title: The binding of substrate analogs to phosphotriesterase.
abstract: Phosphotriesterase (PTE) from Pseudomonas diminuta catalyzes the detoxification of organophosphates such as the widely utilized insecticide paraoxon and 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 strands of parallel beta-sheet. The two zinc ions required for activity are positioned at the C-terminal portion of the beta-barrel. Here, we describe the three-dimensional structure of PTE complexed with the inhibitor diisopropyl methyl phosphonate, which serves as a mimic for sarin. Additionally, the structure of the enzyme complexed with triethyl phosphate is also presented. In the case of the PTE-diisopropyl methyl phosphonate complex, the phosphoryl oxygen of the inhibitor coordinates to the more solvent-exposed zinc ion (2.5 A), thereby lending support to the presumed catalytic mechanism involving metal coordination of the substrate. In the PTE-triethyl phosphate complex, the phosphoryl oxygen of the inhibitor is positioned at 3.4 A from the more solvent-exposed zinc ion. The two structures described in this report provide additional molecular understanding for the ability of this remarkable enzyme to hydrolyze such a wide range of organophosphorus substrates.
authors.affiliation: Department of Biochemistry, University of Wisconsin, Madison, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Benning
authors.forename: S B
authors.initials: SB
authors.lastname: Hong
authors.forename: F M
authors.initials: FM
authors.lastname: Raushel
authors.forename: H M
authors.initials: HM
authors.lastname: Holden
mesh_terms: D043303:Aryldialkylphosphatase; D002619:Chemical Warfare Agents; D002800:Cholinesterase Inhibitors; D018360:Crystallography, X-Ray; D004950:Esterases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D008956:Models, Chemical; D018716:Molecular Mimicry; D010755:Organophosphates / Q000737:chemistry; D009943:Organophosphorus Compounds / Q000737:chemistry* / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011549:Pseudomonas / Q000201:enzymology; D012524:Sarin; D015032:Zinc / Q000737:chemistry
chemical_list: D002619:Chemical Warfare Agents; D002800:Cholinesterase Inhibitors; D010755:Organophosphates; D009943:Organophosphorus Compounds; C023477:diisopropyl methylphosphonate; D012524:Sarin; D004950:Esterases; D043303:Aryldialkylphosphatase; D015032:Zinc; C009549:triethyl phosphate