Probing the mechanism of annexin mediated plasma membrane repair.

Abstract

The integrity of the plasma membrane is essential for maintaining cell homeostasis and eucaryotic cells have developed robust mechanisms for rapidly sealing plasma membrane ruptures. The repair process involves recruitment of multiple proteins to the damage site as triggered by the influx of calcium ions from the cytosol. Several members of the Annexin family are involved in membrane repair although their functional role in membrane remodeling is not fully understood. Biophysical experiments and modeling in synergy with cell experiments offer tools which can provide additional insight into Annexin mediated repair mechanisms. We review our recent studies into membrane remodeling and protein structures induced by Annexin binding. Using a unique platform of planar, free-edged membrane patches, the edge region of a membrane hole can be experimentally mimicked under controlled conditions. Using this platform, Annexins induce spontaneous membrane curvature leading to distinct, curved morphologies. We discuss the theoretical modeling of curvature effects and the formation of membrane necks around holes. We also describe AFM results resolving the organization of Annexins on membranes with molecular detail. Finally, we describe quantification of the calcium influx in cells during subjected to laser rupture. Detailed analysis and modeling of calcium diffusion and pumping allows extraction of key parameters for repair such as the timescale of hole closure.