Despite several engineered variants, applications of OPH suffer from the enzyme's low substrate binding efficiency, hindering its action as an OP scavenger. Here, we focused on designing OPH mutants that yield stronger substrate binding while maintaining catalytic effectiveness. Many previous studies have been done to improve OPH substrate binding through rational design or direct evolution . None of the resulting designed variants, which mainly targeted active-site modifications, improved binding properties to nerve agents sufficiently to prevent lethality. In the current work, we targeted residues surrounding the OPH active site. The selected residues do not coordinate the Zn(II) cations in the active site, and are not directly involved in the hydrolysis reaction. We hypothesized that the alterations of these residues would stabilize the OPH active site by increasing the hydrogen bonding associated with the side chains of the active site residues, thus leading to a more stable substrate binding. In contrast with previously designed OPH variants focused on modification of the active site residues to increase the catalytic activity of OPH, our current findings suggest that mutations near the enzyme active site can enhance the hydrolytic activity against paraoxon.