Abstract
The facultative anaerobe Escherichia coli is able to assemble specific respiratory chains by synthesis of appropriate dehydrogenases and reductases in response to the availability of specific substrates. Under anaerobic conditions in the presence of nitrate, E. coli synthesizes the cytoplasmic membrane-bound quinol-nitrate oxidoreductase (nitrate reductase A; NarGHI), which reduces nitrate to nitrite and forms part of a redox loop generating a proton-motive force. We present here the crystal structure of NarGHI at a resolution of 1.9 Å. The NarGHI structure identifies the number, coordination scheme and environment of the redox-active prosthetic groups, a unique coordination of the molybdenum atom, the first structural evidence for the role of an open bicyclic form of the molybdo-bis(molybdopterin guanine dinucleotide) (Mo-bisMGD) cofactor in the catalytic mechanism and a novel fold of the membrane anchor subunit. Our findings provide fundamental molecular details for understanding the mechanism of proton-motive force generation by a redox loop.
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Acknowledgements
We thank the US Department of Energy for access to data collection facilities at the SSRL and NSLS synchrotrons, and also S. Szigety and D. Mroczko for technical assistance. This work was supported by a Human Frontiers Science Program grant to N.C.J.S., J.H.W. and F.B. N.C.J.S. also acknowledges the Canadian Institutes of Health Research and the Howard Hughes Medical Institute International Scholar program for financial support.
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Bertero, M., Rothery, R., Palak, M. et al. Insights into the respiratory electron transfer pathway from the structure of nitrate reductase A. Nat Struct Mol Biol 10, 681–687 (2003). https://doi.org/10.1038/nsb969
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DOI: https://doi.org/10.1038/nsb969
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