Aryldialkylphosphatase

Aryldialkylphosphatase (EC 3.1.8.1) (more commonly known as phosphotriesterase, and also organophosphate hydrolase, parathion hydrolase, paraoxonase, and parathion aryl esterase) is a metalloenzyme that hydrolyzes the triester linkage found in organophosphate insecticides.1jgmA:44-359 1ez2A:44-359 1dpmA:44-359 1pscA:44-359 1eywA:44-359 1hzyB:44-359 1qw7A:44-359 1pta :44-359 1p6cA:44-359 1p6bA:44-359 2d2hA:43-358 2d2jA:43-358 Aryldialkylphosphatase (EC 3.1.8.1) (more commonly known as phosphotriesterase, and also organophosphate hydrolase, parathion hydrolase, paraoxonase, and parathion aryl esterase) is a metalloenzyme that hydrolyzes the triester linkage found in organophosphate insecticides. Thus, the two substrates of this enzyme are aryldialkylphosphate and H2O, whereas its two products are dialkylphosphate and aryl alcohol. The gene (opd, for organophosphate-degrading) that codes for the enzyme is found in a large plasmid (pSC1, 51Kb) endogenous to Pseudomonas diminuta, although the gene has also been found in many other bacterial species such as Flavobacterium sp. (ATCC27551), where it is also encoded in an extrachromosomal element (pSM55, 43Kb). Organophosphate is the general name for esters of phosphoric acid and is one of the organophosphorus compounds. They can be found as part of insecticides, herbicides, and nerve gases, amongst others. Some less-toxic organophosphates can be used as solvents, plasticizers, and EP additives. The use of organophosphates accounts for approximately 38% of all pesticide use globally. 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). The capacity to hydrolyze organophosphates is not unique to bacteria. A few fungi and cyanobacteria species have been found to also hydrolyze OPs. Moreover, through sequence homology searches of whole genomes, several other bacterial species were identified that also contain sequences from the same gene family as opd, including pathogenic bacteria such as Escherichia coli (yhfV) and Mycobacterium tuberculosis. The gene sequence encoding the enzyme (opd) in Flavobacterium sp. ATCC27551 and Pseudomonas diminuta is highly conserved (100% sequence homology), although the plasmids where the genes are found have very different sequences apart from a 5.1Kb 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.