Title：Conformational change of SNARE proteins in membrane
Speaker：Dr. Binyong LIANG ( Assitant Professor, University of Virginia, USA )
Time：Oct 17, 2016 ( Monday ), 14:00-15:00
Location：Room 120, Chemistry Building
The assembly of three neuronal soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) proteins synaptobrevin 2, syntaxin-1A, and SNAP-25 is the key step that leads to exocytotic fusion of synaptic vesicles. In the fully assembled post-fusion SNARE complex, these three proteins form a coiled-coil four-helix bundle structure by interaction of their respective SNARE motifs. We have solved the solution NMR structures of micelle-bound synaptobrevin and syntaxin-1A in their prefusion conformations. In addition to their respective transmembrane helices, the SNARE motifs of both proteins have considerable degrees of helical content. For synaptobrevin, only the N-terminal half (residues 36-54) of the SNARE motif forms a transient helix, and the fraction of helical content and interfacial association decreases as the protein is moved from micelle to bicelle to bilayer environments, suggesting that membrane curvature affects the folding of synaptobrevin. Interferometric fluorescence measurements in lipid bilayers confirm that the open SNARE motif helices interact with lipid bilayers and that the assembly of SNARE complexes involves the segmented movements of N- and C-terminal halves of SNARE motifs in relation to the membrane surface.
SNARE assembly is mediated by a number of other protein factors in vivo. Complexin is a soluble protein, which binds strongly to fully assembled neuronal SNARE complexes. Complexin is required for Ca2+-triggered fast fusion at nerve terminals; however, its mechanism of action remains elusive and controversial. Inhibitory and fusion-promoting effects have been reported and attributed to different domains of complexin. In addition, preferential binding of complexin to charged and highly curved membranes has been postulated to also contribute to its regulatory effect. We will present a model of how complexin effects SNARE-mediated membrane fusion in a physiological lipid environment.