Cao Yang, Chen Zhong-Jian, Jiang Hui-Di, Chen Jian-Zhong
Institute of Materia Medica, College of Pharmaceutical Sciences, Zhejiang University , Hangzhou, Zhejiang 310058, P. R. China.
J Phys Chem B. 2014 Jan 16;118(2):470-81. doi: 10.1021/jp410296s. Epub 2014 Jan 2.
Catechol-O-methyltransferase (COMT, EC 2.1.1.6) plays a central role in the inactivation of neurotransmitters sharing a catecholic motif by transferring a methyl group from AdoMet. Methylation of the meta-hydroxyl is much more common than that of the para-hydroxyl in many COMT substrates, such as dopamine and norepinephrine. Our experimental data showed that quercetin preferred meta-methylation but luteolin favored a para-methylation. To elucidate the mechanism for different preferences of methylations of quercetin and luteolin, we performed a theoretical investigation on the different regioseletivities of COMT-catalyzed methylations for quercetin and luteolin by a combined approach of MD simulations, ab initio calculations, and QM/MM computations. The ab initio calculation results showed that both quercetin and luteolin have more negative charge distributions on the meta-O atom than the para-O atom, which indicated that meta-O preferred SN2 reaction for their methylation. Our QM/MM computations also confirmed that these two flavonoids have lower reaction energetic barriers for COMT-catalyzed meta-O-methylation than para-O-methylation. On the other hand, our binding free energy computation results indicated that quercetin has a more stable binding mode for meta-O-methylation than para-O-methylation but luteolin has a more stable binding mode for para-O-methylation than meta-O-methylation. We gave a comprehensive explanation considering both thermodynamics and reaction kinetics aspects and discussed the protein-inhibitor interactions as well as the O-methylation mechanism in our present work.
儿茶酚-O-甲基转移酶（COMT，EC 2.1.1.6）通过从腺苷甲硫氨酸转移甲基，在使具有儿茶酚基序的神经递质失活过程中发挥核心作用。在许多COMT底物（如多巴胺和去甲肾上腺素）中，间位羟基的甲基化比对位羟基的甲基化更为常见。我们的实验数据表明，槲皮素更倾向于间位甲基化，而木犀草素则更倾向于对位甲基化。为了阐明槲皮素和木犀草素甲基化偏好不同的机制，我们采用分子动力学（MD）模拟、从头算计算和量子力学/分子力学（QM/MM）计算相结合的方法，对COMT催化槲皮素和木犀草素甲基化的不同区域选择性进行了理论研究。从头算计算结果表明，槲皮素和木犀草素的间位氧原子上的负电荷分布均比对位氧原子更多，这表明间位氧在其甲基化过程中更倾向于SN2反应。我们的QM/MM计算也证实，这两种黄酮类化合物在COMT催化的间位氧甲基化反应中的能量障碍低于对位氧甲基化反应。另一方面，我们的结合自由能计算结果表明，槲皮素在间位氧甲基化时的结合模式比对位氧甲基化更稳定，而木犀草素在对位氧甲基化时的结合模式比间位氧甲基化更稳定。在本工作中，我们从热力学和反应动力学两方面给出了全面解释，并讨论了蛋白质-抑制剂相互作用以及氧甲基化机制。
