Cytochrome oxidase genes from Thermus thermophilus. Nucleotide sequence of the fused gene and analysis of the deduced primary structures for subunits I and III of cytochrome caa3.
Cytochrome caa3, a cytochrome c oxidase from Thermus thermophilus, has been purified and extensively characterized as a two-subunit enzyme containing the metal centers characteristic of cytochrome c oxidases (cytochromes a and a3; copper centers CuA and CuB) and an additional cytochrome c (Fee, J. A., Kuila, D., Mather, M. W., and Yoshida, T. (1986) Biochim. Biophys. Acta 853, 153-185). We have now cloned and sequenced the genes encoding the subunits of this enzyme. The smaller subunit consists of a typical oxidase subunit II sequence fused to a cytochrome c domain (Mather, M. W., Springer, P., and Fee, J. A. (1991) J. Biol. Chem. 266, 5025-5035). The larger subunit, the A-protein, is encoded by a fusion gene lying immediately downstream of the subunit IIc gene. The 5' portion of this gene encodes an oxidase subunit I homolog, whereas the 3' portion is homologous to oxidase subunits III. The A-protein from the purified enzyme appears too small from SDS-polyacrylamide gel electrophoresis and quantitative amino acid analyses to be a complete subunit I/III fusion, but it is currently not known if proteolytic processing occurs. Analyses of the sequences of oxidase subunits are presented which clearly identify T. thermophilus cytochrome caa3 as a bona fide member of the greater family of heme- and copper-requiring oxidases. As one consequence, it is confirmed that the set of invariant histidine residues (potential ligands of the metal centers) in cytochrome c oxidase subunits I and II is reduced to 8. Possible topological and helix packing models are developed based on considerations of homology, hydropathy, and variability.
Biochemistry Section, Los Alamos National Laboratory, New Mexico 87545.
M W
MW
Mather
P
P
Springer
S
S
Hensel
G
G
Buse
J A
JA
Fee
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D003576:Electron Transport Complex IV / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005798:Genes, Bacterial; D008670:Metals / Q000378:metabolism; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D016963:Thermus thermophilus / Q000201:enzymology / Q000235:genetics*
D004269:DNA, Bacterial; D008670:Metals; D003576:Electron Transport Complex IV