Cloning and characterization of three differentially expressed peroxidoxin genes from Leishmania chagasi. Evidence for an enzymatic detoxification of hydroxyl radicals.

Antioxidants have been implicated in protecting cells from oxygen radicals produced as a result of aerobic metabolism and in response to foreign pathogens by phagocytic cells. The mechanisms allowing pathogens to withstand the toxic prooxidant environment within the phagolysosome are poorly understood. We have cloned and characterized three antioxidant genes belonging to the 2-Cys family of peroxidoxins from Leishmania chagasi that may prove to provide these parasites with an enhanced defense mechanism against toxic oxidants. The 5'-untranslated regions and coding regions of each gene are highly conserved, whereas the 3'-untranslated regions have diverged significantly. L. chagasi peroxidoxin 1 (LcPxn1) is predominantly expressed in the amastigote stage, whereas LcPxn2 and LcPxn3 are expressed mainly in the promastigote stage, with LcPxn3 being far less abundant than LcPxn2. LcPxn2 and LcPxn3 possess a nine-amino acid extension at the carboxyl terminus, which LcPxn1 lacks. LcPxn1 appears to exist as high molecular weight multimers in vivo, and recombinant LcPxn1 was shown to detoxify hydrogen peroxide and alkyl hydroperoxides. We also present strong evidence that recombinant LcPxn1 can enzymatically detoxify hydroxyl radicals, an activity never before clearly demonstrated for a protein.