title: v-SNARE transmembrane domains function as catalysts for vesicle fusion.
abstract: 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.
authors.affiliation: Institute for Physiology, Saarland University, Homburg, Germany.
authors.forename: Madhurima
authors.initials: M
authors.lastname: Dhara
authors.affiliation: Institute for Physiology, Saarland University, Homburg, Germany.
authors.forename: Antonio
authors.initials: A
authors.lastname: Yarzagaray
authors.affiliation: Institute for Physiology, Saarland University, Homburg, Germany.
authors.forename: Mazen
authors.initials: M
authors.lastname: Makke
authors.affiliation: Institute for Physiology, Saarland University, Homburg, Germany.
authors.forename: Barbara
authors.initials: B
authors.lastname: Schindeldecker
authors.affiliation: Institute for Physiology, Saarland University, Homburg, Germany.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Schwarz
authors.affiliation: Zentrum für Human- und Molekularbiologie, Saarland University, Homburg, Germany.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Shaaban
authors.affiliation: Group Nanoscale Cell Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
authors.forename: Satyan
authors.initials: S
authors.lastname: Sharma
authors.affiliation: Computational Biology, Department of Biology, Friedrich-Alexander University, Erlangen, Germany.
authors.forename: Rainer A
authors.identifier: 0000-0002-9325-5162
authors.initials: RA
authors.lastname: Böckmann
authors.affiliation: Group Nanoscale Cell Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
authors.forename: Manfred
authors.initials: M
authors.lastname: Lindau
authors.affiliation: Zentrum für Human- und Molekularbiologie, Saarland University, Homburg, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Mohrmann
authors.affiliation: Institute for Physiology, Saarland University, Homburg, Germany.
authors.forename: Dieter
authors.identifier: 0000-0002-2497-1878
authors.initials: D
authors.lastname: Bruns
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004252:DNA Mutational Analysis; D005089:Exocytosis; D008561:Membrane Fusion; D051379:Mice; D008954:Models, Biological; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011487:Protein Conformation; D022142:Secretory Vesicles / Q000378:metabolism*; D050988:Vesicle-Associated Membrane Protein 2 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: D050505:Mutant Proteins; D050988:Vesicle-Associated Membrane Protein 2
keywords: exocytosis; membrane fusion; mouse; neuroscience; neurotransmitter release; synaptobrevin