An activated Q-SNARE/SM protein complex as a possible intermediate in SNARE assembly

EMBO J. 2017 Jun 14;36(12):1788-1802. doi: 10.15252/embj.201696270. Epub 2017 May 8.


Assembly of the SNARE proteins syntaxin1, SNAP25, and synaptobrevin into a SNARE complex is essential for exocytosis in neurons. For efficient assembly, SNAREs interact with additional proteins but neither the nature of the intermediates nor the sequence of protein assembly is known. Here, we have characterized a ternary complex between syntaxin1, SNAP25, and the SM protein Munc18-1 as a possible acceptor complex for the R-SNARE synaptobrevin. The ternary complex binds synaptobrevin with fast kinetics, resulting in the rapid formation of a fully zippered SNARE complex to which Munc18-1 remains tethered by the N-terminal domain of syntaxin1. Intriguingly, only one of the synaptobrevin truncation mutants (Syb1-65) was able to bind to the syntaxin1:SNAP25:Munc18-1 complex, suggesting either a cooperative zippering mechanism that proceeds bidirectionally or the progressive R-SNARE binding via an SM template. Moreover, the complex is resistant to disassembly by NSF Based on these findings, we consider the ternary complex as a strong candidate for a physiological intermediate in SNARE assembly.

Keywords: SNARE; Munc18; NSF; SM‐protein; intermediates.

Publication types

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

MeSH terms

  • Animals
  • Mice
  • Munc18 Proteins / metabolism*
  • Protein Binding
  • Protein Multimerization*
  • R-SNARE Proteins / metabolism*
  • Synaptosomal-Associated Protein 25 / metabolism*
  • Syntaxin 1 / metabolism*


  • Munc18 Proteins
  • R-SNARE Proteins
  • Snap25 protein, mouse
  • Stxbp1 protein, mouse
  • Synaptosomal-Associated Protein 25
  • Syntaxin 1