Search results for "bilayer"
showing 10 items of 391 documents
Coarse-grained models and collective phenomena in membranes: Computer simulation of membrane fusion
2003
We discuss the role coarse-grained models play in in- vestigating collective phenomena in bilayer membranes and place them in the context of alternative approaches. By reducing the de- grees of freedom and applying simple effective potentials, coarse- grained models can address the large time scales and length scales of collective phenomena in mem- branes. Although the mapping from a coarse-grained model onto chemi- cally realistic models is a challenge, such models provide a direct view on the phenomena that occur on the length scales of a few tens of nano- meters. Their relevance is exempli- ied by the study of fusion of model membranes. ' 2003 Wiley Periodicals,
Membrane-mediated Protein-protein Interaction: A Monte Carlo Study
2012
We investigate membrane-mediated interactions between transmembrane proteins using coarse-grained models. We compare the effective potential of mean force (PMF) between two proteins, which are always aligned parallel to the z-axis of the simulation box, with those PMFs obtained for proteins with fluctuating orientations. The PMFs are dominated by an oscillatory packing-driven contribution and a smooth attractive hydrophobic mismatch contribution, which vanishes if the hydrophobic length of the protein matches the thickness of the membrane. If protein orientations are allowed to fluctuate, the oscillations are greatly reduced compared to proteins with fixed orientation. Furthermore, the hydr…
Bilayer graphene lattice-layer entanglement in the presence of non-Markovian phase noise
2018
The evolution of single particle excitations of bilayer graphene under effects of non-Markovian noise is described with focus on the decoherence process of lattice-layer (LL) maximally entangled states. Once that the noiseless dynamics of an arbitrary initial state is identified by the correspondence between the tight-binding Hamiltonian for the AB-stacked bilayer graphene and the Dirac equation -- which includes pseudovector- and tensor-like field interactions -- the noisy environment is described as random fluctuations on bias voltage and mass terms. The inclusion of noisy dynamics reproduces the Ornstein-Uhlenbeck processes: a non-Markovian noise model with a well-defined Markovian limit…
On ripples and rafts: Curvature induced nanoscale structures in lipid membranes
2014
We develop an elastic theory that predicts the spontaneous formation of nanoscale structures in lipid bilayers which locally phase separate between two phases with different spontaneous monolayer curvature. The theory rationalizes in a unified manner the observation of a variety of nanoscale structures in lipid membranes: Rippled states in one-component membranes, lipid rafts in multicomponent membranes. Furthermore, we report on recent observations of rippled states and rafts in simulations of a simple coarse-grained model for lipid bilayers, which are compatible with experimental observations and with our elastic model.
Unusual triskelion patterns and dye-labelled GUVs: consequences of the interaction of cholesterol-containing linear-hyperbranched block copolymers wi…
2015
Cholesterol (Ch) linked to a linear-hyperbranched block copolymer composed of poly(ethylene glycol) (PEG) and poly(glycerol) (hbPG) was investigated for its membrane anchoring properties. Two polyether-based linear-hyperbranched block copolymers with and without a covalently attached rhodamine fluorescence label (Rho) were employed (Ch-PEG30-b-hbPG23 and Ch-PEG30-b-hbPG17-Rho). Compression isotherms of co-spread 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with the respective polymers were measured on the Langmuir trough and the morphology development of the liquid-condensed (LC) domains was studied by epi-fluorescence microsc…
Langmuir−Blodgett Films of Fluorinated Glycolipids and Polymerizable Lipids and Their Phase Separating Behavior
2010
This paper describes the phase separating behavior of Langmuir monolayers from mixtures of different lipids that (i) either carry already a glycopeptide recognition site or can be easily modified to carry one and (ii) polymerizable lipids. To ensure demixing during compression, we used fluorinated lipids for the biological headgroups and hydrocarbon based lipids as polymerizable lipids. As a representative for a lipid monomer, which can be polymerized in the hydrophilic headgroup, a methacrylic monomer was used. As a monomer, which can be polymerized in the hydrophobic tail, a lipid with a diacetylene unit was used (pentacosadiynoic acid, PDA). The fluorinated lipids were on the one hand a …
A lipocentric view of peptide-induced pores
2010
Although lipid membranes serve as effective sealing barriers for the passage of most polar solutes, nonmediated leakage is not completely improbable. A high activation energy normally keeps unassisted bilayer permeation at a very low frequency, but lipids are able to self-organize as pores even in peptide-free and protein-free membranes. The probability of leakage phenomena increases under conditions such as phase coexistence, external stress or perturbation associated to binding of nonlipidic molecules. Here, we argue that pore formation can be viewed as an intrinsic property of lipid bilayers, with strong similarities in the structure and mechanism between pores formed with participation …
Pore formation by Vibrio cholerae cytolysin requires cholesterol in both monolayers of the target membrane
2007
Vibrio cholerae cytolysin (VCC) forms oligomeric transmembrane pores in cholesterol-rich membranes. To better understand this process, we used planar bilayer membranes. In symmetric membranes, the rate of the channel formation by VCC has a superlinear dependency on the cholesterol membrane fraction. Thus, more than one cholesterol molecule can facilitate VCC-pore formation. In asymmetric membranes, the rate of pore formation is limited by the leaflet with the lower cholesterol content. Methyl-beta-cyclodextrin, which removes cholesterol from membranes, rapidly inhibits VCC pore formation, even when it is added to the side opposite that of VCC addition. The results suggest that cholesterol i…
Correct oligomerization is a prerequisite for insertion of the central molecular domain of staphylococcal α-toxin into the lipid bilayer
1995
Staphylococcal alpha-toxin is a primarily hydrophilic molecule that binds as a monomer to target membranes and then aggregates to form amphiphilic oligomers that represent water-filled transmembrane channels. Current evidence indicates that a region located in the center of the molecule inserts deeply into the bilayer. In the present study, we sought to determine whether membrane insertion was triggered by the oligomerization process, and whether insertion correlated with pore formation. Double mutants of alpha-toxin were prepared in which His-35 was replaced by Arg, and cysteine residues were introduced at positions 69, 130 and 186. Substitution of His-35 with Arg rendered the toxin molecu…
Normalization of sphingomyelin levels by 2-hydroxyoleic acid induces autophagic cell death of SF767 cancer cells
2012
The very high mortality rate of gliomas reflects the unmet therapeutic need associated with this type of brain tumor. We have discovered that the plasma membrane fulfills a critical role in the propagation of tumorigenic signals, whereby changes in membrane lipid content can either activate or silence relevant pathways. We have designed a synthetic fatty acid, 2-hydroxyoleic acid (2OHOA), that specifically activates sphingomyelin synthase (SGMS), thereby modifying the lipid content of cancer cell membranes and restoring lipid levels to those found in normal cells. In reverting, the structure of the membrane by activating SGMS, 2OHOA inhibits the RAS-MAPK pathway, which in turn fails to acti…