Organophosphates (OPs) are a class of synthetic compounds used both as pesticides and nerve agents. They are chemically phosphoesters and biologically potent irreversible inhibitors of serine esterases, particularly acetylcholinesterase (ACh), the key enzyme of the nervous system. Enzymes able to degrade these compounds are at the moment the focus of several research studies in the environmental decontamination/detoxification field. OP hydrolysing enzymes have been found in Bacteria, Archaea and Eukarya. The best known and characterised enzyme is phosphotriesterase from the soil bacterium Pseudomonas diminuta (PTE). It shows a high catalytic activity, close to the molecular diffusion limit, against some triester organophosphates. Its natural substrate and its main physiological function are still unknown. In the last few years, two phosphotriesterase activities have been found in the hyperthermoacidophilic archaea Sulfolobus solfataricus and Sulfolobus acidocaldarius, which have been ascribed to two PTE-related genes (ssopox and sacpox). The corresponding proteins, SsoPox and SacPox, have recently been inserted in the Phosphotriesterase-Like-Lactonase (PLL) group. Their lactonase activity is around 100-fold higher than that of phosphotriesterase and it depends on the same active site. These enzymes are thermophilic and extremely thermostable. Stability in high temperatures and in other stressful conditions is an important feature for every biotechnological application in the industrial field. Finally, the lactonase activity would suggest a potential physiological role for SsoPox and SacPox in the quenching of signals involved in the pathways for cell-to-cell communication.
Keywords: Thermostable phosphotriesterase, lactonase, organophosphates, decontamination, Archaea
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