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Caractérisation biochimique et fonctionnelle de glutathion-S-transferases (GSTs) chez Phanerochaete chrysosporium

Abstract : Phanerochaete chrysosporium is a ligninolytic fungus widely studied because of its capacities to degrade wood and xenobiotics through an extracellular enzymatic system. Its genome has been sequenced and has provided researchers with a complete inventory of the predicted proteins produced by this organism. This has allowed the description of many protein superfamilies. Among them, Glutathione S-transferases (GSTs) constitute a complex and widespread superfamily classified as enzymes of secondary metabolism. However, despite the numerous associations of GSTs with stress responses, cell development and metabolism in various organisms, the functions of these enzymes remain usually evasive mainly due to their high diversity and also to the lack of knowledge about their catalytic specificities. In P. chrysosporium 27 GST isoforms have been highlighted and clustered into seven classes. Among them three are extended in saprophytic fungi: the Omega, the Ure2p and the etherase classes. Two members of the Omega class have been characterized at the biochemical level showing difference in substrate specificities. Indeed, PcGTO1 is member of a new class of Sglutathionyl- p-hydroquinone reductase, while PcGTO3 is rather active with phenylacetophenone. The three-dimensional structure of PcGTO1 confirms the hypothesis not only of a new biological class, but also of a new structural class that we propose to name GST xi. The second extended class we have studied is the Ure2p one. It is composed of nine isoforms in P. chrysosporium and clusters into two subclasses. Three Ure2p class members have been studied in more details at transcriptional, biochemical and physiological levels. PcUre2p4 and PcUre2p6 of the first subclass are specifically expressed in cultures treated with polycyclic aromatic hydrocarbons and the recombinant proteins are active as typical glutathione transferases. By contrast, PcUre2p1, which belongs to the second subclass is constitutively expressed whatever the condition tested and is active with small molecules as substrate, such as proteins from the Omega class. Physiological studies have revealed that these proteins do not have the same function than the Saccharomyce cerevisiae isoform, concerning both the response to oxidative stress and its involvement in the nitrogen catabolite repression. These results suggest that fungi, especially those with saprophytic capabilities, have developed specificities of GST function as an adaptation to environmental constraints
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Submitted on : Thursday, March 29, 2018 - 10:25:49 AM
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  • HAL Id : tel-01746168, version 1
  • PRODINRA : 277231



Andrew Anak Ngadin. Caractérisation biochimique et fonctionnelle de glutathion-S-transferases (GSTs) chez Phanerochaete chrysosporium. Sylviculture, foresterie. Université Henri Poincaré - Nancy 1, 2011. Français. ⟨NNT : 2011NAN10020⟩. ⟨tel-01746168⟩



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