A Physiological Approach to Explore How Thioredoxin-Glutathione Reductase (TGR) and Peroxiredoxin (Prx) Eliminate HO in Cysticerci of

Peroxiredoxins (Prxs) and glutathione peroxidases (GPxs) are the main enzymes of the thiol-dependent antioxidant systems responsible for reducing the HO produced via aerobic metabolism or parasitic organisms by the host organism. These antioxidant systems maintain a proper redox state in cells. The cysticerci of tolerate millimolar concentrations of this oxidant. To understand the role played by Prxs in this cestode, two genes for Prxs, identified in the genome of (Prx1 and Prx3), were cloned. The sequence of the proteins suggests that both isoforms belong to the class of typical Prxs 2-Cys. In addition, Prx3 harbors a mitochondrial localization signal peptide and two motifs (-GGLG- and -YP-) associated with overoxidation. Our kinetic characterization assigns them as thioredoxin peroxidases (TPxs). While Prx1 and Prx3 exhibit the same catalytic efficiency, thioredoxin-glutathione reductase from (TGR) was five and eight times higher. Additionally, the latter demonstrated a lower affinity (>30-fold) for HO in comparison with Prx1 and Prx3. The TGR contains a Sec residue in its C-terminal, which confers additional peroxidase activity. The aforementioned aspect implies that Prx1 and Prx3 are catalytically active at low HO concentrations, and the TGR acts at high HO concentrations. These results may explain why the cysticerci can tolerate high HO concentrations.