title: Munc18-1 and the Syntaxin-1 N Terminus Regulate Open-Closed States in a t-SNARE Complex.
abstract: Neuronal exocytosis is mediated by SNARE proteins, which assemble into a highly stable four-helical bundle in a process that is not well understood. Here, electron paramagnetic resonance spectroscopy was used to examine how the t-SNAREs syntaxin and SNAP25 assemble in the presence and absence of the regulatory protein Munc18-1. Syntaxin and SNAP25 form a 2:1 complex, which is structurally heterogeneous and persists in the presence of excess SNAP25. Munc18-1 dissociates this 2:1 complex, but a 1:1 complex is retained where syntaxin is in a closed state. In the absence of an N-terminal fragment of syntaxin, Munc18-1 also stabilizes a 1:1 complex of sytaxin/SNAP25; however, syntaxin now samples an open state. These data demonstrate that the open-closed syntaxin equilibrium is shifted toward the open state when syntaxin and Munc18-1 are associated with SNAP25, and the results indicate that a syntaxin/SNAP25:Munc18-1 complex is a likely starting point for SNARE assembly.
authors.affiliation: Department of Chemistry, Center for Membrane Biology at the University of Virginia, McCormick Road, Charlottesville, VA 22904-4319, USA.
authors.forename: Damian
authors.initials: D
authors.lastname: Dawidowski
authors.affiliation: Department of Chemistry, Center for Membrane Biology at the University of Virginia, McCormick Road, Charlottesville, VA 22904-4319, USA. Electronic address: cafiso@virginia.edu.
authors.forename: David S
authors.initials: DS
authors.lastname: Cafiso
mesh_terms: D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D051938:Munc18 Proteins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D051381:Rats; D050600:SNARE Proteins / Q000378:metabolism*; D050825:Synaptosomal-Associated Protein 25 / Q000378:metabolism*; D050827:Syntaxin 1 / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D051938:Munc18 Proteins; D050600:SNARE Proteins; C494210:Snap25 protein, rat; C494213:Stx1a protein, rat; C497939:Stxbp1 protein, rat; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1