Differential expression of disulfide reductase enzymes in a free-living platyhelminth (Dugesia dorotocephala)

Evaluation of enzymatic activity of Babesia microti thioredoxin reductase (Bmi TrxR)-mutants and screening of its potential inhibitors

Babesia microti is a zoonotic pathogen that mainly parasitizes mammalian erythrocytes. Oxidative stress can induce gene mutation, protein denaturation and lipid peroxidation, such as reactive oxygen species (ROS) induced by hypoxic environment and the host immune system. An antioxidase, B. microti thioredoxin reductase (Bmi TrxR), has been identified in B. microti. We used a combination of homology modeling and domain prediction to explore the functional sites of Bmi TrxR and found that TrxR has three domains. Constructed a mutant pool which His-tag were at the N-terminus (TrxR-Nhis, C105-Nhis, C110-Nhis, C105110-Nhis, C547-Nhis, C552-Nhis, C547552-Nhis) and the His tag were at the N- and C-terminus (TrxR-NChis, C547-NChis, C552-NChis, C547552-NChis). The proteins were expressed as His-tagged fusion proteins in Escherichia coli. The His-tag of TrxR C-terminus were affected the reaction with Trx. The inhibitory efficiency of DNCB was decreased for mutant C547, compared with recombinant TrxR, indicating that the action site of DNCB might be cysteine at position 547. These results indicate that the N-terminal active site of Bmi TrxR plays an important role in accepting electrons and promotes electron transfer. The C-terminus His tag of Bmi TrxR affected the electron transfer and the reducing activity of Bmi TrxR. Reduce reactive oxygen produced in oxidative stress was reduced by Bmi TrxR, which is beneficial to Babesia survival. Therefore, reduction site of TrxR may become a potential target for Babesia microti treatment.

Planarians as models to investigate the bioactivity of gold(I) complexes in vivo

Gold(I)-containing complexes are used in drug discovery research for rheumatoid arthritis, cancer, and parasitic infections. In this study, we tested the bioactivity of gold(I) complexes in vivo using planarians. The planarian Schmidtea mediterranea possesses orthologues of tumor suppressor genes, such as p53, that, when silenced, cause deregulation of cell proliferation and apoptosis. In this context, we tested two triethylphosphine-gold(I) complexes (AdO and AdT) to determine if they can attenuate phenotypes that result from p53 inhibition. First, we identified the drug concentration that did not affect survival or regeneration and evaluated the drug's effect on cell division and apoptosis. We found that AdT treatment decreased the number of mitotic cells and that all drug treatments increased the number of apoptotic cells. We then performed p53(RNAi) and drug treatments concomitantly and observed the phenotype progression. Drug treatment increased survival three-fold and decreased apoptosis, which resulted in an attenuated phenotype. Our results indicate that planarians can be treated with gold(I) complexes, and that this treatment can diminish the p53(RNAi) phenotype and extend survival. In this work we show that planarians can be used as a model to study the in vivo effect of gold(I) complexes and to further investigate their mechanisms of action.