Stereoselective hydrolysis of G‐agents by a chimeric recombinant paraoxonase 1 enzyme

A recombinant paraoxonase 1 (PON1) variant (MG‐2‐IA4), generated by gene shuffling and multiple rounds of directed evolution and expressed in bacteria, has enhanced catalytic efficiency for the hydrolysis of G‐type organophosphorus nerve agents relative to wild type human PON1. We assessed the stereoselectivity of MG‐2‐IA4 for the more and less toxic isomers (P− and P+, respectively) of racemic samples of the nerve agents tabun (GA), sarin (GB), soman (GD) and cyclosarin (GF) using a chiral gas chromatography/mass spectrometry approach. For GD and GF, MG‐2‐IA4 displayed a 2‐ to 5‐fold preference in catalytic efficiency for the less toxic P+ isomers. No stereo‐preference was observed with GA or GB; both stereoisomers were hydrolyzed with almost equal catalytic efficiency. In vivo efficacy studies conducted using guinea pigs pretreated with MG‐2‐IA4 followed by exposure to 2 x LD 50 s of GA, GB, GD, or GF showed that this enzyme affords protection to nerve agent exposed animals. Despite a stereospecific bias for the less toxic P+ isomers of the G agents, the activity of MG‐2‐IA4 against the more toxic P‐ stereoisomers is sufficient to afford survival against otherwise lethal doses of nerve agent.