Syntaxin1a variants lacking an N-peptide or bearing the LE mutation bind to Munc18a in a closed conformation

Proc Natl Acad Sci U S A. 2013 Jul 30;110(31):12637-42. doi: 10.1073/pnas.1303753110. Epub 2013 Jul 15.


In neurons, soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins drive the fusion of synaptic vesicles to the plasma membrane through the formation of a four-helix SNARE complex. Members of the Sec1/Munc18 protein family regulate membrane fusion through interactions with the syntaxin family of SNARE proteins. The neuronal protein Munc18a interacts with a closed conformation of the SNARE protein syntaxin1a (Syx1a) and with an assembled SNARE complex containing Syx1a in an open conformation. The N-peptide of Syx1a (amino acids 1-24) has been implicated in the transition of Munc18a-bound Syx1a to Munc18a-bound SNARE complex, but the underlying mechanism is not understood. Here we report the X-ray crystal structures of Munc18a bound to Syx1a with and without its native N-peptide (Syx1aΔN), along with small-angle X-ray scattering (SAXS) data for Munc18a bound to Syx1a, Syx1aΔN, and Syx1a L165A/E166A (LE), a mutation thought to render Syx1a in a constitutively open conformation. We show that all three complexes adopt the same global structure, in which Munc18a binds a closed conformation of Syx1a. We also identify a possible structural connection between the Syx1a N-peptide and SNARE domain that might be important for the transition of closed-to-open Syx1a in SNARE complex assembly. Although the role of the N-peptide in Munc18a-mediated SNARE complex assembly remains unclear, our results demonstrate that the N-peptide and LE mutation have no effect on the global conformation of the Munc18a-Syx1a complex.

Keywords: SM proteins; membrane trafficking; protein crystallography.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Substitution*
  • Humans
  • Munc18 Proteins / chemistry*
  • Munc18 Proteins / genetics
  • Munc18 Proteins / metabolism
  • Peptides*
  • Protein Binding
  • Protein Structure, Quaternary
  • Protein Structure, Secondary
  • SNARE Proteins / chemistry
  • SNARE Proteins / genetics
  • SNARE Proteins / metabolism
  • Sequence Deletion*
  • Syntaxin 1 / chemistry*
  • Syntaxin 1 / genetics
  • Syntaxin 1 / metabolism


  • Munc18 Proteins
  • Peptides
  • SNARE Proteins
  • STX1A protein, human
  • STXBP1 protein, human
  • Syntaxin 1

Associated data

  • PDB/4JEH
  • PDB/4JEU