A mechanism for exocytotic arrest by the Complexin C-terminus

Elife. 2018 Jul 25;7:e38981. doi: 10.7554/eLife.38981.

Abstract

ComplexinII (CpxII) inhibits non-synchronized vesicle fusion, but the underlying mechanisms have remained unclear. Here, we provide evidence that the far C-terminal domain (CTD) of CpxII interferes with SNARE assembly, thereby arresting tonic exocytosis. Acute infusion of a CTD-derived peptide into mouse chromaffin cells enhances synchronous release by diminishing premature vesicle fusion like full-length CpxII, indicating a direct, inhibitory function of the CTD that sets the magnitude of the primed vesicle pool. We describe a high degree of structural similarity between the CpxII CTD and the SNAP25-SN1 domain (C-terminal half) and show that the CTD peptide lowers the rate of SDS-resistant SNARE complex formation in vitro. Moreover, corresponding CpxII:SNAP25 chimeras do restore complexin's function and even 'superclamp' tonic secretion. Collectively, these results support a so far unrecognized clamping mechanism wherein the CpxII C-terminus hinders spontaneous SNARE complex assembly, enabling the build-up of a release-ready pool of vesicles for synchronized Ca2+-triggered exocytosis.

Keywords: SNAREs; complexin; exocytotic arrest; mouse; neuroscience; neurotransmitter release; vesicle fusion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Vesicular Transport / chemistry*
  • Adaptor Proteins, Vesicular Transport / genetics
  • Animals
  • Calcium / chemistry
  • Cell Membrane / chemistry
  • Cell Membrane / genetics
  • Exocytosis / genetics*
  • Membrane Fusion / genetics
  • Mice
  • Nerve Tissue Proteins / chemistry*
  • Nerve Tissue Proteins / genetics
  • Protein Binding
  • Protein Domains / genetics
  • SNARE Proteins / chemistry
  • SNARE Proteins / genetics
  • Synaptic Vesicles / chemistry*
  • Synaptic Vesicles / genetics
  • Synaptosomal-Associated Protein 25 / chemistry*
  • Synaptosomal-Associated Protein 25 / genetics

Substances

  • Adaptor Proteins, Vesicular Transport
  • Nerve Tissue Proteins
  • SNARE Proteins
  • Synaptosomal-Associated Protein 25
  • complexin II
  • Calcium