title: The inhibition of degradation of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase by sterol regulatory element binding protein cleavage-activating protein requires four phenylalanine residues in span 6 of HMG-CoA reductase transmembrane domain.
abstract: 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) is the rate-limiting enzyme in the cholesterol biosynthetic pathway. This endoplasmic reticulum membrane protein contains a cytosolic catalytic domain and a transmembrane domain with eight membrane spans that are necessary for sterol-accelerated degradation. Competition experiments showed that wild-type transmembrane domains of HMGR and sterol regulatory element binding protein cleavage-activating protein (SCAP) blocked sterol-accelerated degradation of intact HMGR and HMGal, a model protein containing the membrane domain of HMGR linked to Escherichia coli beta-galactosidase. However, mutant transmembrane domains of HMGR and SCAP whose sterol-sensing functions were abolished did not inhibit sterol-accelerated degradation of HMGR and HMGal. In addition, our mutagenesis studies on HMGal indicated that four Phe residues conserved in span 6 of HMGR and the sterol-sensing domains of other sterol-related proteins are required for the regulated degradation of HMGR. These results suggest that HMGR and SCAP compete for binding to a sterol-regulated regulator protein, and this binding may need the four Phe residues.
authors.affiliation: Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020, USA. xuliwen4@stanford.edu <xuliwen4@stanford.edu>
authors.forename: Liwen
authors.initials: L
authors.lastname: Xu
authors.forename: Robert D
authors.initials: RD
authors.lastname: Simoni
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism*; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005204:Farnesol / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000737:chemistry*; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000494:pharmacology*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010649:Phenylalanine / Q000737:chemistry*; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D051780:Sterol Regulatory Element Binding Protein 1; D013261:Sterols / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors; D014162:Transfection; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; C497387:SREBF1 protein, human; D051780:Sterol Regulatory Element Binding Protein 1; D013261:Sterols; D014157:Transcription Factors; D005204:Farnesol; D010649:Phenylalanine; D006903:Hydroxymethylglutaryl CoA Reductases; D001616:beta-Galactosidase