Dual modes of Munc18-1/SNARE interactions are coupled by functionally critical binding to syntaxin-1 N terminus

Mikhail Khvotchev, Irina Dulubova, Jianyuan Sun, Han Dai, Jose Rizo-Rey, Thomas C. Südhof

Research output: Contribution to journalArticle

102 Scopus citations

Abstract

The SM (Sec1/Munc18-like) protein Munc18-1 and the soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) proteins syntaxin-1, SNAP-25, and synaptobrevin/VAMP (vesicle-associated membrane protein) constitute the core fusion machinery for synaptic vesicle exocytosis. Strikingly, Munc18-1 interacts with neuronal SNARE proteins in two distinct modes (i.e., with isolated syntaxin-1 alone in a "closed" conformation and with assembled SNARE complexes containing syntaxin-1 in an "open" conformation). However, it is unclear whether the two modes of Munc18/SNARE interactions are linked. We now show that both Munc18/ SNARE interaction modes involve the same low-affinity binding of the extreme syntaxin-1 N terminus to Munc18-1, suggesting that this binding connects the two Munc18/SNARE interaction modes to each other. Using transfected cells as an in vitro assay system, we demonstrate that truncated syntaxins lacking a transmembrane region universally block exocytosis, but only if they contain a free intact Nterminus. This block is enhanced by coexpression of either Munc18-1 or SNAP-25, suggesting that truncated syntaxins block exocytosis by forming an untethered inhibitory SNARE complex/Munc18-1 assembly in which the N-terminal syntaxin/Munc18 interaction is essential. Introduction of an N-terminal syntaxin peptide that disrupts this assembly blocks neurotransmitter release in the calyx of Held synapse, whereas a mutant peptide that does not disrupt the SNARE complex/Munc18 assembly has no effect. Viewed together, our data indicate that binding of Munc18 to the syntaxin N terminus unites different modes of Munc18/SNARE interactions and is essential for exocytic membrane fusion.

Original languageEnglish (US)
Pages (from-to)12147-12155
Number of pages9
JournalJournal of Neuroscience
Volume27
Issue number45
DOIs
StatePublished - Nov 7 2007

Keywords

  • Calyx of Held
  • FRET
  • Membrane fusion
  • Munc18
  • Neurotransmitter release
  • SM proteins
  • SNARE proteins
  • Synaptic vesicle exocytosis

ASJC Scopus subject areas

  • Neuroscience(all)

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