Identification and functional analysis of a novel mitochondria-localized 2-Cys peroxiredoxin, BbTPx-2, from Babesia bovis

Neospora caninum peroxiredoxin 1 is an essential virulence effector with antioxidant function

Neospora caninum, an obligate intracellular parasitic protozoan discovered by Dubey in 1988, is the pathogen of neosporosis, which causes neurological symptoms in dogs and abortions in cows. Since there is no effective drug or vaccine against N. caninum, a deeper understanding of the molecules critical to parasite survival inside host cells is necessary. This study aimed to determine the role of N. caninum peroxiredoxin 1 (NcPrx1) in maintaining redox homeostasis and virulence of N. caninum. By determining the localization of NcPrx1 protein and establishing NcPrx1 gene knockout strain (ΔNcPrx1), the roles of NcPrx1 in N. caninum for invasion, replication, growth, oxidative stress, as well as pathogenicity were investigated. Our results showed that a predicted Alkyl Hydroperoxide1 (AHP1) domain was found in the amino acid sequence of NcPrx1, which displayed a high degree of similarity to homologs of several protozoa. Immunofluorescence assay (IFA) indicated that NcPrx1 was a cytoplasmic protein in N. caninum tachyzoites. Compared to wild type (WT) strain, ΔNcPrx1 strain showed reduced plaque area, invasion and egress rates. Reactive oxygen species (ROS) and malondialdehyde (MDA) were accumulated, and total antioxidant capacity (T-AOC) was attenuated in ΔNcPrx1 tachyzoites, which indicated that ΔNcPrx1 strain was more sensitive to oxidative stress. Furthermore, ΔNcPrx1 strain-infected C57BL/6 mice showed improved survival rate, reduced parasite burden, alleviated pathological changes in tissues, and decreased secretions of IL-6, IL-12, TNF-α, and IFN-γ in serum compared to the WT strain group. These findings suggested that NcPrx1 was a virulence factor of N. caninum which played an important role in maintaining the redox homeostasis of the parasite.

Characterization of the Neospora caninum peroxiredoxin: a novel peroxidase and antioxidant enzyme

Neospora caninum, an apicomplexan parasite, is the etiological agent of neosporosis, a disease that leads to neurological symptoms in dogs and abortion in cattle. Vaccine or drug treatments for neosporosis remain to be determined. Therefore, it is of undeniable relevance to investigate new molecules involved in the parasite's successful survival within the host cell. The aim of this study was to characterize the N. caninum peroxiredoxin (NcPrx), an enzyme involved in the redox system of the parasite. The NcPrx amino acid sequence showed high identity and similarity compared to homologues representatives of Apicomplexa phylum. The recombinant NcPrx (rNcPrx) was cloned and expressed in Escherichia coli (BL21) with the predicted molecular weight (22 kDa), and the identity of monomer and dimer forms of rNcPrx was confirmed by mass spectrometry. Native and recombinant NcPrx were detected by ELISA and western blot, using the polyclonal anti-rNcPrx serum. Multiphoton analysis showed that NcPrx is localized in tachyzoite cytosol. H₂O₂ treatment increased the rNcPrx dimerization in vitro, and associated with the in silico data, we suggest that NcPrx belongs to typical 2-Cys Prx group (AhpC/Prx1 family). rNcPrx also increased the H₂O₂ clearance and protected plasmidial DNA under oxidative conditions. Finally, H₂O₂ increased the NcPrx dimerization in intracellular and extracellular tachyzoites suggesting that it is enrolled in H₂O₂ clearance and sensing in N. caninum.

Identification of 2-Cys Peroxiredoxin (BmTPx-2) as Antioxidant Active Molecule from Babesia microti

Peroxiredoxins (Prxs) are a family of antioxidant enzymes that reduce peroxides in the presence of thioredoxin, thioredoxin reductase, and nicotinamide adenine dinucleotide phosphate (NADPH) to resist oxidative stress. In this study, we identified and isolated a 2-Cys Prx designated as ‘BmTPx-2’ from Babesia microti, with a full-length cDNA of 826 bp and an open reading frame of 756 bp, which encodes a 251-amino acid protein. BLAST analysis demonstrated that BmTPx-2 shows the typical features of members of the 2-Cys Prx family, which includes harboring two conserved VCP motifs with Cys¹⁰¹ and Cys²²¹ conserved cysteine residues. Recombinant BmTPx-2 was expressed in Escherichia coli and analyzed by western blot. The antioxidant activity of BmTPx-2 was demonstrated using a mixed-function oxidation system and oxidation of NADPH. Furthermore, BmTPx-2 mRNA expression level in parasites at the erythrocytes and tick stages were analyzed by real-time fluorescence quantitative PCR. Peak BmTPx-2 mRNA transcription was detected 8 days after infection at the erythrocyte stage, but not at the tick stage. Taken together, this study characterized BmTPx-2 from B. microti as an antioxidant molecule that was specifically transcribed at the erythrocyte stage.