1,720,992 research outputs found
Specific poly-histidyl and poly-cysteil protein sites involved in Ni(2+) homeostasis in Helicobacter pylori. Impact of Bi(3+) ions on Ni(2+) binding to proteins. Structural and thermodynamic aspects
No full textCysteine and histidine residues are tempting donors for Ni(2+) which coordinates to the sulfur of Cys and amide nitrogen atoms, or, in the absence of available thiol groups, to His imidazoles and amides. Bi(3+), on the other hand, has a very strong affinity towards Cys thiol groups, and can also coordinate an additional His imidazole.
In this review, the complicated pathway of nickel uptake, delivery and regulation in microorganisms is summarized. We show potential binding sites, binding geometries, protein structures and discuss the predicted thermodynamic and kinetic aspects. We focus on the numerous recent observations on the homeostasis of nickel in Helicobacter pylori (H. pylori), a Gram-negative bacterium that colonizes the gastric mucosa in humans, and is the causative agent of acute and chronic gastritis. peptic ulcer disease, gastric carcinoma, and gastric lymphoma.
The homeostasis of Ni(2+) is crucial for the survival of H. pylori in the extremely acidic environment of the stomach. The metal is delivered to urease (which catalyzes the hydrolysis of urea into carbon dioxide and ammonia and therefore neutralizes the low gastric pH) and to hydrogenase (which permits respiratory based energy production for the bacteria in the mucosa) by a set of accessory proteins. Most of the bacterium's metal metabolism is centered upon their expression and maturation.
Below, a detailed description of the structural and thermodynamic aspects of the binding of nickel ions to poly-histidyl and poly-cysteil sites of urease and hydrogenase accessory proteins is given. Because bismuth compounds are one of the treatments for peptic ulcer disease, the inhibitory effect of Bi(3+) ions is described; the affinity of bismuth towards Cys side groups is much stronger than the affinity of nickel towards the same sites, therefore bismuth is able to displace nickel from its binding site, causing the inhibition of nickel chaperones
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Competition between histamine-like and poly-imidazole coordination sites for Cu2+ and Zn2+ ions in zebra-fish peptide of prion-like protein
No full textThe fragment of the zebrafish prion-like protein (PrP-rel-2), encompassing residues 74-86 and unprotected at N-terminus (zf74-86) represents a good model to understand Cu2+ and Zn2+ binding to
ligands containing multi-potential metal donor sites. Zf(74-86) contains four His and His-1 N-terminal amine groups which constitute both copper and zinc anchoring sites. The presence of His at the first
position additionally provides the histamine-like binding mode which could compete with the multi-His binding mode. In this study the speciation profiles of the Cu2+ and Zn2+ complexes with zf74-86 have
been obtained. The main species, dominating at physiological pH, have been fully characterized by using different spectroscopic techniques. The detected NMR chemical shift variations and line broadening enhancements, caused by Zn2+ and Cu2+ respectively, allowed to determine the metal binding sites. Both metal ions showed common binding donor atoms, being 2 or 3 His imidazoles and the N-terminal group involved in Cu2+ and Zn2+ binding
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Poly-His and poly-Gln sequences in bacterial proteins: tempting sites for metal ions to interact with
No full textHpn and Hpn-like are Helicobacter pylori cytoplasmic proteins involved in the homeostasis of nickel, required for the metal-enzymes urease and Ni-Fe hydrogenase, essential for the bacterium colonization in the human stomach. Hpn is an amazingly peculiar protein: almost half of its sequence consists of polyhistydyl repeats. On the other hand, Hpn-like proteins are rich in glutamine residues.
Our research group was recently involved in a study on the Ni(II) and Cu(II) complexes of different fragments and analogues of Hpn and Hpn-like proteins, in order to shed light on the role of the consecutive His and Gln residues in metal-ion binding [1,2] (see Figure).
The encouraging results pushed us to continue this investigation, focusing the attention on the N-terminal domain of Hpn-like proteins. Cu(II) and Ni(II) complexes of peptide models (MAHHE-NH2, MAHHEEQ-NH2, MAHHEQQ-NH2 and MAHHEQQHQA–NH2) were studied by means of different thermodynamic and spectroscopic techniques, as well as through molecular modeling computations
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