1,720,976 research outputs found
A conserved "hydrophobic staple motif" plays a crucial role in the refolding of human glutathione transferase P1-1.
No full textThe specific (i, i+5) hydrophobic staple interaction involving a helix residue and a second residue located in the turn preceding the helix is a recurrent motif at the N terminus of alpha-helices. This motif is strictly conserved in the core of all soluble glutathione transferases (GSTs) as well as in other protein structures. Human GSTP1-1 variants mutated in amino acid Ile(149) and Tyr(154) of the hydrophobic staple motif of the alpha6-helix were analyzed. In particular, a double mutant cycle analysis has been performed to evaluate the role of the hydrophobic staple motif in the refolding process. The results show that this local interaction, by restricting the number of conformations of the alpha6-helix relative to the alpha1-helix, favors the formation of essential interdomain interactions and thereby accelerates the folding process. Thus, for the first time it is shown that the hydrophobic staple interaction has a role in the folding process of an intact protein. In P(i) class GSTs, Tyr(154) appears to be of particular structural importance, since it interacts with conserved residues Leu(21), Asp(24), and Gln(25) of the adjacent alpha1-helix which contributes to the active site. Human GSTP1-1 variants L21A and Y154F have also been analyzed in order to distinguish the role of interdomain interactions from that of the hydrophobic staple. The experimental results reported here suggest that the strict conservation of the hydrophobic staple motif reflects an evolutionary pressure for proteins to fold rapidl
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
Unfolding and refolding of human glyoxalase II and its single-tryptophan mutants.
No full textHere the structure of human glyoxalase II has been investigated by studying unfolding at equilibrium and refolding. Human glyoxalase II contains two tryptophan residues situated at the N-terminal (Trp57) and C-terminal (Trp199) regions of the molecule. Trp57 is a non-conserved residue located within a "zinc binding motif" (T/SHXHX57DH) which is strictly conserved in all known glyoxalase II sequences as well as in metal-dependent beta-lactamase and arylsulfatase. Site-directed mutagenesis has been used to construct single-tryptophan mutants in order to characterize better the guanidine-induced unfolding intermediates. The denaturation at equilibrium of wild-type glyoxalase II, as followed by activity, intrinsic fluorescence and CD, is multiphasic, suggesting that different regions of varying structural stability characterize the native structure of glyoxalase II. At intermediate denaturant concentration (1.2 M guanidine) a molten globule state is attained. The reactivation of the denatured wild-type enzyme occurs only in the presence of Zn(II) ions. The results show that Zn(II) is essential for the maintenance of the native structure of glyoxalase II and that its binding to the apoenzyme occurs during an essential step of refolding. The comparison of unfolding fluorescence transitions of single-trypthophan mutants with that of wild-type enzyme indicates that the strictly conserved "zinc binding motif" is located in a flexible region of the active site in which Zn(II) participates in catalysis
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
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