铜锈环棱螺对沉积物中重金属的生物积累及其与重金属赋存形态的关系

以铜锈环棱螺（Bellamya aeruginosa）为测试生物,采用28 d沉积物生物积累试验研究铜锈环棱螺对污染河流沉积物中重金属的生物积累,并探讨其与重金属赋存形态的关系.结果表明：铜锈环棱螺肝胰脏对Cd、Pb、Cu、Cr、Zn和Mn均具有较强的积累作用.不同重金属的积累量存在较大差别,Zn的积累量最多,占重金属总积累量的84.32%±4.36%,其次为Cu,占7.67%±2.84%;Pb、Cr和Mn的比例相对较少,分别为3.62%±1.84%、2.22%±1.03%和1.33%±0.15%;Cd所占比例最少,为0.83%±0.53%.肝胰脏中重金属元素之间的相关性均不显著.肝胰脏金属污染指数与沉积物污染综合指数具有显著的正相关关系,铜锈环棱螺可以作为沉积物重金属污染的监测生物.不同沉积物Cd、Cr、Zn和Mn的生物-沉积物积累因子（BSAF）具有较大的差异,Cu和Pb的BSAF比较稳定.Cd的生物积累与沉积物中Cd的可交换的与酸可溶态及可氧化态显著相关;Pb的生物积累与Pb的可还原态显著相关;Cu的生物积累与Cu的可氧化态显著相关;Mn的生物积累与Mn的可交换的与酸可溶态和可还原态显著相关;Cr和Mn的生物积累与其不同形态和总量均不相关.BSAF不宜作为衡量铜锈环棱螺对沉积物中重金属生物积累能力的指标.     

Aspartate 458 of human glutathione synthetase is important for cooperativity and active site structure

Human glutathione synthetase (hGS) catalyzes the second ATP-dependent step in the biosynthesis of glutathione (GSH) and is negatively cooperative to the γ-glutamyl substrate. The hGS active site is composed of three highly conserved catalytic loops, notably the alanine rich A-loop. Experimental and computational investigations of the impact of mutation of Asp458 are reported, and thus the role of this A-loop residue on hGS structure, activity, negativity cooperativity and stability is defined. Several Asp458 hGS mutants (D458A, D458N and D458R) were constructed using site-directed mutagenesis and their activities determined (10%, 15% and 7% of wild-type hGS, respectively). The Michaelis–Menten constant (K_m) was determined for all three substrates (glycine, GAB and ATP): glycine K_m increased by 30–115-fold, GAB K_m decreased by 8–17-fold, and the ATP K_m was unchanged. All Asp458 mutants display a change in cooperativity from negative cooperativity to non-cooperative. All mutants show similar stability as compared to wild-type hGS, as determined by differential scanning calorimetry. The findings indicate that Asp458 is essential for hGS catalysis and that it impacts the allostery of hGS.     

Direct observation of chemokine receptors 5 on T-lymphocyte cell surfaces using fluorescent metal nanoprobes 2: Approximation of CCR5 populations

Metal nanoparticle probes were used as molecular imaging agents to detect the expression levels and spatial distributions of the CCR5 receptors on the cell surfaces. Alexa Fluor 647-labeled anti-CCR5 monoclonal antibodies (mAbs) were covalently bound to 20 nm silver nanoparticles to synthesize the mAb–metal complexes. We measured the single nanoparticle emission of the mAb–metal complexes, showing that the complexes displayed enhanced intensities and reduced lifetimes in comparison with the metal-free mAbs. Six HeLa cell lines with various CCR5 expressions were incubated with the mAb–metal complexes for the target-specific binding to the cell surfaces. Fluorescence cell images were recorded on a time-resolved confocal microscope. The collected images expressed clear CCR5 expression-dependent optical properties. Two regression curves were obtained on the basis of the emission intensity and lifetime over the entire cell images against the number of the CCR5 expression on the cells. The emission from the single mAb–metal complexes could be distinctly identified from the cellular autofluorescence on the cell images. The CCR5 spatial distributions on the cells were analyzed on the cell images and showed that the low-expression cells have the CCR5 receptors as individuals or small clusters but the high expression cells have them as the dense and discrete clusters on the cell surfaces.     

Solution structure of an alternate conformation of helix27 from Escherichia coli16S rRNA

Helix (H)27 of 16S ribosomal (r)RNA from Escherichia coli was dubbed the "switch helix" when mutagenesis suggested that two alternative base pair registers may have distinct functional roles in the bacterial ribosome. Although more recent genetic analyses suggest that H27 conformational switching is not required for translation, previous solution studies demonstrated that the isolated E. coli H27 can dynamically convert between the 885 and 888 conformations. Here, we have solved the nuclear magnetic resonance solution structure of a locked 888 conformation. NOE and residual dipolar coupling restraints reveal an architecture that markedly differs from that of the 885 conformation found in crystal structures of the bacterial ribosome. In place of the loop E motif that characterizes the 885 conformer and that the 888 conformer cannot adopt, we find evidence for an asymmetrical A-rich internal loop stabilized by stacking interactions among the unpaired A's. Comparison of the isolated H27 888 solution structure with the 885 crystal structure within the context of the ribosome suggests a difference in overall length of H27 that presents one plausible reason for the absence of H27 conformational switching within the sterically confining ribosome.     

Acidic extracellular pH induces p120-catenin-mediated disruption of adherens junctions via the Src kinase-PKCδ pathway

An acidic microenvironment induces disruption of adherens junctions (AJs) of hepatoma cells. This study investigated the impact of an acidic extracellular pH (pHe) on p120-catenin (p120-ctn) serine phosphorylation. pH 6.6 treatment increased intracellular calcium levels, activated protein kinase C (PKC)α and PKCδ, and decreased serine phosphorylation of p120-ctn. Further knockdown of PKCα and δ by small interference RNA (siRNA) prevented the pH 6.6-induced downregulation of p120-ctn at AJ and the serine dephosphorylation of p120-ctn. Moreover, PP2 pretreatment and siRNA of c-Src abrogated the pH 6.6-induced PKCδ activation. Together, the c-Src-PKCδ cascade and PKCα regulate the acidic pHe-induced AJ disruption.     

Metal complexes of a new class of polydentate Mannich bases: Synthesis and spectroscopic characterisation

A new class of polydentate Mannich bases featuring an N₂S₂ donor system, bis((2-mercapto-N-phenylacetamido)methyl)phosphinic acid H₃L¹ and bis((2-mercapto-N-propylacetamido)methyl)phosphinic acid H₃L², has been synthesised from condensation of phosphinic acid and paraformaldehyde with 2-mercaptophenylacetamide W1 and 2-mercaptopropylacetamide W2, respectively. Monomeric complexes of these ligands, of general formula K₂[Cr^III(Lⁿ)Cl₂], K₃[M′^II(Lⁿ)Cl₂] and K[M(Lⁿ)] (M′ = Mn(II) or Fe(II); M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II) or Hg(II); n = 1, 2) are reported. The structures of new ligands, mode of bonding and overall geometry of the complexes were determined through IR, UV–Vis, NMR, and mass spectral studies, magnetic moment measurements, elemental analysis, metal content, and conductance. These studies revealed octahedral geometries for the Cr(III), Mn(II) and Fe(II) complexes, square planar for Ni(II) and Cu(II) complexes and tetrahedral for the Co(II), Zn(II), Cd(II) and Hg(II) complexes. Complex formation studies via molar ratio in DMF solution were consistent to those found in the solid complexes with a ratio of (M:L) as (1:1).     

Radial (tetracyclopentadienyl)cyclobutadiene pentametals

Radial (tetracyclopentadienyl)cyclobutadiene pentametals have been synthesized by the Pd-catalyzed coupling of cyclopentadienyltin or of (CpM)zinc reagents with (tetraiodocyclobutadiene)iron(tricabonyl). X-ray structural and NMR data reveal that, while these arrays are crowded, the substituents enjoy considerable rotational freedom.The method constitutes a significant complement to currently existing strategies for the construction of persubstituted cyclobutadiene complexes.     

Synthesis, characterization, and luminescence properties of magnesium coordination networks using a thiophene-based linker

By varying the solvents and temperatures under solvothermal conditions, two new magnesium based coordination networks were synthesized using 2,5-thiophenedicarbxoylate as a linker. Mg₃(TDC)₃(DMF)₃ [1; TDC = 2,5 thiophenedicarboxylate; space group P2₁/c, a = 17.747(4) Å, b = 9.805(2) Å, c = 21.359(4) Å, β = 103.13(3)°] is constructed by a combination of magnesium polyhedral trimers, which are connected by the TDC²⁻ linkers to form a 3-D network. Coordinated DMF molecules are present within the channels. Mg(TDC)(H₂O)₂ [2; space group Pnma, a = 7.296(4) Å, b = 17.760(4) Å, c = 6.6631(3) Å] is formed by 1-D chains of magnesium octahedra connected by the TDC²⁻ linker. Water molecules are coordinated at the axial positions of the magnesium octahedra. Compound 1 is formed using DMF as the synthesis solvent at 180 °C, while compound 2 is formed using ethanol as the synthesis solvent at 100 °C. Both compounds show enhanced photoluminescence intensity when excited at 397 nm compared to the free TDC ligand, suggesting a charge transfer between the ligand and the magnesium metal center.     

Three main group metal coordination polymers built by 2-propyl-1H-imidazole-4,5-dicarboxylate

Three coordination polymers, [Sr(H₂PIDC)₂(H₂O)₂]_n (1), [Ba(H₂PIDC)₂(H₂O)₃]_n (2) and [Pb₃(HPIDC)₃]_n (3) (H₃PIDC = 2-propyl-1H-imidazole-4,5-dicarboxylic acid) have been hydrothermally synthesized, and structurally characterized by single-crystal X-ray diffraction. It is shown that the ligand H₃PIDC can be singly deprotonated or doubly deprotonated, and coordinate to main group metal Sr(II), Ba(II) or Pb(II) ions in various modes. Compound 1 exhibits a two-dimensional (2D) sheet built up by μ₂-H₂PIDC⁻ ligands and Sr(II) atoms. Compound 2 assumes an infinite chain composed by μ₂-H₂PIDC⁻ ligands and Ba(II) atoms. Compound 3 possesses a three-dimensional (3D) structure constructed from 2D layer motifs linked by μ₄-HPIDC²⁻ units. The thermal and solid state fluorescence properties of complexes 1-3 have also been investigated at room temperature.     

Identification of novel mimicry epitopes for cardiac myosin heavy chain-α that induce autoimmune myocarditis in A/J mice

Myocarditis is one cause of sudden cardiac death in young adolescents, and individuals affected with myocarditis can develop dilated cardiomyopathy, a frequent reason for heart transplantation. Exposure to environmental microbes has been suspected in the initiation of heart autoimmunity, but the direct causal link is lacking. We report here identification of novel mimicry epitopes that bear sequences similar to those in cardiac myosin heavy chain (MYHC)-α 334–352. These epitopes represent Bacillus spp., Magnetospirillum gryphiswaldense, Cryptococcus neoformans and Zea mays. The mimicry peptides induced varying degrees of myocarditis in A/J mice reminiscent of the disease induced with MYHC-α 334–352. We demonstrate that the mimics induce cross-reactive T cell responses for MYHC-α 334–352 as verified by MHC class II IA^k/tetramer staining and Th-1 and Th-17 cytokines similar to those of MYHC-α 334–352. The data suggest that exposure to environmental microbes which are otherwise innocuous can predispose to heart autoimmunity by molecular mimicry.