Department of Pharmacology, State University of New York Upstate Medical University, Syracuse, NY 13210 United States.
Department of Pharmacology, State University of New York Upstate Medical University, Syracuse, NY 13210 United States.
J Steroid Biochem Mol Biol. 2018 Jul;181:11-19. doi: 10.1016/j.jsbmb.2018.02.009. Epub 2018 Feb 21.
Cytochrome P450 aromatase (AROM) catalyzes the biosynthesis of estrogen from androgen. Previously crystal structures of human AROM in complex with the substrate androstenedione, and inhibitors exemestane, as well as the newly designed steroidal compounds, have been reported. Here we report the first crystal structure of testosterone complex of human placental AROM. Testosterone binds at the androgen-specific heme distal pocket. The polar and hydrophobic interactions with the surrounding residues resemble the interactions observed for other ligands. The heme proximal region comprises the intermolecular interface in AROM, and also the putative interaction surface of its redox partner cytochrome P450 reductase. Unreported previously, the proximal region is characterized by a large surface cavity, unlike most known P450's. Using five best X-ray data sets from androstenedione and testosterone complexes of AROM, we now unequivocally show the presence of an unexplained ligand electron density inside the proximal cavity. The density is interpreted as ordered five ethylene glycol units of polyethylene glycols used as a solvent for steroids and also in crystallization. Interestingly, polyethylene glycol exhibits weak inhibition of AROM enzyme activity in a time dependent manner. Besides its critical role in the redox partner coupling and electron transfer process, the proximal cavity possibly serves as the interaction site for other molecules that may have regulatory effects on AROM activity. In addition, the new data also reveal a previously unidentified water channel linking the active site to the lipid interface. The channel could be the predicted passage for water molecules involved in catalysis.
细胞色素 P450 芳香酶（AROM）催化雄激素转化为雌激素。先前已经报道了人 AROM 与底物雄烯二酮以及抑制剂依西美坦以及新设计的甾体化合物复合物的晶体结构。在这里，我们报告了人胎盘 AROM 与睾酮复合物的首个晶体结构。睾酮结合在雄激素特异性血红素远端袋中。与周围残基的极性和疏水相互作用类似于观察到的其他配体的相互作用。血红素近端区域包含 AROM 中的分子间界面，也是其氧化还原伴侣细胞色素 P450 还原酶的假定相互作用表面。以前未报道过，与大多数已知的 P450 不同，近端区域的特征是一个大的表面腔。使用来自 AROM 与雄烯二酮和睾酮复合物的五个最佳 X 射线数据集，我们现在可以明确地证明在近端腔中存在未解释的配体电子密度。该密度被解释为用作类固醇溶剂的聚乙二醇的五个乙二醇单元的有序排列，也存在于结晶中。有趣的是，聚乙二醇以时间依赖性方式表现出对 AROM 酶活性的弱抑制作用。除了在氧化还原伴侣偶联和电子转移过程中起关键作用外，近端腔可能是与可能对 AROM 活性具有调节作用的其他分子相互作用的位点。此外，新数据还揭示了以前未识别的水通道，该通道将活性位点连接到脂质界面。该通道可能是参与催化的水分子的预测通道。
