Aryldialkylphosphatase

Bacterial isolates capable of degrading organophosphate (OP) pesticides have been identified from soil samples from different parts of the world. The first organophosphate-degrading bacterial species was isolated from a soil sample from the Philippines in 1973, which identified as Flavobacterium sp. ATCC27551. Since then, other species have demonstrated to have OP-degrading abilities, such as Pseudomonas diminuta (isolated from US soil sample), Agrobacterium radiobacter (isolated from Australian soil sample), Alteromonas haloplanktis (isolated from US soil sample), and Pseudomonas sp. WBC-3 (isolated from Chinese soil sample). conserved region where the gene is found. A closer look on the organization of the opd gene from Flavobacterium suggests a potential transposon-like architecture, which accounts for the widespread distribution of the gene among other microbial species that might have occurred through lateral DNA transfer. The opd gene is flanked by transposition insertion sequences, characteristic of Tn3 family of transposons. Moreover, a transposase-like sequence (homologous to TnpA) and a resolvase-like sequence (homologous to TnpR) were also identified in regions upstream of the opd gene, which are characteristics of class II transposons such as Tn3. Furthermore, another open reading frame was identified downstream of opd and encodes a protein that further degrades p-nitrophenol, one of the byproducts of OP degradation. This protein is believed to work as a complex with PTE, since a dramatic increase in activity is observed when PTE is present. Therefore, the characteristic architectural organization of the opd gene region suggests that different species acquired the gene through horizontal transfer through transposition and plasmid transfer. == Protein ==

Structure Phosphotriesterase (PTE) belongs to a family metalloenzymes that has two catalytic Zn2+ metal atoms, bridged via a common ligand and coordinated by imidazole side chains of histidine residues that are clustered around the metal atoms. The protein forms a homodimer. The overall structure consists of an α/β-barrel motif, also present in other 20 catalytic proteins. The active sites of these proteins is located at the C-terminal portion of the β-barrel, which is where the active site of PTE is also located. The turnover rate (kcat) of phosphotriesterase is nearly 104 s−1 for the hydrolysis of paraoxon, and the products are p-nitrophenol and diethyl phosphoric acid. == Species ==

Phosphotriesterase is present in two species, Pseudomonas diminuta and Flavobacterium sp. ATCC27551. Other gene variants that also encode organophosphate-degrading enzymes are present in other species. The list includes bacterial species such as the radioresistant Deinococcus radiodurans, pathogens Mycobacterium tuberculosis and Mycobacterium bovis, the anaerobic bacterium Desulfatibacillum alkenivorans, the thermophilic bacteria Geobacillus sp. and Thermoanaerobacter sp. X514, Escherichia coli (yhfV) and many other groups of bacteria, == Subcellular localization ==

Phosphotriesterase is a membrane-associated protein that is translated with a 29 amino acid-long target peptide (Tat motif), which is then cleaved from the mature protein after insertion in the plasma membrane. == Function ==

The enzyme phosphotriesterase hydrolyzes organophosphate compounds by cleaving the triester linkage in the substrate. The enzyme has a very broad substrate specificity, which indicates that the enzyme is optimally evolved for using this substrate. Some species of bacteria are also able to utilize organophosphates as a nutrient and carbon source. ==Environmental significance ==

Phosphotriesterases are considered a strong candidate biocatalyst for bioremediation purposes. As a result, the use of organophosphate-degrading microorganisms is a potentially effective, low-cost, and environmentally friendly method of removing these toxic compounds from the environment. == History ==

Bacterial species that had the ability to degrade organophosphate pesticides have been isolated from soil samples from different parts of the world. The first bacterial strain identified to be able to hydrolyze organophosphates was Flavobacterium sp. ATCC 27551, found by Sethunathan and Yoshida in 1973 from a soil sample originally from the Philippines. Since then, other species were found to also have organophosphate-degrading enzymes similar to that found in Flavobacterium. == References ==