2014
Elife

A lipid bound actin meshwork organizes liquid phase separation in model membranes

Authors:

Honigmann, A., Sadeghi, S., Keller, J., Hell, S. W., Eggeling, C., & Vink, R.

Keywords:

membrane organization, cortical actin, lipid phase separation, STED microscopy, fluorescence correlation spectroscopy, pinning site

Abstract:

The eukaryotic cell membrane is connected to a dense actin rich cortex. We present FCS and STED experiments showing that dense membrane bound actin networks have severe influence on lipid phase separation. A minimal actin cortex was bound to a supported lipid bilayer via biotinylated lipid streptavidin complexes (pinning sites). In general, actin binding to ternary membranes prevented macroscopic liquid-ordered and liquid-disordered domain formation, even at low temperature. Instead, depending on the type of pinning lipid, an actin correlated multi-domain pattern was observed. FCS measurements revealed hindered diffusion of lipids in the presence of an actin network. To explain our experimental findings, a new simulation model is proposed, in which the membrane composition, the membrane curvature, and the actin pinning sites are all coupled. Our results reveal a mechanism how cells may prevent macroscopic demixing of their membrane components, while at the same time regulate the local membrane composition.