1,721,015 research outputs found
Determination of antimicrobial peptide mechanism of action on bacteria by in vivo molecular-scale solid state NMR
No full textStaphylococcus aureus est une bactérie résistante à de nombreux antibiotiques, et de nouveaux traitements sont recherchés pour la combattre. Le DMS-DA6-NH₂, un peptide antimicrobien d'origine amphibienne, a montré une efficacité remarquable contre les souches Gram-positives, dont S. aureus, avec des concentrations minimales inhibitrices et bactéricides à 1,6 µM. Son mécanisme d'action n'était pas clair, mais utilisant la Résonance Magnétique Nucléaire (RMN) in vivo du deutérium (²H) a permis de mieux le comprendre. Cette technique consiste à marquer la membrane bactérienne avec des acides gras deutérés et à analyser la rigidité membranaire affectée par le peptide. Les résultats obtenus ont été comparés à ceux de peptides lytiques comme l'auréine 1.2 et la caérine 1.1, révélant que le DMS-DA6-NH₂ agit via un mécanisme lytique en formant des pores dans la membrane de S. aureus. Des études supplémentaires par RMN solide et microscopie ont montré que le peptide cible également la paroi bactérienne, en interagissant avec l'acide téichoïque et le peptidoglycane. En parallèle, une méthode pour suivre l'incorporation des acides gras deutérés dans la membrane a été développée. Celle-ci utilise des techniques de chromatographie gazeuse couplée à la spectrométrie de masse pour étudier le marquage actif ou passif des membranes bactériennes, déterminant si les acides gras sont métabolisés et utilisés dans la biosynthèse des phospholipides, ou s'ils sont inchangés dans la membrane, selon le détergent employé.Staphylococcus aureus is a bacterium resistant to many antibiotics, and new treatments are being sought to combat it. DMS-DA6-NH₂, an antimicrobial peptide of amphibian origin, has shown remarkable efficacy against Gram-positive strains, including S. aureus, with minimum inhibitory and bactericidal concentrations of 1.6 µM. Its mechanism of action was unclear, but the use of in vivo Deuterium Nuclear Magnetic Resonance (²H NMR) helped to better understand it. This technique involves labeling the bacterial membrane with deuterated fatty acids, and analyzing the membrane rigidity affected by the peptide. The results were compared to those of lytic peptides such as aurein 1.2 and caerin 1.1, revealing that DMS-DA6-NH₂ acts via a lytic mechanism by forming pores in the S. aureus membrane. Further studies using solid-state NMR and microscopy showed that the peptide also targets the bacterial cell wall by interacting with teichoic acid and peptidoglycan. In parallel, a method was developed to track the incorporation of deuterated fatty acids into the membrane. This method uses gas chromatography coupled with mass spectrometry to study the active or passive labeling of bacterial membranes, determining whether the fatty acids are metabolized and used in the biosynthesis of phospholipids, or remain unchanged in the membrane, depending on the detergent used
Magnetically oriented bicelles with monoalkylphosphocholines: versatile membrane mimetics for nuclear magnetic resonance applications
Get PDFBicelles (bilayered micelles) are model membranes used in the study of peptide structure and membrane interactions. They are traditionally made of long- and short-chain phospholipids, usually dimyristoylphosphatidylcholine (D14PC) and dihexanoyl-PC (D6PC). They are attractive membrane mimetics because their composition and planar surface are similar to the native membrane environment. In this work, to improve the solubilization of membrane proteins and allow their study in bicellar systems, D6PC was replaced by detergents from the monoalkylphosphocholine (MAPCHO) family, of which dodecylphosphocholine (12PC) is known for its ability to solubilize membrane proteins. More specifically 12PC, tetradecyl- (14PC), and hexadecyl-PC (16PC) have been employed. To verify the possibility of making bicelles with different hydrophobic thicknesses to better accommodate membrane proteins, D14PC was also replaced by phospholipids with different alkyl chain lengths: dilauroyl-PC (D12PC), dipalmitoyl-PC (D16PC), distearoyl-PC (D18PC), and diarachidoyl-PC (D20PC). Results obtained by 31P solid-state nuclear magnetic resonance (NMR) and isothermal titration calorimetry (ITC) at several lipid-to-detergent molar ratios (q) and temperatures indicate that these new MAPCHO bicelles can be formed under a variety of conditions. The quality of their alignment is similar to that of classical bicelles, and the low critical micelle concentration (CMC) of the surfactants and their miscibility with phospholipids are likely to be advantageous for the reconstitution of membrane proteins
Tethered or Adsorbed Supported Lipid Bilayers in Nanotubes Characterized by Deuterium Magic Angle Spinning NMR Spectroscopy
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1H–13C polarization transfer in membranes: A tool for probing lipid dynamics and the effect of cholesterol
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Asymmetrical Membranes and Surface Tension
No full textAbstractThe 31P-nuclear magnetic resonance chemical shift of phosphatidic acid in a membrane is sensitive to the lipid head group packing and can report qualitatively on membrane lateral compression near the aqueous interface. We have used high-resolution 31P-nuclear magnetic resonance to evaluate the lateral compression on each side of asymmetrical lipid vesicles. When monooleoylphosphatidylcholine was added to the external monolayer of sonicated vesicles containing dioleoylphosphatidylcholine and dioleoylphosphatidic acid, the variation of 31P chemical shift of phosphatidic acid indicated a lateral compression in the external monolayer. Simultaneously, a slight dilation was observed in the inner monolayer. In large unilamellar vesicles on the other hand the lateral pressure increased in both monolayers after asymmetrical insertion of monooleoylphosphatidylcholine. This can be explained by assuming that when monooleoylphosphatidylcholine is added to large unilamellar vesicles, the membrane bends until the strain is the same in both monolayers. In the case of sonicated vesicles, a change of curvature is not possible, and therefore differential packing in the two layers remains. We infer that a variation of lipid asymmetry by generating a lateral strain in the membrane can be a physiological way of modulating the conformation of membrane proteins
Escherichia Coli as Host for Membrane Protein Structure Determination: A Global Analysis
No full textHattab G, Warschawski DE, Moncoq K, Miroux B. Escherichia coli as host for membrane protein structure determination: a global analysis. Scientific Reports. 2015;5(1): 12097.The structural biology of membrane proteins (MP) is hampered by the difficulty in producing and purifying them. A comprehensive analysis of protein databases revealed that 213 unique membrane protein structures have been obtained after production of the target protein in E. coli. The primary expression system used was the one based on the T7 RNA polymerase, followed by the arabinose and T5 promoter based expression systems. The C41λ(DE3) and C43λ(DE3) bacterial mutant hosts have contributed to 28% of non E. coli membrane protein structures. A large scale analysis of expression protocols demonstrated a preference for a combination of bacterial host-vector together with a bimodal distribution of induction temperature and of inducer concentration. Altogether our analysis provides a set of rules for the optimal use of bacterial expression systems in membrane protein production
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