A Supported Tubulated Bilayer System Shows Effects of Synaptotagmin-7 on Membrane Curvature

Abstract

Fusion and fission of cellular membranes involve dramatic, precisely regulated changes in membrane curvature mediated by a number of proteins. The mechanisms by which proteins influence membrane curvature are not well understood, and current methods for investigating curvature changes using well-controlled systems are limited. We have developed a system based on supported lipid bilayers in which lipid tubules spontaneously form in a manner that can be tuned by varying the ionic character and strength used during bilayer deposition and imaging. Using this supported tubulated bilayer system, which we term “STuBS,” we have investigated membrane-targeting C2 domains from synaptotagmin-7, a member of the synaptotagmin protein family that triggers exocytosis in neurons and neuroendocrine cells. We find that addition of purified synaptotagmin-7 C2AB domains, but not synaptotagmin-1 C2A, leads to a Ca2+-dependent disappearance of tubules with concomitant formation of vesicles. These studies demonstrate that synaptotagmin-7 can alter membrane morphology by driving changes in membrane curvature. STuBS is a novel experimental system useful for monitoring solute- and protein-mediated effects on membrane topology in aqueous media and in real time.