The binding of substrate analogs to phosphotriesterase

Phosphotriesterase (PTE) from Pseudomonas diminuta catalyzes the detoxifica tion of organophosphates such as the widely utilized insecticide paraoxon a nd the chemical warfare agent sarin. The three-dimensional structure of the enzyme is known from high resolution x-ray crystallographic analyses. Each subunit of the homodimer folds into a so-called TIM barrel, with eight str ands of parallel beta-sheet. The two zinc ions required for activity are po sitioned at the C-terminal portion of the beta P-barrel. Here, we describe the three dimensional structure of PTE complexed with the inhibitor diisopr opyl methyl phosphonate, which serves as a mimic for sarin. Additionally, t he structure of the enzyme complexed with triethyl phosphate is also presen ted. In the case of the PTE-diisopropyl methyl phosphonate complex, the pho sphoryl oxygen of the inhibitor coordinates to the more solvent-exposed zin c ion (2.5 Angstrom), thereby lending support to the presumed catalytic mec hanism involving metal coordination of the substrate. In the PTE-triethyl p hosphate complex, the phosphoryl oxygen of the inhibitor is positioned at 3 .4 Angstrom from the more solvent-exposed zinc ion. The two structures desc ribed in this report provide additional molecular understanding for the abi lity of this remarkable enzyme to hydrolyze such a wide range of organophos phorus substrates.