TY - JOUR. T1 - Fluorescence modulation sensing of positively and negatively charged proteins on lipid bilayers. AU - Robison, Aaron D.. AU - Huang, Da. AU - Jung, Hyunsook. AU - Cremer, Paul S.. PY - 2013/1/1. Y1 - 2013/1/1. N2 - Background: Detecting ligand-receptor binding on cell membrane surfaces is required to understand their function and behavior. Detection platforms can also provide an avenue for the development of medical devices and sensor biotechnology. The use of fluorescence techniques for such purposes is highly desirable as they provide high sensitivity. Herein, we describe a technique that utilizes the sensitivity of fluorescence without directly tagging the analyte of interest to monitor ligand-receptor interactions on supported lipid bilayers. The fluorescence signal is modulated according to the charge state of the target analyte. The binding event elicits protonation or deprotonation of pH-responsive reporter dyes embedded in the lipid bilayer. Methods: Supported lipid ...
Lipid flip-flop and its associated transient pore formation are key thermodynamic properties of living cell membranes. However, there is a lack of understanding of whether ionic imbalance that exists ubiquitously across cell membranes affects lipid flip-flop and its associated functions. Potential of mean force calculations show that the free-energy barrier of lipid flip-flop on the extracellular leaflet reduces with the presence of ionic imbalance, whereas the barrier on the intracellular leaflet is generally not affected. The linear decrease of the activation energy of lipid flip-flop on the extracellular leaflet is consistent with the experimentally measured conductance-voltage relationship of zwitterionic lipid bilayers. This suggests: 1) lipid flip-flop has a directionality under physiological conditions and phospholipids accumulate at a rate on the order of 105 mu m(-2) h(-1) on the cytoplasmic side of cell membranes; 2) ion permeation across a lipid membrane is moderated by lipid ...
Defensins are cationic, cysteine-rich peptides (Mr = 3500-4000) found in the cytoplasmic granules of neutrophils and macrophages. These peptides possess broad antimicrobial activity in vitro against bacteria, fungi, tumor cells, and enveloped viruses, and they are believed to contribute to the "oxygen-independent" antimicrobial defenses of neutrophils and macrophages. Pathophysiologic studies in vitro have pointed to the plasma membrane as a possible target for the cytotoxic action of defensins. We report here that defensins form voltage-dependent, weakly anion-selective channels in planar lipid bilayer membranes, and we suggest that this channel-forming ability contributes to their antimicrobial properties observed in vitro.. ...
Large granular lymphocytes, mediators of NK activity, bind to other cells using both the LFA (lymphocyte function-associated)-1-ICAM and the CD2-LFA-3 adhesion pathways. Here we have studied the motility and ultrastructure of large granule lymphocyte (LGL) on lipid bilayers containing purified LFA-1, ICAM-1, and the transmembrane and glycophosphatidylinositol isoforms of LFA-3. LGLs moved at 8 microns/min on ICAM-1 but poorly (less than 1 microns/min) on its receptor pair LFA-1. TM-LFA-3 promoted locomotion at a rate close to ICAM-1, whereas the cells were less motile on GPI-LFA-3. The difference in the rates of locomotion on the two isoforms of LFA-3 is presumably attributable to their difference in anchoring and lateral mobility in the bilayer. In spite of the variation in motility the ultrastructure of the adhering cells was similar on all four ligands. LGLs contacted the membrane variably, i.e., cells adhering only in a few small areas or in larger areas were detected on each ligand. The ...
Large granular lymphocytes, mediators of NK activity, bind to other cells using both the LFA (lymphocyte function-associated)-1-ICAM and the CD2-LFA-3 adhesion pathways. Here we have studied the motility and ultrastructure of large granule lymphocyte (LGL) on lipid bilayers containing purified LFA-1, ICAM-1, and the transmembrane and glycophosphatidylinositol isoforms of LFA-3. LGLs moved at 8 microns/min on ICAM-1 but poorly (less than 1 microns/min) on its receptor pair LFA-1. TM-LFA-3 promoted locomotion at a rate close to ICAM-1, whereas the cells were less motile on GPI-LFA-3. The difference in the rates of locomotion on the two isoforms of LFA-3 is presumably attributable to their difference in anchoring and lateral mobility in the bilayer. In spite of the variation in motility the ultrastructure of the adhering cells was similar on all four ligands. LGLs contacted the membrane variably, i.e., cells adhering only in a few small areas or in larger areas were detected on each ligand. The relative
Detailed understanding of lipid bilayers are of tremendous importance due to their role in many biological processes. This Thesis focuses on structural and dynamical properties of lipid bilayers and their interactions with locally acting anesthetics, studied by Molecular Dynamics simulations.. The effect of dehydration of a lipid bilayer is a biologically important phenomenon which was investigated by detailed examination of a number of structural and dynamical lipid parameters at different levels of hydration. The result shows that whereas the structural properties of the bilayer only moderately depend on the degree of hydration, the dynamics of the system is affected very strongly.. Related to changes in the bilayer caused by hydration are structural and dynamical changes caused by the presence of anesthetics. Lidocaine is a common, locally acting anesthetic that interacts with lipid bilayers. The difference in position, orientation and diffusional behavior for charged and uncharged lidocaine ...
Lipid bilayers constitute one of the critical parts of all biological membranes, including cell membranes. A nice description of lipid bilayers and their function in biological membranes can be found here. They can be exceptionally complex and contain hundreds of different constituents, so simpler model lipid bilayers are often produced in the laboratory and studied experimentally. They form closed spheroidal structures, called liposomes, with a thickness of a few nm, and characteristic linear dimensions up to several microns. Larger such structures are usually called Giant Unilamellar Vesicles, or GUVs. Why should we care about these structures as mechanicians? For a number of reasons, the elastic properties of lipid membranes are thought to play a crucial role in governing their potential configurations. Recent experimental studies of the role of membrane curvature on domain formation in biomembranes, for example, provide testament to this notion. Images of their work are reproduced (with ...
Lipid bilayers constitute one of the critical parts of all biological membranes, including cell membranes. A nice description of lipid bilayers and their function in biological membranes can be found here. They can be exceptionally complex and contain hundreds of different constituents, so simpler model lipid bilayers are often produced in the laboratory and studied experimentally. They form closed spheroidal structures, called liposomes, with a thickness of a few nm, and characteristic linear dimensions up to several microns. Larger such structures are usually called Giant Unilamellar Vesicles, or GUVs. Why should we care about these structures as mechanicians? For a number of reasons, the elastic properties of lipid membranes are thought to play a crucial role in governing their potential configurations. Recent experimental studies of the role of membrane curvature on domain formation in biomembranes, for example, provide testament to this notion. Images of their work are reproduced (with ...
We investigate the structural changes to lipid membrane that ensue from the addition of aliphatic alcohols with various alkyl tail lengths. Small angle neutron diffraction from flat lipid bilayers that are hydrated through water vapor has been employed to eliminate possible artefacts of the membrane curvature and the alcohols membrane-water partitioning. We have observed clear changes to membrane structure in both transversal and lateral directions. Most importantly, our results suggest the alteration of the membrane-water interface. The water encroachment has shifted in the way that alcohol loaded bilayers absorbed more water molecules when compared to the neat lipid bilayers. The experimental results have been corroborated by molecular dynamics simulations to reveal further details. Namely, the order parameter profiles have been fruitful in correlating the mechanical model of structural changes to the effect of anesthesia.
We present optical observations of phase separation in mixed model membranes in the form of giant unilamellar vesicles. These observations are compared to the phase behavior of lipid mixtures, which we determined by X-ray scattering and differential scanning calorimetry or extracted from the existing literature. The domain properties are affected not only by the bulk phase behavior but also by the membrane lamellarity and phase transition pathways. These observations have important implications for how phase behavior determined by bulk methods using dense, multilamellar lipid bilayers are linked to phase separation in giant, unilamellar lipid bilayers as observed by microscopy ...
Detecting ligand-receptor binding on cell membrane surfaces is required to understand their function and behavior. Detection platforms can also provide an avenue for the development of medical devices and sensor biotechnology. The use of fluorescence techniques for such purposes is highly desirable as they provide high sensitivity. Herein, we describe a technique that utilizes the sensitivity of fluorescence without directly tagging the analyte of interest to monitor ligand-receptor interactions on supported lipid bilayers. The fluorescence signal is modulated according to the charge state of the target analyte. The binding event elicits protonation or deprotonation of pH-responsive reporter dyes embedded in the lipid bilayer. Supported lipid membranes containing ortho-conjugated rhodamine B-POPE (1-hexadecanoyl-2-(9Z-octadecenoyl)-sn-glycero-3-phosphoethanolamine), which fluoresces in its protonated but not in its deprotonated form, were utilized as sensor platforms for biotin-avidin and biotin
The perturbation of model lipid bilayer vesicles by halogenated hydrocarbons was investigated to determine if cellular membrane damage could be evaluated and used as a screening technique for toxicity. A fluorescent probe of 1-anilino-8-naphthalene-sulfonate (82768) (ANS) was bound to synthetic phospholipid vesicles prepared from egg lecithin and dimyristoyl-phosphatidyl-choline (DML). The fluores
This study evaluates the use of the planar lipid bilayer as a functional assay of Ca(2+)-activated K+ channel activity for use in purification of the channel protein. Ca(2+)-activated K+ channels from the plasma membrane of an insulin-secreting hamster Beta-cell line (HIT T15) were incorporated into planar lipid bilayers. The single channel conductance was 233 picoSiemens (pS) in symmetrical 140 mmol/l KCl and the channel was strongly K(+)-selective (PCl/PK = 0.046; PNa/PK = 0.027). Channels incorporated into the bilayer with two orientations. In 65% of cases, the probability of the channel being open was increased by raising calcium on the cis side of the bilayer (to which the membrane vesicles were added) or by making the cis side potential more positive. At a membrane potential of + 20 mV, which is close to the peak of the Beta-cell action potential, channel activity was half-maximal at a Ca2+ concentration of about 15 mumol/l. Charybdotoxin greatly reduced the probability of the channel being open
The influenza M2 protein not only forms a proton channel but also mediates membrane scission in a cholesterol-dependent manner to cause virus budding and release. The atomic interaction of cholesterol with M2, as with most eukaryotic membrane proteins, has long been elusive. We have now determined the cholesterol-binding site of the M2 protein in phospholipid bilayers using solid-state NMR spectroscopy. Chain-fluorinated cholesterol was used to measure cholesterol proximity to M2 while sterol-deuterated cholesterol was used to measure bound-cholesterol orientation in lipid bilayers. Carbon-fluorine distance measurements show that at a cholesterol concentration of 17 mol%, two cholesterol molecules bind each M2 tetramer. Cholesterol binds the C-terminal transmembrane (TM) residues, near an amphipathic helix, without requiring a cholesterol recognition sequence motif. Deuterium NMR spectra indicate that bound cholesterol is approximately parallel to the bilayer normal, with the rough face of the sterol
The capability of lipid bilayers to exhibit fluid-phase behavior is a fascinating property, which enables, for example, membrane-associated components, such as lipids (domains) and transmembrane proteins, to diffuse within the membrane. These diffusion processes are of paramount importance for cells, as they are for example involved in cell signaling processes or the recycling of membrane components, but also for recently developed analytical approaches, which use differences in the mobility for certain analytical purposes, such as in-membrane purification of membrane proteins or the analysis of multivalent interactions. Here, models describing the Brownian motion of membrane inclusions (lipids, peptides, proteins, and complexes thereof) in model bilayers (giant unilamellar vesicles, black lipid membranes, supported lipid bilayers) are summarized and model predictions are compared with the available experimental data, thereby allowing for evaluating the validity of the introduced models. It will be
In this article, we investigate fluid-gel transformations of a DPPC lipid bilayer in the presence of nanoparticles, using coarse grained molecular dynamics. Two types of nanoparticles are considered, specifically a 3 nm hydrophobic nanoparticle located in the core of the bilayer and a 6 nm charged nanoparticle located at the interface between the bilayer and water phase. Both negatively and positively charged nanoparticles at the bilayer interface are investigated. We demonstrate that the presence of all types of nanoparticles induces disorder effects in the structure of the lipid bilayer. These effects are characterized using computer visualization of the gel phase in the presence of nanoparticles, radial distribution functions, and order parameters. The 3 nm hydrophobic nanoparticle immersed in the bilayer core and the positively charged nanoparticle at the bilayer surface have no effect on the temperature of the fluid-gel transformation, compared to the bulk case. Interestingly, a negatively ...
1. Wagner ML, Tamm LK (2000) Tethered polymer-supported planar lipid bilayers for reconstitution of integral membrane proteins: silane-polyethyleneglycol-lipid as a cushion and covalent linker. Biophys J 79: 1400-1414.. 2. Sackmann E (1996) Supported membranes: scientific and practical applications. Science 271: 43-48.. 3. Richter RP, Berat R, Brisson AR (2006) Formation of solid-supported lipid bilayers: an integrated view. Langmuir 22: 3497-3505.. 4. Kusters I, Mukherjee N, de Jong MR, Tans S, Koçer A, et al. (2011) Taming Membranes: Functional Immobilization of Biological Membranes in Hydrogels. PLoS ONE 6(5): e20435. doi:10.1371/journal.pone.0020435. 5. Schuler, M. A., Denisov, I. G., Sligar, S. G. (2013) "Nanodiscs as a new tool to examine lipid-protein interactions." Methods Mol Biol. 974, 415-433.. 6. Sloan, C. D., Marty, M. T., Sligar, S. G., Bailey, R. C. (2013) "Interfacing lipid bilayer nanodiscs and silicon photonic sensor arrays for multiplexed protein-lipid and protein-membrane ...
Read "Examining the Origins of the Hydration Force Between Lipid Bilayers Using All-Atom Simulations, The Journal of Membrane Biology" on DeepDyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips.
Several techniques to assemble artificial lipid bilayers involve the zipping of monolayers. Their efficiency is determined by the renewal of the saturated monolayers to be zipped and this proceeds by adsorption of lipids dispersed in oil as aggregates. The size of these lipids aggregates is a key parameter to ensure both the stability of the suspension and a fast release of lipids at the interface. We propose a new method inspired from the solvent-shifting nucleation process allowing to control and tune the lipid aggregates size and that improves the production of artificial membranes. It is simpler and faster than current methods starting from a dry lipid film, which are highly sensitive to environmental conditions. This method opens the route to bilayer production processes with new potentialities in membrane composition.
Recently, the transfer method has been shown to be useful for preparing cell-sized phospholipid bilayer vesicles, within which desired substances at desired concentrations can be encapsulated, with a desired asymmetric lipid composition. Here, we investigated the transfer process of water-in-oil (W/O) droplets coat 2013 Hot Papers
A novel solid-state NMR technique for identifying the asymmetric insertion depths of membrane proteins in lipid bilayers is introduced. By applying Mn2+ ions on the outer but not the inner leaflet of lipid bilayers, the sidedness of protein residues in the lipid bilayer can be determined through paramagnetic relaxation enhancement (PRE) effects. Protein-free lipid membranes with one-side Mn2+-bound surfaces exhibit significant residual 31P and lipid headgroup 13C intensities, in contrast to two-side Mn2+-bound membranes, where lipid headgroup signals are mostly suppressed. Applying this method to a cell-penetrating peptide, penetratin, we found that at low peptide concentrations, penetratin is distributed in both leaflets of the bilayer, in contrast to the prediction of the electroporation model, which predicts that penetratin binds to only the outer lipid leaflet at low peptide concentrations to cause an electric field that drives subsequent peptide translocation. The invalidation of the ...
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Lipid bilayers form the boundaries of the cell and its organelles. Many physiological processes, such as cell movement and division, involve bending and folding of the bilayer at high curvatures. Currently, bending of the bilayer is treated as an elastic deformation, such that its stress-strain response is i
We will discuss the physics that governs the lipid localization and domain formation in multicomponent lipid bilayers coupled to an elastic substrate. Lipid localization and domain formation has been studied extensively in biological cell membranes. In this talk we will extend a previous model for membrane energetics to account for the coupling between the bending and the local lipid composition of the two leaflets. Our aim is to determine the relationship between the localization and domain formation in the presence of lipid flip-flops between the two leaflets and the effect of intrinsic curvature of the lipids. Using a lattice model for the membrane, we simulate the system and study the effect of lipid flip-flop on lipid organization in the membrane. To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.MAR.B41.15. ...
Progress with respect to enrichment and separation of native membrane components in complex lipid environments, such as native cell membranes, has so far been very limited. The reason for the slow progress can be related to the lack of efficient means to generate continuous and laterally fluid supported lipid bilayers (SLBs) made from real cell membranes. We show in this work how the edge of a hydrodynamically driven SLB can be used to induce rupture of adsorbed lipid vesicles of compositions that typically prevent spontaneous SLB formation, such as vesicles made of complex lipid compositions, containing high cholesterol content or being derived from real cell membranes. In particular, upon fusion between the moving edge of a preformed SLB and adsorbed vesicles made directly from 3T3 fibroblast cell membranes, the membrane content of the vesicles was shown to be efficiently transferred to the SLB. The molecular transfer was verified using cholera toxin B subunit (CTB) binding to monosialoganglioside
The transport of palmitic acid (PA) across planar lipid bilayer membranes was measured using a high specific activity [14C]palmitate as tracer for PA. An all-glass trans chamber was employed in order to minimize adsorbance of PA onto the surface. Electrically neutral (diphytanoyl phosphatidylcholine) and charged (Azolectin) planar bilayers were maintained at open electric circuit. We found a permeability to PA of (8.8 +/- 1.9) x 10(-6) cm s(-1) (n = 15) in neutral and of (10.3 +/- 2.2) x 10(-6) cm s(-1) (n = 5) in charged bilayers. These values fall within the order of magnitude of those calculated from desorption constants of PA in different vesicular systems. Differences between data obtained from planar and vesicular systems are discussed in terms of the role of solvent, radius of curvature, and pH changes. ...
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Lipid bilayers are unique soft materials operating in general in the low Reynolds limit. While their shape is predominantly dominated by curvature elasticity as in a solid shell, their in-plane behavior is that of a largely inextensible viscous fluid. Furthermore, lipid membranes are extremely responsive to chemical stimuli. Because in their biological context they are continuously brought out-of-equilibrium mechanically or chemically, it is important to understand their dynamics. Here, we introduce Onsagers variational principle as a general and transparent modeling tool for lipid bilayer dynamics. We introduce this principle with elementary examples, and then use it to study the sorption of curved proteins on lipid membranes.. Link to Chapter ...
One of the key lockers to understand mechanisms of biological action of drugs and natural compounds is their capacity to incorporate/cross lipid bilayer membranes. In the light of demanding experimental techniques, in silico molecular modelling has become a powerful alternative to tackle these issues. In the past few years, molecular dynamics (MD) has opened many perspectives, providing an atomistic description of the related intermolecular interactions. Using MD simulations, we have explored the capacity of several compounds (polyphenols, vitamins E and C, plantazolicin, carprofens) to incorporate lipid bilayer membranes. The different compounds were chosen according to their different biological functions, namely (i) antioxidant activity against lipid peroxidation, (ii) antimicrobial activity with the possibility of trans-membrane pore formation, and (iii) inhibition of enzymes involved in Alzheimers disease. In order to rationalize their mechanisms of action, their position and orientation in
Terminal lipophilization of a unique DNA dodecamer by various nucleolipid headgroups: Their incorporation into artificial lipid bilayers and hydrodynamic properties
9] L. Movileanu, D. Popescu, S. I. Popescu, Transbilayer pores induced by thickness fluctuations, Bull. Math. Biol. 68 (2006) 1231-1255. V. Zhelev, D. Needham, Tension-stabilized pores in giant vesicles: Determination of pore size and pore line tension, Biochim. Biophys. Acta 1147 (1993) 89-104. [11] M. Winterhalter, W. Helfrich, Effect of voltage on pores in membranes, Phys. Rev. A 36 (1987) 5874-5876. Random Processes in the Appearance and Dynamics of an Electropore 33 [12] E. Neumann, M. Schaefer-Ridder, Y. Frey, Polymorphism of monolayers of monomeric and macromolecular lipids: On the defect structure of crystalline phases and the possibility of hexatic order formation in physics of amphiphilic layers, in: J. Meunier, D. Langevin, V. ), Physics of amphiphilic layers, Springer, Berlin (1987). [43] M. Langner, H. Pruchnik, K. Kubica, The effect of the lipid bilayer state on fluorescence intensity of fluorescein-PE in a saturated lipid bilayer, Z. Naturforsch. 55 (2000) 418-424. [44] K. Kubica, ...
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Biological membranes mainly constituent lipid molecules along with some proteins and steroles. The properties of the pure lipid bilayers as well as in the presence of other constituents (in case of two or three component systems) are very important to be studied carefully to model these systems and compare them with the realistic systems. Molecular dynamic simulations provide a good opportunity to model such systems and to study them at microscopic level where experiments fail to do. In this thesis we study the structural and dynamic properties of the pure phospholipid bilayers and the phase behavior of phospholipid bilayers when other constituents are present in them. Material and structural properties like area per lipid and area compressibility of the phospholipids show a big scatter in experiments. These properties are studied for different system sizes and it was found that the increasing undulations in large systems effect these properties. A correction was applied to area per lipid and ...
Proteins and lipids are the building blocks of biological membranes. In the past and at present, only the lipids in the form of bilayers, vesicles, and thin films found/find applications in...
This thesis deals with the study of lipid bilayer systems by solid-state nuclear magnetic resonance. Two-dimensional 1H-13C separated local field experiments under magic-angle spinning were employed to investigate structural and dynamical modifications of cell membranes, resulting from the addition of compounds with some biological relevance. For further interpretation of the segmental order obtained from the 2D experiments other methods, such as 31P-NMR, 2H-NMR and molecular dynamics simulations, were also employed. The work presented in this thesis can be divided into two parts. The first part refers to the setup of experimental conditions. Heating and hydration effects were addressed in order to define both the temperature of the system as well as the number of water molecules per lipid necessary to fully hydrate the bilayer. Application of this experimental setup to lipid membrane systems with biological relevance constitutes the second part. The interaction of monogalactosyl- ...
Biological membranes do not only occur as planar bilayer structures, but bilayers have also been shown to, depending on the lipid composition, curve into intriguing 3D structures. Understanding the biological implication as well as the application of such interfaces, for e.g. drug delivery and other biomedical application, requires the development of well-defined model system.. We have shown that spin-coating the constituting lipids followed by hydration of the lipid layer can be used to form non-lamellar liquid crystalline surfaces of different types on the surface. In order to make the layers more responsive polymer micro-gels with a diameter of about 55 nm can be embedded within the layer. Another way to for non-planar lipid interfaces are to deposit lipids on nanostructured surfaces. Here we demonstrate the formation of fluid supported bilayers on vertical gallium phosphide nanowire (NW) forests using self-assembly from lipid vesicular dispersions.1 The phospholipid mixture used had a ...
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Making and holding an artificial lipid bilayer horizontally in aqueous solution within the microscopic working distance are essential for simultaneous single molecule imaging and single ion-channel electrical current recording of membrane ion-channel proteins. We have designed and developed an unsupported, horizontally held artificial bilayer and used it successfully in studying the ion-channel protein dynamics by simultaneous single-molecule fluorescence imaging and electric current measurements. Further, using the developed lipid bilayer, we have studied the behavior of colicin Ia ion channel protein. The dynamics of the channel transition between open and close states and the translocation of charged ¿¿¿¿-helices across the membrane were studied. Our results have demonstrated that the channel open-close transition is less dependent on the applied voltage and the charged 2-5 helices follow a polar pathway to cross the lipid bilayer. Moreover, we studied about the structural arrangement of light
Page contains details about 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine/1,2-dioleoyl-sn-glycero-3-phosphocholine lipid bilayer . It has composition images, properties, Characterization methods, synthesis, applications and reference articles : nano.nature.com
Творча студія "АРТ КОСЕКОМА": СВІТ ЧУДОВИЙ ТА ДИВНИЙ! Творческая студия "АРТ КОСЕКОМА": МИР ПРЕКРАСЕН И УДИВИТЕЛЕН! Creative studio "ART KOSEKOMA": THE WORLD IS WONDERFUL AND AMAZING! ...
Lipid bilayers are relatively weak. Certainly there are stronger forms of these membranes, but as implied by the fluid mosaic model these membranes sacrifice rigidity and strength for the ability to allow proteins to freely disperse within the membrane. A consequence of this is that differences in pressure on the two different sides of the…
The fluorescence decay of membrane lipid bilayer probes are influenced by the environment of the probe and therefore by the properties of the bilayer in which it resides. Traditionally the fluorescence decay has been analyzed in the form of a multi-exponential. Analysis in the form of continuous distributions can provide a useful alternative to this approach since it introduces a new parameter, the distributional width. The physical basis underlying the distributional width, the fluorophore "environmental heterogeneity", arises from organizational aspects, compositional diversity and solvent effects. The "sampling" of environmental heterogeneity will depend on the intrinsic fluorescence lifetime, the lipid rate of motion and fluorophore charge and shape factors. We have found a good correlation of the distributional width with a number of bilayer properties. Thus as we increase the complexity of a bilayer the distributional width becomes broader, in order, from a single phospholipid molecular ...
Jump to image list below. Many aspects of these images were optimized for discerning the structures of the bilayers. The palmitic and oleic tails are given slightly different hues to help in discerning their positions. The bottom leaflet is darkened relative to the top leaflet, and the last carbons on the tails of the fatty acids in the bottom leaflet are white. One corner (16 PCs in each leaflet) is cut out, and the first two rows of PCs in the top leaflet are cut away. The waters associated with the top leaflet are cut away in front (x <= 7.0). Every second water molecule is deleted to allow seeing through the water cloud. Only the oxygens of the waters are shown, and at much less than actual spacefilling diameter (0.8A). The fatty acid tails are shown thinner than their actual spacefilling diameters, namely as wireframe 0.8A diameter, which leaves some space between them. If you are interested in the PDB files or script which generated these views, ask. These images are slightly smaller ...
Droplet-interface bilayers (DIBs) have applications in disciplines ranging from biology to computing. We present a method for forming them manually using a Teflon tube attached to a syringe pump; this method is simple enough it should be accessible to those without expertise in microfluidics. It exploits the properties of interfaces between three immiscible liquids, and uses fluid flow through the tube to pack together drops coated with lipid monolayers to create bilayers at points of contact. It is used to create functional nanopores in DIBs composed of phosphocholine using the protein α-hemolysin (αHL), to demonstrate osmotically-driven mass transfer of fluid across surfactant-based DIBs, and to create arrays of DIBs. The approach is scalable, and thousands of DIBs can be prepared using a robot in one hour; therefore, it is feasible to use it for high throughput applications.
One of the popular approaches to study cell membranes is to study lipid mixtures phase behaviors. Although the structure of compositionally simple binary and ternary lipid systems have been extensively studied in the last three decades, the effects of proteins on compositional complexity of biological membranes have not been studied in details. Since in some biological membranes, the majority of membrane area is covered by proteins (up to 60-70%), it is reasonable to suppose that membrane proteins would have large effects on bilayer phase behavior. To the best of our knowledge, previously, no 4-component phase diagram, with protein as one of the components, has been reported. This work is the first study of this kind which investigate the effect of polypeptide gramicidin-A on Lo+Ld phase boundaries. In recent years, many studies have focused on the study of lipid rafts, a type of domain structure thought to form spontaneously by lateral phase separation in membranes. Lipid rafts provide domains ...
One of the popular approaches to study cell membranes is to study lipid mixtures phase behaviors. Although the structure of compositionally simple binary and ternary lipid systems have been extensively studied in the last three decades, the effects of proteins on compositional complexity of biological membranes have not been studied in details. Since in some biological membranes, the majority of membrane area is covered by proteins (up to 60-70%), it is reasonable to suppose that membrane proteins would have large effects on bilayer phase behavior. To the best of our knowledge, previously, no 4-component phase diagram, with protein as one of the components, has been reported. This work is the first study of this kind which investigate the effect of polypeptide gramicidin-A on Lo+Ld phase boundaries. In recent years, many studies have focused on the study of lipid rafts, a type of domain structure thought to form spontaneously by lateral phase separation in membranes. Lipid rafts provide domains ...
Received 17 July 2012, Received in revised form 24 September 2012, Accepted 25 September 2012, Available online 1 October 2012 ...
Our Ionotec product line offers instrumentation, consumables, and services centered around membrane biophysics with two options for the automated, reproducible, and hence routine oriented generation of lipid bilayers for the analysis of biomembrane related phenomena. The Ionovation Scout is our second generation of automated bilayer instruments and picks up the traditional concept of an artificial biomembrane spanned vertically between two individually accessible compartments for electrophysiological measurements. And, with its automation and range of consumables, it turns bilayer experiments on reconstituted membrane proteins into a routine technique no longer reserved to the expert.. The Ionovation Explorer has taken the lipid bilayer or BLM concept to a new level of scientific insights. With its unique horizontal bilayer design, dual perfusion and even temperature control option it makes the membrane easily accessible for advanced microscopic analyses and opens novel experimental options to ...
We develop a theoretical framework for understanding dynamic morphologies and stability of droplet interface bilayers (DIBs), accounting for lipid kinetics in the monolayers and bilayer, and droplet evaporation due to imbalance between osmotic and Laplace pressures. Our theory quantitatively describes distinct pathways observed in experiments when DIBs become unstable. We find that when the timescale for lipid desorption is slow compared to droplet evaporation, the lipid bilayer will grow and the droplets approach a hemispherical shape. In contrast, when lipid desorption is fast, the bilayer area will shrink and the droplets eventually detach. Our model also suggests there is a critical size below which DIBs can become unstable, which may explain experimental difficulties in miniaturizing the DIB platform.. ...
The outermost membrane of gram-negative bacteria is a lipopolysaccharide (LPS) rich bilayer assembly that acts as the first line of defense for bacterial cells in adverse physical and chemical environments. Besides the LPS, the outer membrane has radially extending O-antigen polysaccharide chains and β-barrel membrane proteins that make the bacterial membrane physiologically unique compared to the phospholipid cell membranes. To study the molecular complexity and dynamics of the LPS rich membrane, we have developed coarse grained parameter set for the outer membrane compatible with the Martini force field. The coarse grained model was benchmarked against available experimental and atomistic simulations data for properties such as membrane thickness, density profiles of the residues, area per lipid, gel to liquid-crystalline phase transition temperatures, order parameters, and radial distribution functions. More than 17 membrane compositions were studied with a combined simulation time of over 100