title: Pseudo-symmetry of C19 steroids, alternative binding orientations, and multispecificity in human estrogenic 17beta-hydroxysteroid dehydrogenase.
abstract: Steroids are implicated in many physiological processes, such as reproduction, aging, metabolism, and cancer. To understand the molecular basis for steroid recognition and discrimination, we studied the human estrogenic 17beta-hydroxysteroid dehydrogenase (17beta-HSD1) responsible for the last step in the bioactivation of all estrogens. Here we report the first observation of the conversion of dihydrotestosterone (DHT) into 3beta,17beta-androstanediol (3beta-diol) by 17beta-HSD1, an estrogenic enzyme studied for more than half a century. Kinetic observations demonstrate that both the 3beta-reduction of DHT into 3beta-diol (kcat = 0.040 s(-1)1; Km = 32 +/- 9 microM) and the 17beta-oxidation of DHT into androstandione (A-dione) (kcat = 0.19 s(-1); Km = 26 +/-6 microM) are catalyzed by 17beta-HSD1 via alternative binding orientation of the steroid. The reduction of DHT was also observed in intact cells by using HEK-293 cells stably transformed with 17beta-HSD1. The high-resolution structure of a 17beta-HSD1-C19-steroid (testosterone) complex solved at 1.54 A demonstrates that the steroid is reversibly oriented in the active site, which strongly supports the existence of alternative binding mode. Such a phenomenon can be explained by the pseudo-symmetric structure of C19-steroids. Our results confirm the role of the Leu149 residue in C18/C19-steroid discrimination and suggest a possible mechanism of 17beta-HSD1 in the modulation of DHT levels in tissues, such as the breast, where both the enzyme and DHT are present.
authors.affiliation: Oncology and Molecular Endocrinology Research Center, CHUL Research Center and Laval University, Québec, Canada, G1V 4G2.
authors.forename: Anne
authors.initials: A
authors.lastname: Gangloff
authors.forename: Rong
authors.initials: R
authors.lastname: Shi
authors.forename: Virginie
authors.initials: V
authors.lastname: Nahoum
authors.forename: Sheng-Xiang
authors.initials: SX
authors.lastname: Lin
mesh_terms: D015067:17-Hydroxysteroid Dehydrogenases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002250:Carbon Radioisotopes; D002460:Cell Line; D013196:Dihydrotestosterone / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011485:Protein Binding; D013739:Testosterone / Q000737:chemistry / Q000378:metabolism
chemical_list: D002250:Carbon Radioisotopes; D013196:Dihydrotestosterone; D013739:Testosterone; D015067:17-Hydroxysteroid Dehydrogenases; C044256:3 (or 17)-beta-hydroxysteroid dehydrogenase