Expression and characterization of a histidine-rich protein, Hpn: Potential for Ni2+ storage in Helicobacter pylori

Hpn is a small cytoplasmic protein found in Helicobacter pylori, which binds Ni2+ ions with moderate affinity. Consisting of 60 amino acids, the protein is rich in histidine (28 residues, 46.7%), as well as glutamate, glycine and serine residues (in total 31.7%), and contains short repeating motifs. In the present study, we report the detailed biophysical characterization of the multimeric status and Ni2+-binding properties of purified recombinant Hpn under physiologically relevant conditions. The protein exists as an equilibration of multimeric forms in solution, with 20-mers (approx. 136 kDa) being the predominant species. Using equilibrium dialysis, ICP-MS (inductively coupled plasma MS) and UV/visible spectroscopy, Hpn was found to bind five Ni2+ ions per monomer at pH 7.4, with a dissociation constant (Kd) of 7.1 μM. Importantly, Ni2+ binding to Hpn is reversible: metal is released either in the presence of a chelating ligand such as EDTA, or at a slightly acidic pH (pH for half dissociation, pH1/2 ∼6.3). Ni2+ binding induces conformational changes within the protein, increasing β-sheet and reducing α-helical content, from 22% to 37%, and 20% to 10% respectively. Growth curves of Escherichia coli BL21(DE3) both with and without the hpn gene performed under Ni2+ pressure clearly implied a role for Hpn to protect the cells from higher concentrations of external metal ions. Similarly, the accumulation of Ni2+ in these cells expressing Hpn from a plasmid was approx. 4-fold higher than in uninduced controls or control cultures that lacked the plasmid. Similarly, levels of Ni2+ in wild-type H. pylori 26695 cells were higher than those in H. pylori hpn-deletion mutant strains. Hpn may potentially serve multiple roles inside the bacterium: storage of Ni 2+ ions in a 'reservoir'; donation of Ni2+ to other proteins; and detoxification via sequestration of excess Ni2+. © 2006 Biochemical Society.published_or_final_versio

Major and trace-element zoning in metamorphic garnets and their metamorphic process implications

This article introduces some of the modern techniques for analyzing compositional zonings/profiles in metamorphic garnet, emphasizing the significance of two-dimensional composition X-ray mapping for such investigations. The compositional zonings/profiles in garnet can be divided into uniform-changed type and abrupt-changed type. The uniform-changed type is formed in equilibrium-controlled growth; the abrupt-changed type may be subdivided into step-changed subtype and spike-changed subtype, the forming mechanism of each is relatively complex. The step-changed subtype may be related to the processes such as poly-metamorphism, p-T changes with large magnitudes, and changes in metamorphic reactions or disturbance of crustal melting. As an example, the petrography, the major-and trace-element zoning and distribution patterns of REEs in the garnet from the Xiaomiao Group in the East Kunlun Mountains suggest two episodes of regional metamorphism.published_or_final_versio

Antioxidative Activities of Natural Hydroxy-Bearing Cinnamaldehydes and Cinnamic Acids: A Comparative Study

Purpose: To determine the potent antioxidants among six hydroxy-bearing cinnamaldehyde compounds and their corresponding acids.Methods: The antioxidative activities were evaluated by scavenging 2, 2’-diphenyl-1-picrylhydrazyl (DPPH) free radicals and anti-hemolysis of human red blood cells (RBCs). Fourier transform infrared spectrometry（FT-IR, nuclear magnetic resonance (NMR）and mass spectrometer(MS) evaluations were used to determine the synthesized compounds.Results: The scavenging ability of the compounds on DPPH radicals was in the following rank order: caffeic aldehyde (F) ≈ caffeic acid (C) > vitamin C (Vc) > o-coumaraldehyde (D) > p-coumaric acid (B) > p-coumaraldehyde (E) ≈o-coumaric acid. Inhibitory ability against 2′-Azobis(2-methylpropionamidine) dihydrochloride (AAPH)-induced erythrocyte hemolysis was ranked as follows: o-coumaraldehyde (D) > p-coumaraldehyde (E) ≈ caffeic aldehyde (F) > caffeic acid (C) ≈o-coumaric acid (A) > p-coumaric acid (B) > Vitamin C. The corresponding inhibition time (tinh ) of D and Vc was 63.6, and 23.7 min, respectively.Conclusion: Cinnamaldehydes demonstrated superior antioxidative activities to their corresponding acids. DPPH scavenging ability correlated directly with the number of hydroxyl groups on the catechol ring while the degree of lipophilicity of the compounds may be proportional to their anti-hemolytic activity.Keywords: DPPH scavenging, Cinnamaldehyde, Cinnamic acid, Antioxidative, Hemolysis

Formation of P In defect in annealed liquid-encapsulated Czochralski InP

Fourier transform infrared spectroscopy measurements have been carried out on liquid-encapsulated Czochralski-grown undoped InP wafers, which reproducibly become semi-insulating upon annealing in an ambient of phosphorus at 800-900°C. The measurements reveal a high concentration of hydrogen complexes in the form V InH 4 existing in the material before annealing in agreement with recent experimental studies. It is argued that the dominant and essential process producing the semi-insulating behavior is the compensation produced by an EL 2-like deep donor phosphorus antisite defect, which is formed by the dissociation of the hydrogen complexes during the process of annealing. The deep donor compensates acceptors, the majority of which are shallow residual acceptor impurities and deep hydrogen associated V In and isolated V In levels, produced at the first stage of the dissociation of the V InH 4 complex. The high concentration of indium vacancies produced by the dissociation are the precursor of the EL 2-like phosphorus antisite. These results show the importance of hydrogen on the electrical properties of InP and indicate that this largely results from low formation energy of the complex V InH 4 in comparison with that of an isolated V In. © 1998 American Institute of Physics.published_or_final_versio

The low pKa value of iron-binding ligand Tyr188 and its implication in iron release and anion binding of human transferrin

2D NMR-pH titrations were used to determine pKa values for four conserved tyrosine residues, Tyr45, Tyr85, Tyr96 and Tyr188, in human transferrin. The low pKa of Tyr188 is due to the fact that the iron-binding ligand interacts with Lys206 in open-form and with Lys296 in the closed-form of the protein. Our current results also confirm the anion binding of sulfate and arsenate to transferrin and further suggest that Tyr188 is the actual binding site for the anions in solution. These data indicate that Tyr188 is a critical residue not only for iron binding but also for chelator binding and iron release in transferrin. © 2004 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.postprin

Effects of Thioglycolic Acid on Parthenogenetic Activation of Xenopus Oocytes

BACKGROUND: Existing in Permanent-wave solutions (PWS), thioglycolic acid (TGA) is widely used in hairdressing industry for its contribution to hair styling. However, the toxicity of TGA, especially its reproductive toxicity, gradually calls the attention of more and more researchers. METHOD: In this work, xenopus oocytes were pretreated with different concentration of TGA, and then activated by calcium ionophore A23187. During culture, the oocytes activation rates were taken note at different time after adding calcium ionophore A23187. At the end of the culture period, the nuclear status was detected under confocal microscope. In addition, some other samples were collected for Western-Blotting analysis. RESULT: TGA significantly inhibited the oocytes activation rate and pronuclear formation. It may be resulted from the inhibition of the degradation of p-ERK1, Mos and CyclinB2. CONCLUSION: TGA inhibits in vitro parthenogenetic activation of xenopus oocytes with inhibited the degradation of proteins involved in mitogenic-activated protein kinase (MAPK) and maturation-promoting factor (MPF) pathways

Geochemistry of reduced inorganic sulfur, reactive iron, and organic carbon in fluvial and marine surface sediment in the Laizhou Bay region, China

Understanding the geochemical cycling of sulfur in sediments is important because it can have implications for both modern environments (e.g., deterioration of water quality) and interpretation of the ancient past (e.g., sediment C/S ratios can be used as indicators of palaeodepositional environment). This study investigates the geochemical characteristics of sulfur, iron, and organic carbon in fluvial and coastal surface sediments of the Laizhou Bay region, China. A total of 63 sediment samples were taken across the whole Laizhou Bay marine region and the 14 major tidal rivers draining into it. Acid volatile sulfur, chromium (II)-reducible sulfur and elemental sulfur, total organic carbon, and total nitrogen were present in higher concentrations in the fluvial sediment than in the marine sediment of Laizhou Bay. The composition of reduced inorganic sulfur in surface sediments was dominated by acid volatile sulfur and chromium (II)-reducible sulfur. In fluvial sediments, sulfate reduction and formation of reduced inorganic sulfur were controlled by TOC and reactive iron synchronously. High C/S ratios in the marine sediments indicate that the diagenetic processes in Laizhou Bay have been affected by rapid deposition of sediment from the Yellow River in recent decades

Superconductivity at the Border of Electron Localization and Itinerancy

The superconducting state of iron pnictides and chalcogenides exists at the border of antiferromagnetic order. Consequently, these materials could provide clues about the relationship between magnetism and unconventional superconductivity. One explanation, motivated by the so-called bad-metal behaviour of these materials, proposes that magnetism and superconductivity develop out of quasi-localized magnetic moments which are generated by strong electron-electron correlations. Another suggests that these phenomena are the result of weakly interacting electron states that lie on nested Fermi surfaces. Here we address the issue by comparing the newly discovered alkaline iron selenide superconductors, which exhibit no Fermi-surface nesting, to their iron pnictide counterparts. We show that the strong-coupling approach leads to similar pairing amplitudes in these materials, despite their different Fermi surfaces. We also find that the pairing amplitudes are largest at the boundary between electronic localization and itinerancy, suggesting that new superconductors might be found in materials with similar characteristics.Comment: Version of the published manuscript prior to final journal-editting. Main text (23 pages, 4 figures) + Supplementary Information (14 pages, 7 figures, 3 tables). Calculation on the single-layer FeSe is added. Enhancement of the pairing amplitude in the vicinity of the Mott transition is highlighted. Published version is at http://www.nature.com/ncomms/2013/131115/ncomms3783/full/ncomms3783.htm

Electronic Origin of High Temperature Superconductivity in Single-Layer FeSe Superconductor

The latest discovery of high temperature superconductivity signature in single-layer FeSe is significant because it is possible to break the superconducting critical temperature ceiling (maximum Tc~55 K) that has been stagnant since the discovery of Fe-based superconductivity in 2008. It also blows the superconductivity community by surprise because such a high Tc is unexpected in FeSe system with the bulk FeSe exhibiting a Tc at only 8 K at ambient pressure which can be enhanced to 38 K under high pressure. The Tc is still unusually high even considering the newly-discovered intercalated FeSe system A_xFe_{2-y}Se_2 (A=K, Cs, Rb and Tl) with a Tc at 32 K at ambient pressure and possible Tc near 48 K under high pressure. Particularly interesting is that such a high temperature superconductivity occurs in a single-layer FeSe system that is considered as a key building block of the Fe-based superconductors. Understanding the origin of high temperature superconductivity in such a strictly two-dimensional FeSe system is crucial to understanding the superconductivity mechanism in Fe-based superconductors in particular, and providing key insights on how to achieve high temperature superconductivity in general. Here we report distinct electronic structure associated with the single-layer FeSe superconductor. Its Fermi surface topology is different from other Fe-based superconductors; it consists only of electron pockets near the zone corner without indication of any Fermi surface around the zone center. Our observation of large and nearly isotropic superconducting gap in this strictly two-dimensional system rules out existence of node in the superconducting gap. These results have provided an unambiguous case that such a unique electronic structure is favorable for realizing high temperature superconductivity