Control of plasma membrane lipid homeostasis by the extended synaptotagmins

Abstract

Acute metabolic changes of plasma membrane (PM) lipids, such as those mediating signaling reactions, are rapidly compensated by homeostatic responses whose molecular basis is poorly understood. Here we show that the Extended-Synaptotagmins (E-Syts), ER proteins which function as PI(4,5)P2 and Ca2+-regulated tethers to the PM, participate in these responses. E-Syts transfer glycerolipids between bilayers in vitro and such transfer requires Ca2+ and their SMP domain, a lipid-harboring module. Genome edited cells lacking E-Syts do not exhibit abnormalities in the major glycerolipids at rest, but display enhanced and sustained accumulation of PM diacylglycerol (DAG) upon PI(4,5)P2 hydrolysis by PLC activation, which can be rescued by expression of E-Syt1, but not by mutant E-Syt1 lacking the SMP domain. The formation of E-Syts-dependent ER-PM tethers in response to stimuli that cleave PI(4,5)P2 and elevate Ca2+ may help reverse accumulation of DAG in the PM by transferring it to the ER for metabolic recycling.

Trifunctional lipid probes for comprehensive studies of single lipid species in living cells

“…We speculate that the high proportion of cytosolic proteins likely reflects a highly efficient DAG transporting machinery, which requires extraction of DAG from membranes, thereby potentially exposing the cross-linkable group. For example, extended synaptotagmins (E-Syts) were recently shown to extract DAG from the plasma membrane (28). Accordingly, we identified both E-Syt1 and E-Syt2 in screens performed with TFDAG.…”

Shaping the Endoplasmic Reticulum into a Social Network

“…ER-PM tethering can also be mediated by numerous lipid transfer proteins. ER-localized E-Syts engage PI(4,5)P 2 on the PM via their C2 domains [37], and their SMP domain is shown to be a lipid transfer module [38][39][40]. Such interactions are thought to be sensitive to the levels of cytosolic Ca 2+ [41].…”

Single-molecule force spectroscopy of protein-membrane interactions

“…Previous experiments have shown that membrane binding of C2 domains are differentially sensitive to Ca 2+ concentration, ionic strength, and lipid composition, which is pivotal for the biological functions of the proteins harboring C2 domains Saheki et al, 2016;Fernández-Busnadiego et al, 2015;Giordano et al, 2013). To characterize the Ca 2+ -dependence of E-Syt2 C2AB binding to membranes, we first observed its reversible membrane binding in 100 mM Ca 2+ at constant mean force of 3.8 pN ( Figure 4A, black region).…”

“…Different from Syts, E-Syts are located on the endoplasmic reticulum membrane and contain five (for E-Syt1) or three (for E-Syt2 and E-Syt3) C2 domains in addition to the SMP domain (Min et al, 2007;Giordano et al, 2013). E-Syt C2 domains regulate lipid transfer, instead of membrane fusion, between the endoplasmic reticulum and the plasma membrane via the SMP domain (Giordano et al, 2013;Saheki et al, 2016;Yu et al, 2016;Schauder et al, 2014). Therefore, both Syts and E-Syts bind membranes in trans through their multiple C2 domains and are well-positioned to generate force to draw two membranes into proximity required for membrane fusion or lipid exchange (van den Bogaart et al, 2011;Lin et al, 2014;Krishnakumar et al, 2013).…”