title: Structure of a Novel Phosphotriesterase from Sphingobium sp. TCM1: A Familiar Binuclear Metal Center Embedded in a Seven-Bladed β-Propeller Protein Fold.
abstract: A novel phosphotriesterase was recently discovered and purified from Sphingobium sp. TCM1 (Sb-PTE) and shown to catalyze the hydrolysis of a broad spectrum of organophosphate esters with a catalytic efficiency that exceeds 10(6) M(-1) s(-1) for the hydrolysis of triphenyl phosphate. The enzyme was crystallized and the three-dimensional structure determined to a resolution of 2.1 Å using single-wavelength anomalous diffraction (Protein Data Bank entry 5HRM ). The enzyme adopts a seven-bladed β-propeller protein fold, and three disulfide bonds were identified between Cys-146 and Cys-242, Cys-411 and Cys-443, and Cys-542 and Cys-559. The active site of Sb-PTE contains a binuclear manganese center that is nearly identical to that of the structurally unrelated phosphotriesterase from Pseudomonas diminuta (Pd-PTE). The two metal ions in the active site are bridged to one another by Glu-201 and a water molecule. The α-metal ion is further coordinated to the protein by interactions with His-389, His-475, and Glu-407, whereas the β-metal ion is further liganded to His-317 and His-258. Computational docking of mimics of the proposed pentavalent reaction intermediates for the hydrolysis of organophosphates was used to provide a model for the binding of chiral substrates in the active site of Sb-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. The structural basis for this difference in the catalytic properties between Sb-PTE and Pd-PTE, despite the nearly identical binuclear metal centers for the activation of the substrate and nucleophilic water molecule, is at present unclear.
authors.affiliation: Department of Chemistry, Texas A&M University , P.O. Box 30012, College Station, Texas 77842, United States.
authors.forename: Mark F
authors.initials: MF
authors.lastname: Mabanglo
authors.affiliation: Department of Chemistry, Texas A&M University , P.O. Box 30012, College Station, Texas 77842, United States.
authors.forename: Dao Feng
authors.initials: DF
authors.lastname: Xiang
authors.affiliation: Department of Chemistry, Texas A&M University , P.O. Box 30012, College Station, Texas 77842, United States.
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Bigley
authors.affiliation: Department of Chemistry, Texas A&M University , P.O. Box 30012, College Station, Texas 77842, United States.
authors.forename: Frank M
authors.initials: FM
authors.lastname: Raushel
mesh_terms: D055162:Biocatalysis; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D008345:Manganese; D062105:Molecular Docking Simulation; D016296:Mutagenesis; D044345:Phosphoric Triester Hydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000072757:Protein Conformation, beta-Strand; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D042301:Sphingomonadaceae / Q000201:enzymology*
chemical_list: D021122:Protein Subunits; D008345:Manganese; D044345:Phosphoric Triester Hydrolases