title: Accessory proteins stabilize the acceptor complex for synaptobrevin, the 1:1 syntaxin/SNAP-25 complex.
abstract: Syntaxin/SNAP-25 interactions precede assembly of the ternary SNARE complex that is essential for neurotransmitter release. This binary complex has been difficult to characterize by bulk methods because of the prevalence of a 2:1 dead-end species. Here, using single-molecule fluorescence, we find the structure of the 1:1 syntaxin/SNAP-25 binary complex is variable, with states changing on the second timescale. One state corresponds to a parallel three-helix bundle, whereas other states show one of the SNAP-25 SNARE domains dissociated. Adding synaptobrevin suppresses the dissociated helix states. Remarkably, upon addition of complexin, Munc13, Munc18, or synaptotagmin, a similar effect is observed. Thus, the 1:1 binary complex is a dynamic acceptor for synaptobrevin binding, and accessory proteins stabilize this acceptor. In the cellular environment the binary complex is actively maintained in a configuration where it can rapidly interact with synaptobrevin, so formation is not likely a limiting step for neurotransmitter release.
authors.affiliation: Department of Physics, North Carolina State University, Raleigh, NC 27695-8202, USA.
authors.forename: Keith
authors.initials: K
authors.lastname: Weninger
authors.forename: Mark E
authors.initials: ME
authors.lastname: Bowen
authors.forename: Ucheor B
authors.initials: UB
authors.lastname: Choi
authors.forename: Steven
authors.initials: S
authors.lastname: Chu
authors.forename: Axel T
authors.initials: AT
authors.lastname: Brunger
mesh_terms: D031541:Fluorescence Resonance Energy Transfer; D008051:Lipid Bilayers / Q000378:metabolism; D017434:Protein Structure, Tertiary; D050765:Qa-SNARE Proteins / Q000737:chemistry* / Q000378:metabolism; D050683:R-SNARE Proteins / Q000378:metabolism*; D050600:SNARE Proteins / Q000378:metabolism*; D050825:Synaptosomal-Associated Protein 25 / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008051:Lipid Bilayers; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D050600:SNARE Proteins; D050825:Synaptosomal-Associated Protein 25