v-SNARE transmembrane domains function as catalysts for vesicle fusion

• Published in: eLife Vol. 5
• Main Authors: Dhara, Madhurima, Yarzagaray, Antonio, Makke, Mazen, Schindeldecker, Barbara, Schwarz, Yvonne, Shaaban, Ahmed, Sharma, Satyan, Böckmann, Rainer A, Lindau, Manfred, Mohrmann, Ralf, Bruns, Dieter
• Format: Journal Article
• Language: English
• Published: England eLife Science Publications, Ltd 25.06.2016; eLife Sciences Publications Ltd; eLife Sciences Publications, Ltd
• Subjects: Amino acids; Animals; Biology; Calcium; Catalysts; Cells, Cultured; DNA Mutational Analysis; Exocytosis; Experiments; Flexibility; Isoleucine; Leucine; Lipids; Membrane Fusion; Membrane proteins; Mice; Models, Biological; Mutant Proteins - chemistry; Mutant Proteins - genetics; Mutant Proteins - metabolism; Mutation; Neuroscience; neurotransmitter release; Observations; Packaging; Physiological aspects; Protein Conformation; Protein structure; Protein-protein interactions; Proteins; Secretion; Secretory Vesicles - metabolism; SNAP receptors; Synaptobrevin; Transmembrane domains; Valine; Vesicle fusion; Vesicle-Associated Membrane Protein 2 - chemistry; Vesicle-Associated Membrane Protein 2 - genetics; Vesicle-Associated Membrane Protein 2 - metabolism; mouse; synaptobrevin; exocytosis; neurotransmitter release; neuroscience; membrane fusion
• ISSN: 2050-084X; 2050-084X
• DOI: 10.7554/eLife.17571

Vesicle fusion is mediated by an assembly of SNARE proteins between opposing membranes, but it is unknown whether transmembrane domains (TMDs) of SNARE proteins serve mechanistic functions that go beyond passive anchoring of the force-generating SNAREpin to the fusing membranes. Here, we show that conformational flexibility of synaptobrevin-2 TMD is essential for efficient Ca(2+)-triggered exocytosis and actively promotes membrane fusion as well as fusion pore expansion. Specifically, the introduction of helix-stabilizing leucine residues within the TMD region spanning the vesicle's outer leaflet strongly impairs exocytosis and decelerates fusion pore dilation. In contrast, increasing the number of helix-destabilizing, ß-branched valine or isoleucine residues within the TMD restores normal secretion but accelerates fusion pore expansion beyond the rate found for the wildtype protein. These observations provide evidence that the synaptobrevin-2 TMD catalyzes the fusion process by its structural flexibility, actively setting the pace of fusion pore expansion.