A Trajectory of Discovery: Metabolic Regulation by the Conditionally Disordered Chloroplast Protein, CP12

International audienceThe chloroplast protein CP12, which is widespread in photosynthetic organisms, belongs to the intrinsically disordered proteins family. This small protein (80 amino acid residues long) presents a bias in its composition; it is enriched in charged amino acids, has a small number of hydrophobic residues, and has a high proportion of disorder-promoting residues. More precisely, CP12 is a conditionally disordered proteins (CDP) dependent upon the redox state of its four cysteine residues. During the day, reducing conditions prevail in the chloroplast, and CP12 is fully disordered. Under oxidizing conditions (night), its cysteine residues form two disulfide bridges that confer some stability to some structural elements. Like many CDPs, CP12 plays key roles, and its redox-dependent conditional disorder is important for the main function of CP12: the dark/light regulation of the Calvin-Benson-Bassham (CBB) cycle responsible for CO2 assimilation. Oxidized CP12 binds to glyceraldehyde-3-phosphate dehydrogenase and phosphoribulokinase and thereby inhibits their activity. However, recent studies reveal that CP12 may have other functions beyond the CBB cycle regulation. In this review, we report the discovery of this protein, its features as a disordered protein, and the many functions this small protein can have

Location of the photosynthetic carbon metabolism in microcompartments and separated phases in microalgal cells

International audienceCarbon acquisition, assimilation and storage in eukaryotic microalgae and cyanobacteria occur in multiple compartments that have been characterised by the location of the enzymes involved in these functions. These compartments can be delimited by bilayer membranes, such as the chloroplast, the lumen, the peroxisome, the mitochondria or monolayer membranes, such as lipid droplets or plastoglobules. They can also originate from liquid–liquid phase separation such as the pyrenoid. Multiple exchanges exist between the intracellular microcompartments, and these are reviewed for the CO 2 concentration mechanism, the Calvin–Benson–Bassham cycle, the lipid metabolism and the cellular energetic balance. Progress in microscopy and spectroscopic methods opens new perspectives to characterise the molecular consequences of the location of the proteins involved, including intrinsically disordered proteins

Reduction in Phosphoribulokinase Amount and Re-Routing Metabolism in Chlamydomonas reinhardtii CP12 Mutants

International audienceThe chloroplast protein CP12 is involved in the dark/light regulation of the Calvin–Benson–Bassham cycle, in particular, in the dark inhibition of two enzymes: glyceraldehyde−3-phosphate dehydrogenase (GAPDH) and phosphoribulokinase (PRK), but other functions related to stress have been proposed. We knocked out the unique CP12 gene to prevent its expression in Chlamydomonas reinhardtii (ΔCP12). The growth rates of both wild-type and ΔCP12 cells were nearly identical, as was the GAPDH protein abundance and activity in both cell lines. On the contrary, the abundance of PRK and its specific activity were significantly reduced in ΔCP12, as revealed by relative quantitative proteomics. Isolated PRK lost irreversibly its activity over-time in vitro, which was prevented in the presence of recombinant CP12 in a redox-independent manner. We have identified amino acid residues in the CP12 protein that are required for this new function preserving PRK activity. Numerous proteins involved in redox homeostasis and stress responses were more abundant and the expressions of various metabolic pathways were also increased or decreased in the absence of CP12. These results highlight CP12 as a moonlighting protein with additional functions beyond its well-known regulatory role in carbon metabolism

Le temps des saints

Les contributeurs de ce dossier — historiens, spécialistes de la littérature et de l’iconographie — ont souhaité montrer comment se «fabriquent», au sens noble du terme, les saints dans l’Église catholique espagnole. Par l’écrit ou la parole, par les textes et les images, la sainteté est au Siècle d’or le centre d’une production culturelle intense ainsi qu’un enjeu idéologique: il s’agit, d’une part, de réaffirmer un culte très contesté par la Réforme et de souligner la prééminence de l’Espagne de la Contre-Réforme dans un combat partagé par les autres nations méridionales mais aussi, d’autre part, d’ancrer dans les mentalités un culte reposant sur l’intercession et les miracles et qui promet, à défaut du bonheur ici-bas, la communion de tous les saints dans l’au-delà. Los participantes de este dossier—historiadores, especialistas de laliteratura y de la iconografía— muestran cómo se «fabrican», en el sentido noble de la palabra, los santos en la Iglesia católica española. Por la escritura o por la palabra, por los textos y por las imágenes, la santidad es, en el Siglo de Oro, el centro de una producción cultural intensa y un envite ideológico: se trata, por una parte, de reafirmar un culto muy contestado por la Reforma, de subrayar la preeminencia de la España de la Contra-Reforma dentro de un combate com partido por las otras naciones meridionales y, por otra parte, de anclar en las mentalidades un culto basado en la intercesión y los milagros y que promete, a falta de la felicidad en este mundo, la comunión de todos los santos en el más allá

Banquets et manières de table au Moyen Âge

Ce volume rassemble les communications présentées au vingt-et-unième colloque du CUER MA qui s'est tenu à Aix-en-Provence en février 1996 sur le thème : BANQUETS ET MANIÈRES DE TABLE AU MOYEN AGE Comme les années précédentes, nous avons utilisé les dactylogrammes fournis par les conférenciers. Ainsi les communications ont-elles la présentation exacte déterminée par leurs auteurs. Le CUER MA remercie l'Université de Provence qui a fourni son aide pour l'organisation du colloque et l'impression de ce volume d'actes. Il exprime plus particulièrement sa gratitude à mademoiselle Margaret BERTRAND qui a effectué la mise en forme définitive du volume et à monsieur Christian HORY pour la réalisation de la maquette et du montage de cet ouvrage