title: The caa(3) terminal oxidase of Rhodothermus marinus lacking the key glutamate of the D-channel is a proton pump.
abstract: The thermohalophilic bacterium Rhodothermus marinus expresses a caa(3)-type dioxygen reductase as one of its terminal oxidases. The subunit I amino acid sequence shows the presence of all the essential residues of the D- and K-proton channels, defined in most heme-copper oxidases, with the exception of the key glutamate residue located in the middle of the membrane dielectric (E278 in Paracoccus denitrificans). On the basis of homology modeling studies, a tyrosine residue (Y256, R. marinus numbering) has been proposed to act as a functional substitute [Pereira, M. M., Santana, M., Soares, C. M., Mendes, J., Carita, J. N., Fernandes, A. S., Saraste, M., Carrondo, M. A., and Teixeira, M. (1999) Biochim. Biophys. Acta 1413, 1-13]. Here, R. marinus caa(3) oxidase was reconstituted in liposomes and shown to operate as a proton pump, translocating protons from the cytoplasmic side of the bacterial inner membrane to the periplasmatic space with a stoichiometry of 1H(+)/e(-), as in the case in heme-copper oxidases that contain the glutamate residue. Possible mechanisms of proton transfer in the D-channel with the participation of the tyrosine residue are discussed. The observation that the tyrosine residue is conserved in several other members of the heme-copper oxidase superfamily suggests a common alternative mode of action for the D-channel.
authors.affiliation: Helsinki Bioenergetics Group, Department of Medical Chemistry, Institute of Biomedical Sciences and Biocentrum Helsinki, University of Helsinki, Finland.
authors.forename: M M
authors.initials: MM
authors.lastname: Pereira
authors.forename: M L
authors.initials: ML
authors.lastname: Verkhovskaya
authors.forename: M
authors.initials: M
authors.lastname: Teixeira
authors.forename: M I
authors.initials: MI
authors.lastname: Verkhovsky
mesh_terms: D000595:Amino Acid Sequence; D003300:Copper / Q000737:chemistry; D003574:Cytochrome c Group / Q000737:chemistry* / Q000302:isolation & purification; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000302:isolation & purification; D018698:Glutamic Acid; D006088:Gram-Negative Aerobic Bacteria / Q000201:enzymology*; D006418:Heme / Q000031:analogs & derivatives / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011510:Proteolipids / Q000737:chemistry* / Q000378:metabolism*; D017494:Proton Pumps / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014443:Tyrosine
chemical_list: D003574:Cytochrome c Group; D008081:Liposomes; D046911:Macromolecular Substances; D011510:Proteolipids; D017494:Proton Pumps; C020485:proteoliposomes; C027728:heme a; D018698:Glutamic Acid; D014443:Tyrosine; D006418:Heme; D003300:Copper; D003576:Electron Transport Complex IV