Membrane Topology of Human Insig-1, a Protein Regulator of Lipid Synthesis

Jamison D. Feramisco, Joseph L. Goldstein, Michael S. Brown

Research output: Contribution to journalArticle

68 Scopus citations

Abstract

Insig-1 is an intrinsic protein of the endoplasmic reticulum. (ER) that regulates the proteolytic processing of membrane-bound sterol regulatory element-binding proteins (SREBPs), transcription factors that activate the synthesis of cholesterol and fatty acids in mammalian cells. When cellular levels of sterols rise, Insig-1 binds to the membranous sterol-sensing domain of SREBP cleavage-activating protein (SCAP), retaining the SCAP/SREBP complex in the ER and preventing it from moving to the Golgi for proteolytic processing. Under conditions of sterol excess, Insig-1 also binds to the ER enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, facilitating its ubiquitination and proteasomal degradation. Here, we use protease protection, glycosylation site mapping, and cysteine derivitization to define the topology of the 277-amino acid human Insig-1. The data indicate that short segments at the N and C termini of Insig-1 face the cytosol. Most of the protein is buried within the membrane, forming six transmembrane segments separated by five short luminal and cytosolic loops that range from ∼5 to 16 amino acids. The membranous nature of Insig-1 is consistent with its sterol-dependent binding to hydrophobic sterol-sensing domains in SCAP and HMG CoA reductase.

Original languageEnglish (US)
Pages (from-to)8487-8496
Number of pages10
JournalJournal of Biological Chemistry
Volume279
Issue number9
DOIs
StatePublished - Feb 27 2004

    Fingerprint

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Cite this