CATALYTIC MECHANISM OF ALL-TRANS-RETINOIC ACID 4-HYDROXYLATION MEDIATED BY CYTOCHROME P450 2C8: HOW DOES ARGININE 241 AFFECT THE C–H BOND ACTIVATION?
CATALYTIC MECHANISM OF ALL-TRANS-RETINOIC ACID 4-HYDROXYLATION MEDIATED BY CYTOCHROME P450 2C8: HOW DOES ARGININE 241 AFFECT THE C–H BOND ACTIVATION?
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DOI：
10.1142/s0219633613410095
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发表时间：
2013-12
影响因子：
2.4
通讯作者：
Xiaoxuan Li;Jilong Zhang;Qingchuan Zheng;Ying-Lu Cui;Rui-Juan Niu;Hong-Xing Zhang;Chia-Chung Sun
中科院分区：
文献类型：
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作者：
Xiaoxuan Li;Jilong Zhang;Qingchuan Zheng;Ying-Lu Cui;Rui-Juan Niu;Hong-Xing Zhang;Chia-Chung Sun
实验表明，细胞色素P450 2C8酶（CYP2C8）与生理上重要的分子视黄酸有两个不同的底物结合位点，这两个结合位点之间的主要区别在于视黄酸的阴离子羧酸尾部与周围蛋白质环境之间是否存在盐桥相互作用。然而，这种盐桥相互作用对催化的影响仍然难以捉摸。本文采用密度泛函理论（DFT）计算研究CYP2C8介导的全反式视黄酸（atRA）4-羟基化反应机理。我们的DFT计算表明，这种盐桥相互作用对atRA 4-羟基化的反应机理有明显的影响。在 atRA 的阴离子羧酸尾和 Arg241 的阳离子胍基之间含有盐桥相互作用的结合位点中，C-H 键活化通过正常的氢原子转移 (HAT) 机制进行；然而，在没有盐桥相互作用的另一个位点，C-H键激活是通过逐步电子转移和氢原子转移实现的，因此，这是一种新颖的ET/HAT机制。这些发现丰富了金属酶及其仿生体催化C-H键活化的机制模式。同时，我们在真空中计算时遇到的自相互作用误差（SIE）问题由于计算中包含外部电场而受到影响并被消除。
Experiments revealed that cytochrome P450 2C8 enzyme (CYP2C8) has two distinct substrate binding sites to the physiologically important molecules, retinoic acids, and the main difference between these two binding sites is whether there is a salt bridge interaction between the anionic carboxylate tail of retinoic acids and the surrounding protein environment. However, the influence of such salt bridge interaction toward catalysis is still elusive. In the present paper, density functional theory (DFT) calculations were employed to research the reaction mechanism of all-trans-retinoic acid (atRA) 4-hydroxylation mediated by CYP2C8. Our DFT calculations revealed that such salt bridge interaction has obvious effects on the reaction mechanism of atRA 4-hydroxylation. In the binding site containing a salt bridge interaction between the anionic carboxylate tail of atRA and the cationic guanidine group of Arg241, C–H bond activation proceeds via a normal hydrogen atom transfer (HAT) mechanism; in the other site without this salt bridge interaction, however, C–H bond activation is achieved via a stepwise electron transfer and hydrogen atom transfer, thus, a novel ET/HAT mechanism. These findings enrich the mechanism patterns of C–H bond activation catalyzed by metalloenzymes and their biomimetics. Meanwhile, the self-interaction error (SIE) problem encountered during our calculations in vacuum was affected and removed by the inclusion of an external electric field in the calculations.