57 research outputs found
Antibacterial activity and pore-forming properties of ceratotoxins: a mechanism of action based on the barrel stave model.
No full textCeratotoxins are a-helical cationic peptides isolated from the medfly Ceratitis capitata. These amphipathic peptides were found to display strong antibacterial activity and weak hemolytic activity. When reconstituted into planar lipid bilayers, ceratotoxins developed highly asymmetric I/V curves under voltage ramps and formed, in single-channel experiments, well-defined voltage-dependent ion channels according to the barrel stave model. The antibacterial activity and pore-forming properties of these molecules were well correlated. Similar experiments performed with synthesized truncated fragments showed that the C-terminal domain of ceratotoxins, is strongly implicated in the formation of helical bundles in the membrane whereas the largely cationic N-terminal region is likely to anchor ceratotoxins on the lipid surface
Direct Interaction Between the Rice yellow mottle virus (RYMV) VPg and the Central Domain of the Rice eIF(iso)4G1 Factor Correlates with Rice Susceptibility and RYMV Virulence
No full textUnique Features of the Folding Landscape of a Repeat Protein Revealed by Pressure Perturbation
No full textThe volumetric properties of proteins yield information about the changes in packing and hydration between various states along the folding reaction coordinate and are also intimately linked to the energetics and dynamics of these conformations. These volumetric characteristics can be accessed via pressure perturbation methods. In this work, we report high-pressure unfolding studies of the ankyrin domain of the Notch receptor (Nank1-7) using fluorescence, small-angle x-ray scattering, and Fourier transform infrared spectroscopy. Both equilibrium and pressure-jump kinetic fluorescence experiments were consistent with a simple two-state folding/unfolding transition under pressure, with a rather small volume change for unfolding compared to proteins of similar molecular weight. High-pressure fluorescence, Fourier transform infrared spectroscopy, and small-angle x-ray scattering measurements revealed that increasing urea over a very small range leads to a more expanded pressure unfolded state with a significant decrease in helical content. These observations underscore the conformational diversity of the unfolded-state basin. The temperature dependence of pressure-jump fluorescence relaxation measurements demonstrated that at low temperatures, the folding transition state ensemble (TSE) lies close in volume to the folded state, consistent with significant dehydration at the barrier. In contrast, the thermal expansivity of the TSE was found to be equivalent to that of the unfolded state, indicating that the interactions that constrain the folded-state thermal expansivity have not been established at the folding barrier. This behavior reveals a high degree of plasticity of the TSE of Nank1-7
Caractérisation et production de protéines impliquées dans le système de défense " inné " des poissons
No full textLe mucus épidermique de poisson contient de nombreux composés lui conférant un rôle de protection contre les microorganismes. Récemment plusieurs protéines antibactériennes ont été isolées des fractions hydrophobes des mucus épidermiques d'anguille, de tanche et de truite. Ces protéines possédaient une forte activité antibactérienne corrélée à une activité "formeur" de pores, responsable de la perméabilisation des membranes bactériennes. La première partie de ce travail a consisté à montrer que de telles protéines étaient présentes dans le mucus d'un poisson d'eau de mer. A partir du mucus de turbot une protéine de 55 kDa, possédant de telles activités, a été isolée et caractérisée. Dans la seconde partie de cette étude, nous nous sommes intéressés à la protéine de 65 kDa de truite (Tr65). A partir d'une banque d'ADNc de la peau et des séquences primaires de fragments protéiques obtenus après digestions, le gène de Tr65 a pu être identifié. Le fort caractère hydrophobe de Tr65 et sa puissante activité antibactérienne ont rendu impossible sa production dans différents systèmes in vivo ou in vitro. En suivant les prédictions de structure secondaire et surtout la position des hélices transmembranaires, Tr65 a été découpée en trois fragments qui ont été produits et purifiés avec succès. Seuls les fragments possédant les hélices transmembranaires ont pu restaurer l'activité "formeur" de pores. Par contre, l'activité antibactérienne n'a pu être retrouvée. Ce résultat peut s'expliquer par, (i) leur forte insolubilité dans les milieux permettant la croissance bactérienne, (ii) des problèmes de conformation comme le suggèrent des expériences de dichroïsme circulaire.Many compounds are present in skin mucus of fishes were they serve as the first line of defence against bacterial invasion. Recently, several antibacterial proteins have been extracted from mucus of eel, tench and trout. These proteins have strong antimicrobial activity correlated to a pore forming properties inducing permeabilisation of bacterial membranes. In the first part of this work, we have identified a 55 kDa hydrophobic protein with such activities in the mucus of a sea fish, the turbot. In a second part, we have studied the 65 kDa protein of trout (Tr65). Tr65 gene was identified from skin cDNA library and from primary sequences of digested protein fragments. Due to its strong hydrophobic nature and antibacterial activity, Tr65 could not be successfully produced in in vivo and in vitro systems. According to secondary structure predictions, Tr65 was successfully produced as three protein fragments: N-terminal and C-terminal fragments containing transmembrane helices and a middle one. The segments with transmembrane helices were the only ones to show pore-forming activity in planar lipid bilayers. In contrast no antibacterial activity was observed with any segments. This last result can be explained by: (i) the high insolubility of the segments in bacterial culture media, (ii) the unfolding of the segments as revealed by circular dichroism measurements.ROUEN-BU Sciences (764512102) / SudocSudocFranceF
L'urgence au sein de la justice des mineurs : un exemple de la dé-temporalisation de l'intervention sociale
No full textEmergencies in the juvenile justice system : an example of de-temporalisation of social work intervention This article deals with temporality in judicial practices in relation to a general tendency of reduction of temporal horizons and towards “de-temporalisation”, that is a difficulty in seeing present action in relation to the past and with regard to of the future. The educational time of juvenile justice has specific attributes and takes place over a long period. Child judges expect that measures will be of long duration and this time scale is considered as reversible and modifiable, in order to adapt their intervention as function of the evolution of the family. A French nationwide study of emergency child placements enables the author to confirm that judges are going back to traditional legalistic approaches and that the educational concept of juvenile justice is being eroded. As a way of anticipating on the risks run by minors in danger, in a socio-political context where action in the present time is valued to the detriment of an overall temporal perspective, the author shows how procedures for emergencies have been institutionalised, thus leaving aside the longer term educational time perspective
Présences recluses : les ambivalences des interventions (sociales, sanitaires et éducatives) en prison
No full textInternational audienceFar from a logic of success, often brandished to present detained students, the university offer in prison is part of a set of social, health, cultural and educational interventions that respond to diverse needs. These actions, which fall within the scope of care, are analyzed here in terms of social presences in order to emphasize the temporal and gendered implications of these ambivalent processes that are at work in any intervention for others, and in particular the temporal ambivalence linked to secluded presences. In order to present the tensions that cross the activities of accompanying prisoners, between protection and control, approached in a temporal perspective, the article is divided into three parts. First, the author briefly presents his relationship to the prison world, based on his own research on military service and prison care, and on research of doctoral students about the prison institution or on the dynamics of confinement. He then explains the concept of social presence to put forward the idea that any activity of help or accompaniment is part of a moral tension between "watching over" and "caring out", between supporting and punishing. Finally, he supports the idea that this ambivalence should lead us to depart from any justification in terms of success or efficiency to defend the right to study in prison.Loin d’une logique de réussite, souvent brandie pour présenter les étudiants détenus, l’offre universitaire en prison s’inscrit dans un ensemble d’interventions sociales, sanitaires, culturelles et éducatives qui répondent à des besoins divers. Ces actions qui relèvent du care sont ici analysées en termes de présences sociales pour insister sur les enjeux temporels et sexués de ces processus ambivalents qui sont à l’œuvre dans toute intervention pour autrui, et notamment les ambivalences temporelles liées aux présences recluses. Pour présenter les tensions qui traversent les activités d’accompagnement des détenus, entre la protection et le contrôle, abordées dans une perspective temporelle, l’article se déploie en trois parties. L’auteur présente d’abord rapidement ses rapports à l’univers carcéral, à partir de ses propres recherches sur le service militaire et les soins en prison, et de celles qu’il a accompagnées portant sur l’institution pénitentiaire ou sur les dynamiques d’enfermement. Il expose ensuite le concept de présences sociales pour avancer l’idée que toute activité d’aide ou d’accompagnement s’inscrit dans une tension morale entre « surveiller » et « veiller sur », entre soutenir ou punir, entre protéger et contrôler. Il soutient enfin l’idée selon laquelle cette ambivalence devrait inciter à s’écarter de toute justification en termes de réussite ou d’efficacité pour défendre le droit aux études en prison
Présences recluses : les ambivalences des interventions (sociales, sanitaires et éducatives) en prison
No full textInternational audienceFar from a logic of success, often brandished to present detained students, the university offer in prison is part of a set of social, health, cultural and educational interventions that respond to diverse needs. These actions, which fall within the scope of care, are analyzed here in terms of social presences in order to emphasize the temporal and gendered implications of these ambivalent processes that are at work in any intervention for others, and in particular the temporal ambivalence linked to secluded presences. In order to present the tensions that cross the activities of accompanying prisoners, between protection and control, approached in a temporal perspective, the article is divided into three parts. First, the author briefly presents his relationship to the prison world, based on his own research on military service and prison care, and on research of doctoral students about the prison institution or on the dynamics of confinement. He then explains the concept of social presence to put forward the idea that any activity of help or accompaniment is part of a moral tension between "watching over" and "caring out", between supporting and punishing. Finally, he supports the idea that this ambivalence should lead us to depart from any justification in terms of success or efficiency to defend the right to study in prison.Loin d’une logique de réussite, souvent brandie pour présenter les étudiants détenus, l’offre universitaire en prison s’inscrit dans un ensemble d’interventions sociales, sanitaires, culturelles et éducatives qui répondent à des besoins divers. Ces actions qui relèvent du care sont ici analysées en termes de présences sociales pour insister sur les enjeux temporels et sexués de ces processus ambivalents qui sont à l’œuvre dans toute intervention pour autrui, et notamment les ambivalences temporelles liées aux présences recluses. Pour présenter les tensions qui traversent les activités d’accompagnement des détenus, entre la protection et le contrôle, abordées dans une perspective temporelle, l’article se déploie en trois parties. L’auteur présente d’abord rapidement ses rapports à l’univers carcéral, à partir de ses propres recherches sur le service militaire et les soins en prison, et de celles qu’il a accompagnées portant sur l’institution pénitentiaire ou sur les dynamiques d’enfermement. Il expose ensuite le concept de présences sociales pour avancer l’idée que toute activité d’aide ou d’accompagnement s’inscrit dans une tension morale entre « surveiller » et « veiller sur », entre soutenir ou punir, entre protéger et contrôler. Il soutient enfin l’idée selon laquelle cette ambivalence devrait inciter à s’écarter de toute justification en termes de réussite ou d’efficacité pour défendre le droit aux études en prison
L'urgence au sein de la justice des mineurs : un exemple de la dé-temporalisation de l'intervention sociale
No full textL'article traite de la temporalité des pratiques judiciaires, au regard d’une tendance générale au rétrécissement des horizons temporels et à la dé-temporalisation, entendue comme difficulté à envisager l’action présente au regard du passé et en fonction de l’avenir. Le temps éducatif de la justice des mineurs, spécifique, s’inscrit dans la durée : les juges des enfants tablent sur un temps long, pour accompagner les jeunes, un temps réversible et modulable, afin d’adapter leur intervention en fonction de l’évolution familiale. Une enquête menée en France sur les placements d’enfants décidés en urgence permet de confirmer l’effritement des conceptions éducatives de la justice des mineurs et le retour au légalisme des juges des enfants. Pour anticiper les risques encourus par les mineurs en danger, dans un contexte sociopolitique où l’action dans le temps présent est valorisée au détriment de la mise en perspective temporelle, l’auteur montre l’institutionnalisation des procédures d’urgence judiciaire, qui entérine le renoncement au temps éducatif.Emergencies in the juvenile justice system : an example of de-temporalisation of social work intervention This article deals with temporality in judicial practices in relation to a general tendency of reduction of temporal horizons and towards “de-temporalisation”, that is a difficulty in seeing present action in relation to the past and with regard to of the future. The educational time of juvenile justice has specific attributes and takes place over a long period. Child judges expect that measures will be of long duration and this time scale is considered as reversible and modifiable, in order to adapt their intervention as function of the evolution of the family. A French nationwide study of emergency child placements enables the author to confirm that judges are going back to traditional legalistic approaches and that the educational concept of juvenile justice is being eroded. As a way of anticipating on the risks run by minors in danger, in a socio-political context where action in the present time is valued to the detriment of an overall temporal perspective, the author shows how procedures for emergencies have been institutionalised, thus leaving aside the longer term educational time perspective.La urgencia en la justicia de menores : un ejemplo de la destemporalización de la intervención social El artículo trata sobre la temporalidad de las prácticas judiciales, respecto a una tendencia general al estrechamiento de los horizontes temporales y a la destemporalización, entendida como dificultad para plantear la acción presente con relación al pasado y en función del futuro. El tiempo educativo de la justicia de menores, específico, se inscribe en la duración : los jueces de menores cuentan con un tiempo largo, para acompañar a los jóvenes, un tiempo reversible y modulable, para adaptar su intervención en función de la evolución familiar. Una encuesta realizada en Francia sobre los ingresos de menores decididos en urgencia, permite confirmar el desmoronamiento de las concepciones educativas de la justicia de menores y el regreso al legalismo de los jueces de menores. Para anticipar los riesgos que corren los menores en peligro, en un contexto sociopolítico en el que se valoriza la acción en el tiempo presente en detrimento de la puesta en perspectiva temporal, el autor muestra la institucionalización de los procedimientos de urgencia judicial, que confirma la renuncia al tiempo educativo.
Dynamic Expression of DNA Complexation with Self-assembled Biomolecular Clusters
No full textInternational audienceWe report herein the implementation of a dynamic covalent chemistry approach to the generation of multivalent clusters for DNA recognition. We show that biomolecular clusters can be expressed in situ by a programmed self-assembly process using chemoselective ligations. The cationic clusters are shown, by fluorescence displacement assay, gel electrophoresis and isothermal titration calorimetry, to effectively complex DNA through multivalent interactions. The reversibility of the ligation was exploited to demonstrate that template effects occur, whereby DNA imposes component selection in order to favor the most active DNA-binding clusters. Furthermore, we show that a chemical effector can be used to trigger DNA release through component exchange reaction
Antibacterial peptide pleurocidin forms ion channels in planar lipid bilayers
No full textAbstractPleurocidin, a 25-residue α helical cationic peptide, isolated from skin mucous secretions of the winter flounder, displays a strong anti-microbial activity and appears to play a role in innate host defence. This peptide would be responsible for pore formation in the membrane of bacteria leading to lysis and therefore death. In this study, we investigated the behaviour of pleurocidin in different planar lipid bilayers to determine its mechanism of membrane permeabilisation. Macroscopic conductance experiments showed that pleurocidin did not display a pore-forming activity in neutral phosphatidylcholine/phosphatidylethanolamine (PC/PE) lipid bilayers. However, in 7:3:1 PC/PE/phosphatidylserine (PS) lipid bilayers, pleurocidin showed reproducible I/V curves at different peptide concentrations. This activity is confirmed by single-channel experiments since well-defined ion channels were obtained if the lipid mixture was containing an anionic lipid (PS). The ion channel characteristics such as—no voltage dependence, only one unitary conductance, linear relation ship current–voltage—, are not in favour of the membrane permeabilisation according to the barrel model but rather by the toroidal pore formation
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