Hoog S S, Pawlowski J E, Alzari P M, Penning T M, Lewis M
Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia 19104-6084.
Proc Natl Acad Sci U S A. 1994 Mar 29;91(7):2517-21. doi: 10.1073/pnas.91.7.2517.
The 3.0-A-resolution x-ray structure of rat liver 3 alpha-hydroxysteroid dehydrogenase/dihydrodiol dehydrogenase (3 alpha-HSD, EC 1.1.1.50) was determined by molecular replacement using human placental aldose reductase as the search model. The protein folds into an alpha/beta or triose-phosphate isomerase barrel and lacks a canonical Rossmann fold for binding pyridine nucleotide. The structure contains a concentration of hydrophobic amino acids that lie in a cavity near the top of the barrel and that are presumed to be involved in binding hydrophobic substrates (steroids, prostaglandins, and polycyclic aromatic hydrocarbons) and inhibitors (nonsteroidal antiinflammatory drugs). At the distal end of this cavity lie three residues in close proximity that have been implicated in catalysis by site-directed mutagenesis--Tyr-55, Asp-50, and Lys-84. Tyr-55 is postulated to act as the general acid. 3 alpha-HSD shares significant sequence identity with other HSDs that belong to the aldo-keto reductase superfamily and these may show similar architecture. Other members of this family include prostaglandin F synthase and rho-crystallin. By contrast, 3 alpha-HSD shares no sequence identity with HSDs that are members of the short-chain alcohol dehydrogenase family but does contain the Tyr-Xaa-Xaa-Xaa-Lys consensus sequence implicated in catalysis in this family. In the 3 alpha-HSD structure these residues are on the periphery of the barrel and are unlikely to participate in catalysis.
利用人胎盘醛糖还原酶作为搜索模型，通过分子置换法确定了大鼠肝脏3α-羟基类固醇脱氢酶/二氢二醇脱氢酶（3α-HSD，EC 1.1.1.50）的3.0埃分辨率X射线结构。该蛋白质折叠成α/β或磷酸丙糖异构酶桶状结构，缺乏结合吡啶核苷酸的典型罗斯曼折叠。该结构包含一组疏水氨基酸，它们位于桶状结构顶部附近的一个腔内，推测参与结合疏水底物（类固醇、前列腺素和多环芳烃）和抑制剂（非甾体抗炎药）。在这个腔的远端有三个紧邻的残基，通过定点诱变已证明它们参与催化作用——Tyr-55、Asp-50和Lys-84。推测Tyr-55作为通用酸起作用。与属于醛糖-酮糖还原酶超家族的其他HSDs相比，3α-HSD具有显著的序列同一性，并且这些可能显示出相似的结构。该家族的其他成员包括前列腺素F合酶和rho-晶体蛋白。相比之下，3α-HSD与属于短链醇脱氢酶家族的HSDs没有序列同一性，但确实包含该家族中与催化作用相关的Tyr-Xaa-Xaa-Xaa-Lys共有序列。在3α-HSD结构中，这些残基位于桶状结构的外围，不太可能参与催化作用。
