title: DPM1, the catalytic subunit of dolichol-phosphate mannose synthase, is tethered to and stabilized on the endoplasmic reticulum membrane by DPM3.
abstract: Dolichol-phosphate mannose (DPM) synthase is required for synthesis of the glycosylphosphatidylinositol (GPI) anchor, N-glycan precursor, protein O-mannose, and C-mannose. We previously identified DPM3, the third component of this enzyme, which was co-purified with DPM1 and DPM2. Here, we have established mutant Chinese hamster ovary (CHO) 2.38 cells that were defective in DPM3. CHO2.38 cells were negative for GPI-anchored proteins, and microsomes from these cells showed no detectable DPM synthase activity, indicating that DPM3 is an essential component of this enzyme. A coiled-coil domain near the C terminus of DPM3 was important for tethering DPM1, the catalytic subunit of the enzyme, to the endoplasmic reticulum membrane and, therefore, was critical for enzyme activity. On the other hand, two transmembrane regions in the N-terminal portion of DPM3 showed no specific functions. DPM1 was rapidly degraded by the proteasome in the absence of DPM3. Free DPM1 was strongly associated with the C terminus of Hsc70-interacting protein (CHIP), a chaperone-dependent E3 ubiquitin ligase, suggesting that DPM1 is ubiquitinated, at least in part, by CHIP.
authors.affiliation: Department of Immunoregulation, Research Institute for Microbial Diseases, Osaka University, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Ashida
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Maeda
authors.forename: Taroh
authors.initials: T
authors.lastname: Kinoshita
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D018957:CD59 Antigens / Q000096:biosynthesis; D016466:CHO Cells; D002384:Catalysis; D020134:Catalytic Domain; D002462:Cell Membrane / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D003001:Cloning, Molecular; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D004287:Dolichol Monophosphate Mannose / Q000737:chemistry; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005434:Flow Cytometry; D050883:HSC70 Heat-Shock Proteins / Q000737:chemistry; D006801:Humans; D047468:Immunoprecipitation; D008358:Mannose / Q000737:chemistry; D008364:Mannosyltransferases / Q000737:chemistry* / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D018832:Molecular Chaperones / Q000737:chemistry; D008969:Molecular Sequence Data; D009154:Mutation; D009844:Oligosaccharides / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D014162:Transfection
chemical_list: D018957:CD59 Antigens; D050883:HSC70 Heat-Shock Proteins; D008565:Membrane Proteins; D018832:Molecular Chaperones; D009844:Oligosaccharides; D010455:Peptides; D011134:Polysaccharides; D004287:Dolichol Monophosphate Mannose; D000242:Cyclic AMP; D008364:Mannosyltransferases; C429687:DPM3 protein, human; C022755:dolichyl-phosphate beta-D-mannosyltransferase; D046988:Proteasome Endopeptidase Complex; D008358:Mannose