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Ca 2+ releases E‐Syt1 autoinhibition to couple ER ‐plasma membrane tethering with lipid transport
Author(s) -
Bian Xin,
Saheki Yasunori,
De Camilli Pietro
Publication year - 2017
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.15252/embj.201797359
Subject(s) - endoplasmic reticulum , phosphatidylserine , microbiology and biotechnology , tethering , membrane contact site , chemistry , membrane , diacylglycerol kinase , biophysics , biochemistry , biology , membrane protein , phosphorylation , integral membrane protein , phospholipid , protein kinase c
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 Ca 2+ ‐dependent manner, but the role of Ca 2+ in this regulation is unclear. Of the five C2 domains of E‐Syt1, only C2A and C2C contain Ca 2+ ‐binding sites. Using liposome‐based assays, we show that Ca 2+ binding to C2C promotes E‐Syt1‐mediated membrane tethering by releasing an inhibition that prevents C2E from interacting with PI (4,5)P 2 ‐rich membranes, as previously suggested by studies in semi‐permeabilized cells. Importantly, Ca 2+ 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 Ca 2+ 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 Ca 2+ ‐triggered phosphatidylserine scrambling. Thus, a main effect of Ca 2+ on E‐Syt1 is to reverse an autoinhibited state and to couple membrane tethering with lipid transport.