title: Regulation of protein O-glycosylation by the endoplasmic reticulum-localized molecular chaperone Cosmc.
abstract: Regulatory pathways for protein glycosylation are poorly understood, but expression of branchpoint enzymes is critical. A key branchpoint enzyme is the T-synthase, which directs synthesis of the common core 1 O-glycan structure (T-antigen), the precursor structure for most mucin-type O-glycans in a wide variety of glycoproteins. Formation of active T-synthase, which resides in the Golgi apparatus, requires a unique molecular chaperone, Cosmc, encoded on Xq24. Cosmc is the only molecular chaperone known to be lost through somatic acquired mutations in cells. We show that Cosmc is an endoplasmic reticulum (ER)-localized adenosine triphosphate binding chaperone that binds directly to human T-synthase. Cosmc prevents the aggregation and ubiquitin-mediated degradation of the T-synthase. These results demonstrate that Cosmc is a molecular chaperone in the ER required for this branchpoint glycosyltransferase function and show that expression of the disease-related Tn antigen can result from deregulation or loss of Cosmc function.
authors.affiliation: Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, USA. tju@emory.edu
authors.forename: Tongzhong
authors.initials: T
authors.lastname: Ju
authors.forename: Rajindra P
authors.initials: RP
authors.lastname: Aryal
authors.forename: Caleb J
authors.initials: CJ
authors.lastname: Stowell
authors.forename: Richard D
authors.initials: RD
authors.lastname: Cummings
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D045744:Cell Line, Tumor; D017124:Conserved Sequence; D006224:Cricetinae; D003412:Cricetulus; D004220:Disulfides / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D006031:Glycosylation / Q000187:drug effects; D006056:Golgi Apparatus / Q000187:drug effects / Q000201:enzymology; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects / Q000201:enzymology; D007976:Leupeptins / Q000494:pharmacology; D018832:Molecular Chaperones / Q000378:metabolism*; D050505:Mutant Proteins / Q000378:metabolism; D009928:Organ Specificity / Q000187:drug effects; D061988:Proteasome Inhibitors; D021382:Protein Sorting Signals; D021381:Protein Transport / Q000187:drug effects; D012995:Solubility / Q000187:drug effects; D014166:Transferases / Q000302:isolation & purification / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects; D014714:Vertebrates / Q000378:metabolism
chemical_list: C505369:C1GALT1C1 protein, human; D004220:Disulfides; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D007976:Leupeptins; D018832:Molecular Chaperones; D050505:Mutant Proteins; D061988:Proteasome Inhibitors; D021382:Protein Sorting Signals; D000255:Adenosine Triphosphate; D014166:Transferases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde