Jin Y, Stayrook S E, Albert R H, Palackal N T, Penning T M, Lewis M
Department of Pharmacology, Department of Biochemistry and Biophysics, and The Johnson Research Foundation, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Biochemistry. 2001 Aug 28;40(34):10161-8. doi: 10.1021/bi010919a.
The crystal structure of human type III 3alpha-hydroxysteroid dehydrogenase (HSD)/bile acid binding protein (AKR1C2) complexed with NADP(+) and 3alpha,7beta-dihydroxy-5beta-cholanic acid (ursodeoxycholate) at 3.0 A resolution is presented. Thus, the three-dimensional structure has now been solved for a human HSD member of the aldo-keto reductase superfamily. AKR1C2 is implicated in the prostatic production of the potent androgen 5alpha-dihydrotestosterone and the hepatic transport of bile acids. It also catalyzes the formation of the neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one in the central nervous system, and its allosteric modulation by fluoxetine has been linked to the use of this drug for premenstrual dsyphoria. Like other members of the superfamily, AKR1C2 folds into an alpha/beta-barrel and binds NADP(+) in an extended conformation. The carboxylate of ursodeoxycholate binds to AKR1C2 in the oxyanion hole at the active site. More interestingly, the orientation of ursodeoxycholate is essentially "backwards" and "upside-down" from that observed for testosterone in the related rat 3alpha-HSD.NADP(+).testosterone ternary complex, where testosterone assumes the position of a 3-ketosteroid substrate. The orientation of ursodeoxycholate is thus similar to that expected of a 17beta-HSD substrate. The ternary structure explains the ability of AKR1C2 to catalyze 3alpha-, 17beta-, and 20alpha-HSD reactions. Comparison of the steroid binding pocket of AKR1C2 with that of rat 3alpha-HSD reveals significant differences in the positions of conserved and nonconserved loop residues, providing insights into the structural basis for the functional flexibility that is observed in all the human 3alpha-HSD isoforms but not in the rat isoform.
本文展示了人III型3α-羟基类固醇脱氢酶（HSD）/胆汁酸结合蛋白（AKR1C2）与NADP(+)和3α,7β-二羟基-5β-胆烷酸（熊去氧胆酸）形成的复合物在3.0埃分辨率下的晶体结构。因此，醛酮还原酶超家族的人类HSD成员的三维结构现已得到解析。AKR1C2与前列腺中强效雄激素5α-双氢睾酮的产生以及肝脏中胆汁酸的转运有关。它还催化中枢神经系统中神经甾体3α-羟基-5α-孕烷-20-酮的形成，并且其受氟西汀的变构调节与该药物用于经前烦躁障碍的治疗有关。与超家族的其他成员一样，AKR1C2折叠成α/β桶状结构，并以伸展构象结合NADP(+)。熊去氧胆酸的羧酸盐在活性位点的氧负离子孔中与AKR1C2结合。更有趣的是，熊去氧胆酸的取向与相关大鼠3α-HSD.NADP(+).睾酮三元复合物中观察到的睾酮的取向基本“相反”且“颠倒”，在该复合物中睾酮占据3-酮甾体底物的位置。因此，熊去氧胆酸的取向类似于17β-HSD底物的预期取向。三元结构解释了AKR1C2催化3α-、17β-和20α-HSD反应的能力。将AKR1C2的类固醇结合口袋与大鼠3α-HSD的进行比较，发现保守和非保守环残基的位置存在显著差异，这为在所有人类3α-HSD同工型中观察到但在大鼠同工型中未观察到的功能灵活性的结构基础提供了见解。
