Hydrolysis of DFP and the Nerve Agent (S)-Sarin by DFPase Proceeds Along Two Different Reaction Pathways: Implica-tions for Engineering Bioscavengers
- ORNL
- Institut de Biologie Structurale Jean-Pierre Ebel
Organophosphorus (OP) nerve agents such as (S)-sarin are among the most highly toxic compounds that have been synthesized. Engineering enzymes that catalyze the hydrolysis of nerve agents ( bioscavengers ) is an emerging prophylactic approach to diminishing their toxic effects. Although its native function is not known, diisopropyl fluorophosphatase (DFPase) from Loligo vulgaris catalyzes the hydrolysis of OP compounds. Here, we investigate the mechanisms of diisopropylfluorophosphate (DFP) and (S)-sarin hydrolysis by DFPase with quantum mechanical/molecular mechanical (QM/MM) umbrella sampling simulations. We find that the mechanism for hydrolysis of DFP involves nucleophilic attack by Asp229 on phosphorus to form a pentavalent intermediate. P F bond dissociation then yields a phosphoacyl enzyme intermediate in the rate-limiting step. The simulations suggest that a water molecule, coordinated to the catalytic Ca2+, donates a proton to Asp121 and then attacks the tetrahedral phosphoacyl intermediate to liberate the diisopropylphosphate product. In contrast, the calculated free energy barrier for hydrolysis of (S)-sarin by the same mechanism is highly unfavorable, primarily due to the instability of the pentavalent phosphoenzyme species. Instead, simulations suggest that hydrolysis of (S)-sarin proceeds by a mechanism in which Asp229 could activate an intervening water molecule for nucleophilic attack on the substrate. These findings may lead to improved strategies for engineering DFPase and related six-bladed -propeller folds for more efficient degradation of OP compounds.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE National Nuclear Security Administration (NNSA)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 1133537
- Journal Information:
- Journal of Physical Chemistry B, Vol. 118, Issue 17; ISSN 1520--6106
- Country of Publication:
- United States
- Language:
- English
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