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Biophys J. 2017 Sep 19;113(6):1235-1250. doi: 10.1016/j.bpj.2017.04.002. Epub 2017 Apr 26.

Complexin Binding to Membranes and Acceptor t-SNAREs Explains Its Clamping Effect on Fusion.

Author information

1
Department of Chemistry, University of Virginia, Charlottesville, Virginia; Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, Virginia.
2
Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, Virginia; Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia.
3
Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, Virginia; Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia. Electronic address: lkt2e@virginia.edu.
4
Department of Chemistry, University of Virginia, Charlottesville, Virginia; Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, Virginia. Electronic address: cafiso@virginia.edu.

Abstract

Complexin-1 is a SNARE effector protein that decreases spontaneous neurotransmitter release and enhances evoked release. Complexin binds to the fully assembled four-helical neuronal SNARE core complex as revealed in competing molecular models derived from x-ray crystallography. Presently, it is unclear how complexin binding to the postfusion complex accounts for its effects upon spontaneous and evoked release in vivo. Using a combination of spectroscopic and imaging methods, we characterize in molecular detail how complexin binds to the 1:1 plasma membrane t-SNARE complex of syntaxin-1a and SNAP-25 while simultaneously binding the lipid bilayer at both its N- and C-terminal ends. These interactions are cooperative, and binding to the prefusion acceptor t-SNARE complex is stronger than to the postfusion core complex. This complexin interaction reduces the affinity of synaptobrevin-2 for the 1:1 complex, thereby retarding SNARE assembly and vesicle docking in vitro. The results provide the basis for molecular models that account for the observed clamping effect of complexin beginning with the acceptor t-SNARE complex and the subsequent activation of the clamped complex by Ca2+ and synaptotagmin.

PMID:
28456331
PMCID:
PMC5607037
DOI:
10.1016/j.bpj.2017.04.002
[Indexed for MEDLINE]
Free PMC Article

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