Abstract
Organophosphorus (OP) nerve agents are potent toxins that inhibit cholinesterases and produce a rapid and lethal cholinergic crisis. Development of protein-based therapeutics is being pursued with the goal of preventing nerve agent toxicity and protecting against the long-term side effects of these agents. The drug-metabolizing enzyme human carboxylesterase 1 (hCE1) is a candidate protein-based therapeutic because of its similarity in structure and function to the cholinesterase targets of nerve agent poisoning. However, the ability of wild-type hCE1 to process the G-type nerve agents sarin and cyclosarin has not been determined. We report the crystal structure of hCE1 in complex with the nerve agent cyclosarin. We further use stereoselective nerve agent analogs to establish that hCE1 exhibits a 1700- and 2900-fold preference for the PR enantiomers of analogs of soman and cyclosarin, respectively, and a 5-fold preference for the PS isomer of a sarin analog. Finally, we show that for enzyme inhibited by racemic mixtures of bona fide nerve agents, hCE1 spontaneously reactivates in the presence of sarin but not soman or cyclosarin. The addition of the neutral oxime 2,3-butanedione monoxime increases the rate of reactivation of hCE1 from sarin inhibition by more than 60-fold but has no effect on reactivation with the other agents examined. Taken together, these data demonstrate that hCE1 is only reactivated after inhibition with the more toxic PS isomer of sarin. These results provide important insights toward the long-term goal of designing novel forms of hCE1 to act as protein-based therapeutics for nerve agent detoxification.
Footnotes
This work was supported by the National Institutes of Health National Institute of Neurological Disorders and Stroke [Grant NS58089]; the National Institutes of Health National Cancer Institute [Grant CA21765]; and the American Lebanese Syrian Associated Charities.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.109.062356.
-
ABBREVIATIONS:
- OP
- organophosphorus
- sarin
- O-isopropyl methylphosphonofluoridate
- tabun
- ethyl N,N-dimethylphosphoramidocyanidate
- AChE
- human acetylcholinesterase
- soman
- O-pinacolyl methylphosphonofluoridate
- cyclosarin
- O-cyclohexyl methylphosphonofluoridate
- BuChE
- human butyrylcholinesterase
- hCE1
- human carboxylesterase 1
- DAM
- 2,3-butanedione monoxime
- RMSD
- root mean square deviation
- pNPB
- para-nitrophenyl butyrate
- RCSB PDB
- Research Collaboratory for Structural Bioinformatics Protein Data Bank.
- Received November 12, 2009.
- Accepted January 5, 2010.
- U.S. Government work not protected by U.S. copyright
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|