Characterizing the Liquid-liquid Phase Co-existence in Biomembrane: Insights from Local Non-affine Deformation and Topological Rearrangements

Lateral heterogeneities in bio-membranes play a crucial role in various physiological functions of the cell. Such heterogeneities lead to demixing of lipid constituents and formation of distinct liquid domains in the membrane. We study lateral heterogeneities in terms of the topological rearrangements of lipids, to identify liquid-liquid phase co-existence in model membranes. By quantifying the degree of non-affineness associated with individual lipid, we are able to characterize the liquid ordered (Lo) and liquid disordered (Ld) phases in model lipid bilayers, without any prior knowledge on chemical identity of the lipids. We explore the usage of this method on all atom and coarse-grained lipid bilayer trajectories. This method is helpful in defining the instantaneous Lo-Ld domain boundaries in complex multi-component bilayer systems. The characterization can also highlight the effect of line-active molecules on the phase boundaries and domain mixing. Overall, we propose a framework to explore the molecular origin of spatial and dynamical heterogeneity in bio-membranes systems, which can not only be exploited in computer simulation, but also in experiments.