A phosphotriesterase (Sb-PTE) was recently identified from Sphingobium sp. strain TCM1 that is catalytically active against a broad spectrum of substrates including organophosphate plasticizers and flame retardants. The enzyme was purified to homogeneity and the mechanism of action was interrogated using a chiral organophosphate substrate. The enzyme was shown to catalyze the hydrolysis of the RP-enantiomer of O-methyl O-cyclohexyl p-nitrophenyl thiophosphate with net inversion of configuration at the phosphorus center and without the formation of a covalent reaction intermediate. These results demonstrate that Sb-PTE catalyzes the hydrolysis of substrates by activation of a water molecule for a direct nucleophilic attack at the phosphorus center. Sb-PTE was crystallized and the three-dimensional structure determined by x-ray diffraction methods to a resolution of 2.1 Å. The enzyme adopts a seven-bladed β-propeller protein fold and the active site contains a binuclear manganese center that is nearly identical to that of the structurally unrelated phosphotriesterase from Pseudomonas diminuta (Pd-PTE). The most striking difference in the catalytic properties of Sb-PTE, relative to those of Pd-PTE, is the enhanced rate of hydrolysis of organophosphate esters with substantially weaker leaving groups. For example, Sb-PTE catalyzes the efficient hydrolysis of the flame retardant triphenyl phosphate with a kcat/Km of 2 x 106 M-1 s-1, whereas Pd-PTE hydrolyzes this compound with a kcat/Km of less than 1 M-1 s-1. The structural basis for the dramatic differences in the catalytic properties between Sb-PTE and Pd-PTE will be addressed.

Three-dimensional structure and substrate profile for a newly identified phosphotriesterase that catalyzes the hydrolysis of organophosphate flame retardants and plasticizers

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.