Behavior of uncharged oximes compared to HI6 and 2-PAM in the human AChE-tabun conjugate: a molecular modeling approach

Abstract

Tabun is one of the most dangerous nerve agents because it has deleterious effects like inhibition of the essential enzymes acetylcholinesterase (AChE) and butyrylcholinesterase. Some oximes such HI6 as 2-PAM are nucleophiles that are capable to reactivate inhibited human AChE under some conditions. Zwitterionic and cationic species have the best chance of productive action on inhibited AChE. However uncharged oximes can give important interaction information. In order to investigate the interaction and behavior of cationic and uncharged oximes, we performed molecular docking simulations and molecular dynamics and calculated binding energies of complexes of these compounds with human AChE. The uncharged oximes of larger structure were more susceptible to the influence of the substituents on the phosphorus atom and presented low binding energies. In contrast, HI 6 and 2-PAM showed high binding energy values with great contribution of the amino acid Asp74, demonstrating the importance of the quaternary nitrogen to the affinity and interaction of the oximes/AChE tabun-inhibited complexes.

Keywords:

• tabun
• acetylcholinesterase
• uncharged oximes
• chemical defense

Acknowledgments

The Authors wish to thank the Brazilian financial agencies CNPq, FAPERJ, and CAPES/MD (Edital PRODEFESA 2008) for financial support and the Military Institute of Engineering for the physical infrastructure and working space. This paper was also supported by the excellence project FIM and the project of Czech Science Foundation: 15-16701S.