title: Intramembrane aspartic acid in SCAP protein governs cholesterol-induced conformational change.
abstract: The polytopic membrane protein SCAP transports sterol regulatory element-binding proteins (SREBPs) from the endoplasmic reticulum (ER) to the Golgi, thereby activating cholesterol synthesis. Cholesterol accumulation in the ER membranes changes SCAP to an alternate conformation in which it binds ER retention proteins called Insigs, thereby terminating cholesterol synthesis. Here, we show that the conserved Asp-428 in the sixth transmembrane helix of SCAP is essential for SCAP's dissociation from Insigs. In transfected hamster cells, mutant SCAP in which Asp-428 is replaced by alanine (D428A) remained in an Insig-binding conformation when cells were depleted of sterols. As a result, mutant SCAP failed to dissociate from Insigs, and it failed to carry SREBPs to the Golgi. These data identify an important functional residue in SCAP, and they provide genetic evidence that the conformation of SCAP dictates the rate of cholesterol synthesis in animal cells.
authors.affiliation: Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046, USA.
authors.forename: Jamison D
authors.initials: JD
authors.lastname: Feramisco
authors.forename: Arun
authors.initials: A
authors.lastname: Radhakrishnan
authors.forename: Yukio
authors.initials: Y
authors.lastname: Ikeda
authors.forename: Julian
authors.initials: J
authors.lastname: Reitz
authors.forename: Michael S
authors.initials: MS
authors.lastname: Brown
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Goldstein
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001224:Aspartic Acid / Q000502:physiology*; D002478:Cells, Cultured; D002784:Cholesterol / Q000502:physiology*; D006801:Humans; D006868:Hydrolysis; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism / Q000502:physiology*; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014357:Trypsin / Q000378:metabolism
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D011994:Recombinant Proteins; C102196:SREBP cleavage-activating protein; D001224:Aspartic Acid; D002784:Cholesterol; D014357:Trypsin
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