Ackema KB, Prescianotto-Baschong C, Hench J, Wang SC, Chia ZH, Mergentaler H, Bard F, Frank S, Spang A. Sar1, a Novel Regulator of ER-Mitochondrial Contact Sites.
PLoS One 2016;
11:e0154280. [PMID:
27101143 PMCID:
PMC4839682 DOI:
10.1371/journal.pone.0154280]
[Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Accepted: 04/10/2016] [Indexed: 01/14/2023] Open
Abstract
Endoplasmic reticulum (ER)—mitochondrial contact sites play a pivotal role in exchange of lipids and ions between the two organelles. How size and function of these contact sites are regulated remains elusive. Here we report a previously unanticipated, but conserved role of the small GTPase Sar1 in the regulation of ER-mitochondrial contact site size. Activated Sar1 introduces membrane curvature through its N-terminal amphiphatic helix at the ER-mitochondria interphase and thereby reducing contact size. Conversely, the S. cerevisiae N3-Sar1 mutant, in which curvature induction is decreased, caused an increase in ER-mitochondrial contacts. As a consequence, ER tubules are no longer able to mark the prospective scission site on mitochondria, thereby impairing mitochondrial dynamics. Consistently, blocking mitochondrial fusion partially rescued, whereas deletion of the dynamin-like protein enhanced the phenotype in the sar1D32G mutant. We conclude that Sar1 regulates the size of ER-mitochondria contact sites through its effects on membrane curvature.
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