title: Comparative investigation of the reaction mechanisms of the organophosphate-degrading phosphotriesterases from Agrobacterium radiobacter (OpdA) and Pseudomonas diminuta (OPH).
abstract: Metal ion-dependent, organophosphate-degrading enzymes have acquired increasing attention due to their ability to degrade and thus detoxify commonly used pesticides and nerve agents such as sarin. The best characterized of these enzymes are from Pseudomonas diminuta (OPH) and Agrobacterium radiobacter (OpdA). Despite high sequence homology (>90 % identity) and conserved metal ion coordination these enzymes display considerable variations in substrate specificity, metal ion affinity/preference and reaction mechanism. In this study, we highlight the significance of the presence (OpdA) or absence (OPH) of an extended hydrogen bond network in the active site of these enzymes for the modulation of their catalytic properties. In particular, the second coordination sphere residue in position 254 (Arg in OpdA, His in OPH) is identified as a crucial factor in modulating the substrate preference and binding of these enzymes. Inhibition studies with fluoride also support a mechanism for OpdA whereby the identity of the hydrolysis-initiating nucleophile changes as the pH is altered. The same is not observed for OPH.
authors.affiliation: School of Chemistry and Molecular Biosciences, The University of Queensland, St. Lucia, QLD, 4072, Australia.
authors.forename: Marcelo M
authors.initials: MM
authors.lastname: Pedroso
authors.forename: Fernanda
authors.initials: F
authors.lastname: Ely
authors.forename: Nataša
authors.initials: N
authors.lastname: Mitić
authors.forename: Margaret C
authors.initials: MC
authors.lastname: Carpenter
authors.forename: Lawrence R
authors.initials: LR
authors.lastname: Gahan
authors.forename: Dean E
authors.initials: DE
authors.lastname: Wilcox
authors.forename: James L
authors.initials: JL
authors.lastname: Larrabee
authors.forename: David L
authors.initials: DL
authors.lastname: Ollis
authors.forename: Gerhard
authors.initials: G
authors.lastname: Schenk
mesh_terms: D016960:Agrobacterium tumefaciens / Q000201:enzymology* / Q000302:isolation & purification; D002151:Calorimetry; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D005459:Fluorides / Q000737:chemistry / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010755:Organophosphates / Q000737:chemistry / Q000494:pharmacology*; D044345:Phosphoric Triester Hydrolases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011549:Pseudomonas / Q000201:enzymology* / Q000302:isolation & purification; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013816:Thermodynamics
chemical_list: D004791:Enzyme Inhibitors; D010755:Organophosphates; D044345:Phosphoric Triester Hydrolases; D005459:Fluorides
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