MOLECULAR MODELING OF HUMAN P450C17 & P450C21: ADRENARCHE, ANDROGEN

细胞色素P450 c17（17-羟化酶，17，20-裂解酶）催化 C21甾族化合物的17-羟基化和氧化裂解， 人类肾上腺和性腺。 然而，这两项活动 在体外和人体生理学中， 磷酸化和细胞色素b5的变构效应。 P450 c21是一种相关的类固醇生成酶，其催化 21-羟化酶反应 P450 c17和P450 c21具有高序列 相似性和相同的基因结构，两者都利用相同的 底物（双烯醇酮、孕酮及其17-羟基 衍生物）。 它们的底物选择性的细微差别 和催化特异性导致产生不同的 类固醇激素具有截然不同的生物活性。 我们 相信这两种酶的结构-功能比较将 对类固醇生成酶的作用产生重要的见解， 选择性抑制的方法 我们已经完成了一 基于X射线结构的人P450 c17的计算机图形模型 利用UCSF计算机上的资源， 图形实验室 基于我们对P450 c17模型的分析， CGL资源，我们设计了嵌合蛋白，试图 赋予P450 c17 21-羟化酶活性和17-羟化酶活性 P450C21。 我们还分析了细胞色素b5的几种结构 和脱辅基细胞色素b5。 根据这一分析，加上我们的 生物化学研究，我们正在设计b5的突变形式， 将用于探测P450 c17与b5的相互作用。 我们将使用 这些数据来完善模型并将蛋白质表面对接在一起， 目的是描述整个催化剂的结构， 复杂.

Cytochrome P450c17 (17-hydroxylase, 17,20-lyase) catalyzes both the 17-hydroxylation and oxidative cleavage of C21 steroids in both human adrenal glands and gonads. These two activities, however are independently regulated in vitro and in human physiology by such factors as phosphorylation and the allosteric effect of cytochrome b5. P450c21 is a related steroidogenic enzyme that catalyzes the 21-hydroxylase reaction. P450c17 and P450c21 have high sequence similarity and identical gene structures, and both utilize the same substrates (pregnenolone, progesterone, and their 17-hydroxy derivatives). The subtle differences in their substrate selectivities and catalytic specificities lead to the production of different steroid hormones with vastly different biological activities. We believe that structure-function comparisons of the two enzymes will yield important insight to the actions of steroidogenic enzymes and approaches to their selective inhibition. We have completed a computer-graphic model of human P450c17 based on the X-ray structure of the bacterial P450BM-P using the resources at the UCSF Computer Graphics Laboratory. Based on our analysis of the P450c17 model using the CGL resources, we have designed chimeric proteins in an attempt to confer 21-hydroxylase activity to P450c17 and 17-hydroxylase activity to P450c21. We have also analyzed several structures of cytochrome b5 and apo-cytochrome b5 in the CGL. Based on this analysis, plus our biochemical studies, we are engineering mutant forms of b5 which we will use to probe the interaction of P450c17 with b5. We will use these data to refine the model and to dock protein surfaces together, with the goal of describing the structure of the entire catalytic complex.