Thoma Ralf, Schulz-Gasch Tanja, D'Arcy Brigitte, Benz Jörg, Aebi Johannes, Dehmlow Henrietta, Hennig Michael, Stihle Martine, Ruf Armin
F. Hoffmann-La Roche AG, Pharma Research Discovery Chemistry, 4070 Basel, Switzerland.
Nature. 2004 Nov 4;432(7013):118-22. doi: 10.1038/nature02993.
In higher organisms the formation of the steroid scaffold is catalysed exclusively by the membrane-bound oxidosqualene cyclase (OSC; lanosterol synthase). In a highly selective cyclization reaction OSC forms lanosterol with seven chiral centres starting from the linear substrate 2,3-oxidosqualene. Valuable data on the mechanism of the complex cyclization cascade have been collected during the past 50 years using suicide inhibitors, mutagenesis studies and homology modelling. Nevertheless it is still not fully understood how the enzyme catalyses the reaction. Because of the decisive role of OSC in cholesterol biosynthesis it represents a target for the discovery of novel anticholesteraemic drugs that could complement the widely used statins. Here we present two crystal structures of the human membrane protein OSC: the target protein with an inhibitor that showed cholesterol lowering in vivo opens the way for the structure-based design of new OSC inhibitors. The complex with the reaction product lanosterol gives a clear picture of the way in which the enzyme achieves product specificity in this highly exothermic cyclization reaction.
在高等生物中，甾体骨架的形成仅由膜结合的氧化角鲨烯环化酶（OSC；羊毛甾醇合酶）催化。在一个高度选择性的环化反应中，OSC从线性底物2,3-氧化角鲨烯开始形成具有七个手性中心的羊毛甾醇。在过去50年里，利用自杀抑制剂、诱变研究和同源建模，已经收集了关于复杂环化级联反应机制的宝贵数据。然而，人们仍然没有完全理解该酶是如何催化反应的。由于OSC在胆固醇生物合成中的决定性作用，它成为发现新型抗胆固醇药物的靶点，这些药物可以补充广泛使用的他汀类药物。在此，我们展示了人类膜蛋白OSC的两种晶体结构：与一种在体内显示出降低胆固醇作用的抑制剂结合的靶蛋白，为基于结构的新型OSC抑制剂设计开辟了道路。与反应产物羊毛甾醇形成的复合物清晰地展示了该酶在这个高度放热的环化反应中实现产物特异性的方式。
