Une présentation du Languedoc-Roussillon

Robert Ferras Le recours aux textes fondateurs, ceux que l'on cite périodiquement sans trop aller y voir de plus près, est riche d'enseignements dans l'approche d'une région, et pour deux simples raisons. Ils permettent de voir ce qui se répète, à l'infini, et de déceler ce qui innove, dans le vrai comme dans le faux. La démarche n'implique aucun passéisme, elle traduit seulement l'envie de replacer les choses en situation, dans leur temps, dans l'air de leur temps. Pourquoi, comment, une arc..

Intervention diverses

Pierre Desplanques. J'ai relevé que les questions qui se posent dans les trois pays évoqués et le nôtre sont bien les mêmes. On pourrait déterminer un certain nombre de thèmes. J'en ai personnellement un sur la mise en place des programmes. Ils indiquent ce que nous avons à enseigner, et toute réflexion part de là. Ils l'ont indiqué souvent en termes de contenus, découpage spatial. La conception des programmes est-elle fondée sur un découpage spatial, des thèmes géographiques, des notions, de..

Redesigning the stereospecificity of tyrosyl-tRNA synthetase

International audienceD-Amino acids are largely excluded from protein synthesis, yet they are of great interest in biotechnology. Unnatural amino acids have been introduced into proteins using engineered aminoacyl-tRNA synthetases (aaRSs), and this strategy might be applicable to D-amino acids. Several aaRSs can aminoacylate their tRNA with a D-amino acid; of these, tyrosyl-tRNA synthetase (TyrRS) has the weakest stereospecificity. We use computational protein design to suggest active site mutations in Escherichia coli TyrRS that could increase its D-Tyr binding further, relative to L-Tyr. The mutations selected all modify one or more sidechain charges in the Tyr binding pocket. We test their effect by probing the aminoacyl-adenylation reaction through pyrophosphate exchange experiments. We also perform extensive alchemical free energy simulations to obtain L-Tyr/D-Tyr binding free energy differences. Agreement with experiment is good, validating the structural models and detailed thermodynamic predictions the simulations provide. The TyrRS stereospecificity proves hard to engineer through charge-altering mutations in the first and second coordination shells of the Tyr ammonium group. Of six mutants tested, two are active towards D-Tyr; one of these has an inverted stereospecificity, with a large preference for D-Tyr. However, its activity is low. Evidently, the TyrRS stereospecificity is robust towards charge rearrangements near the ligand. Future design may have to consider more distant and/or electrically neutral target mutations, and possibly design for binding of the transition state, whose structure however can only be modeled

First joint observation by the underground gravitational-wave detector, KAGRA, with GEO 600

We report the results of the first joint observation of the KAGRA detector with GEO600. KAGRA is a cryogenic and underground gravitational-wave detector consisting of a laser interferometer with three-kilometer arms, and located in Kamioka, Gifu, Japan. GEO600 is a British–German laser interferometer with 600m arms, and located near Hannover, Germany. GEO600 and KAGRA performed a joint observing run from April 7 to 20, 2020. We present the results of the joint analysis of the GEO–KAGRA data for transient gravitational-wave signals, including the coalescence of neutron-star binaries and generic unmodeled transients. We also perform dedicated searches for binary coalescence signals and generic transients associated with gamma-ray burst events observed during the joint run. No gravitational-wave events were identified. We evaluate the minimum detectable amplitude for various types of transient signals and the spacetime volume for which the network is sensitive to binary neutron-star coalescences. We also place lower limits on the distances to the gamma-ray bursts analysed based on the non-detection of an associated gravitational-wave signal for several signal models, including binary coalescences. These analyses demonstrate the feasibility and utility of KAGRA as a member of the global gravitational-wave detector network