interactions subject to different types of potentials: (i) the Moreira-Netz potential for a pair of strongly charged membranes with an intervening solution of multivalent counterions, (ii) an attractive square well, (iii) the Morse potential, and (iv) a combination of hydration and van der Waals interactions.

  14. Effective interactions between fluid membranes.

    PubMed

    Lu, Bing-Sui; Podgornik, Rudolf

    2015-08-01

    A self-consistent theory is proposed for the general problem of interacting undulating fluid membranes subject to the constraint that they do not interpenetrate. We implement the steric constraint via an exact functional integral representation and, through the use of a saddle-point approximation, transform it into a novel effective steric potential. The steric potential is found to consist of two contributions: one generated by zero-mode fluctuations of the membranes and the other by thermal bending fluctuations. For membranes of cross-sectional area S, we find that the bending fluctuation part scales with the intermembrane separation d as d-2 for d≪√S but crosses over to d-4 scaling for d≫√S, whereas the zero-mode part of the steric potential always scales as d-2. For membranes interacting exclusively via the steric potential, we obtain closed-form expressions for the effective interaction potential and for the rms undulation amplitude σ, which becomes small at low temperatures T and/or large bending stiffnesses κ. Moreover, σ scales as d for d≪√S but saturates at √kBTS/κ for d≫√S. In addition, using variational Gaussian theory, we apply our self-consistent treatment to study intermembrane interactions subject to different types of potentials: (i) the Moreira-Netz potential for a pair of strongly charged membranes with an intervening solution of multivalent counterions, (ii) an attractive square well, (iii) the Morse potential, and (iv) a combination of hydration and van der Waals interactions. PMID:26382349

  15. 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

  16. Investigation of the effect of bilayer membrane structures and fluctuation amplitudes on SANS/SAXS profile for short membrane wavelength

    SciTech Connect

    Lee, Victor; Hawa, Takumi

    2013-09-28

    The effect of bilayer membrane structures and fluctuation amplitudes on small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) profile is investigated based on harmonic motions of the surfactant bilayers with bending as well as thickness fluctuation motions. In this study we consider the case in which the wavelength of the bilayer membrane is shorter than the thickness of the membrane. We find that the thickness of the surfactant bilayer membrane, d{sub m}, affects both q{sub dip} and q{sub peak} of I(q,0) profile, and that the fluctuation amplitude, a, of the membrane changes the peak of I(q,0). A simple formula is derived to estimate the thickness of the bilayer based on the q{sub dip} of the profile obtained from the simulation. The resulting estimates of the thickness of the bilayer with harmonic motion showed accuracy within 1%. Moreover, the bilayer thicknesses estimated from the proposed formula show an excellent agreement with the SANS and SAXS experimental results available in the literatures. We also propose a curve fit model, which describes the relationship between the fluctuation amplitude and the normalized q{sub peak} ratio. The present results show the feasibility of the simple formula to estimate the fluctuation amplitude based on the SANS and SAXS profiles.

  17. Phase Behavior of Dipalmitoylphosphatidylglycerol Bilayer Membrane in Saline Water Under High Pressure

    NASA Astrophysics Data System (ADS)

    Tanaka, Saeko; Goto, Masaki; Tamai, Nobutake; Matsuki, Hitoshi

    The phase transitions of dipalmitoylphosphatidylglycerol (DPPG) bilayer membrane in the aqueous NaCl solution were observed by means of an optical method under atmospheric and high pressures. The temperature-pressure phase diagram of the DPPG bilayer showed that the phase behavior of the DPPG bilayer was similar to that of dipalmitoylphosphatidylcholine (DPPC) bilayer except for the interdigitated gel (LβI) phase. Comparing the phase diagram with the diagram obtained in a phosphate buffer, it turned out that the formation of the LβI phase is suppressed by the shielding effect of NaCl on the repulsive interaction among polar headgroups.

  18. Microfabrication of hybrid fluid membrane for microengines

    NASA Astrophysics Data System (ADS)

    Chutani, R.; Formosa, F.; de Labachelerie, M.; Badel, A.; Lanzetta, F.

    2015-12-01

    This paper describes the microfabrication and dynamic characterization of thick membranes providing a technological solution for microengines. The studied membranes are called hybrid fluid-membrane (HFM) and consist of two thin membranes that encapsulate an incompressible fluid. This work details the microelectromechanical system (MEMS) scalable fabrication and characterization of HFMs. The membranes are composite structures based on Silicon spiral springs embedded in a polymer (RTV silicone). The anodic bonding of multiple stacks of Si/glass structures, the fluid filling and the sealing have been demonstrated. Various HFMs were successfully fabricated and their dynamic characterization demonstrates the agreement between experimental and theoretical results.

  19. 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.

  20. Filament networks attached to membranes: cytoskeletal pressure and local bilayer deformation

    NASA Astrophysics Data System (ADS)

    Auth, Thorsten; Safran, S. A.; Gov, Nir S.

    2007-11-01

    Several cell types, among them red blood cells, have a cortical, two-dimensional (2D) network of filaments sparsely attached to their lipid bilayer. In many mammalian cells, this 2D polymer network is connected to an underlying 3D, more rigid cytoskeleton. In this paper, we consider the pressure exerted by the thermally fluctuating, cortical network of filaments on the bilayer and predict the bilayer deformations that are induced by this pressure. We treat the filaments as flexible polymers and calculate the pressure that a network of such linear chains exerts on the bilayer; we then minimize the bilayer shape in order to predict the resulting local deformations. We compare our predictions with membrane deformations observed in electron micrographs of red blood cells. The polymer pressure along with the resulting membrane deformation can lead to compartmentalization, regulate in-plane diffusion and may influence protein sorting as well as transmit signals to the polymerization of the underlying 3D cytoskeleton.

  1. Ionic conductivity of the aqueous layer separating a lipid bilayer membrane and a glass support.

    PubMed

    White, Ryan J; Zhang, Bo; Daniel, Susan; Tang, John M; Ervin, Eric N; Cremer, Paul S; White, Henry S

    2006-12-01

    The in-plane ionic conductivity of the approximately 1-nm-thick aqueous layer separating a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer membrane and a glass support was investigated. The aqueous layer conductivity was measured by tip-dip deposition of a POPC bilayer onto the surface of a 20- to 75-microm-thick glass membrane containing a single conical-shaped nanopore and recording the current-voltage (i-V) behavior of the glass membrane nanopore/POPC bilayer structure. The steady-state current across the glass membrane passes through the nanopore (45-480 nm radius) and spreads radially outward within the aqueous layer between the glass support and bilayer. This aqueous layer corresponds to the dominant resistance of the glass membrane nanopore/POPC bilayer structure. Fluorescence recovery after photobleaching measurements using dye-labeled lipids verified that the POPC bilayer maintains a significant degree of fluidity on the glass membrane. The slopes of ohmic i-V curves yield an aqueous layer conductivity of (3 +/- 1) x 10(-3) Omega(-1) cm(-1) assuming a layer thickness of 1.0 nm. This conductivity is essentially independent of the concentration of KCl in the bulk solution (10-4 to 1 M) in contact with the membrane. The results indicate that the concentration and mobility of charge carriers in the aqueous layer between the glass support and bilayer are largely determined by the local structure of the glass/water/bilayer interface. PMID:17129059

  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. 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

  4. Effects of Anesthetic Membrane Solutes on Orientational Order in Lecithin Bilayer Membranes: a Deuterium NMR Study.

    NASA Astrophysics Data System (ADS)

    Phonphok, Nason

    _{z^ ' z^'}.. A theory for the molecular mechanism of anesthesia is proposed. Our working hypothesis is that general anesthetics interact with phosphatidylcholine bilayers in the headgroup region, changing its time-averaged conformation and altering the extent of cation binding to the surface of the membrane. In this manner the electrical properties of the membrane are changed. (Abstract shortened with permission of author.).

  5. Composite membranes for fluid separations

    DOEpatents

    Blume, Ingo; Peinemann, Klaus-Viktor; Pinnau, Ingo; Wijmans, Johannes G.

    1991-01-01

    A method for designing and making composite membranes having a microporous support membrane coated with a permselective layer. The method involves calculating the minimum thickness of the permselective layer such that the selectivity of the composite membrane is close to the intrinsic selectivity of the permselective layer. The invention also provides high performance membranes with optimized properties.

  6. Composite membranes for fluid separations

    DOEpatents

    Blume, Ingo; Peinemann, Klaus-Viktor; Pinnau, Ingo; Wijmans, Johannes G.

    1992-01-01

    A method for designing and making composite membranes having a microporous support membrane coated with a permselective layer. The method involves calculating the minimum thickness of the permselective layer such that the selectivity of the composite membrane is close to the intrinsic selectivity of the perselective layer. The invention also provides high performance membranes with optimized properties.

  7. Composite membranes for fluid separations

    DOEpatents

    Blume, Ingo; Peinemann, Klaus-Viktor; Pinnau, Ingo; Wijmans, Johannes G.

    1990-01-01

    A method for designing and making composite membranes having a microporous support membrane coated with a permselective layer. The method involves calculating the minimum thickness of the permselective layer such that the selectivity of the composite membrane is close to the intrinsic selectivity of the permselective layer. The invention also provides high performance membranes with optimized properties.

  8. 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.

  9. Characterization of the Red Beet Plasma Membrane H+-ATPase Reconstituted in a Planar Bilayer System.

    PubMed Central

    Briskin, D. P.; Basu, S.; Assmann, S. M.

    1995-01-01

    The transport activity of the red beet (Beta vulgaris L.) plasma membrane H+-ATPase was examined following reconstitution into a planar bilayer membrane. Fusion of partially purified plasma membrane H+-ATPase with the bilayer membrane was accomplished by perfusion of proteoliposomes against the bilayer under hypoosmotic conditions. Following incorporation into the bilayer, an ATP-dependent current was measured that demonstrated properties consistent with those of the plasma membrane H+-ATPase. Current production was substrate specific for ATP, inhibited by orthovanadate, and insensitive to 200 nM erythrosin B but inhibited by 100 [mu]M erythrosin B. When current production was measured as a function of Mg:ATP concentration, a simple Michaelis-Menten relationship was observed and a Km of 0.62 mM was estimated. Current-voltage analysis of ATP-dependent current in the presence of 0.5 mM ATP, 20 mM ADP, 40 mM orthophosphate, and an opposing 2.5-unit [delta]pH revealed a reversal potential of about -149 mV. Based on the free energy available from ATP hydrolysis, this reversal potential is consistent with an H+/ATP stoichiometry of 1. This study demonstrates the usefulness of a planar bilayer system for investigation of energy coupling to H+ transport by the plasma membrane H+-ATPase. PMID:12228483

  10. Bipolar membranes with fluid distribution passages

    NASA Technical Reports Server (NTRS)

    Hitchens, G. Duncan (Inventor); Archer, Shivaun (Inventor); Tennakoon, Charles L. (Inventor); Gonzalez-Martin, Anuncia (Inventor); Cisar, Alan J. (Inventor)

    1999-01-01

    The present invention provides a bipolar membrane and methods for making and using the membrane. The bipolar membrane comprises a cation-selective region, an anion-selective region, an interfacial region between the anion-selective region and the cation-selective region, and means for delivering fluid directly into the interfacial region. The means for delivering fluid includes passages that may comprise a fluid-permeable material, a wicking material, an open passage disposed within the membrane or some combination thereof. The passages may be provided in many shapes, sizes and configurations, but preferably deliver fluid directly to the interfacial region so that the rate of electrodialysis is no longer limited by the diffusion of fluid through the cation- or anion-selective regions to the interfacial region.

  11. Elastic Properties of Polymerised and Fluid Membranes Under Stress

    NASA Astrophysics Data System (ADS)

    Shillcock, Julian Charles

    The stability of a living cell relies on the properties and interrelations of its constituent parts. The fluid bilayer surrounding the cell separates the cytoplasm inside the cell from the extracellular environment. A cross-linked network of proteins within the cytoplasm supports the fluid bilayer and contributes to the cell's elasticity. Three properties relating to the behaviour of a model fluid bilayer and polymerised network are investigated by Monte Carlo simulation: the phase behaviour of a system of discotic liquid crystal molecules, the elastic properties of a model polymerised network, and the stability and rupture of a model fluid membrane. The isotropic to nematic transition induced by hydrostatic pressure in a system of discotic liquid cystal molecules in three dimensions is presented. The study concentrates on the phase behaviour resulting from the anisotropy of the disks. The transition is present for disks whose thickness to radius ratio is less than 40%, but is absent for thicker disks. A more specialised model of disks restricted to intersect a planar interface between two immiscible fluids is investigated, but has no isotropic -nematic phase transition at finite temperature. The elastic properties of a two-dimensional, triangulated network of Hookean springs are investigated as a function of temperature and applied tension. The compression modulus decreases, and the shear modulus increases, as the tension on the network is increased. The elastic properties of self-avoiding networks at low temperature are well described by a mean field theory. When the self-avoidance constraint is removed, the network undergoes a phase transition to a collapsed state of small area as the tension is reduced to zero. Both types of network show an unstable expansion of their area when the stretching tension exceeds a specified value. Both networks also have the unusual property (referred to as a negative Poisson ratio) of expanding transversely when stretched

  12. Elastic properties and line tension of self-assembled bilayer membranes.

    PubMed

    Li, Jianfeng; Pastor, Kyle A; Shi, An-Chang; Schmid, Friederike; Zhou, Jiajia

    2013-07-01

    The elastic properties of a self-assembled bilayer membrane are studied using the self-consistent field theory, applied to a model system composed of flexible amphiphilic chains dissolved in hydrophilic polymeric solvents. Examining the free energy of bilayer membranes with different geometries allows us to calculate their bending modulus, Gaussian modulus, two fourth-order membrane moduli, and the line tension. The dependence of these parameters on the microscopic characteristics of the amphiphilic chain, characterized by the volume fraction of the hydrophilic component, is systematically studied. The theoretical predictions are compared with the results from a simple monolayer model, which approximates a bilayer membrane by two monolayers. The region of validity of the linear elasticity theory is analyzed by examining the higher-order contributions. PMID:23944501

  13. Elastic properties and line tension of self-assembled bilayer membranes

    NASA Astrophysics Data System (ADS)

    Li, Jianfeng; Pastor, Kyle A.; Shi, An-Chang; Schmid, Friederike; Zhou, Jiajia

    2013-07-01

    The elastic properties of a self-assembled bilayer membrane are studied using the self-consistent field theory, applied to a model system composed of flexible amphiphilic chains dissolved in hydrophilic polymeric solvents. Examining the free energy of bilayer membranes with different geometries allows us to calculate their bending modulus, Gaussian modulus, two fourth-order membrane moduli, and the line tension. The dependence of these parameters on the microscopic characteristics of the amphiphilic chain, characterized by the volume fraction of the hydrophilic component, is systematically studied. The theoretical predictions are compared with the results from a simple monolayer model, which approximates a bilayer membrane by two monolayers. The region of validity of the linear elasticity theory is analyzed by examining the higher-order contributions.

  14. 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

  15. Anionic deep cavitands enable the adhesion of unmodified proteins at a membrane bilayer.

    PubMed

    Ghang, Yoo-Jin; Perez, Lizeth; Morgan, Melissa A; Si, Fang; Hamdy, Omar M; Beecher, Consuelo N; Larive, Cynthia K; Julian, Ryan R; Zhong, Wenwan; Cheng, Quan; Hooley, Richard J

    2014-12-28

    An anionic self-folding deep cavitand is capable of immobilizing unmodified proteins and enzymes at a supported lipid bilayer interface, providing a simple, soft bioreactive surface that allows enzymatic function under mild conditions. The adhesion is based on complementary charge interactions, and the hosts are capable of binding enzymes such as trypsin at the bilayer interface: the catalytic activity is retained upon adhesion, allowing selective reactions to be performed at the membrane surface. PMID:25366572

  16. Interaction of Nuclease Colicins with Membranes: Insertion Depth Correlates with Bilayer Perturbation

    PubMed Central

    Vankemmelbeke, Mireille; O′Shea, Paul; James, Richard; Penfold, Christopher N.

    2012-01-01

    Background Protein transport across cellular membranes is an important aspect of toxin biology. Escherichia coli cell killing by nuclease colicins occurs through DNA (DNases) or RNA (RNases) hydrolysis and to this end their cytotoxic domains require transportation across two sets of membranes. In order to begin to unravel the molecular mechanisms underlying the membrane translocation of colicin nuclease domains, we have analysed the membrane association of four DNase domains (E9, a charge reduction E9 mutant, E8, and E7) and one ribosomal RNase domain (E3) using a biomembrane model system. Principal Results We demonstrate, through the use of large unilamellar vesicles composed of synthetic and E. coli lipids and a membrane surface potential sensor, that the colicin nuclease domains bind anionic membranes only, with micromolar affinity and via a cooperative binding mechanism. The evaluation of the nuclease bilayer insertion depth, through a fluorescence quenching analysis using brominated lipids, indicates that the nucleases locate to differential regions in the bilayer. Colicin DNases target the interfacial region of the lipid bilayer, with the DNase E7 showing the deepest insertion, whereas the ribosomal RNase E3 penetrates into the hydrophobic core region of the bilayer. Furthermore, the membrane association of the DNase E7 and the ribosomal RNase E3 induces vesicle aggregation, lipid mixing and content leakage to a much larger extent than that of the other DNases analysed. Conclusions/Significance Our results show, for the first time, that after the initial electrostatically driven membrane association, the pleiotropic membrane effects induced by colicin nuclease domains relate to their bilayer insertion depth and may be linked to their in vivo membrane translocation. PMID:23029560

  17. Electrical monitoring of gel-protected bilayer lipid membranes using a bipotentiostat

    NASA Astrophysics Data System (ADS)

    Beddow, J. A.; Peterson, Ian R.; Heptinstall, J.; Walton, D. J.

    2001-09-01

    Electrically monitored lipid bilayer membranes, protected form mechanical damage and contact with low-energy liquids by a hydrogel layer, show promise in biosensing applications. We describe the principle and implementation of a bipotentiostatic circuit for the measurement of both resistance and capacitance of gel-protected membranes. We report measurements taken using the bipotentiostat of membranes formed using glycerol 1-monooleate, and the response of these membranes taken using the bipotentiostat of membranes formed using glycerol 1-monooleate, and the response of these membranes to the ionophore, valinomycin.

  18. Continuum electrostatic approach for evaluating positions and interactions of proteins in a bilayer membrane.

    PubMed

    Supunyabut, Chirayut; Fuklang, Sunit; Sompornpisut, Pornthep

    2015-06-01

    Orientations of proteins in the membranes are crucial to their function and stability. Unfortunately the exact positions of these proteins in the lipid bilayer are mostly undetermined. Here, the spatial orientation of membrane proteins within the lipid membrane was evaluated using a Poisson-Boltzmann solvent continuum approach to calculate the electrostatic free energy of the protein solvation at various orientations in an implicit bilayer. The solvation energy was obtained by computing the difference in electrostatic energies of the protein in water and in lipid/water environments, treating each as an implicit solvent model. The optimal position of transmembrane proteins (TMP) in a lipid bilayer is identified by the minimum in the "downhill" pathway of the solvation energy landscape. The energy landscape pattern was considerably conserved in various TMP classes. Evaluation of the position of 1060 membrane proteins from the orientations of proteins in membranes (OPM) database revealed that most of the polytopic and β-barrel proteins were in good agreement with those of the OPM database. The study provides a useful scheme for estimating the membrane solvation energy made by lipid-exposed amino acids in membrane proteins. In addition, our results tested with the bacterial potassium channel model demonstrated the potential usefulness of the approach in assessing the quality of membrane protein models. The present approach should be applicable for constructing transmembrane proteins-lipid configuration suitable for membrane protein simulations and will have utility for the structural modeling of membrane proteins. PMID:25912455

  19. A Bilayered Structure Comprised of Functionalized Carbon Nanotubes for Desalination by Membrane Distillation.

    PubMed

    Bhadra, Madhuleena; Roy, Sagar; Mitra, Somenath

    2016-08-01

    The development of a novel carbon nanotube (CNT) immobilized membrane comprised of a double-layer structure is presented for water desalination by membrane distillation. The bilayered structure is comprised of CNTs functionalized with a hydrophobic octadecyl amine group on the feed side and carboxylated CNTs on the permeate side. The latter is more hydrophilic. The hydrophobic CNTs provide higher water vapor permeation, while the hydrophilic CNTs facilitate the condensation of water vapor. Together, these led to superior performance, and flux in a direct contact membrane distillation mode was found to be as high as 121 kg/m(2)h at 80 °C. The bilayered membrane represented an enhancement of 70% over the unmodified membrane and 37% over a membrane which had a monolayered structure where only the feed side was CNT-modified. PMID:27387851

  20. Plasmonic nanoantenna arrays for surface-enhanced Raman spectroscopy of lipid molecules embedded in a bilayer membrane.

    PubMed

    Kühler, Paul; Weber, Max; Lohmüller, Theobald

    2014-06-25

    We demonstrate a strategy for surface-enhanced Raman spectroscopy (SERS) of supported lipid membranes with arrays of plasmonic nanoantennas. Colloidal lithography refined with plasma etching is used to synthesize arrays of triangular shaped gold nanoparticles. Reducing the separation distance between the triangle tips leads to plasmonic coupling and to a strong enhancement of the electromagnetic field in the nanotriangle gap. As a result, the Raman scattering intensity of molecules that are located at this plasmonic "hot-spot" can be increased by several orders of magnitude. The nanoantenna array is then embedded with a supported phospholipid membrane which is fluid at room temperature and spans the antenna gap. This configuration offers the advantage that molecules that are mobile within the bilayer membrane can enter the "hot-spot" region via diffusion and can therefore be measured by SERS without static entrapment or adsorption of the molecules to the antenna itself. PMID:24896979

  1. Transport methods for probing the barrier domain of lipid bilayer membranes.

    PubMed Central

    Xiang, T X; Chen, X; Anderson, B D

    1992-01-01

    Two experimental techniques have been utilized to explore the barrier properties of lecithin/decane bilayer membranes with the aim of determining the contributions of various domains within the bilayer to the overall barrier. The thickness of lecithin/decane bilayers was systematically varied by modulating the chemical potential of decane in the annulus surrounding the bilayer using different mole fractions of squalene in decane. The dependence of permeability of a model permeant (acetamide) on the thickness of the solvent-filled region of the bilayer was assessed in these bilayers to determine the contribution of this region to the overall barrier. The flux of acetamide was found to vary linearly with bilayer area with Pm = (2.9 +/- 0.3) x 10(-4) cm s-1, after correcting for diffusion through unstirred water layers. The ratio between the overall membrane permeability coefficient and that calculated for diffusion through the hydrocarbon core in membranes having maximum thickness was 0.24, suggesting that the solvent domain contributes only slightly to the overall barrier properties. Consistent with these results, the permeability of acetamide was found to be independent of bilayer thickness. The relative contributions of the bilayer interface and ordered hydrocarbon regions to the transport barrier may be evaluated qualitatively by exploring the effective chemical nature of the barrier microenvironment. This may be probed by comparing functional group contributions to transport with those obtained for partitioning between water and various model bulk solvents ranging in polarity or hydrogen-bonding potential. A novel approach is described for obtaining group contributions to transport using ionizable permeants and pH adjustment. Using this approach, bilayer permeability coefficients of p-toluic acid and p-hydroxymethyl benzoic acid were determined to be 1.1 +/- 0.2 cm s-1 and (1.6 +/- 0.4) x 10(-3) cm s-1, respectively. From these values, the -OH group contribution

  2. Proton switch for modulating oxygen reduction by a copper electrocatalyst embedded in a hybrid bilayer membrane

    NASA Astrophysics Data System (ADS)

    Barile, Christopher J.; Tse, Edmund C. M.; Li, Ying; Sobyra, Thomas B.; Zimmerman, Steven C.; Hosseini, Ali; Gewirth, Andrew A.

    2014-06-01

    Molecular switches gate many fundamental processes in natural and artificial systems. Here, we report the development of an electrochemical platform in which a proton carrier switches the activity of a catalyst. By incorporating an alkyl phosphate in the lipid layer of a hybrid bilayer membrane, we regulate proton transport to a Cu-based molecular oxygen reduction reaction catalyst. To construct this hybrid bilayer membrane system, we prepare an example of a synthetic Cu oxygen reduction reaction catalyst that forms a self-assembled monolayer on Au surfaces. We then embed this Cu catalyst inside a hybrid bilayer membrane by depositing a monolayer of lipid on the self-assembled monolayer. We envisage that this electrochemical system can give a unique mechanistic insight not only into the oxygen reduction reaction, but into proton-coupled electron transfer in general.

  3. Arrayed water-in-oil droplet bilayers for membrane transport analysis.

    PubMed

    Watanabe, R; Soga, N; Hara, M; Noji, H

    2016-08-01

    The water-in-oil droplet bilayer is a simple and useful lipid bilayer system for membrane transport analysis. The droplet interface bilayer is readily formed by the contact of two water-in-oil droplets enwrapped by a phospholipid monolayer. However, the size of individual droplets with femtoliter volumes in a high-throughput manner is difficult to control, resulting in low sensitivity and throughput of membrane transport analysis. To overcome this drawback, in this study, we developed a novel micro-device in which a large number of droplet interface bilayers (>500) are formed at a time by using femtoliter-sized droplet arrays immobilized on a hydrophobic/hydrophilic substrate. The droplet volume was controllable from 3.5 to 350 fL by changing the hydrophobic/hydrophilic pattern on the device, allowing high-throughput analysis of membrane transport mechanisms including membrane permeability to solutes (e.g., ions or small molecules) with or without the aid of transport proteins. Thus, this novel platform broadens the versatility of water-in-oil droplet bilayers and will pave the way for novel analytical and pharmacological applications such as drug screening. PMID:27080052

  4. 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.

  5. 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

  6. Application of self-consistent field theory to self-assembled bilayer membranes

    NASA Astrophysics Data System (ADS)

    Zhang, Ping-Wen; Shi, An-Chang

    2015-12-01

    Bilayer membranes self-assembled from amphiphilic molecules such as lipids, surfactants, and block copolymers are ubiquitous in biological and physiochemical systems. The shape and structure of bilayer membranes depend crucially on their mechanical properties such as surface tension, bending moduli, and line tension. Understanding how the molecular properties of the amphiphiles determine the structure and mechanics of the self-assembled bilayers requires a molecularly detailed theoretical framework. The self-consistent field theory provides such a theoretical framework, which is capable of accurately predicting the mechanical parameters of self-assembled bilayer membranes. In this mini review we summarize the formulation of the self-consistent field theory, as exemplified by a model system composed of flexible amphiphilic chains dissolved in hydrophilic polymeric solvents, and its application to the study of self-assembled bilayer membranes. Project supported by the National Natural Science Foundation of China (Grant Nos. 11421101 and 21274005) and the Natural Sciences and Engineering Research Council (NSERC) of Canada.

  7. The Influence of Hydrogen Bonding on Sphingomyelin/Colipid Interactions in Bilayer Membranes.

    PubMed

    Yasuda, Tomokazu; Al Sazzad, Md Abdullah; Jäntti, Niklas Z; Pentikäinen, Olli T; Slotte, J Peter

    2016-01-19

    The phospholipid acyl chain composition and order, the hydrogen bonding, and properties of the phospholipid headgroup all influence cholesterol/phospholipid interactions in hydrated bilayers. In this study, we examined the influence of hydrogen bonding on sphingomyelin (SM) colipid interactions in fluid uni- and multilamellar vesicles. We have compared the properties of oleoyl or palmitoyl SM with comparable dihydro-SMs, because the hydrogen bonding properties of SM and dihydro-SM differ. The association of cholestatrienol, a fluorescent cholesterol analog, with oleoyl sphingomyelin (OSM) was significantly stronger than its association with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, in bilayers with equal acyl chain order. The association of cholestatrienol with dihydro-OSM, which lacks a trans double bond in the sphingoid base, was even stronger than the association with OSM, suggesting an important role for hydrogen bonding in stabilizing sterol/SM interactions. Furthermore, with saturated SM in the presence of 15 mol % cholesterol, cholesterol association with fluid dihydro-palmitoyl SM bilayers was stronger than seen with palmitoyl SM under similar conditions. The different hydrogen bonding properties in OSM and dihydro-OSM bilayers also influenced the segregation of palmitoyl ceramide and dipalmitoylglycerol into an ordered phase. The ordered, palmitoyl ceramide-rich phase started to form above 2 mol % in the dihydro-OSM bilayers but only above 6 mol % in the OSM bilayers. The lateral segregation of dipalmitoylglycerol was also much more pronounced in dihydro-OSM bilayers than in OSM bilayers. The results show that hydrogen bonding is important for sterol/SM and ceramide/SM interactions, as well as for the lateral segregation of a diglyceride. A possible molecular explanation for the different hydrogen bonding in SM and dihydro-SM bilayers is presented and discussed. PMID:26789766

  8. Magnetically aligned phospholipid bilayers with positive ordering: a new model membrane system.

    PubMed

    Prosser, R S; Hwang, J S; Vold, R R

    1998-05-01

    A stable smectic phospholipid bilayer phase aligned with the director parallel to the magnetic field can be generated by the addition of certain trivalent paramagnetic lanthanide ions to a bicellar solution of dimyristoylphosphatidylcholine (DMPC) and dihexanoylphosphatidylcholine (DHPC) in water. Suitable lanthanide ions are those with positive anisotropy of their magnetic susceptibility, namely Eu3+, Er3+, Tm3+, and Yb3+. For samples doped with Tm3+, this phase extends over a wide range of Tm3+ concentrations (6-40 mM) and temperatures (35-90 degrees C) and appears to undergo a transition from a fluid nematic discotic to a fluid, but highly ordered, smectic phase at a temperature that depends on the thulium concentration. As a membrane mimetic, these new, positively ordered phospholipid phases have high potential for structural studies using a variety of techniques such as magnetic resonance (EMR and NMR), small-angle x-ray and neutron diffraction, as well as optical and infrared spectroscopy. PMID:9591667

  9. Tilted bilayer membranes as simple transmission quarter-wave retardation plates.

    PubMed

    Azzam, R M; Mahmoud, F A

    2001-02-01

    A tilted bilayer membrane, which consists of two thin films of transparent optically isotropic materials of different refractive indices, can function as a transmission quarter-wave retarder (QWR) at a high angle of incidence. A specific design using a cryolite-Si membrane in the infrared is presented, and its tolerances to small shifts of wavelength, incidence angle, and film thickness errors are discussed. Some designs provide a dual QWR in transmission and reflection. Such devices provide simple linear-to-circular (and circular-to-linear) polarization transformers. Bilayer eighth-wave retarders without diattenuation are also introduced. PMID:11205989

  10. 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

  11. 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.

  12. 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.

  13. 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

  14. 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

  15. Electric field increases the phase transition temperature in the bilayer membrane of phosphatidic acid.

    PubMed

    Antonov, V F; Smirnova EYu; Shevchenko, E V

    1990-02-01

    The effect of the electric field on the phase transition temperature (Tc) of acidic 1,2-dipalmitoyl-sn-glycero-3-phosphate (DPPA) and 1,2-dipalmitoyl-sn-glycero-3-thionphosphate (thion-DPPA) and zwitterion, i.e. 1,2-dipalmitoyl-rac-3-phosphocholine and 1,2-distearoyl-rac-glycero-3-phosphocholine (DPPC and DSPC), lipids has been investigated. The phase transition was detected using the jump-like increase effect in the conductance of the planar bilayer membrane. A voltage increase to 150 mV has been shown to increase the phase transition temperature in a bilayer lipid membrane (BLM) of phosphatidic acids (DPPA and thion-DPPA) by 8-12 degrees C while the transition temperature in the bilayer of zwitterion lipids (DPPC and DSPC) increases insignificantly. The increasing of Tt in BLM of acidic lipids is attributed to the voltage-induced changes in the molecule packing density. PMID:2340602

  16. Natural channel protein inserts and functions in a completely artificial, solid-supported bilayer membrane

    PubMed Central

    Zhang, Xiaoyan; Fu, Wangyang; Palivan, Cornelia G.; Meier, Wolfgang

    2013-01-01

    Reconstitution of membrane proteins in artificial membrane systems creates a platform for exploring their potential for pharmacological or biotechnological applications. Previously, we demonstrated amphiphilic block copolymers as promising building blocks for artificial membranes with long-term stability and tailorable structural parameters. However, the insertion of membrane proteins has not previously been realized in a large-area, stable, and solid-supported artificial membrane. Here, we show the first, preliminary model of a channel membrane protein that is functionally incorporated in a completely artificial polymer, tethered, solid-supported bilayer membrane (TSSBM). Unprecedented ionic transport characteristics that differ from previous results on protein insertion into planar, free-standing membranes, are identified. Our findings mark a change in understanding protein insertion and ion flow within natural channel proteins when inserted in an artificial TSSBM, thus holding great potential for numerous applications such as drug screening, trace analyzing, and biosensing. PMID:23846807

  17. Parameters affecting the fusion of unilamellar phospholipid vesicles with planar bilayer membranes.

    PubMed

    Cohen, F S; Akabas, M H; Zimmerberg, J; Finkelstein, A

    1984-03-01

    It was previously shown (Cohen, F. S., J. Zimmerberg, and A. Finkelstein, 1980, J. Gen. Physiol., 75:251-270) that multilamellar phospholipid vesicles can fuse with decane-containing phospholipid bilayer membranes. An essential requirement for fusion was an osmotic gradient across the planar membrane, with the vesicle-containing (cis) side hyperosmotic with respect to the opposite (trans) side. We now report that unilamellar vesicles will fuse with "hydrocarbon-free" membranes subject to these same osmotic conditions. Thus the same conditions that apply to fusion of multilamellar vesicles with planar bilayer membranes also apply to fusion of unilamellar vesicles with these membranes, and hydrocarbon is not required for the fusion process. If the vesicles and/or planar membrane contain negatively charged lipids, divalent cation (approximately 15 mM Ca++) is required in the cis compartment (in addition to the osmotic gradient across the membrane) to obtain substantial fusion rates. On the other hand, vesicles made from uncharged lipids readily fuse with planar phosphatidylethanolamine planar membranes in the near absence of divalent cation with just an osmotic gradient. Vesicles fuse much more readily with phosphatidylethanolamine-containing than with phosphatidylcholine-containing planar membranes. Although hydrocarbon (decane) is not required in the planar membrane for fusion, it does affect the rate of fusion and causes the fusion process to be dependent on stirring in the cis compartment. PMID:6699081

  18. Diffusion in phospholipid bilayer membranes: dual-leaflet dynamics and the roles of tracer–leaflet and inter-leaflet coupling

    PubMed Central

    Hill, Reghan J.; Wang, Chih-Ying

    2014-01-01

    A variety of observations—sometimes controversial—have been made in recent decades when attempting to elucidate the roles of interfacial slip on tracer diffusion in phospholipid membranes. Evans–Sackmann theory (1988) has furnished membrane viscosities and lubrication-film thicknesses for supported membranes from experimentally measured lateral diffusion coefficients. Similar to the Saffman and Delbrück model, which is the well-known counterpart for freely supported membranes, the bilayer is modelled as a single two-dimensional fluid. However, the Evans–Sackman model cannot interpret the mobilities of monotopic tracers, such as individual lipids or rigidly bound lipid assemblies; neither does it account for tracer–leaflet and inter-leaflet slip. To address these limitations, we solve the model of Wang and Hill, in which two leaflets of a bilayer membrane, a circular tracer and supports are coupled by interfacial friction, using phenomenological friction/slip coefficients. This furnishes an exact solution that can be readily adopted to interpret the mobilities of a variety of mosaic elements—including lipids, integral monotopic and polytopic proteins, and lipid rafts—in supported bilayer membranes. PMID:25002822

  19. Receptor Concentration and Diffusivity Control Multivalent Binding of Sv40 to Membrane Bilayers

    PubMed Central

    Szklarczyk, Oliwia M.; González-Segredo, Nélido; Kukura, Philipp; Oppenheim, Ariella; Choquet, Daniel; Sandoghdar, Vahid; Helenius, Ari; Sbalzarini, Ivo F.; Ewers, Helge

    2013-01-01

    Abstract Incoming Simian Virus 40 particles bind to their cellular receptor, the glycolipid GM1, in the plasma membrane and thereby induce membrane deformation beneath the virion leading to endocytosis and infection. Efficient membrane deformation depends on receptor lipid structure and the organization of binding sites on the internalizing particle. To determine the role of receptor diffusion, concentration and the number of receptors required for stable binding in this interaction, we analyze the binding of SV40 to GM1 in supported membrane bilayers by computational modeling based on experimental data. We measure the diffusion rates of SV40 virions in solution by fluorescence correlation spectroscopy and of the receptor in bilayers by single molecule tracking. Quartz-crystal microbalance with dissipation (QCM-D) is used to measure binding of SV40 virus-like particles to bilayers containing the viral receptor GM1. We develop a phenomenological stochastic dynamics model calibrated against this data, and use it to investigate the early events of virus attachment to lipid membranes. Our results indicate that SV40 requires at least 4 attached receptors to achieve stable binding. We moreover find that receptor diffusion is essential for the establishment of stable binding over the physiological range of receptor concentrations and that receptor concentration controls the mode of viral motion on the target membrane. Our results provide quantitative insight into the initial events of virus-host interaction at the nanoscopic level. PMID:24244125

  20. Ambidextrous Binding of Cell and Membrane Bilayers by Soluble Matrix Metalloproteinase-12

    PubMed Central

    Koppisetti, Rama K.; Fulcher, Yan G.; Jurkevich, Alexander; Prior, Stephen H.; Xu, Jia; Lenoir, Marc; Overduin, Michael; Van Doren, Steven R.

    2014-01-01

    Matrix metalloproteinases (MMPs) regulate tissue remodeling, inflammation, and disease progression. Some soluble MMPs are inexplicably active near cell surfaces. Here, we demonstrate binding of MMP-12 directly to bilayers and cellular membranes using paramagnetic NMR and fluorescence. Opposing sides of the catalytic domain engage spin-labeled membrane mimics. Loops project from the β-sheet interface to contact the phospholipid bilayer with basic and hydrophobic residues. The distal membrane interface comprises loops on the other side of the catalytic cleft. Both interfaces mediate MMP-12 association with vesicles and cell membranes. MMP-12 binds plasma membranes and is internalized to hydrophobic perinuclear features, the nuclear membrane, and inside the nucleus within minutes. While binding of TIMP-2 to MMP-12 hinders membrane interactions beside the active site, TIMP-2-inhibited MMP-12 binds vesicles and cells, suggesting compensatory rotation of its membrane approaches. MMP-12 association with diverse cell membranes may target its activities to modulate innate immune responses and inflammation. PMID:25412686

  1. Ambidextrous binding of cell and membrane bilayers by soluble matrix metalloproteinase-12.

    PubMed

    Koppisetti, Rama K; Fulcher, Yan G; Jurkevich, Alexander; Prior, Stephen H; Xu, Jia; Lenoir, Marc; Overduin, Michael; Van Doren, Steven R

    2014-01-01

    Matrix metalloproteinases (MMPs) regulate tissue remodelling, inflammation and disease progression. Some soluble MMPs are inexplicably active near cell surfaces. Here we demonstrate the binding of MMP-12 directly to bilayers and cellular membranes using paramagnetic NMR and fluorescence. Opposing sides of the catalytic domain engage spin-labelled membrane mimics. Loops project from the β-sheet interface to contact the phospholipid bilayer with basic and hydrophobic residues. The distal membrane interface comprises loops on the other side of the catalytic cleft. Both interfaces mediate MMP-12 association with vesicles and cell membranes. MMP-12 binds plasma membranes and is internalized to hydrophobic perinuclear features, the nuclear membrane and inside the nucleus within minutes. While binding of TIMP-2 to MMP-12 hinders membrane interactions beside the active site, TIMP-2-inhibited MMP-12 binds vesicles and cells, suggesting compensatory rotation of its membrane approaches. MMP-12 association with diverse cell membranes may target its activities to modulate innate immune responses and inflammation. PMID:25412686

  2. Stochastic transport through carbon nanotubes in lipid bilayers and live cell membranes

    NASA Astrophysics Data System (ADS)

    Geng, Jia; Kim, Kyunghoon; Zhang, Jianfei; Escalada, Artur; Tunuguntla, Ramya; Comolli, Luis R.; Allen, Frances I.; Shnyrova, Anna V.; Cho, Kang Rae; Munoz, Dayannara; Wang, Y. Morris; Grigoropoulos, Costas P.; Ajo-Franklin, Caroline M.; Frolov, Vadim A.; Noy, Aleksandr

    2014-10-01

    There is much interest in developing synthetic analogues of biological membrane channels with high efficiency and exquisite selectivity for transporting ions and molecules. Bottom-up and top-down methods can produce nanopores of a size comparable to that of endogenous protein channels, but replicating their affinity and transport properties remains challenging. In principle, carbon nanotubes (CNTs) should be an ideal membrane channel platform: they exhibit excellent transport properties and their narrow hydrophobic inner pores mimic structural motifs typical of biological channels. Moreover, simulations predict that CNTs with a length comparable to the thickness of a lipid bilayer membrane can self-insert into the membrane. Functionalized CNTs have indeed been found to penetrate lipid membranes and cell walls, and short tubes have been forced into membranes to create sensors, yet membrane transport applications of short CNTs remain underexplored. Here we show that short CNTs spontaneously insert into lipid bilayers and live cell membranes to form channels that exhibit a unitary conductance of 70-100 picosiemens under physiological conditions. Despite their structural simplicity, these `CNT porins' transport water, protons, small ions and DNA, stochastically switch between metastable conductance substates, and display characteristic macromolecule-induced ionic current blockades. We also show that local channel and membrane charges can control the conductance and ion selectivity of the CNT porins, thereby establishing these nanopores as a promising biomimetic platform for developing cell interfaces, studying transport in biological channels, and creating stochastic sensors.

  3. Interaction between bending and tension forces in bilayer membranes.

    PubMed Central

    Secomb, T W

    1988-01-01

    A theoretical analysis is presented of the bending mechanics of a membrane consisting of two tightly-coupled leaflets, each of which shears and bends readily but strongly resists area changes. Structures of this type have been proposed to model biological membranes such as red blood cell membrane. It is shown that when such a membrane is bent, anisotropic components of resultant membrane tension (shear stresses) are induced, even when the tension in each leaflet is isotropic. The induced shear stresses increase as the square of the membrane curvature, and become significant for moderate curvatures (when the radius of curvature is much larger than the distance between the leaflets). This effect has implications for the analysis of shape and deformation of freely suspended and flowing red blood cells. PMID:3224154

  4. 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

  5. Holographic interferometry of ultrasmall-pressure-induced curvature changes of bilayer lipid membranes

    SciTech Connect

    Picard, G.; Schneider-Henriquez, J.E.; Fendler, J.H. )

    1990-01-25

    Two-exposure interferometric holograms have been shown to sensitively report ultrasmall-pressure (10 natm)-induced curvature changes in glyceryl monooleate (GMO) bilayer lipid membranes (BLMs). The number of concentric fringes observed, and hence the lateral distance between the plane of the Teflon and the BLM, increased linearly with increasing transmembrane pressure and led to a value of 1.1 {plus minus} 0.05 dyn/cm for the surface tension of the BLM. BLMs with appreciable Plateau-Gibbs borders have been shown to undergo nonuniform deformation; the bilayer portion is distorted less than the surrounding Plateau-Gibbs border upon the application of a transmembrane pressure gradient.

  6. Immobilized fluid membranes for gas separation

    DOEpatents

    Liu, Wei; Canfield, Nathan L; Zhang, Jian; Li, Xiaohong Shari; Zhang, Jiguang

    2014-03-18

    Provided herein are immobilized liquid membranes for gas separation, methods of preparing such membranes and uses thereof. In one example, the immobilized membrane includes a porous metallic host matrix and an immobilized liquid fluid (such as a silicone oil) that is immobilized within one or more pores included within the porous metallic host matrix. The immobilized liquid membrane is capable of selective permeation of one type of molecule (such as oxygen) over another type of molecule (such as water). In some examples, the selective membrane is incorporated into a device to supply oxygen from ambient air to the device for electrochemical reactions, and at the same time, to block water penetration and electrolyte loss from the device.

  7. Control of membrane permeability in air-stable droplet interface bilayers

    DOE PAGESBeta

    Mruetusatorn, Prachya; Polizos, Georgios; Datskos, Panos G.; Taylor, Graham; Sarles, Stephen A.; Boreyko, Jonathan; Hayes, Douglas G.; Collier, Pat

    2015-03-19

    Air-stable droplet interface bilayers (airDIBs) on oil-infused surfaces are versatile model membranes for synthetic biology applications, including biosensing of airborne species. However, air-DIBs are subject to evaporation, which can, over time, destabilize them and reduce their useful lifetime compared to traditional DIBs that are fully submerged in oil. Here, we show that lifetimes of air-DIBs can be extended by as much as an order of magnitude by maintaining them at a temperature just above the dew point. We find that raising the temperature from near the dew point (7 C at 38.5 % relative humidity) to room temperature results inmore » loss of water molecules of hydration from the polar head groups of the lipid bilayer membrane due to evaporation in an irreversible process that increases the overall entropy of the system. This dehydration transition affects primarily the bilayer resistance, by increasing ion permeability through the increasingly disordered polar head group region of the bilayer. Temperature and/or relative humidity are conveniently tunable parameters for controlling the stability and composition of air-DIBs membranes, while still allowing for operation in ambient environments.« less

  8. Control of membrane permeability in air-stable droplet interface bilayers

    SciTech Connect

    Mruetusatorn, Prachya; Polizos, Georgios; Datskos, Panos G.; Taylor, Graham; Sarles, Stephen A.; Boreyko, Jonathan; Hayes, Douglas G.; Collier, Pat

    2015-03-19

    Air-stable droplet interface bilayers (airDIBs) on oil-infused surfaces are versatile model membranes for synthetic biology applications, including biosensing of airborne species. However, air-DIBs are subject to evaporation, which can, over time, destabilize them and reduce their useful lifetime compared to traditional DIBs that are fully submerged in oil. Here, we show that lifetimes of air-DIBs can be extended by as much as an order of magnitude by maintaining them at a temperature just above the dew point. We find that raising the temperature from near the dew point (7 C at 38.5 % relative humidity) to room temperature results in loss of water molecules of hydration from the polar head groups of the lipid bilayer membrane due to evaporation in an irreversible process that increases the overall entropy of the system. This dehydration transition affects primarily the bilayer resistance, by increasing ion permeability through the increasingly disordered polar head group region of the bilayer. Temperature and/or relative humidity are conveniently tunable parameters for controlling the stability and composition of air-DIBs membranes, while still allowing for operation in ambient environments.

  9. Control of membrane permeability in air-stable droplet interface bilayers.

    PubMed

    Mruetusatorn, Prachya; Polizos, Georgios; Datskos, Panos G; Taylor, Graham; Sarles, Stephen A; Boreyko, Jonathan B; Hayes, Douglas G; Collier, C Patrick

    2015-04-14

    Air-stable droplet interface bilayers (airDIBs) on oil-infused surfaces are versatile model membranes for synthetic biology applications, including biosensing of airborne species. However, airDIBs are subject to evaporation, which can, over time, destabilize them and reduce their useful lifetime compared to traditional DIBs that are fully submerged in oil. Here, we show that the lifetimes of airDIBs can be extended by as much as an order of magnitude by maintaining the temperature just above the dew point. We find that raising the temperature from near the dew point (which was 7 °C at 38.5% relative humidity and 22 °C air temperature) to 20 °C results in the loss of hydrated water molecules from the polar headgroups of the lipid bilayer membrane due to evaporation, resulting in a phase transition with increased disorder. This dehydration transition primarily affects the bilayer electrical resistance by increasing the permeability through an increasingly disordered polar headgroup region of the bilayer. Temperature and relative humidity are conveniently tunable parameters for controlling the stability and composition of airDIB membranes while still allowing for operation in ambient environments. PMID:25790280

  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

  11. 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

  12. Energy of dissociation of lipid bilayer from the membrane skeleton of red blood cells.

    PubMed Central

    Hwang, W C; Waugh, R E

    1997-01-01

    The association between the lipid bilayer and the membrane skeleton is important to cell function. In red blood cells, defects in this association can lead to various forms of hemolytic anemia. Although proteins involved in this association have been well characterized biochemically, the physical strength of this association is only beginning to be studied. Formation of a small cylindrical strand of membrane material (tether) from the membrane involves separation of the lipid bilayer from the membrane skeleton. By measuring the force required to form a tether, and knowing the contribution to the force due to the deformation of a lipid bilayer, it is possible to calculate the additional contribution to the work of tether formation due to the separation of membrane skeleton from the lipid bilayer. In the present study, we measured the tethering force during tether formation using a microcantilever (a thin, flexible glass fiber) as a force transducer. Numerical calculations of the red cell contour were performed to examine how the shape of the contour affects the calculation of tether radius, and subsequently separation work per unit area W(sk) and bending stiffness k(c). At high aspiration pressure and small external force, the red cell contour can be accurately modeled as a sphere, but at low aspiration pressure and large external force, the contour deviates from a sphere and may affect the calculation. Based on an energy balance and numerical calculations of the cell contour, values of the membrane bending stiffness k(c) = 2.0 x 10(-19) Nm and the separation work per unit area W(sk) = 0.06 mJ/m2 were obtained. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 8 PMID:9168042

  13. Advances in the use of nanoscale bilayers to study membrane protein structure and function.

    PubMed

    Malhotra, Ketan; Alder, Nathan N

    2014-10-01

    Within the last decade, nanoscale lipid bilayers have emerged as powerful experimental systems in the analysis of membrane proteins (MPs) for both basic and applied research. These discoidal lipid lamellae are stabilized by annuli of specially engineered amphipathic polypeptides (nanodiscs) or polymers (SMALPs/Lipodisqs®). As biomembrane mimetics, they are well suited for the reconstitution of MPs within a controlled lipid environment. Moreover, because they are water-soluble, they are amenable to solution-based biochemical and biophysical experimentation. Hence, due to their solubility, size, stability, and monodispersity, nanoscale lipid bilayers offer technical advantages over more traditional MP analytic approaches such as detergent solubilization and reconstitution into lipid vesicles. In this article, we review some of the most recent advances in the synthesis of polypeptide- and polymer-bound nanoscale lipid bilayers and their application in the study of MP structure and function. PMID:25023464

  14. NMR structural studies of the bacterial outer membrane protein OmpX in oriented lipid bilayer membranes

    PubMed Central

    Mahalakshmi, Radhakrishnan; Franzin, Carla M.; Choi, Jungyuen; Marassi, Francesca M.

    2008-01-01

    SUMMARY The β-barrels found in the outer membranes of prokaryotic and eukaryotic organisms constitute an important functional class of proteins. Here we present solid-state NMR spectra of the bacterial outer membrane protein OmpX in oriented lipid bilayer membranes. We show that OmpX is folded in both glass-supported oriented lipid bilayers and in lipid bicelles that can be magnetically oriented with the membrane plane parallel or perpendicular to the direction of the magnetic field. The presence of resolved peaks in these spectra demonstrates that OmpX undergoes rotational diffusion around an axis perpendicular to the membrane surface. A tightly hydrogen-bonded domain of OmpX resists exchange with D2O for days and is assigned to the transmembrane β-barrel, while peaks at isotropic resonance frequencies that disappear rapidly in D2O are assigned to the extracellular and periplasmic loops. The two-dimensional 1H/15N separated local field spectra of OmpX have several resolved peaks, and agree well with the spectra calculated from the crystal structure of OmpX rotated with the barrel axis nearly parallel (5° tilt) to the direction of the magnetic field. The data indicate that it will be possible to obtain site-specific resonance assignments and to determine the structure, tilt, and rotation of OmpX in membranes using the solid-state NMR methods that are currently being applied to α-helical membrane proteins. PMID:17916325

  15. Mycobacterial outer membrane is a lipid bilayer and the inner membrane is unusually rich in diacyl phosphatidylinositol dimannosides

    PubMed Central

    Bansal-Mutalik, Ritu; Nikaido, Hiroshi

    2014-01-01

    Mycobacterium species, including the human pathogen Mycobacterium tuberculosis, are unique among Gram-positive bacteria in producing a complex cell wall that contains unusual lipids and functions as a permeability barrier. Lipids in the cell wall were hypothesized to form a bilayer or outer membrane that would prevent the entry of chemotherapeutic agents, but this could not be tested because of the difficulty in extracting only the cell-wall lipids. We used reverse micellar extraction to achieve this goal and carried out a quantitative analysis of both the cell wall and the inner membrane lipids of Mycobacterium smegmatis. We found that the outer leaflet of the outer membrane contains a similar number of hydrocarbon chains as the inner leaflet composed of mycolic acids covalently linked to cell-wall arabinogalactan, thus validating the outer membrane model. Furthermore, we found that preliminary extraction with reverse micelles permitted the subsequent complete extraction of inner membrane lipids with chloroform–methanol–water, revealing that one-half of hydrocarbon chains in this membrane are contributed by an unusual lipid, diacyl phosphatidylinositol dimannoside. The inner leaflet of this membrane likely is composed nearly entirely of this lipid. Because it contains four fatty acyl chains within a single molecule, it may produce a bilayer environment of unusually low fluidity and may slow the influx of drugs, contributing to the general drug resistance phenotype of mycobacteria. PMID:24639491

  16. A membrane-bound synthetic receptor that promotes growth of a polymeric coating at the bilayer-water interface.

    PubMed

    Liu, Ying; Young, Michael C; Moshe, Orly; Cheng, Quan; Hooley, Richard J

    2012-07-27

    Primed for action: Atom-transfer radical polymerization (ATRP) can be promoted at a bilayer-water interface by anchoring initiator molecules (see scheme; red) in a membrane-bound synthetic receptor (yellow). The bilayer is formed on a calcinated nanofilm (gray) on a gold surface. PMID:22730162

  17. pH regulation of amphotericin B channels activity in the bilayer lipid membrane

    PubMed Central

    Shahmoradi, Tahereh; Sepehry, Hamid; Ashrafpour, Manuchehr

    2016-01-01

    Background: Amphotericin B (AmB) is a polyene antibiotic frequently applied in the treatment of systemic fungal infections in spite of its secondary effects. The pH plays a crucial role in modulating biophysical features of ion channels in the bilayer lipid membranes. Aim: In this study, the role of pH in the regulation of AmB channel was assessed by single channel recording of ion channel incorporated in the artificial membrane. Materials and Methods: Bilayer lipid membrane was formed by phosphatidylcholine in a 350 μm diameter aperture between two chambers, cis and trans contained 200/50 mMKCl solutions, respectively; then AmB was incorporated into the bilayer lipid membrane. Single channel recordings were used to indicate the effects of pH changes on AmB channels activity. The records were analyzed by Clamp fit 10 software. Results: A kinetic analysis of single channel currents indicated a cation ion channel with 500 pS conductance and voltage-dependence of the open probability of the AmB channel (Po). A reduction of cis pH to 6 decreased Po and conductance. This effect was also voltage-dependent, being greater at a more positive above −40. The pH changes in the range of 6-8 had no effect on the reversal potential and ion selectivity. Conclusion: Our data indicated that extracellular acidity can reduce AmB activity. PMID:27003977

  18. Fluctuations of coupled fluid and solid membranes with application to red blood cells.

    PubMed

    Auth, Thorsten; Safran, S A; Gov, Nir S

    2007-11-01

    The fluctuation spectra and the intermembrane interaction of two membranes at a fixed average distance are investigated. Each membrane can either be a fluid or a solid membrane, and in isolation, its fluctuations are described by a bare or a wave-vector-dependent bending modulus, respectively. The membranes interact via their excluded-volume interaction; the average distance is maintained by an external, homogeneous pressure. For strong coupling, the fluctuations can be described by a single, effective membrane that combines the elastic properties. For weak coupling, the fluctuations of the individual, noninteracting membranes are recovered. The case of a composite membrane consisting of one fluid and one solid membrane can serve as a microscopic model for the plasma membrane and cytoskeleton of the red blood cell. We find that, despite the complex microstructure of bilayers and cytoskeletons in a real cell, the fluctuations with wavelengths lambda greater, similar 400 nm are well described by the fluctuations of a single, polymerized membrane (provided that there are no inhomogeneities of the microstructure). The model is applied to the fluctuation data of discocytes ("normal" red blood cells), a stomatocyte, and an echinocyte. The elastic parameters of the membrane and an effective temperature that quantifies active, metabolically driven fluctuations are extracted from the experiments. PMID:18233690

  19. Fluctuations of coupled fluid and solid membranes with application to red blood cells

    NASA Astrophysics Data System (ADS)

    Auth, Thorsten; Safran, S. A.; Gov, Nir S.

    2007-11-01

    The fluctuation spectra and the intermembrane interaction of two membranes at a fixed average distance are investigated. Each membrane can either be a fluid or a solid membrane, and in isolation, its fluctuations are described by a bare or a wave-vector-dependent bending modulus, respectively. The membranes interact via their excluded-volume interaction; the average distance is maintained by an external, homogeneous pressure. For strong coupling, the fluctuations can be described by a single, effective membrane that combines the elastic properties. For weak coupling, the fluctuations of the individual, noninteracting membranes are recovered. The case of a composite membrane consisting of one fluid and one solid membrane can serve as a microscopic model for the plasma membrane and cytoskeleton of the red blood cell. We find that, despite the complex microstructure of bilayers and cytoskeletons in a real cell, the fluctuations with wavelengths λ≳400nm are well described by the fluctuations of a single, polymerized membrane (provided that there are no inhomogeneities of the microstructure). The model is applied to the fluctuation data of discocytes (“normal” red blood cells), a stomatocyte, and an echinocyte. The elastic parameters of the membrane and an effective temperature that quantifies active, metabolically driven fluctuations are extracted from the experiments.

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

    PubMed Central

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

    2010-01-01

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

  1. A Distributed Amplifier System for Bilayer Lipid Membrane (BLM) Arrays With Noise and Individual Offset Cancellation.

    PubMed

    Crescentini, Marco; Thei, Frederico; Bennati, Marco; Saha, Shimul; de Planque, Maurits R R; Morgan, Hywel; Tartagni, Marco

    2015-06-01

    Lipid bilayer membrane (BLM) arrays are required for high throughput analysis, for example drug screening or advanced DNA sequencing. Complex microfluidic devices are being developed but these are restricted in terms of array size and structure or have integrated electronic sensing with limited noise performance. We present a compact and scalable multichannel electrophysiology platform based on a hybrid approach that combines integrated state-of-the-art microelectronics with low-cost disposable fluidics providing a platform for high-quality parallel single ion channel recording. Specifically, we have developed a new integrated circuit amplifier based on a novel noise cancellation scheme that eliminates flicker noise derived from devices under test and amplifiers. The system is demonstrated through the simultaneous recording of ion channel activity from eight bilayer membranes. The platform is scalable and could be extended to much larger array sizes, limited only by electronic data decimation and communication capabilities. PMID:25252284

  2. Photoelectric Effects in Lipid Bilayer Membranes. A Pedagogical Review.

    ERIC Educational Resources Information Center

    Huebner, Jay S.; And Others

    1988-01-01

    Provides information appropriate for introductory lectures on photoelectric effects in membranes. Describes the apparatus and supplies required for laboratory exercises. Outlines typical laboratory exercises. Identifies the chromophores known to induce photoelectric effects. Concludes that this topic can provide useful subjects for undergraduate…

  3. Atomistic simulation of lipid and DiI dynamics in membrane bilayers under tension.

    PubMed

    Muddana, Hari S; Gullapalli, Ramachandra R; Manias, Evangelos; Butler, Peter J

    2011-01-28

    Membrane tension modulates cellular processes by initiating changes in the dynamics of its molecular constituents. To quantify the precise relationship between tension, structural properties of the membrane, and the dynamics of lipids and a lipophilic reporter dye, we performed atomistic molecular dynamics (MD) simulations of DiI-labeled dipalmitoylphosphatidylcholine (DPPC) lipid bilayers under physiological lateral tensions ranging from -2.6 mN m(-1) to 15.9 mN m(-1). Simulations showed that the bilayer thickness decreased linearly with tension consistent with volume-incompressibility, and this thinning was facilitated by a significant increase in acyl chain interdigitation at the bilayer midplane and spreading of the acyl chains. Tension caused a significant drop in the bilayer's peak electrostatic potential, which correlated with the strong reordering of water and lipid dipoles. For the low tension regime, the DPPC lateral diffusion coefficient increased with increasing tension in accordance with free-area theory. For larger tensions, free area theory broke down due to tension-induced changes in molecular shape and friction. Simulated DiI rotational and lateral diffusion coefficients were lower than those of DPPC but increased with tension in a manner similar to DPPC. Direct correlation of membrane order and viscosity near the DiI chromophore, which was just under the DPPC headgroup, indicated that measured DiI fluorescence lifetime, which is reported to decrease with decreasing lipid order, is likely to be a good reporter of tension-induced decreases in lipid headgroup viscosity. Together, these results offer new molecular-level insights into membrane tension-related mechanotransduction and into the utility of DiI in characterizing tension-induced changes in lipid packing. PMID:21152516

  4. Formation and fluidity measurement of supported lipid bilayer on polyvinyl chloride membrane

    SciTech Connect

    Kobayashi, Takuji Kono, Akiteru Sawada, Kazuaki; Futagawa, Masato; Tero, Ryugo

    2014-02-20

    We prepared an artificial lipid bilayer on a plasticized poly(vinyl chloride) (PVC) membrane on a Si3N4 layer deposited on a Si wafer. We optimized the experimental condition for the fabrication of the PVC membrane, and obtained a PVC membrane with a flat and uniform surface on the scale of several hundreds of micrometer suitable for a substrate for supported lipid bilayers (SLBs). The SLB of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) was formed on the PVC membrane by the vesicle fusion method. The observation with a conventional epi-fluorescence microscope and a confocal laser scanning microscope gave geometrically uniform images of the SLB on the PVC membrane. The fluidity and the mobile fraction of the SLB was evaluated by the fluorescence recovery after photobleaching method, and compared with that on a thermally oxidized SiO{sub 2}/Si substrate. The SLB on the PVC membrane contained immobile fraction ∼30%, but the diffusion in the mobile fraction was two times faster than that in the SLB on SiO{sub 2}/Si, which had little immobile fraction.

  5. Formation and fluidity measurement of supported lipid bilayer on polyvinyl chloride membrane

    NASA Astrophysics Data System (ADS)

    Kobayashi, Takuji; Kono, Akiteru; Futagawa, Masato; Sawada, Kazuaki; Tero, Ryugo

    2014-02-01

    We prepared an artificial lipid bilayer on a plasticized poly(vinyl chloride) (PVC) membrane on a Si3N4 layer deposited on a Si wafer. We optimized the experimental condition for the fabrication of the PVC membrane, and obtained a PVC membrane with a flat and uniform surface on the scale of several hundreds of micrometer suitable for a substrate for supported lipid bilayers (SLBs). The SLB of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) was formed on the PVC membrane by the vesicle fusion method. The observation with a conventional epi-fluorescence microscope and a confocal laser scanning microscope gave geometrically uniform images of the SLB on the PVC membrane. The fluidity and the mobile fraction of the SLB was evaluated by the fluorescence recovery after photobleaching method, and compared with that on a thermally oxidized SiO2/Si substrate. The SLB on the PVC membrane contained immobile fraction ˜30%, but the diffusion in the mobile fraction was two times faster than that in the SLB on SiO2/Si, which had little immobile fraction.

  6. Nondisruptive micropatterning of fluid membranes through selective vesicular adsorption and rupture by nanotopography.

    PubMed

    Lee, Sang-Wook; Na, Yu-Jin; Lee, Sin-Doo

    2009-05-19

    We report on a nondisruptive method of patterning fluid membranes into micrometer-scale arrays through a selective vesicular rupture pathway by nanotopography. The site- and pathway-selective formation of supported lipid bilayers (SLBs) was achieved by different vesicular adsorption and rupture processes between nanocorrugated and nanosmooth topographies. The SLBs were first developed in the nanocorrugated region due to fast vesicular adsorption and then grew into the nanosmooth region through bilayer edge-induced vesicular rupture. Our topographic approach provides a viable scheme, yet unattainable in conventional ways, of actively controlling the position and the coverage of the SLBs on a variety of substrates without disrupting two-dimensional fluidity for highly integrated membrane devices. PMID:19368337

  7. Tunable Surface Hydrophobicity and Fluid Transport through Nanoporous Membranes

    NASA Astrophysics Data System (ADS)

    Ostrowski, Joseph H. J.

    There are more than three billion people across the globe that struggle to obtain clean drinkable water. One of the most promising avenues for generating potable water is through reverse osmosis and nanofiltration. Both solutions require a semipermeable membrane that prohibits passage of unwanted solute particles but allows passage of the solvent. Atomically thin two-dimensional membranes based on porous graphene show great promise as semipermeable materials, but modeling fluid flow on length scales between the microscopic (nanometer and smaller) and macroscopic (micron and larger) regimes presents formidable challenges. This thesis explores both equilibrium and nonequilibrium aspects of this problem and develops new methodology for simulating systems away from thermal equilibrium. First, we hypothesize that there is a wetting penalty for water as it tries to breach a sheet of graphene that should be naturally hydrophobic. By using equilibrium molecular dynamics simulations, we show that the hydrophobicity depends sensitively on the degree of electrical doping, offering an opportunity to tune the hydrophobic effect of graphene using small amounts of doping. The wetting contact angle, a measure of hydrophobicity, changes dramatically with the voltage applied to single layer graphene. We find that the sensitivity of the hydrophobic effect to voltage depends not on hydrogen bonding motifs at the interface between graphene and water, but instead on a phenomenon known as electrowetting. The theory of electrowetting predicts that the difference in surface tensions that defines the contact angle is quartic in the voltage, rather than quadratic, as it would be in bilayer graphene or in a two-dimensional metal. To explore the nonequilibrium aspects of fluid passage through atomically thin membranes, we developed a molecular dynamics methodology for simulating fluid flow at constant flux based on Gauss's principle of least constraint. This method develops microscopic

  8. Defining the free-energy landscape of curvature-inducing proteins on membrane bilayers.

    PubMed

    Tourdot, Richard W; Ramakrishnan, N; Radhakrishnan, Ravi

    2014-08-01

    Curvature-sensing and curvature-remodeling proteins, such as Amphiphysin, Epsin, and Exo70, are known to reshape cell membranes, and this remodeling event is essential for key biophysical processes such as tubulation, exocytosis, and endocytosis. Curvature-inducing proteins can act as curvature sensors; they aggregate to membrane regions matching their intrinsic curvature; as well as induce curvature in cell membranes to stabilize emergent high curvature, nonspherical, structures such as tubules, discs, and caveolae. A definitive understanding of the interplay between protein recruitment and migration, the evolution of membrane curvature, and membrane morphological transitions is emerging but remains incomplete. Here, within a continuum framework and using the machinery of Monte Carlo simulations, we introduce and compare three free-energy methods to delineate the free-energy landscape of curvature-inducing proteins on bilayer membranes. We demonstrate the utility of the Widom test particle (or field) insertion methodology in computing the excess chemical potentials associated with curvature-inducing proteins on the membrane-in particular, we use this method to track the onset of morphological transitions in the membrane at elevated protein densities. We validate this approach by comparing the results from the Widom method with those of thermodynamic integration and Bennett acceptance ratio methods. Furthermore, the predictions from the Widom method have been tested against analytical calculations of the excess chemical potential at infinite dilution. Our results are useful in precisely quantifying the free-energy landscape, and also in determining the phase boundaries associated with curvature-induction, curvature-sensing, and morphological transitions. This approach can be extended to studies exploring the role of thermal fluctuations and other external (control) variables, such as membrane excess area, in shaping curvature-mediated interactions on bilayer

  9. Lipid Bilayer-Bound Conformation of an Integral Membrane Beta Barrel Protein by Multidimensional MAS NMR

    PubMed Central

    Eddy, Matthew T.; Su, Yongchao; Silvers, Robert; Andreas, Loren; Clark, Lindsay; Wagner, Gerhard; Pintacuda, Guido; Emsley, Lyndon; Griffin, Robert G.

    2015-01-01

    The human voltage dependent anion channel 1 (VDAC) is a 32 kDa β-barrel integral membrane protein that controls the transport of ions across the outer mitochondrial membrane. Despite the determination of VDAC solution and diffraction structures, a structural basis for the mechanism of its function is not yet fully understood. Biophysical studies suggest VDAC requires a lipid bilayer to achieve full function, motivating the need for atomic resolution structural information of VDAC in a membrane environment. Here we report an essential step toward that goal: extensive assignments of backbone and side chain resonances for VDAC in DMPC lipid bilayers via magic angle spinning nuclear magnetic resonance (MAS NMR). VDAC reconstituted into DMPC lipid bilayers spontaneously forms 2-dimensional lipid crystals, showing remarkable spectral resolution (0.5–0.3 ppm for 13C line width and less than 0.5 ppm 15N line widths at 750 MHz). In addition to the benefits of working in a lipid bilayer, several distinct advantages are observed with the lipid crystalline preparation. First, the strong signals and sharp line widths facilitated extensive NMR resonance assignments for an integral membrane β-barrel protein in lipid bilayers by MAS NMR. Second, a large number of residues in loop regions were readily observed and assigned, which can be challenging in detergent-solubilized membrane proteins where loop regions are often not detected due to line broadening from conformational exchange. Third, complete backbone and side chain chemical shift assignments could be obtained for the first 25 residues, which comprise the functionally important N-terminus. The reported assignments allow us to compare predicted torsion angles for VDAC prepared in DMPC 2D lipid crystals, DMPC liposomes, and LDAO-solubilized samples to address the possible effects of the membrane mimetic environment on the conformation of the protein. Concluding, we discuss the strengths and weaknesses of the reported

  10. Lipid bilayer-bound conformation of an integral membrane beta barrel protein by multidimensional MAS NMR.

    PubMed

    Eddy, Matthew T; Su, Yongchao; Silvers, Robert; Andreas, Loren; Clark, Lindsay; Wagner, Gerhard; Pintacuda, Guido; Emsley, Lyndon; Griffin, Robert G

    2015-04-01

    The human voltage dependent anion channel 1 (VDAC) is a 32 kDa β-barrel integral membrane protein that controls the transport of ions across the outer mitochondrial membrane. Despite the determination of VDAC solution and diffraction structures, a structural basis for the mechanism of its function is not yet fully understood. Biophysical studies suggest VDAC requires a lipid bilayer to achieve full function, motivating the need for atomic resolution structural information of VDAC in a membrane environment. Here we report an essential step toward that goal: extensive assignments of backbone and side chain resonances for VDAC in DMPC lipid bilayers via magic angle spinning nuclear magnetic resonance (MAS NMR). VDAC reconstituted into DMPC lipid bilayers spontaneously forms two-dimensional lipid crystals, showing remarkable spectral resolution (0.5-0.3 ppm for (13)C line widths and <0.5 ppm (15)N line widths at 750 MHz). In addition to the benefits of working in a lipid bilayer, several distinct advantages are observed with the lipid crystalline preparation. First, the strong signals and sharp line widths facilitated extensive NMR resonance assignments for an integral membrane β-barrel protein in lipid bilayers by MAS NMR. Second, a large number of residues in loop regions were readily observed and assigned, which can be challenging in detergent-solubilized membrane proteins where loop regions are often not detected due to line broadening from conformational exchange. Third, complete backbone and side chain chemical shift assignments could be obtained for the first 25 residues, which comprise the functionally important N-terminus. The reported assignments allow us to compare predicted torsion angles for VDAC prepared in DMPC 2D lipid crystals, DMPC liposomes, and LDAO-solubilized samples to address the possible effects of the membrane mimetic environment on the conformation of the protein. Concluding, we discuss the strengths and weaknesses of the reported

  11. 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.

  12. Analysis of Ion Transport through a Single Channel of Gramicidin A in Bilayer Lipid Membranes.

    PubMed

    Kubota, Shintaro; Shirai, Osamu; Kitazumi, Yuki; Kano, Kenji

    2016-01-01

    Ion transport through a single channel of gramicidin A (GA) within the bilayer lipid membrane (BLM) between two aqueous phases (W1 and W2) has been analyzed based on the electroneutrality principle. The single-channel current increases in proportion to the magnitude of the applied membrane potential and is also dependent on the permeability coefficients of electrolyte ions (K(+) and Cl(-)). By varying the ratio of the concentration of KCl in W1 to that in W2, the ratio of the diffusion coefficient of K(+) in the BLM to that of Cl(-) in the BLM can be evaluated. PMID:26860564

  13. Salt-bridge-supported bilayer lipid membrane biosensor for determination of anticancer drug cyclophosphamide

    NASA Astrophysics Data System (ADS)

    Zhang, Yanli; Wang, Tao; Zhang, Chunxu; Shen, Hanxi; Chao, Fuhuan

    2001-09-01

    A novel biosensor for assaying anticancer drug cyclophosphamide was constructed with salt-bridge supported bilayer lipid membrane modified with tetraphenylborate- cyclophosphamide complex. The modification was achieved by the introduction of the complex into the membrane forming solution. The biosensor show a linear response to the drug over the concentration range 8.96 X 10-6 mol L-1. The effects of coexistent substances and pH on assay were evaluated. The results show that the distinguish merits of this kind of biosensor is the excellently biological compatibility and no need of mediator for ions exchange. It also shows good selectivity and sensitivity for cyclophosphamide assay.

  14. 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.

  15. Fuel cell membrane hydration and fluid metering

    DOEpatents

    Jones, Daniel O.; Walsh, Michael M.

    1999-01-01

    A hydration system includes fuel cell fluid flow plate(s) and injection port(s). Each plate has flow channel(s) with respective inlet(s) for receiving respective portion(s) of a given stream of reactant fluid for a fuel cell. Each injection port injects a portion of liquid water directly into its respective flow channel in order to mix its respective portion of liquid water with the corresponding portion of the stream. This serves to hydrate at least corresponding part(s) of a given membrane of the corresponding fuel cell(s). The hydration system may be augmented by a metering system including flow regulator(s). Each flow regulator meters an injecting at inlet(s) of each plate of respective portions of liquid into respective portion(s) of a given stream of fluid by corresponding injection port(s).

  16. Fuel cell membrane hydration and fluid metering

    DOEpatents

    Jones, Daniel O.; Walsh, Michael M.

    2003-01-01

    A hydration system includes fuel cell fluid flow plate(s) and injection port(s). Each plate has flow channel(s) with respective inlet(s) for receiving respective portion(s) of a given stream of reactant fluid for a fuel cell. Each injection port injects a portion of liquid water directly into its respective flow channel. This serves to hydrate at least corresponding part(s) of a given membrane of the corresponding fuel cell(s). The hydration system may be augmented by a metering system including flow regulator(s). Each flow regulator meters an injecting at inlet(s) of each plate of respective portions of liquid into respective portion(s) of a given stream of fluid by corresponding injection port(s).

  17. Bathroom greywater recycling using polyelectrolyte-complex bilayer membrane: Advanced study of membrane structure and treatment efficiency.

    PubMed

    Oh, K S; Poh, P E; Chong, M N; Chan, E S; Lau, E V; Saint, C P

    2016-09-01

    Polyelectrolyte-complex bilayer membrane (PCBM) was fabricated using biodegradable chitosan and alginate polymers for subsequent application in the treatment of bathroom greywater. In this study, the properties of PCBMs were studied and it was found that the formation of polyelectrolyte network reduced the molecular weight cut-off (MWCO) from 242kDa in chitosan membrane to 2.71kDa in PCBM. The decrease in MWCO of PCBM results in better greywater treatment efficiency, subsequently demonstrated in a greywater filtration study where treated greywater effluent met the household reclaimed water standard of <2 NTU turbidity and <30ppm total suspended solids (TSS). In addition, a further 20% improvement in chemical oxygen demand (COD) removal was achieved as compared to a single layer chitosan membrane. Results from this study show that the biodegradable PCBM is a potential membrane material in producing clean treated greywater for non-potable applications. PMID:27185127

  18. Defining the free-energy landscape of curvature-inducing proteins on membrane bilayers

    NASA Astrophysics Data System (ADS)

    Tourdot, Richard W.; Ramakrishnan, N.; Radhakrishnan, Ravi

    2014-08-01

    Curvature-sensing and curvature-remodeling proteins, such as Amphiphysin, Epsin, and Exo70, are known to reshape cell membranes, and this remodeling event is essential for key biophysical processes such as tubulation, exocytosis, and endocytosis. Curvature-inducing proteins can act as curvature sensors; they aggregate to membrane regions matching their intrinsic curvature; as well as induce curvature in cell membranes to stabilize emergent high curvature, nonspherical, structures such as tubules, discs, and caveolae. A definitive understanding of the interplay between protein recruitment and migration, the evolution of membrane curvature, and membrane morphological transitions is emerging but remains incomplete. Here, within a continuum framework and using the machinery of Monte Carlo simulations, we introduce and compare three free-energy methods to delineate the free-energy landscape of curvature-inducing proteins on bilayer membranes. We demonstrate the utility of the Widom test particle (or field) insertion methodology in computing the excess chemical potentials associated with curvature-inducing proteins on the membrane—in particular, we use this method to track the onset of morphological transitions in the membrane at elevated protein densities. We validate this approach by comparing the results from the Widom method with those of thermodynamic integration and Bennett acceptance ratio methods. Furthermore, the predictions from the Widom method have been tested against analytical calculations of the excess chemical potential at infinite dilution. Our results are useful in precisely quantifying the free-energy landscape, and also in determining the phase boundaries associated with curvature-induction, curvature-sensing, and morphological transitions. This approach can be extended to studies exploring the role of thermal fluctuations and other external (control) variables, such as membrane excess area, in shaping curvature-mediated interactions on bilayer

  19. Defining the free-energy landscape of curvature-inducing proteins on membrane bilayers

    PubMed Central

    Tourdot, Richard W.; Ramakrishnan, N.; Radhakrishnan, Ravi

    2015-01-01

    Curvature-sensing and curvature-remodeling proteins, such as Amphiphysin, Epsin, and Exo70, are known to reshape cell membranes, and this remodeling event is essential for key biophysical processes such as tubulation, exocytosis, and endocytosis. Curvature-inducing proteins can act as curvature sensors; they aggregate to membrane regions matching their intrinsic curvature; as well as induce curvature in cell membranes to stabilize emergent high curvature, nonspherical, structures such as tubules, discs, and caveolae. A definitive understanding of the interplay between protein recruitment and migration, the evolution of membrane curvature, and membrane morphological transitions is emerging but remains incomplete. Here, within a continuum framework and using the machinery of Monte Carlo simulations, we introduce and compare three free-energy methods to delineate the free-energy landscape of curvature-inducing proteins on bilayer membranes. We demonstrate the utility of the Widom test particle (or field) insertion methodology in computing the excess chemical potentials associated with curvature-inducing proteins on the membrane—in particular, we use this method to track the onset of morphological transitions in the membrane at elevated protein densities. We validate this approach by comparing the results from the Widom method with those of thermodynamic integration and Bennett acceptance ratio methods. Furthermore, the predictions from the Widom method have been tested against analytical calculations of the excess chemical potential at infinite dilution. Our results are useful in precisely quantifying the free-energy landscape, and also in determining the phase boundaries associated with curvature-induction, curvature-sensing, and morphological transitions. This approach can be extended to studies exploring the role of thermal fluctuations and other external (control) variables, such as membrane excess area, in shaping curvature-mediated interactions on bilayer

  20. 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

  1. Amphipathic amines affect membrane excitability in paramecium: role for bilayer couple.

    PubMed

    Browning, J L; Nelson, D L

    1976-02-01

    Amphipathic amines and local anesthetics stimulated reversal of the ciliary beating direction in wild-type Paramecium. Ca++ influx across the surface membrane and the consequent increase in internal Ca++ causes ciliary reversal and backward swimming. Mutant cells of the "Pawn" class, which lack a "gating" mechanism for regulating Ca++ influx, did not swim backwards in the presence of local anesthetics. Local anesthetics stimulated the passive efflux of K+ but had no effect on the active transport of K+ or Ca++. Apparently passive influx of Ca++ also was stimulated by local anesthetics as evidenced by their effects on swimming direction. These data can be interpreted in terms of the "bilayer couple" hypothesis of Sheetz and Singer [(1974) Proc. Nat. Acad. Sci. USA 71, 4457-4461]: amphipathic drugs affect cells by asymmetric insertion into one face of the lipid bilayer. As predicted by this hypothesis, the drugs' effects were seen only after a short time lag, and quaternary amines were less effective than tertiary amines. The effect on behavior was caused by any of several amphipathic cations, and the relative potency was a function of their hydrophobicity. Amphipathic anions, which according to the hypothesis would insert into the opposite face of the lipid bilayer, had little effect on ciliary reversal. Asymmetric perturbation of the lipid bilayer with amphipathic cations may trigger the opening of the Ca++ gate. PMID:1061147

  2. Magnetically Aligned Bicelles to Study the Orientation of Lipophilic Ligands in Membrane Bilayers

    PubMed Central

    Guo, Jianxin; Yang, De-Ping; Chari, Ravi; Tian, Xiaoyu; Pavlopoulos, Spiro; Lu, Dai; Makriyannis, Alexandros

    2013-01-01

    Magnetically aligned bicelles were used as a model membrane to study the orientation and dynamic properties of two cannabinoids (Δ8-THC and Me-Δ8-THC) using 31P- and 2H-NMR. The uniform alignment of the bicelles allowed us to obtain well resolved deuterium spectra from a solution NMR spectrometer. The preferred orientations of Δ8-THC and Me-Δ8-THC were calculated based on the measurements of individual quadrupolar splittings. Our results agree with previous experiments using multilamellar membranes as well as with molecular dynamics simulation data described here. In conjunction with our earlier report using small and fast tumbling bicelles, the present work of well aligned bicelles shows that bicelle preparations can provide either pseudo-isotropic or anisotropic NMR spectra to study the conformation, orientation and dynamic properties of ligands in membrane bilayers. Such data are of critical value for understanding the interactions of lipophilic drug molecules with membrane proteins. PMID:18834109

  3. Using supported bilayers to study the spatiotemporal organization of membrane bound proteins

    PubMed Central

    Field, Christine M.; Groen, Aaron C.; Mitchison, Timothy J.

    2015-01-01

    Cell division in prokaryotes and eukaryotes is commonly initiated by the well-controlled binding of proteins to the cytoplasmic side of the cell membrane. However, a precise characterization of the spatiotemporal dynamics of membrane-bound proteins is often difficult to achieve in vivo. Here, we present protocols for the use of supported lipid bilayers to rebuild the cytokinetic machineries of cells with greatly different dimensions: the bacterium Escherichia coli and eggs of the vertebrate Xenopus laevis. Combined with total internal reflection fluorescence (TIRF) microscopy, these experimental setups allow for precise quantitative analyses of membrane-bound proteins. The protocols described to obtain glass-supported membranes from bacterial and vertebrate lipids can be used as starting points for other reconstitution experiments. We believe that similar biochemical assays will be instrumental to study the biochemistry and biophysics underlying a variety of complex cellular tasks, such as signaling, vesicle trafficking and cell motility. PMID:25997350

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

    PubMed Central

    Jeuken, Lars J. C.

    2008-01-01

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

  5. 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

  6. Immobilization and activity assay of cytochrome P450 on patterned lipid membranes

    SciTech Connect

    Ueda, Yoshihiro; Morigaki, Kenichi . E-mail: morigaki-kenichi@aist.go.jp; Tatsu, Yoshiro; Yumoto, Noboru; Imaishi, Hiromasa . E-mail: himaish@kobe-u.ac.jp

    2007-04-20

    We report on a methodology for immobilizing cytochrome P450 on the surface of micropatterned lipid bilayer membranes and measuring the enzymatic activity. The patterned bilayer comprised a matrix of polymeric lipid bilayers and embedded fluid lipid bilayers. The polymeric lipid bilayer domains act as a barrier to confine fluid lipid bilayers in defined areas and as a framework to stabilize embedded membranes. The fluid bilayer domains, on the other hand, can contain lipid compositions that facilitate the fusion between lipid membranes, and are intended to be used as the binding agent of microsomes containing rat CYP1A1. By optimizing the membrane compositions of the fluid bilayers, we could selectively immobilize microsomal membranes on these domains. The enzymatic activity was significantly higher on lipid bilayer substrates compared with direct adsorption on glass. Furthermore, competitive assay experiment between two fluorogenic substrates demonstrated the feasibility of bioassays based on immobilized P450s.

  7. Immobilization and activity assay of cytochrome P450 on patterned lipid membranes.

    PubMed

    Ueda, Yoshihiro; Morigaki, Kenichi; Tatsu, Yoshiro; Yumoto, Noboru; Imaishi, Hiromasa

    2007-04-20

    We report on a methodology for immobilizing cytochrome P450 on the surface of micropatterned lipid bilayer membranes and measuring the enzymatic activity. The patterned bilayer comprised a matrix of polymeric lipid bilayers and embedded fluid lipid bilayers. The polymeric lipid bilayer domains act as a barrier to confine fluid lipid bilayers in defined areas and as a framework to stabilize embedded membranes. The fluid bilayer domains, on the other hand, can contain lipid compositions that facilitate the fusion between lipid membranes, and are intended to be used as the binding agent of microsomes containing rat CYP1A1. By optimizing the membrane compositions of the fluid bilayers, we could selectively immobilize microsomal membranes on these domains. The enzymatic activity was significantly higher on lipid bilayer substrates compared with direct adsorption on glass. Furthermore, competitive assay experiment between two fluorogenic substrates demonstrated the feasibility of bioassays based on immobilized P450s. PMID:17335776

  8. Distribution and dynamics of quinones in the lipid bilayer mimicking the inner membrane of mitochondria.

    PubMed

    Kaurola, Petri; Sharma, Vivek; Vonk, Amanda; Vattulainen, Ilpo; Róg, Tomasz

    2016-09-01

    Quinone and its analogues (Q) constitute an important class of compounds that perform key electron transfer reactions in oxidative- and photo-phosphorylation. In the inner membrane of mitochondria, ubiquinone molecules undergo continuous redox transitions enabling electron transfer between the respiratory complexes. In such a dynamic system undergoing continuous turnover for ATP synthesis, an uninterrupted supply of substrate molecules is absolutely necessary. In the current work, we have performed atomistic molecular dynamics simulations and free energy calculations to assess the structure, dynamics, and localization of quinone and its analogues in a lipid bilayer, whose composition mimics the one in the inner mitochondrial membrane. The results show that there is a strong tendency of both quinone and quinol molecules to localize in the vicinity of the lipids' acyl groups, right under the lipid head group region. Additionally, we observe a second location in the middle of the bilayer where quinone molecules tend to stabilize. Translocation of quinone through a lipid bilayer is very fast and occurs in 10-100ns time scale, whereas the translocation of quinol is at least an order of magnitude slower. We suggest that this has important mechanistic implications given that the localization of Q ensures maximal occupancy of the Q-binding sites or Q-entry points in electron transport chain complexes, thereby maintaining an optimal turnover rate for ATP synthesis. PMID:27342376

  9. 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

  10. 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

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

    PubMed Central

    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

  12. The bilayer enhances rhodopsin kinetic stability in bovine rod outer segment disk membranes.

    PubMed

    Corley, Scott C; Sprangers, Peter; Albert, Arlene D

    2011-06-22

    Rhodopsin is a kinetically stable protein constituting >90% of rod outer segment disk membrane protein. To investigate the bilayer contribution to rhodopsin kinetic stability, disk membranes were systematically disrupted by octyl-β-D-glucopyranoside. Rhodopsin kinetic stability was examined under subsolubilizing (rhodopsin in a bilayer environment perturbed by octyl-β-D-glucopyranoside) and under fully solubilizing conditions (rhodopsin in a micelle with cosolubilized phospholipids). As determined by DSC, rhodopsin exhibited a scan-rate-dependent irreversible endothermic transition at all stages of solubilization. The transition temperature (T(m)) decreased in the subsolubilizing stage. However, once the rhodopsin was in a micelle environment there was little change of the T(m) as the phospholipid/rhodopsin ratio in the mixed micelles decreased during the fully solubilized stage. Rhodopsin thermal denaturation is consistent with the two-state irreversible model at all stages of solubilization. The activation energy of denaturation (E(act)) was calculated from the scan rate dependence of the T(m) and from the rate of rhodopsin thermal bleaching at all stages of solubilization. The E(act) as determined by both techniques decreased in the subsolubilizing stage, but remained constant once fully solubilized. These results indicate the bilayer structure increases the E(act) to rhodopsin denaturation. PMID:21689528

  13. Effect of antimicrobial peptide on the dynamics of phosphocholine membrane: role of cholesterol and physical state of bilayer.

    PubMed

    Sharma, V K; Mamontov, E; Anunciado, D B; O'Neill, H; Urban, V S

    2015-09-14

    Antimicrobial peptides are universal in all forms of life and are well known for their strong interaction with the cell membrane. This makes them a popular target for investigation of peptide-lipid interactions. Here we report the effect of melittin, an important antimicrobial peptide, on the dynamics of membranes based on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid in both the solid gel and fluid phases. To probe the phase transition, elastic neutron intensity temperature scans have been carried out on DMPC-based unilamellar vesicles (ULV) with and without melittin. We have found that addition of a small amount (0.2 mol%) melittin eliminates the steep fall in the elastic intensity at 296 K associated with the solid gel to fluid phase transition, which is observed for pure DMPC vesicles. Quasielastic neutron scattering (QENS) experiments have been carried out on DMPC ULV in the solid gel and fluid phases with and without 0.2 mol% melittin. The data analysis invariably shows the presence of lateral and internal motions of the DMPC molecule. We found that melittin does have a profound effect on the dynamics of lipid molecules, especially on the lateral motion, and affects it in a different way, depending on the phase of the bilayers. In the solid gel phase, it acts as a plasticizer, enhancing the lateral motion of DMPC. However, in the fluid phase it acts as a stiffening agent, restricting the lateral motion of the lipid molecules. These observations are consistent with the mean squared displacements extracted from the elastic intensity temperature scans. Their importance lies in the fact that many membrane processes, including signaling and energy transduction pathways, are controlled to a great extent by the lateral diffusion of lipids in the membrane. To investigate the effect of melittin on vesicles supplemented with cholesterol, QENS experiments have also been carried out on DMPC ULV with cholesterol in the presence and absence of 0.2 mol% melittin

  14. Aspirin, acetaminophen and proton transport through phospholipid bilayers and mitochondrial membranes.

    PubMed

    Gutknecht, J

    1992-09-01

    Mechanisms of proton transport were investigated in planar phospholipid bilayer membranes exposed to aspirin (acetylsalicylic acid), acetaminophen (4-acetamidophenol), benzoic acid and three aspirin metabolites (salicylic acid, gentisic acid and salicyluric acid). The objectives were to characterize the conductances and permeabilities of these weak acids in lipid bilayer membranes and then predict their effects on mitochondrial membranes. Of the compounds tested only aspirin, benzoate and salicylate caused significant increases in membrane conductance. The conductance was due mainly to proton current at low pH and to weak acid anion current at neutral pH. Analysis of the concentration and pH dependence suggests that these weak acids act as HA-2-type proton carriers when pH approximately pK and as lipid soluble anions at neutral pH. Salicylate is much more potent than aspirin and benzoate because salicylate contains an internal hydrogen bond which delocalizes the negative charge and increases the permeability of the anion. Model calculations for mitochondria suggest that salicylate causes net H+ uptake by a cyclic process of HA influx and A- efflux. This model can explain the salicylate-induced uncoupling and swelling observed in isolated mitochondria. Since ingested aspirin breaks down rapidly to form salicylate, these results may clarify the mechanisms of aspirin toxicity in humans. The results may also help to explain why the ingestion of aspirin but not acetaminophen is associated with Reye's syndrome, a disease characterized by impaired energy metabolism and mitochondrial swelling. PMID:1334228

  15. Arrayed lipid bilayer chambers allow single-molecule analysis of membrane transporter activity

    PubMed Central

    Watanabe, Rikiya; Soga, Naoki; Fujita, Daishi; Tabata, Kazuhito V.; Yamauchi, Lisa; Hyeon Kim, Soo; Asanuma, Daisuke; Kamiya, Mako; Urano, Yasuteru; Suga, Hiroaki; Noji, Hiroyuki

    2014-01-01

    Nano- to micron-size reaction chamber arrays (femtolitre chamber arrays) have facilitated the development of sensitive and quantitative biological assays, such as single-molecule enzymatic assays, digital PCR and digital ELISA. However, the versatility of femtolitre chamber arrays is limited to reactions that occur in aqueous solutions. Here we report an arrayed lipid bilayer chamber system (ALBiC) that contains sub-million femtolitre chambers, each sealed with a stable 4-μm-diameter lipid bilayer membrane. When reconstituted with a limiting amount of the membrane transporter proteins α-hemolysin or F0F1-ATP synthase, the chambers within the ALBiC exhibit stochastic and quantized transporting activities. This demonstrates that the single-molecule analysis of passive and active membrane transport is achievable with the ALBiC system. This new platform broadens the versatility of femtolitre chamber arrays and paves the way for novel applications aimed at furthering our mechanistic understanding of membrane proteins’ function. PMID:25058452

  16. Voltage-sensitive styryl dyes as singlet oxygen targets on the surface of bilayer lipid membrane.

    PubMed

    Sokolov, V S; Gavrilchik, A N; Kulagina, A O; Meshkov, I N; Pohl, P; Gorbunova, Yu G

    2016-08-01

    Photosensitizers are widely used as photodynamic therapeutic agents killing cancer cells by photooxidation of their components. Development of new effective photosensitive molecules requires profound knowledge of possible targets for reactive oxygen species, especially for its singlet form. Here we studied photooxidation of voltage-sensitive styryl dyes (di-4-ANEPPS, di-8-ANEPPS, RH-421 and RH-237) by singlet oxygen on the surface of bilayer lipid membranes commonly used as cell membrane models. Oxidation was induced by irradiation of a photosensitizer (aluminum phthalocyanine tetrasulfonate) and monitored by the change of dipole potential on the surface of the membrane. We studied the drop of the dipole potential both in the case when the dye molecules were adsorbed on the same side of the lipid bilayer as the photosensitizer (cis-configuration) and in the case when they were adsorbed on the opposite side (trans-configuration). Based on a simple model, we determined the rate of oxidation of the dyes from the kinetics of change of the potential during and after irradiation. This rate is proportional to steady-state concentration of singlet oxygen in the membrane under irradiation. Comparison of the oxidation rates of various dyes reveals that compounds of ANEPPS series are more sensitive to singlet oxygen than RH type dyes, indicating that naphthalene group is primarily responsible for their oxidation. PMID:27236238

  17. PTEN interaction with tethered bilayer lipid membranes containing PI(4,5)P2

    NASA Astrophysics Data System (ADS)

    Moldovan, R.; Shenoy, S.; Shekhar, P.; Kalinowski, A.; Gericke, A.; Heinrich, F.; Loesche, M.

    2009-03-01

    Synthetic lipid membrane models are frequently used for the study of biophysical processes at cell membranes. We use a robust membrane model, the tethered bilayer lipid membrane (tBLM), based on a (C14)2-(PEO)6-thiol anchor, WC14 [1]. Such membranes can be prepared to contain single phospholipids or complex lipid mixtures [2], including functional lipids involved in cell signaling, such as the highly charged phosphatidylinositol phosphates (PIPs). To study the interaction between the tumor suppressor PTEN (phosphatase and tensin homologue deleted on chromosome 10) and model membranes we have incorporated phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) in tBLMs and use fluorescence correlation spectroscopy (FCS), neutron reflectometry (NR) and surface plasmon resonance (SPR) for their characterization. NR shows that tBLMs formed with PI(4,5)P2 are complete. FCS of labeled PI(4,5)P2 shows that diffusion occurs at the time scale characteristic of membrane-incorporated lipid. Finally, SPR shows specific binding of PTEN to the model membrane thus confirming the incorporation of PI(4,5)P2 into the tBLM. [1] McGillivray et al, Biointerphases 2, 21-33 (2007) [2] Heinrich et al, Langmuir, submitted

  18. Fluid bilayer structure determination: Joint refinement in composition space using X-ray and neutron diffraction data

    SciTech Connect

    White, S.H.; Wiener, M.C.

    1994-12-31

    Experimentally-determined structural models of fluid lipid bilayers are essential for verifying molecular dynamics simulations of bilayers and for understanding the structural consequences of peptide interactions. The extreme thermal motion of bilayers precludes the possibility of atomic-level structural models. Defining {open_quote}the structure{close_quote} of a bilayer as the time-averaged transbilayer distribution of the water and the principal lipid structural groups such as the carbonyls and double-bonds (quasimolecular fragments), one can represent the bilayer structure as a sum of Gaussian functions referred to collectively as the quasimolecular structure. One method of determining the structure is by neutron diffraction combined with exhaustive specific deuteration. This method is impractical because of the expense of the chemical syntheses and the limited amount of neutron beam time currently available. We have therefore developed the composition space refinement method for combining X-ray and minimal neutron diffraction data to arrive at remarkably detailed and accurate structures of fluid bilayers. The composition space representation of the bilayer describes the probability of occupancy per unit length across the width of the bilayer of each quasimolecular component and permits the joint refinement of X-ray and neutron lamellar diffraction data by means of a single quasimolecular structure that is fitted simultaneously to both data sets. Scaling of each component by the appropriate neutron or X-ray scattering length maps the composition-space profile to the appropriate scattering length space for comparison to experimental data. The difficulty with the method is that fluid bilayer structures are generally only marginally determined by the experimental data. This means that the space of possible solutions must be extensively explored in conjunction with a thorough analysis of errors.

  19. Phospholipid vesicle fusion on micropatterned polymeric bilayer substrates.

    PubMed

    Okazaki, Takashi; Morigaki, Kenichi; Taguchi, Takahisa

    2006-09-01

    As an approach to create versatile model systems of the biological membrane we have recently developed a novel micropatterning strategy of substrate-supported planar lipid bilayers (SPBs) based on photolithographic polymerization of a diacetylene phospholipid, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine. The micropatterned SPBs are composed of a polymeric bilayer matrix and embedded fluid lipid bilayers. In this study, we investigated the incorporation of fluid bilayers into micropatterned polymeric bilayer matrices through the adsorption and reorganization of phospholipid vesicles (vesicle fusion). Total internal reflection fluorescence microscopy observation showed that vesicle fusion started at the boundary of polymeric bilayers and propagated into the central part of lipid-free regions. On the other hand, quartz crystal microbalance with dissipation monitoring revealed that the transformation from adsorbed vesicles into SPBs was significantly accelerated for substrates with micropatterned polymeric bilayers. These results indicate that the edges of polymeric bilayers catalyze the formation of SPBs by destabilizing adsorbed vesicles and also support the premise that polymeric bilayers and embedded fluid bilayers are forming a continuous hybrid bilayer membrane, sealing energetically unfavorable bilayer edges. PMID:16766614

  20. Effect of Antimicrobial Peptide on Dynamics of Phosphocholine Membrane. Role of Cholesterol and Physical State of Bilayer

    DOE PAGESBeta

    Sharma, Veerendra K; Mamontov, Eugene; Anunciado, Divina B; O'Neill, Hugh Michael; Urban, Volker S

    2015-06-24

    Antimicrobial peptides are universal in all forms of life and are well known for their strong interaction with the cell membrane. This makes them a popular target for investigation of peptide-lipid interactions. Here we report the effect of melittin, an important antimicrobial peptide, on the dynamics of membranes based on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid in both the solid gel and fluid phases. To probe the phase transition, elastic neutron intensity temperature scans have been carried out on DMPC-based unilamellar vesicles (ULV) with and without melittin. We have found that addition of a small amount (0.2 mol%) melittin eliminates the steep fallmore » in the elastic intensity at 296 K associated with the solid gel to fluid phase transition, which is observed for pure DMPC vesicles. Quasielastic neutron scattering (QENS) experiments have been carried out on DMPC ULV in the solid gel and fluid phases with and without 0.2 mol % melittin. The data analysis invariably shows the presence of lateral and internal motions of the DMPC molecule. We found that melittin does have a profound effect on the dynamics of lipid molecules, especially on the lateral motion, and affects it in a different way, depending on the phase of the bilayers. In the solid gel phase, it acts as a plasticizer, enhancing the lateral motion of DMPC. However, in the fluid phase it acts as a stiffening agent, restricting the lateral motion of the lipid molecules. These observations are consistent with the mean squared displacements extracted from the elastic intensity temperature scans. Cholesterol is a vital component of eukaryotic membrane, which is a natural target for melittin. To investigate the effect of melittin on vesicles supplemented with cholesterol, QENS experiments have also been carried out on DMPC ULV with 20 mol% cholesterol in the presence and absence of 0.2 mol% melittin. Remarkably, the effects of melittin on the membrane dynamics disappear in the presence

  1. Effect of Antimicrobial Peptide on Dynamics of Phosphocholine Membrane. Role of Cholesterol and Physical State of Bilayer

    SciTech Connect

    Sharma, Veerendra K; Mamontov, Eugene; Anunciado, Divina B; O'Neill, Hugh Michael; Urban, Volker S

    2015-06-24

    Antimicrobial peptides are universal in all forms of life and are well known for their strong interaction with the cell membrane. This makes them a popular target for investigation of peptide-lipid interactions. Here we report the effect of melittin, an important antimicrobial peptide, on the dynamics of membranes based on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid in both the solid gel and fluid phases. To probe the phase transition, elastic neutron intensity temperature scans have been carried out on DMPC-based unilamellar vesicles (ULV) with and without melittin. We have found that addition of a small amount (0.2 mol%) melittin eliminates the steep fall in the elastic intensity at 296 K associated with the solid gel to fluid phase transition, which is observed for pure DMPC vesicles. Quasielastic neutron scattering (QENS) experiments have been carried out on DMPC ULV in the solid gel and fluid phases with and without 0.2 mol % melittin. The data analysis invariably shows the presence of lateral and internal motions of the DMPC molecule. We found that melittin does have a profound effect on the dynamics of lipid molecules, especially on the lateral motion, and affects it in a different way, depending on the phase of the bilayers. In the solid gel phase, it acts as a plasticizer, enhancing the lateral motion of DMPC. However, in the fluid phase it acts as a stiffening agent, restricting the lateral motion of the lipid molecules. These observations are consistent with the mean squared displacements extracted from the elastic intensity temperature scans. Cholesterol is a vital component of eukaryotic membrane, which is a natural target for melittin. To investigate the effect of melittin on vesicles supplemented with cholesterol, QENS experiments have also been carried out on DMPC ULV with 20 mol% cholesterol in the presence and absence of 0.2 mol% melittin. Remarkably, the effects of melittin on the membrane dynamics disappear in the presence of 20 mol

  2. Structure elucidation of membrane-associated peptides and proteins in oriented bilayers by solid-state NMR spectroscopy.

    PubMed

    Naito, Akira

    2009-10-01

    Solid-state NMR using magnetically oriented bilayer systems provides useful information on the structure and orientation of peptides and proteins bound to lipid bilayers. The ordering of the lipid bilayer along the magnetic field can be achieved in two ways. First, lipid can be macroscopically oriented by pressing lipid-water dispersion between flat glass plates, which is called a mechanically aligned system. Second, lipid molecules themselves can be aligned spontaneously in the magnetic field because of their diamagnetic anisotropy by forming bicelles or magnetically oriented vesicle systems. Structure and orientation of the membrane-associated peptides and proteins can be achieved by analyzing structural constraints obtained from anisotropic chemical shift interactions such as chemical shift oscillation or nuclear dipolar interactions such as dipolar wave and a combination of them such as PISA wheel. Detailed structure elucidation of various kinds of membrane peptides and proteins in such oriented bilayers is presented. PMID:19647984

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  4. Capturing the nanoscale complexity of cellular membranes in supported lipid bilayers

    PubMed Central

    2010-01-01

    The lateral mobility of cell membranes plays an important role in cell signaling, governing the rate at which embedded proteins can interact with other biomolecules. The past two decades have seen a dramatic transformation in understanding of this environment, as the mechanisms and potential implications of nanoscale structure of these systems has become accessible to theoretical and experimental investigation. In particular, emerging micro- and nano-scale fabrication techniques have made possible the direct manipulation of model membranes at the scales relevant to these biological processes. This review focuses on recent advances in nanopatterning of supported lipid bilayers, capturing the impact of membrane nanostructure on molecular diffusion and providing a powerful platform for further investigation of the role of this spatial complexity on cell signaling. PMID:19500676

  5. Fluctuation spectrum of fluid membranes coupled to an elastic meshwork: jump of the effective surface tension at the mesh size.

    PubMed

    Fournier, Jean-Baptiste; Lacoste, David; Raphaël, Elie

    2004-01-01

    We identify a class of composite membranes: fluid bilayers coupled to an elastic meshwork that are such that the meshwork's energy is a function F(el)[A(xi)] not of the real microscopic membrane area A, but of a smoothed membrane's area A(xi), which corresponds to the area of the membrane coarse grained at the mesh size xi. We show that the meshwork modifies the membrane tension sigma both below and above the scale xi, inducing a steep crossover of amplitude deltasigma=dF(el)/dA(xi). The predictions of our model account for the fluctuation spectrum of red blood cell membranes coupled to their cytoskeleton. Our results indicate that the cytoskeleton might be under extensional stress, which would provide a means to regulate available membrane areas. We also predict an observable tension jump for membranes decorated with polymer "brushes." PMID:14754023

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  7. Spreading-wetting method for highly reproducible tertiary growth of perfective bilayer TS-1 membranes

    NASA Astrophysics Data System (ADS)

    Liu, Xuguang; Liu, Yong; Xu, Lei; Zhang, Baoquan; Ma, Laibo

    2015-07-01

    Spreading-wetting method is adopted to seed a support for tertiary growth of hydrophobic TS-1 membrane. It deposits the seed on the macro-hole of the support and results in a dispersive seed distribution. This enables a highly reproducible preparation of the perfective TS-1 membrane, revealed by SEM as a bilayer structure. An intermediate layer of the TS-1 membrane avoids the leaching of Al from the support and ensures the upper layer as the pure hydrophobic TS-1 membrane, proved by XRD, EDS, and water contact angle measurements. Another important advance about the TS-1 membrane is employing a Pd/SiO2 catalytic hydrocracking method to activate it at 593 K. Such a mild method favors maintaining that perfective macrostructure and hydrophobicity. Bearing the thermal stress, generated during the activation process, desires the TS-1 membrane with a sufficient thickness, gained by prolonging the crystallization time. This phenomenon is verified by gas permeation and ascribed with the membrane's mechanical properties.

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

    PubMed

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

    2007-02-01

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

  9. Conformational Transitions in the Membrane Scaffold Protein of Phospholipid Bilayer Nanodiscs*

    PubMed Central

    Morgan, Christopher R.; Hebling, Christine M.; Rand, Kasper D.; Stafford, Darrel W.; Jorgenson, James W.; Engen, John R.

    2011-01-01

    Phospholipid bilayer nanodiscs are model membrane systems that provide an environment where membrane proteins are highly stable and monodisperse without the use of detergents or liposomes. Nanodiscs consist of a discoidal phospholipid bilayer encircled by two copies of an amphipathic alpha helical membrane scaffold protein, which is modeled from apolipoprotein A-1. Hydrogen exchange mass spectrometry was used to probe the structure and dynamics of the scaffold protein in the presence and absence of lipid. On nanodisc self-assembly, the entire scaffold protein gained significant protection from exchange, consistent with a large, protein-wide, structural rearrangement. This protection was short-lived and the scaffold protein was highly deuterated within 2 h. Several regions of the scaffold protein, in both the lipid-free and lipid-associated states, displayed EX1 unfolding kinetics. The rapid deuteration of the scaffold protein and the presence of correlated unfolding events both indicate that nanodiscs are dynamic rather than rigid bodies in solution. This work provides a catalog of the expected scaffold protein peptic peptides in a nanodisc-hydrogen exchange mass spectrometry experiment and their deuterium uptake signatures, data that can be used as a benchmark to verify correct assembly and nanodisc structure. Such reference data will be useful control data for all hydrogen exchange mass spectrometry experiments involving nanodiscs in which transmembrane or lipid-associated proteins are the primary molecule(s) of interest. PMID:21715319

  10. Three-dimensional structure of Bax-mediated pores in membrane bilayers

    PubMed Central

    Xu, X-P; Zhai, D; Kim, E; Swift, M; Reed, J C; Volkmann, N; Hanein, D

    2013-01-01

    B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax) is a member of the Bcl-2 protein family having a pivotal role in triggering cell commitment to apoptosis. Bax is latent and monomeric in the cytosol but transforms into its lethal, mitochondria-embedded oligomeric form in response to cell stress, leading to the release of apoptogenic factors such as cytochrome C. Here, we dissected the structural correlates of Bax membrane insertion while oligomerization is halted. This strategy was enabled through the use of nanometer-scale phospholipid bilayer islands (nanodiscs) the size of which restricts the reconstituted system to single Bax-molecule activity. Using this minimal reconstituted system, we captured structural correlates that precede Bax homo-oligomerization elucidating previously inaccessible steps of the core molecular mechanism by which Bcl-2 family proteins regulate membrane permeabilization. We observe that, in the presence of BH3 interacting domain death agonist (Bid) BH3 peptide, Bax monomers induce the formation of ∼3.5-nm diameter pores and significantly distort the phospholipid bilayer. These pores are compatible with promoting release of ions as well as proteinaceous components, suggesting that membrane-integrated Bax monomers in the presence of Bid BH3 peptides are key functional units for the activation of the cell demolition machinery. PMID:23788040

  11. Three-dimensional structure of Bax-mediated pores in membrane bilayers.

    PubMed

    Xu, X-P; Zhai, D; Kim, E; Swift, M; Reed, J C; Volkmann, N; Hanein, D

    2013-01-01

    B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax) is a member of the Bcl-2 protein family having a pivotal role in triggering cell commitment to apoptosis. Bax is latent and monomeric in the cytosol but transforms into its lethal, mitochondria-embedded oligomeric form in response to cell stress, leading to the release of apoptogenic factors such as cytochrome C. Here, we dissected the structural correlates of Bax membrane insertion while oligomerization is halted. This strategy was enabled through the use of nanometer-scale phospholipid bilayer islands (nanodiscs) the size of which restricts the reconstituted system to single Bax-molecule activity. Using this minimal reconstituted system, we captured structural correlates that precede Bax homo-oligomerization elucidating previously inaccessible steps of the core molecular mechanism by which Bcl-2 family proteins regulate membrane permeabilization. We observe that, in the presence of BH3 interacting domain death agonist (Bid) BH3 peptide, Bax monomers induce the formation of ~3.5-nm diameter pores and significantly distort the phospholipid bilayer. These pores are compatible with promoting release of ions as well as proteinaceous components, suggesting that membrane-integrated Bax monomers in the presence of Bid BH3 peptides are key functional units for the activation of the cell demolition machinery. PMID:23788040

  12. Polyelectrolyte-Mediated Transport of Doxorubicin Through the Bilayer Lipid Membrane

    NASA Astrophysics Data System (ADS)

    Yaroslavov, Alexander A.; Kitaeva, Marina V.; Melik-Nubarov, Nikolay S.; Menger, Frederic M.

    A model is developed for the effect of ionic polymers on the transport of doxorubicin, an antitumor drug, through a bilayer membrane. Accordingly, a protonated (cationic) form of doxorubicin binds to an anionic polymer, poly(acrylic acid), the resulting complex being several hundred nanometers in size. Nevertheless, large complex species associate with neutral egg lecithin liposomes by means of hydrophobic attraction between the doxorubicin and the liposome bilayer. Then, the doxorubicin enters the liposome interior which has been imparted with an acidic buffer to protonate the doxorubicin. The rate of transmembrane Dox permeation decreases when elevating the polyacid-to-doxorubicin ratio. A cationic polymer, polylysine, being coupled with liposomes containing the negative lipid cardiolipin, accelerates membrane transport of doxorubicin with the maximum rate at a complete neutralization of the membrane charge by an interacting polycation. The effect of a polycation on doxorubicin transport becomes more pronounced as small negative liposomes (60-80 nm in diameter) are changed to larger ones (approx. 600 nm in diameter). An opportunity thus opens up for the manipulation of the kinetics of drug uptake by cells and, ultimately, the control of the pharmaceutical action of drugs.

  13. Bilayer porous scaffold based on poly-(ɛ-caprolactone) nanofibrous membrane and gelatin sponge for favoring cell proliferation

    NASA Astrophysics Data System (ADS)

    Zhou, Zhihua; Zhou, Yang; Chen, Yiwang; Nie, Huarong; Wang, Yang; Li, Fan; Zheng, Yan

    2011-12-01

    Electrospun poly-(ɛ-caprolactone) (PCL) nanofibers has been widely used in the medical prosthesis. However, poor hydrophilicity and the lack of natural recognition sites for covalent cell-recognition signal molecules to promote cell attachment have limited its utility as tissue scaffolds. In this study, Bilayer porous scaffolds based on PCL electrospun membranes and gelatin (GE) sponges were fabricated through soft hydrolysis of PCL electrospun followed by grafting gelatin onto the fiber surface, through crosslinking and freeze drying treatment of additional gelatin coat and grafted gelatin surface. GE sponges were stably anchored on PCL membrane surface with the aid of grafted GE molecules. The morphologies of bilayer porous scaffolds were observed through SEM. The contact angle of the scaffolds was 0°, the mechanical properties of scaffolds were measured by tensile test, Young's moduli of PCL scaffolds before and after hydrolysis are 66-77.3 MPa and 62.3-75.4 MPa, respectively. Thus, the bilayer porous scaffolds showed excellent hydrophilic surface and desirable mechanical strength due to the soft hydrolysis and GE coat. The cell culture results showed that the adipose derived mesenchymal stem cells did more favor to adhere and grow on the bilayer porous scaffolds than on PCL electrospun membranes. The better cell affinity of the final bilayer scaffolds not only attributed to the surface chemistry but also the introduction of bilayer porous structure.

  14. Swelling of phospholipid membranes by divalent metal ions depends on the location of the ions in the bilayers.

    PubMed

    Alsop, Richard J; Maria Schober, Rafaëla; Rheinstädter, Maikel C

    2016-08-10

    The Hofmeister series illustrates how salts produce a wide range of effects in biological systems, which are not exclusively explained by ion charge. In lipid membranes, charged ions have been shown to bind to lipids and either hydrate or dehydrate lipid head groups, and also to swell the water layer in multi-lamellar systems. Typically, Hofmeister phenomena are explained by the interaction of the ions with water, as well as with biological interfaces, such as proteins or membranes. We studied the effect of the divalent cations Mg(2+), Ca(2+), Fe(2+), and Zn(2+) on oriented, stacked, phospholipid bilayers made of dimyristoylphosphatidylcholine (DMPC). Using high-resolution X-ray diffraction, we observed that the cations lead to a swelling of the water layer between the bilayers, without causing significant changes to the bilayer structure. The cations swelled the bilayers in different amounts, in the order Fe(2+) > Mg(2+) > Ca(2+) > Zn(2+). By decomposing the total bilayer electron density into different molecular groups, Zn(2+) and Ca(2+) were found to interact with the glycerol groups of the lipid molecules and cause minor swelling of the bilayers. Mg(2+) and Fe(2+) were found to position near the phosphate groups and cause a strong increase in the number of hydration water molecules. Our results present a molecular mechanism-of-action for the Hofmeister series in phospholipid membranes. PMID:27453289

  15. The intermediate scattering function for lipid bilayer membranes: From nanometers to microns

    SciTech Connect

    Watson, Max C.; Peng Yonggang; Zheng Yujun; Brown, Frank L. H.

    2011-11-21

    A numerical scheme based upon established hydrodynamic and elastic considerations is introduced and used to predict the intermediate scattering function for lipid bilayer membranes. The predictions span multiple wavelength regimes, including those studied by dynamic light scattering (DLS; microns) and neutron spin-echo (NSE) spectroscopy (10-100 nm). The results validate a recent theory specific to the NSE regime and expose slight inaccuracies associated with the theoretical results available in the DLS regime. The assumptions that underlie both our numerical methods and the related theoretical predictions are reviewed in detail to explain when certain results can be applied to experiment and where caution must be exercised.

  16. Bilayer registry in a multicomponent asymmetric membrane: Dependence on lipid composition and chain length

    NASA Astrophysics Data System (ADS)

    Polley, Anirban; Mayor, Satyajit; Rao, Madan

    2014-08-01

    A question of considerable interest to cell membrane biology is whether phase segregated domains across an asymmetric bilayer are strongly correlated with each other and whether phase segregation in one leaflet can induce segregation in the other. We answer both these questions in the affirmative, using an atomistic molecular dynamics simulation to study the equilibrium statistical properties of a 3-component asymmetric lipid bilayer comprising an unsaturated palmitoyl-oleoyl-phosphatidyl-choline, a saturated sphingomyelin, and cholesterol with different composition ratios. Our simulations are done by fixing the composition of the upper leaflet to be at the coexistence of the liquid ordered (lo)-liquid disordered (ld) phases, while the composition of the lower leaflet is varied from the phase coexistence regime to the mixed ld phase, across a first-order phase boundary. In the regime of phase coexistence in each leaflet, we find strong transbilayer correlations of the lo domains across the two leaflets, resulting in bilayer registry. This transbilayer correlation depends sensitively upon the chain length of the participating lipids and possibly other features of lipid chemistry, such as degree of saturation. We find that the lo domains in the upper leaflet can induce phase segregation in the lower leaflet, when the latter is nominally in the mixed (ld) phase.

  17. Bilayer registry in a multicomponent asymmetric membrane: Dependence on lipid composition and chain length

    SciTech Connect

    Polley, Anirban; Mayor, Satyajit; Rao, Madan E-mail: madan@ncbs.res.in

    2014-08-14

    A question of considerable interest to cell membrane biology is whether phase segregated domains across an asymmetric bilayer are strongly correlated with each other and whether phase segregation in one leaflet can induce segregation in the other. We answer both these questions in the affirmative, using an atomistic molecular dynamics simulation to study the equilibrium statistical properties of a 3-component asymmetric lipid bilayer comprising an unsaturated palmitoyl-oleoyl-phosphatidyl-choline, a saturated sphingomyelin, and cholesterol with different composition ratios. Our simulations are done by fixing the composition of the upper leaflet to be at the coexistence of the liquid ordered (l{sub o})-liquid disordered (l{sub d}) phases, while the composition of the lower leaflet is varied from the phase coexistence regime to the mixed l{sub d} phase, across a first-order phase boundary. In the regime of phase coexistence in each leaflet, we find strong transbilayer correlations of the l{sub o} domains across the two leaflets, resulting in bilayer registry. This transbilayer correlation depends sensitively upon the chain length of the participating lipids and possibly other features of lipid chemistry, such as degree of saturation. We find that the l{sub o} domains in the upper leaflet can induce phase segregation in the lower leaflet, when the latter is nominally in the mixed (l{sub d}) phase.

  18. Phosphatidylinositol induces fluid phase formation and packing defects in phosphatidylcholine model membranes

    PubMed Central

    Peng, Aaron; Pisal, Dipak S.; Doty, Amy; Balu-Iyer, Sathy V.

    2011-01-01

    Liposomes consisted of phosphatidylinositol (PI) and phosphatidylcholine (PC) have been utilized as delivery vehicle for drugs and proteins. In the present work, we studied the effect of soy PI on physical properties of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes such as phase state of lipid bilayer, lipid packing and phase properties using multiple orthogonal biophysical techniques. The 6-dodecanoyl-2-dimethylamino naphthalene (Laurdan) fluorescence studies showed that presence of PI induces the formation of fluid phases in DMPC. Differential scanning calorimetry (DSC), temperature dependent fluorescence anisotropy measurements, and generalized polarization values for Laurdan showed that the presence of as low as 10 mol% of PI induces substantial broadening and shift to lower temperature of phase transition of DMPC. The fluorescence emission intensity of DPH labeled, PI containing DMPC lipid bilayer decreased possibly due to deeper penetration of water molecules in lipid bilayer. In order to further delineate the effect of PI on the physico chemical properties of DMPC is due to either significant hydrophobic mismatch between the acyl chains of the DMPC and that of soy PI or due to the inositol head group, we systematically replaced soy PI with PC species of similar acyl chain composition (DPPC and 18:2 (Cis) PC) or with diacylglycerol (DAG) respectively. The anisotropy of PC membrane containing soy PI showed largest fluidity change compared to other compositions. The data suggests that addition of PI alters structure and dynamics of DMPC bilayer in that it promotes deeper water penetration in the bilayer, induces fluid phase characteristics and causes lipid packing defects that involve its inositol head group. PMID:22024173

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

    DOE PAGESBeta

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

    2015-05-27

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

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

    SciTech Connect

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

    2015-05-27

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

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

    PubMed Central

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

    2015-01-01

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

  2. Fabrication and characterization of an integrated ionic device from suspended polypyrrole and alamethicin-reconstituted lipid bilayer membranes

    NASA Astrophysics Data System (ADS)

    Northcutt, Robert; Sundaresan, Vishnu-Baba

    2012-09-01

    Conducting polymers are electroactive materials that undergo conformal relaxation of the polymer backbone in the presence of an electrical field through ion exchange with solid or aqueous electrolytes. This conformal relaxation and the associated morphological changes make conducting polymers highly suitable for actuation and sensing applications. Among smart materials, bioderived active materials also use ion transport for sensing and actuation functions via selective ion transport. The transporter proteins extracted from biological cell membranes and reconstituted into a bilayer lipid membrane in bioderived active materials regulate ion transport for engineering functions. The protein transporter reconstituted in the bilayer lipid membrane is referred to as the bioderived membrane and serves as the active component in bioderived active materials. Inspired by the similarities in the physics of transduction in conducting polymers and bioderived active materials, an integrated ionic device is formed from the bioderived membrane and the conducting polymer membrane. This ionic device is fabricated into a laminated thin-film membrane and a common ion that can be processed by the bioderived and the conducting polymer membranes couple the ionic function of these two membranes. An integrated ionic device, fabricated from polypyrrole (PPy) doped with sodium dodecylbenzenesulfonate (NaDBS) and an alamethicin-reconstituted DPhPC bilayer lipid membrane, is presented in this paper. A voltage-gated sodium current regulates the electrochemical response in the PPy(DBS) layer. The integrated device is fabricated on silicon-based substrates through microfabrication, electropolymerization, and vesicle fusion, and ionic activity is characterized through electrochemical measurements.

  3. The dependence of the lipid bilayer membrane: buffer partition coefficient of pentobarbitone on pH and lipid composition.

    PubMed Central

    Miller, K W; Yu, S C

    1977-01-01

    1 The membrane/buffer partition coefficient of [14C]-pentobarbitone has been determined as a function of the lipid composition of bilayer membranes. 2 A new technique based on ultrafiltration gave comparable results to conventional techniques but required less time for equilbration. 3 The membrane/buffer coefficient was independent of pentobarbitone concentration in the range studies. 4 The apparent partition coefficient varied with pH and was a linear function of the degree of dissociation of pentobarbition. 5 Both the charged and uncharged forms of pentobarbitone partitioned into the membrane, the latter to a much greater extent than the former. 6 At low pH the highest partition coefficient observed was in egg phosphatidylcholine bilayer membranes. 7 Incorporation of cholesterol or phosphatidic acid into phosphatidylcholine membranes greatly reduced the partition coefficient. 8 High pressures do not greatly change these partition coefficients. PMID:21013

  4. Alginate/chitosan based bi-layer composite membrane as potential sustained-release wound dressing containing ciprofloxacin hydrochloride

    NASA Astrophysics Data System (ADS)

    Han, Fei; Dong, Yang; Song, Aihua; Yin, Ran; Li, Sanming

    2014-08-01

    The aims of this research were to develop and evaluate a novel ciprofloxacin hydrochloride loaded bi-layer composite membrane based on alginate and chitosan. In vitro antimicrobial activity, drug permeation study, morphology, cytotoxicity, primary skin irritation and in vivo pharmacodynamics were investigated. Results showed that the membranes could inhibit the growth of microorganisms for longer than 7 days. And there was no significant decrease in the metabolic activity of the Hacat fibroblasts cells were treated with the membranes. No edema and erythema were observed after administration of membranes on the rabbit skin after 14 days. Moreover, the results of pharmacodynamics showed that the membranes were more effective in improving the wound healing process. In conclusion, a novel bi-layer composite membrane was developed and results suggested that it could be exploited as sustained-release wound dressings.

  5. Improved 1H amide resonance line narrowing in oriented sample solid-state NMR of membrane proteins in phospholipid bilayers

    NASA Astrophysics Data System (ADS)

    Lu, George J.; Park, Sang Ho; Opella, Stanley J.

    2012-07-01

    We demonstrate 1H amide resonance line widths <300 Hz in 1H/15N heteronuclear correlation (HETCOR) spectra of membrane proteins in aligned phospholipid bilayers. This represents a substantial improvement over typically observed line widths of ˜1 kHz. Furthermore, in a proton detected local field (PDLF) version of the experiment that measures heteronuclear dipolar couplings, line widths <130 Hz are observed. This dramatic line narrowing of 1H amide resonances enables many more individual signals to be resolved and assigned from uniformly 15N labeled membrane proteins in phospholipid bilayers under physiological conditions of temperature and pH. Finding that the decrease in line widths occurs only for membrane proteins that undergo fast rotational diffusion around the bilayer normal, but not immobile molecules, such as peptide single crystals, identifies a potential new direction for pulse sequence development that includes overall molecular dynamics in their design.

  6. Membrane Thinning Due to Antimicrobial Peptide Binding: An Atomic Force Microscopy Study of MSI-78 in Lipid Bilayers

    PubMed Central

    Mecke, Almut; Lee, Dong-Kuk; Ramamoorthy, Ayyalusamy; Orr, Bradford G.; Banaszak Holl, Mark M.

    2005-01-01

    The interaction of an antimicrobial peptide, MSI-78, with phospholipid bilayers has been investigated using atomic force microscopy, circular dichroism, and nuclear magnetic resonance (NMR). Binding of amphipathic peptide helices with their helical axis parallel to the membrane surface leads to membrane thinning. Atomic force microscopy of supported 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers in the presence of MSI-78 provides images of the membrane thinning process at a high spatial resolution. This data reveals that the membrane thickness is not reduced uniformly over the entire bilayer area. Instead, peptide binding leads to the formation of distinct domains where the bilayer thickness is reduced by 1.1 ± 0.2 nm. The data is interpreted using a previously published geometric model for the structure of the peptide-lipid domains. In this model, the peptides reside at the hydrophilic-hydrophobic boundary in the lipid headgroup region, which leads to an increased distance between lipid headgroups. This picture is consistent with concentration-dependent 31P and 2H NMR spectra of MSI-78 in mechanically aligned DMPC bilayers. Furthermore, 2H NMR experiments on DMPC-d54 multilamellar vesicles indicate that the acyl chains of DMPC are highly disordered in the presence of the peptide as is to be expected for the proposed structure of the peptide-lipid assembly. PMID:16183881

  7. Investigations on membrane perturbation by chrysin and its copper complex using self-assembled lipid bilayers.

    PubMed

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

    2011-11-01

    The mechanism of membrane interactions of most of the flavonoids in the presence of transition-metal ions is not well-understood. To understand this phenomenon, the present work aims to synthesize a chrysin-copper complex at room temperature and investigate its influence on the electrical characteristics of planar lipid bilayers. The chrysin-copper complex was characterized by various spectroscopic techniques and was found to have a metal/ligand ratio of 1:2 and of cationic nature. Its ability to inhibit 1,1'-diphenyl-2-picrylhydrazyl (DPPH) radicals was not significant at alkaline pH because of the involvement of the 5-hydroxy group in coordination with the copper ion compared to its parent flavonoid, chrysin (p < 0.05). The addition of different concentrations (20-100 μM) of chrysin and the chrysin-copper complex to lipid bilayers decreases the resistance, indicating a strong surface interaction and partial insertion into the bilayer near the lipid-water interface. The dose-dependent reduction in resistance as a result of the chrysin-copper complex is more pronounced in comparison to chrysin, implying that the bulkier and charged chrysin-copper complex displays greater ability to distort the lipid bilayer architecture. These conclusions were further confirmed by curcumin-loaded liposome permeabilization studies, where both chrysin and its Cu(II) complex increased the fluidity in a dose-dependent manner. However, the extent of fluidization by the chrysin-copper complex was nearly twice that of chrysin alone (p < 0.05). The implications of these surface interactions of chrysin and its copper complex on cell membranes were studied using a hypotonic hemolysis assay. Our results demonstrate that, at low concentrations (20 μM), the chrysin-copper complex exhibited twice the protection against hypotonic stress-induced membrane disruption when compared to chrysin. However, this stabilizing effect gradually decreased and became comparable to chrysin at higher

  8. Chemotherapy Drugs Thiocolchicoside and Taxol Permeabilize Lipid Bilayer Membranes by Forming Ion Pores

    NASA Astrophysics Data System (ADS)

    Ashrafuzzaman, Md; Duszyk, M.; Tuszynski, J. A.

    2011-12-01

    We report ion channel formation by chemotherapy drugs: thiocolchicoside (TCC) and taxol (TXL) which primarily target tubulin but not only. For example, TCC has been shown to interact with GABAA, nuclear envelope and strychnine-sensitive glycine receptors. TXL interferes with the normal breakdown of microtubules inducing mitotic block and apoptosis. It also interacts with mitochondria and found significant chemotherapeutic applications for breast, ovarian and lung cancer. In order to better understand the mechanisms of TCC and TXL actions, we examined their effects on phospholipid bilayer membranes. Our electrophysiological recordings across membranes constructed in NaCl aqueous phases consisting of TCC or TXL under the influence of an applied transmembrane potential (V) indicate that both molecules induce stable ion flowing pores/channels in membranes. Their discrete current versus time plots exhibit triangular shapes which is consistent with a spontaneous time-dependent change of the pore conductance in contrast to rectangular conductance events usually induced by ion channels. These events exhibit conductance (~0.01-0.1 pA/mV) and lifetimes (~5-30 ms) within the ranges observed in e.g., gramicidin A and alamethicin channels. The channel formation probability increases linearly with TCC/TXL concentration and V and is not affected by pH (5.7 - 8.4). A theoretical explanation on the causes of chemotherapy drug induced ion pore formation and the pore stability has also been found using our recently discovered binding energy between lipid bilayer and the bilayer embedded ion channels using gramicidin A channels as tools. This picture of energetics suggests that as the channel forming agents approach to the lipids on bilayer the localized charge properties in the constituents of both channel forming agents (e.g., chemotherapy drugs in this study) and the lipids determine the electrostatic drug-lipid coupling energy through screened Coulomb interactions between the drug

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

    PubMed

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

    1991-06-01

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

  10. Self-assembly of azobenzene bilayer membranes in binary ionic liquid-water nanostructured media.

    PubMed

    Kang, Tejwant Singh; Ishiba, Keita; Morikawa, Masa-aki; Kimizuka, Nobuo

    2014-03-11

    Anionic azobenzene-containing amphiphile 1 (sodium 4-[4-(N-methyl-N-dodecylamino)phenylazo]benzenesulfonate) forms ordered bilayer membranes in binary ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate, [C2mim][C2OSO3])-water mixtures. The binary [C2mim][C2OSO3]-water mixture is macroscopically homogeneous at any mixing ratio; however, it possesses fluctuating nanodomains of [C2mim][C2OSO3] molecules as observed by dynamic light scattering (DLS). These nanodomains show reversible heat-induced mixing behavior with water. Although the amphiphile 1 is substantially insoluble in pure water, it is dispersible in the [C2mim][C2OSO3]-water mixtures. The concentration of [C2mim][C2OSO3] and temperature exert significant influences on the self-assembling characteristics of 1 in the binary media, as shown by DLS, transmission electron microscopy (TEM), UV-vis spectroscopy, and zeta-potential measurements. Bilayer membranes with rod- or dotlike nanostructures were formed at a lower content of [C2mim][C2OSO3] (2-30 v/v %), in which azobenzene chromophores adopt parallel molecular orientation regardless of temperature. In contrast, when the content of [C2mim][C2OSO3] is increased above 60 v/v %, azobenzene bilayers showed thermally reversible gel-to-liquid crystalline phase transition. The self-assembly of azobenzene amphiphiles is tunable depending on the volume fraction of [C2mim][C2OSO3] and temperature, which are associated with the solvation by nanoclusters in the binary [C2mim][C2OSO3]-water media. These observations clearly indicate that mixtures of water-soluble ionic liquids and water provide unique and valiant environments for ordered molecular self-assembly. PMID:24528277

  11. Incorporation in lipid bilayers of a large conductance cationic channel from mitochondrial membranes.

    PubMed Central

    Thieffry, M; Chich, J F; Goldschmidt, D; Henry, J P

    1988-01-01

    Membranes from subcellular fractions of adrenal medulla were incorporated in phospholipid bilayers formed at the tip of microelectrodes. Current fluctuations recorded in the presence of a transmembrane potential revealed the existence of a voltage-dependent channel of large conductance. This channel is characterized by fast kinetics and four conductance levels separated by jumps of 100, 220 and 220 pS in 150 mM NaCl. It is permeant to Na+,K+, tetraethylammonium, Cl- and acetate and has some cation selectivity. Exposure to trypsin or pronase abolished the voltage-dependence. Upon subcellular fractionation, the activity was found to be associated with mitochondria. A similar activity was observed in mitochondrial fractions from other organs. By its kinetics, its selectivity and its potential-dependence, this channel differs from the voltage-dependent anion channel of outer mitochondrial membranes. Images PMID:2457497

  12. Fibrillation of β amyloid peptides in the presence of phospholipid bilayers and the consequent membrane disruption.

    PubMed

    Qiang, Wei; Yau, Wai-Ming; Schulte, Jürgen

    2015-01-01

    Fibrillation of β amyloid (Aβ) peptides and the accumulation of amyloid plaques are considered as an important clinical hallmark to identify Alzheimer's disease (AD). The physiological connection between Aβ plaques and the disruption of neuronal cells has not been clearly understood. One hypothesis to explain the Aβ neurotoxicity is that the fibrillation process induces disruption to the cellular membrane. We studied the Aβ fibrillation process in two biologically relevant conditions with the peptide either pre-incorporated into or externally added to the synthetic phospholipid bilayers. These two sample preparation conditions mimic the physiological membrane proximities of Aβ peptides before and after the enzymatic cleavage of amyloid precursor protein (APP). Using thioflavin T (ThT) fluorescence and transmission electron microscopy (TEM), we were able to monitor the kinetics and morphological evolution of fibril formation, which was highly sensitive to the two sample preparation protocols. While the external addition protocol generates long and mature fibrils through normal fibrillation process, the pre-incubation protocol was found to stabilize the immature protofibrils. Fluorescence spectroscopy studies with doubly-labeled phospholipids indicated that there may be a lipid uptake process associated with the fibril formation. Solid state nuclear magnetic resonance (NMR) spectroscopy provided evidence for high resolution structural variations in fibrils formed with different protocols, and in particular the stabilization of long-range contact between N- and C-terminal β strands. In addition, disruption of phospholipid bilayers was supported by measurements with ³¹P chemical shifts and relaxation time constants. PMID:24769158

  13. Interactions of Graphene Oxide with Model Cell Membranes: Probing Nanoparticle Attachment and Lipid Bilayer Disruption.

    PubMed

    Liu, Xitong; Chen, Kai Loon

    2015-11-10

    With the rapid growth in the application of graphene oxide (GO) in diverse fields, the toxicity of GO toward bacterial and mammalian cells has recently attracted extensive research attention. While several mechanisms have been proposed for the cytotoxicity of GO, the attachment of GO to cell membranes is expected to be the key initial process that precedes these mechanisms. In this study, we investigate the propensity for GO to attach to and disrupt model cell membranes using supported lipid bilayers (SLBs) and supported vesicular layers (SVLs) that are composed of zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). The deposition kinetics of GO on SLBs were determined using quartz crystal microbalance with dissipation monitoring and were observed to increase with increasing electrolyte (NaCl and CaCl2) concentrations, indicating that GO attachment to SLBs was controlled by electrostatic interactions. The GO deposition kinetics measured at elevated electrolyte concentrations were lower than mass-transfer-limited kinetics, likely due to the presence of hydration forces between GO and SLBs. Upon the attachment of GO to supported vesicles that were encapsulated with a fluorescent dye, dye leakage was detected, thus indicating that the lipid vesicles were disrupted. When the exposure of the SVL to the GO suspension was terminated, the leakage of dye decreased significantly, demonstrating that the pores on the lipid bilayers have a self-healing ability. PMID:26466194

  14. 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

  15. Photosensitizer binding to lipid bilayers as a precondition for the photoinactivation of membrane channels.

    PubMed Central

    Rokitskaya, T I; Block, M; Antonenko, Y N; Kotova, E A; Pohl, P

    2000-01-01

    The photodynamic activity of sulfonated aluminum phthalocyanines (AlPcS(n), 1 membrane lipids. Adsorbing to the surface of large unilamellar vesicles (LUVs), aluminum phthalocyanine disulfonate induced the highest changes in their electrophoretic mobility. AlPcS(2) was also most efficient in mediating photoinactivation of gramicidin channels, as revealed by measurements of the electric current across planar lipid bilayers. The increase in the degree of sulfonation of phthalocyanine progressively reduced its affinity for the lipid bilayer as well as its potency of sensitizing gramicidin channel photoinactivation. The portion of photoinactivated gramicidin channels, alpha, increased with rising photosensitizer concentration up to some optimum. The concentration at which alpha was at half-maximum amounted to 80 nM, 30 nM, 200 nM, and 2 microM for AlPcS(1), AlPcS(2), AlPcS(3), and AlPcS(4), respectively. At high concentrations alpha was found to decrease, which was attributed to quenching of reactive oxygen species and self-quenching of the photosensitizer triplet state by its ground state. Fluoride anions were observed to inhibit both AlPcS(n) (2 membrane lipids is a prerequisite for the photodynamic inactivation of gramicidin channels. PMID:10777753

  16. Lipid bilayer membranes: Missing link in the comprehension of synovial lubrication?

    NASA Astrophysics Data System (ADS)

    Packard, Ross; Cowley, Leonie; Dubief, Yves

    2010-03-01

    The human body hosts an extremely efficient tribological system in its synovial joints that operate under very low friction and virtually no wear. It has long been assumed that the higher molecular weight molecules present in the synovial fluid (hyaluronic acid, lubricin) are solely responsible for the mechanical properties of joint. Smaller components, unsaturated phospholipids, have a virtually an undefined role, most probably because of the cancellation of their amphiphilic properties ex vivo caused by oxidation. Using experimental observations of multilamellar arrangements in synovial joints, we formulate the assumption that self-assembling structures provide the anisotropy necessary to synovial fluid to resist drainage under normal compression. Our molecular dynamics simulations demonstrate the tremendous mechanical properties of lipid bilayers and also highlight their weakening consistent with modifications resulting from injuries or joint prosthesis.

  17. Effective lipid-detergent system for study of membrane active peptides in fluid liposomes.

    PubMed

    Sychev, Sergei V; Sukhanov, Stanislav V; Telezhinskaya, Irina N; Ovchinnikova, Tatiana V

    2016-02-01

    The structure of peptide antibiotic gramicidin A (gA) was studied in phosphatidylcholin liposomes modified by nonionic detergent Triton X-100. First, the detergent : lipid ratio at which the saturation of lipid membrane by Triton X-100 occurs (Re (sat)), was determined by light scattering. Measurements of steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene at sublytic concentrations of detergent showed that after saturation of the membrane by Triton X-100 microviscosity of lipid bilayer is reduced by 20%. The equilibrium conformational state of gA in phosphatidylcholine liposomes at Re (sat) was studied by CD spectroscopy. It was found that the conformational state of this channel-forming peptide changed crucially when Triton X-100 induced transition to more fluid membranes. The gA single-channel measurements were made with Triton X-100 containing bilayers. Tentative assignment of the channel type and gA structures was made by correlation of CD data with conductance histograms. Lipid-detergent system with variable viscosity developed in this work can be used to study the structure and folding of other membrane-active peptides. PMID:26751806

  18. Membrane interactions of ternary phospholipid/cholesterol bilayers and encapsulation efficiencies of a RIP II protein.

    PubMed

    Manojlovic, V; Winkler, K; Bunjes, V; Neub, A; Schubert, R; Bugarski, B; Leneweit, G

    2008-07-15

    Membrane interactions of liposomes of ternary phospholipid/cholesterol bilayers are investigated. These interactions lead to discoidal deformations and regular aggregations and are strongly enhanced by the presence of mistletoe lectin (ML), a RIP II type protein. The encapsulation of ML into liposomal nanocapsules is studied with a systematic variation of the lipid composition to monitor its effect on the physical properties: entrapment, mean size, morphology, and stability. Extrusion of multilamellar vesicles through filters 80 nm pore size was used for the generation of liposomes. The mean sizes of liposomes ranged between 120 and 200 nm in diameter with narrow size distributions. The increase in flow rate with pressure for three dioleoylphosphatidylcholine (DOPC)/cholesterol (Chol)/dipalmitoylphosphatidylcholine (DPPC) lipid mixtures was linear and allowed to extrapolate to the minimum burst pressure of the liposomal bilayers. From the minimum pressures P(min), the bilayer lysis tensions gamma(l) were determined. The increase in P(min) and gamma(l) with an increasing content of a saturated phosopholipid (DPPC) indicates that DPPC increases the mechanical strength of lipid bilayers. Apparently, DPPC, like cholesterol, leads to a less compressible surface and a more cohesive membrane. After preparation, vesicle solutions were purified by gel permeation chromatography to separate encapsulated ML from free ML in the extravesicular solution. Purified liposomes were then characterized. The content of entrapped and adsorbed ML was measured using ELISA. Repetitive freezing/thawing cycles prior to extrusion significantly increased ML uptake. On the contrary, adsorption was not affected neither by lipid composition, nor concentration and preparation. Differences in experimental encapsulation efficiency only reflect the differences in the mean vesicle sizes of the different samples as is revealed by a comparison to a theoretical estimate. Cryo-transmission electron

  19. Tethered bilayer membranes as a complementary tool for functional and structural studies: The pyolysin case.

    PubMed

    Preta, Giulio; Jankunec, Marija; Heinrich, Frank; Griffin, Sholeem; Sheldon, Iain Martin; Valincius, Gintaras

    2016-09-01

    We demonstrate the use of tethered bilayer lipid membranes (tBLMs) as an experimental platform for functional and structural studies of membrane associated proteins by electrochemical techniques. The reconstitution of the cholesterol-dependent cytolysin (CDC) pyolysin (PLO) from Trueperella pyogenes into tBLMs was followed in real-time by electrochemical impedance spectroscopy (EIS). Changes of the EIS parameters of the tBLMs upon exposure to PLO solutions were consistent with the dielectric barrier damage occurring through the formation of water-filled pores in membranes. Parallel experiments involving a mutant version of PLO, which is able to bind to the membranes but does not form oligomer pores, strengthen the reliability of this methodology, since no change in the electrochemical impedance was observed. Complementary atomic force microscopy (AFM) and neutron reflectometry (NR) measurements revealed structural details of the membrane bound PLO, consistent with the structural transformations of the membrane bound toxins found for other cholesterol dependent cytolysins. In this work, using the tBLMs platform we also observed a protective effect of the dynamin inhibitor Dynasore against pyolysin as well as pneumolysin. An effect of Dynasore in tBLMs, which was earlier observed in experiments with live cells, confirms the biological relevance of the tBLMs models, as well as demonstrates the potential of the electrochemical impedance spectroscopy to quantify membrane damage by the pore forming toxins. In conclusion, tBLMs are a reliable and complementary method to explore the activity of CDCs in eukaryotic cells and to develop strategies to limit the toxic effects of CDCs. PMID:27211243

  20. Oriented Circular Dichroism: A Method to Characterize Membrane-Active Peptides in Oriented Lipid Bilayers.

    PubMed

    Bürck, Jochen; Wadhwani, Parvesh; Fanghänel, Susanne; Ulrich, Anne S

    2016-02-16

    The structures of membrane-bound polypeptides are intimately related to their functions and may change dramatically with the lipid environment. Circular dichroism (CD) is a rapid analytical method that requires relatively low amounts of material and no labeling. Conventional CD is routinely used to monitor the secondary structure of peptides and proteins in solution, for example, in the presence of ligands and other binding partners. In the case of membrane-active peptides and transmembrane proteins, these measurements can be applied to, and remain limited to, samples containing detergent micelles or small sonicated lipid vesicles. Such traditional CD analysis reveals only secondary structures. With the help of an oriented circular dichroism (OCD) setup, however, based on the preparation of macroscopically oriented lipid bilayers, it is possible to address the membrane alignment of a peptide in addition to its conformation. This approach has been mostly used for α-helical peptides so far, but other structural elements are conceivable as well. OCD analysis relies on Moffitt's theory, which predicts that the electronic transition dipole moments of the backbone amide bonds in helical polypeptides are polarized either parallel or perpendicular to the helix axis. The interaction of the electric field vector of the circularly polarized light with these transitions results in an OCD spectrum of a membrane-bound α-helical peptide, which exhibits a characteristic line shape and reflects the angle between the helix axis and the bilayer normal. For parallel alignment of a peptide helix with respect to the membrane surface (S-state), the corresponding "fingerprint" CD band around 208 nm will exhibit maximum negative amplitude. If the helix changes its alignment via an obliquely tilted (T-state) to a fully inserted transmembrane orientation (I-state), the ellipticity at 208 nm decreases and the value approaches zero due to the decreased interactions between the field and the

  1. Tetra- and Penta-Cyclic Triterpenes Interaction with Lipid Bilayer Membrane: A Structural Comparative Study.

    PubMed

    Abboud, Rola; Charcosset, Catherine; Greige-Gerges, Hélène

    2016-06-01

    The effect of tetracyclic (cortisol, prednisolone, and 9-fluorocortisol acetate) and pentacyclic (uvaol and erythrodiol) triterpenes (TTPs) on the fluidity of dipalmitoyl phosphatidyl choline (DPPC) liposome membrane was investigated by differential scanning calorimetry, Raman spectroscopy, and fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH). Liposomes were prepared in the absence and presence of TTPs at molar ratios DPPC:TTP 100:1, 100:2.5, and 100:10. All the studied TTPs abolished the pre-transition and modified the intensity of the Raman peak at 715 cm(-1) proving the interaction of TTP molecules with the choline head group of phospholipids. An increase in the Raman height intensity ratios of the peaks I 2935/2880, I 2844/2880, and I 1090/1130, giving information about the ratio disorder/order of the alkyl chains, and a decrease of the main transition temperature demonstrated the interaction of TTPs with the alkyl chains. The tetracyclic TTPs produced broadening of the phase transition profile. Besides, a scarcely splitting of the main transition peak was obtained with prednisolone and 9-fluorocortisol acetate. The results of fluorescence depolarization of DPH showed that the studied molecules fluidized the liposomal membrane at 25, 41, and 50 °C. Pentacyclic TTPs, being more hydrophobic than tetracyclic ones, demonstrated higher fluidizing effect than tetracyclic TTPs in the liquid crystalline phase suggesting a deeper incorporation in the lipid bilayer. The presence of a free polar head group at the ring D seems to control the TTP incorporation in the bilayer and consequently its effect on the membrane fluidity. PMID:26759229

  2. Outer membrane phospholipase A in phospholipid bilayers: A model system for concerted computational and experimental investigations of amino acid side chain partitioning into lipid bilayers

    PubMed Central

    Fleming, Patrick J.; Freites, J. Alfredo; Moon, C. Preston; Tobias, Douglas J.; Fleming, Karen G.

    2011-01-01

    Understanding the forces that stabilize membrane proteins in their native states is one of the contemporary challenges of biophysics. To date, estimates of side chain partitioning free energies from water to the lipid environment show disparate values between experimental and computational measures. Resolving the disparities is particularly important for understanding the energetic contributions of polar and charged side chains to membrane protein function because of the roles these residue types play in many cellular functions. In general, computational free energy estimates of charged side chain partitioning into bilayers are much larger than experimental measurements. However, the lack of a protein-based experimental system that uses bilayers against which to vet these computational predictions has traditionally been a significant drawback. Moon & Fleming recently published a novel hydrophobicity scale that was derived experimentally by using a host-guest strategy to measure the side chain energetic perturbation due to mutation in the context of a native membrane protein inserted into a phospholipid bilayer. These values are still approximately an order of magnitude smaller than computational estimates derived from molecular dynamics calculations from several independent groups. Here we address this discrepancy by showing that the free energy differences between experiment and computation become much smaller if the appropriate comparisons are drawn, which suggests that the two fields may in fact be converging. In addition, we present an initial computational characterization of the Moon & Fleming experimental system used for the hydrophobicity scale: OmpLA in DLPC bilayers. The hydrophobicity scale used OmpLA position 210 as the guest site, and our preliminary results demonstrate that this position is buried in the center of the DLPC membrane, validating its usage in the experimental studies. We further showed that the introduction of charged Arg at position 210

  3. Structure and interactions of fluid phospholipid bilayers measured by high-resolution X-ray scattering

    NASA Astrophysics Data System (ADS)

    Petrache, Horia Iosif

    The topic of this work is the biologically relevant fluid phase of phosphatidylcholine lipid bilayers. A first goal is the determination of the average bilayer structure using low-angle X-ray scattering from multilamellar lipid vesicles (MLVs). The MLVs are smectic liquid crystals, for which interbilayer correlations decay algebraically. Consequently, the smectic Bragg peaks have power low tails, with the exponent related to the bilayer fluctuations. The analysis of such peaks requires good instrumental resolution and a sophisticated (and equally good) scattering theory. The high resolution is achieved at the F3 station at CHESS. The scattering theory is an improved version of the modified Caillé theory being developed in our laboratory. Data fitting gives the three pieces of information carried by the scattering peaks: position, amplitude, and power-law exponent. The position and the amplitude (form factor) are used to determine the bilayer structure. The power-law exponent is converted into mean square fluctuations in the interbilayer water spacing. This opens a new window on interbilayer interactions which is the second goal of this work. The fundamental issue of interbilayer interactions is addressed both experimentally and theoretically. We obtain the interbilayer water spacing fluctuation σ, as well as the traditional osmotic pressure P, both as functions of the lamellar repeat spacing D and the aqueous separation a. We show theoretically how to obtain the functional form of the fluctuational free energy from the a data, which is then determined to within a factor that depends upon the bending modulus, Kc. The resulting functional form determined from experimental data has an exponential decay rather than the power law decay that applies for hard confinement in the large a regime, thereby showing that a theory of soft confinement is necessary. The existing theory of soft confinement predicts an exponential decay, but with a smaller decay length λfl than we

  4. Surface-Enhanced Infrared Spectroscopy and Neutron Reflectivity Studies of Ubiquinone in Hybrid Bilayer Membranes under Potential Control.

    PubMed

    Quirk, Amanda; Lardner, Michael J; Tun, Zin; Burgess, Ian J

    2016-03-01

    Surface-enhanced infrared adsorption spectroscopy (SEIRAS) and neutron reflectometry (NR) were employed to characterize ubiquinone (UQ) containing hybrid bilayer membranes. The biomimetic membrane was prepared by fusing phospholipid vesicles on a hydrophobic octadecanethiol monolayer self-assembled on a thin gold film. Using SEIRAS, the assembly of the membrane is monitored in situ. The presence of ubiquinone is verified by the characteristic carbonyl peaks from the quinone ester. A well-ordered distal lipid leaflet results from fusion of vesicles with and without the addition of ubiquinone. With applied potential, the hybrid bilayer membrane in the absence of UQ behaves in the same way as previously reported solid supported phospholipid membranes. When ubiquinone is incorporated in the membrane, electric field induced changes in the distal leaflet are suppressed. Changes in the infrared vibrations of the ubiquinone due to applied potential indicate the head groups are located in both polar and nonpolar environments. The spectroscopic data reveal that the isoprenoid unit of the ubiquinone is likely lying in the midplane of the lipid bilayer while the head has some freedom to move within the hydrophobic core. The SEIRAS experiments show redox behavior of UQ incorporated in a model lipid membrane that are otherwise inaccessible with traditional electrochemistry techniques. PMID:26867110

  5. Thermodynamic free energy methods to investigate shape transitions in bilayer membranes

    PubMed Central

    Ramakrishnan, N.; Tourdot, Richard W.

    2016-01-01

    The conformational free energy landscape of a system is a fundamental thermodynamic quantity of importance particularly in the study of soft matter and biological systems, in which the entropic contributions play a dominant role. While computational methods to delineate the free energy landscape are routinely used to analyze the relative stability of conformational states, to determine phase boundaries, and to compute ligand-receptor binding energies its use in problems involving the cell membrane is limited. Here, we present an overview of four different free energy methods to study morphological transitions in bilayer membranes, induced either by the action of curvature remodeling proteins or due to the application of external forces. Using a triangulated surface as a model for the cell membrane and using the framework of dynamical triangulation Monte Carlo, we have focused on the methods of Widom insertion, thermodynamic integration, Bennett acceptance scheme, and umbrella sampling and weighted histogram analysis. We have demonstrated how these methods can be employed in a variety of problems involving the cell membrane. Specifically, we have shown that the chemical potential, computed using Widom insertion, and the relative free energies, computed using thermodynamic integration and Bennett acceptance method, are excellent measures to study the transition from curvature sensing to curvature inducing behavior of membrane associated proteins. The umbrella sampling and WHAM analysis has been used to study the thermodynamics of tether formation in cell membranes and the quantitative predictions of the computational model are in excellent agreement with experimental measurements. Furthermore, we also present a method based on WHAM and thermodynamic integration to handle problems related to end-point-catastrophe that are common in most free energy methods.

  6. Smart polymer brush nanostructures guide the self-assembly of pore-spanning lipid bilayers with integrated membrane proteins

    NASA Astrophysics Data System (ADS)

    Wilhelmina de Groot, G.; Demarche, Sophie; Santonicola, M. Gabriella; Tiefenauer, Louis; Vancso, G. Julius

    2014-01-01

    Nanopores in arrays on silicon chips are functionalized with pH-responsive poly(methacrylic acid) (PMAA) brushes and used as supports for pore-spanning lipid bilayers with integrated membrane proteins. Robust platforms are created by the covalent grafting of polymer brushes using surface-initiated atom transfer radical polymerization (ATRP), resulting in sensor chips that can be successfully reused over several assays. His-tagged proteins are selectively and reversibly bound to the nitrilotriacetic acid (NTA) functionalization of the PMAA brush, and consequently lipid bilayer membranes are formed. The enhanced membrane resistance as determined by electrochemical impedance spectroscopy and free diffusion of dyed lipids observed as fluorescence recovery after photobleaching confirmed the presence of lipid bilayers. Immobilization of the His-tagged membrane proteins on the NTA-modified PMAA brush near the pore edges is characterized by fluorescence microscopy. This system allows us to adjust the protein density in free-standing bilayers, which are stabilized by the polymer brush underneath. The potential application of the integrated platform for ion channel protein assays is demonstrated.

  7. Inverted micellar structures in bilayer membranes. Formation rates and half-lives.

    PubMed Central

    Siegel, D P

    1984-01-01

    Two sorts of inverted micellar structures have previously been proposed to explain morphological and 31P-NMR observations of bilayer systems. These structures only form in systems with components that can adopt the inverse hexagonal (HII) phase. LIP (lipidic particles) are intrabilayer structures, whereas IMI (inverted micellar intermediates) are structures that form between apposed bilayers. Here, we calculate the formation rates and half-lives of these structures to determine which (or if either) of these proposed structures is a likely explanation of the data. Calculations for the egg phosphatidylethanolamine and the Ca+-cardiolipin systems show that IMI form orders of magnitude faster than LIP, which should form slowly, if at all. This result is probably true in general, and indicates that "lipidic particle" electron micrograph images probably represent interbilayer structures, as some have previously proposed. It is shown here that IMI are likely intermediates in the lamellar----HII phase transitions and in the process of membrane fusion in some systems. The calculated formation rates, half-lives, and vesicle-vesicle fusion rates are in agreement with this observation. PMID:6365189

  8. Effect of submicellar concentrations of conjugated and unconjugated bile salts on the lipid bilayer membrane.

    PubMed

    Mohapatra, Monalisa; Mishra, Ashok K

    2011-11-15

    The interaction of submicellar concentrations of various physiologically important unconjugated [sodium deoxycholate (NaDC), sodium cholate (NaC)] and conjugated [sodium glycodeoxycholate (NaGDC), sodium glycocholate (NaGC), sodium taurodeoxycholate (NaTDC), sodium taurocholate (NaTC)] bile salts with dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) small unilamellar vesicles in solid gel (SG) and liquid crystalline (LC) phases was investigated using the excited-state prototropism of 1-naphthol. Steady-state and time-resolved fluorescence of the two excited-state prototropic forms of 1-naphthol indicate that submicellar bile salt concentration induces hydration of the lipid bilayer membrane into the core region. This hydration effect is a general phenomenon of the bile salts studied. The bilayer hydration efficiency of the bile salt follows the order NaDC > NaC > NaGDC > NaTDC > NaGC > NaTC for both DPPC and DMPC vesicles in their SG and LC phases. PMID:21973323

  9. Organic fluid permeation through fluoropolymer membranes

    SciTech Connect

    Nemser, Stuart M.; Kosaraju, Praveen; Bowser, John

    2015-07-14

    Separation of the components of liquid mixtures is achieved by contacting a liquid mixture with a nonporous membrane having a fluoropolymer selectively permeable layer and imposing a pressure gradient across the membrane from feed side to permeate side. Unusually high transmembrane flux is obtained when the membrane is subjected to one or more process conditions prior to separation. These include (a) leaving some residual amount of membrane casting solvent in the membrane, and (b) contacting the membrane with a component of the mixture to be separated for a duration effective to saturate the membrane with the component.

  10. Micro-patterning of ionic reservoirs within a double bilayer lipid membrane to fabricate a 2D array of ion-channel switch based electrochemical biosensors

    SciTech Connect

    Sansinena, J. M.; Yee, C. K.; Sapuri, A.; Swanson, Basil I.; Redondo, A.; Parikh, A. N.

    2004-01-01

    We present a simple approach for the design of ionic reservoir arrays within a double phospholipid bilayer to ultimately develop a 2D array of ion-channel switch based electrochemical biosensors. As a first step, a primary bilayer lipid membrane is deposited onto an array of electrodes patterned onto a substrate surface. Subsequently, an array of microvoids is created within the bilayer by a wet photolithographic patterning of phospholipid bilayers using a deep UV light source and a quartz/chrome photomask. To ensure registry, the photomask used to pattern bilayers is designed to match up the microvoids within the primary bilayer with the array of electrodes on the substrate surface. The deposition of a secondary bilayer lipid membrane onto the primary bilayer that spans across the patterned microvoids leads to the formation of the array of ionic reservoirs within the double phospholipid bilayer. This is accomplished using giant unilamellar vesicles and by exploiting membrane electrostatics. The use of ion-channels incorporated into the secondary bilayer that covers the individual ionic reservoirs allows the construction of a 2D array of ion-channel switch based electrochemical biosensors that are able to recognize different target-agents simultaneously.

  11. Bilayer Membrane Modulation of Membrane Type 1 Matrix Metalloproteinase (MT1-MMP) Structure and Proteolytic Activity.

    PubMed

    Cerofolini, Linda; Amar, Sabrina; Lauer, Janelle L; Martelli, Tommaso; Fragai, Marco; Luchinat, Claudio; Fields, Gregg B

    2016-01-01

    Cell surface proteolysis is an integral yet poorly understood physiological process. The present study has examined how the pericellular collagenase membrane-type 1 matrix metalloproteinase (MT1-MMP) and membrane-mimicking environments interplay in substrate binding and processing. NMR derived structural models indicate that MT1-MMP transiently associates with bicelles and cells through distinct residues in blades III and IV of its hemopexin-like domain, while binding of collagen-like triple-helices occurs within blades I and II of this domain. Examination of simultaneous membrane interaction and triple-helix binding revealed a possible regulation of proteolysis due to steric effects of the membrane. At bicelle concentrations of 1%, enzymatic activity towards triple-helices was increased 1.5-fold. A single mutation in the putative membrane interaction region of MT1-MMP (Ser466Pro) resulted in lower enzyme activation by bicelles. An initial structural framework has thus been developed to define the role(s) of cell membranes in modulating proteolysis. PMID:27405411

  12. Bilayer Membrane Modulation of Membrane Type 1 Matrix Metalloproteinase (MT1-MMP) Structure and Proteolytic Activity

    PubMed Central

    Cerofolini, Linda; Amar, Sabrina; Lauer, Janelle L.; Martelli, Tommaso; Fragai, Marco; Luchinat, Claudio; Fields, Gregg B.

    2016-01-01

    Cell surface proteolysis is an integral yet poorly understood physiological process. The present study has examined how the pericellular collagenase membrane-type 1 matrix metalloproteinase (MT1-MMP) and membrane-mimicking environments interplay in substrate binding and processing. NMR derived structural models indicate that MT1-MMP transiently associates with bicelles and cells through distinct residues in blades III and IV of its hemopexin-like domain, while binding of collagen-like triple-helices occurs within blades I and II of this domain. Examination of simultaneous membrane interaction and triple-helix binding revealed a possible regulation of proteolysis due to steric effects of the membrane. At bicelle concentrations of 1%, enzymatic activity towards triple-helices was increased 1.5-fold. A single mutation in the putative membrane interaction region of MT1-MMP (Ser466Pro) resulted in lower enzyme activation by bicelles. An initial structural framework has thus been developed to define the role(s) of cell membranes in modulating proteolysis. PMID:27405411

  13. High coverage fluid-phase floating lipid bilayers supported by ω-thiolipid self-assembled monolayers.

    PubMed

    Hughes, Arwel V; Holt, Stephen A; Daulton, Emma; Soliakov, Andrei; Charlton, Timothy R; Roser, Steven J; Lakey, Jeremy H

    2014-09-01

    Large area lipid bilayers, on solid surfaces, are useful in physical studies of biological membranes. It is advantageous to minimize the interactions of these bilayers with the substrate and this can be achieved via the formation of a floating supported bilayer (FSB) upon either a surface bound phospholipid bilayer or monolayer. The FSB's independence is enabled by the continuous water layer (greater than 15 Å) that remains between the two. However, previous FSBs have had limited stability and low density. Here, we demonstrate by surface plasmon resonance and neutron reflectivity, the formation of a complete self-assembled monolayer (SAM) on gold surfaces by a synthetic phosphatidylcholine bearing a thiol group at the end of one fatty acyl chain. Furthermore, a very dense FSB (more than 96%) of saturated phosphatidylcholine can be formed on this SAM by sequential Langmuir-Blodgett and Langmuir-Schaefer procedures. Neutron reflectivity used both isotopic and magnetic contrast to enhance the accuracy of the data fits. This system offers the means to study transmembrane proteins, membrane potential effects (using the gold as an electrode) and even model bacterial outer membranes. Using unsaturated phosphatidylcholines, which have previously failed to form stable FSBs, we achieved a coverage of 73%. PMID:25030385

  14. High coverage fluid-phase floating lipid bilayers supported by ω-thiolipid self-assembled monolayers

    PubMed Central

    Hughes, Arwel V.; Holt, Stephen A.; Daulton, Emma; Soliakov, Andrei; Charlton, Timothy R.; Roser, Steven J.; Lakey, Jeremy H.

    2014-01-01

    Large area lipid bilayers, on solid surfaces, are useful in physical studies of biological membranes. It is advantageous to minimize the interactions of these bilayers with the substrate and this can be achieved via the formation of a floating supported bilayer (FSB) upon either a surface bound phospholipid bilayer or monolayer. The FSB's independence is enabled by the continuous water layer (greater than 15 Å) that remains between the two. However, previous FSBs have had limited stability and low density. Here, we demonstrate by surface plasmon resonance and neutron reflectivity, the formation of a complete self-assembled monolayer (SAM) on gold surfaces by a synthetic phosphatidylcholine bearing a thiol group at the end of one fatty acyl chain. Furthermore, a very dense FSB (more than 96%) of saturated phosphatidylcholine can be formed on this SAM by sequential Langmuir–Blodgett and Langmuir–Schaefer procedures. Neutron reflectivity used both isotopic and magnetic contrast to enhance the accuracy of the data fits. This system offers the means to study transmembrane proteins, membrane potential effects (using the gold as an electrode) and even model bacterial outer membranes. Using unsaturated phosphatidylcholines, which have previously failed to form stable FSBs, we achieved a coverage of 73%. PMID:25030385

  15. 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

  16. The Flip-Flop Diffusion Mechanism across Lipids in a Hybrid Bilayer Membrane.

    PubMed

    Barile, Christopher J; Tse, Edmund C M; Li, Ying; Gewargis, John P; Kirchschlager, Nicholas A; Zimmerman, Steven C; Gewirth, Andrew A

    2016-06-01

    In this study, we examine the mechanism of flip-flop diffusion of proton carriers across the lipid layer of a hybrid bilayer membrane (HBM). The HBM consists of a lipid monolayer appended on top of a self-assembled monolayer containing a Cu-based O2 reduction catalyst on a Au electrode. The flip-flop diffusion rates of the proton carriers dictate the kinetics of O2 reduction by the electrocatalyst. By varying both the tail lengths of the proton carriers and the lipids, we find the combinations of lengths that maximize the flip-flop diffusion rate. These experimental results combined with biophysical modeling studies allow us to propose a detailed mechanism for transmembrane flip-flop diffusion in HBM systems, which involves the bending of the alkyl tail of the proton carrier as the rate-determining step. Additional studies with an unbendable proton carrier further validate these mechanistic findings. PMID:27276263

  17. 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.

  18. Biodegradable, Tethered Lipid Bilayer-Microsphere Systems with Membrane-Integrated α-Helical Peptide Anchors.

    PubMed

    Fried, Eric S; Luchan, Joshua; Gilchrist, M Lane

    2016-04-12

    Supported lipid bilayers (SLBs) are ideally suited for the study of biomembrane-biomembrane interactions and for the biomimicry of cell-to-cell communication, allowing for surface ligand displays that contain laterally mobile elements. However, the SLB paradigm does not include three-dimensionality and biocompatibility. As a way to bypass these limitations, we have developed a biodegradable form of microsphere SLBs, also known as proteolipobeads (PLBs), using PLGA microspheres. Microspheres were synthesized using solvent evaporation and size selected with fluorescence activated cell sorting (FACS). Biomembranes were covalently tethered upon fusion to microsphere supports via short-chain PEG spacers connecting membrane-integrated α-helical peptides and the microsphere surface, affecting membrane diffusivity and mobility as indicated by confocal FRAP analysis. Membrane heterogeneities, which are attributed to PLGA hydrophobicity and rough surface topography, are curtailed by the addition of PEG tethers. This method allows for the presentation of tethered, laterally mobile biomembranes in three dimensions with functionally embedded attachment peptides for mobile ligand displays. PMID:26972467

  19. Interactions between oxicams and membrane bilayers: an explanation for their different COX selectivity.

    PubMed

    Lúcio, M; Ferreira, H; Lima, José L F C; Reis, Salette

    2006-09-01

    Meloxicam was launched as a major new NSAID for the treatment of arthritis following extensive published research confirming its selectivity for COX-2. Several studies proposed possible explanations for its effectiveness and superior safety profile. The proposed theories included chemical structural relationships between meloxicam and other effective NSAIDs with low gastrointestinal toxic effects. However, other oxicams have similar chemical groups, but despite this, are not considered COX-2 selective drugs and exhibit less gastric tolerance. Hence, the aim of this work was to investigate the interactions between oxicams and biomembrane models as it could influence their resorption from the upper gastrointestinal tract and may affect their local gastromucosal tolerability. The partition of oxicams within membranes was determined by calculating their partition coefficients between liposomes and water. Moreover, their location within the bilayer was determined by fluorescence quenching. Finally, zeta-potential measurements were made to complete the information about the binding behaviour of the oxicams and steady-state anisotropy measurements were made to determine their induced perturbation in membrane structure. These studies proved that, in spite of structural similarities, oxicams present different interactions with membranes making possible a virtual division of the class in two groups. Tenoxicam and piroxicam known as COX-1 inhibitors demonstrated higher partition capacity in liposomes/water systems together with a smaller ability to change the membrane fluidity and surface potential. In contrast lornoxicam and meloxicam, which demonstrated activity against COX-2, have revealed smaller partition capacity in liposomes/water systems together with a higher ability to change the membrane fluidity and surface potential. PMID:17017983

  20. Probing the Huntingtin 1-17 Membrane Anchor on a Phospholipid Bilayer by Using All-Atom Simulations

    PubMed Central

    Côté, Sébastien; Binette, Vincent; Salnikov, Evgeniy S.; Bechinger, Burkhard; Mousseau, Normand

    2015-01-01

    Mislocalization and aggregation of the huntingtin protein are related to Huntington’s disease. Its first exon—more specifically the first 17 amino acids (Htt17)—is crucial for the physiological and pathological functions of huntingtin. It regulates huntingtin’s activity through posttranslational modifications and serves as an anchor to membrane-containing organelles of the cell. Recently, structure and orientation of the Htt17 membrane anchor were determined using a combined solution and solid-state NMR approach. This prompted us to refine this model by investigating the dynamics and thermodynamics of this membrane anchor on a POPC bilayer using all-atom, explicit solvent molecular dynamics and Hamiltonian replica exchange. Our simulations are combined with various experimental measurements to generate a high-resolution atomistic model for the huntingtin Htt17 membrane anchor on a POPC bilayer. More precisely, we observe that the single α-helix structure is more stable in the phospholipid membrane than the NMR model obtained in the presence of dodecylphosphocholine detergent micelles. The resulting Htt17 monomer has its hydrophobic plane oriented parallel to the bilayer surface. Our results further unveil the key residues interacting with the membrane in terms of hydrogen bonds, salt-bridges, and nonpolar contributions. We also observe that Htt17 equilibrates at a well-defined insertion depth and that it perturbs the physical properties—order parameter, thickness, and area per lipid—of the bilayer in a manner that could favor its dimerization. Overall, our observations reinforce and refine the NMR measurements on the Htt17 membrane anchor segment of huntingtin that is of fundamental importance to its biological functions. PMID:25762330

  1. Concentration Fluctuation in a Two-Component Fluid Membrane Surrounded with Three-Dimensional Fluids

    NASA Astrophysics Data System (ADS)

    Inaura, Keiichiro; Fujitani, Youhei

    2008-11-01

    We calculate the relaxation rate of the critical concentration fluctuation in a two-component fluid membrane by considering hydrodynamics of the surrounding fluids. Results are compared with the previous results obtained by Seki, Komura, and Imai (2007), who treated the momentum flux from the membrane to its environments using the friction coefficient.

  2. Supported Lipid Bilayer Platform To Test Inhibitors of the Membrane Attack Complex: Insights into Biomacromolecular Assembly and Regulation.

    PubMed

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

    2015-11-01

    Complement activation plays an important role in innate immune defense by triggering formation of the membrane attack complex (MAC), which is a biomacromolecular assembly that exhibits membrane-lytic activity against foreign invaders including various pathogens and biomaterials. Understanding the details of MAC structure and function has been the subject of extensive work involving bulk liposome and erythrocyte assays. However, it is difficult to characterize the mechanism of action of MAC inhibitor drug candidates using the conventional assays. To address this issue, we employ a biomimetic supported lipid bilayer platform to investigate how two MAC inhibitors, vitronectin and clusterin, interfere with MAC assembly in a sequential addition format, as monitored by the quartz crystal microbalance-dissipation (QCM-D) technique. Two experimental strategies based on modular assembly were selected, precincubation of inhibitor and C5b-7 complex before addition to the lipid bilayer or initial addition of inhibitor followed by the C5b-7 complex. The findings indicate that vitronectin inhibits membrane association of C5b-7 via a direct interaction with C5b-7 and via competitive membrane association onto the supported lipid bilayer. On the other hand, clusterin directly interacts with C5b-7 such that C5b-7 is still able to bind to the lipid bilayer, and clusterin affects the subsequent binding of other complement proteins involved in the MAC assembly. Taken together, the findings in this study outline a biomimetic approach based on supported lipid bilayers to explore the interactions between complement proteins and inhibitors, thereby offering insight into MAC assembly and regulation. PMID:26444518

  3. Bordetella pertussis major outer membrane porin protein forms small, anion-selective channels in lipid bilayer membranes.

    PubMed Central

    Armstrong, S K; Parr, T R; Parker, C D; Hancock, R E

    1986-01-01

    The major outer membrane protein of molecular weight 40,000 (the 40K protein) of a virulent isolate of Bordetella pertussis was purified to apparent homogeneity. The purified protein formed an oligomer band (of apparent molecular weight 90,000) on sodium dodecyl sulfate-polyacrylamide gels after solubilization at low temperatures. The porin function of this protein was characterized by the black lipid bilayer method. The 40K protein formed channels smaller than all other constitutive major outer membrane porins studied to date. The average single-channel conductance in 1 M KCl was 0.56 nS. This was less than a third of the conductance previously observed for Escherichia coli porins. Zero-current potential measurements made of the porin to determine its ion selectivity revealed the porin to be more than 100-fold selective for anions over cations. The single-channel conductance was measured as a function of salt concentration. The data could be fitted to a Lineweaver-Burk plot suggesting an anion binding site with a Kd of 1.17 M Cl- and a maximum possible conductance through the channel of 1.28 nS. Images PMID:2420780

  4. Flow over a membrane-covered, fluid-filled cavity

    PubMed Central

    Mongeau, Luc; Frankel, Steven H.

    2014-01-01

    The flow-induced response of a membrane covering a fluid-filled cavity located in a section of a rigid-walled channel was explored using finite element analysis. The membrane was initially aligned with the channel wall and separated the channel fluid from the cavity fluid. As fluid flowed over the membrane-covered cavity, a streamwise-dependent transmural pressure gradient caused membrane deformation. This model has application to synthetic models of the vocal fold cover layer used in voice production research. In this paper, the model is introduced and responses of the channel flow, the membrane, and the cavity flow are summarized for a range of flow and membrane parameters. It is shown that for high values of cavity fluid viscosity, the intracavity pressure and the beam deflection both reached steady values. For combinations of low cavity viscosity and sufficiently large upstream pressures, large-amplitude membrane vibrations resulted. Asymmetric conditions were introduced by creating cavities on opposing sides of the channel and assigning different stiffness values to the two membranes. The asymmetry resulted in reduction in or cessation of vibration amplitude, depending on the degree of asymmetry, and in significant skewing of the downstream flow field. PMID:24723738

  5. Flow over a membrane-covered, fluid-filled cavity.

    PubMed

    Thomson, Scott L; Mongeau, Luc; Frankel, Steven H

    2007-01-01

    The flow-induced response of a membrane covering a fluid-filled cavity located in a section of a rigid-walled channel was explored using finite element analysis. The membrane was initially aligned with the channel wall and separated the channel fluid from the cavity fluid. As fluid flowed over the membrane-covered cavity, a streamwise-dependent transmural pressure gradient caused membrane deformation. This model has application to synthetic models of the vocal fold cover layer used in voice production research. In this paper, the model is introduced and responses of the channel flow, the membrane, and the cavity flow are summarized for a range of flow and membrane parameters. It is shown that for high values of cavity fluid viscosity, the intracavity pressure and the beam deflection both reached steady values. For combinations of low cavity viscosity and sufficiently large upstream pressures, large-amplitude membrane vibrations resulted. Asymmetric conditions were introduced by creating cavities on opposing sides of the channel and assigning different stiffness values to the two membranes. The asymmetry resulted in reduction in or cessation of vibration amplitude, depending on the degree of asymmetry, and in significant skewing of the downstream flow field. PMID:24723738

  6. 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.

  7. 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.

  8. Electrically silent anion transport through bilayer lipid membrane induced by tributyltin and triethyllead.

    PubMed

    Antonenko YuN

    1990-02-01

    The method of the measurement of the nonelectrogenic fluxes of hydrogen (or hydroxyl) ions (JH) based on the local proton gradients formation in the unstirred layers near a bilayer lipid membrane (BLM) is applied for recording the nonelectrogenic anion/OH- exchange on BLM induced by tributyltin (TBT) and a novel carrier (Hager, A., Moser, I., & Berthold, W. 1987. Z. Naturforsch., 42C:1116-1120), triethyllead (TEL). This method has been used previously for measuring the cation fluxes through BLM. TBT and TEL are shown to be equally efficient in the induction of Cl-/OH- exchange. JH induced by TBT is constant at 4 less than pH less than 7. JH decreases at pH less than 4 and pH greater than 7. Both ionophores have a transport sequence: I- greater than Br- greater than Cl- greater than F-. The quantitative measurements reveal that TEL better discriminates these four anions than TBT. It is concluded that this method may prove helpful in a search and study of anion/OH(-)-exchangers isolated from natural membranes. PMID:2319590

  9. Modeling of Fluid-Membrane Interaction in Cellular Microinjection Process

    NASA Astrophysics Data System (ADS)

    Karzar-Jeddi, Mehdi; Diaz, Jhon; Olgac, Nejat; Fan, Tai-Hsi

    2009-11-01

    Cellular microinjection is a well-accepted method to deliver matters such as sperm, nucleus, or macromolecules into biological cells. To improve the success rate of in vitro fertilization and to establish the ideal operating conditions for a novel computer controlled rotationally oscillating intracytoplasmic sperm injection (ICSI) technology, we investigate the fluid-membrane interactions in the ICSI procedure. The procedure consists of anchoring the oocyte (a developing egg) using a holding pipette, penetrating oocyte's zona pellucida (the outer membrane) and the oolemma (the plasma or inner membrane) using an injection micropipette, and finally to deliver sperm into the oocyte for fertilization. To predict the large deformation of the oocyte membranes up to the piercing of the oolemma and the motion of fluids across both membranes, the dynamic fluid-pipette-membrane interactions are formulated by the coupled Stokes' equations and the continuum membrane model based on Helfrich's energy theory. A boundary integral model is developed to simulate the transient membrane deformation and the local membrane stress induced by the longitudinal motion of the injection pipette. The model captures the essential features of the membranes shown on optical images of ICSI experiments, and is capable of suggesting the optimal deformation level of the oolemma to start the rotational oscillations for piercing into the oolemma.

  10. Monitoring of cholesterol oxidation in a lipid bilayer membrane using streptolysin O as a sensing and signal transduction element.

    PubMed

    Shoji, Atsushi; Ikeya, Kana; Aoyagi, Miki; Takatsuji, Ryutaro; Yanagida, Akio; Shibusawa, Yoichi; Sugawara, Masao

    2016-09-01

    Streptolysin O (SLO), which recognizes sterols and forms nanopores in lipid membranes, is proposed as a sensing element for monitoring cholesterol oxidation in a lipid bilayer. The structural requirements of eight sterols for forming nanopores by SLO confirmed that a free 3-OH group in the β-configuration of sterols is required for recognition by SLO in a lipid bilayer. The extent of nanopore formation by SLO in lipid bilayers increased in the order of cholestanolbilayer. The potential of the SLO nanopore-based method for monitoring cholesterol oxidation in a lipid bilayer by other oxidative enzymes is also discussed. PMID:27362457

  11. 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.

  12. The temperature-dependent physical state of polar lipids and their miscibility impact the topography and mechanical properties of bilayer models of the milk fat globule membrane.

    PubMed

    Murthy, Appala Venkata Ramana; Guyomarc'h, Fanny; Lopez, Christelle

    2016-09-01

    The polar lipid assembly and biophysical properties of the biological membrane enveloping the milk fat globules (the MFGM) are yet poorly known, especially in connection with the temperature history that milk can experience after its secretion. However, bioactive mechanisms depend on biological structure, which itself highly depend on temperature. The objectives of this study were to investigate polar lipid packing in hydrated bilayers, models of the MFGM, and to follow at intermolecular level temperature-induced changes in the range 60-6°C, using the combination of differential scanning calorimetry, X-ray diffraction, atomic force microscopy (AFM) imaging and force spectroscopy. MFGM polar lipids, especially sphingomyelin, contain long chain saturated fatty acids with high phase transition temperatures. On cooling, the liquid disordered ld to solid ordered so (gel) phase transition of MFGM polar lipids started at about 40°C, leading to phase separation and formation of so phase domains protruding by about 1nm from the ld phase. Indentation measurements using AFM revealed that the resistance of the so phase domains to rupture was significantly higher than that of the ld phase and that it increased for both the domain and fluid phases with decreasing temperature. However, packing and stability of the bilayers were adversely affected by fast cooling to 6°C or by cooling-rewarming cycle. This study showed that MFGM polar lipid bilayers are dynamic systems. Heterogeneity in the structure and mechanical properties of the membrane was induced by temperature-dependent so/ld phase immiscibility of the lipid components. This could have consequences on the MFGM technological and biological functions (e.g. immunity and milk lipid digestion). PMID:27349732

  13. Fluid Mosaic Membranes and the Light Reactions of Photosynthesis.

    ERIC Educational Resources Information Center

    Hannay, Jack

    1985-01-01

    Discusses: (1) the fluid mosaic membrane structure and light reactions of photosynthesis as exemplified by the Hill and Bendall "Z-scheme"; (2) the arrangement of light-harvesting pigments, electron transport components, and ATP synthesis on chloroplast membranes; and (3) how these topics are treated in A-level textbooks. (JN)

  14. Computer Simulations of Small Molecules in Membranes: Insights from Computer Simulations into the Interactions of Small Molecules with Lipid Bilayers

    NASA Technical Reports Server (NTRS)

    Pohorille, Andrew; New, Michael H.; Schweighofer, Karl; Wilson, Michael A.; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    Two of Ernest Overton's lasting contributions to biology are the Meyer-Overton relationship between the potency of an anesthetic and its solubility in oil, and the Overton rule which relates the permeability of a membrane to the oil-water partition coefficient of the permeating molecule. A growing body of experimental evidence, however, cannot be reconciled with these theories. In particular, the molecular nature of membranes, unknown to Overton, needs to be included in any description of these phenomena. Computer simulations are ideally suited for providing atomic-level information about the behavior of small molecules in membranes. The authors discuss simulation studies relevant to Overton's ideas. Through simulations it was found that anesthetics tend to concentrate at interfaces and their anesthetic potency correlates better with solubility at the water-membrane interface than with solubility in oil. Simulation studies of membrane permeation revealed the anisotropic nature of the membranes, as evidenced, for example, by the highly nonuniform distribution of free volume in the bilayer. This, in turn, influences the diffusion rates of solutes, which increase with the depth in the membrane. Small solutes tend to move by hopping between voids in the bilayer, and this hopping motion may be responsible for the deviation from the Overton rule of the permeation rates of these molecules.

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

    PubMed

    Wang, Xin; Deserno, Markus

    2015-10-28

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

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

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Deserno, Markus

    2015-10-01

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

  17. Lipid bilayers in the gel phase become saturated by triton X-100 at lower surfactant concentrations than those in the fluid phase.

    PubMed

    Ahyayauch, Hasna; Collado, M Isabel; Alonso, Alicia; Goñi, Felix M

    2012-06-01

    It has been repeatedly observed that lipid bilayers in the gel phase are solubilized by lower concentrations of Triton X-100, at least within certain temperature ranges, or other nonionic detergents than bilayers in the fluid phase. In a previous study, we showed that detergent partition coefficients into the lipid bilayer were the same for the gel and the fluid phases. In this contribution, turbidity, calorimetry, and 31P-NMR concur in showing that bilayers in the gel state (at least down to 13-20°C below the gel-fluid transition temperature) become saturated with detergent at lower detergent concentrations than those in the fluid state, irrespective of temperature. The different saturation may explain the observed differences in solubilization. PMID:22713566

  18. Order Parameters of a Transmembrane Helix in a Fluid Bilayer: Case Study of a WALP Peptide

    PubMed Central

    Holt, Andrea; Rougier, Léa; Réat, Valérie; Jolibois, Franck; Saurel, Olivier; Czaplicki, Jerzy; Killian, J. Antoinette; Milon, Alain

    2010-01-01

    Abstract A new solid-state NMR-based strategy is established for the precise and efficient analysis of orientation and dynamics of transmembrane peptides in fluid bilayers. For this purpose, several dynamically averaged anisotropic constraints, including 13C and 15N chemical shift anisotropies and 13C-15N dipolar couplings, were determined from two different triple-isotope-labeled WALP23 peptides (2H, 13C, and 15N) and combined with previously published quadrupolar splittings of the same peptide. Chemical shift anisotropy tensor orientations were determined with quantum chemistry. The complete set of experimental constraints was analyzed using a generalized, four-parameter dynamic model of the peptide motion, including tilt and rotation angle and two associated order parameters. A tilt angle of 21° was determined for WALP23 in dimyristoylphosphatidylcholine, which is much larger than the tilt angle of 5.5° previously determined from 2H NMR experiments. This approach provided a realistic value for the tilt angle of WALP23 peptide in the presence of hydrophobic mismatch, and can be applied to any transmembrane helical peptide. The influence of the experimental data set on the solution space is discussed, as are potential sources of error. PMID:20441750

  19. Electro-optics of membrane electroporation in diphenylhexatriene-doped lipid bilayer vesicles.

    PubMed

    Kakorin, S; Stoylov, S P; Neumann, E

    1996-01-16

    The electric (linear) dichroisms observed in the membrane electroporation of salt-filled lipid bilayer vesicles (diameter O = 2 alpha = 0.32 micron; inside [NaCl] = 0.2 M) in isotonic aqueous 0.284 M sucrose-0.2 mM NaCl solution indicate orientation changes of the anisotropic light scattering centers (lipid head groups) and of the optical transition moments of the membrane-inserted probe 1,6-diphenyl-1,3,5-hexatriene (DPH). Both the turbidity dichroism and DPH absorbance dichroism show peculiar features: (1) at external electric fields E > or = Esat the time course of the dichroism shows a maximum value (reversal): Esat = 4.0 (+/- 0.2) MV m-1, T = 293 K (20 degrees C), (2) this reversal value is independent of the field strength for E > or = Esat, (3) the dichroism amplitudes exhibit a maximum value Emax = 3.0 (+/- 0.5) MV m-1, (4) for the pulse duration of 10 microseconds there is one dominant visible normal mode, the relaxation rate increases up to tau-1 approximately 0.6 x 10(6) s-1 at Esat and then decreases for E > Esat. The data can be described in terms of local lipid phase transitions involving clusters Ln of n lipids in the pore edges according to the three-state scheme C<-->HO<-->HI, C being the closed bilayer state, HO the hydrophobic pore state and HI the hydrophilic or inverted pore state with rotated lipid and DPH molecules. At E > or = Esat, further transitions HO<-->HO* and HI<-->HI* are rapidly coupled to the C<-->HO transition, which is rate-limiting. The vesicle geometry conditions a cos theta dependence of the local membrane field effects relative to the E direction and the data reflect cos theta averages. The stationary induced transmembrane voltage delta phi (theta, lambda m) = -1.5 aEf(lambda m) magnitude of cos theta does not exceed the limiting value delta phi sat = -0.53 V, corresponding to the field strength Em,sat = -delta phi sat/d = 100 MV m-1 (10(3) kV cm-1), due to increasing membrane conductivity lambda m. At E = Esat, f(lambda m

  20. Enhanced oxygen separation through robust freeze-cast bilayered dual-phase membranes.

    PubMed

    Gaudillere, Cyril; Garcia-Fayos, Julio; Balaguer, María; Serra, José M

    2014-09-01

    Dual-phase oxygen-permeable asymmetric membranes with enhanced oxygen permeation were prepared by combining freeze-casting, screen-printing, and constraint-sintering techniques. The membranes were evaluated under oxyfuel operating conditions. The prepared membranes are composed of an original ice-templated La(0.6)Sr(0.4)Co(0.2)Fe(0.8)O(3-δ) support with hierarchically oriented porosity and a top fully densified bilayered coating comprising a 10 μm-thick La(0.6)Sr(0.4)Co(0.2)Fe(0.8)O(3-δ) layer and a top protective 8 μm-thick layer made of an optimized NiFe2O4/Ce(0.8)Tb(0.2)O(2-δ) composite synthesized by the one-pot Pechini method. Preliminary analysis confirmed the thermochemical compatibility of the three involved phases at high temperature without any additional phase detected. This membrane exhibited a promising oxygen permeation value of 4.8 mL min(-1)  cm(-2) at 1000 °C upon using Ar and air as the sweep and feed gases, respectively. Mimicking oxyfuel operating conditions by switching argon to pure CO2 as a sweep gas at 1000 °C and air as feed enabled an oxygen flux value of 5.6 mL min(-1)  cm(-2) to be reached. Finally, under the same conditions and increasing the oxygen partial pressure to 0.1 MPa in the feed, the oxygen permeation reached 12 mL min(-1)  cm(-2). The influence of CO2 content in the sweep gas was studied and its reversible and positive effect over oxygen permeation at temperatures equal to or above 950 °C was revealed. Finally, the membrane stability over a period of 150 h under CO2-rich sweep gas showed a low degradation rate of 2.4×10(-2)  mL min(-1)  cm(-2) per day. PMID:25070608

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

    PubMed

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

    1976-01-01

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

  2. Curvature-undulation coupling as a basis for curvature sensing and generation in bilayer membranes.

    PubMed

    Bradley, Ryan P; Radhakrishnan, Ravi

    2016-08-30

    We present coarse-grained molecular dynamics simulations of the epsin N-terminal homology domain interacting with a lipid bilayer and demonstrate a rigorous theoretical formalism and analysis method for computing the induced curvature field in varying concentrations of the protein in the dilute limit. Our theory is based on the description of the height-height undulation spectrum in the presence of a curvature field. We formulated an objective function to compare the acquired undulation spectrum from the simulations to that of the theory. We recover the curvature field parameters by minimizing the objective function even in the limit where the protein-induced membrane curvature is of the same order as the amplitude due to thermal undulations. The coupling between curvature and undulations leads to significant predictions: (i) Under dilute conditions, the proteins can sense a site of spontaneous curvature at distances much larger than their size; (ii) as the density of proteins increases the coupling focuses and stabilizes the curvature field to the site of the proteins; and (iii) the mapping of the protein localization and the induction of a stable curvature is a cooperative process that can be described through a Hill function. PMID:27531962

  3. 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.

  4. A Ca2+-activated channel from Xenopus laevis oocyte membranes reconstituted into planar bilayers.

    PubMed Central

    Young, G P; Young, J D; Deshpande, A K; Goldstein, M; Koide, S S; Cohn, Z A

    1984-01-01

    Plasma membrane fractions from Xenopus laevis oocytes were incorporated into planar lipid bilayers. We show the existence of numerous Ca2+-activated nonspecific channels that are more permeable to anions. These channels are activated by Ca2+ at micromolar concentration but not by Mg2+, Zn2+, or Mn2+, even at millimolar concentrations. Decreasing Ca2+ concentration to less than 1 microM decreases the time of channel opening until channels close completely in the absence of Ca2+ and in the presence of EGTA. I- and Br- are more permeable through this channel than Cl-. The time during which the channels remain open is also voltage-dependent, with the channels switching off at higher voltages in both polarities. Single-channel activity shows a conductance of 380 pS in 1 M NaCl and 1 mM CaCl2, with an average open lifetime of 1.5 s at 40 mV. Similar channels are found in different stages of oocyte maturation. These observations support the hypothesis that an increase in oocyte-free Ca2+ activates directly these channels, and the resultant Cl- efflux forms the ionic basis for the fertilization potential in X. laevis. PMID:6089180

  5. Formation and characterization of microcrystalline semiconductor particles on bilayer lipid membranes

    SciTech Connect

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

    1987-05-21

    Microcrystalline cadmium, indium, copper, and zinc sulfides were generated in situ on the surface of bilayer lipid membranes (BLMs) prepared from bovine-brain phosphatidylserine (PS), glyceryl monooleate (GMO), and a synthetic, polymerizable surfactant (n-C/sub 15/H/sub 31/CO/sub 2/(CH/sub 2/)/sub 2/)/sub 2/N/sup +/(CH/sub 3/)CH/sub 2/C/sub 6/H/sub 4/CH double bond CH/sub 2/, Cl/sup -/ (STYRS). Semiconductor-containing BLMs remained stable for days. Semiconductor formation on the BLM surface was monitored by optical microscopy, voltage-dependent capacitance measurements, and absorption and intracavity-laser-absorption spectroscopy. Band gap excitation of GMO- BLM-incorporated CdS resulted in the development of photovoltage. Irradiation of CdS incorporated into BLMs formed from STYRS (using a 350-nm cutoff filter) led to absorption losses due to the styrene moiety in the surfactant. Apparently, CdS sensitized the photopolymerization of STRYS BLMs.

  6. Diffusion and spectroscopy of water and lipids in fully hydrated dimyristoylphosphatidylcholine bilayer membranes

    SciTech Connect

    Yang, J.; Martí, J.; Calero, C.

    2014-03-14

    Microscopic structure and dynamics of water and lipids in a fully hydrated dimyristoylphosphatidylcholine phospholipid lipid bilayer membrane in the liquid-crystalline phase have been analyzed with all-atom molecular dynamics simulations based on the recently parameterized CHARMM36 force field. The diffusive dynamics of the membrane lipids and of its hydration water, their reorientational motions as well as their corresponding spectral densities, related to the absorption of radiation, have been considered for the first time using the present force field. In addition, structural properties such as density and pressure profiles, a deuterium-order parameter, surface tension, and the extent of water penetration in the membrane have been analyzed. Molecular self-diffusion, reorientational motions, and spectral densities of atomic species reveal a variety of time scales playing a role in membrane dynamics. The mechanisms of lipid motion strongly depend on the time scale considered, from fast ballistic translation at the scale of picoseconds (effective diffusion coefficients of the order of 10{sup −5} cm{sup 2}/s) to diffusive flow of a few lipids forming nanodomains at the scale of hundreds of nanoseconds (diffusion coefficients of the order of 10{sup −8} cm{sup 2}/s). In the intermediate regime of sub-diffusion, collisions with nearest neighbors prevent the lipids to achieve full diffusion. Lipid reorientations along selected directions agree well with reported nuclear magnetic resonance data and indicate two different time scales, one about 1 ns and a second one in the range of 2–8 ns. We associated the two time scales of reorientational motions with angular distributions of selected vectors. Calculated spectral densities corresponding to lipid and water reveal an overall good qualitative agreement with Fourier transform infrared spectroscopy experiments. Our simulations indicate a blue-shift of the low frequency spectral bands of hydration water as a result of

  7. Diffusion and spectroscopy of water and lipids in fully hydrated dimyristoylphosphatidylcholine bilayer membranes.

    PubMed

    Yang, J; Calero, C; Martí, J

    2014-03-14

    Microscopic structure and dynamics of water and lipids in a fully hydrated dimyristoylphosphatidylcholine phospholipid lipid bilayer membrane in the liquid-crystalline phase have been analyzed with all-atom molecular dynamics simulations based on the recently parameterized CHARMM36 force field. The diffusive dynamics of the membrane lipids and of its hydration water, their reorientational motions as well as their corresponding spectral densities, related to the absorption of radiation, have been considered for the first time using the present force field. In addition, structural properties such as density and pressure profiles, a deuterium-order parameter, surface tension, and the extent of water penetration in the membrane have been analyzed. Molecular self-diffusion, reorientational motions, and spectral densities of atomic species reveal a variety of time scales playing a role in membrane dynamics. The mechanisms of lipid motion strongly depend on the time scale considered, from fast ballistic translation at the scale of picoseconds (effective diffusion coefficients of the order of 10(-5) cm(2)/s) to diffusive flow of a few lipids forming nanodomains at the scale of hundreds of nanoseconds (diffusion coefficients of the order of 10(-8) cm(2)/s). In the intermediate regime of sub-diffusion, collisions with nearest neighbors prevent the lipids to achieve full diffusion. Lipid reorientations along selected directions agree well with reported nuclear magnetic resonance data and indicate two different time scales, one about 1 ns and a second one in the range of 2-8 ns. We associated the two time scales of reorientational motions with angular distributions of selected vectors. Calculated spectral densities corresponding to lipid and water reveal an overall good qualitative agreement with Fourier transform infrared spectroscopy experiments. Our simulations indicate a blue-shift of the low frequency spectral bands of hydration water as a result of its interaction with

  8. Diffusion and spectroscopy of water and lipids in fully hydrated dimyristoylphosphatidylcholine bilayer membranes

    NASA Astrophysics Data System (ADS)

    Yang, J.; Calero, C.; Martí, J.

    2014-03-01

    Microscopic structure and dynamics of water and lipids in a fully hydrated dimyristoylphosphatidylcholine phospholipid lipid bilayer membrane in the liquid-crystalline phase have been analyzed with all-atom molecular dynamics simulations based on the recently parameterized CHARMM36 force field. The diffusive dynamics of the membrane lipids and of its hydration water, their reorientational motions as well as their corresponding spectral densities, related to the absorption of radiation, have been considered for the first time using the present force field. In addition, structural properties such as density and pressure profiles, a deuterium-order parameter, surface tension, and the extent of water penetration in the membrane have been analyzed. Molecular self-diffusion, reorientational motions, and spectral densities of atomic species reveal a variety of time scales playing a role in membrane dynamics. The mechanisms of lipid motion strongly depend on the time scale considered, from fast ballistic translation at the scale of picoseconds (effective diffusion coefficients of the order of 10-5 cm2/s) to diffusive flow of a few lipids forming nanodomains at the scale of hundreds of nanoseconds (diffusion coefficients of the order of 10-8 cm2/s). In the intermediate regime of sub-diffusion, collisions with nearest neighbors prevent the lipids to achieve full diffusion. Lipid reorientations along selected directions agree well with reported nuclear magnetic resonance data and indicate two different time scales, one about 1 ns and a second one in the range of 2-8 ns. We associated the two time scales of reorientational motions with angular distributions of selected vectors. Calculated spectral densities corresponding to lipid and water reveal an overall good qualitative agreement with Fourier transform infrared spectroscopy experiments. Our simulations indicate a blue-shift of the low frequency spectral bands of hydration water as a result of its interaction with lipids

  9. Reconstitution of the native mitochondrial outer membrane in planar bilayers. Comparison with the outer membrane in a patch pipette and effect of aluminum compounds.

    PubMed

    Mirzabekov, T; Ballarin, C; Nicolini, M; Zatta, P; Sorgato, M C

    1993-04-01

    Detergent-free rat brain outer mitochondrial membranes were incorporated in planar lipid bilayers in the presence of an osmotic gradient, and studied at high (1 M KCl) and low (150 mM KCl) ionic strength solutions. By comparison, the main outer mitochondrial membrane protein, VDAC, extracted from rat liver with Triton X-100, was also studied in 150 mM KCl. In 1 M KCl, brain outer membranes gave rise to electrical patterns which resembled very closely those widely described for detergent-extracted VDAC, with transitions to several subconducting states upon increase of the potential difference, and sensitivity to polyanion. The potential dependence of the conductance of the outer membrane, however, was steeper and the extent of closure higher than that observed previously for rat brain VDAC. In 150 mM KCl, bilayers containing only one channel had a conductance of 700 +/- 23 pS for rat brain outer membranes, and 890 +/- 29 pS for rat liver VDAC. Use of a fast time resolution setup allowed demonstration of open-close transitions in the millisecond range, which were independent of the salt concentration and of the protein origin. We also found that a potential difference higher than approx. +/- 60 mV induced an almost irreversible decrease of the single channel conductance to few percentages of the full open state and a change in the ionic selectivity. These results show that the behavior of the outer mitochondrial membrane in planar bilayers is close to that detected with the patch clamp (Moran et al., 1992, Eur. Biophys. J. 20:311-319). The neurotoxicological action of aluminum was studied in single outer membrane channels from rat brain mitochondria. We found that microM concentrations of Al Cl3 and aluminum lactate decreased the conductance by about 50%, when the applied potential difference was positive relative to the side of the metal addition. PMID:7685821

  10. Channels Formed by Botulinum, Tetanus, and Diphtheria Toxins in Planar Lipid Bilayers: Relevance to Translocation of Proteins across Membranes

    NASA Astrophysics Data System (ADS)

    Hoch, David H.; Romero-Mira, Miryam; Ehrlich, Barbara E.; Finkelstein, Alan; Dasgupta, Bibhuti R.; Simpson, Lance L.

    1985-03-01

    The heavy chains of both botulinum neurotoxin type B and tetanus toxin form channels in planar bilayer membranes. These channels have pH-dependent and voltage-dependent properties that are remarkably similar to those previously described for diphtheria toxin. Selectivity experiments with anions and cations show that the channels formed by the heavy chains of all three toxins are large; thus, these channels could serve as ``tunnel proteins'' for translocation of active peptide fragments. These findings support the hypothesis that the active fragments of botulinum neurotoxin and tetanus toxin, like that of diphtheria toxin, are translocated across the membranes of acidic vesicles.

  11. Photodynamic inactivation of gramicidin channels in bilayer lipid membranes: protective efficacy of singlet oxygen quenchers depends on photosensitizer location.

    PubMed

    Rokitskaya, T I; Firsov, A M; Kotova, E A; Antonenko, Y N

    2015-06-01

    The impact of double bonds in fatty acyl tails of unsaturated lipids on the photodynamic inactivation of ion channels formed by the pentadecapeptide gramicidin A in a planar bilayer lipid membrane was studied. The presence of unsaturated acyl tails protected gramicidin A against photodynamic inactivation, with efficacy depending on the depth of a photosensitizer in the membrane. The protective effect of double bonds was maximal with membrane-embedded chlorin e6-monoethylenediamine monoamide dimethyl ester, and minimal - in the case of water-soluble tri-sulfonated aluminum phthalocyanine (AlPcS3) known to reside at the membrane surface. By contrast, the protective effect of the hydrophilic singlet oxygen scavenger ascorbate was maximal for AlPcS3 and minimal for amide of chlorin e6 dimethyl ester. The depth of photosensitizer position in the lipid bilayer was estimated from the quenching of photosensitizer fluorescence by iodide. Thus, the protective effect of a singlet oxygen scavenger against photodynamic inactivation of the membrane-inserted peptide is enhanced upon location of the photosensitizer and scavenger molecules in close vicinity to each other. PMID:26531019

  12. Anomalous and anisotropic nanoscale diffusion of hydration water molecules in fluid lipid membranes.

    PubMed

    Toppozini, Laura; Roosen-Runge, Felix; Bewley, Robert I; Dalgliesh, Robert M; Perring, Toby; Seydel, Tilo; Glyde, Henry R; García Sakai, Victoria; Rheinstädter, Maikel C

    2015-11-14

    We have studied nanoscale diffusion of membrane hydration water in fluid-phase lipid bilayers made of 1,2-dimyristoyl-3-phosphocholine (DMPC) using incoherent quasi-elastic neutron scattering. Dynamics were fit directly in the energy domain using the Fourier transform of a stretched exponential. By using large, 2-dimensional detectors, lateral motions of water molecules and motions perpendicular to the membranes could be studied simultaneously, resulting in 2-dimensional maps of relaxation time, τ, and stretching exponent, β. We present experimental evidence for anomalous (sub-diffusive) and anisotropic diffusion of membrane hydration water molecules over nanometer distances. By combining molecular dynamics and Brownian dynamics simulations, the potential microscopic origins for the anomaly and anisotropy of hydration water were investigated. Bulk water was found to show intrinsic sub-diffusive motion at time scales of several picoseconds, likely related to caging effects. In membrane hydration water, however, the anisotropy of confinement and local dynamical environments leads to an anisotropy of relaxation times and stretched exponents, indicative of anomalous dynamics. PMID:26338138

  13. Oxidation of Membrane Curvature-Regulating Phosphatidylethanolamine Lipid Results in Formation of Bilayer and Cubic Structures.

    PubMed

    Sankhagowit, Shalene; Lee, Ernest Y; Wong, Gerard C L; Malmstadt, Noah

    2016-03-15

    Oxidation is associated with conditions related to chronic inflammations and aging. Cubic structures have been observed in the smooth endoplasmic reticulum and mitochondrial membranes of cells under oxidative stress (e.g., tumor cells and virus-infected cells). It has been previously suspected that oxidation can result in the rearrangement of lipids from a fluid lamellar phase to a cubic structure in organelles containing membranes enriched with amphiphiles that have nonzero intrinsic curvature, such as phosphatidylethanolamine (PE) and cardiolipin. This study focuses on the oxidation of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), a lipid that natively forms an inverted hexagonal phase at physiological conditions. The oxidized samples contain an approximately 3:2 molar ratio of nonoxidized to oxidized DOPE. Optical microscopy images collected during the hydration of this mixture from a dried film suggest that the system evolves into a coexistence of a stable fluid lamellar phase and transient square lattice structures with unit cell sizes of 500-600 nm. Small-angle X-ray scattering of the same lipid mixture yielded a body-centered Im3m cubic phase with the lattice parameter of 14.04 nm. On average, the effective packing parameter of the oxidized DOPE species was estimated to be 0.657 ± 0.069 (standard deviation). This suggests that the oxidation of PE leads to a group of species with inverted molecular intrinsic curvature. Oxidation can create amphiphilic subpopulations that potently impact the integrity of the membrane, since negative Gaussian curvature intrinsic to cubic phases can enable membrane destabilization processes. PMID:26866900

  14. Kinetics of symmetry and asymmetry in a phase-separating bilayer membrane

    NASA Astrophysics Data System (ADS)

    Williamson, J. J.; Olmsted, P. D.

    2015-11-01

    We simulate a phase-separating bilayer in which the leaflets experience a direct coupling favoring local compositional symmetry ("registered" bilayer phases), and an indirect coupling due to hydrophobic mismatch that favors strong local asymmetry ("antiregistered" bilayer phases). For wide ranges of overall leaflet compositions, multiple competing states are possible. For estimated physical parameters, a quenched bilayer may first evolve toward a metastable state more asymmetric than if the leaflets were uncorrelated; subsequently, it must nucleate to reach its equilibrium, more symmetric, state. These phase-transition kinetics exhibit characteristic signatures through which fundamental and opposing interleaflet interactions may be probed. We emphasize how bilayer phase diagrams with a separate axis for each leaflet can account for overall and local symmetry or asymmetry, and capture a range of observations in the experiment and simulation literature.

  15. The modulating effect of mechanical changes in lipid bilayers caused by apoE-containing lipoproteins on Aβ induced membrane disruption.

    PubMed

    Legleiter, Justin; Fryer, John D; Holtzman, David M; Kowalewski, Andtomasz

    2011-10-19

    A major feature of Alzheimer's disease (AD), a late-onset neurodegenerative disorder, is the ordered aggregation of the β-amyloid peptide (Aβ) into fibrils that comprise extracellular neuritic plaques found in the disease brain. One of many potential pathways for Aβ toxicity may be modulation of lipid membrane function. Here, we show by in situ atomic force microscopy (AFM) that astrocyte secreted lipoprotein particles (ASLPs) containing different isoforms of apolipoprotein E (apoE), of which the apoE4 allele is a major risk factor for the development of AD, can protect total brain lipid extract bilayers from Aβ(1-40) induced disruption. The apoE4 allele was less effective in protecting lipid bilayers from disruption compared with apoE3. Size analysis of apoE-containing ASLPs and mechanical studies of bilayer properties revealed that apoE-containing ASLPs modulate the mechanical properties of bilayers by acquiring some bilayer components (most likely cholesterol and/or oxidatively damaged lipids). Measurement of bilayer mechanical properties was accomplished with scanning probe acceleration microscopy (SPAM). These measurements demonstrated that apoE4 was also less effective in modulating mechanical properties of bilayers in comparison with apoE3. This ability of apoE to alter the mechanical properties of lipid membranes may represent a potential mechanism for the suppression of Aβ(1-40) induced bilayer disruption. PMID:22125665

  16. Cell membrane causes the lipid bilayers to behave as variable capacitors: A resonance with self-induction of helical proteins.

    PubMed

    Monajjemi, Majid

    2015-12-01

    Cell membrane has a unique feature of storing biological energies in a physiologically relevant environment. This study illustrates a capacitor model of biological cell membrane including DPPC structures. The electron density profile models, electron localization function (ELF) and local information entropy have been applied to study the interaction of proteins with lipid bilayers in the cell membrane. The quantum and coulomb blockade effects of different thicknesses in the membrane have also been specifically investigated. It has been exhibited the quantum effects can appear in a small region of the free space within the membrane thickness due to the number and type of phospholipid layers. In addition, from the viewpoint of quantum effects by Heisenberg rule, it is shown the quantum tunneling is allowed in some micro positions while it is forbidden in other forms of membrane capacitor systems. Due to the dynamical behavior of the cell membrane, its capacitance is not fixed which results a variable capacitor. In presence of the external fields through protein trance membrane or ions, charges exert forces that can influence the state of the cell membrane. This causes to appear the charge capacitive susceptibility that can resonate with self-induction of helical coils; the resonance of which is the main reason for various biological pulses. PMID:26529673

  17. Microparticles as biomarkers of lung disease: enumeration in biological fluids using lipid bilayer microspheres.

    PubMed

    McVey, Mark J; Spring, Christopher M; Semple, John W; Maishan, Mazharul; Kuebler, Wolfgang M

    2016-05-01

    Extracellular vesicles, specifically microparticles (MPs), are rapidly gaining attention for their capacity to act as biomarkers for diagnosis, prognosis, or responsiveness to therapy in lung disease, in keeping with the concept of precision medicine. However, MP analysis by high-sensitivity flow cytometry (FCM) is complicated by a lack of accurate means for MP enumeration. To address this gap, we report here an enhanced FCM MP gating and enumeration technique based on the use of novel engineered lipid bilayer microspheres (LBMs). By comparison of LBM-based MP enumeration with conventional bead- or fluorescent-based FCM enumeration techniques and a gravimetric consumption gold standard, we found LBMs to be superior to commercial bead preparations, showing the smallest fixed bias and limits of agreement in Bland Altman analyses. LBMs had simultaneous capacity to aid FCM enumeration of MPs in plasma, BAL, and cell culture supernatants. LBM enumeration detected differences in MP counts in mice exposed to intraperitoneal lipopolysaccharide or saline. LBMs provided for 1) higher sensitivity for gating MPs populations, 2) reduced background within MP gates, 3) more appropriate size, and 4) an inexpensive alternative amenable to different fluorescent tags. LBM-based MP enumeration was useful for a series of different FCM systems assessed, whereas LBM gating benefited high- but not low-sensitivity FCM systems compared with fluorescence gating. By offering exclusive advantages over current means of gating and enumerating MPs, LBMs are uniquely suited to realizing the potential of MPs as biomarkers in biological lung fluids and facilitating precision medicine in lung disease. PMID:26944090

  18. Fundamental Studies of Assembly and Mechanical Properties of Lipid Bilayer Membranes and Unilamellar Vesicles

    NASA Astrophysics Data System (ADS)

    Wang, Xi

    This dissertation work focuses on: (i) obtaining a phospholipid bilayer membrane (LBM)/conducting electrode system with low defect density and optimized rigidity; (ii) investigating vesicle stability and mechanical properties. LBM is a simplified yet representative cell membrane model. LBMs assembled on conductive surfaces can probe protein-LBM interactions activities electrochemically. Sterically stabilized vesicles could be used as cell models or for drug delivery. The main challenges for LBM assembly on gold are vesicles do not spontaneously rupture to form LBMs on gold and the roughness of the gold substrate has considerable influence on molecular film defect density. In this study, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) vesicles were functionalized with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine- N-poly(ethylene glycol)-2000-N-[3-(2-pyridyldithio)propionate] (DSPE-PEG-PDP) to yield stable LBMs on gold without surface modification. A template-stripping method was used to obtain atomically flat and pristine gold surfaces. The critical force to initiate vesicle rupture decreases with increasing DSPE-PEG-PDP concentration, indicating that gold-thiolate bonding between DSPE-PEG-PDP and gold substrates promotes LBM formation. Mechanical properties of LBMs and vesicles were investigated as a function of DSPE-PEG-PDP concentration via Atomic Force Microscopy. The elastic moduli of LBMs were determined with DSPE-PEG-PDP concentration ranging from 0mol% to 24mol% and were found to depend on PEG chain conformation. Incorporating DSPE-PEG-PDP molecules with PEG in mushroom conformation results in a decrease of LBM rigidity, while incorporating PEG in brush conformation leads to LBM stiffening. Contrarily, mechanical properties of functionalized vesicles did not vary significantly by varying DSPE-PEG-PDP concentration. LBM with tunable rigidity by adjusting DSPE-PEG-PDP concentration provides a versatile cell membrane model for studying protein or

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

    NASA Astrophysics Data System (ADS)

    Todorov, Angelio Todorov

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

  20. Microarrays of phospholipid bilayers generated by inkjet printing.

    PubMed

    Yamada, Misato; Imaishi, Hiromasa; Morigaki, Kenichi

    2013-05-28

    We report an efficient and reproducible method to generate a microarray of model biological membranes on a solid substrate by applying the inkjet printing technology. Although inkjet printing is currently widely used for industrial fabrication processes, including biological materials, printing lipid membranes remains technically challenging due to the hydrophobic nature of droplets and instability of the lipid bilayer structure against dehydration. In the present study, we printed lipids onto a glass substrate covered with a micropatterned membrane of a polymeric phospholipid bilayer. Polymeric bilayers were formed by the lithographic photopolymerization of a diacetylene-containing phospholipid, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DiynePC). After removal of nonpolymerized DiynePC with a detergent solution, natural lipid membranes were incorporated into the polymer-free regions (corrals) by using an electric-field-based inkjet printing device that can eject subfemtoliter volume droplets. To avoid rapid dehydration and destabilization, we preprinted an aqueous solution containing agarose and trehalose onto the corrals and subsequently printed lipid suspensions ("two-step-printing method"). After rinsing, stable lipid bilayer membranes were formed in the corrals. The bilayers were continuous and fluid as confirmed by fluorescence recovery after photobleaching. We could introduce multiple bilayer patches having different lipid compositions into the neighboring corrals. The present results demonstrate that the combination of a patterned polymeric bilayer and inkjet printing technology enables efficient, reliable, and scalable generation of the model membrane microarrays having varied compositions. PMID:23627772

  1. Labeled Protein Recognition at a Membrane Bilayer Interface by Embedded Synthetic Receptors

    PubMed Central

    2015-01-01

    Self-folding deep cavitands embedded in a supported lipid bilayer are capable of recognizing suitably labeled proteins at the bilayer interface. The addition of a choline derived binding “handle” to a number of different proteins allows their selective noncovalent recognition, with association constants on the order of 105 M–1. The proteins are displayed at the water:bilayer interface, and a single binding handle allows recognition of the large, charged protein by a small molecule synthetic receptor via complementary shape and charge interactions. PMID:25130415

  2. Micropipette aspiration of an inflated fluid-filled spherical membrane

    NASA Astrophysics Data System (ADS)

    Sohail, Touqeer; Tang, Tian; Nadler, Ben

    2012-08-01

    The micropipette technique has been widely used to determine the mechanical response of living cells. Cell is a complex structure and has highly nonlinear behavior when aspirated by the micropipette. Different models exist in the literature to determine the physical properties of the cells from the micropipette aspiration. In this work, we model the cell's response during micropipette aspiration using continuum nonlinear membrane theory. The peripheral surface of the cell is modeled as a nonlinear membrane. The membrane is homogenous, isotropic, and of hyper-elastic material. The cytoplasm of the cell is modeled as an incompressible fluid. Our results show good agreement with the experiments reported in the literature.

  3. Study of pH (low) insertion peptides (pHLIPs) interaction with lipid bilayer of membrane

    NASA Astrophysics Data System (ADS)

    Weerakkody, Dhammika

    The pH-dependent interactions of pHLIPsRTM (pH (Low) Insertion Peptides) with lipid bilayer of membrane provides an opportunity to study and address fundamental questions of protein folding/insertion into membrane and unfolding/exit, as well as develop novel approach to target acidic diseased tissue such as cancer, ischemic myocardium, infection and others. The main goal of the work presented here is to answer the following questions: - What is the molecular mechanism of spontaneous insertion and folding of a peptide in a lipid bilayer of membrane; - What is the molecular mechanism of unfolding and exit of a peptide from a lipid bilayer of membrane; - How polar cargo attached to a peptide's inserting end might affect the process of insertion into a lipid bilayer of membrane; How sequence variation will affect a peptide's interactions with a lipid bilayer of membrane (partitioning into bilayer at neutral and low pH; apparent pK of insertion) with the main goal to identify the best pHLIP variants for imaging and therapy of pathological states such as cancer and others. It has been demonstrated that pHLIP insertion into a membrane is associated with the protonation of Asp/Glu residues, which leads to an increase of hydrophobicity that triggers the folding and insertion of the peptide across a lipid bilayer. The insertion of the pHLIP is unidirectional and it is accompanied by the release of energy. Therefore, the energy of membrane associated-folding can be used to favor the movement of cell-impermeable polar cargo molecules across the hydrophobic membrane bilayer when they are attached to the inserting end of pHLIP. Both pH-targeting behavior and molecular translocation have been demonstrated in cultured cells and in vivo. Thus, there is an opportunity to develop a novel concept in drug delivery, which is based on the use of a monomeric, pH-sensitive peptide molecular transporter, to deliver agents that are significantly more polar than conventional drugs

  4. Bilayer mass transport model for determining swelling and diffusion in coated, ultrathin membranes.

    PubMed

    Nadermann, Nichole K; Chan, Edwin P; Stafford, Christopher M

    2015-02-18

    Water transport and swelling properties of an ultrathin, selective polyamide layer with a hydrophilic polymer coating, i.e., a polymer bilayer, are studied using quartz crystal microbalance with dissipation (QCM-D). Specifically, QCM-D is used to measure the dynamic and equilibrium change in mass in a series of differential sorption experiments to determine the dependence of the apparent diffusion coefficient and equilibrium swelling of the bilayer as a function of the water vapor activity. To determine transport properties specific to the polyamide layer, sorption kinetics of the bilayer was modeled with a bilayer mass transport model. The swelling and water diffusion coefficients are interpreted according to the Painter-Shenoy polymer network swelling model and the solution-diffusion model, respectively. PMID:25597964

  5. 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.

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

    PubMed

    Vögele, Martin; Hummer, Gerhard

    2016-08-25

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

  7. Stable and fluid ethylphosphocholine membranes in a poly(dimethylsiloxane) microsensor for toxin detection in flooded waters.

    PubMed

    Phillips, K Scott; Dong, Yi; Carter, David; Cheng, Quan

    2005-05-01

    Highly stable and fluid supported bilayer membranes were fabricated by fusion of positively charged ethylphosphocholine (DOPC+) vesicles into poly(dimethylsiloxane) (PDMS) microchannels for immunosensing of cholera toxin (CT) in flooded waters. Compared to phosphatidylcholine (PC) layers in the microchannels, DOPC+ membranes show exceptionally strong resistance to air-dry damage, as demonstrated by fluorescence recovery after photobleaching (FRAP) measurements and protein adsorption studies. In FRAP experiments, the mobile fraction of PC membranes was found to decrease by 10% upon drying/rehydration and the lateral diffusion coefficient decreased from 2.2 to 1.6 microm(2)/s, whereas the mobile fraction and diffusion coefficient for DOPC+ membranes remain virtually unchanged during this process. Characterization by confocal microscopy reveals that only 1% of the DOPC+ membrane in the microchannels was removed by the drying/rehydration process, as compared to 11% for PC. Protein adsorption trends indicate that the charge of DOPC+ membranes allows for tuning of solution conditions to enable the desired protein-membrane interaction to predominate at the interface. A flow-based immunoassay for bacterial toxin was developed with 5% GM1/DOPC+ membranes in PDMS channels, and a detection limit of 250 amol for CT was obtained from the calibration curves. The assay was successfully applied to detection of CT spiked in water samples from the Santa Ana River, with nearly identical response and sensitivity. PMID:15859616

  8. Architecture of a single membrane spanning cytochrome P450 suggests constraints that orient the catalytic domain relative to a bilayer

    PubMed Central

    Monk, Brian C.; Tomasiak, Thomas M.; Keniya, Mikhail V.; Huschmann, Franziska U.; Tyndall, Joel D. A.; O’Connell, Joseph D.; Cannon, Richard D.; McDonald, Jeffrey G.; Rodriguez, Andrew; Finer-Moore, Janet S.; Stroud, Robert M.

    2014-01-01

    Bitopic integral membrane proteins with a single transmembrane helix play diverse roles in catalysis, cell signaling, and morphogenesis. Complete monospanning protein structures are needed to show how interaction between the transmembrane helix and catalytic domain might influence association with the membrane and function. We report crystal structures of full-length Saccharomyces cerevisiae lanosterol 14α-demethylase, a membrane monospanning cytochrome P450 of the CYP51 family that catalyzes the first postcyclization step in ergosterol biosynthesis and is inhibited by triazole drugs. The structures reveal a well-ordered N-terminal amphipathic helix preceding a putative transmembrane helix that would constrain the catalytic domain orientation to lie partly in the lipid bilayer. The structures locate the substrate lanosterol, identify putative substrate and product channels, and reveal constrained interactions with triazole antifungal drugs that are important for drug design and understanding drug resistance. PMID:24613931

  9. Architecture of a single membrane spanning cytochrome P450 suggests constraints that orient the catalytic domain relative to a bilayer.

    PubMed

    Monk, Brian C; Tomasiak, Thomas M; Keniya, Mikhail V; Huschmann, Franziska U; Tyndall, Joel D A; O'Connell, Joseph D; Cannon, Richard D; McDonald, Jeffrey G; Rodriguez, Andrew; Finer-Moore, Janet S; Stroud, Robert M

    2014-03-11

    Bitopic integral membrane proteins with a single transmembrane helix play diverse roles in catalysis, cell signaling, and morphogenesis. Complete monospanning protein structures are needed to show how interaction between the transmembrane helix and catalytic domain might influence association with the membrane and function. We report crystal structures of full-length Saccharomyces cerevisiae lanosterol 14α-demethylase, a membrane monospanning cytochrome P450 of the CYP51 family that catalyzes the first postcyclization step in ergosterol biosynthesis and is inhibited by triazole drugs. The structures reveal a well-ordered N-terminal amphipathic helix preceding a putative transmembrane helix that would constrain the catalytic domain orientation to lie partly in the lipid bilayer. The structures locate the substrate lanosterol, identify putative substrate and product channels, and reveal constrained interactions with triazole antifungal drugs that are important for drug design and understanding drug resistance. PMID:24613931

  10. Molecular Mechanism of Ionic-Liquid-Induced Membrane Disruption: Morphological Changes to Bilayers, Multilayers, and Vesicles.

    PubMed

    Yoo, Brian; Zhu, Yingxi; Maginn, Edward J

    2016-05-31

    The application of ionic liquids (ILs) in many industrially relevant processes provides an urgent need to better understand their molecular interactions with biological systems. A detailed understanding of the cytotoxicity mechanism of ILs can be helpful in facilitating the molecular design of nontoxic ILs. Using coarse-grained molecular dynamics (MD) simulations, we investigate the effects of imidazolium-based ILs on several lipid bilayer morphologies. Our results demonstrate that the asymmetric insertion of IL cations into one side of a lipid bilayer leaflet enhances the leaflet strain, which upon reaching a critical value triggers a morphological disruption in the bilayer. Consistently, the bending modulus of the bilayer is reduced by 1 to 2 orders of magnitude relative to that of an IL-free planar bilayer prior to the disruption event. Our results suggest that ILs that can easily insert into the lipid bilayer without diffusing across or inducing lipid flip-flop can be more disruptive to a lipid biomembrane. PMID:27159842

  11. Formation of lipid bilayer membrane in a poly(dimethylsiloxane) microchip integrated with a stacked polycarbonate membrane support and an on-site nanoinjector.

    PubMed

    Teng, Wei; Ban, Changill; Hahn, Jong Hoon

    2015-03-01

    This paper describes a new and facile approach for the formation of pore-spanning bilayer lipid membranes (BLMs) within a poly(dimethylsiloxane) (PDMS) microfluidic device. Commercially, readily available polycarbonate (PC) membranes are employed for the support of BLMs. PC sheets with 5 μm, 2 μm, and 0.4 μm pore diameters, respectively, are thermally bonded into a multilayer-stack, reducing the pore density of 0.4 μm-pore PC by a factor of 200. The BLMs on this support are considerably stable (a mean lifetime: 17 h). This multilayer-stack PC (MSPC) membrane is integrated into the PDMS chip by an epoxy bonding method developed to secure durable bonding under the use of organic solvents. The microchip has a special channel for guiding a micropipette in the proximity of the MSPC support. With this on-site injection technique, tens to hundreds of nanoliters of solutions can be directly dispensed to the support. Incorporating gramicidin ion channels into BLMs on the MSPC support has confirmed the formation of single BLMs, which is based on the observation from current signals of 20 pS conductance that is typical to single channel opening. Based on the bilayer capacitance (1.4 pF), about 15% of through pores across the MSPC membrane are estimated to be covered with BLMs. PMID:26015832

  12. Formation of lipid bilayer membrane in a poly(dimethylsiloxane) microchip integrated with a stacked polycarbonate membrane support and an on-site nanoinjector

    PubMed Central

    Teng, Wei; Ban, Changill; Hahn, Jong Hoon

    2015-01-01

    This paper describes a new and facile approach for the formation of pore-spanning bilayer lipid membranes (BLMs) within a poly(dimethylsiloxane) (PDMS) microfluidic device. Commercially, readily available polycarbonate (PC) membranes are employed for the support of BLMs. PC sheets with 5 μm, 2 μm, and 0.4 μm pore diameters, respectively, are thermally bonded into a multilayer-stack, reducing the pore density of 0.4 μm-pore PC by a factor of 200. The BLMs on this support are considerably stable (a mean lifetime: 17 h). This multilayer-stack PC (MSPC) membrane is integrated into the PDMS chip by an epoxy bonding method developed to secure durable bonding under the use of organic solvents. The microchip has a special channel for guiding a micropipette in the proximity of the MSPC support. With this on-site injection technique, tens to hundreds of nanoliters of solutions can be directly dispensed to the support. Incorporating gramicidin ion channels into BLMs on the MSPC support has confirmed the formation of single BLMs, which is based on the observation from current signals of 20 pS conductance that is typical to single channel opening. Based on the bilayer capacitance (1.4 pF), about 15% of through pores across the MSPC membrane are estimated to be covered with BLMs. PMID:26015832

  13. Interactions of Pleckstrin Homology Domains with Membranes: Adding Back the Bilayer via High-Throughput Molecular Dynamics.

    PubMed

    Yamamoto, Eiji; Kalli, Antreas C; Yasuoka, Kenji; Sansom, Mark S P

    2016-08-01

    A molecular simulation pipeline for determining the mode of interaction of pleckstrin homology (PH) domains with phosphatidylinositol phosphate (PIP)-containing lipid bilayers is presented. We evaluate our methodology for the GRP1 PH domain via comparison with structural and biophysical data. Coarse-grained simulations yield a 2D density landscape for PH/membrane interactions alongside residue contact profiles. Predictions of the membrane localization and interactions of 13 PH domains reveal canonical, non-canonical, and dual PIP-binding sites on the proteins. Thus, the PH domains associate with the PIP molecules in the membrane via a highly positively charged loop. Some PH domains exhibit modes of interaction with PIP-containing membranes additional to this canonical binding mode. All 13 PH domains cause a degree of local clustering of PIP molecules upon binding to the membrane. This provides a global picture of PH domain interactions with membranes. The high-throughput approach could be extended to other families of peripheral membrane proteins. PMID:27427480

  14. The effect of the hydrophilic spacer length on the functionality of a mercury-supported tethered bilayer lipid membrane.

    PubMed

    Becucci, Lucia; Faragher, Robert J; Schwan, Adrian

    2015-02-01

    A biomimetic membrane consisting of a thiolipid monolayer tethered to a mercury electrode, with a dioleoylphosphatidylcholine (DOPC) monolayer on top of it, was fabricated. The thiolipid, referred to as DPOL, consisted of an octaethyleneoxy (OEO) chain terminated at one end with a lipoic acid residue and covalently linked at the other end to two phytanyl chains. The functionality of this biomimetic membrane, referred to as a tethered bilayer lipid membrane (tBLM), was tested by incorporating gramicidin and alamethicin and verifying their ion channel activity. Advantages and drawbacks with respect to a tBLM using a thiolipid, referred to as DPTL, with a tetraethyleneoxy (TEO) chain were examined by using electrochemical impedance spectroscopy, potential-step chronocoulometry and cyclic voltammetry. The maximum charge surface density of potassium ions stored in the OEO spacer amounts to 70μCcm(-2), as compared to a charge surface density of 45μCcm(-2) in the TEO spacer. The lipid bilayer moiety of the DPOL/DOPC tBLM is somewhat leakier than that of the DPTL/DOPC tBLM at potentials negative of about -0.65V vs. the saturated calomel electrode. The estimated value of the surface dipole potential of the OEO spacer amounts to -0.180V and is, therefore, smaller than that, -0.230V, of the TEO spacer. PMID:25180906

  15. The pathway of ligand entry from the membrane bilayer to a lipid G protein-coupled receptor

    PubMed Central

    Stanley, Nathaniel; Pardo, Leonardo; Fabritiis, Gianni De

    2016-01-01

    The binding process through the membrane bilayer of lipid-like ligands to a protein target is an important but poorly explored recognition process at the atomic level. In this work we succeeded in resolving the binding of the lipid inhibitor ML056 to the sphingosine-1-phosphate receptor 1 (S1P1R) using unbiased molecular dynamics simulations with an aggregate sampling of over 800 μs. The binding pathway is a multi-stage process consisting of the ligand diffusing in the bilayer leaflet to contact a “membrane vestibule” at the top of TM 7, subsequently moving from this lipid-facing vestibule to the orthosteric binding cavity through a channel formed by TMs 1 and 7 and the N-terminal of the receptor. Unfolding of the N-terminal alpha-helix increases the volume of the channel upon ligand entry, helping to reach the crystallographic pose that also corresponds to the predicted favorable pose. The relaxation timescales of the binding process show that the binding of the ligand to the “membrane vestibule” is the rate-limiting step in the multi microseconds timescale. We comment on the significance and parallels of the binding process in the context of other binding studies. PMID:26940769

  16. Peptide-induced membrane leakage by lysine derivatives of gramicidin A in liposomes, planar bilayers, and erythrocytes.

    PubMed

    Sorochkina, Alexandra I; Kovalchuk, Sergei I; Omarova, Elena O; Sobko, Alexander A; Kotova, Elena A; Antonenko, Yuri N

    2013-11-01

    Introducing a charged group near the N-terminus of gramicidin A (gA) is supposed to suppress its ability to form ion channels by restricting its head-to-head dimerization. The present study dealt with the activity of [Lys1]gA, [Lys3]gA, [Glu1]gA, [Glu3]gA, [Lys2]gA, and [Lys5]gA in model membrane systems (planar lipid bilayers and liposomes) and erythrocytes. In contrast to the Glu-substituted peptides, the lysine derivatives of gA caused non-specific liposomal leakage monitored by fluorescence dequenching of lipid vesicles loaded with carboxyfluorescein or other fluorescent dyes. Measurements of electrical current through a planar lipid membrane revealed formation of giant pores by Lys-substituted analogs, which depended on the presence of solvent in the bilayer lipid membrane. The efficacy of unselective pore formation in liposomes depended on the position of the lysine residue in the amino acid sequence, increasing in the row: [Lys2]gA<[Lys5]gA<[Lys1]gA<[Lys3]gA. The similar series of potency was exhibited by the Lys-substituted gA analogs in facilitating erythrocyte hemolysis, whereas the Glu-substituted analogs showed negligible hemolytic activity. Oligomerization of the Lys-substituted peptides is suggested to be involved in the process of nonselective pore formation. PMID:23806648

  17. Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins.

    PubMed

    Ramakrishnan, N; Sunil Kumar, P B; Radhakrishnan, Ravi

    2014-10-01

    Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across the various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham - Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this

  18. Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins

    NASA Astrophysics Data System (ADS)

    Ramakrishnan, N.; Sunil Kumar, P. B.; Radhakrishnan, Ravi

    2014-10-01

    Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham-Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this description, the

  19. Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins

    PubMed Central

    Ramakrishnan, N.; Sunil Kumar, P. B.; Radhakrishnan, Ravi

    2014-01-01

    Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across the various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham - Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this

  20. Scanning electrochemical microscopy. 38. Application of SECM to the study of charge transfer through bilayer lipid membranes.

    PubMed

    Tsionsky, M; Zhou, J; Amemiya, S; Fan, F R; Bard, A J; Dryfe, R A

    1999-10-01

    The use of the scanning electrochemical microscope (SECM) to probe the kinetics of charge-transfer processes at bilayer lipid membranes (BLM) is presented. Analysis of the SECM tip response demonstrates that an unmodified BLM behaves as an insulator, whereas a BLM doped with iodine shows some positive feedback. The SECM technique thus allows one to probe processes at a BLM and determine the kinetics of the charge-transfer process. The SECM can also be used to determine the shape of the BLM. PMID:10660439

  1. REVIEW ARTICLE: Network models of fluid, hexatic and polymerized membranes

    NASA Astrophysics Data System (ADS)

    Gompper, G.; Kroll, D. M.

    1997-10-01

    The thermal behaviour of membranes - surfaces of nearly vanishing tension - depends strongly on their internal state, which can be either fluid, crystalline (or polymerized), or hexatic. Thermal fluctuations have a dramatic effect on the conformation and elastic properties of membranes. We describe in this review both the continuum models of membranes which are used for theoretical analyses as well as the network models employed in simulations. The fruitful interaction between these two approaches, which has lead to recent progress in this field, is emphasized. We summarize the essential results of recent research on fluctuating membranes; in particular, the effects of bending rigidity, self-avoidance, attractive interactions, disorder, topological defects and external compression forces are discussed in detail.

  2. A Fluid Membrane-Based Soluble Ligand Display System for Live CellAssays

    SciTech Connect

    Nam, Jwa-Min; Nair, Pradeep N.; Neve, Richard M.; Gray, Joe W.; Groves, Jay T.

    2005-10-14

    Cell communication modulates numerous biological processes including proliferation, apoptosis, motility, invasion and differentiation. Correspondingly, there has been significant interest in the development of surface display strategies for the presentation of signaling molecules to living cells. This effort has primarily focused on naturally surface-bound ligands, such as extracellular matrix components and cell membranes. Soluble ligands (e.g. growth factors and cytokines) play an important role in intercellular communications, and their display in a surface-bound format would be of great utility in the design of array-based live cell assays. Recently, several cell microarray systems that display cDNA, RNAi, or small molecules in a surface array format were proven to be useful in accelerating high-throughput functional genetic studies and screening therapeutic agents. These surface display methods provide a flexible platform for the systematic, combinatorial investigation of genes and small molecules affecting cellular processes and phenotypes of interest. In an analogous sense, it would be an important advance if one could display soluble signaling ligands in a surface assay format that allows for systematic, patterned presentation of soluble ligands to live cells. Such a technique would make it possible to examine cellular phenotypes of interest in a parallel format with soluble signaling ligands as one of the display parameters. Herein we report a ligand-modified fluid supported lipid bilayer (SLB) assay system that can be used to functionally display soluble ligands to cells in situ (Figure 1A). By displaying soluble ligands on a SLB surface, both solution behavior (the ability to become locally enriched by reaction-diffusion processes) and solid behavior (the ability to control the spatial location of the ligands in an open system) could be combined. The method reported herein benefits from the naturally fluid state of the supported membrane, which allows

  3. Fluid displacement under elastic membranes: Dynamics and interfacial instabilities

    NASA Astrophysics Data System (ADS)

    Al-Housseiny, Talal; Christov, Ivan; Juel, Anne; Stone, Howard

    2012-11-01

    The spreading of fluids under a flexible membrane is a feature of many systems such as the lateral intrusion of magma under a terrestrial crust, or when blood spreads underneath the skin giving the signature color of bruises. In this work, we investigate the displacement of a viscous fluid by a gas underneath an elastic membrane. We consider a radial Hele-Shaw cell where the upper plate is an elastic sheet. The dynamics of the interface between the injected gas and the displaced fluid are fundamentally modified by the presence of an elastic boundary, which leads to the suppression of viscous fingering below a critical flow rate. We demonstrate theoretically the mechanism of suppression and find the corresponding critical flow rate. In addition, we study the dynamics of a stable (circular) interface propagating underneath an elastic membrane and derive the scaling laws for both the position of the interface and the shape of the elastic membrane. Our theoretical findings agree very well with the experimental results of D. Pihler-Puzovic et al. (PRL 2012). T. T. Al-Housseiny is supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-0646086.

  4. [The effect of the homogenates from different developmental stages of the nematode Protostrongylus rufescens (Leuckart, 1895) on mitochondrial and lipid bilayer membranes].

    PubMed

    Kuchboev, A E; Kazakov, I; Asrarov, M I; Isakova, D T; Azimov, D A; Golovanov, V I

    2007-01-01

    The effect of the homogenates from different developmental stages of the nematode Protostrongylus rufescens on mitochondrial and lipid bilayer membranes has been studied. The homogenate of P. rufescens affects efficiently the cell energy by the inhibition of the mitochondrial respiration in the metabolic state V3, uncouples oxidative phosphorylation and affects the functions of mitochondria at the level of cyclosporine A-sensitive pore by making it highly permeable. Moreover, the nematode homogenate at the concentration of 1 mkg/ml increases efficiently the integral permeability of lipid bilayer membranes. An increase in this permeability is connected apparently with the formation of single ion channels. The channels of lipid bilayer membranes induced by the nematode homogenate show cation selectivity. PMID:17460939

  5. General model of phospholipid bilayers in fluid phase within the single chain mean field theory

    SciTech Connect

    Guo, Yachong; Baulin, Vladimir A.; Pogodin, Sergey

    2014-05-07

    Coarse-grained model for saturated phospholipids: 1,2-didecanoyl-sn-glycero-3-phosphocholine (DCPC), 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and unsaturated phospholipids: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1,2- dioleoyl-sn-glycero-3-phosphocholine (DOPC) is introduced within the single chain mean field theory. A single set of parameters adjusted for DMPC bilayers gives an adequate description of equilibrium and mechanical properties of a range of saturated lipid molecules that differ only in length of their hydrophobic tails and unsaturated (POPC, DOPC) phospholipids which have double bonds in the tails. A double bond is modeled with a fixed angle of 120°, while the rest of the parameters are kept the same as saturated lipids. The thickness of the bilayer and its hydrophobic core, the compressibility, and the equilibrium area per lipid correspond to experimentally measured values for each lipid, changing linearly with the length of the tail. The model for unsaturated phospholipids also fetches main thermodynamical properties of the bilayers. This model is used for an accurate estimation of the free energies of the compressed or stretched bilayers in stacks or multilayers and gives reasonable estimates for free energies. The proposed model may further be used for studies of mixtures of lipids, small molecule inclusions, interactions of bilayers with embedded proteins.

  6. Asymmetric bi-layer PFSA membranes as model systems for the study of water management in the PEMFC.

    PubMed

    Peng, Z; Peng, A Z; Morin, A; Huguet, P; Lanteri, Y; Deabate, S

    2014-10-14

    New bi-layer PFSA membranes made of Nafion® NRE212 and Aquivion™ E79-05s with different equivalent weights are prepared with the aim of managing water repartition in the PEMFC. The membrane water transport properties, i.e. back-diffusion and electroosmosis, as well as the electrochemical performances, are compared to those of state-of-art materials. The actual water content (the inner water concentration profile across the membrane thickness) is measured under operation in the fuel cell by in situ Raman microspectroscopy. The orientation of the equivalent weight gradient with respect to the water external gradient and to the proton flow direction affects the membrane water content, the water transport ability and, thus, the fuel cell performances. Higher power outputs, related to lower ohmic losses, are observed when the membrane is assembled with the lower equivalent weight layer (Aquivion™) at the anode side. This orientation, corresponding to enhanced water transport by back-flow while electroosmosis remains unaffected, results in the higher hydration of the membrane and of the anode active layer during operation. Also, polarization data suggest a different water repartition in the fuel cell along the on-plane direction. Even if the interest in multi-layer PFSA membranes as perspective electrolytes for PEMFCs is not definitively attested, these materials appear to be excellent model systems to establish relationships between the membrane transport properties, the water distribution in the fuel cell and the electrochemical performances. Thanks to the micrometric resolution, in situ Raman microspectroscopy proves to be a unique tool to measure the actual hydration of the membrane at the surface swept by the hydrated feed gases during operation, so that it can be used as a local probe of the water concentration evolution along the gas distribution channels according to changing working conditions. PMID:25171457

  7. Solid-state NMR of the Yersinia pestis outer membrane protein Ail in lipid bilayer nanodiscs sedimented by ultracentrifugation

    PubMed Central

    Ding, Yi; Fujimoto, L. Miya; Yao, Yong; Marassi, Francesca M.

    2015-01-01

    Solid-state NMR studies of sedimented soluble proteins has been recently developed as an attractive approach for overcoming the size limitations of solution NMR spectroscopy and bypassing the need for sample crystallization or precipitation (Bertini et al. 2011). Inspired by the potential benefits of this method, we have investigated the ability to sediment lipid bilayer nanodiscs reconstituted with a membrane protein. In this study, we show that nanodiscs containing the outer membrane protein Ail from Yersinia pestis can be sedimented for solid-state NMR structural studies, without the need for precipitation or lyophilization. Optimized preparations of Ail in phospholipid nanodiscs support both the structure and the fibronectin binding activity of the protein. The same sample can be used for solution NMR, solid-state NMR and activity assays, facilitating structure-activity correlation experiments across a wide range of timescales. PMID:25578899

  8. Solid-state NMR of the Yersinia pestis outer membrane protein Ail in lipid bilayer nanodiscs sedimented by ultracentrifugation.

    PubMed

    Ding, Yi; Fujimoto, L Miya; Yao, Yong; Marassi, Francesca M

    2015-04-01

    Solid-state NMR studies of sedimented soluble proteins has been developed recently as an attractive approach for overcoming the size limitations of solution NMR spectroscopy while bypassing the need for sample crystallization or precipitation (Bertini et al. Proc Natl Acad Sci USA 108(26):10396-10399, 2011). Inspired by the potential benefits of this method, we have investigated the ability to sediment lipid bilayer nanodiscs reconstituted with a membrane protein. In this study, we show that nanodiscs containing the outer membrane protein Ail from Yersinia pestis can be sedimented for solid-state NMR structural studies, without the need for precipitation or lyophilization. Optimized preparations of Ail in phospholipid nanodiscs support both the structure and the fibronectin binding activity of the protein. The same sample can be used for solution NMR, solid-state NMR and activity assays, facilitating structure-activity correlation experiments across a wide range of timescales. PMID:25578899

  9. Boronated derivatives of chlorin e(6) and fluoride-containing porphyrins as penetrating anions: a study using bilayer lipid membranes.

    PubMed

    Rokitskaya, T I; Zaitsev, A V; Ol'shevskaya, V A; Kalinin, V N; Moisenovich, M M; Agapov, I I; Antonenko, Y N

    2012-09-01

    Boronated derivatives of porphyrins are studied extensively as promising compounds for boron-neutron capture therapy and photodynamic therapy. Understanding of the mechanism of their permeation across cell membranes is a key step in screening for the most efficient compounds. In the present work, we studied the ability of boronated derivatives of chlorin e(6) and porphyrins, which are mono-, di-, and tetra-anions, to permeate through planar bilayer lipid membranes (BLM). The translocation rate constants through the hydrophobic part of the lipid bilayer were estimated for monocarborane and its conjugate with chlorin e(6) by the method of electrical current relaxation. They were similar, 6.6 and 6.8 sec(-1), respectively. Conjugates of porphyrins carrying two and four carborane groups were shown to permeate efficiently through a BLM although they carry two charges and four charges, respectively. The rate of permeation of the tetraanion estimated by the BLM current had superlinear dependence on the BLM voltage. Because the resting potential of most mammalian cells is negative inside, it can be concluded that the presence of negatively-charged boronated groups in compounds should hinder the accumulation of the porphyrins in cells. PMID:23157256

  10. Changes of conductance and compressibility of bilayer lipid membranes induced by oligonucleotide-cationic polyene antibiotic complexes.

    PubMed

    Hianik, Tibor; Ostatnik, Lukas; Polohova, Vladimira; Bolard, Jacques

    2008-11-01

    The positively charged polyene molecule amphotericin B 3-dimethylaminopropylamide (AMA) is an efficient agent for the delivery of antisense oligodeoxyribonucleotides (ODN) into target cells. In the present study, bilayer lipid membrane (BLM) conductance, elasticity modulus perpendicular to the membrane plane, surface potential and electrical capacitance were measured by conductance and electrostriction methods in the presence of AMA, pure or complexed to 20-mer single stranded ODN at different ratios. Pure AMA did not induce changes in conductance of cholesterol-containing BLM, but did induce an increase in elasticity modulus and surface potential. ODN/AMA complexes changed BLM properties depending on the charge ratio. The most pronounced effect on membrane conductance was observed for positively charged ODN/AMA complexes (charge ratio rho-/+=0.1), while for negatively charged complexes these changes were less marked/apparent, correlating to substantially lower binding constants. The effect of ODN/AMA complexes on elasticity modulus and charge potential was biphasic. After an increase in both values, a decrease was observed for higher incubation times and ODN/AMA concentrations. These results are interpreted as indicating that the membrane property changes result from the large AMA aggregates induced by the presence of the negatively charged ODN, which condensate on these aggregates. It is suggested that the decrease of elasticity modulus and surface potential in the presence of increasing incubation time and AMA concentration result from desorption of the complexes in the complex-free compartment of the BLM cell, or appearance of a non-linear conductance of the lipid bilayer. The first alternative would explain the AMA-induced transmembrane transfer of ODN. PMID:17904427

  11. Peptide-induced membrane curvature in edge-stabilized open bilayers: a theoretical and molecular dynamics study.

    PubMed

    Pannuzzo, Martina; Raudino, Antonio; Böckmann, Rainer A

    2014-07-14

    Peptide- or protein-induced curvatures of lipid membranes may be studied in molecular dynamics (MD) simulations. In these, membranes are usually modeled as infinitely extended bilayers by using periodic boundary conditions. However, the enforced periodicity results in an underestimation of the bending power of peptides, unless the patch size is much larger than the induced curvature radii. In this letter, we propose a novel approach to evaluate the bending power of a given distribution and/or density of peptides based on the use of flat open-edged lipid patches. To ensure long-lived metastable structures, the patch rim is stabilized in MD simulations by a local enrichment with short-chain lipids. By combining the theory of continuum elastic media with MD simulations, we prove that open-edged patches evolve from a planar state to a closed vesicle, with a transition rate that strongly depends on the concentration of lipid soluble peptides. For close-to-critical values for the patch size and edge energy, the response to even small changes in peptide concentration adopts a transition-like behavior (buckling instability). The usage of open-edged membrane patches amplifies the bending power of peptides, thereby enabling the analysis of the structural properties of membrane-peptide systems. We applied the presented method to investigate the curvature induced by aggregating β -amyloid peptides, unraveling a strong sensitivity of membrane deformation to the peptide concentration. PMID:25028040

  12. Peptide-induced membrane curvature in edge-stabilized open bilayers: A theoretical and molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Pannuzzo, Martina; Raudino, Antonio; Böckmann, Rainer A.

    2014-07-01

    Peptide- or protein-induced curvatures of lipid membranes may be studied in molecular dynamics (MD) simulations. In these, membranes are usually modeled as infinitely extended bilayers by using periodic boundary conditions. However, the enforced periodicity results in an underestimation of the bending power of peptides, unless the patch size is much larger than the induced curvature radii. In this letter, we propose a novel approach to evaluate the bending power of a given distribution and/or density of peptides based on the use of flat open-edged lipid patches. To ensure long-lived metastable structures, the patch rim is stabilized in MD simulations by a local enrichment with short-chain lipids. By combining the theory of continuum elastic media with MD simulations, we prove that open-edged patches evolve from a planar state to a closed vesicle, with a transition rate that strongly depends on the concentration of lipid soluble peptides. For close-to-critical values for the patch size and edge energy, the response to even small changes in peptide concentration adopts a transition-like behavior (buckling instability). The usage of open-edged membrane patches amplifies the bending power of peptides, thereby enabling the analysis of the structural properties of membrane-peptide systems. We applied the presented method to investigate the curvature induced by aggregating β -amyloid peptides, unraveling a strong sensitivity of membrane deformation to the peptide concentration.

  13. Development of an eco-sensor based on bilayer lipid membrane for the continuous monitoring of environmental pollutants

    NASA Astrophysics Data System (ADS)

    Ishimori, Yoshio; Kawano, Koichiro; Ishizuka, Masaru; Murahashi, Mizuho; Tamiya, Eiichi

    2004-03-01

    In recent years, we have developed an advanced environmental monitoring system (AEMS) containing the eco-sensor, which means a sensor for the measurement of environmental pollutants, based on lipid membranes for continuous monitoring of ground water in industry areas such as semiconductor factories. The AEMS project is composed of three work packages as follows, 1) Eco -sensor, 2) Prediction of plume propagation using a computer simulation technique, and 3) Environmental protection method. In this paper, we would like to focus on the study of the eco-sensor. We considered that modified lipid membranes serve as good models for cell membranes because they would be ideal hosts for receptor molecules of biological origin or disruptive environmental pollutants. Thus, we selected lipid membrane as a sensing element for environmental pollutants. We have already confirmed that the eco-sensor could detect a 10 ppb level of volatile organic chlorinated compounds (VOCs) such as trichloroethylene in ground water. Here, we tried to apply the eco-sensor to measure other environmental pollutants containing pesticides and endocrine disrupting chemicals. We made a novel automatic bilayer lipid membrane preparation device and a new system for the continuous measurement of environmental pollutants in ground water.

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

    PubMed

    Deserno, Markus

    2015-01-01

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

  15. The influence of oscillating electromagnetic fields on membrane structure and function: Synthetic liposome and natural membrane bilayer systems with direct application to the controlled delivery of chemical agents

    SciTech Connect

    Liburdy, R.P.; de Manincor, D.; Fingado, B.

    1989-09-01

    Investigations have been conducted to determine if an imposed electromagnetic field can influence membrane transport, and ion and drug permeability in both synthetic and natural cell membrane systems. Microwave fields enhance accumulation of sodium in the lymphocyte and induce protein shedding at Tc. Microwaves also trigger membrane permeability of liposome systems under specific field exposure conditions. Sensitivity varies in a defined way in bilayers displaying a membrane structural phase transition temperature, Tc; maximal release was observed at or near Tc. Significantly, liposome systems without a membrane phase transition were also found to experience permeability increases but, in contrast, this response was temperature independent. The above results indicate that field-enhanced drug release occurs in liposome vesicles that possess a Tc as well as non-Tc liposomes. Additional studies extend non-Tc liposome responses to the in vivo case in which microwaves trigger Gentamicin release from a liposome depot'' placed subcutaneously in the rat hind leg. In addition, evidence is provided that cell surface sequestered liposomes can be triggered by microwave fields to release drugs directly into target cells. 24 refs., 6 figs.

  16. The quantum casimir effect may be a universal force organizing the bilayer structure of the cell membrane.

    PubMed

    Pawlowski, Piotr H; Zielenkiewicz, Piotr

    2013-05-01

    A mathematic-physical model of the interaction between cell membrane bilayer leaflets is proposed based on the Casimir effect in dielectrics. This model explains why the layers of a lipid membrane gently slide one past another rather than penetrate each other. The presented model reveals the dependence of variations in the free energy of the system on the membrane thickness. This function is characterized by the two close minima corresponding to the different levels of interdigitation of the lipids from neighbor layers. The energy barrier of the compressing transition between the predicted minima is estimated to be 5.7 kT/lipid, and the return energy is estimated to be 3.1 kT/lipid. The proposed model enables estimation of the value of the membrane elastic thickness modulus of compressibility, which is 1.7 × 10⁹ N/m², and the value of the interlayer friction coefficient, which is 1.9 × 10⁸ Ns/m³. PMID:23612889

  17. All electrochemical fabrication of a bilayer membrane composed of nanotubular photocatalyst and palladium toward high-purity hydrogen production

    NASA Astrophysics Data System (ADS)

    Hattori, Masashi; Noda, Kei

    2015-12-01

    We developed an all-electrochemical technique for fabricating a bilayer structure of a titanium dioxide (TiO2) nanotube array (TNA) and a palladium film (TNA/Pd membrane), which works for photocatalytic high-purity hydrogen production. Electroless plating was used for depositing the Pd film on the TNA surface prepared by anodizing a titanium foil. A 3-μm-thick TNA/Pd membrane without any pinholes in a 1.5-cm-diameter area was fabricated by transferring a 1-μm-thick TNA onto an electroless-plated 2-μm-thick Pd film with a mechanical peel-off process. This ultrathin membrane with sufficient mechanical robustness showed photocatalytic H2 production via methanol reforming under ultraviolet illumination on the TNA side, immediately followed by the purification of the generated H2 gas through the Pd layer. The hydrogen production rate and the apparent quantum yield for high-purity H2 production from methanol/water mixture with the TNA/Pd membrane were also examined. This work suggests that palladium electroless plating is more suitable and practical for preparing a well-organized TNA/Pd heterointerface than palladium sputter deposition.

  18. Formaldehyde assay by capacitance versus voltage and impedance measurements using bi-layer bio-recognition membrane.

    PubMed

    Ben Ali, M; Korpan, Y; Gonchar, M; El'skaya, A; Maaref, M A; Jaffrezic-Renault, N; Martelet, C

    2006-12-15

    A novel formaldehyde sensitive biosensor based on bacterial formaldehyde dehydrogenase (FDH) as a bio-recognition element has been developed. The bio-recognition membrane had bi-layer architecture and consisted of FDH, cross-linked with albumin, and of the cofactor NAD at a high concentration level (first layer). The second layer was a negatively charged Nafion membrane, which prevented a leakage of negatively charged NAD molecules from the bio-membrane. As transducers, gold electrodes SiO(2)/Si/SiO(2)/Ti/Au and electrolyte-insulator-semiconductor Si/SiO(2) (EIS) structures have been used. Changes in capacitance and impedance properties of the bio-recognition membrane have been used for monitoring formaldehyde concentration in a bulk solution. It has been shown that formaldehyde can be detected within a concentration range from 1 microM to 20mM depending on the type of transduction used, with a detection limit of 1 and 100 microM for gold-based and EIS-based transducers, respectively. PMID:16516460

  19. Charge Equilibration Force Fields for Molecular Dynamics Simulations of Lipids, Bilayers, and Integral Membrane Protein Systems

    PubMed Central

    Lucas, Timothy R.; Bauer, Brad A.; Patel, Sandeep

    2014-01-01

    With the continuing advances in computational hardware and novel force fields constructed using quantum mechanics, the outlook for non-additive force fields is promising. Our work in the past several years has demonstrated the utility of polarizable force fields, those based on the charge equilibration formalism, for a broad range of physical and biophysical systems. We have constructed and applied polarizable force fields for lipids and lipid bilayers. In this review of our recent work, we discuss the formalism we have adopted for implementing the charge equilibration (CHEQ) method for lipid molecules. We discuss the methodology, related issues, and briefly discuss results from recent applications of such force fields. Application areas include DPPC-water monolayers, potassium ion permeation free energetics in the gramicidin A bacterial channel, and free energetics of permeation of charged amino acid analogues across the water-bilayer interface. PMID:21967961

  20. pH-induced conformational changes of membrane-bound influenza hemagglutinin and its effect on target lipid bilayers.

    PubMed Central

    Gray, C.; Tamm, L. K.

    1998-01-01

    Influenza virus hemagglutinin (HA) has served as a paradigm for both pH-dependent and -independent viral membrane fusion. Although large conformational changes were observed by X-ray crystallography when soluble fragments of HA were subjected to fusion-pH conditions, it is not clear whether the same changes occur in membrane-bound HA, what the spatial relationship is between the conformationally changed HA and the target and viral membranes, and in what way HA perturbs the target membrane at low pH. We have taken a spectroscopic approach using an array of recently developed FTIR techniques to address these questions. Difference attenuated total reflection FTIR spectroscopy was employed to reveal reversible and irreversible components of the pH-induced conformational change of the membrane-bound bromelain fragment of HA, BHA. Additional proteolytic fragments of BHA were produced which permitted a tentative assignment of the observed changes to the HA1 and HA2 subunits, respectively. The membrane-bound HA1 subunit undergoes a reversible conformational change, which most likely involves the loss of a small proportion of beta-sheet at low pH. BHA was found to undergo a partially reversible tilting motion relative to the target membrane upon exposure to pH 5, indicating a previously undescribed hinge near the anchoring point to the target membrane. Time-resolved amide H/D exchange experiments revealed a more dynamic (tertiary) structure of membrane-bound BHA and its HA2, but not its HA1, subunit. Finally BHA and, to a lesser degree, HA1 perturbed the lipid bilayer of the target membrane at the interface, as assessed by spectral changes of the lipid ester carbonyl groups. These results are discussed in the context of a complementary study of HA that was bound to viral membranes through its transmembrane peptide (Gray C, Tamm LK, 1997, Protein Sci 6:1993-2006). A distinctive role for the HA1 subunit in the conformational change of HA becomes apparent from these combined

  1. Structure and thermotropic properties of 1-stearoyl-2-acetyl-phosphatidylcholine bilayer membranes.

    PubMed

    Shah, J; Duclos, R I; Shipley, G G

    1994-05-01

    The structural and thermotropic properties of 1-stearoyl-2-acetyl-phosphatidylcholine (C(18):C(2)-PC) were studied as a function of hydration. A combination of differential scanning calorimetry and x-ray diffraction techniques have been used to investigate the phase behavior of C(18):C(2)-PC. At low hydration (e.g., 20% H2O), the differential scanning calorimetry heating curve shows a single reversible endothermic transition at 44.6 degrees C with transition enthalpy delta H = 6.4 kcal/mol. The x-ray diffraction pattern at -8 degrees C shows a lamellar structure with a small bilayer periodicity d = 46.3 A and two wide angle reflections at 4.3 and 3.95 A, characteristic of a tilted chain, L beta' bilayer gel structure. Above the main transition temperature, a liquid crystalline L alpha phase is observed with d = 53.3 A. Electron density profiles at 20% hydration suggest that C(18):C(2)-PC forms a fully interdigitated bilayer at -8 degrees C and a noninterdigitated, liquid crystalline phase above its transition temperature (T > Tm). Between 30 and 50% hydration, on heating C(18):C(2)-PC converts from a highly ordered, fully interdigitated gel phase (L beta') to a less ordered, interdigitated gel phase (L beta), which on further heating converts to a noninterdigitated liquid crystalline L alpha phase. However, the fully hydrated (> 60% H2O) C(18):C(2)-PC, after incubation at 0 degrees C, displays three endothermic transitions at 8.9 degrees C (transition I, delta H = 1.6 kcal/mol), 18.0 degrees C (transition II), and 20.1 degrees C (transition III, delta HII+III = 4.8 kcal/mol). X-ray diffraction at -8 degrees C again showed a lamellar gel phase (L beta') with a small periodicity d = 52.3 A. At 14 degrees C a less ordered, lamellar gel phase (L beta) is observed with d = 60.5 A. However, above the transition III, a broad, diffuse reflection is observed at approximately 39 A, consistent with the presence of a micellar phase. The following scheme is proposed for

  2. The rotational diffusion of cytochrome b5 in lipid bilayer membranes. Influence of the lipid physical state.

    PubMed Central

    Vaz, W L; Austin, R H; Vogel, H

    1979-01-01

    A derivative of the integral membranes protein, cytochrome b5, has been prepared in which the native heme group has been replaced by the structurally similar rhodium(III)-protoporphyrin IX. This metalloporphyrin has a finite triplet yield with a single exponential decay time of 22 microsecond in water. After insertion of the metalloporphyrin into the protein, its triplet-state decay becomes strongly nonexponential with at least three equal amplitude components with time constants varying over a range of 100. The derivatized protein has been incorporated into unilamellar liposomes prepared from dimyristoyllecithin, and the rotational diffusion of the protein in the lipid bilayer has been studied at temperatures above and below the lipid phase transition temperature via triplet absorbance anisotropy decay. The anisotropy decay curves are biphasic both above and below the lipid phase transition. The rotational diffusion constant is found to be 2.4 X 10(5) s-1 at 35 degrees C, and 1.1 X 10(4) s-1 at 10 degrees C, both being calculated from the fast decay component. The ratio of the limiting anisotropy to the initial anisotropy is 0.6 at both temperatures. This implies a cone of restricted motion of 34 degrees for the protein in the bilayer. PMID:262426

  3. The green function of an infinite, fluid loaded membrane

    NASA Astrophysics Data System (ADS)

    Crighton, D. G.

    1983-02-01

    In this paper the response of a fluid loaded plane structure (a membrane) to a concentrated line force excitation is considered in great detail. The normalized velocity response—here called the Green function G—depends upon a dimensionless range x0= km| x|, where km is the free wavenumber on the membrane in a vacuum, on the Mach number M= {k 0}/{k m}, the ratio of wave phase speed ω/ km on the unloaded membrane to the sound speed ω/ k0, and on a parameter ɛ which can be regarded as a measure of fluid loading at the "coincidence" condition M=1. In the analogous problem involving a thin elastic plate, the corresponding parameter is independent of frequency and plate thickness and may be regarded as an intrinsic measure of fluid loading; moreover, in cases of common interest (steel in water, aluminium in air) that parameter is small. In the present paper, the asymptotic structure of G( x0, M, ɛ) is therefore sought in the limit ɛ → 0. Naturally, no single asymptotic expansion can be expected to be valid throughout the ( x0, M) plane, and the programme therefore involves the delineation of regions of that plane in which distinct asymptotic results apply, the construction and discussion of those results, and the asymptotic matching (according to the procedures of the method of matched asymptotic expansions) of results holding in adjoining regions. The Fourier integral for G is broken into surface wave and acoustic components, and the asymptotic structure obtained for each. Previously obtained results for the behaviour at large distances are recovered, with a demonstration that very large distances indeed ( x0 ≫ ɛ-2) may be needed for their validity for some ranges of M; and the drive point behaviour, of G( x0=0, M, ɛ) as ɛ → 0 qua function of M, is shown to correspond to that already discussed in the literature. Elsewhere, in the covering of the whole ( x0, M) plane by different asymptotic expressions, a wide variety of analytical results is found

  4. Formation of oxygen from water, photosensitized by (bpy)/sub 2/Ru(bpy(C/sub 17/)/sub 2/)/sup 2+/, immobilized in a lipid bilayer membrane

    SciTech Connect

    Knerel'man, E.I.; Shafirovich, V.Ya.

    1988-04-01

    A system has been constructed, composed of (bpy)/sub 2/Ru(bpy(C/sub 17/)/sub 2/)/sup 2+/, as photosensitizer, immobilized in a lipid bilayer membrane, K/sub 2/S/sub 2/O/sub 8/ as electron acceptor, in the surrounding outer solution, and a cobalt catalyst attached to the membrane. Irradiation of this system with visible light leads to the formation of oxygen from water, in quantum yields ranging from 20-40%.

  5. Biological Evaluation (In Vitro and In Vivo) of Bilayered Collagenous Coated (Nano Electrospun and Solid Wall) Chitosan Membrane for Periodontal Guided Bone Regeneration.

    PubMed

    Lotfi, Ghogha; Shokrgozar, Mohammad Ali; Mofid, Rasoul; Abbas, Fatemeh Mashhadi; Ghanavati, Farzin; Baghban, Alireza Akbarzadeh; Yavari, Seyedeh Kimia; Pajoumshariati, Seyedramin

    2016-07-01

    The application of barrier membranes in guided bone regeneration (GBR) has become a commonly used surgical technique in periodontal research. The objectives of this study were to evaluate the in vitro biocompatibility and osteogenic differentiation of mesenchymal stem cells (MSCs) on two different collagenous coatings (nano electrospun fibrous vs. solid wall) of bilayered collagen/chitosan membrane and their histological evaluation on bone regeneration in rabbit calvarial defects. It was found that chitosan-nano electrospun collagen (CNC) membranes had higher proliferation/metabolic activity compared to the chitosan-collagen (CC) and pristine chitosan membranes. The qRT-PCR analysis demonstrated the CNC membranes induced significant expression of osteogenic genes (Osteocalcin, RUNX2 and Col-α1) in MSCs. Moreover, higher calcium content and alkaline phosphatase activity of MSCs were observed compared to the other groups. Histologic and histomorphometric evaluations were performed on the uncovered (negative control) as well as covered calvarial defects of ten adult white rabbits with different membranes (CNC, CC, BioGide (BG, positive control)) at 1 and 2 months after surgery. More bone formation was detected in the defects covered with CNC and BG membranes than those covered by CC and the negative control. No inflammation and residual biomaterial particles were observed on the membrane surface or in the surrounding tissues in the surgical areas. These results suggest that bilayer CNC membrane can have the potential for use as a GBR membrane material facilitating bone formation. PMID:26586588

  6. Membrane Elasticity in Giant Vesicles with Fluid Phase Coexistence

    PubMed Central

    Baumgart, T.; Das, S.; Webb, W. W.; Jenkins, J. T.

    2005-01-01

    Biological membranes are known to contain compositional heterogeneities, often termed rafts, with distinguishable composition and function, and these heterogeneities participate in vigorous transport processes. Membrane lipid phase coexistence is expected to modulate these processes through the differing mechanical properties of the bulk domains and line tension at phase boundaries. In this contribution, we compare the predictions from a shape theory derived for vesicles with fluid phase coexistence to the geometry of giant unilamellar vesicles with coexisting liquid-disordered (Ld) and liquid-ordered (Lo) phases. We find a bending modulus for the Lo phase higher than that of the Ld phase and a saddle-splay (Gauss) modulus difference with the Gauss modulus of the Lo phase being more negative than the Ld phase. The Gauss modulus critically influences membrane processes that change topology, such as vesicle fission or fusion, and could therefore be of significant biological relevance in heterogeneous membranes. Our observations of experimental vesicle geometries being modulated by Gaussian curvature moduli differences confirm the prediction by the theory of Juelicher and Lipowsky. PMID:15894634

  7. (13) C-TmDOTA as versatile thermometer compound for solid-state NMR of hydrated lipid bilayer membranes.

    PubMed

    Umegawa, Yuichi; Tanaka, Yuya; Nobuaki, Matsumori; Murata, Michio

    2016-03-01

    Recent advances in solid-state nuclear magnetic resonance (NMR) techniques, such as magic angle spinning and high-power decoupling, have dramatically increased the sensitivity and resolution of NMR. However, these NMR techniques generate extra heat, causing a temperature difference between the sample in the rotor and the variable temperature gas. This extra heating is a particularly crucial problem for hydrated lipid membrane samples. Thus, to develop an NMR thermometer that is suitable for hydrated lipid samples, thulium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (TmDOTA) was synthesized and labeled with (13) C (i.e., (13) C-TmDOTA) to increase the NMR sensitivity. The complex was mixed with a hydrated lipid membrane, and the system was subjected to solid-state NMR and differential scanning calorimetric analyses. The physical properties of the lipid bilayer and the quality of the NMR spectra of the membrane were negligibly affected by the presence of (13) C-TmDOTA, and the (13) C chemical shift of the complex exhibited a large-temperature dependence. The results demonstrated that (13) C-TmDOTA could be successfully used as a thermometer to accurately monitor temperature changes induced by (1) H decoupling pulses and/or by magic angle spinning and the temperature distribution of the sample inside the rotor. Thus, (13) C-TmDOTA was shown to be a versatile thermometer for hydrated lipid assemblies. Copyright © 2015 John Wiley & Sons, Ltd. PMID:26460094

  8. Construction of a patterned hydrogel-fibrous mat bilayer structure to mimic choroid and Bruch's membrane layers of retina.

    PubMed

    Komez, Aylin; Baran, Erkan T; Erdem, Uzeyir; Hasirci, Nesrin; Hasirci, Vasif

    2016-09-01

    Deterioration of retina and death of the retinal cells due to age, diabetes, or occlusion can cause retinal degeneration which leads to loss of vision. In this study, it is aimed to design a bilayered matrix to mimic the choroid and the Bruch's membrane of the retinal tissue. As choroid, a microchanneled network resembling a fractal tree design was fabricated by photolithography over photo-cross-linkable methacrylated hyaluronic acid hydrogel. Gelatin or collagen was immobilized into the microchannels to enhance adherence of Human Umbilical Vein Endothelial Cells (HUVEC). At late culture periods (2 weeks), formation of tubular structures due to proliferation of the attached cells was observed. As Bruch's membrane, an electrospun fibroin nanofiber mat was produced to grow retinal pigment epithelium (RPE) cells on. Cellular interactions between RPE and HUVEC in the microchannels were investigated in a coculture model in a noncontact mode. It was deduced that by combining the RPE layer on the highly permeable Bruch's membrane with the choroid layer populated by HUVECs, a retinal substitute which might have a potential for use in the treatment of retinal diseases is possible. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2166-2177, 2016. PMID:27102366

  9. Electrogenic proton transport across lipid bilayer membranes mediated by cationic derivatives of rhodamine 19: comparison with anionic protonophores.

    PubMed

    Rokitskaya, Tatyana I; Ilyasova, Tatyana M; Severina, Inna I; Antonenko, Yuri N; Skulachev, Vladimir P

    2013-06-01

    Protonophores can be considered as candidates for anti-obesity drugs and tools to prevent excessive reactive oxygen species production in mitochondria by means of a limited decrease in the mitochondrial potential. Experimentally used protonophores are weak acids that can carry protons across a membrane in a neutral (protonated) form, and they come back in an anionic (deprotonated) form. A cationic derivative of rhodamine 19 and plastoquinone (SkQR1) was recently shown to possess uncoupling activity in mitochondria and in intact cells. In this article, we studied the mechanism of action of SkQR1 and its plastoquinone-lacking analog (C12R1) on a planar bilayer lipid membrane by applying voltage jumps. The steady-state current was proportional to the C12R1 concentration in a manner as if the monomeric form of the carrier were operative. As predicted by the carrier model, at high pH, when rhodamines were mainly deprotonated, the current changed immediately following a jump in the applied potential and then remained constant. By contrast, at low pH, the current relaxed from an initially high value to a lower value since the protonated carrier cations were redistributed in the membrane. An inverse pH dependence was revealed with the anionic protonophore CCCP. The dependence of the SkQR1 protonophorous activity on voltage exhibited an increase at high voltages, an effect that might facilitate mild (self-limited) uncoupling of mitochondria. PMID:23558512

  10. Monitoring the Transmembrane Proton Gradient Generated by Cytochrome bo3 in Tethered Bilayer Lipid Membranes Using SEIRA Spectroscopy.

    PubMed

    Wiebalck, Swantje; Kozuch, Jacek; Forbrig, Enrico; Tzschucke, C Christoph; Jeuken, Lars J C; Hildebrandt, Peter

    2016-03-10

    Membrane proteins act as biocatalysts or ion/proton pumps to convert and store energy from ubiquitous environmental sources. Interfacing these proteins to electrodes allows utilizing the energy for enzymatic biofuel cells or other auspicious biotechnological applications. To optimize the efficiency of these devices, appropriate membrane models are required that ensure structural and functional integrity of the embedded enzymes and provide structural insight. We present a spectroelectrochemical surface-enhanced infrared absorption (SEIRA) and electrical impedance spectroscopy (EIS) study of the bacterial respiratory ubiquinol/cytochrome bo3 (cyt bo3) couple incorporated into a tethered bilayer lipid membrane (tBLM). Here, we employed a new lipid tether (WK3SH, dihydrocholesteryl (2-(2-(2-ethoxy)ethoxy)ethanethiol), which was synthesized using a three-step procedure with very good yield and allowed measuring IR spectra without significant spectral interference of the tBLM. The functional integrity of the incorporated cyt bo3 was demonstrated by monitoring the enzymatic O2 reduction current and the formation of the transmembrane proton gradient. Based on a SEIRA-spectroscopic redox titration, a shift of the pH-dependent redox potential of the ubiquinones under turnover conditions was correlated with an alkalinization of the submembrane reservoir by +0.8 pH units. This study demonstrates the high potential of tBLMs and the SEIRA spectroscopic approach to study bioenergetic processes. PMID:26898921

  11. Marine sponge cyclic peptide theonellamide A disrupts lipid bilayer integrity without forming distinct membrane pores.

    PubMed

    Espiritu, Rafael Atillo; Cornelio, Kimberly; Kinoshita, Masanao; Matsumori, Nobuaki; Murata, Michio; Nishimura, Shinichi; Kakeya, Hideaki; Yoshida, Minoru; Matsunaga, Shigeki

    2016-06-01

    Theonellamides (TNMs) are antifungal and cytotoxic bicyclic dodecapeptides derived from the marine sponge Theonella sp. These peptides specifically bind to 3β-hydroxysterols, resulting in 1,3-β-D-glucan overproduction and membrane damage in yeasts. The inclusion of cholesterol or ergosterol in phosphatidylcholine membranes significantly enhanced the membrane affinity of theonellamide A (TNM-A) because of its direct interaction with 3β-hydroxyl groups of sterols. To better understand TNM-induced membrane alterations, we investigated the effects of TNM-A on liposome morphology. (31)P nuclear magnetic resonance (NMR) and dynamic light scattering (DLS) measurements revealed that the premixing of TNM-A with lipids induced smaller vesicle formation. When giant unilamellar vesicles were incubated with exogenously added TNM-A, confocal micrographs showed dynamic changes in membrane morphology, which were more frequently observed in cholesterol-containing than sterol-free liposomes. In conjunction with our previous data, these results suggest that the membrane action of TNM-A proceeds in two steps: 1) TNM-A binds to the membrane surface through direct interaction with sterols and 2) accumulated TNM-A modifies the local membrane curvature in a concentration-dependent manner, resulting in dramatic membrane morphological changes and membrane disruption. PMID:27003125

  12. Preferred dialysis fluid for the high-performance membrane.

    PubMed

    Tomo, Tadashi

    2011-01-01

    In the present study, we investigated the effect of hemodialysis (HD) with high-performance membrane filter (HPM-HD) using acetate-free bicarbonate dialysis (AFD) fluid on bioincompatibility as represented by inflammatory markers in patients undergoing maintenance HD therapy and compared it with conventional acetate-containing bicarbonate dialysis (ACD) fluid. A total of 36 maintenance HD patients were registered for study during the 4-month study period (22 males and 14 females, aged 63.5 ± 10.2 years, mean duration of dialysis 12.2 ± 8.6 years, chronic glomerular nephritis in 27 patients, diabetic nephropathy in 6 patients, and nephrosclerosis in 3 patients). These patients were subjected to ACD for the first 2 months followed by AFD fluid for the latter 2 months. Predialysis blood pH and bicarbonate were examined after each of the first and latter 2-month period. Blood variables of C-reactive protein (CRP) and interleukin-6 (IL-6) or fetuin-A were also determined. The filters (membrane surface area, raw material), the conditions of HD (blood flow rate, dialysate flow rate, dialysis time, dry weight) and drug regimen including erythrocyte-simulating agent (drug type, dosage) were unchanged throughout the study. There appeared to be significantly higher levels of predialysis blood pH and bicarbonate in the AFD phase than in the ACD phase. Blood CRP and IL-6 levels were significantly decreased in the AFD group as compared with those seen in the ACD group. From these results, it can be suggested that HPM-HD using AFD fluid contributes to correcting metabolic acidosis and alleviating microinflammation in HD patients. PMID:21865775

  13. Membrane with internal passages to permit fluid flow and an electrochemical cell containing the same

    NASA Technical Reports Server (NTRS)

    Cisar, Alan J. (Inventor); Gonzalez-Martin, Anuncia (Inventor); Hitchens, G. Duncan (Inventor); Murphy, Oliver J. (Inventor)

    1997-01-01

    The invention provides an improved proton exchange membrane for use in electrochemical cells having internal passages parallel to the membrane surface, an apparatus and process for making the membrane, membrane and electrode assemblies fabricated using the membrane, and the application of the membrane and electrode assemblies to a variety of devices, both electrochemical and otherwise. The passages in the membrane extend from one edge of the membrane to another and allow fluid flow through the membrane and give access directly to the membrane for purposes of hydration.

  14. Water at the Surfaces of Aligned Phospholipid Multi-Bilayer Model Membranes Probed with Ultrafast Vibrational Spectroscopy

    PubMed Central

    Zhao, Wei; Moilanen, David E.; Fenn, Emily E.; Fayer, Michael D.

    2009-01-01

    The dynamics of water at the surface of artificial membranes composed of aligned multibilayers of the phospholipid dilauroyl phosphatidylcholine (DLPC) are probed with ultrafast polarization selective vibrational pump-probe spectroscopy. The experiments are performed at various hydration levels, x = 2 – 16 water molecules per lipid at 37 °C. The water molecules are ~1 nm above or below the membrane surface. The experiments are conducted on the OD stretching mode of dilute HOD in H2O to eliminate vibrational excitation transfer. The FT-IR absorption spectra of the OD stretch in the DLPC bilayer system at low hydration levels shows a red-shift in frequency relative to bulk water, which is in contrast to the blue shift often observed in systems such as water nanopools in reverse micelles. The spectra for x = 4 – 16 can be reproduced by a superposition of the spectra for x = 2 and bulk water. IR Pump-probe measurements reveal that the vibrational population decays (lifetimes) become longer as the hydration level is decreased. The population decays are fit well by biexponential functions. The population decays, measured as a function of the OD stretch frequency, suggest the existence of two major types of water molecules in the interfacial region of the lipid bilayers. One component may be a clathrate-like water cluster near the hydrophobic choline group and the other may be related to the hydration water molecules mainly associated with the phosphate group. As the hydration level increases, the vibrational lifetimes of these two components decrease, suggesting a continuous evolution of the hydration structures in the two components associated with the swelling of the bilayers. The agreement of the magnitudes of the two components obtained from IR spectra with those from vibrational lifetime measurements further supports the two component model. The vibrational population decay fitting also gives an estimation of the number of phosphate-associated water molecules

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

    PubMed Central

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

    2007-01-01

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

  16. Spatial distribution and activity of Na(+)/K(+)-ATPase in lipid bilayer membranes with phase boundaries.

    PubMed

    Bhatia, Tripta; Cornelius, Flemming; Brewer, Jonathan; Bagatolli, Luis A; Simonsen, Adam C; Ipsen, John H; Mouritsen, Ole G

    2016-06-01

    We have reconstituted functional Na(+)/K(+)-ATPase (NKA) into giant unilamellar vesicles (GUVs) of well-defined binary and ternary lipid composition including cholesterol. The activity of the membrane system can be turned on and off by ATP. The hydrolytic activity of NKA is found to depend on membrane phase, and the water relaxation in the membrane on the presence of NKA. By collapsing and fixating the GUVs onto a solid support and using high-resolution atomic-force microscopy (AFM) imaging we determine the protein orientation and spatial distribution at the single-molecule level and find that NKA is preferentially located at lo/ld interfaces in two-phase GUVs and homogeneously distributed in single-phase GUVs. When turned active, the membrane is found to unbind from the support suggesting that the protein function leads to softening of the membrane. PMID:26994932

  17. Fluid Mechanics of the Vascular Basement Membrane in the Brain

    NASA Astrophysics Data System (ADS)

    Coloma, Mikhail; Hui, Jonathan; Chiarot, Paul; Huang, Peter; Carare, Roxana; McLeod, Kenneth; Schaffer, David

    2013-11-01

    Beta-amyloid is a normal product of brain metabolic function and is found within the interstitial fluid of the brain. Failure of the clearance of beta-amyloid from the aging brain leads to its accumulation within the walls of arteries and to Alzheimer's disease. The vascular basement membrane (VBM) within the walls of cerebral arteries surrounds the spirally arranged smooth muscle cells and represents an essential pathway for removal of beta-amyloid from the brain. This process fails with the stiffening of arterial walls associated with aging. In this study we hypothesize that the deformation of the VBM associated with arterial pulsations drives the interstitial fluid to drain in the direction opposite of the arterial blood flow. This hypothesis is theoretically investigated by modeling the VBM as a thin, coaxial, fluid-filled porous medium surrounding a periodically deforming cylindrical tube. Flow and boundary conditions required to achieve such a backward clearance are derived through a control volume analysis of mass, momentum, and energy.

  18. Structural evolution and membrane interaction of the 40-residue β amyloid peptides: differences in the initial proximity between peptides and the membrane bilayer studied by solid-state nuclear magnetic resonance spectroscopy.

    PubMed

    Qiang, Wei; Akinlolu, Rumonat D; Nam, Mimi; Shu, Nicolas

    2014-12-01

    Interactions between the β amyloid (Aβ) peptides and cellular membranes have severe consequences such as neuronal cell disruption and therefore may play important roles in Alzheimer's disease. Understanding the structural basis behind such interactions, however, is hindered by the complexity of the Aβ-membrane systems. In particular, because the Aβ peptides are partially incorporated in the membrane bilayer after enzymatic cleavage, there are multiple possibilities in terms of the initial proximity between the peptides and membranes. Structural studies using in vitro model systems with either externally added or preincorporated Aβ in membrane bilayers resulted in distinct evolution pathways. Previous work has shown that the externally added Aβ formed long and mature filaments, while preincorporated Aβ generated short and curvy fibrils. In this study, we perform detailed characterizations on the structural evolution and membrane interaction for these two pathways, using a combination of solid-state nuclear magnetic resonance spectroscopy and other techniques. For the externally added Aβ, we determined the residue-specific structural evolution during the fibrillation process. While the entire fibrillation process for the externally added Aβ was slow, the preincorporated Aβ generated Aβ-lipid complexes rapidly. Specific interactions between the lipids and peptides were observed, suggesting the colocalization of lipids and peptides within the complex. Formation of such a complex induced molecular-level changes in the lipid bilayer, which may serve as a possible mechanism of membrane disruption. PMID:25397729

  19. Lipid bilayer preparations of membrane proteins for oriented and magic-angle spinning solid-state NMR samples

    PubMed Central

    Das, Nabanita; Murray, Dylan T; Cross, Timothy A

    2014-01-01

    Solid-state NMR spectroscopy has been used successfully for characterizing the structure and dynamics of membrane proteins as well as their interactions with other proteins in lipid bilayers. such an environment is often necessary for achieving native-like structures. sample preparation is the key to this success. Here we present a detailed description of a robust protocol that results in high-quality membrane protein samples for both magic-angle spinning and oriented-sample solid-state NMR. the procedure is demonstrated using two proteins: CrgA (two transmembrane helices) and rv1861 (three transmembrane helices), both from Mycobacterium tuberculosis. the success of this procedure relies on two points. First, for samples for both types of NMR experiment, the reconstitution of the protein from a detergent environment to an environment in which it is incorporated into liposomes results in ‘complete’ removal of detergent. second, for the oriented samples, proper dehydration followed by rehydration of the proteoliposomes is essential. By using this protocol, proteoliposome samples for magic-angle spinning NMR and uniformly aligned samples (orientational mosaicity of <1°) for oriented-sample NMR can be obtained within 10 d. PMID:24157546

  20. Concentration dependence of lipopolymer self-diffusion in supported bilayer membranes

    PubMed Central

    Zhang, Huai-Ying; Hill, Reghan J.

    2011-01-01

    Self-diffusion coefficients of poly(ethylene glycol)2k-derivatized lipids (DSPE-PEG2k-CF) in glass-supported DOPC phospholipid bilayers are ascertained from quantitative fluorescence recovery after photobleaching (FRAP). We developed a first-order reaction–diffusion model to ascertain the bleaching constant, mobile fraction and lipopolymer self-diffusion coefficient Ds at concentrations in the range c ≈ 0.5–5 mol%. In contrast to control experiments with 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl) (ammonium salt) (DOPE-NBD) in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), the lipopolymer self-diffusion coefficient decreases monotonically with increasing concentration, without a distinguishing mushroom-to-brush transition. Our data yield a correlation Ds = D0/(1 + αc), where D0 ≈ 3.36 µm2 s−1 and α ≈ 0.56 (with c expressed as a mole percent). Interpreting the dilute limit with the Scalettar–Abney–Owicki statistical mechanical theory for transmembrane proteins yields an effective disc radius ae ≈ 2.41 nm. On the other hand, the Bussell–Koch–Hammer theory, which includes hydrodynamic interactions, yields ae ≈ 2.92 nm. As expected, both measures are smaller than the Flory radius of the 2 kDa poly(ethylene glycol) (PEG) chains, RF ≈ 3.83 nm, and significantly larger than the nominal radius of the phospholipid heads, al ≈ 0.46 nm. The diffusion coefficient at infinite dilution D0 was interpreted using the Evans–Sackmann theory, furnishing an inter-leaflet frictional drag coefficient bs ≈ 1.33 × 108 N s m−3. Our results suggest that lipopolymer interactions are dominated by the excluded volume of the PEG-chain segments, with frictional drag dominated by the two-dimensional bilayer hydrodynamics. PMID:20504804

  1. Channel properties of the purified acetylcholine receptor from Torpedo californica reconstituted in planar lipid bilayer membranes.

    PubMed Central

    Montal, M; Labarca, P; Fredkin, D R; Suarez-Isla, B A

    1984-01-01

    The electrophysiological properties of the cation channel of the purified nicotinic acetylcholine receptor (AChR) reconstituted in planar lipid bilayers were characterized. Single-channel currents were activated by acetylcholine, carbamylcholine and suberyldicholine. The single channel conductance (28 pS in 0.3 M NaCl) was ohmic and independent of the agonist. Single channel currents increased with Na+ concentration to a maximum conductance of 95 pS and showed a half-saturation point of 395 mM. The apparent ion selectivity sequence, derived from single-channel current recordings, is: NH+4 greater than Cs+ greater than Rb+ greater than or equal to Na+ Cl-, F-, SO2-(4). The distribution of channel open times was fit by a sum of two exponentials, reflecting the existence of at least two distinct open states. The time constants depend on the choice of agonist, being consistently longer for suberyldicholine than for carbamylcholine. Similar channel properties were recorded in bilayers formed from monolayers at the tip of patch pipets . Single-channel currents occur in paroxysms of channel activity followed by quiescent periods. This pattern is more pronounced as the agonist concentration increases, and is reflected in histograms of channel-opening frequencies. Computer simulations with a three-state model, consisting of two closed (unliganded and liganded) and one open state, do not resemble the recorded pattern of channel activity, especially at high agonist concentration. Inclusion of a desensitized liganded state reproduces the qualitative features of channel recordings. The occurrence of paroxysms of channel activity thus seems to result from the transit of AChR through its active conformation, from which it can open several times before desensitizing. PMID:6324900

  2. 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.

  3. A bilayer composite composed of TiO2-incorporated electrospun chitosan membrane and human extracellular matrix sheet as a wound dressing.

    PubMed

    Woo, Chang Hee; Choi, Young Chan; Choi, Ji Suk; Lee, Hee Young; Cho, Yong Woo

    2015-01-01

    We designed bilayer composites composed of an upper layer of titanium dioxide (TiO2)-incorporated chitosan membrane and a sub-layer of human adipose-derived extracellular matrix (ECM) sheet as a wound dressing for full-thickness wound healing. The dense and fibrous top layer, which aims to protect the wound from bacterial infection, was prepared by electrospinning of chitosan solution followed by immersion in TiO2 solution. The sponge-like sub-layer, which aims to promote new tissue regeneration, was prepared with acellular ECM derived from human adipose tissue. Using a modified drop plate method, there was a 33.9 and 69.6% reduction in viable Escherichia coli and Staphylococcus aureus on the bilayer composite, respectively. In an in vivo experiment using rats, the bilayer composites exhibited good biocompatibility and provided proper physicochemical and compositional cues at the wound site. Changes in wound size and histological examination of full-thickness wounds showed that the bilayer composites induced faster regeneration of granulation tissue and epidermis with less scar formation, than control wounds. Overall results suggest that the TiO2-incorporated chitosan/ECM bilayer composite can be a suitable candidate as a wound dressing, with an excellent inhibition of bacterial penetration and wound healing acceleration effects. PMID:26096447

  4. The Structure of Herpesvirus Fusion Glycoprotein B-Bilayer Complex Reveals the Protein-Membrane and Lateral Protein-Protein Interaction

    PubMed Central

    Maurer, Ulrike E.; Zeev-Ben-Mordehai, Tzviya; Pandurangan, Arun Prasad; Cairns, Tina M.; Hannah, Brian P.; Whitbeck, J. Charles; Eisenberg, Roselyn J.; Cohen, Gary H.; Topf, Maya; Huiskonen, Juha T.; Grünewald, Kay

    2013-01-01

    Summary Glycoprotein B (gB) is a key component of the complex herpesvirus fusion machinery. We studied membrane interaction of two gB ectodomain forms and present an electron cryotomography structure of the gB-bilayer complex. The two forms differed in presence or absence of the membrane proximal region (MPR) but showed an overall similar trimeric shape. The presence of the MPR impeded interaction with liposomes. In contrast, the MPR-lacking form interacted efficiently with liposomes. Lateral interaction resulted in coat formation on the membranes. The structure revealed that interaction of gB with membranes was mediated by the fusion loops and limited to the outer membrane leaflet. The observed intrinsic propensity of gB to cluster on membranes indicates an additional role of gB in driving the fusion process forward beyond the transient fusion pore opening and subsequently leading to fusion pore expansion. PMID:23850455

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

    PubMed Central

    Zhan, Huan; Lazaridis, Themis

    2011-01-01

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

  6. Method of separating organic contaminants from fluid feedstreams with polyphosphazene membranes

    SciTech Connect

    McCaffrey, R.R.; Cummings, D.G.

    1990-12-31

    A method is provided for separating polar hydrocarbons from a fluid feedstream. The fluid feedstream is flowed across a first surface of a polyphosphazene semipermeable membrane. At least one polar hydrocarbon from the fluid feedstream permeates through the polyphosphazene semipermeable membrane to a second opposed surface of the semipermeable membrane. Then the permeated polar hydrocarbon is removed from the second opposed surface of the polyphosphazene semipermeable membrane. Outstanding and unexpected separation selectivities on the order of 10,000 were obtained for methylene chloride when a methylene chloride in water feedstream was flowed across the polyphosphazene semipermeable membrane in the invented method.

  7. Method of separating organic contaminants from fluid feedstreams with polyphosphazene membranes

    DOEpatents

    McCaffrey, Robert R.; Cummings, Daniel G.

    1991-01-01

    A method is provided for separating halogenated hydrocarbons from a fluid feedstream. The fluid feedstream is flowed across a first surface of a polyphosphazene semipermeable membrane. At least one halogenated hydrocarbon from the fluid feedstream permeates through the polyphosphazene semipermeable membrane to a second opposed surface of the semipermeable membrane. Then the permeated polar hydrocarbon is removed from the second opposed surface of the polyphosphazene semipermeable membrane. Outstanding and unexpected separation selectivities on the order of 10,000 were obtained for methylene chloride when a methylene chloride in water feedstream was flowed across the polyphosphazene semipermeable membrane in the invented method.

  8. Size-selective permeation of water-soluble polymers through the bilayer membrane of cyclodextrin vesicles investigated by PFG-NMR.

    PubMed

    Himmelein, Sabine; Sporenberg, Nora; Schönhoff, Monika; Ravoo, Bart Jan

    2014-04-15

    Cyclodextrin vesicles (CDVs) consist of a bilayer of amphiphilic cyclodextrins (CDs). CDVs exhibit CD cavities at their surface that are able to recognize and bind hydrophobic guest molecules via size-selective inclusion. In this study, the permeability of α- and β-CDVs is investigated by pulsed field gradient-stimulated echo (PFG-STE) nuclear magnetic resonance. Diffusion experiments with water and two types of water-soluble polymers, polyethylene glycol (PEG) and polypropylene glycol (PPG), revealed three main factors that influence the exchange rate and permeability of CDVs. First, the length of the hydrophobic chain of the CD amphiphile plays a crucial role. Reasonably, vesicles consisting of amphiphiles with a longer aliphatic chain are less permeable since both membrane thickness and melting temperature T(m) increase. Second, the exchange rate through the bilayer membrane depends on the molecular weight of the polymer and decreases with increasing weight of the polymer. Most interestingly, a size-selective distinction of permeation due to the embedded CDs in the bilayer membrane was found. The mechanism of permeation is shown to occur through the CD cavity, such that depending on the size of the cavity, permeation of polymers with different cross-sectional diameters takes place. Whereas PPG permeates through the membrane of β-CD vesicles, it does not permeate α-CD vesicles. PMID:24650278

  9. Fabrication of charged membranes by the solvent-assisted lipid bilayer (SALB) formation method on SiO2 and Al2O3.

    PubMed

    Tabaei, Seyed R; Vafaei, Setareh; Cho, Nam-Joon

    2015-05-01

    In this study, we employed the solvent-assisted lipid bilayer (SALB) formation method to fabricate charged membranes on solid supports. The SALB formation method exploits a ternary mixture of lipid-alcohol-aqueous buffer to deposit lamellar phase structures on solid supports upon gradual increase of the buffer fraction. Using the quartz crystal microbalance with dissipation (QCM-D) technique, we investigated the formation of negatively and positively charged membranes via the SALB formation method and directly compared with the vesicle fusion method on two different oxide films. Bilayers containing an increasing fraction of negatively charged DOPS lipid molecules were successfully formed on both SiO2 and Al2O3 substrates using the SALB formation method at physiological pH (7.5). In contrast, the vesicle fusion method did not support bilayer formation on Al2O3 and those containing more than 10% DOPS ruptured on SiO2 only under acidic conditions (pH 5). Characterization of the fraction of negatively charge DOPS by in situ annexin 5A binding assay revealed that the fraction of DOPS lipid molecules in the bilayers formed on Al2O3 is significantly higher than that formed on SiO2. This suggests that the SALB self-assembly of charged membranes is predominantly governed by the electrostatic interaction. Furthermore, our findings indicate that when multicomponent lipid mixtures are used, the relative fraction of lipids in the bilayer may differ from the fraction of lipids in the precursor mixture. PMID:25858554

  10. On the dynamics of molecular self-assembly and the structural analysis of bilayer membranes using coarse-grained molecular dynamics simulations.

    PubMed

    Schindler, Tanja; Kröner, Dietmar; Steinhauser, Martin O

    2016-09-01

    We present a molecular dynamics simulation study of the self-assembly of coarse-grained lipid molecules from unbiased random initial configurations. Our lipid model is based on a well-tried CG polymer model with an additional potential that mimics the hydrophobic properties of lipid tails. We find that several stages of self-organization of lipid clusters are involved in the dynamics of bilayer formation and that the resulting equilibrium structures sensitively depend on the strength of hydrophobic interactions hc of the lipid tails and on temperature T. The obtained stable lipid membranes are quantitatively analyzed with respect to their local structure and their degree of order. At equilibrium, we obtain self-stabilizing bilayer membrane structures that exhibit a bending stiffness κB and compression modulus KC comparable to experimental measurements under physiological conditions. We present a phase diagram of our lipid model which covers a sol-gel transition, a liquid (or gel-like) phase including stable bilayer structures and vesicle formation, as well as a quasi-crystalline phase. We also determine the exact conditions for temperature T and degree of hydrophobicity hc for stable bilayer formation including closed vesicles. PMID:27216316

  11. X-ray diffraction study of lipid bilayer membranes interacting with amphiphilic helical peptides: diphytanoyl phosphatidylcholine with alamethicin at low concentrations.

    PubMed Central

    Wu, Y; He, K; Ludtke, S J; Huang, H W

    1995-01-01

    A variety of amphiphilic helical peptides have been shown to exhibit a transition from adsorbing parallel to a membrane surface at low concentrations to inserting perpendicularly into the membrane at high concentrations. Furthermore, this transition has been correlated to the peptides' cytolytic activities. X-ray lamellar diffraction of diphytanoyl phosphatidylcholine-alamethicin mixtures revealed the changes of the bilayer structure with alamethicin concentration. In particular, the bilayer thickness decreases with increasing peptide concentration in proportion to the peptide-lipid molar ratio from as low as 1:150 to 1:47; the latter is near the threshold of the critical concentration for insertion. From the decreases of the bilayer thickness, one can calculate the cross sectional expansions of the lipid chains. For all of the peptide concentrations studied, the area expansion of the chain region for each adsorbed peptide is a constant 280 +/- 20 A2, which is approximately the cross sectional area of an adsorbed alamethicin. This implies that the peptide is adsorbed at the interface of the hydrocarbon region, separating the lipid headgroups laterally. Interestingly, the chain disorder caused by a peptide adsorption tends to spread over a large area, as much as 100 A in diameter. The theoretical basis of the long range nature of bilayer deformation is discussed. PMID:7647240

  12. Trio engagement via plasma membrane phospholipids and the myristoyl moiety governs HIV-1 matrix binding to bilayers

    PubMed Central

    Vlach, Jiri; Saad, Jamil S.

    2013-01-01

    Localization of the HIV type-1 (HIV-1) Gag protein on the plasma membrane (PM) for virus assembly is mediated by specific interactions between the N-terminal myristoylated matrix (MA) domain and phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P2]. The PM bilayer is highly asymmetric, and this asymmetry is considered crucial in cell function. In a typical mammalian cell, the inner leaflet of the PM is enriched in phosphatidylserine (PS) and phosphatidylethanolamine (PE) and contains minor populations of phosphatidylcholine (PC) and PI(4,5)P2. There is strong evidence that efficient binding of HIV-1 Gag to membranes is sensitive not only to lipid composition and net negative charge, but also to the hydrophobic character of the acyl chains. Here, we show that PS, PE, and PC interact directly with MA via a region that is distinct from the PI(4,5)P2 binding site. Our NMR data also show that the myristoyl group is readily exposed when MA is bound to micelles or bicelles. Strikingly, our structural data reveal a unique binding mode by which the 2′-acyl chain of PS, PE, and PC lipids is buried in a hydrophobic pocket whereas the 1′-acyl chain is exposed. Sphingomyelin, a major lipid localized exclusively on the outer layer of the PM, does not bind to MA. Our findings led us to propose a trio engagement model by which HIV-1 Gag is anchored to the PM via the 1′-acyl chains of PI(4,5)P2 and PS/PE/PC and the myristoyl group, which collectively bracket a basic patch projecting toward the polar leaflet of the membrane. PMID:23401539

  13. 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

  14. Fluid Mechanical Matching of H+-ATP Synthase Subunit c-Ring with Lipid Membranes Revealed by 2H Solid-State NMR

    PubMed Central

    Kobayashi, Masatoshi; Struts, Andrey V.; Fujiwara, Toshimichi; Brown, Michael F.; Akutsu, Hideo

    2008-01-01

    The F1Fo-ATP synthase utilizes the transmembrane H+ gradient for the synthesis of ATP. Fo subunit c-ring plays a key role in transporting H+ through Fo in the membrane. We investigated the interactions of Escherichia coli subunit c with dimyristoylphosphatidylcholine (DMPC-d54) at lipid/protein ratios of 50:1 and 20:1 by means of 2H-solid-state NMR. In the liquid-crystalline state of DMPC, the 2H-NMR moment values and the order parameter (SCD) profile were little affected by the presence of subunit c, suggesting that the bilayer thickness in the liquid-crystalline state is matched to the transmembrane hydrophobic surface of subunit c. On the other hand, hydrophobic mismatch of subunit c with the lipid bilayer was observed in the gel state of DMPC. Moreover, the viscoelasticity represented by a square-law function of the 2H-NMR relaxation was also little influenced by subunit c in the fluid phase, in contrast with flexible nonionic detergents or rigid additives. Thus, the hydrophobic matching of the lipid bilayer to subunit c involves at least two factors, the hydrophobic length and the fluid mechanical property. These findings may be important for the torque generation in the rotary catalytic mechanism of the F1Fo-ATPse molecular motor. PMID:18310246

  15. Reconstruction of Osteochondral Defects by Combined Bone Grafting and a Bilayer Collagen Membrane as a Sandwich Technique

    PubMed Central

    Petri, Maximilian; Ettinger, Max; von Falck, Christian; Hawi, Nael; Jagodzinski, Michael; Haasper, Carl

    2013-01-01

    Treatment of osteochondral lesions of the knee remains a major challenge in orthopedic surgery. Recently established procedures like autologous chondrocyte implantation or matrix-associated chondrocyte implantation yield good results, but include the disadvantage of two-step procedures. The purpose of this study was to evaluate the clinical and magnetic resonance imaging outcome of repairs of osteochondral defects of the knee by a combined procedure of bone grafting and covering with a bilayer collagen membrane in a sandwich technique. Seven male patients with a mean age of 42 (range 30-55) years and symptomatic focal osteochondral lesions of the knee grade IV according to the International Cartilage Repair Society classification were included. The mean diameter of defects was 28.6 (range 15-40) mm. Results were evaluated at a minimum of 24 months after surgery by International Knee Documentation Committee score, Lysholm-score, visual analogue scale, and magnetic resonance imaging with specific cartilage sequences, evaluating the ICRS score and the Magnetic Observation of Cartilage Repair Tissue (MOCART) score. All patients judged the operation as successful. Among the patients available for the long-term follow-up, mean visual analogue scale value was 1.3 (range 0-3) out of 10 points. Mean International Knee Documentation Committee score was 80.8 (range 63.2-88.5) out of 100 points. Mean Lysholm score was 85 (range 55-95) out of 100 points. None of the patients had to be reoperated until today. Evaluation of magnetic resonance imaging using the MOCART score revealed a good correlation to the clinical outcome. This is the first study reporting results after reconstruction of osteochondral defects of the knee joint by bone grafting and a bilayer collagen membrane. This new method offers the advantage of a one-step-procedure and yields both good clinical and magnetic resonance findings. We conclude that this procedure can be a valuable tool to improve joint function

  16. Solution NMR of membrane proteins in bilayer mimics: Small is beautiful, but sometimes bigger is better

    PubMed Central

    Poget, Sébastien F.; Girvin, Mark E.

    2007-01-01

    Considerable progress has been made recently on solution NMR studies of multi-transmembrane helix membrane protein systems of increasing size. Careful correlation of structure with function has validated the physiological relevance of these studies in detergent micelles. However, larger micelle and bicelle systems are sometimes required to stabilize the active forms of dynamic membrane proteins, such as the bacterial small multidrug resistance transporters. Even in these systems with aggregate molecular weights well over 100 kDa, solution NMR structural studies are feasible – but challenging. PMID:17961504

  17. Solution NMR of membrane proteins in bilayer mimics: small is beautiful, but sometimes bigger is better.

    PubMed

    Poget, Sébastien F; Girvin, Mark E

    2007-12-01

    Considerable progress has been made recently on solution NMR studies of multi-transmembrane helix membrane protein systems of increasing size. Careful correlation of structure with function has validated the physiological relevance of these studies in detergent micelles. However, larger micelle and bicelle systems are sometimes required to stabilize the active forms of dynamic membrane proteins, such as the bacterial small multidrug resistance transporters. Even in these systems with aggregate molecular weights well over 100 kDa, solution NMR structural studies are feasible-but challenging. PMID:17961504

  18. The structural role of cholesterol in cell membranes: from condensed bilayers to lipid rafts.

    PubMed

    Krause, Martin R; Regen, Steven L

    2014-12-16

    CONSPECTUS: Defining the two-dimensional structure of cell membranes represents one of the most daunting challenges currently facing chemists, biochemists, and biophysicists. In particular, the time-averaged lateral organization of the lipids and proteins that make up these natural enclosures has yet to be established. As the classic Singer-Nicolson model of cell membranes has evolved over the past 40 years, special attention has focused on the structural role played by cholesterol, a key component that represents ca. 30% of the total lipids that are present. Despite extensive studies with model membranes, two fundamental issues have remained a mystery: (i) the mechanism by which cholesterol condenses low-melting lipids by uncoiling their acyl chains and (ii) the thermodynamics of the interaction between cholesterol and high- and low-melting lipids. The latter bears directly on one of the most popular notions in modern cell biology, that is, the lipid raft hypothesis, whereby cholesterol is thought to combine with high-melting lipids to form "lipid rafts" that float in a "sea" of low-melting lipids. In this Account, we first describe a chemical approach that we have developed in our laboratories that has allowed us to quantify the interactions between exchangeable mimics of cholesterol and low- and high-melting lipids in model membranes. In essence, this "nearest-neighbor recognition" (NNR) method involves the synthesis of dimeric forms of these lipids that contain a disulfide moiety as a linker. By means of thiolate-disulfide interchange reactions, equilibrium mixtures of dimers are then formed. These exchange reactions are initiated either by adding dithiothreitol to a liposomal dispersion to generate a small amount of thiol monomer or by including a small amount of thiol monomer in the liposomes at pH 5.0 and then raising the pH to 7.4. We then show how such NNR measurements have allowed us to distinguish between two very different mechanisms that have been

  19. Biomembrane disruption by silica-core nanoparticles: effect of surface functional group measured using a tethered bilayer lipid membrane

    PubMed Central

    Liu, Ying; Zhang, Zhen; Zhang, Quanxuan; Baker, Gregory L.; Worden, R. Mark

    2013-01-01

    Engineered nanomaterials (ENM) have desirable properties that make them well suited for many commercial applications. However, a limited understanding of how ENM’s properties influence their molecular interactions with biomembranes hampers efforts to design ENM that are both safe and effective. This paper describes the use of a tethered bilayer lipid membrane (tBLM) to characterize biomembrane disruption by functionalized silica-core nanoparticles. Electrochemical impedance spectroscopy was used to measure the time trajectory of tBLM resistance following nanoparticle exposure. Statistical analysis of parameters from an exponential resistance decay model was then used to quantify and analyze differences between the impedance profiles of nanoparticles that were unfunctionalized, amine-functionalized, or carboxyl-functionalized. All of the nanoparticles triggered a decrease in membrane resistance, indicating nanoparticle-induced disruption of the tBLM. Hierarchical clustering allowed the potency of nanoparticles for reducing tBLM resistance to be ranked in the order amine > carboxyl ~ bare silica. Dynamic light scattering analysis revealed that tBLM exposure triggered minor coalescence for bare and amine-functionalized silica nanoparticles but not for carboxyl-functionalized silica nanoparticles. These results indicate that the tBLM method can reproducibly characterize ENM-induced biomembrane disruption and can distinguish the BLM-disruption patterns of nanoparticles that are identical except for their surface functional groups. The method provides insight into mechanisms of molecular interaction involving biomembranes and is suitable for miniaturization and automation for high-throughput applications to help assess the health risk of nanomaterial exposure or identify ENM having a desired mode of interaction with biomembranes. PMID:24060565

  20. 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

  1. 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

  2. Photophysical Studies of Bioconjugated Ruthenium Metal-Ligand Complexes Incorporated in Phospholipid Membrane Bilayers

    PubMed Central

    Sharmin, Ayesha; Salassa, Luca; Rosenberg, Edward; Ross, J. B. Alexander; Abbott, Geoffrey; Black, Labe; Terwilliger, Michelle; Brooks, Robert

    2013-01-01

    Luminescent, mono-diimine, ruthenium complexes, [(H)Ru(CO)(PPh3)2(dcbpy)][PF6] (1, dcbpy = 4,4′-dicarboxy bipyridyl) and [(H)Ru(CO)(dppene)(5-amino-1,10-phen)][PF6] (2, dppene = bis diphenylphosphino-ethylene, phen = 9,10-phenanthroline), have been conjugated with 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DPPE) and with cholesterol in the case of 2. Compound 1 gives the bis-lipid derivative [(H)Ru(CO)(PPh3)2(dcbpy-N-DPPE2)][PF6] (3), while 2 provides the mono-lipid conjugate [(H)Ru(CO)(dppene)(1,10-phen-5-NHC(S)-N-DPPE)][ PF6] (4), and the cholesterol derivative [(H)Ru(CO)(dppene)(1,10-phen-5-NHC(O)OChol)][PF6] (5, Chol = cholesteryl), using standard conjugation techniques. These compounds were characterized by spectroscopic methods, and their photophysical properties were measured in organic solvents. The luminescence of lipid conjugates 3 and is quenched in organic solvents while compound 4 a weak, short-lived, blue-shifted emission in solution. The cholesterol conjugate shows the long-lived, microsecond-timescale emission associated with triplet metal-to-ligand charge-transfer (3MLCT) excited states. Incorporation of conjugate 3 in lipid bilayer vesicles restores the luminescence, but with blue shifts (~80 nm) accompanied by nanosecond-timescale lifetimes. In the vesicles conjugate 4 shows a similar short-lived and blue-shifted emission to that observed in solution but with increased intensity. Conjugation of the complex [(H)Ru(CO)(PhP2C2H4C(O)O-N-succinimidyl)2(bpy)][PF6] (6”) with DPPE gives the phosphine-conjugated complex [(H)Ru(CO)(PhP2C2H4C(O)-N-DPPE)2(bpy)][PF6] (7). Complex 7 also exhibits a short-lived and blue-shifted emission in solution and in vesicles as observed for 3 and 4. We have also conjugated the complex [Ru(bpy)2(5-amino-1,10-phenanthroline)][PF6]2 (8) with both cholesterol (9) and DPPE (10). Neither 9 nor the previously reported 10 exhibited the blue shifts observed for 3 and 4 when incorporated into LUVs. The anisotropies of

  3. Size Control and Fractionation of Ionic Liquid Filled Polymersomes with Glassy and Rubbery Bilayer Membranes.

    PubMed

    So, Soonyong; Lodge, Timothy P

    2016-05-17

    We demonstrate control over the size of ionic liquid (IL) filled polymeric vesicles (polymersomes) by three distinct methods: mechanical extrusion, cosolvent-based processing in an IL, and fractionation of polymersomes in a biphasic system of IL and water. For the representative ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([EMIM][TFSI])), the size and dispersity of polymersomes formed from 1,2-polybutadiene-b-poly(ethylene oxide) (PB-PEO) and polystyrene-b-poly(ethylene oxide) (PS-PEO) diblock copolymers were shown to be sensitive to assembly conditions. During mechanical extrusion through a polycarbonate membrane, the relatively larger polymersomes were broken up and reorganized into vesicles with mean size comparable to the membrane pore (100 nm radius); the distribution width also decreased significantly after only a few passes. Other routes were studied using the solvent-switch or cosolvent (CS) method, whereby the initial content of the cosolvent and the PEO block length of PS-PEO were systemically changed. The nonvolatility of the ionic liquid directly led to the desired concentration of polymersomes in the ionic liquid using a single step, without the dialysis conventionally used in aqueous systems, and the mean vesicle size depended on the amount of cosolvent employed. Finally, selective phase transfer of PS-PEO polymersomes based on size was used to extract larger polymersomes from the IL to the aqueous phase via interfacial tension controlled phase transfer. The interfacial tension between the PS membrane and the aqueous phase was varied with the concentration of sodium chloride (NaCl) in the aqueous phase; then the larger polymersomes were selectively separated to the aqueous phase due to differences in shielding of the hydrophobic core (PS) coverage by the hydrophilic corona brush (PEO). This novel fractionation is a simple separation process without any special apparatus and can help to prepare monodisperse polymersomes

  4. Antioxidant effect of 4-nerolidylcatechol and α-tocopherol in erythrocyte ghost membranes and phospholipid bilayers

    PubMed Central

    Fernandes, K.S.; Silva, A.H.M.; Mendanha, S.A.; Rezende, K.R.; Alonso, A.

    2013-01-01

    4-Nerolidylcatechol (4-NC) is found in Pothomorphe umbellata root extracts and is reported to have a topical protective effect against UVB radiation-induced skin damage, toxicity in melanoma cell lines, and antimalarial activity. We report a comparative study of the antioxidant activity of 4-NC and α-tocopherol against lipid peroxidation initiated by two free radical-generating systems: 2,2′-azobis(2-aminopropane) hydrochloride (AAPH) and FeSO4/H2O2, in red blood cell ghost membranes and in egg phosphatidylcholine (PC) vesicles. Lipid peroxidation was monitored by membrane fluidity changes assessed by electron paramagnetic resonance spectroscopy of a spin-labeled lipid and by the formation of thiobarbituric acid-reactive substances. When lipoperoxidation was initiated by the hydroxyl radical in erythrocyte ghost membranes, both 4-NC and α-tocopherol acted in a very efficient manner. However, lower activities were observed when lipoperoxidation was initiated by the peroxyl radical; and, in this case, the protective effect of α-tocopherol was lower than that of 4-NC. In egg PC vesicles, malondialdehyde formation indicated that 4-NC was effective against lipoperoxidation initiated by both AAPH and FeSO4/H2O2, whereas α-tocopherol was less efficient in protecting against lipoperoxidation by AAPH, and behaved as a pro-oxidant for FeSO4/H2O2. The DPPH (2,2-diphenyl-1-picrylhydrazyl) free-radical assay indicated that two free radicals were scavenged per 4-NC molecule, and one free radical was scavenged per α-tocopherol molecule. These data provide new insights into the antioxidant capacity of 4-NC, which may have therapeutic applications for formulations designed to protect the skin from sunlight irradiation. PMID:24068194

  5. Molecular dynamics simulation of the evolution of hydrophobic defects in one monolayer of a phosphatidylcholine bilayer: relevance for membrane fusion mechanisms.

    PubMed Central

    Tieleman, D Peter; Bentz, Joe

    2002-01-01

    The spontaneous formation of the phospholipid bilayer underlies the permeability barrier function of the biological membrane. Tears or defects that expose water to the acyl chains are spontaneously healed by lipid lateral diffusion. However, mechanical barriers, e.g., protein aggregates held in place, could sustain hydrophobic defects. Such defects have been postulated to occur in processes such as membrane fusion. This gives rise to a new question in bilayer structure: What do the lipids do in the absence of lipid lateral diffusion to minimize the free energy of a hydrophobic defect? As a first step to understand this rather fundamental question about bilayer structure, we performed molecular dynamic simulations of up to 10 ns of a planar bilayer from which lipids have been deleted randomly from one monolayer. In one set of simulations, approximately one-half of the lipids in the defect monolayer were restrained to form a mechanical barrier. In the second set, lipids were free to diffuse around. The question was simply whether the defects caused by removing a lipid would aggregate together, forming a large hydrophobic cavity, or whether the membrane would adjust in another way. When there are no mechanical barriers, the lipids in the defect monolayer simply spread out and thin with little effect on the other intact monolayer. In the presence of a mechanical barrier, the behavior of the lipids depends on the size of the defect. When 3 of 64 lipids are removed, the remaining lipids adjust the lower one-half of their chains, but the headgroup structure changes little and the intact monolayer is unaffected. When 6 to 12 lipids are removed, the defect monolayer thins, lipid disorder increases, and lipids from the intact monolayer move toward the defect monolayer. Whereas this is a highly simplified model of a fusion site, this engagement of the intact monolayer into the fusion defect is strikingly consistent with recent results for influenza hemagglutinin mediated

  6. Interaction of antimicrobial peptide Plantaricin149a and four analogs with lipid bilayers and bacterial membranes

    PubMed Central

    de Souza Lopes, José Luiz; Hissa, Denise Cavalcante; Melo, Vânia Maria Maciel; Beltramini, Leila Maria

    2013-01-01

    The amidated analog of Plantaricin149, an antimicrobial peptide from Lactobacillus plantarum NRIC 149, directly interacts with negatively charged liposomes and bacterial membranes, leading to their lysis. In this study, four Pln149-analogs were synthesized with different hydrophobic groups at their N-terminus with the goal of evaluating the effect of the modifications at this region in the peptide’s antimicrobial properties. The interaction of these peptides with membrane models, surface activity, their hemolytic effect on red blood cells, and antibacterial activity against microorganisms were evaluated. The analogs presented similar action of Plantaricin149a; three of them with no hemolytic effect (< 5%) until 0.5 mM, in addition to the induction of a helical element when binding to negative liposomes. The N-terminus difference between the analogs and Plantaricin149a retained the antibacterial effect on S. aureus and P. aeruginosa for all peptides (MIC50 of 19 μM and 155 μM to Plantaricin149a, respectively) but resulted in a different mechanism of action against the microorganisms, that was bactericidal for Plantaricin149a and bacteriostatic for the analogs. This difference was confirmed by a reduction in leakage action for the analogs. The lytic activity of Plantaricin149a is suggested to be a result of the peptide-lipid interactions from the amphipathic helix and the hydrophobic residues at the N-terminus of the antimicrobial peptide. PMID:24688525

  7. 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.

  8. Thermal-mechanical fluctuations of fluid membranes in confined geometries: The case of soft confinement

    SciTech Connect

    Podgornik, R.; Parsegian, V.A. )

    1992-02-01

    By definition, membrane or macromolecular assembly is an event of molecular confinement against the configurational entropy of a disordered state. Bilayer membranes under progressive confinement experience a continual damping of undulatory fluctuations, first interpreted as a steric force (Helfrich. Z. Naturforsch. 1978). This paper uses a new, diffusion-equation formalism based on the Feynman-type variational principle to describe how direct interbilayer forces - of hydration, electrostatic double layers, and van der Waals attraction - confine membrane fluctuations. We recover theoretical results to examine measured forces in multilamellar arrays showing that [open quotes]soft[close quotes] collisions, through long-range forces, create a mutual enhancement of both the direct forces and the undulatory steric interactions. Thus, there is yet another way to resolve the old, but false, dilemma to choose between steric and direct forces driving membrane assembly. One may develop a systematic connection between bilayer charge, hydration, and flexibility and the action of configurational entropic forces. The results make clear that one should measure forces between membranes or macromolecules in a way that allows them to express their native mechanical freedom. 15 refs., 3 figs.

  9. Highly efficient integration of the viral portal proteins from different types of phages into planar bilayers for the black lipid membrane analysis.

    PubMed

    Jing, Peng; Paraiso, Hallel; Burris, Benjamin

    2016-02-01

    The planar lipid bilayer technology is a technique that yields incredibly useful structural function information about a single channel protein. It is also currently actively utilized as a powerful platform using biological protein nanopores for the development of single-molecule nanopore sensing technology, as well as ultrafast DNA sequencing technology. The portal protein, GP10, from the bacteriophage Φ29 was the first phage portal protein shown to be successfully inserted into planar bilayer membranes, thereby it may inspire more researchers to apply the techniques to portal proteins from the other bacteriophages. However, the technology is far from perfect since the insertion of the channel proteins into planar bilayer membranes is not only technically difficult but also time-consuming. For the fusion of phage portal proteins, vesicles are typically needed to be reconstituted with the portal proteins to form proteoliposomes. However, most of the phage portal proteins have low solubility, and may self-aggregate during the preparation of the proteoliposomes. Furthermore, the fusion of the formed proteoliposomes is sporadic, unpredictable and varied from person to person. Due to the lack of experimental consistency between labs, the results from different methodologies reported for generating fusible proteoliposomes are highly variable. In this research, we propose a new method for the preparation of the fusible proteoliposomes containing portal proteins from bacteriophages, to circumvent the problems aforementioned. Compared to the conventional methods, this method was able to avoid the protein aggregation issues during the vesicle preparation by eliminating the need for detergents and the subsequent time-consuming step for detergent removal. The proteoliposomes prepared by the method were shown to be more efficiently and rapidly inserted into planar bilayer membranes bathed in different conducting buffer solutions including those with nonelectrolytes such as

  10. Docosahexaenoic acid and eicosapentaenoic acid induce changes in the physical properties of a lipid bilayer model membrane.

    PubMed

    Onuki, Yoshinori; Morishita, Mariko; Chiba, Yoshiyuki; Tokiwa, Shinji; Takayama, Kozo

    2006-01-01

    We investigated the effect of fatty acids such as stearic acid (SA, 18:0), oleic acid (OA, 18:1), eicosapentaenoic acid (EPA, 20:5), and docosahexaenoic acid (DHA, 22:6) on a dipalmitoylphosphatidylcholine (DPPC) bilayer by determining the phase transition temperature, fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH), and detergent insolubility. Treatment with unsaturated fatty acid broadened and shifted the phase transitions of the DPPC bilayer to a lower temperature. The phase transition temperature and the value of fluorescence anisotropy of DPH at 37 degrees C decreased progressively with increasing treatment amounts of unsaturated fatty acid. A large amount of the DPPC bilayer treated with unsaturated fatty acid was dissolved in Triton X-100, obtaining a low level of detergent insolubility. These modifications of the bilayer physical properties were most pronounced with DHA and EPA treatment. These data show that unsaturated fatty acids, particularly DHA and EPA, induce a marked change in the lipid bilayer structure. The composition of fatty acids in the DPPC bilayer was similar after treatment with various unsaturated fatty acids, suggesting that the different actions of unsaturated fatty acids are attributed to change in the molecular structure (e.g., kinked conformation by double bonds). We further explored the change in physical properties induced by fatty acids dispersed in a water-in-oil-in-water multiple emulsion and found that unsaturated fatty acids acted efficiently on the DPPC bilayer, even when incorporated in emulsion form. PMID:16394552

  11. Water-Protein Interactions of an Arginine-Rich Membrane Peptide in Lipid Bilayers Investigated by Solid-State NMR Spectroscopy

    PubMed Central

    Li, Shenhui; Su, Yongchao; Luo, Wenbin; Hong, Mei

    2010-01-01

    The interaction of an arginine (Arg) residue with water in a transmembrane antimicrobial peptide, PG-1, is investigated by two-dimensional heteronuclear correlation (HETCOR) solid-state NMR spectroscopy. Using 13C and 15N dipolar-edited 1H-15N HETCOR experiments, we unambiguously assigned a water-guanidinium cross peak that is distinct from intramolecular protein-protein cross peaks. This water-Arg cross peak was detected within a short 1H spin diffusion mixing time of 1 ms, indicating that water is in close contact with the membrane-inserted guanidinium. Together with previously observed short guanidinium-phosphate distances, these solid-state NMR data suggest that the Arg sidechains of PG-1 are stabilized by both hydration water and neutralizing lipid headgroups. The membrane deformation that occurs when water and lipid headgroups are pulled into the hydrophobic region of the bilayer is symptomatic of the membrane-disruptive function of this antimicrobial peptide. The water-Arg interactions observed here provide direct experimental evidence for molecular dynamics simulations of the solvation of Arg sidechains of membrane proteins by deeply embedded water in lipid bilayers. PMID:20199036

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

    PubMed Central

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

    1996-01-01

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

  13. Diffusion studies on permeable nitroxyl spin probe through lipid bilayer membrane

    SciTech Connect

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

    2014-04-24

    Electron spin resonance (ESR) studies were carried out for 2mM {sup 14}N labeled deutrated permeable 3- methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (MC-PROXYL) in pure water, 1 mM, 2 mM, 3 mM and 4 mM concentration of MC-PROXYL in 300 mM concentration of liposomal solution by using a L-band ESR spectrometer. The ESR parameters such as linewidth, hyperfine coupling constant, g-factor, partition parameter and permeability were reported. The partition parameter and permeability values indicate the maximum spin distribution in the lipid phase at 2 mM concentration. 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 radical concentration was optimized as 2 mM in liposomal solution for ESR phantom studies and experiments.

  14. Diffusion studies on permeable nitroxyl spin probe through lipid bilayer membrane

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    Electron spin resonance (ESR) studies were carried out for 2mM 14N labeled deutrated permeable 3- methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (MC-PROXYL) in pure water, 1 mM, 2 mM, 3 mM and 4 mM concentration of MC-PROXYL in 300 mM concentration of liposomal solution by using a L-band ESR spectrometer. The ESR parameters such as linewidth, hyperfine coupling constant, g-factor, partition parameter and permeability were reported. The partition parameter and permeability values indicate the maximum spin distribution in the lipid phase at 2 mM concentration. 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 radical concentration was optimized as 2 mM in liposomal solution for ESR phantom studies and experiments.

  15. Cholesterol Decreases the Size and the Mechanical Resistance to Rupture of Sphingomyelin Rich Domains, in Lipid Bilayers Studied as a Model of the Milk Fat Globule Membrane.

    PubMed

    Murthy, Appala Venkata Ramana; Guyomarc'h, Fanny; Lopez, Christelle

    2016-07-01

    Sphingomyelin-rich microdomains have been observed in the biological membrane surrounding milk fat globules (MFGM). The role played by cholesterol in these domains and in the physical properties and functions of the MFGM remains poorly understood. The objective of this work was therefore to investigate the phase state, topography, and mechanical properties of MFGM polar lipid bilayers as a function of cholesterol concentration, by combining X-ray diffraction, atomic force microscopy imaging, and force spectroscopy. At room temperature, i.e. below the phase transition temperature of the MFGM polar lipids, the bilayers showed the formation of sphingomyelin-rich domains in the solid ordered (so) phase that protruded about 1 nm above the liquid disordered (ld) phase. These so phase domains have a higher mechanical resistance to rupture than the ld phase (30 nN versus 15 nN). Addition of cholesterol in the MFGM polar lipid bilayers (i) induced the formation of liquid ordered (lo) phase for up to 27 mol % in the bilayers, (ii) decreased the height difference between the thicker ordered domains and the surrounding ld phase, (iii) promoted the formation of small sized domains, and (iv) decreased the mechanical resistance to rupture of the sphingomyelin-rich domains down to ∼5 nN. The biological and functional relevance of the lo phase cholesterol/sphingomyelin-rich domains in the membrane surrounding fat globules in milk remains to be elucidated. This study brought new insight about the functional role of cholesterol in milk polar lipid ingredients, which can be used in the preparation of food emulsions, e.g. infant milk formulas. PMID:27300157

  16. Cell-penetrating peptides do not cross mitochondrial membranes even when conjugated to a lipophilic cation: evidence against direct passage through phospholipid bilayers

    PubMed Central

    2004-01-01

    CPPs (cell-penetrating peptides) facilitate the cellular uptake of covalently attached oligonucleotides, proteins and other macromolecules, but the mechanism of their uptake is disputed. Two models are proposed: direct movement through the phospholipid bilayer and endocytic uptake. Mitochondria are a good model system to distinguish between these possibilities, since they have no vesicular transport systems. Furthermore, CPP-mediated delivery of macromolecules to the mitochondrial matrix would be a significant breakthrough in the study of mitochondrial function and dysfunction, and could also lead to new therapies for diseases caused by mitochondrial damage. Therefore we investigated whether two CPPs, penetratin and Tat, could act as mitochondrial delivery vectors. We also determined whether conjugation of the lipophilic cation TPP (triphenylphosphonium) to penetratin or Tat facilitated their uptake into mitochondria, since TPP leads to uptake of attached molecules into mitochondria driven by the membrane potential. Neither penetratin nor Tat, nor their TPP conjugates, are internalized by isolated mitochondria, indicating that these CPPs cannot cross mitochondrial phospholipid bilayers. Tat and TPP–Tat are taken up by cells, but they accumulate in endosomes and do not reach mitochondria. We conclude that CPPs cannot cross mitochondrial phospholipid bilayers, and therefore cannot deliver macromolecules directly to mitochondria. Our findings shed light on the mechanism of uptake of CPPs by cells. The lack of direct movement of CPPs through mitochondrial phospholipid bilayers, along with the observed endosomal accumulation of Tat and TPP–Tat in cells, makes it unlikely that CPPs enter cells by direct membrane passage, and instead favours cellular uptake via an endocytic pathway. PMID:15270716

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

    PubMed Central

    Smejtek, P; Paulis-Illangasekare, M

    1979-01-01

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

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

    PubMed

    Smejtek, P; Paulis-Illangasekare, M

    1979-06-01

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

  19. Cryo-transmission electron microscopy of a superstructure of fluid dioleoylphosphatidylcholine (DOPC) membranes.

    PubMed Central

    Klösgen, B; Helfrich, W

    1997-01-01

    Using cryo-transmission electron microscopy, we have obtained abundant and reproducible evidence for a superstructure of dioleoylphosphatidylcholine (DOPC) bilayers. Dispersions of vesicles were prepared by gentle shaking of a 2% suspension of DOPC in water followed in part by extrusion through a porous technical membrane. Sampling and cryofixation took place at various times within 3 weeks after the preparation. From the micrographs we infer that the small fraction of vesicles enclosing one another develop passages (connections) between the bilayers. In contrast, the superstructure is basically a feature of disconnected membranes. Among its modifications are isolated membrane bends or folds and a grainy membrane texture with a minimal grain spacing of 4-6 nm. In the extruded dispersions the passages and the superstructure seem to be formed mostly within the first day. The fraction of smooth and unilamellar vesicles is large at all times and in all dispersions. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 6 FIGURE 7 FIGURE 8 FIGURE 9 FIGURE 11 FIGURE 12 FIGURE 13 FIGURE 14 FIGURE 15 FIGURE 16 FIGURE 17 FIGURE 18 FIGURE 19 PMID:9414216

  20. A new technique of depositing phospholipid bilayers on quartz surfaces: its use in membrane spin-label studies.

    PubMed

    Kawano, I; Floyd, R A; Sridhar, R

    1981-03-01

    We have developed a new improved technique termed the parallel-beam spattering (PBS) method for depositing phospholipid bilayers on quartz surfaces. This technique involves atomizing the phospholipid mixture with a stream of nitrogen gas and passing this atomized mixture through two orifices separated by a distance to achieve a parallel beam of atomized particles before deposition on the quartz plate. A static electric field can easily be applied to the quartz surface. Also a goniometer of new design has been constructed to allow precise positioning of the deposited phospholipid bilayers with reference to the magnetic field. We have utilized the PBS method to deposit phosphatidylcholine/nitroxyl labeled cholestane mixtures on quartz plates and have found that hydrated bilayers of these mixtures yield ESR spectra with essentially the same characteristics as those obtained using more conventional techniques. The distinct advantage of the new technique for depositing bilayers is that there is no spectral anomaly present which usually is present when the more conventional method of depositing bilayers is used. The spectral anomaly is apparently caused by a portion of the bilayers aligned in directions not directly parallel to the quartz surface. For precision work the spectral anomaly is unacceptable. It is not observed with the new PBS method which has yielded highly reproducible results. PMID:6263962

  1. Membrane simulations mimicking acidic pH reveal increased thickness and negative curvature in a bilayer consisting of lysophosphatidylcholines and free fatty acids.

    PubMed

    Lähdesmäki, Katariina; Ollila, O H Samuli; Koivuniemi, Artturi; Kovanen, Petri T; Hyvönen, Marja T

    2010-05-01

    Phospholipids are key components of biological membranes and their lipolysis with phospholipase A(2) (PLA(2)) enzymes occurs in different cellular pH environments. Since no studies are available on the effect of pH on PLA(2)-modified phospholipid membranes, we performed 50-ns atomistic molecular dynamics simulations at three different pH conditions (pH 9.0, 7.5, and 5.5) using a fully PLA(2)-hydrolyzed phosphatidylcholine (PC) bilayer which consists solely of lysophosphatidylcholine and free fatty acid molecules. We found that a decrease in pH results in lateral squeezing of the membrane, i.e. in decreased surface area per headgroup. Thus, at the decreased pH, the lipid hydrocarbon chains had larger S(CD) order parameter values, and also enhanced membrane thickness, as seen in the electron density profiles across the membrane. From the lateral pressure profiles, we found that the values of spontaneous curvature of the two opposing monolayers became negative when the pH was decreased. At low pH, protonation of the free fatty acid headgroups reduces their mutual repulsion and accounts for the pH dependence of all the above-mentioned properties. The altered structural characteristics may significantly affect the overall surface properties of biomembranes in cellular vesicles, lipid droplets, and plasma lipoproteins, play an important role in membrane fission and fusion, and modify interactions between membrane lipids and the proteins embedded within them. PMID:20132791

  2. Self-formation of bilayer lipid membranes on agarose-coated silicon surfaces studied by simultaneous electrophysiological and surface infrared spectroscopic measurements

    NASA Astrophysics Data System (ADS)

    Hirano-Iwata, Ayumi; Oshima, Azusa; Onodera, Kota; Aoto, Kouji; Taira, Tasuku; Yamaguchi, Ryo-taro; Kimura, Yasuo; Niwano, Michio

    2009-06-01

    Self-formation process of bilayer lipid membranes (BLMs) cushioned on agarose-coated Si surfaces was in situ monitored by simultaneous electrophysiological and infrared absorption spectroscopic (IRAS) measurements using IRAS with the multiple internal reflection geometry. IRAS signals corresponding to self-thinning of lipid solution to form BLMs were demonstrated. It was found that the appearance of IRAS bands due to C=O modes of phosphstidylcholine is related to formation of BLMs with a gigaohm seal. The functionality of the present BLM system was also demonstrated by incorporating gramicidin into the BLMs and recording its channel activities.

  3. Permeation of protons, potassium ions, and small polar molecules through phospholipid bilayers as a function of membrane thickness.

    PubMed Central

    Paula, S; Volkov, A G; Van Hoek, A N; Haines, T H; Deamer, D W

    1996-01-01

    Two mechanisms have been proposed to account for solute permeation of lipid bilayers. Partitioning into the hydrophobic phase of the bilayer, followed by diffusion, is accepted by many for the permeation of water and other small neutral solutes, but transient pores have also been proposed to account for both water and ionic solute permeation. These two mechanisms make distinctively different predictions about the permeability coefficient as a function of bilayer thickness. Whereas the solubility-diffusion mechanism predicts only a modest variation related to bilayer thickness, the pore model predicts an exponential relationship. To test these models, we measured the permeability of phospholipid bilayers to protons, potassium ions, water, urea, and glycerol. Bilayers were prepared as liposomes, and thickness was varied systematically by using unsaturated lipids with chain lengths ranging from 14 to 24 carbon atoms. The permeability coefficient of water and neutral polar solutes displayed a modest dependence on bilayer thickness, with an approximately linear fivefold decrease as the carbon number varied from 14 to 24 atoms. In contrast, the permeability to protons and potassium ions decreased sharply by two orders of magnitude between 14 and 18 carbon atoms, and leveled off, when the chain length was further extended to 24 carbon atoms. The results for water and the neutral permeating solutes are best explained by the solubility-diffusion mechanism. The results for protons and potassium ions in shorter-chain lipids are consistent with the transient pore model, but better fit the theoretical line predicted by the solubility-diffusion model at longer chain lengths. PMID:8770210

  4. Permeation of protons, potassium ions, and small polar molecules through phospholipid bilayers as a function of membrane thickness

    NASA Technical Reports Server (NTRS)

    Paula, S.; Volkov, A. G.; Van Hoek, A. N.; Haines, T. H.; Deamer, D. W.

    1996-01-01

    Two mechanisms have been proposed to account for solute permeation of lipid bilayers. Partitioning into the hydrophobic phase of the bilayer, followed by diffusion, is accepted by many for the permeation of water and other small neutral solutes, but transient pores have also been proposed to account for both water and ionic solute permeation. These two mechanisms make distinctively different predictions about the permeability coefficient as a function of bilayer thickness. Whereas the solubility-diffusion mechanism predicts only a modest variation related to bilayer thickness, the pore model predicts an exponential relationship. To test these models, we measured the permeability of phospholipid bilayers to protons, potassium ions, water, urea, and glycerol. Bilayers were prepared as liposomes, and thickness was varied systematically by using unsaturated lipids with chain lengths ranging from 14 to 24 carbon atoms. The permeability coefficient of water and neutral polar solutes displayed a modest dependence on bilayer thickness, with an approximately linear fivefold decrease as the carbon number varied from 14 to 24 atoms. In contrast, the permeability to protons and potassium ions decreased sharply by two orders of magnitude between 14 and 18 carbon atoms, and leveled off, when the chain length was further extended to 24 carbon atoms. The results for water and the neutral permeating solutes are best explained by the solubility-diffusion mechanism. The results for protons and potassium ions in shorter-chain lipids are consistent with the transient pore model, but better fit the theoretical line predicted by the solubility-diffusion model at longer chain lengths.

  5. Renormalization of curvature elastic constants for elastic and fluid membranes

    NASA Astrophysics Data System (ADS)

    Ami, S.; Kleinert, H.

    1987-02-01

    We study the fluctuations of membranes with area and curvature elasticity and calculate the renormalization of the curvature elastic constants due to thermal fluctuations. For the mean curvature elastic constant the result is the same as obtained previously for “ideal membranes” which resist only to curvature deformations. The renormalization of the gaussian curvature, on the other hand, depends on the elastic contants. In an incompressible membrane, it is five times weaker than in an ideal membrane.

  6. Membrane water deaerator investigation. [fluid filter breadboard model

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    The purpose of the membrane water deaerator program was to develop data on a breadboard hollow fiber membrane unit that removes both dissolved and evolved gas from a water transfer system in order to: (1) assure a hard fill of the EVLSS expendable water tank; (2) prevent flow blockage by gas bubbles in circulating systems; and (3) prevent pump cavitation.

  7. A molecular basis explanation of the dynamic and thermal effects of vinblastine sulfate upon dipalmitoylphosphatidylcholine bilayer membranes.

    PubMed

    Maswadeh, H; Demetzos, C; Daliani, I; Kyrikou, I; Mavromoustakos, T; Tsortos, A; Nounesis, G

    2002-12-23

    Differential scanning calorimetry has been employed to study the thermal effects of vinblastine sulfate upon aqueous, single and multiple bilayer dispersions of 1,2-dipalmitoyl-3-sn-phosphatidylcholine (DPPC). The calorimetric results summarized to an increase in the gel to liquid-crystalline phase transition enthalpy and the abolishment of the L(beta)' (gel phase) to P(beta)' (ripple phase) pretransition for the uni- and multilamellar dispersions, as well as an increase in the transition temperature T(m) and the transition cooperativity for single bilayer DPPC/vinblastine mixed vesicles, are consistent with an induced, partially interdigitated, gel phase. Computational analysis has been successfully applied to clarify the intermolecular effects and verify the feasibility of the proposed interdigitation for the vinblastine sulfate molecules and also for the ursodeoxycholic acid (UDCAH) and bromocylated taxanes, which have been shown to induce an interdigitated gel phase in DPPC bilayers. PMID:12488037

  8. Laser flash photolysis as a probe of redox protein-membrane interactions: Effect of binding of spinach plastocyanin and horse cytochrome c to lipid bilayer vesicles on the kinetics of reduction by flavin semiquinone

    SciTech Connect

    Senthilathipan, V.; Tollin, G. )

    1989-02-07

    Spinach plastocyanin binds to both electrically neutral and positively charged lipid bilayer vesicles whereas cytochrome c only binds electrostatically to negatively charged vesicles. Laser flash photolysis using lumiflavin semiquinone as a reductant demonstrates that the reactivity of plastocyanin is increased as much as 6-fold when it is membrane bound whereas the rate constant for cytochrome c reduction is decreased by approximately a factor of 3. Membrane-bound plastocyanin reduction occurs via a two-step mechanism, probably involving prior association of lumiflavin semiquinone with the bilayer. In contrast, cytochrome c reduction in the membrane-bound state follows simple second-order kinetics, implying that the redox site in the bound state is still accessible to lumiflavin semiquinone in solution, although the rate constant is decreased by approximately 3-fold. These results are interpreted as indicating that the bilayer-protein interaction with plastocyanin leads to a steric blockage of the electron-transfer site from the aqueous phase. Little or no hindrance of the redox site occurs with cytochrome c, suggesting a high degree of mobility of this protein on the bilayer surface. Although the increase in plastocyanin reactivity upon binding to the bilayer is quite interesting, its cause remains unclear and requires further study. The results illustrate the utility of laser flash photolysis as a probe of membrane-protein interactions.

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

    PubMed Central

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

    2013-01-01

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

  10. 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

  11. Kinetics of the lamellar gel-fluid transition in phosphatidylcholine membranes in the presence of sugars

    SciTech Connect

    Lenné, Thomas; Garvey, Christopher J.; Koster, Karen L.; Bryant, Gary

    2014-09-24

    Phase diagrams are presented for dipalmitoylphosphatidylcholine (DPPC) in the presence of sugars (sucrose) over a wide range of relative humidities (RHs). The phase information presented here, determined by small angle X-ray scattering (SAXS), is shown to be consistent with previous results achieved by differential scanning calorimetry (DSC). Both techniques show a significant effect of sucrose concentration on the phase behaviour of this phospholipid bilayer. An experimental investigation into the effect of sugars on the kinetic behaviour of the gel to fluid transition is also presented showing that increasing the sugar content appears to slightly increase the rate at which the transition occurs.

  12. 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

  13. Structure of single-supported DMPC lipid bilayer membranes as a function of hydration level studied by neutron reflectivity and Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Miskowiec, A.; Schnase, P.; Bai, M.; Taub, H.; Hansen, F. Y.; Dubey, M.; Singh, S.; Majewski, J.

    2012-02-01

    We have recently been investigating the diffusion of water on single-supported DMPC lipid bilayer membranes at different levels of hydration, using high-resolution quasielastic neutron scattering (QNS). To aid in the interpretation of these QNS studies, we have conducted neutron reflectivity (NR) measurements on SPEAR at LANSCE to characterize the structure of similarly prepared samples. Protonated DMPC membranes were deposited onto SiO2-coated Si(100) substrates and characterized by Atomic Force Microscopy (AFM) at different levels of hydration. We find reasonable agreement between the membrane thickness determined by NR and AFM at room temperature. We also find consistency between the scattering length density (SLD) profile in the vicinity of the upper leaflet of the supported DMPC membrane and that found in a molecular dynamics simulation of a freestanding membrane at 303 K. However, the fit to the reflectivity curve can be improved by modifying the SLD profile near the leaflet closest to the SiO2 surface.

  14. Interleaflet mixing and coupling in liquid-disordered phospholipid bilayers.

    PubMed

    Capponi, Sara; Freites, J Alfredo; Tobias, Douglas J; White, Stephen H

    2016-02-01

    Organized as bilayers, phospholipids are the fundamental building blocks of cellular membranes and determine many of their biological functions. Interactions between the two leaflets of the bilayer (interleaflet coupling) have been implicated in the passage of information through membranes. However, physically, the meaning of interleaflet coupling is ill defined and lacks a structural basis. Using all-atom molecular dynamics simulations of fluid phospholipid bilayers of five different lipids with differing degrees of acyl-chain asymmetry, we have examined interleaflet mixing to gain insights into coupling. Reasoning that the transbilayer distribution of terminal methyl groups is an appropriate measure of interleaflet mixing, we calculated the transbilayer distributions of the acyl chain terminal methyl groups for five lipids: dioleoylphosphatidylcholine (DOPC), palmitoyloleoylphosphatidylcholine (POPC), stearoyloleoylphosphatidylcholine (SOPC), oleoylmyristoylphosphatidylcholine (OMPC), and dimyristoylphosphatidylcholine (DMPC). We observed in all cases very strong mixing across the bilayer midplane that diminished somewhat with increasing acyl-chain ordering defined by methylene order parameters. A hallmark of the interleaflet coupling idea is complementarity, which postulates that lipids with short alkyl chains in one leaflet will preferentially associate with lipids with long alkyl chains in the other leaflet. Our results suggest a much more complicated picture for thermally disordered bilayers that we call distributed complementarity, as measured by the difference in the peak positions of the sn-1 and sn-2 methyl distributions in the same leaflet. PMID:26657692

  15. Development of electron spin echo envelope modulation spectroscopy to probe the secondary structure of recombinant membrane proteins in a lipid bilayer.

    PubMed

    Zhang, Rongfu; Sahu, Indra D; Gibson, Kaylee R; Muhammad, Nefertiti B; Bali, Avnika P; Comer, Raven G; Liu, Lishan; Craig, Andrew F; Mccarrick, Robert M; Dabney-Smith, Carole; Sanders, Charles R; Lorigan, Gary A

    2015-11-01

    Membrane proteins conduct many important biological functions essential to the survival of organisms. However, due to their inherent hydrophobic nature, it is very difficult to obtain structural information on membrane-bound proteins using traditional biophysical techniques. We are developing a new approach to probe the secondary structure of membrane proteins using the pulsed EPR technique of Electron Spin Echo Envelope Modulation (ESEEM) Spectroscopy. This method has been successfully applied to model peptides made synthetically. However, in order for this ESEEM technique to be widely applicable to larger membrane protein systems with no size limitations, protein samples with deuterated residues need to be prepared via protein expression methods. For the first time, this study shows that the ESEEM approach can be used to probe the local secondary structure of a (2) H-labeled d8 -Val overexpressed membrane protein in a membrane mimetic environment. The membrane-bound human KCNE1 protein was used with a known solution NMR structure to demonstrate the applicability of this methodology. Three different α-helical regions of KCNE1 were probed: the extracellular domain (Val21), transmembrane domain (Val50), and cytoplasmic domain (Val95). These results indicated α-helical structures in all three segments, consistent with the micelle structure of KCNE1. Furthermore, KCNE1 was incorporated into a lipid bilayer and the secondary structure of the transmembrane domain (Val50) was shown to be α-helical in a more native-like environment. This study extends the application of this ESEEM approach to much larger membrane protein systems that are difficult to study with X-ray crystallography and/or NMR spectroscopy. PMID:26355804

  16. 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.

  17. Relaxation rate of the shape fluctuation of a fluid membrane immersed in a near-critical binary fluid mixture.

    PubMed

    Fujitani, Youhei

    2016-03-01

    We consider the two-time correlation of the shape fluctuation of a fluid membrane immersed in a near-critical binary fluid mixture. Usually one component of the mixture is preferably attracted by the membrane. Adsorption layers, where the preferred component is more concentrated, are generated on both sides of the membrane significantly because of the near-criticality. The resultant gradient of the local mass-density difference between the two components generates additional stress, including the osmotic pressure, to influence the membrane motion. Assuming the mixture to be in the homogeneous phase near, but not too close to, the demixing critical point, we use the Gaussian free-energy functional to calculate the relaxation rate for a wavelength much longer than the correlation length of the mixture. Our calculation supposes weak preferential attraction and weak dependence of the mixture viscosity on the mass-density difference, and is performed within the linear approximation with respect to the undulation amplitude. It is shown for small wave number that the additional stress makes the relaxation more rapid independently of whether the preferred component is more viscous or not and that the relaxation rate can be regarded as proportional to the wave number even for a tensionless membrane. This linear dependence comes from the balance between the frictional force due to the mixture viscosity and the restoring force of the adsorption layer. PMID:26993992

  18. Ultrafast molecular dynamics of biofuel extraction for microalgae and bacteria milking: blocking membrane folding pathways to damaged lipid-bilayer conformations with nanomicelles.

    PubMed

    Gillet, Jean-Numa

    2015-01-01

    Cell milking is a 100% renewable green energy for CO2 by extraction of biofuels inside the cytosol of photosynthetic micro-organisms as microalgae and bacteria. The cells are exposed to a hydrophobic solvent forming holes and cracks through their membranes from which the biofuels can leak out. In protein folding, the goal would be to find pathways to the unique functional protein conformer. However, in the lipid-bilayer interaction with the solvent for milking, the objective is to block the pathways for damaged membrane conformations of low free energy with undesired nanostructures, using the solvent properties, as shown with an ab initio structural bioinformatic model. Statistical thermodynamics is used to compute the free energy (including entropy) from the molecular dynamics trajectory of the biomolecular system with many conformational changes. This model can be extended to the general problem of biomolecules folding as for proteins and nucleic acids. Using an adaptation of the Einstein diffusion law, the conformational change dynamics of the lipid bilayer depends on the two diffusion coefficients of the solvent: D1 before the irreversible folding transition time and the much smaller D2 thereafter. In contrast to the n-hexane and n-heptane hydrocarbons of smaller size, the residual D2=4.7 × 10(-7)cm(2)/s of the n-decane solvent, with the highest partition coefficient among the three extractors, is the only to present a D2 value that is significantly below the critical threshold of 10(-6)cm(2)/s. Therefore, the membrane would resist to long hydrocarbons and the exposed cells would remain viable for milking. PMID:24735062

  19. 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

  20. Solution Asymmetry and Salt Expand Fluid-Fluid Coexistence Regions of Charged Membranes.

    PubMed

    Kubsch, Bastian; Robinson, Tom; Lipowsky, Reinhard; Dimova, Rumiana

    2016-06-21

    Liquid-liquid phase separation in giant unilamellar vesicles (GUVs) leads to the formation of intramembrane domains. To mimic charged biological membranes, we studied phase separation and domain formation in GUVs of ternary lipid mixtures composed of egg sphingomyelin, cholesterol, and the negatively charged lipid dioleoylphosphatidylglycerol. The GUVs were exposed to solutions of sucrose and high-saline buffer. The phase diagram was determined using epifluorescence microscopy for vesicle populations with symmetric and asymmetric solution compositions across the membranes. Trans-membrane solution asymmetry was found to affect the membrane phase state. Furthermore, compared to the case of salt-free conditions, the phase diagram in the presence of high-saline buffer (both symmetrically or asymmetrically present across the membrane) was found to exhibit a significantly extended region of liquid-ordered and liquid-disordered coexistence. These observations were confirmed on single GUVs using microfluidics and confocal microscopy. Moreover, we found that the miscibility temperatures markedly increased for vesicles in the presence of symmetric and asymmetric salt solutions. Our results demonstrate a substantial effect of salt and solution asymmetry on the phase behavior of charged membranes, which has direct implications for protein adsorption onto these membranes and for the repartitioning of proteins within the membrane domains. PMID:27288275

  1. LIPID RAFTS, FLUID/FLUID PHASE SEPARATION, AND THEIR RELEVANCE TO PLASMA MEMBRANE STRUCTURE AND FUNCTION

    PubMed Central

    Sengupta, Prabuddha; Baird, Barbara; Holowka, David

    2007-01-01

    Novel biophysical approaches combined with modeling and new biochemical data have helped to recharge the lipid raft field and have contributed to the generation of a refined model of plasma membrane organization. In this review, we summarize new information in the context of previous literature to provide new insights into the spatial organization and dynamics of lipids and proteins in the plasma membrane of live cells. Recent findings of large-scale separation of liquid-ordered and liquid-disordered phases in plasma membrane vesicles demonstrate this capacity within the complex milieu of plasma membrane proteins and lipids. Roles for membrane heterogeneity and reorganization in immune cell activation are discussed in light of this new information. PMID:17764993

  2. 2NH and 3OH are crucial structural requirements in sphingomyelin for sticholysin II binding and pore formation in bilayer membranes.

    PubMed

    Maula, Terhi; Isaksson, Y Jenny E; García-Linares, Sara; Niinivehmas, Sanna; Pentikäinen, Olli T; Kurita, Mayuko; Yamaguchi, Shou; Yamamoto, Tetsuya; Katsumura, Shigeo; Gavilanes, José G; Martínez-del-Pozo, Alvaro; Slotte, J Peter

    2013-05-01

    Sticholysin II (StnII) is a pore-forming toxin from the sea anemone Stichodactyla heliantus which belongs to the large actinoporin family. The toxin binds to sphingomyelin (SM) containing membranes, and shows high binding specificity for this lipid. In this study, we have examined the role of the hydrogen bonding groups of the SM long-chain base (i.e., the 2NH and the 3OH) for StnII recognition. We prepared methylated SM-analogs which had reduced hydrogen bonding capability from 2NH and 3OH. Both surface plasmon resonance experiments, and isothermal titration calorimetry measurements indicated that StnII failed to bind to bilayers containing methylated SM-analogs, whereas clear binding was seen to SM-containing bilayers. StnII also failed to induce calcein release (i.e., pore formation) from vesicles made to contain methylated SM-analogs, but readily induced calcein release from SM-containing vesicles. Molecular modeling of SM docked to the phosphocholine binding site of StnII indicated that the 2NH and 3OH groups were likely to form a hydrogen bond with Tyr135. In addition, it appeared that Tyr111 and Tyr136 could donate hydrogen bonds to phosphate oxygen, thus stabilizing SM binding to the toxin. We conclude that the interfacial hydrogen bonding properties of SM, in addition to the phosphocholine head group, are crucial for high-affinity SM/StnII-interaction. PMID:23376330

  3. Molecular simulation of pressure-driven fluid flow in nanoporous membranes

    NASA Astrophysics Data System (ADS)

    Takaba, Hiromitsu; Onumata, Yasushi; Nakao, Shin-ichi

    2007-08-01

    An extended nonequilibrium molecular dynamics technique has been developed to investigate the transport properties of pressure-driven fluid flow in thin nanoporous membranes. Our simulation technique allows the simulation of the pressure-driven permeation of liquids through membranes while keeping a constant driving pressure using fluctuating walls. The flow of argon in the liquid state was simulated on applying an external pressure difference of 2.4×106Pa through the slitlike and cylindrical pores. The volume flux and velocity distribution in the membrane pores were examined as a function of pore size, along with the interaction with the pore walls, and these were compared with values estimated using the Hagen-Poiseuille flow. The calculated velocity strongly depends on the strength of the interaction between the fluid and the atoms in the wall when the pore size is approximately <20σ. The calculated volume flux also shows a dependence on the interaction between the fluid and the atoms in the wall. The Hagen-Poiseuille law overestimates or underestimates the flux depending on the interaction. From the analysis of calculated results, a good linear correlation between the density of the fluid in the membrane pores and the deviation of the flux estimated from the Hagen-Poiseuille flow was found. This suggests that the flux deviation in nanopore from the Hagen-Poiseuille flow can be predicted based on the fluid density in the pores.

  4. Open channel current noise analysis of S6 peptides from KvAP channel on bilayer lipid membrane shows bimodal power law scaling

    NASA Astrophysics Data System (ADS)

    Shrivastava, Rajan; Malik, Chetan; Ghosh, Subhendu

    2016-06-01

    Open channel current noise in synthetic peptide S6 of KvAP channel was investigated in a voltage clamp experiment on bilayer lipid membrane (BLM). It was observed that the power spectral density (PSD) of the component frequencies follows power law with different slopes in different frequency ranges. In order to know the origin of the slopes PSD analysis was done with signal filtering. It was found that the first slope in the noise profile follows 1 / f pattern which exists at lower frequencies and has high amplitude current noise, while the second slope corresponds to 1 /f 2 - 3 pattern which exists at higher frequencies with low amplitude current noise. In addition, white noise was observed at very large frequencies. It was concluded that the plausible reason for the multiple power-law scaling is the existence of different modes of non-equilibrium ion transport through the S6 channel.

  5. 7,7,8,8-tetracyanoquinodimethane chemiluminescence sensitized by Rhodamine B on surfactant bilayer membrane assemblies for determination of sulphide by a flow-injection method.

    PubMed

    Xue-Xin, Q; Yue-Ying, G; Yamada, M; Kobayashi, E; Suzuki, S

    1989-04-01

    A new chemiluminescence system is described for selective determination of sulphide by a flow-injection method. The weak light emitted from the reaction between 7,7,8,8-tetracyanoquinodimethane and sulphide is efficiently sensitized by Rhodamine B in alkaline solution containing dioctadecyldimethylammonium chloride bilayer membrane aggregates and acetonitrile. The limit of determination is 0.05 ng (injection of 30 mul of 5 x 10(-8)M sulphide), the linear range is two orders of magnitude, the sampling rate is 240/hr, and the relative standard deviation is 3.0% for 0.3 ng of sulphide. Manganese(II), the strongest enhancing species after sulphide ion, provides a signal 1.1% of that for sulphide ion. Manganese(II), iron(II), and species forming precipitates with sulphide ion interfere, but other sulphur anions such as sulphite, sulphate, thiosulphate, and thiocyanate do not. PMID:18964747

  6. Air-stable droplet interface bilayers on oil-infused surfaces

    PubMed Central

    Boreyko, Jonathan B.; Polizos, Georgios; Datskos, Panos G.; Sarles, Stephen A.; Collier, C. Patrick

    2014-01-01

    Droplet interface bilayers are versatile model membranes useful for synthetic biology and biosensing; however, to date they have always been confined to fluid reservoirs. Here, we demonstrate that when two or more water droplets collide on an oil-infused substrate, they exhibit noncoalescence due to the formation of a thin oil film that gets squeezed between the droplets from the bottom up. We show that when phospholipids are included in the water droplets, a stable droplet interface bilayer forms between the noncoalescing water droplets. As with traditional oil-submerged droplet interface bilayers, we were able to characterize ion channel transport by incorporating peptides into each droplet. Our findings reveal that droplet interface bilayers can function in ambient environments, which could potentially enable biosensing of airborne matter. PMID:24821774

  7. Quantifying the Diffusion of a Fluid through Membranes by RemoteDetection MRI

    SciTech Connect

    Telkki, Ville-Veikko; Hilty, Christian; Garcia, Sandra; Harel,Elad; Pines, Alexander

    2006-10-24

    We present a method to measure self-diffusion acrossmembranes without the need for concentration or pressure gradients.Hyperpolarized xenon in combination with remote detection of NMR allowsthe measurement of membrane permeation, even in the gas phase. Theresulting images allow quantification of the amount of fluid diffusedthrough the membrane, and represent an alternative, potentially moreprecise way of measuring a membrane diffusion coefficient. The use ofremote detection of NMR allows for non-invasive signal encoding coupledto sensitive detection, making this approach ideal for the study ofdiffusion in intact devices such as fuel cells or separationsystems.

  8. Polyurethane membrane/knitted mesh-reinforced collagen-chitosan bilayer dermal substitute for the repair of full-thickness skin defects via a two-step procedure.

    PubMed

    Wang, Xingang; Wu, Pan; Hu, Xiuyuan; You, Chuangang; Guo, Rui; Shi, Haifei; Guo, Songxue; Zhou, Hanlei; Chaoheng, Yu; Zhang, Yuanhai; Han, Chunmao

    2016-03-01

    The advent of dermal substitutes provides a revolutionary strategy for the repair and reconstruction of deep skin defects. Dermal substitutes form a regenerative template that provides the porous structure and mechanical support necessary to guide cell migration, deposition of the extracellular matrix (ECM) and angiogenesis. Commercially available dermal substitutes, particularly collagen-based dermal scaffolds, are widely used in clinical practice. However, the poor mechanical properties of collagen-based dermal scaffolds compromise their biological effects, as well as the repair outcomes. Here, we describe a bilayer dermal substitute prepared by integrating a hybrid dermal scaffold with a polyurethane (PU) membrane to obtain a PU membrane/knitted mesh-reinforced collagen-chitosan bilayer dermal substitute (PU-PLGAm/CCS). The morphology of PU-PLGAm/CCS was investigated and, to characterize the effects of PU-PLGAm/CCS on tissue regeneration, dermal substitutes were transplanted to repair full-thickness skin wounds in Sprague-Dawley rats using a two-step surgical procedure. These results were then compared with those obtained using the PELNAC™ Artificial Dermis. In the weeks after the first operation, wound changes were analysed based on macroscopic observations, and tissue specimens were harvested for histology, immunohistochemistry, immunofluorescence real-time quantitative PCR, and Western blotting analysis. Following the second operation (i.e., transplantation of split-thickness skin grafts), the repair outcomes were investigated based on the mechanical strength and ECM expression. PU-PLGAm/CCS significantly inhibited wound contracture, promoted angiogenesis, and facilitated the ordered arrangement of neotissue, such that the repair outcomes were improved in the PU-PLGAm/CCS group compared with the PELNAC™ group. In conclusion, the favourable microstructure and structural stability of dermal substitutes facilitated tissue regeneration. PU-PLGAm/CCS achieved

  9. Interaction of cholesterol with sphingomyelin in bilayer membranes: Evidence that the hydroxy group of sphingomyelin does not modulate the rate of cholesterol exchange between vesicles

    SciTech Connect

    Chucheng Kan; Zhongshi Ruan; Bittman, R. )

    1991-08-06

    Cholesterol undergoes exchange between membranes containing sphingomyelin at a much slower rate than between membranes lacking sphingomyelin. To investigate the role of the hydroxy group at the 3-position of sphingomyelin in the interaction between sphingomyelin and cholesterol, the authors have measured the rates of (4-{sup 14}C)cholesterol exchange between unilamellar vesicles prepared with N-alkyl group or with hydrogen. Vesicles prepared from 3-deoxy- and 3-0-methyl-N-stearoylsphingomyelin had the same rate of ({sup 14}C) cholesterol desorption. The half-times for exchange from vesicles prepared with 3-0-methyl- and 3-deoxy-N-stearoylsphingomyelins and 10 mol% of cholesterol were only slightly faster than that found from vesicles prepared from N-stearoylsphingomyelin and 10 mol% cholesterol. The rate of cholesterol desorption from vesicles could be accelerated by preparing vesicles from bulky 3-0-alkyl analogues of sphingomyelin. These data indicate that insertion of sterically bulky groups at the 3-position of sphingomyelin in place of hydroxy interferes markedly with the molecular packing of cholesterol and sphingomyelin in bilayer membranes; however, the hydroxy group of sphingomyelin is not critical for the strong interaction of cholesterol with sphingomyelin. These results suggest that van der Waals interactions are more important than hydrogen-bonding interactions involving the hydroxy group in contributing to tight lateral packing of cholesterol with sphingomyelin.

  10. Interstitial fluid flow: simulation of mechanical environment of cells in the interosseous membrane

    NASA Astrophysics Data System (ADS)

    Yao, Wei; Ding, Guang-Hong

    2011-08-01

    In vitro experiments have shown that subtle fluid flow environment plays a significant role in living biological tissues, while there is no in vivo practical dynamical measurement of the interstitial fluid flow velocity. On the basis of a new finding that capillaries and collagen fibrils in the interosseous membrane form a parallel array, we set up a porous media model simulating the flow field with FLUENT software, studied the shear stress on interstitial cells' surface due to the interstitial fluid flow, and analyzed the effect of flow on protein space distribution around the cells. The numerical simulation results show that the parallel nature of capillaries could lead to directional interstitial fluid flow in the direction of capillaries. Interstitial fluid flow would induce shear stress on the membrane of interstitial cells, up to 30 Pa or so, which reaches or exceeds the threshold values of cells' biological response observed in vitro. Interstitial fluid flow would induce nonuniform spacial distribution of secretion protein of mast cells. Shear tress on cells could be affected by capillary parameters such as the distance between the adjacent capillaries, blood pressure and the permeability coefficient of capillary's wall. The interstitial pressure and the interstitial porosity could also affect the shear stress on cells. In conclusion, numerical simulation provides an effective way for in vivo dynamic interstitial velocity research, helps to set up the vivid subtle interstitial flow environment of cells, and is beneficial to understanding the physiological functions of interstitial fluid flow.

  11. A second generation mesoscopic lipid bilayer model: Connections to field-theory descriptions of membranes and nonlocal hydrodynamics

    NASA Astrophysics Data System (ADS)

    Ayton, Gary S.; McWhirter, J. Liam; Voth, Gregory A.

    2006-02-01

    A new mesoscopic membrane model is developed in order to examine long-wavelength structural and dynamical membrane phenomena. Two different explicit mesoscopic solvent models are employed. The first mesoscopic solvent is denoted the big liquid oscillating blob system, which is parametrized to model water at a coarse-grained level and is motivated by a Langevin-like approach; the resulting membrane dynamics predict a solvent viscosity dependence consistent with the known viscosity of water. The second mesoscopic solvent is a Weeks-Chandler-Anderson model. Here, it is found that the correct mesoscopic hydrodynamic scaling of the membrane undulation dynamics is still preserved, although accelerated. When the behavior of the two membranes in close proximity to one another is examined, very little correlated motion is observed. However, the theoretically predicted scaling of the entropic undulation energy is confirmed, demonstrating that the entropic interaction between two membranes becomes increasingly repulsive with decreasing separation.

  12. Probing Membrane Order and Topography in Supported Lipid Bilayers by Combined Polarized Total Internal Reflection Fluorescence-Atomic Force Microscopy

    PubMed Central

    Oreopoulos, John; Yip, Christopher M.

    2009-01-01

    Determining the local structure, dynamics, and conformational requirements for protein-protein and protein-lipid interactions in membranes is critical to understanding biological processes ranging from signaling to the translocating and membranolytic action of antimicrobial peptides. We report here the application of a combined polarized total internal reflection fluorescence microscopy-in situ atomic force microscopy platform. This platform's ability to image membrane orientational order was demonstrated on DOPC/DSPC/cholesterol model membranes containing the fluorescent membrane probe, DiI-C20 or BODIPY-PC. Spatially resolved order parameters and fluorophore tilt angles extracted from the polarized total internal reflection fluorescence microscopy images were in good agreement with the topographical details resolved by in situ atomic force microscopy, portending use of this technique for high-resolution characterization of membrane domain structures and peptide-membrane interactions. PMID:19254557

  13. 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.

  14. Molecular dynamics investigations of PRODAN in a DLPC bilayer.

    PubMed

    Nitschke, William K; Vequi-Suplicy, Cíntia C; Coutinho, Kaline; Stassen, Hubert

    2012-03-01

    Molecular dynamics computer simulations have been performed to identify preferred positions of the fluorescent probe PRODAN in a fully hydrated DLPC bilayer in the fluid phase. In addition to the intramolecular charge-transfer first vertical excited state, we considered different charge distributions for the electronic ground state of the PRODAN molecule by distinct atomic charge models corresponding to the probe molecule in vacuum as well as polarized in a weak and a strong dielectric solvent (cyclohexane and water). Independent on the charge distribution model of PRODAN, we observed a preferential orientation of this molecule in the bilayer with the dimethylamino group pointing toward the membrane's center and the carbonyl oxygen toward the membrane's interface. However, changing the charge distribution model of PRODAN, independent of its initial position in the equilibrated DLPC membrane, we observed different preferential positions. For the ground state representation without polarization and the in-cyclohexane polarization, the probe maintains its position close to the membrane's center. Considering the in-water polarization model, the probe approaches more of the polar headgroup region of the bilayer, with a strong structural correlation with the choline group, exposing its oxygen atom to water molecules. PRODAN's representation of the first vertical excited state with the in-water polarization also approaches the polar region of the membrane with the oxygen atom exposed to the bilayer's hydration shell. However, this model presents a stronger structural correlation with the phosphate groups than the ground state. Therefore, we conclude that the orientation of the PRODAN molecule inside the DLPC membrane is well-defined, but its position is very sensitive to the effect of the medium polarization included here by different models for the atomic charge distribution of the probe. PMID:22329741

  15. Cytolytic activity in T cell clones derived from human synovial rheumatoid membrane: inhibition by synovial fluid.

    PubMed Central

    Miltenburg, A M; Van Laar, J M; De Kuiper, P; Daha, M R; Breedveld, F C

    1990-01-01

    A panel of T cell clones was derived from the synovial membrane of a patient with rheumatoid arthritis (RA). We investigated whether T cell clones with cytolytic properties were present and whether T cell cytotoxicity was influenced by the presence of synovial fluid. These issues were studied using anti-CD3 and lectin-induced cytotoxicity assays. The majority of the T cell clones derived from the synovial membrane showed cytotoxic properties although non-cytotoxic clones were also found. Three clones (N11, N6 and N15) showed strong cytotoxicity (more than 40% lysis at an effector-to-target cell ratio of 10:1) whereas three clones (N16, N4 and N14) were non-cytotoxic (less than 20% lysis at an effector-to-target cell ratio of 10:1). The induction of cytotoxicity in the anti-CD3-driven system was shown to be dependent on the dose of anti-CD3 present. When synovial fluid was added to these assays a strong inhibition of cytotoxicity was found. This inhibition of cytotoxicity was found with synovial fluid samples of RA patients, as well as with non-RA synovial fluids. Both anti-CD3 and lectin-dependent cytotoxicity assays were strongly inhibited. In conclusion, T cell clones with cytotoxic activity can be isolated from rheumatoid synovial membrane. In the presence of synovial fluid these cytotoxic cells are inhibited to exert their cytotoxic function. PMID:2148285

  16. 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

  17. Pore formation in lipid bilayer membranes made of phosphatidylinositol and oxidized cholesterol followed by means of alternating current.

    PubMed Central

    Gallucci, E; Micelli, S; Monticelli, G

    1996-01-01

    The kinetics of porin incorporation into black lipid membranes (BLM) made of phosphatidylinositol (PI) or oxidized cholesterol (Ox Ch) were studied by means of alternating current; the set-up was able to acquire resistance and capacitance simultaneously by means of a mixed double-frequency approach at 1 Hz and 1 KHz, respectively. Conductance was dependent on the interaction between protein-forming pores and lipids. For PI membranes below a porin concentration of 12.54 ng/ml, there was no membrane conductivity, whereas at 200 ng/ml a steady-state value was reached. Different behavior was displayed by Ox Ch membranes, in which a concentration of 12.54 ng/ml was sufficient to reach a steady state. The incorporation kinetics when porin was added after membrane formation were sigmoidal. When porin was present in the medium before membrane formation, the kinetics were sigmoidal for PI membranes but became exponential for Ox Ch membranes. Furthermore, for BLM made of PI, the conductance-versus-porin concentration relationship is sigmoidal, with a Hill coefficient of 5.6 +/- 0.07, which is functional evidence corroborating the six-channel repeating units seen previously. For BLM made of Ox Ch, this relationship followed a binding isotherm curve with a Hill coefficient of 0.934 +/- 0.129. PMID:8842220

  18. High Membrane Curvature Enhances Binding, Conformational Changes, and Fibrillation of Amyloid-β on Lipid Bilayer Surfaces.

    PubMed

    Sugiura, Yuuki; Ikeda, Keisuke; Nakano, Minoru

    2015-10-27

    Aggregation of the amyloid-β (Aβ) protein and the formation of toxic aggregates are the possible pathogenic pathways in Alzheimer's disease. Accumulating evidence suggests that lipid membranes play key roles in protein aggregation, although the intermolecular forces that drive the interactions between Aβ-(1-40) and the membranes vary in different membrane systems. Here, we observed that a high positive curvature of lipid vesicles with diameters of ∼30 nm enhanced the association of Aβ with anionic phosphatidylglycerol membranes in the liquid-crystalline phase and with zwitterionic phosphatidylcholine membranes in the gel phase. The binding modes of Aβ to these membranes differ in terms of the location of the protein on the membrane and of the protein secondary structure. The fibrillation of Aβ was accelerated in the presence of the vesicles and at high protein-to-lipid ratios. Under these conditions, the protein accumulated on the surfaces, as demonstrated by a high (10(7) M(-1)) binding constant. Our findings suggest that packing defects on membranes with high curvatures, such as the intraluminal vesicles in multivesicular bodies and the exosomes, might result in the accumulation of toxic protein aggregates. PMID:26474149

  19. Membrane-Introduction Mass Spectrometry Analysis of Desflurane, Propofol and Fentanyl in Plasma and Cerebrospinal Fluid for Estimation BBB Properties.

    PubMed

    Cherebillo, Vyacheslav Yu; Elizarov, Andrei Yu; Polegaev, Andrei V

    2015-09-01

    A possibility to use the Membrane-Introduction Mass Spectrometry (MIMS) with membrane separator interface has evolved into a powerful method for measurement of anaesthetic agents absolute concentration in blood plasma and cerebrospinal fluid for the study of blood-brain barrier (BBB) properties. Recent advanced a new membrane material was used for drug concentration measurement in biologic fluids. A hydrophobic membrane was used in the interface to separate anaesthetic agents from biological fluids: inhalational anaesthetic desflurane,hypnotic propofol, analgesic fentanyl. The selective detection of volatile anesthetic agents in blood does not require long-term sample processing before injecting the sample into mass-spectrometer interface, in contrast to chromatographic methods. Mass-spectrometric interface for the measurement of anaesthetic agent concentration in biological fluids (blood plasma and cerebrospinal fluid) is described. Sampling of biological fluids was performed during balanced inhalational (desflurane, fentanyl) anaesthesia and total intravenous (propofol, fentanyl) anaesthesia. PMID:26412969

  20. Vascular basement membranes as pathways for the passage of fluid into and out of the brain.

    PubMed

    Morris, Alan W J; Sharp, Matthew MacGregor; Albargothy, Nazira J; Fernandes, Rute; Hawkes, Cheryl A; Verma, Ajay; Weller, Roy O; Carare, Roxana O

    2016-05-01

    In the absence of conventional lymphatics, drainage of interstitial fluid and solutes from the brain parenchyma to cervical lymph nodes is along basement membranes in the walls of cerebral capillaries and tunica media of arteries. Perivascular pathways are also involved in the entry of CSF into the brain by the convective influx/glymphatic system. The objective of this study is to differentiate the cerebral vascular basement membrane pathways by which fluid passes out of the brain from the pathway by which CSF enters the brain. Experiment 1: 0.5 µl of soluble biotinylated or fluorescent Aβ, or 1 µl 15 nm gold nanoparticles was injected into the mouse hippocampus and their distributions determined at 5 min by transmission electron microscopy. Aβ was distributed within the extracellular spaces of the hippocampus and within basement membranes of capillaries and tunica media of arteries. Nanoparticles did not enter capillary basement membranes from the extracellular spaces. Experiment 2: 2 µl of 15 nm nanoparticles were injected into mouse CSF. Within 5 min, groups of nanoparticles were present in the pial-glial basement membrane on the outer aspect of cortical arteries between the investing layer of pia mater and the glia limitans. The results of this study and previous research suggest that cerebral vascular basement membranes form the pathways by which fluid passes into and out of the brain but that different basement membrane layers are involved. The significance of these findings for neuroimmunology, Alzheimer's disease, drug delivery to the brain and the concept of the Virchow-Robin space are discussed. PMID:26975356

  1. 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

  2. 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

  3. Aspirin Increases the Solubility of Cholesterol in Lipid Membranes

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  4. Development of modifications to the material point method for the simulation of thin membranes, compressible fluids, and their interactions

    SciTech Connect

    York, A.R. II

    1997-07-01

    The material point method (MPM) is an evolution of the particle in cell method where Lagrangian particles or material points are used to discretize the volume of a material. The particles carry properties such as mass, velocity, stress, and strain and move through a Eulerian or spatial mesh. The momentum equation is solved on the Eulerian mesh. Modifications to the material point method are developed that allow the simulation of thin membranes, compressible fluids, and their dynamic interactions. A single layer of material points through the thickness is used to represent a membrane. The constitutive equation for the membrane is applied in the local coordinate system of each material point. Validation problems are presented and numerical convergence is demonstrated. Fluid simulation is achieved by implementing a constitutive equation for a compressible, viscous, Newtonian fluid and by solution of the energy equation. The fluid formulation is validated by simulating a traveling shock wave in a compressible fluid. Interactions of the fluid and membrane are handled naturally with the method. The fluid and membrane communicate through the Eulerian grid on which forces are calculated due to the fluid and membrane stress states. Validation problems include simulating a projectile impacting an inflated airbag. In some impact simulations with the MPM, bodies may tend to stick together when separating. Several algorithms are proposed and tested that allow bodies to separate from each other after impact. In addition, several methods are investigated to determine the local coordinate system of a membrane material point without relying upon connectivity data.

  5. Hydraulic optimization of membrane bioreactor via baffle modification using computational fluid dynamics.

    PubMed

    Yan, Xiaoxu; Xiao, Kang; Liang, Shuai; Lei, Ting; Liang, Peng; Xue, Tao; Yu, Kaichang; Guan, Jing; Huang, Xia

    2014-11-01

    Baffles are a key component of an airlift membrane bioreactor (MBR), which could enhance membrane surface shear for fouling control. In order to obtain an optimal hydraulic condition of the reactor, the effects of baffle location and size were systematically explored in this study. Computational fluid dynamics (CFD) was used to investigate the hydrodynamics in a bench-scale airlift flat sheet MBR with various baffle locations and sizes. Validated simulation results showed that side baffles were more effective in elevating membrane surface shear than front baffles. The maximum average shear stress was achieved by adjusting baffle size when both front and side baffles were installed. With the optimized baffle configuration, the shear stress was 10-30% higher than that without baffles at a same aeration intensity (specific air demand per membrane area in the range of 0-0.45m(3)m(-2)h(-1)). The effectiveness of baffles was particularly prominent at lower aeration intensities. PMID:25465790

  6. Substitution of ether linkage for ester bond in phospholipids increases permeability of bilayer lipid membrane for SkQ1-type penetrating cations.

    PubMed

    Il'yasova, T M; Rokitskaya, T I; Severina, I I; Antonenko, Y N; Skulachev, V P

    2012-09-01

    Using dialkylphospholipid (diphytanyl phosphatidylcholine) instead of the conventional diacylphospholipid (diphytanoyl phosphatidylcholine) in planar lipid bilayer membranes (BLM) led to an increase in the diffusion potential of the penetrating cation plastoquinonyl-decyl-triphenylphosphonium (SkQ1), making it close to the Nernst value, and accelerated translocation of SkQ1 across the BLM as monitored by the kinetics of a decrease in the transmembrane electric current after applying a voltage (current relaxation). The consequences of changing from an ester to an ether linkage between the head groups and the hydrocarbon chains are associated with a substantial reduction in the membrane dipole potential known to originate from dipoles of tightly bound water molecules and carbonyl groups in ester bonds. The difference in the dipole potential between BLM formed of the ester phospholipid and that of the ether phospholipid was estimated to be 100 mV. In the latter case, suppression of SkQ1-mediated proton conductivity of the BLM was also observed. PMID:23157264

  7. Effect of a glucose-triazole-hydrogenated cardanol conjugate on lipid bilayer membrane organization and thermotropic phase transition

    NASA Astrophysics Data System (ADS)

    Swain, Jitendriya; Kamalraj, M.; Surya Prakash Rao, H.; Mishra, Ashok K.

    2015-02-01

    This work focuses on the membrane perturbation, solubilisation and thermotropic phase transition process of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) MLVs induced by a glucose-triazole-hydrogenated cardanol conjugate (GTHCC). GTHCC is a recently introduced non toxic sugar derivative. Differential scanning calorimetry (DSC) and fluorescence molecular probe based techniques have been used to understand the concentration dependent membrane perturbation, solubilisation and thermotropic phase transition process of DPPC MLVs. The phase transition temperature of DPPC MLVs decreases with increase in mol% of GTHCC. At higher concentration above 10 mol%, GTHCC was significantly perturbed the membrane organization. The intrinsic fluorescence of GTHCC is also found to be sensitive towards phase behaviour and changes in membrane organization of DPPC MLVs.

  8. Effect of the Dialysis Fluid Buffer on Peritoneal Membrane Function in Children

    PubMed Central

    Nau, Barbara; Gemulla, Gita; Bonzel, Klaus E.; Hölttä, Tuula; Testa, Sara; Fischbach, Michel; John, Ulrike; Kemper, Markus J.; Sander, Anja; Arbeiter, Klaus; Schaefer, Franz

    2013-01-01

    Summary Background and objectives Double-chamber peritoneal dialysis fluids exert less toxicity by their neutral pH and reduced glucose degradation product content. The role of the buffer compound (lactate and bicarbonate) has not been defined in humans. Design, setting, participants, & measurements A multicenter randomized controlled trial in 37 children on automated peritoneal dialysis was performed. After a 2-month run-in period with conventional peritoneal dialysis fluids, patients were randomized to neutral-pH, low-glucose degradation product peritoneal dialysis fluids with 35 mM lactate or 34 mM bicarbonate content. Clinical and biochemical monitoring was performed monthly, and peritoneal equilibration tests and 24-hour clearance studies were performed at 0, 3, 6, and 10 months. Results No statistically significant difference in capillary blood pH, serum bicarbonate, or oral buffer supplementation emerged during the study. At baseline, peritoneal solute equilibration and clearance rates were similar. During the study, 4-hour dialysis to plasma ratio of creatinine tended to increase, and 24-hour dialytic creatinine and phosphate clearance increased with lactate peritoneal dialysis fluid but not with bicarbonate peritoneal dialysis fluid. Daily net ultrafiltration, which was similar at baseline (lactate fluid=5.4±2.6 ml/g glucose exposure, bicarbonate fluid=4.9±1.9 ml/g glucose exposure), decreased to 4.6±1.0 ml/g glucose exposure in the lactate peritoneal dialysis fluid group, whereas it increased to 5.1±1.7 ml/g glucose exposure in the bicarbonate content peritoneal dialysis fluid group (P=0.006 for interaction). Conclusions When using biocompatible peritoneal dialysis fluids, equally good acidosis control is achieved with lactate and bicarbonate buffers. Improved long-term preservation of peritoneal membrane function may, however, be achieved with bicarbonate-based peritoneal dialysis fluids. PMID:23124784

  9. Calculation of free energies in fluid membranes subject to heterogeneous curvature fields

    NASA Astrophysics Data System (ADS)

    Agrawal, Neeraj J.; Radhakrishnan, Ravi

    2009-07-01

    We present a computational methodology for incorporating thermal effects and calculating relative free energies for elastic fluid membranes subject to spatially dependent intrinsic curvature fields using the method of thermodynamic integration. Based on a simple model for the intrinsic curvature imposed only in a localized region of the membrane, we employ thermodynamic integration to calculate the free-energy change as a function of increasing strength of the intrinsic curvature field and a thermodynamic cycle to compute free-energy changes for different sizes of the localized region. By explicitly computing the free-energy changes and by quantifying the loss of entropy accompanied with increasing membrane deformation, we show that the membrane stiffness increases with increasing intrinsic field, thereby, renormalizing the membrane bending rigidity. The second main conclusion of this work is that the entropy of the membrane decreases with increasing size of the localized region subject to the curvature field. Our results help to quantify the free-energy change when a planar membrane deforms under the influence of curvature-inducing proteins at a finite temperature.

  10. Simulation and optimization of airlift external circulation membrane bioreactor using computational fluid dynamics.

    PubMed

    Qing, Zhang; Rongle, Xu; Xiang, Zheng; Yaobo, Fan

    2014-01-01

    The airlift external circulation membrane bioreactor (AEC-MBR) is a new MBR consisting of a separated aeration tank and membrane tank with circulating pipes fixed between the two tanks. The circulating pipe is called a H circulating pipe (HCP) because of its shape. With the complex configuration, it was difficult but necessary to master the AEC-MBR's hydraulic characteristics. In this paper, simulation and optimization of the AEC-MBR was performed using computational fluid dynamics. The distance from diffusers to membrane modules, i.e. the height of gas-liquid mixing zone (h(m)), and its effect on velocity distribution at membrane surfaces were studied. Additionally, the role of HCP and the effect of HCP's diameter on circulation were simulated and analyzed. The results showed that non-uniformity of cross-flow velocity existed in the flat-plate membrane modules, and the problem could be alleviated by increasing hm to an optimum range (h(m)/B ≥ 0.55; B is total static depth). Also, the low velocity in the boundary layer on the membrane surface was another reason for membrane fouling. The results also suggested that HCP was necessary and it had an optimum diameter to make circulation effective in the AEC-MBR. PMID:24804658

  11. Membrane Thickening by the Antimicrobial Peptide PGLa

    PubMed Central

    Pabst, Georg; Grage, Stephan L.; Danner-Pongratz, Sabine; Jing, Weiguo; Ulrich, Anne S.; Watts, Anthony; Lohner, Karl; Hickel, Andrea

    2008-01-01

    Using x-ray diffraction, solid-state 2H-NMR, differential scanning calorimetry, and dilatometry, we have observed a perturbation of saturated acyl chain phosphatidylglycerol bilayers by the antimicrobial peptide peptidyl-glycylleucine-carboxyamide (PGLa) that is dependent on the length of the hydrocarbon chain. In the gel phase, PGLa induces a quasi-interdigitated phase, previously reported also for other peptides, which is most pronounced for C18 phosphatidylglycerol. In the fluid phase, we found an increase of the membrane thickness and NMR order parameter for C14 and C16 phosphatidylglycerol bilayers, though not for C18. The data is best understood in terms of a close hydrophobic match between the C18 bilayer core and the peptide length when PGLa is inserted with its helical axis normal to the bilayer surface. The C16 acyl chains appear to stretch to accommodate PGLa, whereas tilting within the bilayer seems to be energetically favorable for the peptide when inserted into bilayers of C14 phosphatidylglycerol. In contrast to the commonly accepted membrane thinning effect of antimicrobial peptides, the data demonstrate that pore formation does not necessarily relate to changes in the overall bilayer structure. PMID:18835902

  12. PMP1 18-38, a yeast plasma membrane protein fragment, binds phosphatidylserine from bilayer mixtures with phosphatidylcholine: a (2)H-NMR study.

    PubMed

    Roux, M; Beswick, V; Coïc, Y M; Huynh-Dinh, T; Sanson, A; Neumann, J M

    2000-11-01

    PMP1 is a 38-residue plasma membrane protein of the yeast Saccharomyces cerevisiae that regulates the activity of the H(+)-ATPase. The cytoplasmic domain conformation results in a specific interfacial distribution of five basic side chains, thought to strongly interact with anionic phospholipids. We have used the PMP1 18-38 fragment to carry out a deuterium nuclear magnetic resonance ((2)H-NMR) study for investigating the interactions between the PMP1 cytoplasmic domain and phosphatidylserines. For this purpose, mixed bilayers of 1-palmitoyl, 2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl, 2-oleoyl-sn-glycero-3-phosphoserine (POPS) were used as model membranes (POPC/POPS 5:1, m/m). Spectra of headgroup- and chain-deuterated POPC and POPS phospholipids, POPC-d4, POPC-d31, POPS-d3, and POPS-d31, were recorded at different temperatures and for various concentrations of the PMP1 fragment. Data obtained from POPS deuterons revealed the formation of specific peptide-POPS complexes giving rise to a slow exchange between free and bound PS lipids, scarcely observed in solid-state NMR studies of lipid-peptide/protein interactions. The stoichiometry of the complex (8 POPS per peptide) was determined and its significance is discussed. The data obtained with headgroup-deuterated POPC were rationalized with a model that integrates the electrostatic perturbation induced by the cationic peptide on the negatively charged membrane interface, and a "spacer" effect due to the intercalation of POPS/PMP1f complexes between choline headgroups. PMID:11053135

  13. PMP1 18-38, a yeast plasma membrane protein fragment, binds phosphatidylserine from bilayer mixtures with phosphatidylcholine: a (2)H-NMR study.

    PubMed Central

    Roux, M; Beswick, V; Coïc, Y M; Huynh-Dinh, T; Sanson, A; Neumann, J M

    2000-01-01

    PMP1 is a 38-residue plasma membrane protein of the yeast Saccharomyces cerevisiae that regulates the activity of the H(+)-ATPase. The cytoplasmic domain conformation results in a specific interfacial distribution of five basic side chains, thought to strongly interact with anionic phospholipids. We have used the PMP1 18-38 fragment to carry out a deuterium nuclear magnetic resonance ((2)H-NMR) study for investigating the interactions between the PMP1 cytoplasmic domain and phosphatidylserines. For this purpose, mixed bilayers of 1-palmitoyl, 2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl, 2-oleoyl-sn-glycero-3-phosphoserine (POPS) were used as model membranes (POPC/POPS 5:1, m/m). Spectra of headgroup- and chain-deuterated POPC and POPS phospholipids, POPC-d4, POPC-d31, POPS-d3, and POPS-d31, were recorded at different temperatures and for various concentrations of the PMP1 fragment. Data obtained from POPS deuterons revealed the formation of specific peptide-POPS complexes giving rise to a slow exchange between free and bound PS lipids, scarcely observed in solid-state NMR studies of lipid-peptide/protein interactions. The stoichiometry of the complex (8 POPS per peptide) was determined and its significance is discussed. The data obtained with headgroup-deuterated POPC were rationalized with a model that integrates the electrostatic perturbation induced by the cationic peptide on the negatively charged membrane interface, and a "spacer" effect due to the intercalation of POPS/PMP1f complexes between choline headgroups. PMID:11053135

  14. The Balance of Fluid and Osmotic Pressures across Active Biological Membranes with Application to the Corneal Endothelium.

    PubMed

    Cheng, Xi; Pinsky, Peter M

    2015-01-01

    The movement of fluid and solutes across biological membranes facilitates the transport of nutrients for living organisms and maintains the fluid and osmotic pressures in biological systems. Understanding the pressure balances across membranes is crucial for studying fluid and electrolyte homeostasis in living systems, and is an area of active research. In this study, a set of enhanced Kedem-Katchalsky (KK) equations is proposed to describe fluxes of water and solutes across biological membranes, and is applied to analyze the relationship between fluid and osmotic pressures, accounting for active transport mechanisms that propel substances against their concentration gradients and for fixed charges that alter ionic distributions in separated environments. The equilibrium analysis demonstrates that the proposed theory recovers the Donnan osmotic pressure and can predict the correct fluid pressure difference across membranes, a result which cannot be achieved by existing KK theories due to the neglect of fixed charges. The steady-state analysis on active membranes suggests a new pressure mechanism which balances the fluid pressure together with the osmotic pressure. The source of this pressure arises from active ionic fluxes and from interactions between solvent and solutes in membrane transport. We apply the proposed theory to study the transendothelial fluid pressure in the in vivo cornea, which is a crucial factor maintaining the hydration and transparency of the tissue. The results show the importance of the proposed pressure mechanism in mediating stromal fluid pressure and provide a new interpretation of the pressure modulation mechanism in the in vivo cornea. PMID:26719894

  15. The Balance of Fluid and Osmotic Pressures across Active Biological Membranes with Application to the Corneal Endothelium

    PubMed Central

    Cheng, Xi; Pinsky, Peter M.

    2015-01-01

    The movement of fluid and solutes across biological membranes facilitates the transport of nutrients for living organisms and maintains the fluid and osmotic pressures in biological systems. Understanding the pressure balances across membranes is crucial for studying fluid and electrolyte homeostasis in living systems, and is an area of active research. In this study, a set of enhanced Kedem-Katchalsky (KK) equations is proposed to describe fluxes of water and solutes across biological membranes, and is applied to analyze the relationship between fluid and osmotic pressures, accounting for active transport mechanisms that propel substances against their concentration gradients and for fixed charges that alter ionic distributions in separated environments. The equilibrium analysis demonstrates that the proposed theory recovers the Donnan osmotic pressure and can predict the correct fluid pressure difference across membranes, a result which cannot be achieved by existing KK theories due to the neglect of fixed charges. The steady-state analysis on active membranes suggests a new pressure mechanism which balances the fluid pressure together with the osmotic pressure. The source of this pressure arises from active ionic fluxes and from interactions between solvent and solutes in membrane transport. We apply the proposed theory to study the transendothelial fluid pressure in the in vivo cornea, which is a crucial factor maintaining the hydration and transparency of the tissue. The results show the importance of the proposed pressure mechanism in mediating stromal fluid pressure and provide a new interpretation of the pressure modulation mechanism in the in vivo cornea. PMID:26719894

  16. Properties of mixed DOTAP-DPPC bilayer membranes as reported by differential scanning calorimetry and dynamic light scattering measurements.

    PubMed

    Cinelli, S; Onori, G; Zuzzi, S; Bordi, F; Cametti, C; Sennato, S; Diociaiuti, M

    2007-08-23

    We have investigated the effect of a cationic lipid [DOTAP] on both the thermotropic phase behavior and the structural organization of aqueous dispersions of dipalmitoyl-phosphatidylcholine [DPPC] by means of high-sensitivity differential scanning calorimetry and dynamic light scattering measurements. We find that the incorporation of increasing quantities of DOTAP progressively reduces the temperature and the enthalpy of the gel-to-liquid crystalline transition. We are further showing that, in mixed DOTAP-DPPC systems, the reduction of the phase transition temperature is accompanied by a reduction of the average size of the structures present in the aqueous mixtures, whatever the DOTAP concentration is. These results, which extend a previous investigation by Campbell et al. (Campbell, R. B.; Balasubramanian, S. V.; Straubinger, R. M.; Biochim. Biosphys. Acta 2001, 27, 1512.) limited to a DOTAP concentration below 20 mol %, confirm that the insertion of cationic head groups in zwitterionic phosphatidylcholine bilayers facilitates the formation of stable, relatively small, unilamellar vesicles. This self-assembling restructuring from an aqueous multilamellar structure toward a liposomal phase is favored by decreasing the phospholipid phase transition temperature and by increasing the temperature of the system. This reduction of the average size and the appearance of a stable liposomal phase is also promoted by a heating and cooling thermal treatment. PMID:17663578

  17. Actuation of flexoelectric membranes in viscoelastic fluids with applications to outer hair cells.

    PubMed

    Herrera-Valencia, E E; Rey, Alejandro D

    2014-11-28

    Liquid crystal flexoelectric actuation uses an imposed electric field to create membrane bending, and it is used by the outer hair cells (OHCs) located in the inner ear, whose role is to amplify sound through generation of mechanical power. Oscillations in the OHC membranes create periodic viscoelastic flows in the contacting fluid media. A key objective of this work on flexoelectric actuation relevant to OHCs is to find the relations and impact of the electromechanical properties of the membrane, the rheological properties of the viscoelastic media, and the frequency response of the generated mechanical power output. The model developed and used in this work is based on the integration of: (i) the flexoelectric membrane shape equation applied to a circular membrane attached to the inner surface of a circular capillary and (ii) the coupled capillary flow of contacting viscoelastic phases, such that the membrane flexoelectric oscillations drive periodic viscoelastic capillary flows, as in OHCs. By applying the Fourier transform formalism to the governing equation, analytical expressions for the transfer function associated with the curvature and electrical field and for the power dissipation of elastic storage energy were found. PMID:25332388

  18. Syrinx fluid transport: modeling pressure-wave-induced flux across the spinal pial membrane.

    PubMed

    Elliott, N S J

    2012-03-01

    Syrinxes are fluid-filled cavities of the spinal cord that characterize syringomyelia, a disease involving neurological damage. Their formation and expansion is poorly understood, which has hindered successful treatment. Syrinx cavities are hydraulically connected with the spinal subarachnoid space (SSS) enveloping the spinal cord via the cord interstitium and the network of perivascular spaces (PVSs), which surround blood vessels penetrating the pial membrane that is adherent to the cord surface. Since the spinal canal supports pressure wave propagation, it has been hypothesized that wave-induced fluid exchange across the pial membrane may play a role in syrinx filling. To investigate this conjecture a pair of one-dimensional (1-d) analytical models were developed from classical elastic tube theory coupled with Darcy's law for either perivascular or interstitial flow. The results show that transpial flux serves as a mechanism for damping pressure waves by alleviating hoop stress in the pial membrane. The timescale ratio over which viscous and inertial forces compete was explicitly determined, which predicts that dilated PVS, SSS flow obstructions, and a stiffer and thicker pial membrane-all associated with syringomyelia-will increase transpial flux and retard wave travel. It was also revealed that the propagation of a pressure wave is aided by a less-permeable pial membrane and, in contrast, by a more-permeable spinal cord. This is the first modeling of the spinal canal to include both pressure-wave propagation along the spinal axis and a pathway for fluid to enter and leave the cord, which provides an analytical foundation from which to approach the full poroelastic problem. PMID:22482686

  19. [Distribution of proteins in neural membranes as a factor of reabsorption of endoneural (interstitial) fluid].

    PubMed

    Banin, V V; Gasymov, E K

    1990-09-01

    An investigation on distribution of horseradish peroxidase (HP) product in the sciatic nerve membranes of albino rats, after HP intravenous injection, has been performed. Getting into the interstitial space of epineurium across the microvessel walls, HP spreads as far as the internal layer of the perineural membrane, forming a distinct gradient of concentration of protein at its border. In 60 min after injection of the tracer the value of the perineural-endoneural gradient for proteins is about 70-80% of the value of the plasma-endoneural gradient. A possible mechanism of the endoneural fluid evacuation, connected with various values of protein concentration in the endoneural space and within the nerve perineural membrane is discussed. PMID:2275614

  20. Experiences with nonlinear dynamics of panels and membranes considering fluid-structure interaction and acoustic fatigue

    SciTech Connect

    Ferman, M.A.

    1994-12-31

    A collection of some highlights of the Author`s experiences with nonlinear dynamics in analyses and tests of Panels and Membranes encountered over the past 40 years is given. The primary focus is placed on a major block of his work since the early 70`s, involving work with fluid-structure interaction with Panels and Membranes, and with efforts in Acoustic Fatigue of Panels. While the Author had encountered nonlinear problems throughout Ins career involving flutter, vibration in general, and dynamic thrust instability; it was the more recent work with panels and membranes that greatly expanded his experience. This was triggered by the advent of highly maneuverable aircraft, powered by large powerful, noisy engines, and new materials in the mid 70`s. The significance of nonlinearity for these applications is most obvious from the results shown here-it simply cannot be ignored for optimal, safe design.

  1. Membranes having aligned 1-D nanoparticles in a matrix layer for improved fluid separation

    DOEpatents

    Revanur, Ravindra; Lulevich, Valentin; Roh, Il Juhn; Klare, Jennifer E.; Kim, Sangil; Noy, Aleksandr; Bakajin, Olgica

    2015-12-22

    Membranes for fluid separation are disclosed. These membranes have a matrix layer sandwiched between an active layer and a porous support layer. The matrix layer includes 1-D nanoparticles that are vertically aligned in a porous polymer matrix, and which substantially extend through the matrix layer. The active layer provides species-specific transport, while the support layer provides mechanical support. A matrix layer of this type has favorable surface morphology for forming the active layer. Furthermore, the pores that form in the matrix layer tend to be smaller and more evenly distributed as a result of the presence of aligned 1-D nanoparticles. Improved performance of separation membranes of this type is attributed to these effects.

  2. Structural Determinants of Drug Partitioning in Surrogates of Phosphatidylcholine Bilayer Strata

    PubMed Central

    Lukacova, Viera; Natesan, Senthil; Peng, Ming; Tandlich, Roman; Wang, Zhanbin; Lynch, Sandra; Subramaniam, Rajesh; Balaz, Stefan

    2013-01-01

    The knowledge of drug concentrations in bilayer headgroups, core, and at the interface between them is a prerequisite for quantitative modeling of drug interactions with many membrane-bound transporters, metabolizing enzymes and receptors, which have the binding sites located in the bilayer. This knowledge also helps understand the rates of trans-bilayer transport because balanced interactions of drugs with the bilayer strata lead to high rates, while excessive affinities for any stratum cause a slowdown. Experimental determination of bilayer location is so tedious and costly that the data are only available for some fifty compounds. To extrapolate these valuable results to more compounds at a higher throughput, surrogate phases have been used to obtain correlates of the drug affinities for individual strata. We introduced a novel system, consisting of a diacetyl phosphatidylcholine (DAcPC) solution with the water content of the fluid bilayer as the headgroup surrogate and n-hexadecane (C16) representing the core. The C16/DAcPC partition coefficients were measured for 113 selected compounds, containing structural fragments that are frequently occurring in approved drugs. The data were deconvoluted into the ClogP-based fragment solvation characteristics and processed using a solvatochromic correlation. Increased H-bond donor ability and excess molar refractivity of compounds promote solvation in the DAcPC phase as compared to bulk water, contrary to H-bond acceptor ability, dipolarity/polarizability, and volume. The results show that aromates have more balanced distribution in bilayer strata, and thus faster trans-bilayer transport, than similar alkanes. This observation is in accordance with the frequent occurrence of aromatic rings in approved drugs and with the role of rigidity of drug molecules in promoting intestinal absorption. Bilayer locations, predicted using the C16/DAcPC system, are in excellent agreement with available experimental data, in contrast to

  3. Arachnoid Membrane Suturing for Prevention of Subdural Fluid Collection in Extracranial-intracranial Bypass Surgery

    PubMed Central

    Kim, Gun Woo; Kim, Tae Sun; Moon, Hyung Sik; Jang, Jae Won; Seo, Bo Ra; Lee, Jung Kil; Kim, Jae Hyoo; Kim, Soo Han

    2014-01-01

    Objective Water-tight closure of the dura in extracranial-intracranial (EC-IC) bypass is impossible because the superficial temporal artery (STA) must run through the dural defect. Consequently, subdural hygroma and subcutaneous cerebrospinal fluid (CSF) collection frequently occur postoperatively. To reduce these complications, we prospectively performed suturing of the arachnoid membrane after STA-middle cerebral artery (STA-MCA) and evaluated the clinical usefulness. Materials and Methods Between Mar. 2005 and Oct. 2010, extracranial-intracranial arterial bypass (EIAB) with/without encephalo-myo-synangiosis was performed in 88 cases (male : female = 53 : 35). As a control group, 51 patients (57 sides) underwent conventional bypass surgery without closure of the arachnoid membrane. Postoperative computed tomography (CT) scan was performed twice in three days and seven days later, respectively, for evaluation of the presence of subdural fluid collection and other mass lesions. Results The surgical result was excellent, with no newly developing ischemic event until recent follow-up. The additional time needed for arachnoid suture was five to ten minutes, when three to eight sutures were required. Post-operative subdural fluid collection was not seen on follow-up computed tomography scans in all patients. Conclusion Arachnoid suturing is simple, safe, and effective for prevention of subdural fluid collection in EC-IC bypass surgery, especially the vulnerable ischemic hemisphere. PMID:25045645