THE STRUCTURE OF A COMPLEX OF HUMAN 17-BETA-HYDROXYSTEROID DEHYDROGENASE WITH ESTRADIOL AND NADP(+) IDENTIFIES 2 PRINCIPAL TARGETS FOR THE DESIGN OF INHIBITORS

Background: The steroid hormone 17 beta-estradiol is important in the genesis and development of human breast cancer. Its intracellular conc entration is regulated by 17 beta-hydroxysteroid dehydrogenase, which catalyzes the reversible reduction of estrone to 17 beta-estradiol. Th is enzyme is thus an important target for inhibitor design. The precis e localization and orientation of the substrate and cofactor in the ac tive site is of paramount importance for the design of such inhibitors , and for an understanding of the catalytic mechanism. Results: The st ructure of recombinant human 17 beta-hydroxysteroid dehydrogenase of t ype 1 (17 beta-HSD1) in complex with estradiol at room temperature has been determined at 1.7 Angstrom resolution, and a ternary 17 beta-HSD 1 -estradiol-NADP(+) complex at -150 degrees C has been solved and ref ined at 2.20 A resolution, The structures show that estradiol interact s with the enzyme through three hydrogen bonds (involving side chains of Ser142, Tyr155 and His221), and hydrophobic interactions between th e core of the steroid and nine other residues. The NADP(+) molecule bi nds in an extended conformation, with the nicotinamide ring close to t he estradiol molecule. Conclusions: From the structure of the complex of the enzyme with the substrate and cofactor of the oxidation reactio n, the orientation of the substrates for the reduction reaction can be deduced with confidence, A triangular hydrogen-bond network between T yr155, Ser142 and O17 from estradiol probably facilitates the deproton ation of the reactive tyrosine, while the conserved Lys159 appears not to be directly involved in catalysis, Both the steroid-binding site a nd the NADPH-binding site can be proposed as targets for the design of inhibitors.