Lee-Robichaud P, Akhtar M E, Akhtar M
Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, U.K.
Biochem J. 1999 Sep 1;342 ( Pt 2)(Pt 2):309-12.
Human CYP17 (17alpha-hydroxylase-17,20-lyase; also cytochrome P450c17 or cytochrome P450(17alpha)) catalyses a hydroxylation reaction and another reaction involving the cleavage of a C-C bond (the lyase activity) that is required only for androgen production. Single amino acid mutations in human CYP17, Arg(347)-->His and Arg(358)-->Gln, have been reported to result in the loss of the lyase activity and to cause sexual phenotypic changes in 46XY male patients. By using site-directed mutagenesis we show here that another mutation in human CYP17, Arg(449)-->Ala, for which human variants have yet not been described, also leads to selective lyase deficiency. Furthermore, all the three types of mutants display a loss of responsiveness to cytochrome b(5), an interaction that is essential for lyase activity, and hence male sex-hormone biosynthesis. That the defect could be essentially reversed by lysine mutagenesis has led to the conclusion that the cationic charges on all three residues (at the positions of Arg(347), Arg(358), Arg(449)) are vital for the functional interaction of CYP17 with cytochrome b(5) and that the loss of any one of these cationic charges is catastrophic.
人细胞色素P450 17α（17α-羟化酶-17,20-裂解酶；也称为细胞色素P450c17或细胞色素P450(17α)）催化一种羟化反应以及另一种涉及碳-碳键断裂的反应（裂解酶活性），该裂解酶活性仅在雄激素生成过程中是必需的。据报道，人细胞色素P450 17α中的单氨基酸突变，即精氨酸(347)→组氨酸和精氨酸(358)→谷氨酰胺，会导致裂解酶活性丧失，并使46XY男性患者出现性表型变化。通过定点诱变，我们在此表明人细胞色素P450 17α中的另一种突变，即精氨酸(449)→丙氨酸，尚未发现其人类变体，也会导致选择性裂解酶缺乏。此外，所有这三种类型的突变体都表现出对细胞色素b5的反应性丧失，细胞色素b5与细胞色素P450 17α的相互作用对裂解酶活性至关重要，因此对雄性激素生物合成也至关重要。赖氨酸诱变可基本逆转该缺陷，由此得出结论，所有三个残基（精氨酸(347)、精氨酸(358)、精氨酸(449)位置）上的阳离子电荷对于细胞色素P450 17α与细胞色素b5的功能相互作用至关重要，并且这些阳离子电荷中任何一个的丧失都是灾难性的。
