Complexin Suppresses Spontaneous Exocytosis by Capturing the Membrane-Proximal Regions of VAMP2 and SNAP25

Cell Rep. 2020 Jul 21;32(3):107926. doi: 10.1016/j.celrep.2020.107926.


The neuronal protein complexin contains multiple domains that exert clamping and facilitatory functions to tune spontaneous and action potential-triggered synaptic release. We address the clamping mechanism and show that the accessory helix of complexin arrests assembly of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex that forms the core machinery of intracellular membrane fusion. In a reconstituted fusion assay, site- and stage-specific photo-cross-linking reveals that, prior to fusion, the complexin accessory helix laterally binds the membrane-proximal C-terminal ends of SNAP25 and VAMP2. Corresponding complexin interface mutants selectively increase spontaneous release of neurotransmitters in living neurons, implying that the accessory helix suppresses final zippering/assembly of the SNARE four-helix bundle by restraining VAMP2 and SNAP25.

Keywords: SNARE; complexin; cross-linking; membrane fusion; neurotransmission; synaptotagmin; syntaxin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calcium / metabolism
  • Cell Membrane / metabolism*
  • Cross-Linking Reagents / chemistry
  • Exocytosis*
  • Humans
  • Light
  • Membrane Fusion
  • Models, Biological
  • Mutant Proteins / metabolism
  • Neurons / metabolism
  • Neurotransmitter Agents / metabolism
  • Protein Binding
  • Protein Interaction Mapping
  • Protein Structure, Secondary
  • Proteolipids / metabolism
  • Synapses / metabolism
  • Synaptic Vesicles / metabolism
  • Synaptosomal-Associated Protein 25 / chemistry*
  • Synaptosomal-Associated Protein 25 / metabolism*
  • Vesicle-Associated Membrane Protein 2 / chemistry*
  • Vesicle-Associated Membrane Protein 2 / metabolism*


  • Cross-Linking Reagents
  • Mutant Proteins
  • Neurotransmitter Agents
  • Proteolipids
  • Synaptosomal-Associated Protein 25
  • Vesicle-Associated Membrane Protein 2
  • proteoliposomes
  • Calcium