title: NMR analysis of the closed conformation of syntaxin-1.
abstract: The Sec1/Munc18 (SM) protein Munc18-1 and the SNAREs syntaxin-1, SNAP-25 and synaptobrevin form the core of the membrane fusion machinery that triggers neurotransmitter release. Munc18-1 binds to syntaxin-1 folded into a closed conformation and to the SNARE complex formed by the three SNAREs, which involves an open syntaxin-1 conformation. The former interaction is likely specialized for neurotransmitter release, whereas SM protein/SNARE complex interactions are likely key for all types of intracellular membrane fusion. It is currently unclear whether the closed conformation is highly or only marginally populated in isolated syntaxin-1, and whether Munc18-1 stabilizes the close conformation or helps to open it to facilitate SNARE complex formation. A detailed NMR analysis now suggests that the closed conformation is almost quantitatively populated in isolated syntaxin-1 in the absence of oligomerization, and indicates that its structure is very similar to that observed previously in the crystal structure of the Munc18-1/syntaxin-1 complex. Moreover, we demonstrate that Munc18-1 binding prevents opening of the syntaxin-1 closed conformation. These results support a model whereby the closed conformation constitutes a key intrinsic property of isolated syntaxin-1 and Munc18-1 binding stabilizes this conformation; in this model, Munc18-1 plays in addition an active role in downstream events after another factor(s) helps to open the syntaxin-1 conformation.
authors.affiliation: Department of Biochemistry, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA.
authors.forename: Xiaocheng
authors.initials: X
authors.lastname: Chen
authors.forename: Jun
authors.initials: J
authors.lastname: Lu
authors.forename: Irina
authors.initials: I
authors.lastname: Dulubova
authors.forename: Josep
authors.initials: J
authors.lastname: Rizo
mesh_terms: D008958:Models, Molecular; D051938:Munc18 Proteins / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D050827:Syntaxin 1 / Q000737:chemistry*
chemical_list: D051938:Munc18 Proteins; D050827:Syntaxin 1