A brain detoxifying enzyme for organophosphorus nerve poisons

Organophosphorus (OP) insecticides and chemical warfare agents act primarily by inhibiting acetylcholinesterase. There are many secondary targets for OP toxicants as observed for example with the major insecticide chlorpyrifos and its bioactivated metabolite chlorpyrifos oxon (CPO). Therefore, it was surprising that the predominant mouse brain protein labeled in vitro by [3H-ethyl]CPO (1 nM) (designated CPO-binding protein or CPO-BP) is not one of these known OP toxicant targets. CPO-BP is a 50-kDa membrane-bound serine hydrolase measured by derivatization with [3H]CPO and SDS/PAGE or filtration binding assay. It appears to undergo rapid diethylphosphorylation by [3H]CPO followed by either dephosphorylation and reactivation or aging on loss of an ethyl group. CPO and several other OP toxicants potently inhibit CPO-BP in vivo (i.p., 2 h) (50% inhibition at 2-25 mg/kg) and in vitro (50% inhibition at 8-68 nM). Using three chemical labeling reagents, i.e., [3H]CPO and the activity-based proteomic probes fluorophosphonate-biotin and fluorophosphonate-rhodamine, mouse brain CPO-BP is identified as serine hydrolase KIAA1363 of unknown function. Brains from KIAA1363-/- mice show greatly reduced levels of CPO labeling and hydrolytic metabolism compared to brains from wild-type mice. KIAA1363 therefore is the principal enzyme for metabolizing low levels of CPO in brain and may play a more general role in detoxification of OP nerve poisons.

[1]  Patrick Masson,et al.  Role of water in aging of human butyrylcholinesterase inhibited by echothiophate: the crystal structure suggests two alternative mechanisms of aging. , 2005, Biochemistry.

[2]  E. Duysen,et al.  Albumin, a new biomarker of organophosphorus toxicant exposure, identified by mass spectrometry. , 2004, Toxicological sciences : an official journal of the Society of Toxicology.

[3]  A. Ishigami,et al.  Senescence marker protein‐30 is a unique enzyme that hydrolyzes diisopropyl phosphorofluoridate in the liver , 2004, FEBS letters.

[4]  J. Casida,et al.  Organophosphate toxicology: safety aspects of nonacetylcholinesterase secondary targets. , 2004, Chemical research in toxicology.

[5]  J. Casida,et al.  Evidence that mouse brain neuropathy target esterase is a lysophospholipase , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[6]  George M Yousef,et al.  Genomic overview of serine proteases. , 2003, Biochemical and biophysical research communications.

[7]  Dale L Boger,et al.  Discovering potent and selective reversible inhibitors of enzymes in complex proteomes , 2003, Nature Biotechnology.

[8]  Nasreen S Jessani,et al.  Enzyme activity profiles of the secreted and membrane proteome that depict cancer cell invasiveness , 2002, Proceedings of the National Academy of Sciences of the United States of America.

[9]  Yong Li,et al.  Human Neuropathy Target Esterase Catalyzes Hydrolysis of Membrane Lipids* , 2002, The Journal of Biological Chemistry.

[10]  J. Burbaum,et al.  Direct visualization of serine hydrolase activities in complex proteomes using fluorescent active site‐directed probes , 2001, Proteomics.

[11]  J. Casida,et al.  Synthesis of high specific activity [ethyl‐1,2‐3H]‐labeled chlorpyrifos oxon and diazoxon , 2000 .

[12]  B. Cravatt,et al.  Activity-based protein profiling: the serine hydrolases. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[13]  M. Ferguson,et al.  Synthesis of 6-N-Biotinylaminohexyl Isopropyl Phosphorofluoridate: A Potent Tool for the Inhibition/Isolation of Serine Esterases and Proteases , 1999 .

[14]  R H Hill,et al.  Pesticide residues in urine of adults living in the United States: reference range concentrations. , 1995, Environmental research.

[15]  B. Clothier,et al.  Reactivation and aging of neurotoxic esterase inhibited by a variety of organophosphorus esters. , 1980, The Biochemical journal.

[16]  M. M. Bradford.  A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. , 1976, Analytical biochemistry.

[17]  R. O'brien.  Enzyme inhibitors as substrates: W. N. Aldridge and Elsa Reiner, Frontiers in Biology Series, Vol. 26, North Holland-American Elsevier, Amsterdam-New York, 1973. $22.50 , 1974 .

[18]  L. Costa,et al.  Paraoxonase (PON1) in Health and Disease , 2002 .

[19]  G. Koelle.  Cholinesterases and Anticholinesterase Agents , 1963 .