Altered Cyp19a1 and Cyp3a4 Activities Due to Mutations in the Flavin Mononucleotide Binding Domain of Human P450 Oxidoreductase

Cytochromes P450 proteins are responsible for the metabolism of many steroid hormones as well as drugs and xenobiotics. All cytochromes P450s in the endoplasmic reticulum rely on P450 oxidoreductase (POR) for their catalytic activities. Previously we and others have shown that mutations in POR cause metabolic disorders of steroid hormone biosynthesis and also affect certain drug metabolizing P450 activities. Human POR has distinct subdomains, which bind flavin molecules and interact with redox partners. We studied the mutations identified in flavin mononucleotide (FMN) binding domain of POR that interacts with partner proteins. We found that mutations A115V, T142A located close to the FMN binding site had reduced flavin content compared to wild type POR and lost almost all activity to metabolize androstenedione via CYP19A1 and also showed reduced CYP3A4 activity. The variant A284L identified from normal subjects also had severe loss of both CYP19A1 and CYP3A4 activities, indicating this to be a potentially disease causing mutation. The mutation Q153R initially identified in a patient with disordered steroidogenesis showed remarkably increased activities of both CYP19A1 and CYP3A4 without any significant change in flavin content, indicating improved protein-protein interactions between POR Q153R and some P450 proteins. Such improved activities could be exploited for biotechnological applications to improve product yields. These results indicate that effects of mutations on activities of individual cytochromes P450 can be variable and a detailed analysis of each variant with different partner proteins is necessary to accurately determine the genotype-phenotype correlations of POR variants. Support or Funding Information This work was supported by a grant from the Swiss National Science Foundation (31003A-134926) to Amit V Pandey. The estrogen biosynthesis process requires CYP19A1 activity that is dependent on POR. The deficiency in POR can alter the enzymatic reactions of many cytochrome P450 enzymes and these changes can be variable based on structural properties of the mutation and nature of the redox partner (Pandey, A.V., and Flück, C.E. NADPH P450 oxidoreductase: structure, function, and pathology of diseases. Pharmacol Ther 2013, 138: 229–254). The estrogen biosynthesis process requires CYP19A1 activity that is dependent on POR. The deficiency in POR can alter the enzymatic reactions of many cytochrome P450 enzymes and these changes can be variable based on structural properties of the mutation and nature of the redox partner (Pandey, A.V., and Flück, C.E. NADPH P450 oxidoreductase: structure, function, and pathology of diseases. Pharmacol Ther 2013, 138: 229–254).