Human Paraoxonase Double Mutants Hydrolyze V and G Class Organophosphorus Nerve Agents.

Variants of human paraoxonase 1 (PON1) are being developed as catalytic bioscavengers for the organophosphorus chemical warfare agents (OP). It is preferable that the new PON1 variants have broad spectrum hydrolase activities to hydrolyze both G- and V-class OPs. H115W PON1 has shown improvements over wild type PON1 in its capacity to hydrolyze some OP compounds. We improved upon these activities either by substituting a tryptophan (F347W) near the putative active site residues for enhanced substrate binding or by reducing a bulky group (Y71A) at the periphery of the putative enzyme active site. When compared to H115W alone, we found that H115W/Y71A and H115W/F347W maintained VX catalytic efficiency but showed mixed results for the capacity to hydrolyze paraoxon. Testing our double mutants against racemic sarin, we observed reduced values of KM for H115W/F347W that modestly improved catalytic efficiency over wild type and H115W. Contrary to previous reports, we show that H115W can hydrolyze soman, and the double mutant H115W/Y71A is nearly 4-fold more efficient than H115W for paraoxon hydrolysis. We also observed modest stereoselectivity for hydrolysis of the P(-) stereoisomer of tabun by H115W/F347W. These data demonstrate enhancements made in PON1 for the purpose of developing an improved catalytic bioscavenger to protect cholinesterase against chemical warfare agents.Personal Author B. J. Bahnson D. M. Cerasoli J. R. Norris J. R. Smith S. D. Kirby
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