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Kessler, Félix

Nom
Kessler, Félix
Affiliation principale
Fonction
Professeur.e ordinaire
Email
felix.kessler@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/320
_
0000-0001-6409-5043

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  • Publication
    Accès libre
    A Toc159 Import Receptor Mutant, Defective in Hydrolysis of GTP, Supports Preprotein Import into Chloroplasts
    (2009)
    Agne, Birgit
    ;
    Infanger, Sibylle
    ;
    Wang, Fei
    ;
    Hofstetter, Valère
    ;
    Rahim, Gwendoline
    ;
    Martin, Meryll
    ;
    Lee, Dong Wook
    ;
    Hwang, Inhwan
    ;
    Schnell, Danny
    ;
    Kessler, Félix 
    The heterotrimeric Toc core complex of the chloroplast protein import apparatus contains two GTPases, Toc159 and Toc34, together with the protein-conducting channel Toc75. Toc159 and Toc34 are exposed at the chloroplast surface and function in preprotein recognition. Together, they have been shown to facilitate the import of photosynthetic proteins into chloroplasts in Arabidopsis. Consequently, the ppi2 mutant lacking at Toc159 has a non-photosynthetic albino phenotype. Previous mutations in the conserved G1 and G3 GTPase motifs abolished the function of Toc159 in vivo by disrupting targeting of the receptor to chloroplasts. Here, we demonstrate that a mutant in a conserved G1 lysine (atToc159 K868R) defective in GTP binding and hydrolysis can target and assemble into Toc complexes. We show that atToc159 K868R can support protein import into isolated chloroplasts, albeit at lower preprotein binding and import efficiencies compared with the wild-type receptor. Considering the absence of measurable GTPase activity in the K868R mutant, we conclude that GTP hydrolysis at atToc159 is not strictly required for preprotein translocation. The data also indicate that preprotein import requires at least one additional GTPase other than Toc159.
  • Publication
    Accès libre
    The major protein import receptor of plastids is essential for chloroplast biogenesis
    (2000)
    Bauer, Jörg
    ;
    Chen, Kunhua
    ;
    Hiltbunner, Andreas
    ;
    Wehrli, Ernst
    ;
    Eugster, Monika
    ;
    Schnell, Danny
    ;
    Kessler, Félix 
    Light triggers the developmental programme in plants that leads to the production of photosynthetically active chloroplasts from non-photosynthetic proplastids1. During this chloroplast biogenesis, the photosynthetic apparatus is rapidly assembled, mostly from nuclear-encoded imported proteins2, 3, 4, which are synthesized in the cytosol as precursors with cleavable amino-terminal targeting sequences called transit sequences. Protein translocon complexes at the outer (Toc complex)5, 6, 7 and inner (Tic complex)6, 8, 9 envelope membranes recognize these transit sequences, leading to the precursors being imported. The Toc complex in the pea consists of three major components, Toc75, Toc34 and Toc159 (formerly termed Toc86)6, 7, 10, 11. Toc159, which is an integral membrane GTPase12, functions as a transit-sequence receptor5, 6, 7, 13. Here we show that Arabidopsis thaliana Toc159 (atToc159) is essential for the biogenesis of chloroplasts. In an Arabidopsis mutant (ppi2) that lacks atToc159, photosynthetic proteins that are normally abundant are transcriptionally repressed, and are found in much smaller amounts in the plastids, although ppi2 does not affect either the expression or the import of less abundant non-photosynthetic plastid proteins. These findings indicate that atToc159 is required for the quantitative import of photosynthetic proteins. Two proteins that are related to atToc159 (atToc120 and atToc132) probably help to maintain basal protein import in ppi2, and so constitute components of alternative, atToc159-independent import pathways.