title: Role of residues 363 and 206 in conversion of cytochrome P450 2B1 from a steroid 16-hydroxylase to a 15 alpha-hydroxylase.
abstract: Four double and four triple site-directed mutants of cytochrome P450 2B1 were constructed, expressed in COS cells, and assayed for androstenedione and testosterone hydroxylation. The mutants combined a Val-363-->Ala substitution with an Ile-114-->Val or Ala substitution and/or a Gly-478-->Ala or Ser substitution. Each of the individual mutations enhances androgen 15 alpha-hydroxylation, and the appropriate combination of Val or Ala at position 114 with Ala or Ser at position 478 has recently been shown to convert P450 2B1 from an androstenedione and testosterone 16 beta-hydroxylase to a 15 alpha-hydroxylase (Halpert, J. R., and He, Y.-A. (1993) J. Biol. Chem. 268, 4453-4457). All eight mutants containing the Val-363-->Ala substitution preferentially hydroxylated androstenedione and testosterone in the 15 alpha-position and thus functionally resemble mouse P450 2A4. However, unlike P450 2A4, various single and multiple 2B1 mutants at positions 114, 363, and 478 mainly hydroxylated progesterone in the 16 alpha- rather than 15 alpha-position. By combining the Ile-114-->Ala substitution with a Phe-206-->Leu mutation (corresponding to Ala-117 and Leu-209 in P450 2A4), P450 2B1 was converted to a progesterone 15 alpha-hydroxylase with retention of testosterone 15 alpha-hydroxylase activity. These studies document the importance of residues 363 and 206 in determining the substrate specificity of P450 2B1 and strongly support the hypothesis that the judicious combination of a small number of discrete mutations can be used to confer new specificities on P450 enzymes.
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson 85721.
authors.forename: Z
authors.initials: Z
authors.lastname: Luo
authors.forename: Y A
authors.initials: YA
authors.lastname: He
authors.forename: J R
authors.initials: JR
authors.lastname: Halpert
mesh_terms: D000735:Androstenedione / Q000378:metabolism; D001189:Aryl Hydrocarbon Hydroxylases; D002460:Cell Line; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000072467:Cytochrome P450 Family 2; D004926:Escherichia coli / Q000235:genetics; D006900:Hydroxylation; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011374:Progesterone / Q000378:metabolism; D013250:Steroid Hydroxylases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013739:Testosterone / Q000378:metabolism; D014162:Transfection
chemical_list: D013739:Testosterone; D000735:Androstenedione; D011374:Progesterone; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C460223:Cyp2a4 protein, mouse; D000072467:Cytochrome P450 Family 2; C050356:steroid 15-alpha-hydroxylase; C025619:steroid 16-beta-hydroxylase