Munc18-1 and the Syntaxin-1 N Terminus Regulate Open-Closed States in a t-SNARE Complex

Structure. 2016 Mar 1;24(3):392-400. doi: 10.1016/j.str.2016.01.005. Epub 2016 Feb 11.


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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Binding Sites
  • Crystallography, X-Ray
  • Models, Molecular
  • Munc18 Proteins / chemistry
  • Munc18 Proteins / metabolism*
  • Protein Binding
  • Protein Structure, Secondary
  • Rats
  • SNARE Proteins / metabolism*
  • Synaptosomal-Associated Protein 25 / metabolism*
  • Syntaxin 1 / chemistry*
  • Syntaxin 1 / metabolism*


  • Munc18 Proteins
  • SNARE Proteins
  • Snap25 protein, rat
  • Stx1a protein, rat
  • Stxbp1 protein, rat
  • Synaptosomal-Associated Protein 25
  • Syntaxin 1