Crystal Structure of Bovine 3-Hydroxyanthranilate 3,4-Dioxygenase

3-Hydroxyanthranilate 3,4-dioxygenase, the enzyme that catalyzes the conversion of 3-hydroxyanthranilate to quinolinic acid, has been extracted and purified from bovine kidney, crystallized and its structure determined at 2.5 \uc5 resolution. The enzyme, which crystallizes in the triclinic P1 space group, is a monomer, characterized by the so-called cupin fold. The monomer of the bovine enzyme mimics the dimer present in lower species, such as bacteria and yeast, since it is composed of two domains: one of them is equivalent to one monomer, whilst the second domain corresponds to only a portion of it. The active site consists of an iron ion coordinated by two histidine residues, one glutamate and an external ligand, which has been interpreted as a solvent molecule. It is contained in the N-terminal domain, whilst the function of the C-terminal domain is possibly structural. The catalytic mechanism very likely has been conserved through all species, since the positions of all residues considered relevant for the reaction are present from bacteria to humans

Supramolecular Hexagon and Chain Coordination Polymer Containing the MoO22+ Core: Structural Transformation in the SolidState

The reaction of [MoO2(acac)2] (where acac = acetylacetonate ligand) with the salicylaldehyde isonicotinyl hydrazonate ligand (SIH2 12) yielded a zigzag chain polymer [MoO2(SIH)]n (1), an interwoven hexagon [MoO2(SIH)]6 (2), or the mononuclear complexes [MoO2(SIH)(C2H5OH)] (3EtOH) and [MoO2(SIH)(C3H7OH)] (3PrOH). Diversity in the formation of dioxomolybdenum(VI) compounds illustrates their sensitivity to the reaction conditions. Crystal and molecular structures of all of the investigated molybdenum(VI) compounds were determined by the single crystal X-ray diffraction method. Solid-state reactions lead to the transformation of the supramolecular hexagon or the mononuclear complexes into the chain coordination polymer. These thermally induced conversions were characterized by the X-ray powder diffraction method. All of the investigated compounds were further characterized by elemental analysis, thermogravimetric analyses, Fourier transform infrared (FT-IR), and NMR spectroscopy

Zigzag Chain, Square Tetranuclear, and Polyoxometalate-Based Inorganic-Organic Hybrid Compounds - Molybdenum vs. Tungsten

Substitution of the acetylacetonate ligands in [MO2(acac)2] (M=Moor W; acac=acetylacetonate) by 2-oxy-1- naphthaldehyde izonicotinoyl hydrazonate (NIH2-) or 3-methoxy-2-oxybenzaldehyde izonicotinoyl hydrazonate (VIH2-) gives rise to either zigzag chain polymers, [MO2(NIH)]n (1 and 2), square complexes [MO2(VIH)]4 (3 and 4), mononuclear complexes [MO2(VIH)(C2H5OH)] (5 and 6), to polyoxomolybdate hybrid compounds [{MoO2(HNIH)}2Mo6O19] (7) and [MoO2(HVIH)(H2O)]2Mo6O19 (8), depending on the reaction conditions

Three Polymorphic Forms of a Monomeric Mo(VI) Complex: Building Blocks for Two Metal-Organic Supramolecular Isomers. Intermolecular Interactions and Ligand Substituent Effects

Three polymorphic forms of the molybdenum- (VI) complex [MoO2(L)(EtOH)] (1\u3b1, 1\u3b2, and 1\u3b3) (L2 12 = 4- methoxy-2-oxybenzaldehyde isonicotinylhydrazonate) were synthesized by the reaction of H2L with the dioxobis- (acetylacetonato)molybdenum(VI) complex, [MoO2(acac)2], in ethanol. Removal of the coordinated ethanol molecule upon grinding or heating led to the solid-state transformation of the polymorphs 1\u3b1, 1\u3b2, or 1\u3b3 into the coordination polymer [MoO2(L)]n (2a). The square inclusion complex [MoO2(L)]4 83CH2Cl2\ub74CH2Cl2 (2b 83CH2Cl2\ub74CH2Cl2) was obtained by a self-assembly reaction in dichloromethane. Standard Gibbs energies of binding for molybdenum(VI) compounds [MoO2(L)(D)] with the sixth coordination site occupied by a nitrogen or an oxygen donor D were estimated using quantum chemical calculations. Crystal and molecular structures of the molybdenum(VI) compounds [MoO2(L)(EtOH)] (1\u3b1, 1\u3b2, and 1\u3b3), [MoO2(L)]4 83CH2Cl2\ub74CH2Cl2 (2b 83CH2Cl2\ub74CH2Cl2), [MoO2(L)(\u3b3-pic)]\ub7\u3b3-pic (3\ub7\u3b3-pic), [MoO2(L)(py)] (4), and [MoO2(L)(DMSO)] (5) were determined by the single crystal X-ray diffraction method. The compounds were further characterized by chemical analysis, thermogravimetric, and differential scanning calorimetry measurements, IR, UV 12vis, one- and two-dimensional NMR spectroscopies, and the powder X-ray diffraction method

Crystal structure of the B subunit of human E. coli heat-labile enterotoxin carrying peptides with anti-HSV activit

Two chimetic proteins, consisting of the B subunit of Escherichia coli heat-labile enterotoxin with different peptides fused to the COOH-terminal ends, have been crystallized and their three-dimensional structure determined. The two extensions correspond to (a) a non-apeptide representing the COOH-terminal sequence of the small subunit of herpes simplex virus type 1 ribonucleotide reductase and (b) a 27-amino acid long peptide, corresponding to the COOH-terminal end of the catalytic subunit (POL) of DNA polymerase from the same virus. Both proteins crystallize in the P4 12 12 space group with one pentameric molecule per asymmetric unit, corresponding to a solvent content of about 75%. The overall conformation of the B subunit pentamer in the two chimeric proteins, which consists of five identical polypeptide chains, is very similar to that in the native AB complex and conforms strictly to 5-fold symmetry. On the contrary, the peptide extensions are essentially disordered: in the case of the nonapeptide, only 5 and 6 amino acids were, respectively, positioned in two monomers, while in the other three only 2 residues are ordered. The extension is fully confined to the surface of the pentamer opposite to the face that interacts with the membrane and consequently it does not interfere with the ability of the B subunit to interact with membrane receptors. Moreover, the conformational flexibility of the two peptide extensions could be correlated to their propensity for proteolytic processing and consequent release of a biologically active molecule into cultured cells