Interconversion of the Androstenedione Hydroxylase Specificities of Cytochromes P450 2B4 and 2B5 upon Simultaneous Site-Directed Mutagenesis of Four Key Substrate Recognition Residues

Based on recent studies of single reciprocal mutants of cytochrome P450 2B4 and the highly related P450 2B5 at positions 114, 294, 363, and 367 [G. D. Szklarz, Y. Q. He, K. M. Kedzie, J. R. Halpert, and V. L. Burnett (1996)Arch. Biochem. Biophys.327, 308–318], a number of multiple mutants were constructed, expressed inEscherichia coli,and assayed with androstenedione, progesterone, and benzyloxyresorufin. Simultaneous substitutions of Ile-114, Ser-294, Ile-363, and Val-367 in cytochrome P450 2B4 with Phe, Thr, Val, and Ala, respectively from 2B5, resulted in a marked increase in androstenedione 15α- and 16α-hydroxylation compared with the wild-type enzyme and yielded a metabolite profile indistinguishable from that of cytochrome P450 2B5. Likewise, the reciprocal P450 2B5 quadruple mutant exhibited the specificity for 16β-hydroxylation characteristic of the 2B4 wild type. The two reciprocal quadruple mutants of P450 2B4 and 2B5 also displayed benzyloxyresorufin dealkylase activities similar to those of the wild-type P450 2B5 and 2B4, respectively. However, the progesterone metabolite profile of P450 2B5 was not identical to that of the 2B4 quadruple mutant or of a quintuple mutant in which residue 370 was also mutated to the 2B5 residue. Therefore, the 17β-acetyl group on progesterone as opposed to the oxo group on androstenedione may lead to interaction with additional amino acid residues.