title: Topological analysis of Niemann-Pick C1 protein reveals that the membrane orientation of the putative sterol-sensing domain is identical to those of 3-hydroxy-3-methylglutaryl-CoA reductase and sterol regulatory element binding protein cleavage-activating protein.
abstract: The Niemann-Pick C1 (NPC1) protein is predicted to be a polytopic glycoprotein, and it contains a region with extensive homology to the sterol-sensing domains (SSD) of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-R) and sterol regulatory element binding protein cleavage-activating protein (SCAP). To aid the functional characterization of NPC1, a model of NPC1 topology was evaluated by expression of epitope-tagged NPC1 proteins and investigation of epitope accessibility in selectively permeabilized cells. These results were further confirmed by expression of NPC1 and identification of glycosylated domains that are located in the lumen of the endoplasmic reticulum. Our data indicate that this glycoprotein contains 13 transmembrane domains, 3 large and 4 small luminal loops, 6 small cytoplasmic loops, and a cytoplasmic tail. Furthermore, our data show that the putative SSD of NPC1 is oriented in the same manner as those of HMG-R and SCAP, providing strong evidence that this domain is functionally important.
authors.affiliation: Department of Human Genetics, Mount Sinai School of Medicine, New York, New York 10029, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Davies
authors.forename: Y A
authors.initials: YA
authors.lastname: Ioannou
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002352:Carrier Proteins; D005372:Filipin / Q000032:analysis; D006031:Glycosylation; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000737:chemistry*; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D000077296:Niemann-Pick C1 Protein; D009542:Niemann-Pick Diseases; D017433:Protein Structure, Secondary; D011506:Proteins / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D013261:Sterols / Q000378:metabolism; D014162:Transfection
chemical_list: D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C106881:NPC1 protein, human; D000077296:Niemann-Pick C1 Protein; D011506:Proteins; D011994:Recombinant Proteins; C102196:SREBP cleavage-activating protein; D013261:Sterols; D005372:Filipin; D006903:Hydroxymethylglutaryl CoA Reductases