A Quaternary SNARE-Synaptotagmin-Ca2+-Phospholipid Complex in Neurotransmitter Release

Han Dai, Nan Shen, Demet Araç, Jose Rizo-Rey

Research output: Contribution to journalArticle

92 Scopus citations

Abstract

The function of synaptotagmin as a Ca2+ sensor in neurotransmitter release involves Ca2+-dependent phospholipid binding to its two C2 domains, but this activity alone does not explain why Ca2+ binding to the C2B domain is more critical for release than Ca2+ binding to the C2A domain. Synaptotagmin also binds to SNARE complexes, which are central components of the membrane fusion machinery, and displaces complexins from the SNAREs. However, it is unclear how phospholipid binding to synaptotagmin is coupled to SNARE binding and complexin displacement. Using supported lipid bilayers deposited within microfluidic channels, we now show that Ca2+ induces simultaneous binding of synaptotagmin to phospholipid membranes and SNARE complexes, resulting in an intimate quaternary complex that we name SSCAP complex. Mutagenesis experiments show that Ca2+ binding to the C2B domain is critical for SSCAP complex formation and displacement of complexin, providing a clear rationale for the preponderant role of the C2B domain in release. This and other correlations between the effects of mutations on SSCAP complex formation and their functional effects in vivo suggest a key role for this complex in release. We propose a model whereby the highly positive electrostatic potential at the tip of the SSCAP complex helps to induce membrane fusion during release.

Original languageEnglish (US)
Pages (from-to)848-863
Number of pages16
JournalJournal of Molecular Biology
Volume367
Issue number3
DOIs
StatePublished - Mar 30 2007

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Keywords

  • Ca binding
  • SNAREs
  • neurotransmitter release
  • phospholipid binding
  • synaptotagmin

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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