Binding abilities of dehydropeptides towards Cu(II) and Ni(II) ions. Impact of Z-E isomerization on metal ion binding

The study on the binding ability of dehydro-tri- and tetrapeptides has shown that the ,β-double bond has a critical effect on the peptide coordination to metal ions. It may affect the binding of the vicinal amide nitrogens by the electronic effect and stabilize the complex due to steric effects. The (Z) isomer is the most effective in stabilizing of the complexes formed. The presence of large side chain in the dehydroamino acid residue may also be critical for the coordination mode in the metallopeptide systems.     

Functional and structural changes due to a serine to alanine mutation in the active-site flap of enolase

Crystallographic and kinetic methods have been used to characterize a site-specific variant of yeast enolase in which Ser 39 in the active-site flap has been changed to Ala. In the wild-type enzyme, the carbonyl and hydroxyl groups of Ser 39 chelate the second equivalent of divalent metal ion, effectively anchoring the flap over the fully liganded active site. With Mg(2+) as the activating cation, S39A enolase has <0.01% of wild-type activity as reported previously [J.M. Brewer, C.V. Glover, M.J. Holland, L. Lebioda, Biochim. Biophys. Acta 1383 (2) (1998) 351-355]. Measurements of (2)H kinetic isotope effects indicate that the proton abstraction from 2-phosphoglycerate (2-PGA) is significantly rate determining. Analysis of the isotope effects provides information on the relative rates of formation and breakdown of the enolate intermediate. Moreover, assays with different species of divalent metal ions reveal that with S39A enolase (unlike the case of wild-type enolase), more electrophilic metal ions promote higher activities. The kinetic results with the S39A variant support the notions that a rate-limiting product release lowers the activity of wild-type enolase with more electrophilic metal ions and that the metal ions are used to acidify the C2-proton of 2-PGA. The S39A enolase was co-crystallized with Mg(2+) and the inhibitor phosphonoacetohydroxamate (PhAH). The structure was solved and refined at a resolution of 2.1 A. The structure confirms the conjecture that the active-site flap is opened in the mutant protein. PhAH chelates to both Mg ions as in the corresponding structure of the wild-type complex. Positions of the side chains of catalytic groups, Lys 345 and Glu 211, and of "auxiliary" residues Glu 168 and Lys 396 are virtually unchanged relative to the complex with the wild-type protein. His 159, which hydrogen bonds to the phosphonate oxygens in the wild-type complex, is 5.7 A from the closest phosphonate oxygen, and the loop (154-166) containing His 159 is shifted away from the active center. A peripheral loop, Glu 251-Gly 275, also moves to open access to the active site.     

The Pco proteins are involved in periplasmic copper handling in Escherichia coli

The interactions between the plasmid-borne copper resistance determinant, pco, and the main copper export system in Escherichia coli have been investigated and no direct interaction has been found. The PcoE and PcoC proteins are periplasmic and PcoC binds one Cu ion per protein molecule. PcoA is also periplasmic and can substitute for the chromosomally encoded CueO protein. The pco determinant is proposed to exert its effect through periplasmic handling of excess copper ions and to increase the level of resistance to copper ions above that conferred by copA alone.     

The effect of copper/zinc replacement on the folding free energy of wild type and Cys3Ala/Cys26Ala azurin

The effect of copper/zinc metal ion replacement on the folding free energy of wild type (w.t.) and disulfide bridge depleted (C3A/C26A) azurin has been investigated by differential scanning calorimetry (DSC) and fluorescence techniques. The denaturation experiments have shown that, in both cases, the thermal transitions of the zinc derivative of azurins can be depicted in terms of the classical Lumry–Eyring model, NUF, thus resembling the unfolding path of the two copper proteins. The thermally induced transition of Zn azurin, monitored by fluorescence occurs at lower temperature than the DSC scans indicating that a local conformational rearrangement of the Trp microenvironment, takes place before protein denaturation. For Zn C3A/C26A azurin, the two techniques reveal the same transition temperature. Comparison of the thermodynamic data shows that the presence of Zn in the active site stabilises the three-dimensional structure of azurin only when the disulfide bridge is present. Compared to the copper form of the protein, the unfolding temperature of Zn azurin has increased by 4 °C, while the unfolding free energy, ΔG, is 31 kJ/mol higher. Both enthalpic and entropic factors contribute to the observed ΔG increase. However, the copper/zinc replacement has no effect on the unfolding free energy of C3A/C26A azurin. Taking Cu azurin w.t. as the reference state, for both Cu and Zn C3A/C26A azurin the unfolding free energy is decreased by about 28 kJ/mol, indicating that metal substitution is not able to compensate the destabilising effect induced by the disulfide bridge depletion. It is noteworthy that the thermal denaturation of the Zn derivative, which thermodynamically is the most stable form of azurin, is also characterized by the highest value of the activation energy, E_a, as derived from the kinetic stability analysis.     

Nickel and cobalt phytoextraction by the hyperaccumulator Berkheya coddii: implications for polymetallic phytomining and phytoremediation

We investigated the potential of the South African high-biomass Ni hyperaccumulator Berkheya coddii to phytoextract Co and/or Ni from artificial metalliferous media. Plant accumulation of both metals from single-element substrates indicate that the plant/media metal concentration quotient (bioaccumulation coefficient) increases as total metal concentrations increase. Cobalt was readily taken up by B. coddii with and without the presence of Ni. Nickel uptake was, however, inhibited by the presence of an equal concentration of Co. Bioaccumulation coefficients of Ni and Co for the single element substrates (total metal concentration of 1000 micrograms g-1) were 100 and 50, respectively. Cobalt phytotoxicity was observed above a total Co concentration in plant growth media of 20 micrograms g-1. Elevated Co concentrations significantly decreased the biomass production of B. coddii without affecting the bioaccumulation coefficients. The mixed Ni-Co substrate produced bioaccumulation coefficients of 22 for both Ni and Co. Cobalt phytotoxicity in mixed Ni-Co substrate occurred above a total Co concentration of 15 micrograms g-1. When grown in the presence of both Ni and Co, the bioaccumulation coefficients of each metal were reduced, as compared to single-element substrate. This may indicate competition for binding sites in the root zone. The interference relationship between Ni and Co uptake demonstrated by B. coddii suggests a significant limitation to phytoextraction where both metals are present.     

Changes in zinc,copper and metallothionein contents during oocyte growth and early development of the teleost Danio rerio (zebrafish)

In the present report, we investigated zinc, copper and metallothionein (MT) contents in zebrafish oocytes and embryos. Our results demonstrate that the metal content increases during oocytes maturation. Zinc increases from 30 ng/oocyte (stage-1 oocytes) to 100 ng/oocyte (stage-3 oocytes); copper varied from 1 ng/oocyte (stage-1 oocytes) to 3.5 ng/oocyte (stage-3 oocytes). During embryogenesis, zinc and copper contents dramatically increase after fertilisation around the 512-cells stage, then slowly decrease until the mid-gastrula stage. During oocyte growth, the changes in the MT level are proportional to metal content, whereas during embryogenesis the pattern of MT accumulation does not parallel that of the two metals. Indeed, the maternal pool of MT decreases steadily during the early stages of the development until the gastrula stage. We have examined the effect of cadmium on the expression of MT during zebrafish development. After cadmium exposure, MT content increases in embryos at the blastula stage, whereas no induction occurs in embryos at the gastrula stage. However, pre-treatment of embryos at the gastrula stage with 5-aza-2'-deoxycytidine induces MT synthesis following exposure to cadmium. These observations show that changes in metal levels are not correlated to MT content in the embryo, whereas DNA methylation is one of the factors regulating MT expression.     

Recent advances in the analysis of oxidized proteins

Summary. Glutamic semialdehyde is a product of oxidation of arginine and proline, and aminoadipic semialdehyde, of oxidation of lysine. These two carbonyl-containing compounds are the main carbonyl products of metal-catalyzed oxidation of proteins, accounting for 55–100% of the total carbonyl value. Accordingly, they are quantitatively very important contributors to the total value of protein carbonyls in tissues as measured by the classic spectophotometric assay. Sensitive gas chromatography-mass spectrometry based analytical methods allow their quantitation in a variety of biological samples, including tissue protein, cell cultures and lipoproteins. These measurements provide specific information on the oxidative status of proteins that is complementary to that afforded by protein carbonyls, and will be useful tools in the ongoing effort to define and assess the role of protein oxidation in pathology and aging.     

The use of chemically modified and unmodified cassava waste for the removal of Cd, Cu and Zn ions from aqueous solution

The use of different chemically modified cassava waste biomass for the enhancement of the adsorption of three metal ions Cd, Cu and Zn from aqueous solution is reported in this paper. Treating with different concentrations of thioglycollic acid modified the cassava waste biomass.

The sorption rates of the three metals were 0.2303 min⁻¹ (Cd²⁺), 0.0051 min⁻¹ (Cu²⁺), 0.0040 min⁻¹ (Zn²⁺) and 0.109 min⁻¹ (Cd²⁺), 0.0069 min⁻¹ (Cu²⁺), 0.0367 min⁻¹ (Zn²⁺) for 0.5 and 1.00 M chemically modified levels, respectively. The adsorption rates were quite rapid and within 20–30 min of mixing, about 60–80% of these ions were removed from the solutions by the biomass and that chemically modifying the binding groups in the biomass enhanced its adsorption capacity towards the three metals. The results further showed that increased concentration of modifying reagent led to increased incorporation, or availability of more binding groups, in the biomass matrix, resulting in improved adsorptivity of the cassava waste biomass. The binding capacity study showed that the cassava waste, which is a serious environmental nuisance, due to foul odour released during decomposition, has the ability to adsorb trace metals from solutions.     

滇池水-植物系统金属元素的分布特征和相关性研究

对滇池优势水生植物凤眼莲、旱生莲子草、红线草、聚草和茭草及其对应水环境中的Ｋ、Ｎａ、Ｃａ、Ｍｇ、Ｆｅ、Ｍｎ、Ｚｎ、Ｃｕ、Ｐｂ、Ｃｄ进行了化学分析,初步揭示了滇池水－植物系统金属元素的分布特征和关性。结果表明,滇池水域属Ｋ、Ｃａ、Ｍｇ、Ｆｅ高背景生物地球化学区,植物体内金属元素的含量,既与植物种属特性有关,又明显地受环境因素的影响,植物对营养元素的吸收不一定与环境中相应元素的浓度呈简单的线性关系,而