Caractérisation structurale et enzymatique, cibles potentielles et rôles physiologiques de glutathion transférases à cystéine catalytique de Phanerochaete chrysosporium

Abstract : Phanerochaete chrysosporium is a model fungus well studied for its lignolytic properties towards wood compounds and various toxic aromatic derivatives such as polycyclic aromatic hydrocarbons. These degradation processes lead first to the formation of highly reactive and toxic compounds, which are then catabolized or excreted outside the cell. Genomic data allowed the identification of genes coding for superfamilies of enzymes putatively involved in these tolerance mechanisms. Among them, glutathione transferases are present in all kingdoms and constitute a multigenic superfamily of enzymes involved in cell protection and detoxification. However, although numerous studies have been performed on vertebrate enzymes, the role of these enzymes in the detoxication of toxic aromatic compounds is still unknown in basidiomycetes. The comparative analysis of GST sequences from various kingdoms of life reveals that fungal GSTs have evolved differently from their orthologs, in particular through the expansion of sub-classes poorly represented in vertebrates. Among them, GSTs with a catalytic cysteine represent 30% of this superfamily of enzymes in P. chrysosporium. Three Cys containing fungal isoforms have been characterized at the biochemical and structural levels, including an orthologue from lignolytic bacteria. All these enzymes are involved in deglutathionylation processes using a wide range of aromatic halogenated electrophilic compounds, including potentially toxic derivatives arising from the degradation of halogenated aromatic polymers. This GSTs family can be organized in various functional groups based on their substrate specificities, but still the catalytic process remains the same with the direct attack of the glutathionylated compound by the catalytic cysteine which is then reduced and regenerated. The comparative analysis of three isoforms revealed a new structural and functional class called glutathionyl hydroquinone reductase absent in vertebrates. These proteins exhibit a new mode of dimerization as well as the ability to deglutathionylate quinones. These results suggest that fungi have developed resistance mechanisms in response to environmental stresses, notably through the evolution of multigenic families such as catalytic cysteine bearing GSTs which are likely involved in the metabolism and tolerance towards a wide range of exogenous or endogenous compounds
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Edgar Meux. Caractérisation structurale et enzymatique, cibles potentielles et rôles physiologiques de glutathion transférases à cystéine catalytique de Phanerochaete chrysosporium. Biologie végétale. Université de Lorraine, 2012. Français. ⟨NNT : 2012LORR0256⟩. ⟨tel-01749639⟩

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