Glutaredoxins in fungi

Glutaredoxins (GRXs) can be subdivided into two subfamilies: dithiol GRXs with the CPY/FC active site motif, and monothiol GRXs with the CGFS motif. Both subfamilies share a thioredoxin-fold structure. Some monothiol GRXs exist with a single-Grx domain while others have a thioredoxin-like domain (Trx) and one or more Grx domains in tandem. Most fungi have both dithiol and monothiol GRXs with different subcellular locations. GRX-like molecules also exist in fungi that differ by one residue from one of the canonical active site motifs. Additionally, Omega-class glutathione transferases (GSTs) are active as GRXs. Among fungi, the GRXs more extensively studied are those from Saccharomyces cerevisiae. This organism contains two dithiol GRXs (ScGrx1 and ScGrx2) with partially overlapping functions in defence against oxidative stress. In this function, they cooperate with GSTs Gtt1 and Gtt2. While ScGrx1 is cytosolic, two pools exist for ScGrx2, a major one at the cytosol and a minor one at mitochondria. On the other hand, S. cerevisiae cells have two monothiol GRXs with the Trx-Grx structure (ScGrx3 and ScGrx4) that locate at the nucleus and probably regulate the activity of transcription factors such as Aft1, and one monothiol GRX with the Grx structure (ScGrx5) that localizes at the mitochondrial matrix, where it participates in the synthesis of iron-sulphur clusters. The function of yeast Grx5 seems to be conserved along the evolutionary scale.