1,720,981 research outputs found
Release of autoinhibition converts ESCRT-III components into potent inhibitors of HIV-1 budding
Full text linkThe endosomal sorting complex ESCRT-III, which is formed by the structurally related CHMP proteins, is engaged by HIV-1 to promote viral budding. Here we show that progressive truncations into the C-terminal acidic domains of CHMP proteins trigger an increasingly robust anti-HIV budding activity. Together with biochemical evidence for specific intramolecular interactions between the basic and acidic halves of CHMP3 and CHMP4B, these results suggest that the acidic domains are autoinhibitory. The acidic half of CHMP3 also interacts with the endosome-associated ubiquitin isopeptidase AMSH, and the coexpression of AMSH or its CHMP3-binding domain converts wild-type CHMP3 into a potent inhibitor of HIV-1 release. Point mutations in CHMP3 that prevent binding to AMSH abrogate this effect, suggesting that binding to AMSH relieves the autoinhibition of CHMP3. Collectively, our results indicate that CHMP proteins are regulated through an autoinhibitory switch mechanism that allows tight control of ESCRT-III assembly
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
Role of SUMOylation in SAMHD1 activities, a restriction factor of HIV-1 in non-cycling cells
No full textDepuis sa découverte il y a sept ans, les recherches intensives sur SAMHD1 en ont fait un facteur cellulaire important qui limite la réplication du virus de l’immunodéficience humaine de type 1 (VIH-1) à l’étape de transcription inverse dans les cellules immunitaires non-cyclantes. Le VIH-2 et certains virus de l’immunodéficience simienne (VIS) surmontent cette restriction en exprimant la protéine Vpx, qui conduit SAMHD1 à sa dégradation protéasomique. De nombreuses données expérimentales indiquent que l’activité triphosphohydrolase (dNTPase) de SAMHD1, qui diminue les niveaux cellulaires de dNTP, est responsable de la restriction. Cependant, la seule expression de SAMHD1 ne suffit pas à rendre les cellules résistantes à l’infection par le VIH-1 et ce quel que soit le type cellulaire. De plus, il n’existe pas de corrélation stricte entre la fonction neutralisante de SAMHD1 et sa capacité à dégrader les dNTP. Il a été suggéré que la phosphorylation du résidu T592 puisse inhiber les fonctions antivirales de SAMHD1 dans les cellules en division. Cependant, l’étude de mutants phospho-mimétiques ou phospho-ablatifs mène à des résultats contradictoires. Ces données permettent d’envisager que l’activité antivirale de SAMHD1 ne repose pas exclusivement sur son activité dNTPase et que sa régulation ne peut pas être expliquée que par la phosphorylation. Nous avons démontré que SAMHD1 est modifiée par la SUMOylation, i.e. une modification post-traductionnelle consistant en la conjugaison réversible des protéines SUMO ; et avons identifié les sites principaux modifiés. Nos résultats indiquent que les mutations empêchant la SUMOylation de SAMHD1, particulièrement celle du résidu K595 adjacent au résidu phosphorylable T592, invalident sa fonction antivirale sans affecter son activité dNTPase. Un phénotype similaire est observé après suppression de la région C-terminale de SAMHD1 (résidus 595-626). Nous suggérons donc que les résidus K595 SUMOylé et T592 phosphorylé font partie d’une interface responsable du recrutement d’un co-facteur méconnu, dépendant du type cellulaire, et pouvant jouer un rôle dans le mécanisme de restriction de l’infection par le VIH-1. Notre travail permet d’entrevoir un nouvel aspect de la régulation de SAMHD1 et contribue à la caractérisation des mécanismes moléculaires sous-jacents à son pouvoir antiviral. L’identification d’un ou plusieurs partenaires cellulaires de SAMHD1 permettra de mieux comprendre le mécanisme de restriction et pourra servir de cible thérapeutique pour combattre l’infection par le VIH-1Since its discovery seven years ago, SAMHD1 has emerged as an important cellular factor that limits the replication of the Human immunodeficiency virus type 1 (HIV-1) at the reverse transcription step in non-cycling immune cells. HIV-2 and some SIV overcome this restriction by encoding the Vpx protein, which bridges SAMHD1 to the proteasomal degradation pathway. A wealth of experimental evidence indicates that SAMHD1 triphosphohydrolase (dNTPAse) activity, which is responsible for cellular dNTP pools depletion, accounts for the premature termination of viral replication. Notably, SAMHD1 expression is not sufficient to render any tested cell type resistant to HIV-1. Besides, there is no strict link between SAMHD1 capacity to deplete dNTP pools and its neutralizing function. Phosphorylation of residue T592 is proposed to downregulate the antiviral function of SAMHD1 in cycling cells. However, the analysis of phosphomimetic or unphosphorytable mutants of SAMHD1 leads to contradictory results. Altogether, these data suggest that SAMHD1-mediated restriction may neither exclusively rely on its dNTPase activity, nor solely depend on the phosphorylation status of T592.We have demonstrated that SAMHD1 undergoes SUMOylation, i.e. a post-translational modification consisting in the reversible conjugation of SUMO on a target protein; and have identified the major sites of modification. Our results show that mutations preventing SAMHD1 SUMOylation, in particular at residue K595 that lies close to the phosphorytable T592 site, inhibit its antiviral properties without impairing its dNTPase activity. Notably, an analogous phenotype is observed upon deletion of SAMHD1 C-terminus (Δ595-626). Based on these data, we speculate that phosphorytable T592 and SUMOylated K595 residues are part of an interface in SAMHD1 C-terminal tail that is responsible for the recruitment of still unknown cofactor(s) involved in the mechanism of HIV-1 infection restriction. Our work highlights a novel aspect of SAMHD1 regulation and participates to the characterization of molecular basis underlying its antiviral function. The identification of one or several cellular partners will allow a better understanding of retroviral restriction mechanism and could serve as new therapeutic targets to fight HIV-1 infection
Multiple activities of allosteric inhibitors of the interaction between HIV-1 Integrase and its cofactor LEDGF/p75
No full textVIH-1, l’agent étiologique du Syndrome de l’Immunodéficience Acquise, est un rétrovirus qui infecte les cellules immunitaires et détourne leur machinerie cellulaire pour se répliquer rapidement. Lors de l’infection, le génome ARN est rétrotranscrit en ADN par la transcriptase inverse virale (RT), puis l’insertion du génome proviral dans l’ADN de la cellule hôte est une étape obligatoire du cycle viral catalysée par l’enzyme virale Intégrase (IN). L’interaction de l’IN avec son cofacteur essentiel, la protéine nucléaire LEDGF/p75, dirige l’intégration à l’intérieur de gènes dans des régions fortement exprimées de la chromatine, ce qui permet la production efficace de nouveaux virions. Les Inhibiteurs Allostériques Intégrase-LEDGF (INLAIs) sont une nouvelle classe de molécules antirétrovirales se liant à l’IN au site de liaison de LEDGF/p75. Conçus pour inhiber compétitivement l’interaction protéine-protéine IN-LEDGF/p75, ils inhibent également les activités enzymatiques de l’Intégrase et augmentent son niveau de multimérisation.Nous avons étudié plusieurs nouvelles séries d’INLAIs de la société Mutabilis, et avons pu démontrer que ces molécules inhibent l’intégration, mais ont aussi un effet antirétroviral plus puissant et indépendant de LEDGF/p75 post-intégration au cours de la maturation des virions, qui conduit à la production de virus non infectieux, ayant une morphologie excentrique caractérisée par un défaut d’encapsidation du génome viral. Lors de l’infection de cellules par ces virus, le cycle viral s’arrête à l’étape de rétrotranscription du génome viral. Nous avons montré que ces virions contiennent pourtant un génome viral stable et fonctionnel, une RT active et l’ARNtLys3 qui sert d’amorce à la rétrotranscription, et ont également conservé leur immunoréactivité pour les lymphocytes B et T. En évaluant l’impact du polymorphisme de l’IN au voisinage du site de liaison, nous avons identifié le variant polymorphe Ala125, pour lequel l’INLAI MUT-A perd concomitamment son effet sur la maturation des virions et sur la multimérisation de l’IN, tandis qu’il inhibe aussi bien l’intégration et l’interaction IN-LEDGF, prouvant que l’effet tardif des INLAIs est associé à l’induction de la multimérisation de l’IN. Nous avons pu associer la multimérisation de l’IN à une déstabilisation du dimère par les INLAIs en analysant les co-structures de MUT-A avec les intégrases polymorphes. Les INLAIs, outre leur intérêt thérapeutique sont de remarquables réactifs qui ont permis de démontrer le rôle essentiel de l’intégrase à trois étapes clés du cycle viral du VIH-1 : la rétrotranscription, l’intégration et la maturation des virions.HIV-1, the causative agent of AIDS, is a retrovirus that infects immune cells and hijacks their cell machinery to achieve rapid replication. In the course of infection, the RNA genome is reverse transcribed into DNA by the viral Reverse Transcriptase (RT) before the obligatory insertion of the proviral genome into the host cell DNA catalyzed by the viral enzyme Integrase (IN). The interaction of IN with its essential cofactor, the nuclear protein LEDGF/p75, targets integration within gene introns in highly transcribed chromatine regions, which allows efficient production of new virions. IN-LEDGF Allosteric Inhibitors (INLAIs) are a novel class of antiretroviral molecules binding IN at the LEDGF/p75-binding site. Designed to competitively inhibit IN-LEDGF/p75 protein-protein interaction, they are also capable of inhibiting IN enzymatic activities and raising the IN multimerization level.We studied several new INLAI series from the company Mutabilis. We could demonstrate that these molecules inhibit integration, but also have a more potent, LEDGF-independent, antiretroviral effect during virion maturation, resulting in the production of non-infectious virions. Virions produced upon INLAI treatment have an eccentric morphology characterized by an encapsidation defect of the viral genome, and lead to an infection block at reverse transcription. Yet, we showed that these virions package a stable and functional viral genome, an active RT and the tRNALys3 primer for reverse transcription, and also keep their immunoreactivity towards B- and T-cell lymphocytes. When evaluating the influence of polymorphism at the edge of the binding site, we identified the IN Ala125 polymorphic variant which causes the concomitant loss of MUT-A effect on virion maturation and IN multimerization, whereas inhibition of integration and IN-LEDGF interaction are maintained. This proves that INLAIs exert their late stage effect through induction of IN multimerization. We could associate IN multimerization to INLAI-induced dimer destabilization by analyzing MUT-A co-structures with polymorphic integrases. Beside their therapeutic interest INLAIs are highly valuable reagents that allowed to demonstrate the essential role of integrase at three key steps of the HIV-1 replication cycle, reverse transcription, integration and virus maturation
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