title: Differential affinity of BsSCO for Cu(II) and Cu(I) suggests a redox role in copper transfer to the Cu(A) center of cytochrome c oxidase.
abstract: SCO (synthesis of cytochrome c oxidase) proteins are involved in the assembly of the respiratory chain enzyme cytochrome c oxidase acting to assist in the assembly of the Cu(A) center contained within subunit II of the oxidase complex. The Cu(A) center receives electrons from the reductive substrate ferrocytochrome c, and passes them on to the cytochrome a center. Cytochrome a feeds electrons to the oxygen reaction site composed of cytochrome a(3) and Cu(B). Cu(A) consists of two copper ions positioned within bonding distance and ligated by two histidine side chains, one methionine, a backbone carbonyl and two bridging cysteine residues. The complex structure and redox capacity of Cu(A) present a potential assembly challenge. SCO proteins are members of the thioredoxin family which led to the early suggestion of a disulfide exchange function for SCO in Cu(A) assembly, whereas the copper binding capacity of the Bacillus subtilis version of SCO (i.e., BsSCO) suggests a direct role for SCO proteins in copper transfer. We have characterized redox and copper exchange properties of apo- and metalated-BsSCO. The release of copper (II) from its complex with BsSCO is best achieved by reducing it to Cu(I). We propose a mechanism involving both disulfide and copper exchange between BsSCO and the apo-Cu(A) site. This article is part of a Special Issue entitled: Biogenesis/Assembly of Respiratory Enzyme Complexes.
authors.affiliation: Department of Biochemistry and Protein Function Discovery Group, Queen's University, Kingston, Ontario, Canada K7L 3N6. hillb@queensu.ca
authors.forename: Bruce C
authors.initials: BC
authors.lastname: Hill
authors.forename: Diann
authors.initials: D
authors.lastname: Andrews
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D004229:Dithiothreitol / Q000737:chemistry; D003576:Electron Transport Complex IV / Q000096:biosynthesis*; D006861:Hydrogen Peroxide / Q000737:chemistry; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry*; D016877:Oxidants / Q000737:chemistry; D010084:Oxidation-Reduction; D010720:Phosphines / Q000737:chemistry; D011485:Protein Binding; D019163:Reducing Agents / Q000737:chemistry; D013053:Spectrophotometry; D013879:Thioredoxins / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D003300:Copper; D004229:Dithiothreitol; D003576:Electron Transport Complex IV; D006861:Hydrogen Peroxide; D008565:Membrane Proteins; D016877:Oxidants; D010720:Phosphines; D019163:Reducing Agents; D013879:Thioredoxins; C482909:Sco protein, Bacillus subtilis; C042514:cuprous ion; C080938:tris(2-carboxyethyl)phosphine