Field Theoretic Study of Bilayer Membrane Fusion III: Membranes with Leaves of Different Composition

TL;DR

This study uses self-consistent field theory to analyze the energy barriers of bilayer membrane fusion with asymmetric leaf compositions, revealing low barriers that suggest rapid fusion once membranes are close.

Contribution

It extends previous homogeneous bilayer models to asymmetric bilayers with different amphiphiles, exploring fusion pathways and barrier heights relevant to biological membranes.

Findings

Fusion barriers are approximately 13 kT, indicating rapid fusion once membranes are close.

Both standard and alternative pathways show comparable, small energy barriers.

Asymmetry in leaf composition influences the fusion process but maintains low energy barriers.

Abstract

We extend previous work on homogeneous bilayers to calculate the barriers to fusion of planar bilayers which contain two different amphiphiles, a lamellae-former and a hexagonal former, with different compositions of the twoin each leaf. Self-consistent field theory is employed, and both standard and alternative pathways are explored. We first calculate these barriers as the amount of hexagonal former is increased equally in both leaves to levels appropriate to the plasma membrane of human red blood cells. We follow these barriers as the composition of hexagonal-formers is then increased in the cis layer and decreased in the trans layer, again to an extent comparable to the biological system. We find that, while the fusion pathway exhibits two barriers in both the standard and alternative pathways, in both cases the magnitudes of these barriers are comparable to one another, and small, on the order of 13 kT. As a consequence, one expects that once the bilayers are brought sufficiently close to one another to initiate the process, fusion should occur rapidly.