Liquid-liquid phase separation of a surfactant-solubilized membrane protein

TL;DR

This study demonstrates that pH-sensitive surfactant ionization induces reversible liquid-liquid phase separation in a membrane protein, affecting its functional properties and revealing complex phase behavior influenced by temperature and salt.

Contribution

It uncovers the role of surfactant ionization in inducing phase separation of membrane proteins, a phenomenon not previously characterized in this context.

Findings

Phase separation occurs within a narrow pH range due to surfactant ionization.

Temperature increases promote phase segregation, while salt addition inhibits it.

Phase segregation significantly impacts the protein's light absorption and electron cycling.

Abstract

The phase behavior of membrane proteins stems from a complex synergy with the amphiphilic molecules required for their solubilization. We show that ionization of a pH-sensitive surfactant, LDAO, bound to a bacterial photosynthetic protein, the Reaction Center (RC), leads in a narrow pH range to protein liquid-liquid phase separation in surprisingly stable `droplets', forerunning reversible aggregation at lower pH. Phase segregation is promoted by increasing temperature and hindered by adding salt. RC light-absorption and photoinduced electron cycle are moreover strongly affected by phase segregation.