title: The characterization and role of zinc binding in yeast Cox4.
abstract: Yeast Cox4 is a zinc binding subunit of cytochrome c oxidase. Cox4 is the only cofactor-containing subunit that is not directly part of the catalytic core of the enzyme located in the mitochondrial inner membrane. The Zn(II) site is shown to be distinct from the bovine ortholog, as it results from the x-ray structure of the entire cytochrome c oxidase in having a single histidyl residue and three conserved cysteines residues in the coordination sphere. Substitutions at the Cys ligand positions result in non-functional Cox4 proteins that fail to lead to cytochrome oxidase assembly. Limited function exists in His-119 mutants when overexpressed. Zn(II) binding in Cox4 is, therefore, important for the stability of the complex. The solution structure of yeast Cox4 elucidated by multidimensional NMR reveals a C-terminal globular domain consisting of two beta sheets analogous to the bovine ortholog except the loop containing the coordinating His in the yeast protein and the fourth Cys in the bovine protein are in different positions in the two structures. The conformation of this loop is dictated by the different sequence position of the fourth coordinating zinc ligand. The Zn(II) ion is buried within the domain, consistent with its role in structural stability. Potential functions of this matrix-facing subunit are discussed.
authors.affiliation: University of Utah Health Sciences Center, Department of Medicine, Salt Lake City, Utah 84132, USA.
authors.forename: H Jerome
authors.initials: HJ
authors.lastname: Coyne
authors.forename: Simone
authors.initials: S
authors.lastname: Ciofi-Baffoni
authors.forename: Lucia
authors.initials: L
authors.lastname: Banci
authors.forename: Ivano
authors.initials: I
authors.lastname: Bertini
authors.forename: Limei
authors.initials: L
authors.lastname: Zhang
authors.forename: Graham N
authors.initials: GN
authors.lastname: George
authors.forename: Dennis R
authors.initials: DR
authors.lastname: Winge
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002104:Cadmium / Q000737:chemistry; D002417:Cattle; D003035:Cobalt / Q000737:chemistry; D018360:Crystallography, X-Ray; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000502:physiology; D006639:Histidine / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D011485:Protein Binding; D017433:Protein Structure, Secondary; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D015032:Zinc / Q000737:chemistry*
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D002104:Cadmium; D003035:Cobalt; D006639:Histidine; C519173:Cox4 protein, S cerevisiae; D003576:Electron Transport Complex IV; D015032:Zinc