期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1999
卷号：96
期号：3
页码：840-845
DOI：10.1073/pnas.96.3.840
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Excess 17{beta}-estradiol (E2), the most potent of human estrogens, is known to act as a stimulus for the growth of breast tumors. Human estrogenic 17{beta}-hydroxysteroid dehydrogenase type 1 (17{beta}-HSD1), which catalyzes the reduction of inactive estrone (E1) to the active 17{beta}-estradiol in breast tissues, is a key enzyme responsible for elevated levels of E2 in breast tumor tissues. We present here the structure of the ternary complex of 17{beta}-HSD1 with the cofactor NADP+ and 3-hydroxyestra-1,3,5,7-tetraen-17-one (equilin), an equine estrogen used in estrogen replacement therapy. The ternary complex has been crystallized with a homodimer, the active form of the enzyme, in the asymmetric unit. Structural and kinetic data presented here show that the 17{beta}-HSD1-catalyzed reduction of E1 to E2 in vitro is specifically inhibited by equilin. The crystal structure determined at 3.0-A resolution reveals that the equilin molecule is bound at the active site in a mode similar to the binding of substrate. The orientation of the 17-keto group with respect to the nicotinamide ring of NADP+ and catalytic residues Tyr-155 and Ser-142 is different from that of E2 in the 17{beta}-HSD1-E2 complex. The ligand and substrate-entry loop densities are well defined in one subunit. The substrate-entry loop adopts a closed conformation in this subunit. The result demonstrates that binding of equilin at the active site of 17{beta}-HSD1 is the basis for inhibition of E1-to-E2 reduction by this equine estrogen in vitro. One possible outcome of estrogen replacement therapy in vivo could be reduction of E2 levels in breast tissues and hence the reduced risk of estrogen-dependent breast cancer.
