Etude fonctionnelle des glutathion peroxydases de peuplier, une famille de peroxydases thiorédoxine-dépendantes

Abstract : In plant cells, reactive oxygen species (ROS) concentration is controlled by different systems. Thioredoxins (Trx) and glutaredoxins (Grx) play a crucial role in providing reducing power to peroxiredoxins (Prx), also called thiol-dependent peroxidases, which scavenge oxygen- or nitrogen-derived reactive compounds. The work presented in this manuscript describes mainly the glutathione peroxidases (Gpx) family in a model species, the poplar tree. Although Gpx are thiol-dependent peroxidases, their primary sequence differs from the Prx sequences characterized to date. The gene expression of this family was assessed in different plant organs and it was compared to those of other Prx. The abundance of different Gpx is also modified under stress conditions, notably in the presence of heavy-metals like cadmium. Localization of two isoforms in the chloroplast (Gpx1, Gpx3) and in mitochondria (Gpx3) was demonstrated using GFP fusion proteins. Enzymatic studies performed on wild-type and cysteine-mutated Gpx3 recombinant proteins showed: (i) a catalytic mechanism different from the mammalian Gpx, involving two of the three conserved cysteines, which form (ii) an intramolecular disulfide bridge (redox potential: -290 mV) that will then specifically be reduced by certain Trx in vitro. Studies also showed that these enzymes are active as non-covalent homodimers in solution.
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Nicolas Navrot. Etude fonctionnelle des glutathion peroxydases de peuplier, une famille de peroxydases thiorédoxine-dépendantes. Sciences agricoles. Université Henri Poincaré - Nancy 1, 2006. Français. ⟨NNT : 2006NAN10132⟩. ⟨tel-01754307⟩

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