Characterization of 2-Cys peroxiredoxin 3 and 4 in common carp and the immune response against bacterial infection

Accumulating evidence suggests that peroxiredoxins (Prxs) eliminate excessive cellular H₂O₂ and are important factors in redox signaling pathways. In this study, we cloned the full-length cDNAs and genomic sequences of Prx3 and Prx4 from common carp. The common carp Prx3 and Prx4 open reading frames were 753 base pairs (bp) and 783bp in length, respectively, and contained seven exons and six introns. Multiple sequence alignment and phylogenetic analyses revealed that the common carp Prx1-4 proteins share high identities and similar characteristics with other known animal Prxs. Prx3 and Prx4 mRNA were constitutively expressed in all tissues, and the highest Prx3 and Prx4 transcript abundances occurred in head kidney. Although the highest Prx4 protein and mRNA expression were also observed in head kidney, many differences were detected between Prx4 mRNA and protein expression levels in other tissues. Prx3 expression increased significantly in the head kidney 12h after an Aeromonas hydrophila challenge. The A. hydrophila challenge upregulated Prx3 mRNA expression in liver and spleen, increased Prx4 mRNA expression levels in liver and spleen excluding at 36h in spleen, but decreased Prx4 mRNA expression level in the head kidney. The mature Prx4 peptide was recombinantly expressed and purified using Dextrin Beads 6FF and it exhibited thioredoxin (Trx)-dependent peroxidase activity. These data suggest that Prx3 and Prx4 are constitutive and inducible proteins that might play important roles in innate immune function. The Trx-dependent peroxidase activity analysis of recombinant Prx4 further verified the important role of Prxs in the redox system of fish.