title: Glycoproteins form mixed disulphides with oxidoreductases during folding in living cells.
abstract: The formation of intra- and interchain disulphide bonds constitutes an integral part of the maturation of most secretory and membrane-bound proteins in the endoplasmic reticulum. Evidence indicates that members of the protein disulphide isomerase (PDI) superfamily are part of the machinery needed for proper oxidation and isomerization of disulphide bonds. Models based on in vitro studies predict that the formation of mixed disulphide bonds between oxidoreductase and substrate is intermediate in the generation of the native intrachain disulphide bond in the substrate polypeptide. Whether this is how thiol oxidoreductases work inside the endoplasmic reticulum is not clear. Nor has it been established which of the many members of the PDI superfamily interacts directly with newly synthesized substrate proteins, because transient mixed disulphides have never been observed in the mammalian endoplasmic reticulum during oxidative protein folding. Here we describe the mechanisms involved in co- and post-translational protein oxidation in vivo. We show that the endoplasmic-reticulum-resident oxidoreductases PDI and ERp57 are directly involved in disulphide oxidation and isomerization, and, together with the lectins calnexin and calreticulin, are central in glycoprotein folding in the endoplasmic reticulum of mammalian cells.
authors.affiliation: Swiss Federal Institute of Technology Zurich, Institute of Biochemistry.
authors.forename: M
authors.initials: M
authors.lastname: Molinari
authors.forename: A
authors.initials: A
authors.lastname: Helenius
mesh_terms: D000477:Alkylating Agents; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004220:Disulfides / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide; D006023:Glycoproteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism*; D007212:Indolizines / Q000494:pharmacology; D007535:Isomerases / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D011233:Precipitin Tests; D019704:Protein Disulfide-Isomerases / Q000378:metabolism*; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D012672:Semliki forest virus / Q000378:metabolism; D014759:Viral Envelope Proteins / Q000235:genetics / Q000378:metabolism; D054836:Indolizidines
chemical_list: D000477:Alkylating Agents; D004220:Disulfides; D004791:Enzyme Inhibitors; D005033:Ethylmaleimide; D006023:Glycoproteins; D006360:Heat-Shock Proteins; D007212:Indolizines; D007535:Isomerases; D010088:Oxidoreductases; D019704:Protein Disulfide-Isomerases; D014759:Viral Envelope Proteins; C037806:castanospermine; D054836:Indolizidines