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Homeostatic Regulation of Serine Palmitoyltransferase (SPT) is Mediated by a Direct Interaction of Ceramide with the SPT/ORMDL Complex
Author(s) -
Davis Deanna,
Wattenberg Binks
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.946.1
Subject(s) - sphingolipid , ceramide , sphingosine , microbiology and biotechnology , lipid signaling , biology , signal transduction , phosphorylation , endoplasmic reticulum , biochemistry , cytosol , ceramide synthase , enzyme , receptor , apoptosis
Sphingolipids, the large class of lipids based on the sphingosine backbone, have diverse functions in health and disease. The overall rate of synthesis of the sphingolipid pool is determined by serine palmitoyltransferase (SPT), the initiating enzyme in the de novo biosynthetic pathway. SPT is subject to homeostatic regulation such that elevated cellular sphingolipid results in decreased SPT activity. This regulation is mediated by small proteins of the endoplasmic reticulum: the Orms in yeast and ORMDLs in mammalian cells. The Orms and ORMDLs are negative regulators of SPT. Here we describe the mechanism by which sphingolipids are sensed by the ORMDL/SPT system. The mammalian ORMDLs are not phosphorylated under any conditions, in contrast to the yeast Orms, which are regulated by phosphorylation. To characterize regulation of the ORMDL/SPT complex we devised a cell free system that recapitulates that regulation. Using isolated membranes we demonstrate that the triggering sphingolipid is ceramide. Moreover, regulation does not require ATP or cytosolic proteins, eliminating the role of protein expression or post‐translational modification as potential regulatory mechanisms. A distinct spectrum of ceramide structures activate ORMDL regulation of SPT. Strikingly, only the native stereoisomer of ceramide will trigger this regulation, the hallmark of a specific binding interaction. These data strongly suggest that ORMDL dependent regulation of SPT is not due to a complex signal transduction pathway or sphingolipid‐induced changes in membrane properties but instead is due to direct binding of ceramide to a membrane‐bound ceramide sensor, likely ORMDL. Support or Funding Information University of Louisville Bridge Grant National Institutes of Health‐R01HL131340