1,720,998 research outputs found
Dps proteins prevent Fenton mediated oxidative damage by trapping hydroxyl radicals within the protein shell.
No full textDps (DNA-binding proteins from starved cells) proteins belong to a widespread bacterial family of proteins expressed under nutritional and oxidative stress conditions. In particular, Dps proteins protect DNA against Fenton-mediated oxidative stress, as they catalyze iron oxidation by hydrogen peroxide at highly conserved ferroxidase centers and thus reduce significantly hydroxyl radical production. This work investigates the possible generation of intraprotein radicals during the ferroxidation reaction by Escherichia coli and Listeria innocua Dps, two representative members of the family. Stopped-flow analyses show that the conserved tryptophan and tyrosine residues located near the metal binding/oxidation center are in a radical form after iron oxidation by hydrogen peroxide. DNA protection assays indicate that the presence of both residues is necessary to limit release of hydroxyl radicals in solution and the consequent oxidative damage to DNA. In general terms, the demonstration that conserved protein residues act as a trap that dissipates free electrons generated during the oxidative process brings out a novel role for the Dps protein cag
Typical 2-cys peroxiredoxins in human parasites: several physiological roles for a potential chemotherapy target
No full textPeroxiredoxins (Prxs) are ubiquitary proteins able to play multiple physiological roles, that include thiol-dependent peroxidase, chaperone holdase, sensor of H2O2, regulator of H2O2-dependent signal cascades, and modulator of the immune response. Prxs have been found in a great number of human pathogens, both eukaryotes and prokaryotes. Gene knock-out studies demonstrated that Prxs are essential for the survival and virulence of at least some of the pathogens tested, making these proteins potential drug targets. However, the multiplicity of roles played by Prxs constitutes an unexpected obstacle to drug development. Indeed, selective inhibitors of some of the functions of Prxs are known (namely of the peroxidase and holdase functions) and are here reported. However, it is often unclear which function is the most relevant in each pathogen, hence which one is most desirable to inhibit. Indeed there are evidences that the main physiological role of Prxs may not be the same in different parasites. We here review which functions of Prxs have been demonstrated to be relevant in different human parasites, finding that the peroxidase and chaperone activities figure prominently, whereas other known functions of Prxs have rarely, if ever, been observed in parasites, or have largely escaped detection thus far
DNA-Binding Proteins From Starved Cells (Dps Proteins)
No full textIn the recent past over 200 Dps (DNA-binding proteins from starved cells) proteins have been identified in bacterial genomes. Dps proteins belong to the ferritin superfamily. They are expressed under conditions of oxidative and/or nutritional stress and are characterized by a highly conserved shell-like structure of 12 identical subunits assembled with 23 symmetry. The internal cavity is designed to accommodate up to 500 iron/atoms per molecule in a soluble and bioavailable form. Dps proteins play an important role in the complex protection mechanism against oxidative damage. The presence of a highly conserved ferroxidase center, which uses hydrogen peroxide as physiological iron oxidant, confers to all Dps proteins the capacity to decrease the production of the hydroxyl-radicals and, hence, to prevent the damage to DNA and other cellular components. Ferroxidase activity is of special importance in pathogenic bacteria since production of hydrogen peroxide in macrophages and neutrophiles represents one of the first host defense mechanisms. The capacity to bind DNA in a nonspecific manner and pack it into condensed structures, an attribute limited to some members of the family, represents the second distinctive mechanism used to advantage by Dps proteins for the survival of the organism
One ring (or two) to hold them all - on the structure and function of protein nanotubes
No full textUnderstanding the structural determinants relevant to the formation of supramolecular assemblies of homo-oligomeric proteins is a traditional and central scope of structural biology. The knowledge thus gained is crucial both to infer their physiological function and to exploit their architecture for bionanomaterials design. Protein nanotubes made by one-dimensional arrays of homo-oligomers can be generated by either a commutative mechanism, yielding an open' structure (e.g. actin), or a noncommutative mechanism, whereby the final structure is formed by hierarchical self-assembly of intermediate closed' structures. Examples of the latter process are poorly described and the rules by which they assemble have not been unequivocally defined. We have collected and investigated examples of homo-oligomeric circular arrangements that form one-dimensional filaments of stacked rings by the noncommutative mechanism invivo and invitro. Based on their quaternary structure, circular arrangements of protein subunits can be subdivided into two groups that we term Rings of Dimers (e.g. peroxiredoxin and stable protein 1) and Dimers of Rings (e.g. thermosome/rosettasome), depending on the sub-structures that can be identified within the assembly (and, in some cases, populated in solution under selected experimental conditions). Structural analysis allowed us to identify the determinants by which ring-like molecular chaperones form filamentous-like assemblies and to formulate a novel hypothesis by which nanotube assembly, molecular chaperone activity and macromolecular crowding may be interconnected
DNA-Binding Proteins From Starved Cells (Dps Proteins)
No full textIn the recent past over 200 Dps (DNA-binding proteins from starved cells) proteins have been identified in bacterial genomes. Dps proteins belong to the ferritin superfamily. They are expressed under conditions of oxidative and/or nutritional stress and are characterized by a highly conserved shell-like structure of 12 identical subunits assembled with 23 symmetry. The internal cavity is designed to accommodate up to 500 iron/atoms per molecule in a soluble and bioavailable form. Dps proteins play an important role in the complex protection mechanism against oxidative damage. The presence of a highly conserved ferroxidase center, which uses hydrogen peroxide as physiological iron oxidant, confers to all Dps proteins the capacity to decrease the production of the hydroxyl-radicals and, hence, to prevent the damage to DNA and other cellular components. Ferroxidase activity is of special importance in pathogenic bacteria since production of hydrogen peroxide in macrophages and neutrophiles represents one of the first host defense mechanisms. The capacity to bind DNA in a nonspecific manner and pack it into condensed structures, an attribute limited to some members of the family, represents the second distinctive mechanism used to advantage by Dps proteins for the survival of the organism
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
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