Puig Eduard, Mixcoha Edgar, Garcia-Viloca Mireia, González-Lafont Angels, Lluch José M
Departament de Química, Universitat Autònoma de Barcelona, Bellaterra (Barcelona), Spain.
J Am Chem Soc. 2009 Mar 18;131(10):3509-21. doi: 10.1021/ja806012h.
Molecular Dynamics simulations with a Molecular Mechanics force field and a quite complete exploration of the QM/MM potential energy surfaces have been performed to study the D-glutamate --> L-glutamate reaction catalyzed by Bacillus subtilis glutamate racemase. The results show that the whole process involves four successive proton transfers that occur in three different steps. The Michaelis complex is already prepared to make the first proton transfer (from Cys74 to Asp10) possible. The second step involves two proton transfers (from the alpha-carbon to Cys74, and from Cys185 to the alpha-carbon), which occurs in a concerted way, although highly asynchronic. Finally, in the third step, the nascent deprotonated Cys185 is protonated by His187. The positively charged ammonium group of the substrate plays a very important key role in the reaction. It accompanies each proton transfer in a concerted and coupled way, but moving itself in the opposite direction from Asp10 to His187. Thus, the catalytic action of Bacillus subtilis glutamate racemase is driven by its own substrate of the reaction, D-glutamate.
已使用分子力学力场进行分子动力学模拟，并对QM/MM势能面进行了相当全面的探索，以研究枯草芽孢杆菌谷氨酸消旋酶催化的D-谷氨酸→L-谷氨酸反应。结果表明，整个过程涉及四个连续的质子转移，分三个不同步骤发生。米氏复合物已为首次质子转移（从Cys74转移至Asp10）做好准备。第二步涉及两个质子转移（从α-碳转移至Cys74，以及从Cys185转移至α-碳），这两个质子转移以协同方式发生，尽管高度异步。最后，在第三步中，新生的去质子化Cys185被His187质子化。底物带正电荷的铵基团在反应中起着非常重要的关键作用。它以协同和耦合的方式伴随每次质子转移，但自身沿与Asp10到His187相反的方向移动。因此，枯草芽孢杆菌谷氨酸消旋酶的催化作用由其自身的反应底物D-谷氨酸驱动。
