Membrane Fusion in Synaptic Transmission
The 'SNARE hypothesis' states that neurotransmitter-loaded secretory vesicles fuse (in milliseconds) with presynaptic membranes by zippering v-SNAREs on vesicle membranes and t-SNAREs on target membranes into a 4-helix coiled coil structure. How the force of this highly exothermic reaction is transmitted into deforming membranes and how the fusion trigger Ca/synaptotagmin plays into this process is unclear and a major focus of our research.
In a large collaborative effort with the groups of Reinhard Jahn and Dirk Fasshauer at the Max-Planck Institute in Göttingen, Germany, and David Cafiso in the Chemistry Department at UVA, we are taking a multi-pronged cell-biological, biochemical, and biophysical approach to this problem. We are studying the structures of the relevant fusion proteins by combined NMR and EPR approaches in membranes. High-resolution structural information of individual components and domains is then integrated into the understanding of this multi-component molecular machine by single molecule fluorescence studies. By reconstitution of the relevant components in supported bilayers, ms time resolution of functional fusion events can be observed and dissected. FRET experiments permit us to determine changing spatial relationships of protein and lipid components in this process. Similar studies with native plasma membranes of secretory cells and synaptic vesicles allow us to link the reconstitution approach with the cell physiology of this process.