Structural view of fungal glutathionyl-hydroquinone reductases

International audienceGlutathione transferases (GSTs) constitute a widespread super-family of enzymes with highly specific to overlapping functions. These enzymes have been extensively studied in mammals because of their roles in xenobiotic conjugation. Despite this, GST functions are largely unexplored, especially in microorganisms. Our work focused on fungal glutathionyl-hydroquinone reductases (GHRs). These singular GSTs catalyze the reduction of hydroquinones-SG (Xun et al., 2010), and are present in all kingdoms but animals. The first GHR structure to be described in the saprotrophic fungus Phanerochaete chrysosporium (PcGHR1) has unveiled original features. An original dimerization mode led us to establish a new structural class named Xi (GSTX) (Meux et al., 2011). Here we report the crystal structures of two GHRs, TvGHR1 from the basidiomycete Trametes versicolor and ScECM4 from the yeast Saccharomyces cerevisiae, at 2.28 and 1.45 Å resolution, respectively. TvGHR1 andScECM4 share the classical GST fold which consists in a thioredoxin N-terminal domain and an all α C-terminal domain. Besides the features that have been uncovered in PcGHR1, additional secondary structures were found in the yeast ScECM4 structure. Like its characterized homologs, ScEcM4 is specific to the reduction of quinones conjugated with glutathione (Lallement et al., 2014). TvGHR1 is more polyvalent because it also reduces substrates rather accepted by Omega-class GSTs like phenylacetophenone-SG. Compared with known GHR structures, TvGHR1 exhibits a larger substrate binding site with an original motif that could explain the substrate versatility. Phylogenetic analyses revealed that fungal GHRs could be separated in two families : the ‘classic’ GHRs and the ‘atypical’ GHRs that exhibit motif variations as observed in TvGHR1. Furthermore, the conservation of GHRs in fungi suggests that they could fulfill a crucial role. Their diversification in wood-degrading basidiomycetes agrees with the hypothesis that GHRs would play a role in the metabolism of phenolic compounds (Belchik & Xun, 2011)