title: Determinants of synaptobrevin regulation in membranes.
abstract: Neuronal exocytosis is driven by the formation of SNARE complexes between synaptobrevin 2 on synaptic vesicles and SNAP-25/syntaxin 1 on the plasma membrane. It has remained controversial, however, whether SNAREs are constitutively active or whether they are down-regulated until fusion is triggered. We now show that synaptobrevin in proteoliposomes as well as in purified synaptic vesicles is constitutively active. Potential regulators such as calmodulin or synaptophysin do not affect SNARE activity. Substitution or deletion of residues in the linker connecting the SNARE motif and transmembrane region did not alter the kinetics of SNARE complex assembly or of SNARE-mediated fusion of liposomes. Remarkably, deletion of C-terminal residues of the SNARE motif strongly reduced fusion activity, although the overall stability of the complexes was not affected. We conclude that although complete zippering of the SNARE complex is essential for membrane fusion, the structure of the adjacent linker domain is less critical, suggesting that complete SNARE complex assembly not only connects membranes but also drives fusion.
authors.affiliation: Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
authors.forename: Tabrez J
authors.initials: TJ
authors.lastname: Siddiqui
authors.forename: Olga
authors.initials: O
authors.lastname: Vites
authors.forename: Alexander
authors.initials: A
authors.lastname: Stein
authors.forename: Rainer
authors.initials: R
authors.lastname: Heintzmann
authors.forename: Reinhard
authors.initials: R
authors.lastname: Jahn
authors.forename: Dirk
authors.initials: D
authors.lastname: Fasshauer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology*; D006801:Humans; D008561:Membrane Fusion / Q000502:physiology; D008969:Molecular Sequence Data; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D011510:Proteolipids / Q000378:metabolism; D050683:R-SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D050600:SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D013572:Synaptic Vesicles / Q000378:metabolism / Q000648:ultrastructure; D016708:Synaptophysin / Q000378:metabolism
chemical_list: D002147:Calmodulin; D011510:Proteolipids; D050683:R-SNARE Proteins; D050600:SNARE Proteins; D016708:Synaptophysin; C020485:proteoliposomes; D002118:Calcium