School of Chemistry, National University of Ireland-Galway, Galway, Ireland.
J Phys Chem B. 2011 Mar 3;115(8):1918-26. doi: 10.1021/jp111525p. Epub 2011 Feb 3.
The catalytic mechanism of 2-methyl-3-hydroxypyridine-5-carboxylic acid (MHPC) oxygenase (MHPCO) has been systematically studied using DFT and ONIOM(DFT:MM) methods. MHPCO catalyzes the hydroxylation and subsequent ring-opening of the aromatic substrate MHPC to give the aliphatic product α-(N-acetylaminomethylene)succinic acid (AAMS). Our calculations show that the active-site residues Arg211 and Tyr223 have a minor effect on the reaction, while the peptide bond of Pro295-Ala296, the side chain of Tyr82 and several crystal water molecules affect the reaction energy profile considerably. Both DFT and ONIOM calculations show that the ring-opening pathway B, in which an epoxy transition state is formed, is more favored than the direct C2-C3 cleavage pathway A. Different QM/MM partitioning schemes have been used to study the enzymatic reaction, and the results show that both the reaction barriers for the hydroxylation and the ring-opening pathways are sensitive to the QM/MM partitioning.
使用 DFT 和 ONIOM(DFT:MM)方法系统地研究了 2-甲基-3-羟基吡啶-5-羧酸（MHPC）加氧酶（MHPCO）的催化机制。MHPCO 催化芳香族底物 MHPC 的羟化和随后的开环，生成脂肪族产物α-（N-乙酰氨基亚甲基）琥珀酸（AAMS）。我们的计算表明，活性位点残基 Arg211 和 Tyr223 对反应的影响较小，而 Pro295-Ala296 肽键、Tyr82 的侧链和几个结晶水分子对反应能量曲线有相当大的影响。DFT 和 ONIOM 计算都表明，开环途径 B，其中形成环氧化物过渡态，比直接 C2-C3 断裂途径 A 更有利。使用了不同的 QM/MM 分区方案来研究酶促反应，结果表明，羟化和开环途径的反应势垒都对 QM/MM 分区敏感。
