Plasmodium knowlesi thioredoxin peroxidase 1 binds to nucleic acids and has RNA chaperone activity

Malaria parasites are under oxidative attack throughout their life cycle in human body and mosquito vector. Therefore, Plasmodium antioxidant defenses are crucial for its survival and being considered as interesting target for antimalarial drug design. Plasmodium knowlesi has emerged recently from its simian host to human in Southeast Asia and has been recognized as the fifth Plasmodium species that can cause human malaria. In this study, we cloned and characterized thioredoxin peroxidase 1 from P. knowlesi (PkTPx-1). PkTPx-1 gene was cloned, and recombinant protein was produced by heterologous overexpression in Escherichia coli. The recombinant protein was used for evaluation of enzymatic activity and polyclonal antibody production. Using the recombinant PkTPx-1 protein, its antioxidant activity was confirmed in a mixed-function oxidation assay where PkTPx-1 prevented nicking of DNA by hydroxyl radicals. PkTPx-1 was able to bind to double-strand DNA and RNA and had RNA chaperone activity in a nucleic acid melting assay indicating new function of PkTPx-1 other than antioxidant activity. Using specific polyclonal antibodies, it was indicated that PkTPx-1 is expressed in the cytoplasm of the parasite. Altogether, these results suggest that PkTPx-1 not only protects the parasite from the adverse effects of reactive oxygen species but also has RNA chaperone activity

Mitochondrial peroxidase TPx-2 is not essential in the blood and insect stages of <it>Plasmodium berghei</it>

Abstract Background Malaria parasites actively proliferate in the body of their vertebrate and insect hosts, and are subjected to the toxic effects of reactive oxygen species. The antioxidant defenses of malaria parasites are considered to play essential roles in their survival and are thus considered promising targets for intervention. We sought to identify the cellular function of thioredoxin peroxidase-2 (TPx-2), which is expressed in the mitochondria, by disrupting the TPx-2 gene (pbtpx-2) of the rodent malaria parasite Plasmodium berghei. Findings In three independent experiments, two disruptant populations (TPx-2 KO) and three wild-type parasite populations with pyrimethamine resistance (dhfr-ts/mt at the DHFR-TS locus) and intact pbtpx-2 (TPx-2 WT) were obtained and cloned. Null expression of TPx-2 in the KO population was confirmed by RT-PCR and Western blot analyses. The TPx-2 KO parasite developed normally in mouse erythrocytes and multiplied at a rate similar to that of the TPx-2 WT parasite during the experimental period. The peak period of gametocytemia was delayed by 1 day in the TPx-2 KO compared with that of the TPx-2 WT and the parent parasite, however, the highest gametocyte number was comparable. The number of midgut oocysts in the TPx-2 KO at 14 days post feeding was comparable to that of the TPx-2 WT. Conclusions The present finding suggests that mitochondrial Prx TPx-2 is not essential for asexual and the insect stage development of the malaria parasite.</p