Système tutoriel intelligent pour la résolution de problèmes en thermodynamique

L'enseignement stratégique a traduit plusieurs principes de l'approche cognitive dans une démarche d'enseignement en faisant de la résolution de problèmes une partie importante du curriculum scolaire. Cet article présente un système tutoriel intelligent qui accompagne l'étudiant dans sa démarche de résolution et lui offre des interventions spécifiques et graduées, lorsqu'il éprouve des difficultés. Le tutoriel s'appuie sur un ensemble de catégories d'erreurs déterminées expérimentalement et utilise le formalisme mathématique associé au domaine d'application à travers les formules, les hypothèses et les valeurs numériques. Appliqué à la thermodynamique, un prototype a été expérimenté et a fourni des résultats intéressants

Regulation of cardiac nitric oxide signaling by nuclear β-adrenergic and endothelin receptors.

International audienceAt the cell surface, βARs and endothelin receptors can regulate nitric oxide (NO) production. β-adrenergic receptors (βARs) and type B endothelin receptors (ETB) are present in cardiac nuclear membranes and regulate transcription. The present study investigated the role of the NO pathway in the regulation of gene transcription by these nuclear G protein-coupled receptors. Nitric oxide production and transcription initiation were measured in nuclei isolated from the adult rat heart. The cell-permeable fluorescent dye 4,5-diaminofluorescein diacetate (DAF2 DA) was used to provide a direct assessment of nitric oxide release. Both isoproterenol and endothelin increased NO production in isolated nuclei. Furthermore, a β3AR-selective agonist, BRL 37344, increased NO synthesis whereas the β1AR-selective agonist xamoterol did not. Isoproterenol increased, whereas ET-1 reduced, de novo transcription. The NO synthase inhibitor l-NAME prevented isoproterenol from increasing either NO production or de novo transcription. l-NAME also blocked ET-1-induced NO-production but did not alter the suppression of transcription initiation by ET-1. Inhibition of the cGMP-dependent protein kinase (PKG) using KT5823 also blocked the ability of isoproterenol to increase transcription initiation. Furthermore, immunoblotting revealed eNOS, but not nNOS, in isolated nuclei. Finally, caged, cell-permeable isoproterenol and endothelin-1 analogs were used to selectively activate intracellular β-adrenergic and endothelin receptors in intact adult cardiomyocytes. Intracellular release of caged ET-1 or isoproterenol analogs increased NO production in intact adult cardiomyocytes. Hence, activation of the NO synthase/guanylyl cyclase/PKG pathway is necessary for nuclear β3ARs to increase de novo transcription. Furthermore, we have demonstrated the potential utility of caged receptor ligands in selectively modulating signaling via endogenous intracellular G protein-coupled receptors

Crystal structures of fusion proteins with large-affinity tags

The fusion of a protein of interest to a large-affinity tag, such as the maltose-binding protein (MBP), thioredoxin (TRX), or glutathione-S-transferase (GST), can be advantageous in terms of increased expression, enhanced solubility, protection from proteolysis, improved folding, and protein purification via affinity chromatography. Unfortunately, crystal growth is hindered by the conformational heterogeneity induced by the fusion tag, requiring that the tag is removed by a potentially problematic cleavage step. The first three crystal structures of fusion proteins with large-affinity tags have been reported recently. All three structures used a novel strategy to rigidly fuse the protein of interest to MBP via a short three- to five-amino acid spacer. This strategy has the potential to aid structure determination of proteins that present particular experimental challenges and are not conducive to more conventional crystallization strategies (e.g., membrane proteins). Structural genomics initiatives may also benefit from this approach as a way to crystallize problematic proteins of significant interest

Hydrogenases and H2 metabolism in sulfate-reducing bacteria of the Desulfovibrio genus

International audienceHydrogen metabolism plays a central role in sulfate-reducing bacteria of the Desulfovibrio genus and is based on hydrogenases that catalyze the reversible conversion of protons into dihydrogen. These metabolically versatile microorganisms possess a complex hydrogenase system composed of several enzymes of both [FeFe]- and [NiFe]-type that can vary considerably from one Desulfovibrio species to another. This review covers the molecular and physiological aspects of hydrogenases and H2 metabolism in Desulfovibrio but focuses particularly on our model bacterium Desulfovibrio fructosovorans. The search of hydrogenase genes in more than 30 sequenced genomes provides an overview of the distribution of these enzymes in Desulfovibrio. Our discussion will consider the significance of the involvement of electron-bifurcation in H2 metabolism