Equilibrium theory and geometrical constraint equation for two-component lipid bilayer vesicles.
Ontology highlight
ABSTRACT:
SUBMITTER: Yin Y
PROVIDER: S-EPMC2603267 | biostudies-other | 2008 Dec
REPOSITORIES: biostudies-other
Similar Datasets
Project description: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 independent of the rate at which bending strain is applied. We present here the first direct measurement of viscoelastic response in a lipid bilayer vesicle. We used a dual-beam optical trap (DBOT) to stretch 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) giant unilamellar vesicles (GUVs). Upon application of a step optical force, the vesicle membrane deforms in two regimes: a fast, instantaneous area increase, followed by a much slower stretching to an eventual plateau deformation. From measurements of dozens of GUVs, the average time constant of the slower stretching response was 0.225 ± 0.033 s (standard deviation, SD). Increasing the fluid viscosity did not affect the observed time constant. We performed a set of experiments to rule out heating by laser absorption as a cause of the transient behavior. Thus, we demonstrate here that the bending deformation of lipid bilayer membranes should be treated as viscoelastic.
| S-EPMC4573909 | biostudies-literature
Project description:Haptotaxis is a mechanism proposed at the end of the 1960s to explain cell motility. It describes cell movement induced by an adhesion gradient. In this work, we present evidence for self-induced haptotaxis using negatively charged giant vesicles interacting with positively charged supported lipid bilayers, which has not been previously described. Depending on the charge of the vesicle, we observed different behaviors. At low charge, no adhesion occurs. At high charge, the vesicle adheres but does not move. In a restricted range of intermediate charge densities, we found that the vesicle moves spontaneously with velocities of the order of a few micrometers per second over distances of >100 microm. We show that a local lipid transfer between the giant vesicle and the supported lipid bilayer takes place during the adhesion, breaking the symmetry and inducing a lateral charge gradient. This charge gradient polarizes the giant vesicle and induces its motion. To explain our observations, we propose a scaling model that relates the adhesion energy to the velocity of vesicle motion and to the characteristic lipid transfer time. Our measurements indicate that the effective adhesion energy is strongly reduced by counterions, which are dynamically trapped between the vesicle and the supported bilayer.
| S-EPMC1567888 | biostudies-literature
Project description:The lipid bilayer environment around membrane proteins strongly affects their structure and functions. Here, we aimed to study the fusion of proteoliposomes (PLs) derived from cultured cells with an artificial lipid bilayer membrane and the distribution of the PL components after the fusion. PLs, which were extracted as a crude membrane fraction from Chinese hamster ovary (CHO) cells, formed isolated domains in a supported lipid bilayer (SLB), comprising phosphatidylcholine (PC), phosphatidylethanolamine (PE), and cholesterol (Chol), after the fusion. Observation with a fluorescence microscope and an atomic force microscope showed that the membrane fusion occurred selectively at microdomains in the PC?+?PE?+?Chol-SLB, and that almost all the components of the PL were retained in the domain. PLs derived from human embryonic kidney 293 (HEK) cells also formed isolated domains in the PC?+?PE?+?Chol-SLB, but their fusion kinetics was different from that of the CHO-PLs. We attempted to explain the mechanism of the PL-SLB fusion and the difference between CHO- and HEK-PLs, based on a kinetic model. The domains that contained the whole cell membrane components provided environments similar to that of natural cell membranes, and were thus effective for studying membrane proteins using artificial lipid bilayer membranes.
| S-EPMC5738377 | biostudies-literature
Project description:The rapid and non-invasive pulmonary drug delivery (PDD) has attracted great attention compared to the other routes. However, nanoparticle platforms, like liposomes (LPs) and extracellular vesicles (EVs), require extensive reformulation to suit the requirements of PDD. LPs are artificial vesicles composed of lipid bilayers capable of encapsulating hydrophilic and hydrophobic substances, whereas EVs are natural vesicles secreted by cells. Additionally, novel LPs-EVs hybrid vesicles may confer the best of both. The preparation methods of EVs are distinguished from LPs since they rely mainly on extraction and purification, whereas the LPs are synthesized from their basic ingredients. Similarly, drug loading methods into/onto EVs are distinguished whereby they are cell- or non-cell-based, whereas LPs are loaded via passive or active approaches. This review discusses the progress in LPs and EVs as well as hybrid vesicles with a special focus on PDD. It also provides a perspective comparison between LPs and EVs from various aspects (composition, preparation/extraction, drug loading, and large-scale manufacturing) as well as the future prospects for inhaled therapeutics. In addition, it discusses the challenges that may be encountered in scaling up the production and presents our view regarding the clinical translation of the laboratory findings into commercial products.
| S-EPMC9866119 | biostudies-literature
Project description:alpha-Sarcin is a cytotoxic protein produced by the mould Aspergillus giganteus. Insertion of alpha-sarcin into asolectin membranes has been demonstrated by protein labelling with photoreactive phospholipids. alpha-Sarcin added externally to tRNA-containing asolectin liposomes degrades the entrapped tRNA. Trypsin-containing asolectin liposomes were also prepared. Encapsulated trypsin degrades alpha-sarcin, even in the presence of a large excess of external hen egg-white trypsin inhibitor to prevent any alpha-sarin degradation outside the vesicles. These processes occur only with acidic phospholipids and were not observed when phosphatidylcholine vesicles were used. These results indicate that alpha-sarcin penetrates the lipid bilayer and becomes exposed to the lumen of negatively charged liposomes.
| S-EPMC1134842 | biostudies-other
Project description:Understanding the behavior of low-dimensional nanomaterials confined in intracellular vesicles has been limited by the resolution of bioimaging techniques and the complex nature of the problem. Recent studies report that long, stiff carbon nanotubes are more cytotoxic than flexible varieties, but the mechanistic link between stiffness and cytotoxicity is not understood. Here we combine analytical modeling, molecular dynamics simulations, and in vitro intracellular imaging methods to reveal 1D carbon nanotube behavior within intracellular vesicles. We show that stiff nanotubes beyond a critical length are compressed by lysosomal membranes causing persistent tip contact with the inner membrane leaflet, leading to lipid extraction, lysosomal permeabilization, release of cathepsin B (a lysosomal protease) into the cytoplasm, and cell death. The precise material parameters needed to activate this unique mechanical pathway of nanomaterials interaction with intracellular vesicles were identified through coupled modeling, simulation, and experimental studies on carbon nanomaterials with wide variation in size, shape, and stiffness, leading to a generalized classification diagram for 1D nanocarbons that distinguishes pathogenic from biocompatible varieties based on a nanomechanical buckling criterion. For a wide variety of other 1D material classes (metal, oxide, polymer), this generalized classification diagram shows a critical threshold in length/width space that represents a transition from biologically soft to stiff, and thus identifies the important subset of all 1D materials with the potential to induce lysosomal permeability by the nanomechanical mechanism under investigation.
| S-EPMC5098676 | biostudies-literature
Project description:Self-assembly is a ubiquitous approach to the design and fabrication of novel supermolecular architectures. Here we report a strategy termed 'lipid-bilayer-assisted self-assembly' that is used to assemble DNA origami nanostructures into two-dimensional lattices. DNA origami structures are electrostatically adsorbed onto a mica-supported zwitterionic lipid bilayer in the presence of divalent cations. We demonstrate that the bilayer-adsorbed origami units are mobile on the surface and self-assembled into large micrometre-sized lattices in their lateral dimensions. Using high-speed atomic force microscopy imaging, a variety of dynamic processes involved in the formation of the lattice, such as fusion, reorganization and defect filling, are successfully visualized. The surface modifiability of the assembled lattice is also demonstrated by in situ decoration with streptavidin molecules. Our approach provides a new strategy for preparing versatile scaffolds for nanofabrication and paves the way for organizing functional nanodevices in a micrometer space.
| S-EPMC4560778 | biostudies-literature
Project description:Supported lipid bilayers (SLB) are important for the study of membrane-based phenomena and as coatings for biosensors. Nevertheless, there is a fundamental lack of understanding of the process by which they form from vesicles in solution. We report insights into the mechanism of SLB formation by vesicle adsorption using temperature-controlled time-resolved fluorescence microscopy at low vesicle concentrations. First, lipid accumulates on the surface at a constant rate up to approximately 0.8 of SLB coverage. Then, as patches of SLB nucleate and spread, the rate of accumulation increases. At a coverage of approximately 1.5 x SLB, excess vesicles desorb as SLB patches rapidly coalesce into a continuous SLB. Variable surface fluorescence immediately before SLB patch formation argues against the existence of a critical vesicle density necessary for rupture. The accelerating rate of accumulation and the widespread, abrupt loss of vesicles coincide with the emergence and disappearance of patch edges. We conclude that SLB edges enhance vesicle adhesion to the surface and induce vesicle rupture, thus playing a key role in the formation of continuous SLB.
| S-EPMC2800963 | biostudies-literature
Project description:Monte Carlo simulations and integral equation theory were used to predict the thermodynamics and structure of a two-dimensional Coulomb fluid. We checked the possibility that integral equations reproduce Kosterlitz-Thouless and vapor-liquid phase transitions of the electrolyte and critical points. Integral equation theory results were compared to Monte Carlo data and the correctness of selected closure relations was assessed. Among selected closures hypernetted-chain approximation results matched computer simulation data best, but these equations unfortunately break down at temperatures well above the Kosterlitz-Thouless transition. The Kovalenko-Hirata closure produces results even at very low temperatures and densities, but no sign of phase transition was detected.
| S-EPMC4032415 | biostudies-other
Project description:Ras proteins are attached to the inner leaflet of the plasma membrane via a lipid-modified anchor. Membrane-bound Ras proteins laterally segregate into nanoscale signaling platforms called nanoclusters. It has been shown that the membrane domain preference of Ras nanoclusters varies with the nature of lipidation but their effect on the membrane has not been well understood. To investigate the effect of Ras insertion on membrane structure, we carried out numerous coarse-grained molecular dynamics (CGMD) simulations on a two-domain DPPC/DLiPC/cholesterol lipid bilayer in which different number and type of H-ras peptides were attached on one side. We have shown previously that this lipid mixture forms co-existing liquid-ordered/liquid-disordered (L o /L d ) domains and that different H-ras peptides form clusters that variously accumulate at the L o /L d regions or the boundary between them. Here we show that asymmetric insertion of each of these peptides induces a vertical relative displacement of the domains and deforms the bilayer, with the domain boundary serving as the center of deformation. The extent of the deformation, however, varies with the type and number of lipid modification. This is because the number and type of the Ras lipid tails determines the degree to which the stress caused by asymmetric peptide insertion is relieved by inter-leaflet cholesterol transfer and lipid tilt. In addition, we have characterized the mechanism of bilayer deformation based on the collective effect of the Ras peptides on inter-leaflet surface area, pressure profile and line tension differences. This allowed us to elucidate how Ras lipid modification affects membrane geometry and how a two-domain bilayer adjusts its shape through boundary deformation. The result contributes to a better understanding of Ras signaling platforms and highlights some of the mechanisms by which a multi-domain membrane responds to external perturbation.
| S-EPMC3864742 | biostudies-literature