Structure of Cytochrome P450 Reductase in an Open Conformation Capable of Reducing Cytochrome P450

Abstract

NADPH‐cytochrome P450 oxidoreductase (CYPOR) catalyzes the transfer of electrons to all known microsomal cytochromes P450 (cyt P450). A CYPOR variant, with a four amino acid deletion in the hinge connecting the FMN domain to the rest of the protein, has been crystallized in three extended conformations. The variant donates an electron to cytochrome P450 at the same rate as wild type, when provided with sufficient electrons. Nevertheless, it is defective in its ability to transfer electrons intramolecularly from FAD to FMN. The three extended CYPOR structures demonstrate that by pivoting on the C‐terminus of the hinge, the FMN domain is able to execute a large movement in the course of transferring electrons from FAD to its physiological partner, cytochrome P450. A model of the complex between CYPOR and cytochrome P450 is presented that satisfies mutagenesis constraints. Neither lengthening the linker nor mutating its sequence influenced the activity of CYPOR. It is likely that the analogous linker in other members of the diflavin family functions in a similar manner. Both NIH and VA Merit grants supported this research.