Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States.
Department of Chemistry, Westmont College, Santa Barbara, California 93108, United States.
J Phys Chem B. 2023 Jun 8;127(22):4931-4938. doi: 10.1021/acs.jpcb.2c08969. Epub 2023 May 23.
Thiohemiacetals are key intermediates in the active sites of many enzymes catalyzing a variety of reactions. In the case of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), this intermediate connects the two hydride transfer steps where a thiohemiacetal is the product of the first hydride transfer and its breakdown forms the substrate of the second one, serving as the intermediate during cofactor exchange. Despite the many examples of thiohemiacetals in a variety of enzymatic reactions, there are few studies that detail their reactivity. Here, we present computational studies on the decomposition of the thiohemiacetal intermediate in HMGR using both QM-cluster and QM/MM models. This reaction mechanism involves a proton transfer from the substrate hydroxyl to an anionic Glu83 followed by a C-S bond elongation stabilized by a cationic His381. The reaction provides insight into the varying roles of the residues in the active site that favor this multistep mechanism.
硫代半缩醛是许多催化各种反应的酶活性中心的关键中间体。在 3-羟基-3-甲基戊二酰辅酶 A 还原酶 (HMGR) 的情况下，该中间体连接了两个氢化物转移步骤，其中硫代半缩醛是第一个氢化物转移的产物，其分解形成第二个氢化物转移的底物，在辅酶交换过程中作为中间体。尽管在各种酶促反应中有许多硫代半缩醛的例子，但很少有研究详细描述它们的反应性。在这里，我们使用 QM 簇和 QM/MM 模型对 HMGR 中硫代半缩醛中间体的分解进行了计算研究。该反应机制涉及从底物羟基向阴离子 Glu83 的质子转移，随后 C-S 键伸长由阳离子 His381 稳定。该反应深入了解了活性位点中有利于这种多步机制的残基的不同作用。
