Structural and functional studies on membrane fusion proteins-SNAREs

Membrane fusion is a ubiquitous and essential intracellular function. Membrane fusion is mediated by a protein superfamily known as N-ethymaleimide-sensitive fusion protein attachment protein receptors (SNAREs). From plant to mammal, there is a remarkable sequence similarity among the SNARE-family related to the conserved function of this family. The function of SNAREs has been proposed to be the key to membrane fusion as minimal fusion machinery. Depending on their distinct membrane distribution, SNAREs were classified into v (vesicle)-SNAREs and t (target)-SNAREs. It is widely believed that SNARE complex assembly by v- and t-SNAREs on opposite membranes offers the ultimate driving force for membrane fusion.; The purpose of this work is to investigate the structure dependent SNARE functions. Here we use biophysical methods of EPR (Electron paramagnetic resonance) to study the structure of SNARE proteins. Florescence lipid mixing assay is the biochemical method which is used to monitor SNAREs facilitated liposomes fusion in vitro. EPR study of SNARE assembly and v-SNARE membrane proximal region topology unravel that constitutive or regulated membrane fusion is determined by a protein structure difference. Yeast v-SNARE transmembrane domain (TMD) structure was modeled by the EPR method. The TMD of yeast v-SNARE half truncated mutant is designed from this structure. This mutant and the low SNAREs surface density lead to the discovery of membrane fusion intermediate state-hemifusion. Finally, lipid mixing assays help to identify the neuronal SNARE motif is the position to adopt the regulator of fast neuron transmitter release -SynaptotagminI for its function.