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Kessler, Félix
Nom
Kessler, Félix
Affiliation principale
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Professeur.e ordinaire
Email
felix.kessler@unine.ch
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Voici les éléments 1 - 10 sur 14
- PublicationAccès libreThe novel chloroplast outer membrane kinase KOC1 is a required component of the plastid protein import machinery(2017)
Toc159 joue un rôle essentiel dans la biogenèse du chloroplaste. Les bases de données de phosphoprotéomique montrent que le domaine A de Toc159 est fortement phosphorylé. La protéine cytosolique caséine kinase II phosphoryle le domaine A in vitro. Toutefois d’autres kinases ayant la même fonction ont aussi été prédites. Tandis que la phosphorylation contrôle l’assemblage et l’activité des complexes d’importation de protéines dans les chloroplastes et les mitochondries, aucune kinase organite-spécifique n’a été identifiée jusqu’à présent. Par co-purification avec Toc159, nous avons découvert une protéine kinase dans la membrane externe du chloroplaste (KOC1 « Kinase at the Outer Chloroplast membrane 1 »). KOC1 est une protéine intégrale de membrane orientée vers le cytosol et associée de manière stable avec le complexe TOC. KOC1 phosphoryle le domaine A chez les membres de la famille Toc159 in vitro. Dans les chloroplastes des mutants koc1, l’efficience de l’importation des protéines a été réduite. Par ailleurs, les plantules koc1 ont un taux de survie réduit quand elles sont déplacées de l’obscurité à la lumière, quand une importation rapide des pré-protéines est nécessaire pour une biogenèse de chloroplastes complète. Nos résultats indiquent que KOC1 est un composant de la machinerie d’importation TOC en phosphorylant les récepteurs, en soutenant l’importation de pré-protéines et en contribuant à une biogenèse de chloroplastes efficiente., The chloroplast constitutes the site of photosynthesis and is an essential organelle in plant cells. An endosymbiotic event was at the origin of the chloroplast, an ancestral eukaryotic cell engulfing a photosynthetic cyanobacterium. During evolution, the majority of ancestral chloroplast genes were lost or transferred to the nucleus. The protein products of the successfully transferred genes are now synthesized by cytosolic ribosomes and imported into the chloroplast. The chloroplast destined proteins (preproteins) acquired an additional sequence that encodes a cleavable N-terminal targeting peptide (transit peptides). The transit peptide is recognized by the chloroplast import machinery, which initiates import. The import machinery consists of translocon complexes at the outer (TOC) and inner membrane of the chloroplast (TIC). The import of hundreds of different chloroplast proteins depends on TOC and TIC complexes. The TOC complex core contains three proteins, the GTPase receptors: Toc159, Toc34 and the channel Toc75, together they recognize and transfer the pre-proteins across the outer membrane of the chloroplast. Both Toc34 and Toc159 are exposed at the surface of the chloroplast, consistent with a receptor function, and have homologous GTP-binding domains (G-domain). In addition to the G-domain, Toc159 has a N-terminal A- (acidic) domain that extends into the cytosol and controls receptor specificity and a C-terminal membrane anchoring M-domain. Toc75 belongs to the OMP85 family that serves to integrate proteins into the outer membrane of gram negative bacteria, in chloroplasts it has evolved to provide a protein translocation channel across the outer membrane.
Toc159 plays an essential role in chloroplast biogenesis. Phosphoproteomics databases show that Toc159 is highly phosphorylated at the A domain. Cytosolic casein kinase II phosphorylates the A-domain in vitro, however other A-domain kinases have been predicted.
While phosphorylation controls assembly and activity of protein import complexes in both mitochondria and chloroplasts no organelle-specific kinases have been identified so far. By co-purification with Toc159, we discovered "Kinase at the Outer Chloroplast membrane 1" (KOC1). KOC1 is an integral membrane protein facing the cytosol and stably associating with TOC. KOC1 phosphorylated the A-domain of Toc159 family members in vitro. In mutant koc1 chloroplasts preprotein import efficiency was diminished. Moreover, koc1 seedlings had reduced survival rates when moved from the dark to the light when protein import is required to rapidly complete chloroplast biogenesis. Our data indicate that KOC1 is a functional component of the TOC machinery phosphorylating import receptors, supporting preprotein import and contributing to efficient chloroplast biogenesis. - PublicationAccès librePlastoglobules: a new destination for recombinant proteins produced in transplastomic plants and characterization of plastidial At-SOUL heme binding protein(2012)
In addition to lipids and PGLs, the PG harbours other proteins: The PG proteome in Arabidopsis consist of about two dozen proteins including uncharacterized plastoglobule protein AtSOUL4, which has a predicted heme-binding motif. The Arabidopsis genome contains six proteins with a SOUL motif; two of them AtSOUL4 and AtSOUL5 are predicted to be plastid localized and AtSOUL5 was found in the thylakoid proteome. A SOUL homolog, AtSOUL1, is highly expressed and the soul1 mutant is hypersensitive to red light. In addition, C. reinhardtii eyespot phosphoproteins contained SOUL3. However, due to the presence of SOUL-heme binding proteins in light perception systems and their implication in plant photomorphogenesis, the SOUL heme binding proteins may be involved in light signalling. The heterologously expressed recombinant AtSOUL4 protein binds to heme in vitro as well as in vivo. Moreover, AtPGL35 and AtSOUL4 fluorescent fusion proteins colocalized in chloroplasts. Furthermore, immunoblot analysis of chloroplast membrane fractions shows that AtSOUL4 localized at the plastoglobule. AtSOUL4 has a highly conserved CKII phosphorylation site in C-terminal. Moreover, In vitro phosphorylation studies revealed that AtSOUL4 is phosphorylated most likely by a stromal CKII like kinase. The double knock out of AtSOUL4 and AtSOUL5 revealed a conditional shade avoidance behavior, indicating that AtSOUL4 heme-binding protein might also be involved in the light signalling. - PublicationAccès libreIntersection of the tocopherol and plastoquinol metabolic pathways at the plastoglobule(2010)
; ; Dörmann, PeterPlastoglobules, lipid–protein bodies in the stroma of plant chloroplasts, are enriched in non-polar lipids, in particular prenyl quinols. In the present study we show that, in addition to the thylakoids, plastoglobules also contain a considerable proportion of the plastidial PQ-9 (plastoquinol-9), the redox component of photosystem II, and of the cyclized product of PQ-9, PC-8 (plastochromanol-8), a tocochromanol with a structure similar to γ-tocopherol and γ-tocotrienol, but with a C-40 prenyl side chain. PC-8 formation was abolished in the Arabidopsis thaliana tocopherol cyclase mutant vte1, but accumulated in VTE1-overexpressing plants, in agreement with a role of tocopherol cyclase (VTE1) in PC-8 synthesis. VTE1 overexpression resulted in the proliferation of the number of plastoglobules which occurred in the form of clusters in the transgenic lines. Simultaneous overexpression of VTE1 and of the methyltransferase VTE4 resulted in the accumulation of a compound tentatively identified as 5-methyl-PC-8, the methylated form of PC-8. The results of the present study suggest that the existence of a plastoglobular pool of PQ-9, along with the partial conversion of PQ-9 into PC-8, might represent a mechanism for the regulation of the antioxidant content in thylakoids and of the PQ-9 pool that is available for photosynthesis. - PublicationAccès libreProtein transport in organelles: The Toc complex way of preprotein import(2009)
- PublicationAccès libreA plant split-ubiquitin system and TAP-tagging to study in vivo protein interactions in the chloroplast protein import machinery(2008)
- PublicationMétadonnées seulementThe function and diversity of plastid protein import pathways: A multilane GTPase highway into plastids(2006)
; Schnell, DannyThe photosynthetic chloroplast is the hallmark organelle of green plants. During the endosymbiotic evolution of chloroplasts, the vast majority of genes from the original cyanobacterial endosymbiont were transferred to the host cell nucleus. Chloroplast biogenesis therefore requires the import of nucleus-encoded proteins from their site of synthesis in the cytosol. The majority of proteins are imported by the activity of Toc and Tic complexes located within the chloroplast envelope. In addition to chloroplasts, plants have evolved additional, non-photosynthetic plastid types that are essential components of all cells. Recent studies indicate that the biogenesis of various plastid types relies on distinct but homologous Toc-Tic import pathways that have specialized in the import of specific classes of substrates. These different import pathways appear to be necessary to balance the essential physiological role of plastids in cellular metabolism with the demands of cellular differentiation and plant development. - PublicationAccès libreThe Function and Diversity of Plastid Protein Import Pathways : A Multilane GTPase Highway into Plastids(2006)
; Schnell, Danny J.The photosynthetic chloroplast is the hallmark organelle of green plants. During the endosymbiotic evolution of chloroplasts, the vast majority of genes from the original cyanobacterial endosymbiont were transferred to the host cell nucleus. Chloroplast biogenesis therefore requires the import of nucleus-encoded proteins from their site of synthesis in the cytosol. The majority of proteins are imported by the activity of Toc and Tic complexes located within the chloroplast envelope. In addition to chloroplasts, plants have evolved additional, non-photosynthetic plastid types that are essential components of all cells. Recent studies indicate that the biogenesis of various plastid types relies on distinct but homologous Toc–Tic import pathways that have specialized in the import of specific classes of substrates. These different import pathways appear to be necessary to balance the essential physiological role of plastids in cellular metabolism with the demands of cellular differentiation and plant development. - PublicationMétadonnées seulementAtToc90, a new GTP-binding component of the Arabidopsis chloroplast protein import machinery(2004)
- PublicationAccès libreAtToc90, a New GTP-Binding Component of the Arabidopsis Chloroplast Protein Import Machinery(2004)
- PublicationMétadonnées seulementSorting activities in plant cells(2003)
; Eucaryotic cells (plants, animals, fungi, etc.) are subdivided in membrane-bound compartments (organelles), such as the nucleus, mitochondria, chloroplasts, vacuoles, etc. Most organellar proteins are encoded in the nucleus and synthesized in the cytoplasm. Proper sorting of proteins is required to establish and maintain organellar identity. Molecular machineries at the organelle surfaces specifically recognize targeting sequences of their cognate proteins and mediate their translocation across membranes. Proteins destined for the vacuoles are first translocated across the endoplasmic reticulum membrane, packaged into vesicles, transported to the Golgi, where they are sorted into specific vesicles and subsequently carried to the different types of vacuoles. Though plant cells share many features with animal and yeast cells, chloroplasts and distinct lytic and storage vacuoles are unique to plants. Here, we discuss import of proteins into the chloroplast as well as selective sorting of proteins to either the lytic or the storage vacuole.