Structural Genomics Consortium, University of Toronto, 101 College Street, Toronto, Ontario, Canada.
J Mol Biol. 2010 Apr 9;397(4):1067-78. doi: 10.1016/j.jmb.2010.01.075. Epub 2010 Feb 10.
The obligatory step in sterol biosynthesis in eukaryotes is demethylation of sterol precursors at the C14-position, which is catalyzed by CYP51 (sterol 14-alpha demethylase) in three sequential reactions. In mammals, the final product of the pathway is cholesterol, while important intermediates, meiosis-activating sterols, are produced by CYP51. Three crystal structures of human CYP51, ligand-free and complexed with antifungal drugs ketoconazole and econazole, were determined, allowing analysis of the molecular basis for functional conservation within the CYP51 family. Azole binding occurs mostly through hydrophobic interactions with conservative residues of the active site. The substantial conformational changes in the B' helix and F-G loop regions are induced upon ligand binding, consistent with the membrane nature of the protein and its substrate. The access channel is typical for mammalian sterol-metabolizing P450 enzymes, but is different from that observed in Mycobacterium tuberculosis CYP51. Comparison of the azole-bound structures provides insight into the relative binding affinities of human and bacterial P450 enzymes to ketoconazole and fluconazole, which can be useful for the rational design of antifungal compounds and specific modulators of human CYP51.
真核生物甾醇生物合成中的强制性步骤是甾醇前体在 C14 位的脱甲基化，这由 CYP51（甾醇 14-α脱甲基酶）在三个连续反应中催化。在哺乳动物中，该途径的最终产物是胆固醇，而重要的中间体减数分裂激活甾醇则由 CYP51 产生。已确定三种人 CYP51 的晶体结构，即无配体和与抗真菌药物酮康唑和依康唑结合的结构，从而分析了 CYP51 家族内功能保守的分子基础。唑类结合主要通过与活性位点保守残基的疏水相互作用发生。配体结合后，B' 螺旋和 F-G 环区域会发生实质性的构象变化，这与该蛋白及其底物的膜性质一致。该进入通道是典型的哺乳动物甾醇代谢 P450 酶，但与结核分枝杆菌 CYP51 观察到的不同。唑类结合结构的比较提供了对人源和细菌 P450 酶与酮康唑和氟康唑相对结合亲和力的深入了解，这对于合理设计抗真菌化合物和人 CYP51 的特异性调节剂可能是有用的。
