The caa3 Terminal Oxidase of Rhodothermus marinus Lacking the Key Glutamate of the D-Channel Is a Proton Pump

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• 作者：Manuela M. Pereira ; Marina L. Verkhovskaya ; Miguel Teixeira ; and Michael I. Verkhovsky
• 刊名：Biochemistry
• 出版年：2000
• 出版时间：May 30, 2000
• 年：2000
• 卷：39
• 期：21
• 页码：6336 - 6340
• 全文大小：96K
• 年卷期：v.39,no.21(May 30, 2000)
• ISSN：1520-4995

文摘

The thermohalophilic bacterium Rhodothermus marinus expresses a caa₃-type dioxygenreductase as one of its terminal oxidases. The subunit I amino acid sequence shows the presence of all theessential residues of the D- and K-proton channels, defined in most heme-copper oxidases, with theexception of the key glutamate residue located in the middle of the membrane dielectric (E278 inParacoccus denitrificans). On the basis of homology modeling studies, a tyrosine residue (Y256, R. marinusnumbering) 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 caa₃ oxidase was reconstituted in liposomes andshown to operate as a proton pump, translocating protons from the cytoplasmic side of the bacterial innermembrane to the periplasmatic space with a stoichiometry of 1H⁺/e^-, as in the case in heme-copperoxidases that contain the glutamate residue. Possible mechanisms of proton transfer in the D-channelwith the participation of the tyrosine residue are discussed. The observation that the tyrosine residue isconserved in several other members of the heme-copper oxidase superfamily suggests a common alternativemode of action for the D-channel.