Structure and Mechanism of HpcG, a Hydratase in the Homoprotocatechuate Degradation Pathway of Escherichia coli
作者:Atsushi Izumi、Dean Rea、Tomoko Adachi、Satoru Unzai、Sam-Yong Park、David I. Roper、Jeremy R.H. Tame
DOI:10.1016/j.jmb.2007.05.006
日期:2007.7
without the aid of any cofactor other than a simple divalent metal ion such as Mg(2+). Since the substrate has a nearby carbonyl group, it is believed that it first isomerises to form a pair of conjugated double bonds in the enol tautomer before Michael addition of water. Previous chemical studies of the reaction, and that of the related enzyme MhpD, have failed to provide a clear picture of the mechanism
HpcG 催化碳-碳双键的水合,无需任何辅助因子(如 Mg(2+) 等简单的二价金属离子)。由于底物附近有一个羰基,据信它首先异构化,在迈克尔加水之前在烯醇互变异构体中形成一对共轭双键。以前对该反应的化学研究以及相关酶 MhpD 的化学研究未能提供清晰的机理图。底物本身不稳定,会阻止晶体的共结晶或浸泡,但草酸盐是一种强竞争性抑制剂。我们已经解决了 apo 形式的蛋白质的晶体结构,并与镁和草酸盐结合。将底物建模到活性位点表明攻击性水分子不是金属配位壳的一部分,与之前的提议相反。我们的模型表明几何应变的顺式异构体中间体不位于反应途径上,并且不同的基团参与异构化和水合步骤。