Properties of Asymmetric Membranes from Coarse Grained Molecular Dynamics Simulations

Abstract

Biological lipid membranes exhibit compositional asymmetry between the leaflets of the bilayer. This fact leads to membranes which exhibit properties not found in single-component lipid bilayers, such as spontaneous curvature and differential stress. Molecular dynamics simulations can be, and have been utilized to study these effects, but all-atom simulations are relatively slow and size-restrictive compared to more coarse grained models. However, simulation of asymmetric membranes with highly coarse-grained models has been difficult in the past due to the accelerated dynamics of various processes, notably transbilayer lipid motion (flip-flop), which leads to the decay of asymmetric states in simulation before statistically significant measurements can be made. We propose a version of the highly coarse grained Cooke lipid model, gently reparameterized to strongly suppresses flip-flop, and employ it to probe elastic properties of membranes with stress asymmetry and leaflet spontaneous curvature mismatch. We also calculate and present lateral stress profiles for the different cases to illustrate the changes that take place on a local level throughout the bilayer leaflets as a result of asymmetry.