title: The enantiomer of progesterone (ent-progesterone) is a competitive inhibitor of human cytochromes P450c17 and P450c21.
abstract: Human cytochrome P450c17 (17alpha-hydroxylase, 17,20-lyase) (CYP17) and cytochrome P450c21 (21-hydroxylase) (CYP21) differ by only 14 amino acids in length and share 29% amino acid identity. Both enzymes hydroxylate progesterone at carbon atoms that lie only 2.6A apart, but CYP17 also metabolizes other steroids and demonstrates additional catalytic activities. To probe the active site topologies of these related enzymes, we synthesized the enantiomer of progesterone and determined if ent-progesterone is a substrate or inhibitor of CYP17 and CYP21. Neither enzyme metabolizes ent-progesterone; however, ent-progesterone is a potent competitive inhibitor of CYP17 (K(I)=0.2 microM). The ent-progesterone forms a type I difference spectrum with CYP17, but molecular dynamics simulations suggest different binding orientations for progesterone and its enantiomer. The ent-progesterone also inhibits CYP21, with weaker affinity than for CYP17. We conclude that CYP17 accommodates the stereochemically unnatural ent-progesterone better than CYP21. Enantiomeric steroids can be used to probe steroid binding sites, and these compounds may be effective inhibitors of steroid biosynthesis.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Bovlevard, Dallas 75390-8857, USA. Richard.Auchus@UTSouthwestern.edu
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Auchus
authors.forename: A
authors.initials: A
authors.lastname: Sampath Kumar
authors.forename: C
authors.initials: C
authors.lastname: Andrew Boswell
authors.forename: Manisha K
authors.initials: MK
authors.lastname: Gupta
authors.forename: Kristen
authors.initials: K
authors.lastname: Bruce
authors.forename: Nigam P
authors.initials: NP
authors.lastname: Rath
authors.forename: Douglas F
authors.initials: DF
authors.lastname: Covey
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D006801:Humans; D007700:Kinetics; D008861:Microsomes / Q000378:metabolism; D008956:Models, Chemical; D008958:Models, Molecular; D010957:Plasmids / Q000378:metabolism; D011374:Progesterone / Q000737:chemistry* / Q000494:pharmacology; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D013053:Spectrophotometry; D013237:Stereoisomerism; D013254:Steroid 17-alpha-Hydroxylase / Q000737:chemistry*; D013255:Steroid 21-Hydroxylase / Q000737:chemistry*; D013379:Substrate Specificity; D013696:Temperature; D013997:Time Factors
chemical_list: D011374:Progesterone; D013255:Steroid 21-Hydroxylase; D013254:Steroid 17-alpha-Hydroxylase