1,720,992 research outputs found
Molecular Mapping of Functionalities in the Solution Structure of Reduced Grx4, a Monothiol Glutaredoxin from Escherichia coli
Full text linkThe ubiquitous glutaredoxin protein family is present in both prokaryotes and eukaryotes, and is closely related to the thioredoxins, which reduce their substrates using a dithiol mechanism as part of the cellular defense against oxidative stress. Recently identified monothiol glutaredoxins, which must use a different functional mechanism, appear to be essential in both Escherichia coli and yeast and are well conserved in higher order genomes. We have employed high resolution NMR to determine the three-dimensional solution structure of a monothiol glutaredoxin, the reduced E. coli Grx4. The Grx4 structure comprises a glutaredoxin-like alpha-beta fold, founded on a limited set of strictly conserved and structurally critical residues. A tight hydrophobic core, together with a stringent set of secondary structure elements, is thus likely to be present in all monothiol glutaredoxins. A set of exposed and conserved residues form a surface region, implied in glutathione binding from a known structure of E. coli Grx3. The absence of glutaredoxin activity in E. coli Grx4 can be understood based on small but significant differences in the glutathione binding region, and through the lack of a conserved second GSH binding site. MALDI experiments suggest that disulfide formation on glutathionylation is accompanied by significant structural changes, in contrast with dithiol thioredoxins and glutaredoxins, where differences between oxidized and reduced forms are subtle and local. Structural and functional implications are discussed with particular emphasis on identifying common monothiol glutaredoxin properties in substrate specificity and ligand binding events, linking the thioredoxin and glutaredoxin systems
Characterization and function of Escherichia coli glutaredoxins
No full textEscherichia coli employs two separate pathways, driven by NADPH to reduce protein disulfides: the thioredoxin and glutaredoxin systems. Both systems function via redox active disulfides and are involved in many cellular functions including, the synthesis of DNA building blocks (by reducing the essential enzyme ribonucleotide reductase), the generation of reduced sulfur (via PAPS reductase), and the repair of oxidative damage to protein (by methionine sulfoxide reductase).This work aims in a better understanding of the two systems with emphasis on glutaredoxins. Sensitive ELISAs for the two thioredoxins (Trx1, Trx2) and the three glutaredoxins (Grx1, Grx2, Grx3) of E. coli were developed, and protein levels measured at different stages of growth and in different genetic backgrounds.We found that glutaredoxins, were involved in antioxidant defense. Levels of all three glutaredoxins were elevated in catalase deficient strains, particularly when combined with null mutants for the thioredoxin or glutaredoxin systems. OxyR did not affect the levels of Grx2 or Grx3, as it does for Grx1, instead Grx2 levels were elevated in an oxyR null mutant. Grx1 and Grx2 contributed to the defense against protein carbonylation damage caused by hydrogen peroxide.Measurements of thymidine incorporation in newly synthesized DNA in relevant null mutants, showed that it is mainly Grx 1 and to a lesser extent Trx 1 that are involved in the reduction of deoxyribonucleotides. Grx2 was the most abundant glutaredoxin, with levels increasing at the stationary phase of growth up to one per cent of total soluble protein. Guanosine-3',5'-tetraphoshate (ppGpp) and sigma-s that regulate the transcription of genes in the stationary phase of growth, affected dramatically the expression of Grx2, as did osmotic pressure and cAMP, presumably via a.In accordance with the role of Grx2 as a stationary phase protein, null mutants for grxB were lysing at the stationary phase of growth and exhibited a distorted morphology. Null mutants for grxB and all three glutaredoxin genes were viable in rich and minimal media. However, a combined null mutant for all three glutaredoxins and glutathione reductase (gor-grxA-grxB-grxC) was barely growing on minimal media, suggesting the possibility of a mixed disulfide mechanism for the regulation of the activity of PAPS reductase. In fact, a glutathionylated species was detected in vivo in poorly growing gor-grxA-grxB-grxC.In vitro incubation of PAPS reductase with oxidized glutathione lead to the enzyme's inactivation with simultaneous formation of a mixed disulfide between glutathione and the active site Cys239. This species could be reduced and its activity restored by glutaredoxins. Reversible glutathionylation may thus regulate the activity of PAPS reductase. A novel highly abundant monothiol glutaredoxin (Grx4) was identified with maximum levels at the stationary phase of growth (750-2000 ng/mg). Expression of Grx4 is likely to be regulated by ppGpp, but not sigma-s.List of scientific papersI. Vlamis-Gardikas A, Potamitou A, Zarivach R, Hochman A, Holmgren A (2002). Characterization of Escherichia coli null mutants for glutaredoxin 2. J Biol Chem. 277(13): 10861-8. https://pubmed.ncbi.nlm.nih.gov/11741965II. Potamitou A, Holmgren A, Vlamis-Gardikas A (2002). Protein levels of Escherichia coli thioredoxins and glutaredoxins and their relation to null mutants, growth phase, and function. J Biol Chem. 277(21): 18561-7. https://pubmed.ncbi.nlm.nih.gov/11893749III. Potamitou A, Neubauer P, Holmgren A, Vlamis-Gardikas A (2002). Expression of Escherichia coli glutaredoxin 2 is mainly regulated by ppGpp and sigmaS. J Biol Chem. 277(20): 17775-80. https://pubmed.ncbi.nlm.nih.gov/11889138IV. Lillig CH, Potamitou A, Schwenn JD, Vlamis-Gardikis A, Holmgren A (2003). Redox regulation of 3-phosphoadenylylsulfate reductase from Escherichia coli by glutathione and glutaredoxins. [Manuscript]V. Potamitou A, Fladvad M, Achebach S, Unden G, Sunnerhagen M, Neubauer P, Holmgren A, Vlamis-Gardikas A (2003). Cloning and characterization of a novel Escherichia coli monothiol glutaredoxin. [Manuscript]</p
The -Cys-X1-X2-Cys- Motif of Reduced Glutaredoxins Adopts a Consensus Structure That Explains the Low p<i>K</i><sub>a</sub> of Its Catalytic Cysteine
No full text
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
- …
