Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur 721302, India.
J Phys Chem B. 2023 Dec 7;127(48):10279-10294. doi: 10.1021/acs.jpcb.3c04721. Epub 2023 Nov 20.
Extensive computer simulation studies have been carried out to probe the pH-dependent structure and dynamics of the two most efficient isoenzymes II and IX of human carbonic anhydrase (HCA) that control the pH in the human body. The equilibrium structure and hydration of their catalytic domains are found to be largely unaffected by the variation of pH in the range studied, in close agreement with the known experimental results. In contrast, a significant effect of the change in pH is observed for the first time on the local electrostatic potential of the active site walls and the dynamics of active site water molecules. We also report for the first time the free energy and kinetics of coupled fluctuations of orientation and protonation states of the well-known His-mediated proton shuttle (His-64) in both isozymes at pH 7 and 8. The transitions between different tautomers of in or out conformations of His-64 side chain range between 10 and 10 s depending on pH. Possible implications of these results on conformation-dependent p of His-64 side chain and its role in driving the catalysis toward hydration of CO or dehydration of HCO with varying pH are discussed.
已经进行了广泛的计算机模拟研究，以探究两种最有效的人碳酸酐酶 (HCA) 同工酶 II 和 IX 的 pH 依赖性结构和动力学，这两种同工酶控制着人体的 pH 值。研究发现，它们的催化结构域的平衡结构和水合作用在研究范围内的 pH 变化时基本不受影响，这与已知的实验结果非常吻合。相比之下，pH 值的变化首次对活性位点壁的局部静电势和活性位点水分子的动力学产生了显著影响。我们还首次报道了在 pH 值为 7 和 8 时，两种同工酶中著名的 His 介导质子转移 (His-64) 的取向和质子化状态耦合波动的自由能和动力学。根据 pH 值的不同，His-64 侧链的内或外构象的不同互变异构体之间的转变时间在 10 到 10 s 之间。讨论了这些结果对 His-64 侧链构象依赖性 p 的可能影响及其在驱动 CO 水合或 HCO 脱水反应随 pH 值变化的作用。
