Diversity of polyphenols interacting with omega glutathione transferases of Trametes versicolor
Fungi play a key role in the organic matter recycling and some of them; especially basidiomycetes are the most efficient microorganisms to degrade lignocellulosic materials. Wood decaying fungi are thus in contact with many compounds resulting from wood decay and also compounds already present in wood. Among these latters, wood extractives (flavonoids, terpenoids, stilbenes…) are potentially toxic. Indeed wood extractives have several ways to cause fungal damages. They could disrupt the fungal cell wall and plasma membrane, or alter ion homeostasis in the fungal cell. They can also inhibit enzymes involved in detoxification processes (laccases …), in wood degradation (cellulases, cellobiohydrolases …) by chelating metals, by scavenging reactive oxygen species and by fixing directly inside the protein.
To cope with this potential harmful environment, fungi have developed detoxification system involving multigenic families such as cytochrome P450 monooxygenases (involved in the first oxidation step of detoxification) and glutathione transferases (acting in the second conjugaison step). Concerning the fungal glutathione transferase family, it has been showed that several members are able to interact with extracts of various wood species. However, their physiological roles remain mysterious and their substrates and ligands are still unknown.We have particularly worked on glutathione transferases from the white-rot Trametes versicolor focusing on isoforms belonging to the omega class (TvGSTO) which is the most important GST class in this fungus. Among the sixteen TvGSTOs identified, we performed the biochemical and structural characterization of two isoforms: TvGSTO3S and TvGSTO6S. After that, we focused our attention on the research of potential ligands by using high-throughput screening and co-crystallization methods especially by affinity crystallization. This method allowed us to isolate a natural ligand (initially containing in a wood extract) retrieved in the active site of TvGSTO3S.
Here, we report that flavonoids and benzophenones are recognized by glutathione transferases.