Spontaneous Curvature Measurements for Zwitterionic and Anionic Phospholipids under Biomimetic Perturbations and their Implications to the Mechanisms of Lamellar-Nonlamellar Phase Transitions

Abstract

cyclopropane and/or cyclohexane rings. Such structure of the hydrophobic part of the molecule not only helps the archaea to live at high temperatures, but also protects their membranes from harmful influence of various phospholipases, secreted by other organisms, and from oxidative stress. However, the role of the branched chain structure in the permeability of archaeal membranes to various ions, gases and water is still an open question. Pores, being conducting defects in a membrane, are the one of the most general causes of loss of membrane barrier function leading to cell death. So structural peculiarities of archaeal lipid should have some influence on membrane resistance to pore formation. We have studied process of pore formation in bilayer lipid membranes formed by ether and ester branched and unbranched lipids using electrical breakdown technique and molecular dynamics simulations. We have shown that branched lipid tails have a great influence on probability of pore formation and dynamics of its growth. A theoretical model connecting pore edge line tension and dynamics of pore widening was proposed. 1204-Pos Board B155Effect of Electrostatic Repulsion on DMPG Bilayers It is well known that ionic strength plays a fundamental role in the structure of DMPG (dimyristoyl phosphatidylglycerol) anionic vesicles in water medium. In buffer, at pH values above 4 and at high ionic strength (above~100 mM), the morphology of DMPG vesicles are rather similar to that of DMPC (dimyristoyl phosphatidylcholine) vesicles. However, at low ionic strength (~4 mM), DMPG dispersions display several anomalous characteristics, which were interpreted as the opening of bilayer pores along the wide bilayer gel-fluid transition region (from~18 o C to 30 o C) 1 . Here, we revisit DMPG in pure water 2 , to emphasize electrostatic interactions between the polar head-groups, which will not be shielded by ions in solution. For comparison, we used several techniques that have been recently applied to DMPG in buffer: light scattering, both static (SLS) and dynamic (DLS); differential scanning calorimetry (DSC); electron spin resonance (ESR) of spin labels incorporated into the aggregates; and viscosity, turbidity and electrical conductivity measurements. DSC and spin labels indicate that, in water, the bilayer gel-fluid transition is even wider, starting around 10 o C but still ending~30 o C. However, high electric conductivity, high viscosity and low turbidity found only in the gel-fluid transition region for DMPG in buffer, are found at higher temperatures in water, when lipid bilayers are already in the fluid state. Moreover, different from DMPG in buffer, in water, vesicles were found to fuse along the transition region. Data suggest that the strong PG --PGelectrostatic repulsion in water leads not only to pore formation in DMPG bilayers, but also to the opening of the vesicles and vesicle fusion.[1]Enoki,T. A.; Henriques, V. B.; M. T. Lamy, Chem. Electrochemistry is a technique that can be used to detect the contents of neurotransmitter...