MOLECULAR DOCKING AND SITE DIRECTED MUTAGENIC APPROACH TO INVESTIGATE THE ROLE OF trp86 OF HUMAN ACETYLCHOLINESTERASE WITH ORGANOPHOSPHATES

Docking and site directed mutagenesis approach was used to explore mode of binding and inhibition for human acetylcholinesterase (hAChE) and organophosphates (OPs). More than 200 OP molecules were investigated using Glide docking module of Schrodinger suit as co-crystal structure between two are not available in Protein Data Bank. In initial screening Trp86 was found to be involved in maximum Pi-Cation interaction on anionic subsite of hAChE other than Ser203 (Catalytic site). With extra precision glide docking Phoxim Ethyl Phosphonate (PEP) tops among 200 OPs based on glide docking score and  interacted with Trp86, Gly121 and Ser203 whereas MM-GBSA score shows less binding affinity than heptenophos and dichlorovos. Trp86 preferred Pi interaction with ring bearing OPs and hydrophobic interactions with smaller OPs without ring bearing structures. Site directed mutagenesis at Trp86 (Trp86 to Ala86) shown the deterioration of the binding site in terms of size reduction, loss of electrostatic and geometric stabilization in binding cavity and significant reduction in binding of OPs in preferred orientation. Dock score of both wild and mutated hAChE shows a perfect qualitative agreement (R²=64.1%) towards the study.  Study suggests role of Trp86 on binding site is inevitably important for inhibition of Human AChE. This study also infers that development of antidotes could be more efficient when Tr86 is also taken into consideration during development of pharmacophores.