Molecular identification of a thioredoxin peroxidase in Babesia gibsoni with potential against oxidative stress

Babesia gibsoni is the infectious agent of canine babesiosis, a vector-borne infection that poses a global threat to the canine health. As B. gibsoni is an erythrocytic intracellular parasite, the completion of its genome and transcriptome sequencing and analysis facilitates the elucidation of the mechanism of B. gibsoni residue in the erythrocyte. The main function of red blood cells (RBCs) is oxygen delivery; thus, B. gibsoni may be exposed to high levels of oxidative stress. To date, no report is available on the mechanism by which B. gibsoni survives oxidative stress inside the RBCs. In this study, the thioredoxin peroxidase, an important type of peroxidoxin, was identified from B. gibsoni, with 255 amino acids and a molecular weight of 27.7 kDa. There are two conserved "VCP" domains at the N- and C-termini, respectively, indicating that this gene was a 2-Cys peroxiredoxin belonging to the PTZ00137 superfamily. It was named BgTPx-2 and was detected to be located in the B. gibsoni-infected erythrocytes through an indirect immunofluorescence assay using the polyclonal antibody against the recombinant TPx-2. Additionally, its antioxidant activity was analyzed by mixed-function oxidation assay, and BgTPx-2 could protect the pBluescript SK ( +) plasmid from oxidative damage, suggesting an antioxidant function of BgTPx-2. Moreover, the immunogenicity of BgTPx-2 was tested by Western blotting and ELISA using the serum of beagle dogs infected with B. gibsoni, and the positive serum exhibited a detectable and significant antibody response against BgTPx-2 on day 4 and day 9 post-infection, respectively.