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    Molecular basis of proton uptake in single and double mutants of cytochrome c oxidase


    Henry, Rowan M. and Caplan, David and Fadda, Elisa and Pomès, Régis (2011) Molecular basis of proton uptake in single and double mutants of cytochrome c oxidase. Journal of Physics: Condensed Matter, 23 (22). p. 234102. ISSN 0953-8984

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    Abstract

    Cytochrome c oxidase, the terminal enzyme of the respiratory chain, utilizes the reduction of dioxygen into water to pump protons across the mitochondrial inner membrane. The principal pathway of proton uptake into the enzyme, the D channel, is a 2.5 nm long channel-like cavity named after a conserved, negatively charged aspartic acid (D) residue thought to help recruiting protons to its entrance (D132 in the first subunit of the S. sphaeroides enzyme). The single-point mutation of D132 to asparagine (N), a neutral residue, abolishes enzyme activity. Conversely, replacing conserved N139, one-third into the D channel, by D, induces a decoupled phenotype, whereby oxygen reduction proceeds but not proton pumping. Intriguingly, the double mutant D132N/N139D, which conserves the charge of the D channel, restores the wild-type phenotype. We use molecular dynamics simulations and electrostatic calculations to examine the structural and physical basis for the coupling of proton pumping and oxygen chemistry in single and double N139D mutants. The potential of mean force for the conformational isomerization of N139 and N139D side chains reveals the presence of three rotamers, one of which faces the channel entrance. This out-facing conformer is metastable in the wild-type and in the N139D single mutant, but predominant in the double mutant thanks to the loss of electrostatic repulsion with the carboxylate group of D132. The effects of mutations and conformational isomerization on the pKa of E286, an essential proton-shuttling residue located at the top of the D channel, are shown to be consistent with the electrostatic control of proton pumping proposed recently (Fadda et al 2008 Biochim. Biophys. Acta 1777 277–84). Taken together, these results suggest that preserving the spatial distribution of charges at the entrance of the D channel is necessary to guarantee both the uptake and the relay of protons to the active site of the enzyme. These findings highlight the interplay of long-range electrostatic forces and local structural fluctuations in the control of proton movement and provide a physical explanation for the restoration of proton pumping activity in the double mutant.

    Item Type: Article
    Keywords: Molecular basis; proton uptake; single and double mutants; cytochrome c oxidase;
    Academic Unit: Faculty of Science and Engineering > Chemistry
    Item ID: 7734
    Identification Number: https://doi.org/10.1088/0953-8984/23/23/234102
    Depositing User: Elisa Fadda
    Date Deposited: 12 Jan 2017 12:12
    Journal or Publication Title: Journal of Physics: Condensed Matter
    Publisher: IOP Publishing
    Refereed: Yes
    URI:

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