1,720,962 research outputs found
Conformational Dynamics of the Mitochondrial TIM23 Preprotein Translocase
Full text linkThe vast majority of mitochondrial proteins are synthesized by the cytosolic ribosomes as precursor proteins which have to be transported into the organelle to reach their sites of function. The whole process of recognition, translocation, intra-mitochondrial sorting of and assembly of precursor proteins is achieved by the concerted action of different mitochondrial translocases. All proteins destined for the mitochondrial matrix and some inner membrane proteins are imported first by the TOM complex of the outer membrane and subsequently by the TIM23 complex of the inner membrane in an energy-driven process. The TIM23 complex was found to consist of ten components, conventionally divided into two sectors: membrane sector harbouring the translocation channel and the import motor on the matrix side of the membrane sector.
In the first part of the present work, the two most recently discovered subunits of the TIM23 complex, Pam17 and Tim21 were characterized. A systematic characterization revealed that both of these non-essential subunits of the translocase are associated with Tim17-Tim23 core of the membrane sector of the TIM23 translocase. A functional connection between the two non-essential components was discovered. Results presented in this part showed that Pam17 and Tim21 modulate the functions of the TIM23 complex in an antagonistic manner.
The second part of the work was directed towards understanding the motor sector of the translocase in terms of the regulated interaction between Tim44 and Ssc1. Previous studies on the Tim44:Ssc1 interaction were able to discern the steady-state properties of Tim44:Ssc1 interaction in organello and in vitro. However, due to the limitations of the techniques used, they were unable to shed light on the kinetics and dynamics of the process. The translocation event is a dynamic event with conformational cycling of the various components. Therefore, the kinetic components essential in defining the cycle of events in the motor sector were explored. A FRET based assay to analyze the Tim44:Ssc1 interaction in real time was developed. The same set of tools was also used to resolve the regions of the two proteins that determine their interaction. The substrate induced dissociation of Tim44:Ssc1 complex was found to be too slow to support a physiological rate of protein translocation. ATP-induced dissociation was observed to be fast enough to be physiologically relevant. The dissociation of Ssc1 from Tim44 occurred in a one step manner without Tim44 anchored conformational changes. Furthermore, peptide-array scanning of mitochondrial matrix proteins revealed that Ssc1 and Tim44 share complementary binding sites on the precursor proteins which could prevent backsliding of preproteins. The data support the Brownian ratchet model mediated translocation of preproteins into the mitochondrial matrix.
The third part of the work aimed at dissecting the chaperone cycle of Ssc1 in the mitochondrial matrix, in terms of conformational changes and binding of co-chaperones. Using the FRET sensors developed, the inter-domain conformation and lid-base conformations of the PBD of Ssc1 could be investigated. Single particle FRET (SpFRET) analysis showed that in the ATP-bound form Ssc1 populates a homogeneous conformational state with respect to the inter-domain conformation and conformation of the lid to base of the PBD. On the contrary, in the ADP-bound state the conformation of the chaperone is heterogenous. Using the same sensors on bacterial homologue DnaK, specific differences in conformational distributions were observed. Furthermore, the active role of substrates in determining the inter-domain conformation and lid-closing was evident from the SpFRET based conformational analyses. Using ensemble time resolved FRET, the kinetics and dynamics of conformational changes along with binding of co-chaperones were explored. This provided a better understanding of the conformational dynamics of Ssc1 in the context of functional chaperone cycle in the mitochondrial matrix
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
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
Understanding the effect of locked nucleic acid and 2′-O-methyl modification on the hybridization thermodynamics of a miRNA–mRNA pair in the presence and absence of AfPiwi protein
No full textmiRNAs are some of the key epigenetic regulators of gene expression. They act through hybridization with their target mRNA and modulate the level of respective proteins via different mechanisms. Various cancer conditions are known to be associated with up- and downregulation of the oncogenic and tumor suppressor miRNAs, respectively. The levels of aberrantly expressed oncogenic miRNAs can be downregulated in different ways. Similarly, restoration of tumor suppressor miRNAs to their normal levels can be achieved using miRNA mimics. However, the use of miRNA mimics is limited by their reduced biostability and function. We have studied the hybridization thermodynamics of the miRNA 26a (11-mer, including the seed sequence) guide strand with the mRNA (11-mer) target strand in the absence and presence of AfPiwi protein. We have also inserted locked nucleic acids (LNAs) and 2′-O-methyl-modified nucleotides into the guide strand, in a walk-through manner, to assess their effect on the binding efficiency between guide and target RNA. Insertion of LNA and 2′-O-methyl-modified nucleotides into the guide strand helped to strengthen the binding affinity irrespective of the position of insertion. However, in the presence of AfPiwi protein, these modifications reduced the binding affinity to different extents depending on the position of insertion. Insertion of a modification leads to an increase in the enthalpic contribution with an increased unfavorable entropic contribution, which negatively compensates for the higher favorable enthalpy
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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