Ca 2+ releases E-Syt1 autoinhibition to couple ER-plasma membrane tethering with lipid transport

EMBO J. 2018 Jan 17;37(2):219-234. doi: 10.15252/embj.201797359. Epub 2017 Dec 8.

Abstract

The extended synaptotagmins (E-Syts) are endoplasmic reticulum (ER) proteins that bind the plasma membrane (PM) via C2 domains and transport lipids between them via SMP domains. E-Syt1 tethers and transports lipids in a Ca2+-dependent manner, but the role of Ca2+ in this regulation is unclear. Of the five C2 domains of E-Syt1, only C2A and C2C contain Ca2+-binding sites. Using liposome-based assays, we show that Ca2+ binding to C2C promotes E-Syt1-mediated membrane tethering by releasing an inhibition that prevents C2E from interacting with PI(4,5)P2-rich membranes, as previously suggested by studies in semi-permeabilized cells. Importantly, Ca2+ binding to C2A enables lipid transport by releasing a charge-based autoinhibitory interaction between this domain and the SMP domain. Supporting these results, E-Syt1 constructs defective in Ca2+ binding in either C2A or C2C failed to rescue two defects in PM lipid homeostasis observed in E-Syts KO cells, delayed diacylglycerol clearance from the PM and impaired Ca2+-triggered phosphatidylserine scrambling. Thus, a main effect of Ca2+ on E-Syt1 is to reverse an autoinhibited state and to couple membrane tethering with lipid transport.

Keywords: C2 domain; SMP domain; extended synaptotagmin; lipid transfer; phosphatidylserine scrambling.

Publication types

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

MeSH terms

  • Biological Transport, Active / physiology
  • Calcium / metabolism*
  • Calcium Signaling / physiology*
  • Cell Line
  • Cell Membrane / genetics
  • Cell Membrane / metabolism*
  • Endoplasmic Reticulum / genetics
  • Endoplasmic Reticulum / metabolism*
  • Humans
  • Lipid Metabolism / physiology*
  • Phosphatidylinositol 4,5-Diphosphate / genetics
  • Phosphatidylinositol 4,5-Diphosphate / metabolism
  • Protein Domains
  • Synaptotagmins / genetics
  • Synaptotagmins / metabolism*

Substances

  • ESYT1 protein, human
  • Phosphatidylinositol 4,5-Diphosphate
  • Synaptotagmins
  • Calcium