Organophosphorus acid anhydrolase

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Organophosphorus acid anhydrolase (OPAA) is an enzyme that been shown to be particularly effective in detoxifying organophosphorus-containing compounds, such as deadly nerve gas used in chemical warfare. [1] The enzyme is found in a diverse range of organisms, including protozoa, [2] squid and clams, [3] mammals, [4] and soil bacteria. [5] A highly active form of the enzyme is typically isolated from the marine bacteria Alteromonas undina for laboratory study. [6] This form is both halophilic and thermophilic, making it particularly useful for detoxification applications. A slightly less active variant of OPAA has also been isolated in mung beans and slime mold duckweed. [7]

Contents

Enzyme mechanism

Figure 1: OPAA reaction mechanism OPAA mechanism.png
Figure 1: OPAA reaction mechanism

Although the exact mechanism of OPAA’s nerve-agent detoxification is unclear, researchers have deduced that the basic reaction follows a general base mechanism with a simple in-line displacement of fluoride at the phosphorus center using an activated water molecule, as seen in Figure 1. [8]

OPAA activity is enhanced by reducing agents such as dithiothreitol (DTT) and beta-mercaptoethanol. [9] OPAA is also catalytically active over a wide pH range between 6.5 and 9.5 and temperature range between 10 and 65 °C, and is stimulated by manganese. [10]

Enzyme structure

Figure 2: OPAA trimer OPAA trimer.png
Figure 2: OPAA trimer

OPAA is a single polypeptide composed of 517 amino acids, with a molecular weight of 58 kDa. [11] [12] The three-dimensional crystal structure of OPAA is a trimer, as seen in Figure 2. The enzyme has a 22% amino acid homology with human prolidase and a 30% homology to E. coli aminopeptidase P. [12]

The enzyme is unstable under harsh conditions, losing its activity in the presence of organic solvents, at elevated temperature, and over long-term storage. [1] Unprotected OPAA enzymes are also vulnerable to inhibition from other enzymes. [1]

Biological function

The native biological role of OPAAs remains unknown. Its similarity to prolidase has led some researchers to theorize that it may be involved in cellular dipeptide metabolism, although conclusions about its true function remains elusive. [9] [12]

Industrial relevance

OPAA’s susbstrate-specificity to organophosphorus-containing compounds, especially fluoride-containing G-type nerve agents such as sarin, cyclosarin, tabun, and soman, [13] [14] have drawn the interest of the U.S. Army . That attention has resulted in the establishment of a biodegradation program in search of safe and effective means of disposal for chemical weapons in the 1980s; the program is currently called the Advanced Catalytic Enzyme System (ACES). [15]

Related Research Articles

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Protease Enzyme that cleaves other proteins into smaller peptides

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Histidine Chemical compound

Histidine (symbol His or H) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH3+ form under biological conditions), a carboxylic acid group (which is in the deprotonated –COO− form under biological conditions), and an imidazole side chain (which is partially protonated), classifying it as a positively charged amino acid at physiological pH. Initially thought essential only for infants, it has now been shown in longer-term studies to be essential for adults also. It is encoded by the codons CAU and CAC.

Soman Chemical compound (nerve agent)

Soman is an extremely toxic chemical substance. It is a nerve agent, interfering with normal functioning of the mammalian nervous system by inhibiting the enzyme cholinesterase. It is an inhibitor of both acetylcholinesterase and butyrylcholinesterase. As a chemical weapon, it is classified as a weapon of mass destruction by the United Nations according to UN Resolution 687. Its production is strictly controlled, and stockpiling is outlawed by the Chemical Weapons Convention of 1993 where it is classified as a Schedule 1 substance. Soman was the third of the so-called G-series nerve agents to be discovered along with GA (tabun), GB (sarin), and GF (cyclosarin).

Phosphonate

Phosphonates or phosphonic acids are organophosphorus compounds containing C−PO(OH)2 or C−PO(OR)2 groups (where R = alkyl, aryl). Phosphonic acids, typically handled as salts, are generally nonvolatile solids that are poorly soluble in organic solvents, but soluble in water and common alcohols. Many commercially important compounds are phosphonates, including glyphosate (the active molecule of the herbicide "Roundup"), and ethephon, a widely used plant growth regulator. Bisphosphonates are popular drugs for treatment of osteoporosis.

Monoacylglycerol lipase

Monoacylglycerol lipase, also known as MAG lipase, acylglycerol lipase, MAGL, MGL or MGLL is an enzyme that, in humans, is encoded by the MGLL gene. MAGL is a 33-kDa, membrane-associated member of the serine hydrolase superfamily and contains the classical GXSXG consensus sequence common to most serine hydrolases. The catalytic triad has been identified as Ser122, His269, and Asp239.

GV (nerve agent) Chemical compound

GV is an organophosphate nerve agent. GV is a part of a new series of nerve agents with properties similar to both the "G-series" and "V-series". It is a potent acetylcholinesterase inhibitor with properties similar to other nerve agents, being a highly poisonous vapour. Treatment for poisoning with GV involves drugs such as atropine, benactyzine, obidoxime, and HI-6.

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GMP synthase

Guanosine monophosphate synthetase, also known as GMPS is an enzyme that converts xanthosine monophosphate to guanosine monophosphate.

Cystathionine beta-lyase

Cystathionine beta-lyase, also commonly referred to as CBL or β-cystathionase, is an enzyme that primarily catalyzes the following α,β-elimination reaction

Acetylcholinesterase Primary cholinesterase in the body

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Aryldialkylphosphatase

Aryldialkylphosphatase is a metalloenzyme that hydrolyzes the triester linkage found in organophosphate insecticides.

Diisopropyl-fluorophosphatase

In enzymology, a diisopropyl-fluorophosphatase (EC 3.1.8.2) is an enzyme that catalyzes the chemical reaction

PEPD

Xaa-Pro dipeptidase, also known as prolidase, is an enzyme that in humans is encoded by the PEPD gene.

Dipeptidase 1

Dipeptidase 1 (DPEP1), or renal dipeptidase, is a membrane-bound glycoprotein responsible for hydrolyzing dipeptides. It is found in the microsomal fraction of the procine kidney cortex. It exists as a disulfide-linked homodimer that is glygosylphosphatidylinositol (GPI)-anchored to the renal brush border of the kidney. The active site on each homodimer is made up of a barrel subunit with binuclear zinc ions that are bridged by the Gly125 side-chain located at the bottom of the barrel.

Enzyme promiscuity is the ability of an enzyme to catalyse a fortuitous side reaction in addition to its main reaction. Although enzymes are remarkably specific catalysts, they can often perform side reactions in addition to their main, native catalytic activity. These promiscuous activities are usually slow relative to the main activity and are under neutral selection. Despite ordinarily being physiologically irrelevant, under new selective pressures these activities may confer a fitness benefit therefore prompting the evolution of the formerly promiscuous activity to become the new main activity. An example of this is the atrazine chlorohydrolase from Pseudomonas sp. ADP that evolved from melamine deaminase, which has very small promiscuous activity toward atrazine, a man-made chemical.

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EA-1356 Chemical compound

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Carbonyl sulfide hydrolase (EC 3.13.1.7; abbreviated as COSase) is an enzyme that degrades carbonyl sulfide (COS) to hydrogen sulfide (H2S) and carbon dioxide (CO2). Isolated from Thiobacillus thioparus bacterium, the potential of COSase would reduce the high global warming effect of COS and change the ozone chemistry, because COS is the source of sulfur in the troposphere.

References

  1. 1 2 3 Hoskin, F. C. G.; Rousch, A. H. (1982). "Hydrolysis of nerve gas by squid type diisopropylphosphorofluoridate hydrolyzing enzyme on agarose resin". Science. 215 (4537): 1255–1257. Bibcode:1982Sci...215.1255H. doi:10.1126/science.7058344. PMID   7058344.
  2. ↑ Landis, W. G.; Durst, H. D.; Savage Jr., R. E.; Haley, D. M.; Haley, M. V.; Johnson, D. W. (1987). "Discovery of multiple organofluorophosphate hydrolyzing activities in the protozoan Tetrahymena thermophila". J. Appl. Toxicol. 7 (1): 35–41. doi:10.1002/jat.2550070107. PMID   3611595. S2CID   9077312.
  3. ↑ Anderson, R. S.; Durst, H. D.; Landis, W. G. (1988). "Initial characterization of the organophosphate acid anhydrase activity in the clam, Rangia cuneata". Comp. Biochem. Physiol. 91C: 575–578.
  4. ↑ Little, J. S., C. A. Broomfield, L. J. Boucher, and M. K. Fox-Talbot. 1986. Partial characterization of a rat liver enzyme that hydrolyzes sarin, soman, tabun and DFP. Fed. Proc. 45:791.
  5. ↑ DeFrank, J. J.; Cheng, T.-C. (1991). "Purification and properties of an organophosphorus acid anhydrase from a halophilic bacterial isolate". J. Bacteriol. 173 (6): 1938–1943. doi:10.1128/jb.173.6.1938-1943.1991. PMC   207724 . PMID   2001997.
  6. ↑ Cheng, T.; Harvey, S.; Stroup, A. (1993). "Purification and properties of a highly active organophosphorus acid anhydrolase from alteromonas undina". Applied and Environmental Microbiology. 59 (9): 3138–3140. Bibcode:1993ApEnM..59.3138C. doi:10.1128/AEM.59.9.3138-3140.1993. PMC   182420 . PMID   16349054.
  7. ↑ Hoskin, F.; Walker, J.; Mello, C. (1999). "Organophosphorus acid anhydrolase in slime mold duckweed and mung bean: a continuing search for a physiological role and a natural substrate". Chemico-Biological Interactions. 119–120: 399–404. doi:10.1016/S0009-2797(99)00051-4. PMID   10421476.
  8. ↑ Dumas, DP; Caldwell, SR; Wild, JR; Raushel, FM (1989). "Purification and Properties of the Phosphotriesterase from Pseudomonas diminuta". Journal of Biological Chemistry. 264 (33): 19659–19665. doi: 10.1016/S0021-9258(19)47164-0 . PMID   2555328.
  9. 1 2 Elashvili, I, DeFrank, JJ, and Culotta, VC, Purification and characterization of DFPase from Alteromonas haloplanktis ATCC 14393, Proceedings of the 1998 ERDEC Scientific Conference on Chemical and Biological Defense Research, 17–20 November 1998, AD-A375 171.
  10. ↑ Lewis, VE; Donarski, WJ; Wild, JR; Raushel, FM (1988). "Mechanism and Stereochemical course at phosphorus of the reaction catalyzed by a bacterial phosphotriesterase". Biochemistry. 27 (5): 1591–1597. doi:10.1021/bi00405a030. PMID   2835095.
  11. ↑ Cheng, T-c, Harvey, SP, and Chen, GL, Cloning and Expression of a Gene Encoding a Bacterial Enzyme for Decontamination of Organophosphorus Nerve Agents and Nucleotide Sequence of the Enzyme, Applied and Environmental Microbiology, 62 (1996) 1636-1641.
  12. 1 2 3 Cheng, T-c, Liu, L, DeFrank, JJ, Anderson, D, and Hamilton, AB, Bacterial Nerve Agent Degrading Enzymes that are Similar to Prolidase Protein Sequence and Activity, Proceedings of the 1995 ERDEC Scientific Conference on Chemical Defense Research, 14–17 November 1995, AD-A315 812.
  13. ↑ Cheng,T-c and Calomiris, JJ Stability of a nerve-agent-degrading enzyme in blast containment and firefighting foams, Proceedings of the 1994 ERDEC Scientific Conference on Chemical Defense Research, 15–18 November 1994, ADE 479952-001
  14. ↑ Cheng, T-c, DeFrank, JJ, Rastogi, VK, Alteromonas prolidase for the organophosphorus G-agent decontamination, Chemico-Biological Interactions 119-120(1999) 455-462.
  15. ↑ DeFrank, JJ, Cheng, T-c, Harvey, SP, and Rastogi, VK, Advanced catalytic enzyme system (ACES)-dual use capabilities, Proceedings of the 2002 Joint Service Scientific Conference on Chemical & Biological Defense Research, 19–21 November 2002, AD-M001 523.
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