Synaptotagmin-1 binds to PIP(2)-containing membrane but not to SNAREs at physiological ionic strength

Nat Struct Mol Biol. 2015 Oct;22(10):815-23. doi: 10.1038/nsmb.3097. Epub 2015 Sep 21.


The Ca(2+) sensor synaptotagmin-1 is thought to trigger membrane fusion by binding to acidic membrane lipids and SNARE proteins. Previous work has shown that binding is mediated by electrostatic interactions that are sensitive to the ionic environment. However, the influence of divalent or polyvalent ions, at physiological concentrations, on synaptotagmin's binding to membranes or SNAREs has not been explored. Here we show that binding of rat synaptotagmin-1 to membranes containing phosphatidylinositol 4,5-bisphosphate (PIP2) is regulated by charge shielding caused by the presence of divalent cations. Surprisingly, polyvalent ions such as ATP and Mg(2+) completely abrogate synaptotagmin-1 binding to SNAREs regardless of the presence of Ca(2+). Altogether, our data indicate that at physiological ion concentrations Ca(2+)-dependent synaptotagmin-1 binding is confined to PIP2-containing membrane patches in the plasma membrane, suggesting that membrane interaction of synaptotagmin-1 rather than SNARE binding triggers exocytosis of vesicles.

Publication types

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

MeSH terms

  • Animals
  • Calcium / metabolism
  • Cations, Divalent / metabolism
  • Cell Membrane / metabolism*
  • Chromaffin Granules / metabolism
  • Chromatography, Ion Exchange
  • Exocytosis / physiology*
  • Fluorescence Polarization
  • Fluorescence Resonance Energy Transfer
  • Models, Molecular*
  • Models, Theoretical
  • Patch-Clamp Techniques
  • Phosphatidylinositol 4,5-Diphosphate / metabolism*
  • Protein Conformation
  • Rats
  • SNARE Proteins / metabolism
  • Spectrum Analysis
  • Synaptotagmin I / chemistry*
  • Synaptotagmin I / metabolism*


  • Cations, Divalent
  • Phosphatidylinositol 4,5-Diphosphate
  • SNARE Proteins
  • Synaptotagmin I
  • Syt1 protein, rat
  • Calcium