Structural basis for the hydrolytic dehalogenation of the fungicide chlorothalonil

Cleavage of aromatic carbon–chlorine bonds is critical for the degradation of toxic industrial compounds. Here, we solved the X-ray crystal structure of chlorothalonil dehalogenase (Chd) from Pseudomonas sp. CTN-3, with 15 of its N-terminal residues truncated (ChdT), using single-wavelength anomalous dispersion refined to 1.96 Å resolution. Chd has low sequence identity (<15%) compared with all other proteins whose structures are currently available, and to the best of our knowledge, we present the first structure of a Zn(II)-dependent aromatic dehalogenase that does not require a coenzyme. ChdT forms a “head-to-tail” homodimer, formed between two α-helices from each monomer, with three Zn(II)-binding sites, two of which occupy the active sites, whereas the third anchors a structural site at the homodimer interface. The catalytic Zn(II) ions are solvent-accessible via a large hydrophobic (8.5 × 17.8 Å) opening to bulk solvent and two hydrophilic branched channels. Each active-site Zn(II) ion resides in a distorted trigonal bipyramid geometry with His117, His257, Asp116, Asn216, and a water/hydroxide as ligands. A conserved His residue, His114, is hydrogen-bonded to the Zn(II)-bound water/hydroxide and likely functions as the general acid-base. We examined substrate binding by docking chlorothalonil (2,4,5,6-tetrachloroisophtalonitrile, TPN) into the hydrophobic channel and observed that the most energetically favorable pose includes a TPN orientation that coordinates to the active-site Zn(II) ions via a CN and that maximizes a π–π interaction with Trp227. On the basis of these results, along with previously reported kinetics data, we propose a refined catalytic mechanism for Chd-mediated TPN dehalogenation.

Crystal structure of μ-4-oxidobenzoato-κ2O1:O4-bis[bis(1,10-phenanthroline-κ2N,N′)copper(II)] bis(4-hydroxybenzoate) 7.5-hydrate

The title hydrated complex, [Cu2(C7H4O3)(C12H8N2)4](C7H5O3)2·7.5H2O, is composed of dinuclear CuIIcomplex cations, noncoordinating 4-hydroxybenzoate anions and water molecules of crystallization. In the dinuclear complex cation, the CuIIions are bridged by a 4-oxidobenzoate ligand and thus each metal ion is five-coordinated by two chelating 1,10-phenanthroline (phen) molecules and one anionic O atom in a distorted trigonal-bipyramid geometry. In the crystal, aromatic π–π stacking occurs between phen rings of neighbouring dinuclear CuIIcomplex cations, forming two-dimensional supramolecular systems parallel to (100).

Crystal structure of a dimeric 1-methylcytosine mercuric chloride complex

Di-μ-chloro-bis[chloro(1-methylcytosine-O,N3)mercury(II)] belongs to space group P21/c with cell dimensions a = 9.932(2), b = 14.051(3), c = 9.198(2) Å, and β = 135.41(2)°. The structure was solved by the heavy-atom method and refined to an R factor of 0.027 for 1271 independent reflections. The crystal is composed of centrosymmetric dimeric molecules in which two mercury atoms are attached by a pair of symmetrical chlorine bridges. The 1-methylcytosine ligand is bidentate via N(3) and O(2). The metal atom has a (2 + 3) coordination with a very distorted trigonal bipyramid geometry. A chlorine atom at 2.322(3) Å and ring nitrogen N(3) at 2.17(1) Å form strong axial bonds with mercury. Two bridging chlorine atoms at 2.719(2) and 2.745(3) Å, and carbonyl oxygen O(2) at 2.84(1) Å form weaker equatorial bonds. The amino group is hydrogen-bonded to a bridging chlorine of the same molecule [Formula: see text] and a carbonyl oxygen of a neighboring molecule [Formula: see text]