Molecular cloning and characterization of two genes encoding 2-Cys peroxiredoxins from Fasciola gigantica.

In Fasciola species, peroxiredoxin (Prx) serves as the major antioxidant enzyme to remove hydrogen peroxide that is generated from various metabolic reactions, because the parasites lack catalase, and only express glutathione peroxidases at minimal levels. We have cloned and characterized two genes, FgPrx-1 and FgPrx-2, belonging to the 2-Cys Prx family, by immunoscreening of an expressed adult stage Fasciola gigantica cDNA library using a rabbit anti-serum against its tegumental antigens. Predicted FgPrx-1 and FgPrx-2 consisted of 218 amino acids each with predicted molecular weights at 24.63 kDa and 24.57 kDa, respectively. The two predicted F. gigantica Prx proteins exhibited 98% identity to each other, and 52% identity to Prx from oxen which is the natural host. A phylogenetic analysis revealed that FgPrx-1 and FgPrx-2 appear to be closely related to those of Fasciola hepatica. The nucleotide sequences of FgPrx-2 are 654 bp, which is similar to that cloned from newly excysted juveniles of F. hepatica. The FgPrx genes were found to be constitutively expressed in all developmental stages, and with a similar pattern. In the adult parasite, FgPrx transcripts were located in the gut epithelial cells, tegument cells, and cells of reproductive organs, including prostate gland, vitelline glands, testis and ovary. In 4-week-old juveniles, a similar distribution pattern was observed. Metacercaria and newly excysted juveniles exhibited strongest signals for mRNA transcripts in the gut epithelium, and moderately in the tegumental cells. Because of their key role in protecting the parasite and specificities, these proteins may have immunodiagnostic as well as vaccine potentials.