title: Structure and multistate function of the transmembrane electron transporter CcdA.
abstract: The mechanism by which transmembrane reductases use a single pair of cysteine residues to relay electrons between protein substrates across biological membranes is a long-standing mystery in thiol-redox biochemistry. Here we show the NMR structure of a reduced-state mimic of archaeal CcdA, a protein that transfers electrons across the inner membrane, by using a redox-active NMR sample. The two cysteine positions in CcdA are separated by 20 Å. Whereas one is accessible to the cytoplasm, the other resides in the protein core, thus implying that conformational exchange is required for periplasmic accessibility. In vivo mixed disulfide-trapping experiments validated the functional positioning of the cysteines, and in vitro accessibility results confirmed conformational exchange. Our NMR and functional data together show the existence of multiple conformational states and suggest a four-state model for relaying electrons from cytosolic to periplasmic redox substrates.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Jessica A
authors.identifier: http://orcid.org/0000-0002-5530-8657
authors.initials: JA
authors.lastname: Williamson
authors.affiliation: WELBIO, Brussels, Belgium.|Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA.|de Duve Institute, Université Catholique de Louvain, Brussels, Belgium.
authors.forename: Seung-Hyun
authors.initials: SH
authors.lastname: Cho
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Jiqing
authors.initials: J
authors.lastname: Ye
authors.affiliation: WELBIO, Brussels, Belgium.|de Duve Institute, Université Catholique de Louvain, Brussels, Belgium.
authors.forename: Jean-Francois
authors.initials: JF
authors.lastname: Collet
authors.affiliation: Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Beckwith
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: Chou
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D019295:Computational Biology; D003545:Cysteine / Q000378:metabolism; D004583:Electrons; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011487:Protein Conformation
chemical_list: D019843:Archaeal Proteins; D002352:Carrier Proteins; D008565:Membrane Proteins; D010088:Oxidoreductases; D003545:Cysteine