CONTRIBUTION A L'ETUDE BIOCHIMIQUE DU COMPLEXE CYTOCHROME B 6F DE CHLAMYDOMONAS REINHARDTII (MANIPULATION IN VITRO ET STABILISATION, ORGANISATION SPATIALE DES HEMES ET SPECTROSCOPIE DE LA CHLOROPHYLLE A)

LE CYTOCHROME B 6F DE CHLAMYDOMONAS REINHARDTII A ETE ETUDIE DANS UNE DOUBLE OPTIQUE. D'UNE PART, C'EST UN COMPLEXE TRES FRAGILE, CE QUI EN FAIT UN BON MODELE POUR LE DEVELOPPEMENT DE NOUVEAUX TENSIOACTIFS DESTINES A FACILITER LA MANIPULATION IN VITRO DES PROTEINES MEMBRANAIRES INTEGRALES. LE CYTOCHROME B 6F PRESENTE PAR AILLEURS UN GRAND INTERET PROPRE, CAR IL RESTE LE COMPLEXE PHOTOSYNTHETIQUE DE LOIN LE MOINS BIEN CONNU. NOS MESURES DE DICHROISME LINEAIRE ET CIRCULAIRE SUGGERENT QUE L'ORGANISATION SPATIALE DES HEMES B DES CYTOCHROMES B 6F ET BC 1 (SON HOMOLOGUE MITOCHONDRIAL) SONT SIMILAIRES. CHAQUE DIMERE DE CYTOCHROME B 6F CONTIENT DEUX MOLECULES DE CHLOROPHYLLE A, DONT LA FONCTION ET LA LOCALISATION SONT ENCORE INCONNUES. NOUS MONTRONS L'EXISTENCE DANS NOS PREPARATIONS DE PLUSIEURS POPULATIONS DE CHLOROPHYLLES DE DUREES DE VIE DE FLUORESCENCE DIFFERENTES, CORRESPONDANT PROBABLEMENT A DES MOLECULES LIEES SUR LE SITE NATIF, LIEES SUR UN SITE PARTIELLEMENT DEMASQUE, OU EN SOLUTION DANS LE DETERGENT. L'EXISTENCE D'UN SIGNAL DE DICHROISME CIRCULAIRE EXCITONIQUE SUGGERE QUE LES DEUX CHLOROPHYLLES PRESENTES AU SEIN DE CHAQUE DIMERE SONT SUFFISAMMENT PROCHES L'UNE DE L'AUTRE POUR INTERAGIR ELECTRONIQUEMENT. BIEN QU'INDISPENSABLES A LA SOLUBILISATION ET A LA MANIPULATION DES PROTEINES MEMBRANAIRES EN SOLUTION AQUEUSE, LES DETERGENTS INDUISENT FREQUEMMENT UNE DESTABILISATION POUVANT ALLER JUSQU'A LA DENATURATION. DEUX MECANISMES ENTRENT PROBABLEMENT EN JEU DANS CE PHENOMENE : LA DILUTION DANS LA PHASE MICELLAIRE DE COFACTEURS ESSENTIELS A LA STABILITE DE LA PROTEINE, ET UNE INTRUSION DIRECTE DU DETERGENT DANS LA REGION TRANSMEMBRANAIRE DE CELLE-CI. PARTANT DE L'OBSERVATION QUE LES PERFLUOROALCANES SONT DES MOLECULES RELATIVEMENT RIGIDES ET PEU MISCIBLES AVEC LES HYDROCARBURES, NOUS AVONS MIS AU POINT UN TENSIOACTIF HEMIFLUORE, NON DETERGENT MAIS NEANMOINS CAPABLE DE MAINTENIR EN SOLUTION LE CYTOCHROME B 6F SOUS UNE FORME INTACTE, ACTIVE, MONODISPERSE ET STABLE.PARIS-BIUSJ-Thèses (751052125) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

On the spatial organization of hemes and chlorophyll in cytochrome b(6)f. A linear and circular dichroism study.

International audienceThe organization of chromophores in the cytochrome b(6) f from Chlamydomonas reinhardtii has been studied spectroscopically. Linear dichroism (LD) measurements, performed on the complex co-reconstituted into vesicles with photosynthetic reaction centers as an internal standard, allow the determination of the orientations of the chromophore with respect to the membrane plane. The orientations of the b(H)- and b(L)-hemes are comparable to those determined crystallographically on the cytochrome bc(1). The excitonic CD signal, resulting from the interaction between b-hemes, is similar to that reported for the cytochrome bc(1). LD and CD data are consistent with the differences between the b(6) f and bc(1) leaving the orientation of the b-hemes unaffected. By contrast, the LD data yield a different orientation for the heme f as compared either to the heme c(1) in the crystallographic structures or to the heme f as studied by electron paramagnetic resonance. This difference could either result from incorrect assumptions regarding the orientations of the electronic transitions of the f-heme or may point to the possibility of a redox-dependent movement of cytochrome f. The chlorophyll a was observed in a well defined orientation, further corroborating a specific binding site for it in the b(6) f complex

Sitedirected photochemical coupling of cytochrome b6f-associated chlorophyll. Biochemistry 42

ABSTRACT: Cytochrome b 6 f complexes contain a molecule of chlorophyll a (Chla), which, in Chlamydomonas reinhardtii, can be exchanged for extraneous chlorophyll during protracted incubation of the purified complex in detergent solution. The specificity of the site and its location in the complex have been studied by photochemical coupling and circular dichroism spectroscopy

On the spatial organization of hemes and chlorophyll in cytochrome b(6)f. A linear and circular dichroism study.

International audienceThe organization of chromophores in the cytochrome b(6) f from Chlamydomonas reinhardtii has been studied spectroscopically. Linear dichroism (LD) measurements, performed on the complex co-reconstituted into vesicles with photosynthetic reaction centers as an internal standard, allow the determination of the orientations of the chromophore with respect to the membrane plane. The orientations of the b(H)- and b(L)-hemes are comparable to those determined crystallographically on the cytochrome bc(1). The excitonic CD signal, resulting from the interaction between b-hemes, is similar to that reported for the cytochrome bc(1). LD and CD data are consistent with the differences between the b(6) f and bc(1) leaving the orientation of the b-hemes unaffected. By contrast, the LD data yield a different orientation for the heme f as compared either to the heme c(1) in the crystallographic structures or to the heme f as studied by electron paramagnetic resonance. This difference could either result from incorrect assumptions regarding the orientations of the electronic transitions of the f-heme or may point to the possibility of a redox-dependent movement of cytochrome f. The chlorophyll a was observed in a well defined orientation, further corroborating a specific binding site for it in the b(6) f complex

Perceptions mentales et changement institutionnel : apports tirés d'une étude empirique sur la participation des organisations agricoles au processus de mise en place des politiques au Costa Rica

International audienceDo ideas matter? North’s analysis is that actors’ mental perceptions guide their strategic choices and thus shape the institutional environment. This latter point seems particularly relevant regarding the participation of economic organizations in the political making process. Nevertheless the empirical description of this role has not been clearly established: Few works try to make the impact of actors’ mental perceptions on institutional change operational (Dinar and Saleth, 2004). Our aim is to contribute to this empirical description, by leading a comparative study of two farm sectors in Costa Rica, based on a dynamic approach of mental perceptions in relation with the institutional change occurring during the liberalisation process. To do so, we carry out a statistical analysis of mental perceptions through a textual analysis of actors’ perceptions of the political making process. Thus, we provide an empirical confirmation that mental models are influenced by specific institutional environments and lead to different political strategies. Then, we show that when an exogenous change occurs in the institutional environment, previous mental models can persist and lead to inefficient behaviours. More generally, our study empirically emphasizes the interest of taking into account agents’ mental perceptions for a better understanding of institutional and economic dynamics

Chitinase-resistant hydrophilic symbiotic factors secreted by Frankia activate both Ca2+ spiking and NIN gene expression in the actinorhizal plant Casuarina glauca

Although it is now well-established that decorated lipo-chitooligosaccharide Nod factors are the key rhizobial signals which initiate infection/nodulation in host legume species, the identity of the equivalent microbial signaling molecules in the Frankia/actinorhizal association remains elusive. With the objective of identifying Frankia symbiotic factors we present a novel approach based on both molecular and cellular pre-infection reporters expressed in the model actinorhizal species Casuarina glauca. By introducing the nuclear-localized cameleon Nup-YC2.1 into Casuarina glauca we show that cell-free culture supernatants of the compatible Frankia CcI3 strain are able to elicit sustained high frequency Ca2+ spiking in host root hairs. Furthermore, an excellent correlation exists between the triggering of nuclear Ca2+ spiking and the transcriptional activation of the ProCgNIN:GFP reporter as a function of the Frankia strain tested. These two pre-infection symbiotic responses have been used in combination to show that the signal molecules present in the Frankia CcI3 supernatant are hydrophilic, of low molecular weight and resistant to chitinase degradation. In conclusion, the biologically active symbiotic signals secreted by Frankia appear to be chemically distinct from the currently known chitin-based rhizobial/arbuscular mycorrhizal signaling molecules. Convenient bioassays in Casuarina glauca are now available for their full characterization

Chitotetraose activates the fungal-dependent endosymbiotic signaling pathway in actinorhizal plant species

Mutualistic plant-microbe associations are widespread in natural ecosystems and have made major contributions throughout the evolutionary history of terrestrial plants. Amongst the most remarkable of these are the so-called root endosymbioses, resulting from the intra-cellular colonization of host tissues by either arbuscular mycorrhizal (AM) fungi or nitrogen-fixing bacteria that both provide key nutrients to the host in exchange for energy-rich photo-synthates. Actinorhizal host plants, members of the Eurosid 1 clade, are able to associate with both AM fungi and nitrogen-fixing actinomycetes known as Frankia. Currently, little is known about the molecular signaling that allows these plants to recognize their fungal and bacterial partners. In this article, we describe the use of an in vivo Ca 2+ reporter to identify symbiotic signaling responses to AM fungi in roots of both Casuarina glauca and Discaria tri-nervis, actinorhizal species with contrasting modes of Frankia colonization. This approach has revealed that, for both actinorhizal hosts, the short-chain chitin oligomer chitotetraose is able to mimic AM fungal exudates in activating the conserved symbiosis signaling pathway (CSSP) in epidermal root cells targeted by AM fungi. These results mirror findings in other AM host plants including legumes and the monocot rice. In addition, we show that chitote-traose is a more efficient elicitor of CSSP activation compared to AM fungal lipo-chitooligo-saccharides. These findings reinforce the likely role of short-chain chitin oligomers during the initial stages of the AM association, and are discussed in relation to both our current knowledge about molecular signaling during Frankia recognition as well as the different microsymbiont root colonization mechanisms employed by actinorhizal hosts. PLOS ONE | https://doi.org/10.1371/journal.pone