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Human paraoxonase 1 exhibits stereoselectivity in the hydrolysis of soman

Human paraoxonase 1 (HuPON1) is an HDL‐associated serum protein capable of hydrolyzing a broad range of substrates including several organophosphorus (OP) nerve agents. The OP nerve agent soman (GD) contains two chiral centers (at a carbon and a phosphorus atom), resulting in four stereoisomers (C+P+, C−P+, C+P−, and C−P−); the former two of these stereoisomers exhibit a mammalian toxicity that is ~1000‐fold less than the latter two, respectively. Using a GC/MS‐based approach, we have examined the capacity of recombinant HuPON1 to hydrolyze each of the four stereoisomers of GD in vitro at pH 7.4 and 25°C. Under these conditions, HuPON1 displayed stereospecific hydrolysis of a racemic mixture of GD. The relative order of hydrolysis of GD stereoisomers was C−P+ > C+P+ > C+P− > C−P−, based on the simultaneously determined kinetic rate constants of each stereoisomer. This investigation demonstrates that wild‐type HuPON1 is capable of stereoselective hydrolysis of OP nerve agents; substrate stereospecificity should be considered in future genetic engineering efforts to enhance OPase activity.