Crystal Structures of Human 17<i>β</i>-Hydroxysteroid Dehydrogenase Type 1 Complexed with the Dual-Site Inhibitor EM-139

Abstract

Human 17 β -hydroxysteroid dehydrogenase type 1 (17 β -HSD1) catalyzes the biosynthesis of the most potent natural estrogen 17 β -estradiol (E2) from estrone (E1) in the ovary and peripheral tissues, playing a pivotal role in the progression of estrogen-dependent diseases. N - n -Butyl- N -methyl-ll-(16' α -chloro-3',17' β -dihydroxyestra-1',3',5'(10')-trien-7' α -yl)undecanamide (EM-139) was previously described as a dual-site inhibitor that can inhibit 17 β -HSD1 transforming E1 into E2 and also inhibit estrogen receptor. In the present report, we describe the co-crystallization of EM-139 with 17 β -HSD1 as well as the analysis of the three-dimensional structure of the enzyme/inhibitor complex. The crystal is grown under similar condition as native crystals, whereas the space group is changed to I121 never observed in other 17 β -HSD1 crystals before. The steroidal moiety of the bound EM-139 molecule has shown a binding pattern similar to E2 in the E2 binary complex. The O-3 of the inhibitor develops hydrogen bonds with residues His 221 and Glu 282 , whereas the O-17 makes hydrogen bonds with Ser 142 and Tyr 155 . The bulky 7 α -alkyl moiety of the inhibitor, which is essential for its anti-estrogenic activity but cannot be defined in the electron density, may compromise the inhibitory effect of EM-139 to 17 β -HSD1. Moreover, the 16 α -Cl atom shows no obvious interaction with surrounding residues. The atomic level understanding of the inhibitory mechanism of EM-139 provides important information for the inhibitor design of 17 β -HSD1, which will facilitate future development of more potent and selective inhibitors of the enzyme for therapeutic purposes.