Functional characterization of eight human CYP1A2 variants: the role of cytochrome b(5)

Background Interindividual variability in cytochrome P450 (CYP)-mediated xenobiotic metabolism is extensive. CYP metabolism requires two electrons, which can be donated by NADPH cytochrome P450 oxidoreductase (CYPOR) and/or cytochrome b5 (b5). Although substantial number of studies have reported on the function and effect of b5 in CYP-mediated catalysis, its mode of action is still not fully understood. Objective The aim of this work was to examine the effect of b5 on the activities of eight natural-occurring variants of human CYP1A2, namely, T83M, S212C, S298R, G299S, I314V, I386F, C406Y, and R456H. Materials and methods An approach, as used in our former study was applied, coexpressing these polymorphic CYP1A2 variants separately with CYPOR and b(5) in the bacterial cell model BTC-CYP. For each variant, 16 different activity parameters were measured, using eight different substrates. This heterogeneous data set was merged with the one of our former study (i.e. without b(5)) and a multivariate analysis was carried out. Results This analysis indicated that b(5) seems to have the ability to affect CYP1A2 variants to behave more like the wild-type variant. This was especially the case for variant I386F, for which the presence of b(5) was crucial to show activity. Variants T83M and C406Y showed considerably different activity-profiles when in the presence of b5. Furthermore, our data seem to implicate CYP1A2 residue G299 in its interaction with CYPOR and/or b5. Conclusion Results indicate the ability of b(5) to affect CYP1A2 variants to behave more like the wild-type variant, attenuating detrimental effects of structural mutations of these variants, seemingly through extensive allosteric effects. Pharmacogenetics and Genomics 23:41-52 (C) 2013 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins. Pharmacogenetics and Genomics 2013, 23:41-52