School of Pharmacy, Shujitsu University, 1-6-1 Nishigawara, Naka-ku, Okayama 703-8516, Japan.
J Pharm Pharm Sci. 2019;22(1):332-339. doi: 10.18433/jpps30558.
Hydroxylation activity at the 6β-position of steroid hormones (testosterone, progesterone, and cortisol) by human cytochromes P450 (P450 or CYP) 3A4 and CYP3A5 and their molecular docking energy values were compared to understand the catalytic properties of the major forms of human CYP3A, namely, CYP3A4 and CYP3A5.
Testosterone, progesterone, and cortisol 6β-hydroxylation activities of recombinant CYP3A4 and CYP3A5 were determined by liquid chromatography. Docking simulations of these substrates to the heme moiety of reported crystal structures of CYP3A4 (Protein Data Bank code ITQN) and CYP3A5 (6MJM) were conducted.
Michaelis constants (Km) for CYP3A5- mediated 6β-hydroxylation of testosterone and progesterone were approximately twice those for CYP3A4, whereas the value for cortisol 6β-hydroxylation mediated by CYP3A5 was similar to the value for that by CYP3A4. Maximal velocities (Vmax) of the three steroid hormones 6β-hydroxylation catalyzed by CYP3A5 were 30%-63% of those by CYP3A4. Thus, Vmax/ Km values of these hormones for CYP3A5 resulted in 22%- 31% of those for CYP3A4. The differences in the docking energies between CYP3A4 and CYP3A5 for steroid hormones were slightly correlated to the logarithm of CYP3A5/CYP3A4 ratios for Km values (substrate affinity).
The Vmax, rather than Km values, for CYP3A5-mediated 6β-hydroxylation of three steroid hormones were different from those for CYP3A4. Molecular docking simulations could partially explain the differences in the accessibility of substrates to the heme moiety of human CYP3A molecules, resulting in the enzymatic affinity of CYP3A4 and CYP3A5.
比较人细胞色素 P450（P450 或 CYP）3A4 和 CYP3A5 对甾体激素（睾酮、孕酮和皮质醇）6β-位的羟化活性及其分子对接能值，以了解主要人 CYP3A 形式（即 CYP3A4 和 CYP3A5）的催化特性。
采用液相色谱法测定重组 CYP3A4 和 CYP3A5 对睾酮、孕酮和皮质醇 6β-羟化的活性。对报道的 CYP3A4（蛋白数据库代码 ITQN）和 CYP3A5（6MJM）晶体结构血红素部分的这些底物进行对接模拟。
CYP3A5 介导的睾酮和孕酮 6β-羟化的米氏常数（Km）约为 CYP3A4 的两倍，而 CYP3A5 介导的皮质醇 6β-羟化的 Km 值与 CYP3A4 相似。三种甾体激素 6β-羟化由 CYP3A5 催化的最大速度（Vmax）分别为 CYP3A4 的 30%-63%。因此，这些激素对 CYP3A5 的 Vmax/Km 值导致 CYP3A4 的 22%-31%。甾体激素与 CYP3A4 和 CYP3A5 之间的对接能差异与 Km 值（底物亲和力）的 CYP3A5/CYP3A4 比值的对数略有相关。
与 CYP3A4 相比，CYP3A5 介导的三种甾体激素 6β-羟化的 Vmax 值而不是 Km 值不同。分子对接模拟可以部分解释底物对人 CYP3A 分子血红素部分的可及性的差异，从而导致 CYP3A4 和 CYP3A5 的酶亲和力。
