EXPRESSION AND CHARACTERIZATION OF GLUTATHIONE-PEROXIDASE ACTIVITY INTHE HUMAN BLOOD FLUKE SCHISTOSOMA-MANSONI

Antioxidants may play an important role in immune evasion by schistoso me parasites. Previous studies have focused on the roles of superoxide dismutase and glutathione S-transferase. In the present study, glutat hione peroxidase (GPX) activity was measured in different fractions of worm extracts from several developmental stages of Schistosoma manson i. The enzyme activity was shown to be developmentally regulated, with higher specific activities being found in the tegument-enriched Nonid et P-40 extract of adult worms (the stage least susceptible to immune killing) than in the larval stages (which are most susceptible to immu ne elimination). In all extracts tested, the activity against cumene h ydroperoxide, even when glutathione S-transferase activity was removed , was higher than that for hydrogen peroxide. The expression of GPX cD NA in pGEX-2T by bacteria produced a 50-kDa fusion protein and a 32-kD a truncated protein. The latter was due to termination at the internal UGA codon that codes for selenocysteine. GPX activity was detected in the recombinantly produced GPX but not with Sj26-glutathione S-transf erase from the vector. Mutating the TGA codon to TGT produced a full-l ength product, GPXm (19 kDa), that was used to produce 19 monoclonal a ntibodies. Anti-GPXm monoclonal antibodies recognized a 19-kDa molecul e in adult-worm extract which, upon removal by immunoprecipitation, re sulted in the loss of over 90% of the GPX activity,suggesting that a s ingle form of GPX exists in the schistosome.