Conclusion
In this study, we demonstrate that the protonated Glu202 is important in maintaining the key hydrogen bond network and hence supporting the catalytic triad. The key hydrogen bond network has a water molecule sitting at the center. Due to the multiple hydrogen bonds associate with the centered water molecule, the Glu202 needs to be protonated to join and stabilize this hydrogen bond network, whereas the deprotonated Glu202 results in the collapse of the key hydrogen bond network which consequently destabilizes the catalytic His447. Although different protonation states of Glu202 merely alters the binding mode of ACh in the enzyme, the catalytic efficiency of ACh hydrolysis should be remarkably decreased if Glu202 is deprotonated, since the disrupted His447 can not facilitate the nucleophilic attack performed by Ser203.
Our findings suggest that it is necessary to take into account the protonation states of Glu202 for AChE related studies. In particular, when designing and developing highly active AChE inhibitors, or proposing mechanistic hypotheses for AChE-catalyzed reactions, the protonated state of Glu202 should be considered.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This work was financially supported in part by the Open Project Program of Key Laboratory of Drug Prevention and Control Technology of Zhejiang Province (No. 2020005), and by the National Natural Science Foundation of China Grants (21102050). The computational work in this paper is supported by the public computing service platform provided by the Network and Computing Center of HUST.