The role of Ile 255 in the OPH active site is not described in the literature, to our knowledge. To test whether a subtle change near the important active site residues would affect the stability of the interactions and the flexibility of the substrate binding pocket, we coupled the mutation D253E with a second mutation at position 255. Then, we investigated whether the double mutation disrupted the coupled interactions observed in the OPH active site. Our MD simulations performed on the D253E-I255G mutant in complex with paraoxon showed the same hydrogen bonding profile observed during the simulations of WT OPH. One additional hydrogen bond between Asp 100 and His 257 was found in the trajectory of the D253E-I255G mutant form (Figure ). This finding suggests that position 255 has an indirect role in stabilizing interactions in the OPH active site.