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A more recent version of this article appeared on June 1, 2007
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Submitted on January 24, 2007
Accepted on March 2, 2007
Departments of *Neurobiology and Molecular Biology, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen, Germany
Monitoring Editor: Patrick Brennwald
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 while 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.
Molecular NeuroPathology Laboratory, Cancer Research UK London Research Institute, 44 Lincoln’s Inn Fields, WC2A 3PX, United Kingdom; King’s College London, Randall Division of Cell and Molecular Biophysics, New Hunt’s House, Guy’s Campus, London SE1 1UL, United Kingdom.
Address correspondence to:
Dirk Fasshauer (dfassha{at}gwdg.de)
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