title: Domains I and III of the human copper chaperone for superoxide dismutase interact via a cysteine-bridged Dicopper(I) cluster.
abstract: Copper binding to the human copper chaperone for superoxide dismutase (hCCS) has been investigated by X-ray absorption spectroscopy. Stoichiometry measurements on the dialyzed, as-isolated protein indicated that up to 3.5 Cu ions bound per hCCS molecule. Reduction with either sodium dithionite or dithiothreitol decreased the copper binding ratio to 2 coppers per hCCS monomer. Analysis of the as-isolated EXAFS data indicated coordination of Cu by a mixture of S and N backscatterers, suggestive of heterogeneous binding of copper between Cu-cysteine binding sites of domain I or III and copper-histidine SOD1-like metal binding sites of domain II. The best fit was obtained with 1.6 Cu-S (cysteine) at 2.24 A (2sigma(2) = 0.011 A(2)) and 1.1 N (histidine) at 1.98 A (2sigma(2) = 0.005 A(2)). A peak of variable intensity in the Fourier transform (FT) of the as-isolated protein at 2.7 A was suggestive of the presence of a heavy atom scatterer such as Cu. Analysis of the dithionite- and DTT-reduced derivatives indicated that copper was lost from the histidine coordinating sites, resulting in a S-only environment with copper coordinated to three S backscatterers at 2. 26 A. The heavy atom scatterer peak was now prominent in the FT and could be well fit by a Cu-Cu interaction at 2.72 A. The data were best interpreted by a dinuclear mu(2)()-bridged cluster with doubly bridging cysteine ligands similar to the cluster proposed to exist in the cytochrome c oxidase chaperone COX17. Analysis of primary sequence and X-ray structural information on yeast CCS strongly suggests that this cluster bridges between domains I and III in hCCS. A mechanism for copper translocation is briefly discussed.
authors.affiliation: Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland 97201, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Eisses
authors.forename: J P
authors.initials: JP
authors.lastname: Stasser
authors.forename: M
authors.initials: M
authors.lastname: Ralle
authors.forename: J H
authors.initials: JH
authors.lastname: Kaplan
authors.forename: N J
authors.initials: NJ
authors.lastname: Blackburn
mesh_terms: D060365:Chloroplast Proteins; D004577:Electron Probe Microanalysis; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D010940:Plant Proteins; D011485:Protein Binding; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000737:chemistry / Q000378:metabolism*
chemical_list: C109655:Ccs1 protein, Chlamydomonas reinhardtii; D060365:Chloroplast Proteins; D010940:Plant Proteins; D015800:Protozoan Proteins; D013482:Superoxide Dismutase