Proton Translocation in Proteins

Copeland, Robert A.; Chan, Sunney I.

doi:10.1146/annurev.pc.40.100189.003323

Cited by 44 publications

(34 citation statements)

References 21 publications

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“…The four redox-active metal centers of the enzyme can be functionally divided into two groups, two low potential primary acceptors of electrons from ferrocytochrome c (cytochrome a and CuA) and a binuclear oxygen binding site (cytochrome a3 and CUB) (1, 2). Electron transfer reactions at one or more of these metal centers provide the thermodynamic driving force for ion transport in this enzyme.Several models for redox-linked proton pumping in cytochrome c oxidase have emerged (1)(2)(3)(4)(5). Babcock and coworkers (3) have proposed a model in which hydrogen bonding between the cytochrome a formyl oxygen and an amino acid side-chain proton provides the structural basis for electron transfer-driven proton pumping.…”

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Conformational switching at cytochrome a during steady-state turnover of cytochrome c oxidase.

Copeland

1991

Proc. Natl. Acad. Sci. U.S.A.

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As an electron transfer-driven proton pump, cytochrome c oxidase (ferrocytochrome-c:oxygen oxidoreductase, EC 1.9.3.1) must alternate between two conformations in each valence state of the redox element associated with ion translocation. Using second derivative absorption spectroscopy, the conformation of the cytochrome a cofactor has been investigated during steady-state turnover of this enzyme. Resting cytochrome c oxidase displays a transition for ferric cytochrome a at 430 nm. During aerobic steady-state turnover, this band is replaced by a ferrous cytochrome a transition at 450 rm. When anaerobicity is achieved, the transition occurs at 444 mm. The 450-nm-absorbing species is thus the dominant form during turnover, suggesting that conformational transitions of cytochrome a direct electron transfer during catalysis and may direct as well proton transocation in the last step of the respiratory electron transfer chain.Cytochrome c oxidase (ferrocytochrome-c:oxygen oxidoreductase, EC 1.9.3.1) is a metalloenzyme that functions as an electron transfer-driven proton pump during mitochondrial and bacterial respiration. The four redox-active metal centers of the enzyme can be functionally divided into two groups, two low potential primary acceptors of electrons from ferrocytochrome c (cytochrome a and CuA) and a binuclear oxygen binding site (cytochrome a3 and CUB) (1, 2). Electron transfer reactions at one or more of these metal centers provide the thermodynamic driving force for ion transport in this enzyme.Several models for redox-linked proton pumping in cytochrome c oxidase have emerged (1)(2)(3)(4)(5). Babcock and coworkers (3) have proposed a model in which hydrogen bonding between the cytochrome a formyl oxygen and an amino acid side-chain proton provides the structural basis for electron transfer-driven proton pumping. An alternative model has been put forth by Chan and coworkers (4), in which proton translocation is driven by redox-dependent changes in ligand coordination at CUA. A third model has recently been put forth by Malmstrom (5), in which proton translocation occurs in response to a conformational transition of the enzyme, which is triggered by reduction of both cytochrome a and CUA.A common feature of all of the proposed models of proton translocation in cytochrome c oxidase is that they require redox-dependent protein conformational transitions to provide the proton pumping machinery with alternative access to the two sides of the respiratory membrane. For optimum efficiency, this conformational switch should be in allosteric communication with the oxygen binding site of the enzyme (5, 6). These two conformational states [E1 and E2 in the nomenclature ofMalmstrom (5)] would be present in both the oxidized and reduced forms of the metal center which serves as the site of coupling; the equilibrium between E1 and E2 would be strongly dependent on electron occupancy at the coupling site. Recently, our group (7) has shown that ferrous cytochrome a can adopt two distinct conformations in diffe...

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Conformational switching at cytochrome a during steady-state turnover of cytochrome c oxidase.

Copeland

1991

Proc. Natl. Acad. Sci. U.S.A.

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“…Our results also indicate that the transmembrane electron transfer coupled with a proton pump may not involve any global change in conformation. The structural rearrangements associated with localized fluctuations in the protein backbone and/or in the amino acid side chains [9] may possibly be involved in the redox changes of the protein and such rearrangements in the protein structure may not cause changes in the environment of the tryptophan residues.…”

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Time‐resolved study of tryptophan fluorescence in vesicle reconstituted cytochrome oxidase

Das

Mazumdar

1993

FEBS Letters

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Time-resolved study of fluorescence decay of the tryptophan residue in bovine cytochrome c oxidase in phospholipid vesicles is reported for the first time. The effect of the redox state of the protein on its conformation has been investigated using time-resolved decay of tryptophan fluorescence in the oxidised and reduced protein. The fluorescence decay was best fitted using a discrete three exponential model. Amplitude distribution of lifetimes also showed three distinct regions in the analysis of decay profiles by the maximum entropy method (MEM). Results of the time resolved studies showed that the amplitudes as well as the lifetimes of the trytophan fluorescence remain the same for the oxidised and the reduced states of cytochrome c oxidase, indicating that the environment around tryptophan residues remains more or less unaltered on reduction of the protein.The results suggest that there is no global conformational change in the protein on electron transfer and support the possibility of the existence of local fluctuations in the protein during the redox cycle.

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“…As one of the most ubiquitous interactions in chemistry, the hydrogen bond is profoundly influential in determining the structural organization and processes that occur in a variety of environments, from hydrogen bonding solvents to entire living organisms. The proton transfer reaction, 18 • 1 9,20,21,22,23 perhaps the most general and important reaction in chemistry, is governed in hydrogen bonding solvents by hydrogen bonded "cluster" species. A great many studies have been made of the solvated proton in the liquid and solid phases, using x-ray and neutron diffraction, infrared and nuclear magnetic resonance (NMR) spectroscopy and other techniques.…”

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confidence: 99%