Key Lab of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China.
J Mol Graph Model. 2011 Sep;30:148-52. doi: 10.1016/j.jmgm.2011.06.012. Epub 2011 Jul 7.
The quantum-mechanical/molecular-mechanical (QM/MM) method was used to study the glycosylation mechanism of rice BGlu1 β-glucosidase in complex with laminaribiose. The calculation results reveal that the glycosylation step experiences a concerted process from the reactant to the glycosyl-enzyme complex with an activation barrier of 15.7 kcal/mol, in which an oxocarbenium cation-like transition state (TS) is formed. At the TS, the terminal saccharide residue planarizes toward the half-chair conformation, and the glycosidic bond cleavage is promoted by the attacks of proton donor (E176) on glycosidic oxygen and nucleophilic residue (E386) on the anomeric carbon of laminaribiose. Both the nucleophilic glutamate (E386) and acid/base catalyst (E176) establish shorter hydrogen bridges with the C₂-hydroxyl groups of sugar ring, which play an important role in the catalytic reaction of rice BGlu1 β-glucosidase.
采用量子力学/分子力学(QM/MM)方法研究了米氏 BGlu1β-葡萄糖苷酶与纤维二糖复合物的糖化机制。计算结果表明，糖化步骤经历了从反应物到糖基化酶复合物的协同过程，其活化势垒为 15.7 kcal/mol，其中形成了氧杂碳正离子似的过渡态(TS)。在 TS 处，末端糖残基平面化至半椅构象，并且糖苷键的断裂由质子供体(E176)对糖苷氧原子的攻击和纤维二糖的糖苷碳原子上的亲核残基(E386)促进。亲核谷氨酸(E386)和酸碱催化剂(E176)与糖环的 C₂-羟基建立了较短的氢键，这在米氏 BGlu1β-葡萄糖苷酶的催化反应中起着重要作用。
