Nonequilibrium Fluctuations, Travelling Waves, and Instabilities in Active Membranes

TL;DR

This paper investigates how active proteins influence membrane stability, revealing conditions for stable fluctuations, traveling waves, and instabilities driven by protein activity and asymmetry.

Contribution

It demonstrates the dependence of membrane stability on protein structure and asymmetry, and predicts wave propagation and spontaneous undulations due to activity.

Findings

Stable active membranes exhibit nonequilibrium fluctuations governed by protein activity.

Long-wavelength disturbances propagate as waves with speed related to pump velocity.

Unstable membranes undergo spontaneous undulations with protein clustering.

Abstract

The stability of a flexible fluid membrane containing a distribution of mobile, active proteins (e.g. proton pumps) is shown to depend on the structure and functional asymmetry of the proteins. A stable active membrane is in a nonequilibrium steady state with height fluctuations whose statistical properties are governed by the protein activity. Disturbances are predicted to travel as waves at sufficiently long wavelength, with speed set by the normal velocity of the pumps. The unstable case involves a spontaneous, pump-driven undulation of the membrane, with clumping of the proteins in regions of high activity.