Intramembrane Aspartic Acid in SCAP Protein Governs Cholesterol-Induced Conformational Change

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 102; no. 9; pp. 3242 - 3247
• Main Authors: Feramisco, Jamison D., Radhakrishnan, Arun, Ikeda, Yukio, Reitz, Julian, Brown, Michael S., Goldstein, Joseph L.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 01.03.2005; National Acad Sciences
• Subjects: Acids; Amino Acid Sequence; Amino acids; Animal cells; Animals; Aspartic Acid - physiology; Biochemistry; Biological Sciences; Cells, Cultured; Cellular immunity; CHO cells; Cholesterol; Cholesterol - physiology; Cholesterols; Gels; Genetics; Humans; Hydrolysis; Intracellular Signaling Peptides and Proteins; Membrane Proteins - chemistry; Membrane Proteins - isolation & purification; Membrane Proteins - metabolism; Membrane Proteins - physiology; Membranes; Molecular Sequence Data; P branes; Plasmids; Protein Conformation; Proteins; Recombinant Proteins - chemistry; Recombinant Proteins - isolation & purification; Recombinant Proteins - metabolism; Sequence Homology, Amino Acid; Sterols; Transfection; Trypsin - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0500206102

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.