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Metal Ligands (metal + ligand)
Selected AbstractsDOTTADs , Readily Made Novel Metal Ligands with Multivariant Functionality.CHEMINFORM, Issue 36 2003Andrea Arany Abstract For Abstract see ChemInform Abstract in Full Text. [source] Thermosynechoccus elongatus DpsA binds Zn(II) at a unique three histidine-containing ferroxidase center and utilizes O2 as iron oxidant with very high efficiency, unlike the typical Dps proteinsFEBS JOURNAL, Issue 4 2010Flaminia Alaleona The cyanobacterium Thermosynechococcus elongatus is one the few bacteria to possess two Dps proteins, DpsA-Te and Dps-Te. The present characterization of DpsA-Te reveals unusual structural and functional features that differentiate it from Dps-Te and the other known Dps proteins. Notably, two Zn(II) are bound at the ferroxidase center, owing to the unique substitution of a metal ligand at the A-site (His78 in place of the canonical aspartate) and to the presence of a histidine (His164) in place of a hydrophobic residue at a metal-coordinating distance in the B-site. Only the latter Zn(II) is displaced by incoming iron, such that Zn(II),Fe(III) complexes are formed upon oxidation, as indicated by absorbance and atomic emission spectroscopy data. In contrast to the typical behavior of Dps proteins, where Fe(II) oxidation by H2O2 is about 100-fold faster than by O2, in DpsA-Te the ferroxidation efficiency of O2 is very high and resembles that of H2O2. Oxygraphic experiments show that two Fe(II) are required to reduce O2, and that H2O2 is not released into solution at the end of the reaction. On this basis, a reaction mechanism is proposed that also takes into account the formation of Zn(II),Fe(III) complexes. The physiological significance of the DpsA-Te behavior is discussed in the framework of a possible localization of the protein at the thylakoid membranes, where photosynthesis takes place, with the consequent increased formation of reactive oxygen species. Structured digital abstract ,,MINT-7312099: DpsA (uniprotkb:Q8DL82) and DpsA (uniprotkb:Q8DL82) bind (MI:0407) by x-ray crystallography (MI:0114) [source] Functional characterization of an orphan cupin protein from Burkholderia xenovorans reveals a mononuclear nonheme Fe2+ -dependent oxygenase that cleaves ,-diketonesFEBS JOURNAL, Issue 20 2009Stefan Leitgeb Cupins constitute a large and widespread superfamily of ,-barrel proteins in which a mononuclear metal site is both a conserved feature of the structure and a source of functional diversity. Metal-binding residues are contributed from two core motifs that provide the signature for the superfamily. On the basis of conservation of this two-motif structure, we have identified an ORF in the genome of Burkholderia xenovorans that encodes a novel cupin protein (Bxe_A2876) of unknown function. Recombinant Bxe_A2876, as isolated from Escherichia coli cell extract, was a homotetramer in solution, and showed mixed fractional occupancy of its 16.1 kDa subunit with metal ligands (0.06 copper; 0.11 iron; 0.17 zinc). Our quest for possible catalytic functions of Bxe_A2876 focused on Cu2+ and Fe2+ oxygenase activities known from related cupin enzymes. Fe2+ elicited enzymatic catalysis of O2 -dependent conversion of various ,-diketone substrates via a nucleophilic mechanism of carbon,carbon bond cleavage. Data from X-ray absorption spectroscopy (XAS) support a five-coordinate or six-coordinate Fe2+ center where the metal is bound by three imidazole nitrogen atoms at 1.98 Å. Results of structure modeling studies suggest that His60, His62 and His102 are the coordinating residues. In the ,best-fit' model, one or two oxygens from water and a carboxylate oxygen (presumably from Glu96) are further ligands of Fe2+ at estimated distances of 2.04 Å and 2.08 Å, respectively. The three-histidine Fe2+ site of Bxe_A2876 is compared to the mononuclear nonheme Fe2+ centers of the structurally related cysteine dioxygenase and acireductone dioxygenase, which also use a facial triad of histidines for binding of their metal cofactor but promote entirely different substrate transformations. [source] Outer sphere mutagenesis of Lactobacillus plantarum manganese catalase disrupts the cluster coreFEBS JOURNAL, Issue 6 2003Mechanistic implications X-ray crystallography of the nonheme manganese catalase from Lactobacillus plantarum (LPC) [Barynin, V.V., Whittaker, M.M., Antonyuk, S.V., Lamzin, V.S., Harrison, P.M., Artymiuk, P.J. & Whittaker, J.W. (2001) Structure9, 725,738] has revealed the structure of the dimanganese redox cluster together with its protein environment. The oxidized [Mn(III)Mn(III)] cluster is bridged by two solvent molecules (oxo and hydroxo, respectively) together with a µ1,3 bridging glutamate carboxylate and is embedded in a web of hydrogen bonds involving an outer sphere tyrosine residue (Tyr42). A novel homologous expression system has been developed for production of active recombinant LPC and Tyr42 has been replaced by phenylalanine using site-directed mutagenesis. Spectroscopic and structural studies indicate that disruption of the hydrogen-bonded web significantly perturbs the active site in Y42F LPC, breaking one of the solvent bridges and generating an ,open' form of the dimanganese cluster. Two of the metal ligands adopt alternate conformations in the crystal structure, both conformers having a broken solvent bridge in the dimanganese core. The oxidized Y42F LPC exhibits strong optical absorption characteristic of high spin Mn(III) in low symmetry and lower coordination number. MCD and EPR measurements provide complementary information defining a ferromagnetically coupled electronic ground state for a cluster containing a single solvent bridge, in contrast to the diamagnetic ground state found for the native cluster containing a pair of solvent bridges. Y42F LPC has less than 5% of the catalase activity and much higher Km for H2O2 (,1.4 m) at neutral pH than WT LPC, although the activity is slightly restored at high pH where the cluster is converted to a diamagnetic form. These studies provide new insight into the contribution of the outer sphere tyrosine to the stability of the dimanganese cluster and the role of the solvent bridges in catalysis by dimanganese catalases. [source] Structural-based mutational analysis of d -aminoacylase from Alcaligenes faecalis DA1PROTEIN SCIENCE, Issue 11 2002Cheng-Sheng Hsu Abstract d -Aminoacylase is an attractive candidate for commercial production of d -amino acids through its catalysis in the zinc-assistant hydrolysis of N -acyl- d -amino acids. We report here the cloning, expression, and structural-based mutation of the d -aminoacylase from Alcaligenes faecalis DA1. A 1,007-bp PCR product amplified with degenerate primers, was used to isolate a 4-kb genomic fragment, encoding a 484-residue d -aminoacylase. The enzyme amino-terminal segment shared significant homology within a variety of enzymes including urease. The structural fold was predicted by 3D-PSSM to be similar to urease and dihydroorotase, which have grouped into a novel ,/,-barrel amidohydrolase superfamily with a virtually indistinguishable binuclear metal centers containing six ligands, four histidines, one aspartate, and one carboxylated lysine. Three histidines, His-67, His-69, and His-250, putative metal ligands in d -aminoacylase, have been mutated previously, the remaining histidine (His-220) and aspartate (Asp-366) Asp-65, and four cysteines were then characterized. Substitution of Asp-65, Cys-96, His-220, and Asp-366 with alanine abolished the enzyme activity. The H220A mutant bound approximately half the normal complement of zinc ion as did H250N. However, the C96A mutant showed little zinc-binding ability, revealing that Cys-96 may replace the carboxylated lysine to serve as a bridging ligand. According to the urease structure, the conserved amino-terminal segment including Asp-65 may be responsible for structural stabilization. [source] | ||||||||||