Cytochrome c oxidase assembly

Genetic defects of cytochrome c oxidase assembly. Physiol. Res. 2004 53 213-223. 34. 

Cooperative Interaction between Mitochondrial and Nuclear Genomes Cytochrome c Oxidase Assembly as a Model... 

OXPHOS, oxidative phosphorylation NDUF, nuclear-encoded subunits of human complex I Fp, flavoprotein ANT, adenine nucleotide translocase SCO, synthesis of cytochrome c oxidase (assembly gene) COX, cytochrome c oxidase. 

Leary, S.C., Cobine, P.A., Kaufinan, B.A., Gueicin, G.H., Mattman, A., Palaty, J., Lockitch, G., Winge, D.R., Rustin, P, Horvath, R., and Shoubridge, E.A. (2007). The human cytochrome c oxidase assembly factors SCOl and SC02 have regulatory roles in the maintenance of cellular copper homeostasis. Cell Metab. 5,9-20. 

The active site of bovine heart cytochrome c oxidase is constituted by a multimetallic assembly (Cu, Mg, Fe, Zn),4 but it is thought that... 

Gibney BR, Isogai Y, Rabanal F et al (2000) Self-assembly of heme A and heme B in a designed four-helix bundle implications for a cytochrome c oxidase maquette. Biochemistry 39(11041-11049) 2... 

Coxl7, an 8.1-kDa cysteine-rich protein, was the first copper chaperone to be identified. Saccharomyces cerevisiae harboring mutations in coxl 7 are respiratory deficient, a phenotype resulting from their inability to assemble a functional cytochrome c oxidase complex (Glerum et al., 1996a). coxl7 mutant yeast are, however, able to express all the subunits of the cytochrome c oxidase complex, indicating that the lesion must lie in a posttranslational step that is essential for assembly of the functional complex in the mitochondrial membrane. Unlike other cytochrome c... 

The overall assembly of cytochrome c oxidase on the inner mitochondrial membrane is controlled by a large number of nuclear encoded genes (Tzagoloff and Dieckmann, 1990). Four of these genes, scol, sco2, coxl 1, and coxl 7, encode proteins that appear to be involved in copper incorporation into the catalytic core of the enzyme, though precisely which one(s) is (are) responsible for insertion of copper into the complex remains unclear (Horvath et al., 2000). Scol is anchored in the inner mitochondrial membrane and is essential for the accumulation of Coxl and CoxII subunits as well as the proper assembly of the cytochrome c... 

Considerable progress has been made toward the elucidation of the function of Cox 17 since its identification 5 years ago. It has been shown to be a copper-containing protein that is essential for assembly of the cytochrome c oxidase complex and is present in both the mitochondria and the cytosol. These features are strongly indicative of a copper chaperonelike function. It appears that Cox 17 interacts directly with Scol and Sco2, but the delineation of the remainder of the copper-trafficking pathway from the chaperone to the cytochrome c oxidase complex remains unclear. It is also unclear exactly how Cox 17 binds copper, since the CCXC motif is unique to date. If it binds three copper atoms with only three cysteine residues, the coordination of the metal ions will be extremely interesting, and elucidation of the protein structure will undoubtedly yield new insights into copper transportation in the cell. 

Pantothenic acid has a central role in energy-yielding metabolism as the functional moiety of coenzyme A (CoA), in the biosynthesis of fatty acids as the prosthetic group of acyl carrier protein, and through its role in CoA in the mitochondrial elongation of fatty acids the biosynthesis of steroids, porphyrins, and acetylcholine and other acyl transfer reactions, including postsynthetic acylation of proteins. Perhaps 4% of all known enzymes utilize CoA derivatives. CoA is also bound by disulfide links to protein cysteine residues in sporulating bacteria, where it may be involved with heat resistance of the spores, and in mitochondrial proteins, where it seems to be involved in the assembly of active cytochrome c oxidase and ATP synthetase complexes. 

The electron carriers in the respiratory assembly of the inner mitochondrial membrane are quinones, flavins, iron-sulfur complexes, heme groups of cytochromes, and copper ions. Electrons from NADH are transferred to the FMN prosthetic group of NADH-Q oxidoreductase (Complex I), the first of four complexes. This oxidoreductase also contains Fe-S centers. The electrons emerge in QH2, the reduced form of ubiquinone (Q). The citric acid cycle enzyme succinate dehydrogenase is a component of the succinate-Q reductase complex (Complex II), which donates electrons from FADH2 to Q to form QH2.This highly mobile hydrophobic carrier transfers its electrons to Q-cytochrome c oxidoreductase (Complex III), a complex that contains cytochromes h and c j and an Fe-S center. This complex reduces cytochrome c, a water-soluble peripheral membrane protein. Cytochrome c, like Q, is a mobile carrier of electrons, which it then transfers to cytochrome c oxidase (Complex IV). This complex contains cytochromes a and a 3 and three copper ions. A heme iron ion and a copper ion in this oxidase transfer electrons to O2, the ultimate acceptor, to form H2O. 

While the in vitro studies on assembly have provided relatively little information, in vivo data can give us some suggestions on possible pathway of assembly. For a long time it has been known that in rho yeast cells, where cytochrome b is not produced, cytochrome c, is still accumulated in the inner membrane. This agrees with the plasmid studies of overproduction. On the other hand the cytoplasmically synthesized subunits of cytochrome c oxidase accumulate in much lower quantities in the absence of subunits I, II and III, which are mitochondrial products. It is unlikely that this diminished accumulation is due to substantially reduced gene expression. This may indicate that certain subunits are stabilized by their counterparts. 

The last of the three proton-pumping assemblies of the respiratory chain is cytochrome c oxidase (Complex IV). Cytochrome oxidase catalyzes the transfer of electrons from the reduced form of cytochrome c to molecular oxygen, the final acceptor. 

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