Using Hyperfine Electron Paramagnetic Resonance Spectroscopy to Define the Proton-Coupled Electron Transfer Reaction at Fe-S Cluster N2 in Respiratory Complex I.
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Authors
Le Breton, Nolwenn
Wright, John J
Jones, Andrew JY
Salvadori, Enrico
Publication Date
2017-11-15Journal Title
J Am Chem Soc
ISSN
0002-7863
Publisher
American Chemical Society (ACS)
Volume
139
Issue
45
Pages
16319-16326
Language
eng
Type
Article
This Version
VoR
Physical Medium
Print-Electronic
Metadata
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Le Breton, N., Wright, J. J., Jones, A. J., Salvadori, E., Bridges, H., Hirst, J., & Roessler, M. M. (2017). Using Hyperfine Electron Paramagnetic Resonance Spectroscopy to Define the Proton-Coupled Electron Transfer Reaction at Fe-S Cluster N2 in Respiratory Complex I.. J Am Chem Soc, 139 (45), 16319-16326. https://doi.org/10.1021/jacs.7b09261
Abstract
Energy-transducing respiratory complex I (NADH:ubiquinone oxidoreductase) is one of the largest and most complicated enzymes in mammalian cells. Here, we used hyperfine electron paramagnetic resonance (EPR) spectroscopic methods, combined with site-directed mutagenesis, to determine the mechanism of a single proton-coupled electron transfer reaction at one of eight iron-sulfur clusters in complex I, [4Fe-4S] cluster N2. N2 is the terminal cluster of the enzyme's intramolecular electron-transfer chain and the electron donor to ubiquinone. Because of its position and pH-dependent reduction potential, N2 has long been considered a candidate for the elusive "energy-coupling" site in complex I at which energy generated by the redox reaction is used to initiate proton translocation. Here, we used hyperfine sublevel correlation (HYSCORE) spectroscopy, including relaxation-filtered hyperfine and single-matched resonance transfer (SMART) HYSCORE, to detect two weakly coupled exchangeable protons near N2. We assign the larger coupling with A(1H) = [-3.0, -3.0, 8.7] MHz to the exchangeable proton of a conserved histidine and conclude that the histidine is hydrogen-bonded to N2, tuning its reduction potential. The histidine protonation state responds to the cluster oxidation state, but the two are not coupled sufficiently strongly to catalyze a stoichiometric and efficient energy transduction reaction. We thus exclude cluster N2, despite its proton-coupled electron transfer chemistry, as the energy-coupling site in complex I. Our work demonstrates the capability of pulse EPR methods for providing detailed information on the properties of individual protons in even the most challenging of energy-converting enzymes.
Keywords
Animals, Cattle, Protons, Ubiquinone, Electron Transport Complex I, Histidine, Electron Spin Resonance Spectroscopy, Electron Transport, Oxidation-Reduction, Hydrogen Bonding, Hydrogen-Ion Concentration, Electrons
Sponsorship
Medical Research Council (MC_U105663141)
MRC (MC_UU_00015/2)
Identifiers
External DOI: https://doi.org/10.1021/jacs.7b09261
This record's URL: https://www.repository.cam.ac.uk/handle/1810/276489
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