Biochemical and structural characterization of the Arabidopsis bifunctional enzyme dethiobiotin synthetase-diaminopelargonic acid aminotransferase: evidence for substrate channeling in biotin synthesis.

International audienceDiaminopelargonic acid aminotransferase (DAPA-AT) and dethiobiotin synthetase (DTBS) catalyze the antepenultimate and the penultimate steps, respectively, of biotin synthesis. Whereas DAPA-AT and DTBS are encoded by distinct genes in bacteria, in biotin-synthesizing eukaryotes (plants and most fungi), both activities are carried out by a single enzyme encoded by a bifunctional gene originating from the fusion of prokaryotic monofunctional ancestor genes. In few angiosperms, including Arabidopsis thaliana, this chimeric gene (named BIO3-BIO1) also produces a bicistronic transcript potentially encoding separate monofunctional proteins that can be produced following an alternative splicing mechanism. The functional significance of the occurrence of a bifunctional enzyme in biotin synthesis pathway in eukaryotes and the relative implication of each of the potential enzyme forms (bifunctional versus monofunctional) in the plant biotin pathway are unknown. In this study, we demonstrate that the BIO3-BIO1 fusion protein is the sole protein form produced by the BIO3-BIO1 locus in Arabidopsis. The enzyme catalyzes both DAPA-AT and DTBS reactions in vitro and is targeted to mitochondria in vivo. Our biochemical and kinetic characterizations of the pure recombinant enzyme show that in the course of the reaction, the DAPA intermediate is directly transferred from the DAPA-AT active site to the DTBS active site. Analysis of several structures of the enzyme crystallized in complex with and without its ligands reveals key structural elements involved for acquisition of bifunctionality and brings, together with mutagenesis experiments, additional evidences for substrate channeling

Assessment of vector/host contact: comparison of animal-baited traps and UV-light/suction trap for collecting Culicoides biting midges (Diptera: Ceratopogonidae), vectors of Orbiviruses

BACKGROUND The emergence and massive spread of bluetongue in Western Europe during 2006-2008 had disastrous consequences for sheep and cattle production and confirmed the ability of Palaearctic Culicoides (Diptera: Ceratopogonidae) to transmit the virus. Some aspects of Culicoides ecology, especially host-seeking and feeding behaviors, remain insufficiently described due to the difficulty of collecting them directly on a bait animal, the most reliable method to evaluate biting rates.Our aim was to compare typical animal-baited traps (drop trap and direct aspiration) to both a new sticky cover trap and a UV-light/suction trap (the most commonly used method to collect Culicoides). METHODS/RESULTS Collections were made from 1.45 hours before sunset to 1.45 hours after sunset in June/July 2009 at an experimental sheep farm (INRA, Nouzilly, Western France), with 3 replicates of a 4 sites×4 traps randomized Latin square using one sheep per site. Collected Culicoides individuals were sorted morphologically to species, sex and physiological stages for females. Sibling species were identified using a molecular assay. A total of 534 Culicoides belonging to 17 species was collected. Abundance was maximal in the drop trap (232 females and 4 males from 10 species) whereas the diversity was the highest in the UV-light/suction trap (136 females and 5 males from 15 species). Significant between-trap differences abundance and parity rates were observed. CONCLUSIONS Only the direct aspiration collected exclusively host-seeking females, despite a concern that human manipulation may influence estimation of the biting rate. The sticky cover trap assessed accurately the biting rate of abundant species even if it might act as an interception trap. The drop trap collected the highest abundance of Culicoides and may have caught individuals not attracted by sheep but by its structure. Finally, abundances obtained using the UV-light/suction trap did not estimate accurately Culicoides biting rate.This study was funded partly by CIRAD and partly by the Ministry of Agriculture, Food, Fishing and Rural Affairs

Modélisation du comportement effectif du combustible MOX par une analyse micromécanique en champs de transformation non uniformes

La répartition hétérogène du plutonium dans le combustible nucléaire MOX implique que la modélisation de son comportement, durant l'irradiation, passe par la construction de lois macroscopiques faisant intervenir les effets microstructuraux. Pour homogénéiser ce problème local, nous avons choisi une méthode d'analyse par champs de transformation non uniformes, abrégé anglais NTFA (cf-Michel, Suquet IJSS 2003). Nous présentons donc ici, les travaux menés sur ce modèle pour l'adapter au comportement du MOX, et les résultats effectifs et locaux de celui-ci par rapport à des calculs de références

Reconnaissance au travail (la)

La « reconnaissance » est devenue un nouvel enjeu de société. Le désir d’être reconnu envahit le monde du travail et imprègne les relations et les discours des individus. Reconnaissance de compétences, reconnaissance de la personne à travers son positionnement dans l’organisation, reconnaissance vis à vis de la hiérarchie et du groupe. Que revendiquet-on dans le monde du travail, quand on demande « une plus grande reconnaissance » ? quelles formes celle-ci peut-elle prendre, en particulier dans les démarches d’évaluation ou de validation de l’expérience ? Comment les entreprises abordent-elles ces attentes collectives et individuelles de reconnaissance

Linking cocoa polyphenol composition to chocolate quality with Average-Mass-Spectra fingerprints

Linking cocoa polyphenol composition to chocolate quality with Average-Mass-Spectra fingerprints. CoCoTea 2019 (5. International Congress on Cocoa Coffee and Tea

Associations between peer victimization and suicidal ideation and suicide attempt during adolescence : results from a prospective population-based birth cohort

Objective:To test whether adolescents who are victim-ized by peers are at heightened risk for suicidal ideationand suicide attempt, using both cross-sectional andprospective investigations.Method:Participants are from the Quebec LongitudinalStudy of Child Development, a general population sampleof children born in Quebec in 1997 through 1998 andfollowed up until 15 years of age. Information aboutvictimization and serious suicidal ideation and suicideattempt in the past year was obtained at ages 13 and15 years from self-reports (N¼1,168).Results:Victims reported concurrently higher rates ofsuicidal ideation at age 13 years (11.6–14.7%) and suicideattempt at age 15 years (5.4–6.8%) compared to those whohad not been victimized (2.7–4.1% for suicidal ideationand 1.6–1.9% for suicide attempt). Being victimized bypeers at 13 years predicted suicidal ideation (odds ratio[OR]¼2.27; 95% CI¼1.25–4.12) and suicideattempt (OR¼3.05, 95% CI¼1.36–6.82) 2 years later,even after adjusting for baseline suicidality andmental health problems and a series of confounders(socioeconomic status, intelligence, family’s functioningand structure, hostile-reactive parenting, maternal lifetimesuicidal ideation/suicide attempt). Those who werevictimized at both 13 and 15 years had the highest risk ofsuicidal ideation (OR¼5.41, 95% CI¼2.53–11.53) andsuicide attempt (OR¼5.85, 95% CI¼2.12–16.18) at15 years.Conclusion:Victimization is associated with an increasedrisk of suicidal ideation and suicide attempt over andabove concurrent suicidality and prior mental healthproblems. The longer the history of victimization, thegreater the risk

Polarization state of the optical near-field

The polarization state of the optical electromagnetic field lying several nanometers above complex dielectric structures reveals the intricate light-matter interaction that occurs in this near-field zone. This information can only be extracted from an analysis of the polarization state of the detected light in the near-field. These polarization states can be calculated by different numerical methods well-suited to near--field optics. In this paper, we apply two different techniques (Localized Green Function Method and Differential Theory of Gratings) to separate each polarisation component associated with both electric and magnetic optical near-fields produced by nanometer sized objects. The analysis is carried out in two stages: in the first stage, we use a simple dipolar model to achieve insight into the physical origin of the near-field polarization state. In the second stage, we calculate accurate numerical field maps, simulating experimental near-field light detection, to supplement the data produced by analytical models. We conclude this study by demonstrating the role played by the near-field polarization in the formation of the local density of states.Comment: 9 pages, 11 figures, accepted for publication in Phys. Rev.