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Publication Abstract from PubMed

NADPH-Cytochrome P450 oxidoreductase (CYPOR) transfers electrons from NADPH to cytochromes P450 via its FAD and FMN. To understand the biochemical and structural basis of electron transfer from FMN-hydroquinone to its partners, three deletion-mutants in a conserved loop near the FMN were characterized. Comparison of oxidized and reduced wild type and mutant structures reveals that the basis for the air-stability of the neutral-blue semiquinone is protonation of the flavin N5 and strong H-bond formation with the Gly-141 carbonyl. The Gly-143 protein had moderately decreased activity with cytochrome P450 and cytochrome c. It formed a flexible loop, which transiently interacts with the flavin N5, resulting in the generation of both an unstable neutral-blue semiquinone and hydroquinone. The Gly-141 and Gly-141/Glu-142Asn mutants were inactive with cytochrome P450, but fully active with reduced cytochrome c . In the Gly-141 mutants, the backbone amide of Glu/Asn 142 forms an H-bond to the N5 of the oxidized flavin, which leads to formation of an unstable red-anionic semiquinone with a more negative potential than the hydroquinone. The semiquinone of G141/E142N was slightly more stable than that of G141, consistent with its crystallographically demonstrated more rigid loop. Nonetheless, both Gly-141 red semiquinones were less stable than those of the corresponding loop in cytochrome P450 BM3 and the nNOS mutant (DeltaGly-810). Our results indicate that the catalytic activity of CYPOR is a function of the length, sequence, and flexibility of the 140s loop and illustrate the sophisticated variety of biochemical mechanisms employed in fine-tuning its redox properties and function.

Mutants of Cytochrome P450 Reductase Lacking Either Gly-141 or Gly-143 Destabilize Its FMN Semiquinone.,Rwere F, Xia C, Im S, Haque MM, Stuehr DJ, Waskell L, Kim JP J Biol Chem. 2016 May 9. pii: jbc.M116.724625. PMID:27189945^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.