Chaperones for cytochrome c oxidase

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 

King Cobra Chicken Xenopus laevis Zabrafish 

Drosophila melanogaster Caenorhabditis elegans Necator ame rican us Chlamydomonas reinhardtii Schizosaccharomyces pombe 

Sequence References for the Copper Chaperones for Cytochrome c Oxidase 

---

Figure 12.2 Copper chaperone function, (a) Copper homeostasis in Enterococcus hirae is affected by the proteins encoded by the cop operon. CopA, Cu1+-import ATPase CopB, Cu1+-export ATPase CopY, Cu1+-responsive repressor copZ, chaperone for Cu1+ delivery to CopY. (b) The CTR family of proteins transports copper into yeast cells. Atxlp delivers copper to the CPx-type ATPases located in the post Golgi apparatus for the maturation of Fet3p. (c) Coxl7p delivers copper to the mitochondrial intermembrane space for incorporation into cytochrome c oxidase (CCO). (d) hCTR, a human homologue of CTR, mediates copper-ion uptake into human cells. CCS delivers copper to cytoplasmic Cu/Zn superoxide dismutase (SOD1). Abbreviations IMM, inner mitochondrial membrane OMM, outer mitochondrial membrane PM, plasma membrane PGV, post Golgi vessel. Reprinted from Harrison et al., 2000. Copyright (2000), with permission from Elsevier Science.

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. 

Bacterial copper proteins are found only in the plasma membrane (Gram-positive bacteria) or in the plasma membrane and the periplasm (Gram-negative bacteria), not in the bacterial cytoplasm. However, cyanobacteria do have copper proteins in their cytoplasm. These important photosynthetic bacteria require copper for plastocyanin, which plays a critical role in the photosynthetic electron transport chain. Both plastocyanin and cytochrome c oxidase are found in the thylakoid compartments within the cytoplasm. In Synechocystis, the Cu(I) Pie-ATPase CtaA imports Cu(I). A second ATPase, PacS, imports Cu(I) into the thylakoid, and the Atxl-like copper chaperone ScAtxl is believed to deliver Cu(I) from CtaA to PacS (Fig. 8.6). 

Figure 1 Copper trafficking pathways in yeast. Atx, antioxidant Ccci, cross-compiements Ca -sensitive phenotype of csgl CCS, copper chaperone for SOD COX, cytochrome c oxidase Ctr, copper transporter Fet, ferrous transport Fre, FerriReductase-encoding Ftr, Fe transporter IMS, intermembrane space MT, metaiiothienoin Sco, suppressor of cytochrome c oxidase deficiency SOD, superoxide dismutase. Reproduced from F. Arnesano L. Banci, In Handbook of Metalloproteins, A. Messerschmidt, Ed. John Wiley Sons Chichester, 2007 Voi. 4, pp 1-21, with permission from John Wiiey Sons.

---