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

Ca2+ releases E-Syt1 autoinhibition to couple ER-plasma membrane tethering with lipid transport.

Bian X1,2,3,4, Saheki Y5,2,3,4,6, De Camilli P5,2,3,4,7.

Author information

1
Department of Neuroscience, Yale University School of Medicine, New Haven, CT, USA.
2
Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.
3
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT, USA.
4
Program in Cellular Neuroscience, Neurodegeneration, and Repair, Yale University School of Medicine, New Haven, CT, USA.
5
Department of Neuroscience, Yale University School of Medicine, New Haven, CT, USA yasunori.saheki@ntu.edu.sg pietro.decamilli@yale.edu.
6
Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Singapore.
7
Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT, USA.

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

PMID:
29222176
PMCID:
PMC5770786
DOI:
10.15252/embj.201797359
[Indexed for MEDLINE]
Free PMC Article

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