Bending rigidities and interdomain forces in membranes with coexisting lipid domains

TL;DR

This study quantifies the interactions and bending rigidities of coexisting lipid domains in membranes using osmotic stress SAXS and Monte Carlo analysis, revealing the dominant role of undulation and hydration forces in domain alignment.

Contribution

It introduces a novel Monte Carlo based method to accurately determine interdomain forces and bending moduli without relying on mean-field approximations.

Findings

Undulation interactions dominate in liquid-disordered domains.

Hydration forces significantly influence domain alignment.

Van der Waals attractions are similar across phases.

Abstract

In order to precisely quantify the fundamental interactions between heterogeneous lipid membranes with coexisting liquid-ordered (Lo) and liquid-disordered (Ld) domains, we performed detailed osmotic stress SAXS experiments by exploiting the domain alignment in raft-mimicking lipid multibilayers. Performing a Monte Carlo (MC) based analysis allowed us to determine with high reliability the magnitude and functional dependence of interdomain forces concurrently with the bending elasticity moduli. In contrast to previous methodologies, this approach enabled us to consider the entropic undulation repulsions on a fundamental level, without having to take recourse to crudely justified mean-field like additivity assumptions. Our detailed Hamaker coefficient calculations indicated only small differences in the van der Waals attractions of coexisting Lo and Ld phases. In contrast, the repulsive hydration and undulation interactions differed significantly, with the latter dominating the overall repulsions in the Ld phase. Therefore, alignment of like domains in multibilayers appears to originate from both, hydration and undulation repulsions.