title: Division of labor among oxidoreductases: TMX1 preferentially acts on transmembrane polypeptides.
abstract: The endoplasmic reticulum (ER) is the site of maturation for secretory and membrane proteins in eukaryotic cells. The lumen of the mammalian ER contains >20 members of the protein disulfide isomerase (PDI) superfamily, which ensure formation of the correct set of intramolecular and intermolecular disulfide bonds as crucial, rate-limiting reactions of the protein folding process. Components of the PDI superfamily may also facilitate dislocation of misfolded polypeptides across the ER membrane for ER-associated degradation (ERAD). The reasons for the high redundancy of PDI family members and the substrate features required for preferential engagement of one or the other are poorly understood. Here we show that TMX1, one of the few transmembrane members of the family, forms functional complexes with the ER lectin calnexin and preferentially intervenes during maturation of cysteine-containing, membrane-associated proteins while ignoring the same cysteine-containing ectodomains if not anchored at the ER membrane. As such, TMX1 is the first example of a topology-specific client protein redox catalyst in living cells.
authors.affiliation: Institute for Research in Biomedicine, CH-6500 Bellinzona, Switzerland Università della Svizzera Italiana, CH-6900 Lugano, Switzerland.
authors.forename: Giorgia Brambilla
authors.initials: GB
authors.lastname: Pisoni
authors.affiliation: Faculty of Biochemistry and Molecular Medicine, University of Oulu, 90014 Oulu, Finland.
authors.forename: Lloyd W
authors.initials: LW
authors.lastname: Ruddock
authors.affiliation: Institute of Molecular Cell and Systems Biology, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
authors.forename: Neil
authors.initials: N
authors.lastname: Bulleid
authors.affiliation: Institute for Research in Biomedicine, CH-6500 Bellinzona, Switzerland Università della Svizzera Italiana, CH-6900 Lugano, Switzerland Ecole Polytechnique Fédérale de Lausanne, School of Life Sciences, CH-1015 Lausanne, Switzerland.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Molinari
mesh_terms: D000818:Animals; D015153:Blotting, Western; D037281:Calnexin / Q000378:metabolism; D002478:Cells, Cultured; D004220:Disulfides / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000201:enzymology / Q000378:metabolism; D037102:Lectins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D010088:Oxidoreductases / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism*; D017510:Protein Folding
chemical_list: D004220:Disulfides; D037102:Lectins; D008565:Membrane Proteins; D010455:Peptides; D037281:Calnexin; D010088:Oxidoreductases