Biology subjects

Dimova, R.

Publications and source records attributed to Dimova, R..

5 recordsLinked to original sources

bioRxiv2020

To close or to collapse: the role of charges on membrane stability upon pore formation

Resealing of membrane pores is crucial for cell survival. We study membrane surface charge and medium composition as defining regulators of membrane stability. Pores are generated by electric field or detergents. Giant vesicles composed of zwitterionic and negatively charged lipids mixed at varying ratios are subjected to a single strong electric pulse. Charged vesicles are prone to catastrophic collapse transforming them into tubular structures. The spectrum of destabilization responses includes the generation of long-living submicroscopic pores and partial vesicle bursting. The origin of these phenomena is related to the membrane edge tension, which governs pore closure. This edge tension significantly decreases as a function of the fraction of charged lipids. Destabilization of charged vesicles upon pore formation is universal - it is also observed with other poration stimuli. Disruption propensity is enhanced for membranes made of lipids with higher degree of unsaturation. It can be reversed by screening membrane charge in the presence of calcium ions. We interpret the observed findings in light of theories of stability and curvature generation and discuss mechanisms acting in cells to prevent total membrane collapse upon poration. Enhanced membrane stability is crucial for the success of electroporation-based technologies for cancer treatment and gene transfer.

biophysics↗

bioRxiv2020

Super-elasticity of plasma- and synthetic membranes by coupling of membrane asymmetry and liquid-liquid phase separation

Biological cells are contained by a fluid lipid bilayer (plasma membrane, PM) that allows for large deformations, often exceeding 50% of the initial (or projected) PM area. Biochemically isolated lipids self-organize into membranes, but the extraordinary deformability of the plasma membrane is lost. Pure lipid bilayers are prone to rupture at small (<2-4%) area strains and this limits progress for synthetic reconstitution of cellular features such as migration, phagocytosis and division. Here, we show that by preserving PM structure and composition during isolation from cells, vesicles with cell-like elasticity are obtained. We found that these plasma membrane vesicles store significant area in the form of nanotubes in their lumen. These are recruited by mechanical tension applied to the outer vesicle membrane showing an apparent elastic response. This "super-elastic" response emerges from the interplay of lipid liquid-liquid phase separation and membrane asymmetry. This finding allows for bottom-up engineering of synthetic vesicles that appear over one magnitude softer and with three fold larger deformability than conventional lipid vesicles.

biophysics↗

bioRxiv2020

Interferon-Induced Transmembrane Protein 3 Blocks Fusion of Diverse Enveloped Viruses by Locally Altering Mechanical Properties of Cell Membranes

Interferon-induced transmembrane protein 3 (IFITM3) potently inhibits entry of diverse enveloped viruses by trapping the viral fusion at a hemifusion stage, but the underlying mechanism remains unclear. Here, we show that recombinant IFITM3 reconstituted into lipid vesicles induces negative membrane curvature and that this effect maps to its small amphipathic helix (AH). We demonstrate that AH: (i) partitions into lipid-disordered domains where IAV fusion occurs, (ii) induces negative membrane curvature, and (iii) increases lipid order and membrane stiffness. Additionally, replacing the IFITM3 AH with AH from an unrelated protein did not compromise its antiviral activity. These effects on membrane properties correlate with the fusion-inhibitory activity, as exogenous addition of AH to insulin-producing cells reduces glucose-stimulated insulin secretion. Our results thus imply that IFITM3 inhibits the transition from hemifusion to full fusion by imposing an unfavorable membrane curvature and increasing the order and stiffness of the cytoplasmic leaflet of endosomal membranes.

biophysics↗

bioRxiv2020

Fluctuation spectroscopy of giant unilamellar vesicles using confocal and phase contrast microscopy

A widely used method to measure the bending rigidity of bilayer membranes is fluctuation spectroscopy, which analyses the thermally-driven membrane undulations of giant unilamellar vesicles recorded with either phase-contrast or confocal microscopy. Here, we analyze the fluctuations of the same vesicle using both techniques and obtain consistent values for the bending modulus. We discuss the factors that may lead to discrepancies.

biophysics↗

bioRxiv2019

Mechanical properties of plasma membrane vesicles correlate with lipid order and viscosity and depend on cell density

Plasma membranes dynamically respond to external cues and changing environment. Quantitative measurements of these adaptations can elucidate the mechanism that cells exploit to survive, adapt and function. However, cell-based assays are affected by active processes while measurements on synthetic models suffer from compositional limitations. Here, as a model system we employ giant plasma membrane vesicles (GPMVs), which largely preserve the plasma membrane lipidome and proteome. From analysis of fluorescence emission and lifetime of environment-sensitive dyes, and membrane shape fluctuations, we investigate how plasma membrane order, viscosity and bending rigidity are affected by different stimuli such as cell seeding density in three different cell models. Our studies reveal that bending rigidity of plasma membranes vary with lipid order and microviscosity in a highly correlated fashion. Thus, readouts from polarity- and viscosity-sensitive probes represent a promising indicator of membrane mechanical properties. Quantitative analysis of the data allows for comparison to synthetic lipid membranes as plasma membrane mimetics.

biophysics↗