Molecular and enzymatic characterization of Schistosoma mansoni thioredoxin peroxidase

The ability of Schistosoma mansoni to escape oxidative damage from immune s ystem-generated reactive oxygen intermediates has been extensively document ed. The limiting step in the parasite's detoxification process appears to b e at the level of hydrogen peroxide neutralization. In the present study, t he possible role of a novel class of antioxidant enzymes, thioredoxin perox idase (TPx), in hydrogen peroxide neutralization by schistosomes was invest igated. An expressed sequence tag was characterized from the Schistosoma Ge nome Initiative with high similarity to TPx from other organisms. The gene encodes a polypeptide containing 2 conserved active-site cysteines and flan king amino acids, and 60-70% identity with previously characterized TPx pro teins. Recombinant schistosome TPx was enzymatically active and found to ha ve thioredoxin-dependent hydrogen peroxide reducing activity of 4500 nmol h ydrogen peroxide/min/mg protein. Native TPx activity was determined to be 4 8.1 nmol hydrogen peroxide/min/mg protein in adult worm homogenates compare d with 46.9 for glutathione peroxidase. TPx activity was precipitated from adult worm homogenates with antibodies prepared against the recombinant pro tein. Western blotting with antibodies made against recombinant protein sho wed that TPx was expressed in both male and female adult worms. This is the first demonstration of a TPx activity in schistosomes and our results sugg est that TPx plays a significant role in schistosome-host interactions.