title: Two phases of disulfide bond formation have differing requirements for oxygen.
abstract: Most proteins destined for the extracellular space require disulfide bonds for folding and stability. Disulfide bonds are introduced co- and post-translationally in endoplasmic reticulum (ER) cargo in a redox relay that requires a terminal electron acceptor. Oxygen can serve as the electron acceptor in vitro, but its role in vivo remains unknown. Hypoxia causes ER stress, suggesting a role for oxygen in protein folding. Here we demonstrate the existence of two phases of disulfide bond formation in living mammalian cells, with differential requirements for oxygen. Disulfide bonds introduced rapidly during protein synthesis can occur without oxygen, whereas those introduced during post-translational folding or isomerization are oxygen dependent. Other protein maturation processes in the secretory pathway, including ER-localized N-linked glycosylation, glycan trimming, Golgi-localized complex glycosylation, and protein transport, occur independently of oxygen availability. These results suggest that an alternative electron acceptor is available transiently during an initial phase of disulfide bond formation and that post-translational oxygen-dependent disulfide bond formation causes hypoxia-induced ER stress.
authors.affiliation: Ontario Cancer Institute and Campbell Family Institute for Cancer Research, University Health Network, Toronto, Ontario M5G 2M9, Canada.
authors.forename: Marianne
authors.initials: M
authors.lastname: Koritzinsky
authors.forename: Fiana
authors.initials: F
authors.lastname: Levitin
authors.forename: Twan
authors.initials: T
authors.lastname: van den Beucken
authors.forename: Ryan A
authors.initials: RA
authors.lastname: Rumantir
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Harding
authors.forename: Kenneth C
authors.initials: KC
authors.lastname: Chu
authors.forename: Paul C
authors.initials: PC
authors.lastname: Boutros
authors.forename: Ineke
authors.initials: I
authors.lastname: Braakman
authors.forename: Bradly G
authors.initials: BG
authors.lastname: Wouters
mesh_terms: D015687:Cell Hypoxia / Q000187:drug effects / Q000235:genetics; D004220:Disulfides / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D045325:HCT116 Cells; D006367:HeLa Cells; D006801:Humans; D007536:Isomerism; D008954:Models, Biological; D010100:Oxygen / Q000494:pharmacology*; D017510:Protein Folding / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D004220:Disulfides; D012333:RNA, Messenger; D010100:Oxygen