This family contains a number of eukaryotic Insulin-induced proteins (INSIG-1 and INSIG-2) approximately 200 residues long. INSIG-1 and INSIG-2 are found in the endoplasmic reticulum and bind the sterol-sensing domain of SREBP cleavage-activating protein (SCAP), preventing it from escorting SREBPs to the Golgi. Their combined action permits feedback regulation of cholesterol synthesis over a wide range of sterol concentrations [1,2].

1: Crucial step in cholesterol homeostasis: sterols promote binding of SCAP to INSIG-1, a membrane protein that facilitates retention of SREBPs in ER. Yang T, Espenshade PJ, Wright ME, Yabe D, Gong Y, Aebersold R, Goldstein JL, Brown MS; Cell 2002;110:489-500. PMID:12202038

2: Insig-2, a second endoplasmic reticulum protein that binds SCAP and blocks export of sterol regulatory element-binding proteins. Yabe D, Brown MS, Goldstein JL; Proc Natl Acad Sci U S A 2002;99:12753-12758. PMID:12242332