Monolayer curvature stabilizes nanoscale raft domains in mixed lipid bilayers

TL;DR

This study demonstrates that monolayer curvature coupled with local composition can stabilize nanoscale raft domains in multicomponent lipid bilayers, providing insight into the physical mechanisms behind lipid raft formation.

Contribution

It introduces a novel mechanism where monolayer curvature stabilizes finite-sized raft domains, advancing understanding of membrane heterogeneity.

Findings

Raft-like nanodomains are observed in a coarse-grained lipid bilayer model.

Coupling between monolayer curvature and composition stabilizes nanometer-sized rafts.

Elastic interactions reduce line tension, favoring stable raft sizes.

Abstract

According to the lipid raft hypothesis, biological lipid membranes are laterally heterogeneous and filled with nanoscale ordered "raft" domains, which are believed to play an important role for the organization of proteins in membranes. However, the mechanisms stabilizing such small rafts are not clear, and even their existence is sometimes questioned. Here we report the observation of raft-like structures in a coarse-grained molecular model for multicomponent lipid bilayers. On small scales, our membranes demix into a liquid ordered (lo) and a liquid disordered (ld) phase. On large scales, phase separation is suppressed and gives way to a microemulsion-type state that contains nanometer size lo domains in a ld environment. Furthermore, we introduce a mechanism that generates rafts of finite size by a coupling between monolayer curvature and local composition. We show that mismatch between the spontaneous curvatures of monolayers in the lo and ld phase induces elastic interactions, which reduce the line tension between the lo and ld phase and can stabilize raft domains with a characteristic size of the order of a few nanometers. Our findings suggest that rafts in multicomponent bilayers might be closely related to the modulated ripple phase in one-component bilayers.