title: Bioenergetics at extreme temperature: Thermus thermophilus ba(3)- and caa(3)-type cytochrome c oxidases.
abstract: Seven years into the completion of the genome sequencing projects of the thermophilic bacterium Thermus thermophilus strains HB8 and HB27, many questions remain on its bioenergetic mechanisms. A key fact that is occasionally overlooked is that oxygen has a very limited solubility in water at high temperatures. The HB8 strain is a facultative anaerobe whereas its relative HB27 is strictly aerobic. This has been attributed to the absence of nitrate respiration genes from the HB27 genome that are carried on a mobilizable but highly-unstable plasmid. In T. thermophilus, the nitrate respiration complements the primary aerobic respiration. It is widely known that many organisms encode multiple biochemically-redundant components of the respiratory complexes. In this minireview, the presence of the two cytochrome c oxidases (CcO) in T. thermophilus, the ba(3)- and caa(3)-types, is outlined along with functional considerations. We argue for the distinct evolutionary histories of these two CcO including their respective genetic and molecular organizations, with the caa(3)-oxidase subunits having been initially 'fused'. Coupled with sequence analysis, the ba(3)-oxidase crystal structure has provided evolutionary and functional information; for example, its subunit I is more closely related to archaeal sequences than bacterial and the substrate-enzyme interaction is hydrophobic as the elevated growth temperature weakens the electrostatic interactions common in mesophiles. Discussion on the role of cofactors in intra- and intermolecular electron transfer and proton pumping mechanism is also included.
authors.affiliation: Department of Chemical and Environmental Sciences, University of Limerick, Limerick, Ireland.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Radzi Noor
authors.forename: Tewfik
authors.initials: T
authors.lastname: Soulimane
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003573:Cytochrome b Group / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004734:Energy Metabolism; D019143:Evolution, Molecular; D006358:Hot Temperature; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D016963:Thermus thermophilus / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D003573:Cytochrome b Group; C058557:cytochrome ba3; D003576:Electron Transport Complex IV; D010100:Oxygen