Orientational Texture of Membrane Domains: Effect of Lipid Composition and Binding of a Bacterial Toxin

Abstract

The principles governing the in-plane organization of biomembranes remains enigmatic more than 20 years after the proposition of the raft hypothesis.The recent discovery of orientational texture of membrane gel domains represents a previously hidden level of membrane complexity[1]. Using polarized two-photon fluorescence imaging we have shown that gel domains in phospholipid membranes may contain long-ranged orientational texture patterns originating from the projection of the tilted acyl chains on the bilayer plane. Fourier analysis of the signal variations with respect to polarization angle enables the lipid orientation to be resolved spatially. We find that the texture of gel domains can exhibit topological defects including a vortex, pairs of half-integer vortices, and line defects[2]. Membrane texture resembles texture found in liquid crystals and Langmuir monolayers and have also been associated with hexatic positional order of the lipids.The texture pattern in membranes is closely linked to the lipid composition as demonstrated by the occurrence of uniformly aligned domains for some compositions. Specifically, a close correlation has been found between the hydrophobic (thickness) mismatch at the border of domains and the texture pattern[3].Recently we have explored the possibility that the Shiga toxin protein from the bacteria Shigella dysenteriae may remodel texture patterns in membranes. A significant effect of the toxin is found, possibly related to decreased lipid mobility [4].Here we will provide an overview of membrane texture in a range of systems and describe our efforts to understand and systematize the observations.[1] JACS (2009). DOI:10.1021/ja903375m[2] Soft Matter. (2012). DOI:10.1039/c2sm07290d[3] Langmuir, (2014). DOI:10.1021/la5023054[4] V. Solovyeva et. al. In review. (2014)