title: Solution structure of Cox11, a novel type of beta-immunoglobulin-like fold involved in CuB site formation of cytochrome c oxidase.
abstract: Cytochrome c oxidase assembly process involves many accessory proteins including Cox11, which is a copper-binding protein required for Cu incorporation into the Cu(B) site of cytochrome c oxidase. In a genome wide search, a number of Cox11 homologs are found in all of the eukaryotes with complete genomes and in several Gram-negative bacteria. All of them possess a highly homologous soluble domain and contain an N-terminal fragment that anchors the protein to the membrane. An anchor-free construct of 164 amino acids was obtained from Sinorhizobium meliloti, and the first structure of this class of proteins is reported here. The apoform has an immunoglobulin-like fold with a novel type of beta-strand organization. The copper binding motif composed of two highly conserved cysteines is located on one side of the beta-barrel structure. The apoprotein is monomeric in the presence of dithiothreitol, whereas it dimerizes in the absence of the reductant. When copper(I) binds, NMR and extended x-ray absorption fine structure (EXAFS) data indicate a dimeric protein state with two thiolates bridging two copper(I) ions. The present results advance the knowledge on the poorly understood molecular aspects of cytochrome c oxidase assembly.
authors.affiliation: Magnetic Resonance Center CERM and Department of Chemistry, University of Florence, Via Luigi Sacconi 6, Sesto Fiorentino 50019, Florence, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Banci
authors.forename: Ivano
authors.initials: I
authors.lastname: Bertini
authors.forename: Francesca
authors.initials: F
authors.lastname: Cantini
authors.forename: Simone
authors.initials: S
authors.lastname: Ciofi-Baffoni
authors.forename: Leonardo
authors.initials: L
authors.lastname: Gonnelli
authors.forename: Stefano
authors.initials: S
authors.lastname: Mangani
mesh_terms: D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000737:chemistry; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry*; D002462:Cell Membrane / Q000378:metabolism; D003300:Copper / Q000737:chemistry*; D019992:Databases as Topic; D019281:Dimerization; D003576:Electron Transport Complex IV / Q000737:chemistry*; D016680:Genome, Bacterial; D007136:Immunoglobulins / Q000737:chemistry; D007477:Ions; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D020033:Protein Isoforms; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016962:Sinorhizobium meliloti / Q000378:metabolism*; D014965:X-Rays
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D007136:Immunoglobulins; D007477:Ions; D020033:Protein Isoforms; D003300:Copper; D003576:Electron Transport Complex IV