Cloud Microorganisms, an Interesting Source of Biosurfactants

A new scientific hypothesis states that biosurfactants from cloud microorganism origin could change the surface tension of aerosols and thus the mode of precipitations. In order to check this hypothesis, our team has screened a collection of 480 microbial strains isolated from cloud waters for the production of biosurfactants and showed that 42% of these strains were producing such molecules. In the present work, we isolated and identified by LC-MS-MS lipopeptides produced from three strains issued from this screening. Viscosin and massetolide E (cyclic lipopeptides) were produced by Pseudomonas sp. PDD-14b-2, and syringafactins (linear lipopeptides) were produced by Xanthomonas campestris PDD-32b-52 and Pseudomonas syringae PDD-32b-74. The critical micelle concentration (CMC) of these biosurfactants was determined using the pendant drop method. Finally, two approaches of molecular dynamics were used to model the conformation of viscosin and syringafactin A at the water-air interface: one is based on all-atoms simulation (CHARMM force field), while the other one on coarse-grain (CG) simulation (MARTINI force field). To conclude, this work shows how the biodiversity of the cloud microbiota can be explored to search and produce biosurfactants of interest both for atmospheric sciences and also for biotechnological applications

Solution structures of the Bacillus cereus metallo-β-lactamase BcII and its complex with the broad spectrum inhibitor R-thiomandelic acid

Metallo-β-lactamases, enzymes which inactivate β-lactam antibiotics, are of increasing biological and clinical significance as a source of antibiotic resistance in pathogenic bacteria. In the present study we describe the high-resolution solution NMR structures of the Bacillus cereus metallo-β-lactamase BcII and of its complex with R-thiomandelic acid, a broad-spectrum inhibitor of metallo-β-lactamases. This is the first reported solution structure of any metallo-β-lactamase. There are differences between the solution structure of the free enzyme and previously reported crystal structures in the loops flanking the active site, which are important for substrate and inhibitor binding and catalysis. The binding of R-thiomandelic acid and the roles of active-site residues are defined in detail. Changes in the enzyme structure upon inhibitor binding clarify the role of the mobile β3–β4 loop. Comparisons with other metallo-β-lactamases highlight the roles of individual amino-acid residues in the active site and the β3–β4 loop in inhibitor binding and provide information on the basis of structure–activity relationships among metallo-β-lactamase inhibitors

Le problème Vareille(s) - Vazeille(s)

Nauton Pierre. Le problème Vareille(s) - Vazeille(s). In: Revue Internationale d'Onomastique, 3e année N°1, mars 1951. pp. 9-30

Sand supply, sources and evolution of the mid-Carboniferous Clare Basin, western Ireland: insights from multi-proxy provenance approaches

Sedimentary provenance analysis aims to improve the understanding of all factors associated with sediment production, transport and deposition. This has implications for a wide range of geosciences, helping towards reconstructing palaeogeography, palaeodrainage, and palaeoenvironment. However, multiple factors hinder optimum interpretation of provenance signals in sediments and sedimentary rocks. Some of these factors are investigated in this study, including the impacts of sedimentary recycling and sediment storage in the hinterland, prior to final deposition. This project applies a multi-proxy provenance approach to ancient sandstones from the mid-Carboniferous Clare Basin, western Ireland, to answer key provenance analysis questions and also to better constrain sedimentary routing and sources, basin infill, and palaeogeographic evolution. A large provenance dataset is presented here, comprising zircon U-Pb geochronology data from 13 samples (1624 grains), apatite U-Pb geochronology and trace element results from 10 samples (587 grains), heavy mineral analysis of 31 samples and standard petrographic analysis of 57 samples. The use of zircon and apatite U-Pb geochronology, heavy minerals analysis, apatite trace elements, and petrographic analysis is proven a powerful combination in the identification of sedimentary recycling in mineralogically mature sandstones. The results enable the identification of multiple source terranes supplying the sandstones of the Clare Basin. A major first cycle southern peri-Gondwanan associated input is identified. Additionally, polycyclic zircon (of Laurentian and Caledonian affinity) and apatite (Caledonian affinity) are established as ultimately being derived from the north but recycled through Old Red Sandstone sedimentary basins to the south (e.g. Dingle and Munster basins). Sedimentary recycling is therefore clearly favoured over intensive first cycle chemical weathering, to explain the mineralogical maturity of sandstones in the Clare Basin. The multi-proxy provenance approach identifies sedimentary sourcing in the Clare Basin as being continuously from the WSW-SSW throughout the entire sampled stratigraphy. Comparing provenance signals from the entire basin, both temporally and spatially, using detrital geochronology and heavy mineral indices, enables a better understanding of hinterland and shelf configuration evolution. Furthermore, southern hinterland uplift, linked with the Variscan Orogeny, is envisaged to impact supply during the later infill of the Clare Basin. In addition, heavy mineral indices in Tullig Cyclothem deltaic sandstones indicate a link between detrital mineralogy, sedimentary facies and sediment pre-depositional history. Relatively higher apatite-tourmaline index values are seen in channelised sandstones compared to sandstones associated with mouth bar and interdistributary bay facies. The apatite-tourmaline index highlights variations in the extent of chemical weathering experienced by the sediment prior to deposition. Such findings likely indicate that chemical weathering occurring prior to deposition is dependent on the sediment residence time in the hinterland and this signal appears to carry through to ultimate deposition. This highlights the potential of this specific index for use in reconstructing palaeoweathering and palaeoclimate at a deep-geological time scale. This project advances the utility of provenance analysis and highlights the need for a multi-proxy provenance approach to fully understand sedimentary routing. For the first time, the Clare Basin infill has been fully constrained through a multi-proxy provenance approach. Learnings from this case study from a well-known Irish sedimentary basin can be applied to other sedimentary successions, with a specific applicability to quartz-rich sedimentary rocks

Le patois de Saugues (Haute-Loire). Aperçu linguistique. Terminologie rurale. Littérature orale.

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QM/MM Study of Human Transketolase: Thiamine Diphosphate Activation Mechanism and Complete Catalytic Cycle

International audienceA computational model for human transketolase was proposed, showing that thiamine diphosphate activation was based on His110 in place of His481 reported in yeast transketolase. In addition, a complete catalytic reaction pathway was investigated using d-xylulose-5-phosphate and d-ribose-5-phosphate as substrates, showing at every step a perfect superimposition of our model with high-resolution crystallographic structures 3MOS, 4KXV, and 4KXX. This study shows that H2N4′ of the active thiamine diphosphate “V form” no longer has a self-activating role but allows self-stabilization of the cofactor and of the Breslow intermediate. These advances in our knowledge of the human transketolase mechanism offer interesting prospects for the design of new drugs, this enzyme being involved in several diseases, and for a better understanding of the reactions catalyzed by transketolases from other sources

Synthesis and molecular modelling study of new trimeric quinoline derivatives

International audienceDi- and trimeric quinoline derivatives have been recently described as potential modulators of Bcl-2 family protein interactions. However, only a few trimeric compounds have been described so far and an enlargement of the number of analogs of this class is needed to expand the structure-activity relationship study. Therefore, the synthesis of six new trimeric quinoline derivatives is reported. Moreover molecular modeling experiments were performed to study the conformational arrangement of compound 36 in Bak binding site of Bcl-xL, showing that these compounds could be potential ligands for Bcl-xL

A multi-scale modelling of an enzymatic PET degradation.

International audienc

Insights into the Thiamine Diphosphate Enzyme Activation Mechanism: Computational Model for Transketolase Using a Quantum Mechanical/Molecular Mechanical Method.

International audienceWe propose the first computational model for transketolase (TK), a thiamine diphosphate (ThDP)-dependent enzyme, using a quantum mechanical/molecular mechanical method on the basis of crystallographic TK structures from yeast and Escherichia coli, together with experimental kinetic data reported in the literature with wild-type and mutant TK. This model allowed us to define a new route for ThDP activation in the enzyme environment. We evidenced a strong interaction between ThDP and Glu418B of the TK active site, itself stabilized by Glu162A. The crucial point highlighted here is that deprotonation of ThDP C2 is not performed by ThDP N4′ as reported in the literature, but by His481B, involving a HOH688A molecule bridge. Thus, ThDP N4′ is converted from an amino form to an iminium form, ensuring the stabilization of the C2 carbanion or carbene. Finally, ThDP activation proceeds via an intermolecular process and not by an intramolecular one as reported in the literature. More generally, this proposed ThDP activation mechanism can be applied to some other ThDP-dependent enzymes and used to define the entire TK mechanism with donor and acceptor substrates more accurately