This is the final edited PDF created by the publisher. This research was originally published in Journal of Biological Chemistry. Ellis, J., Gutierrez, A., Barsukov, I.L., Huanh, W-C., Grossman, J.G., Roberts, G.C.k., Domain motion in cytochrome P450 reductase: conformational equilibria revealed by NMR and small-angle X-Ray scattering, Journal of Biological Chemistry, 2009, 284, pp. 36628-36637. @the American Society for Biochemistry and Molecular Biology. This article is available at http://www.jbc.org/, doi:10.1074/jbc.M109.054304NADPH-cytochrome P450 reductase (CPR), a diflavin reductase,\ud plays a key role in the mammalian P450 mono-oxygenase\ud system. In its crystal structure, the two flavins are close together,\ud positioned for interflavin electron transfer but not for electron\ud transfer to cytochrome P450.Anumber of lines of evidence suggest\ud that domain motion is important in the action of the\ud enzyme. We report NMR and small-angle x-ray scattering experiments\ud addressing directly the question of domain organization\ud in human CPR. Comparison of the 1H-15N heteronuclear\ud single quantum correlation spectrum of CPR with that of the\ud isolatedFMNdomain permitted identification of residues in the\ud FMN domain whose environment differs in the two situations.\ud These include several residues that are solvent-exposed in the\ud CPR crystal structure, indicating the existence of a second conformation\ud in which the FMN domain is involved in a different\ud interdomain interface. Small-angle x-ray scattering experiments\ud showed that oxidized and NADPH-reduced CPRs have\ud different overall shapes. The scattering curve of the reduced\ud enzyme can be adequately explained by the crystal structure,\ud whereas analysis of the data for the oxidized enzyme indicates\ud that it exists as a mixture of approximately equal amounts of two\ud conformations, one consistent with the crystal structure and\ud one a more extended structure consistent with that inferred\ud from the NMR data. The correlation between the effects of\ud adenosine 2’,5’-bisphosphate and NADPH on the scattering\ud curve and their effects on the rate of interflavin electron transfer\ud suggests that this conformational equilibrium is physiologically\ud relevant.Wellcome Trus
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