Preferential regeneration of thioredoxin from parasitic flatworm Fasciola gigantica using glutathione system

Molecular characterization and functional analysis of peroxiredoxin 1 (Prx1) from roughskin sculpin (Trachidermus fasciatus)

Peroxiredoxin1(Prx1), also known as natural killer enhancing factor A (NKEF-A), is a crucial antioxidant involving in various cellular activities and immune response against bacterial and viral infection in fish. In the present study, a full-length Prx1 cDNA sequence (TfPrx1) was firstly cloned from roughskin sculpin (Trachidermus fasciatus), which was composed of 1044 bp nucleotides encoding a peptide of 199 amino acids with a molecular weight of 22.35 kDa and a theoretical pI of 6.42, respectively. The predicted peptide was a typical 2-cys Prx containing two conserved characteristic motifs 43FYPLDFTFVCPTEI56 and 170GEVCPA175 with the two conserved peroxidatic and resolving cysteine residuals forming disulfide bond. Quantitative real-time PCR analysis showed that TfPrx1 was ubiquitously expressed in all tested tissues with the highest expression in the intestine. It could be significantly induced following LPS injection and heavy metal exposure. Recombinant TfPrx1 (rTfPrx1) displayed insulin disulfide reduction and ROS-scavenging activity in a concentration-dependent manner, and further exhibited DNA and cytoprotective effects under oxidative stress. These results suggested that TfPrx1 protein may play an important role in fish immune protection from oxidative damage.

Functional expression, localization, and biochemical characterization of thioredoxin glutathione reductase from air-breathing magur catfish, Clarias magur

The glutathione (GSH) and thioredoxin (Trx) systems regulate cellular redox homeostasis and maintain antioxidant defense in most eukaryotes. We earlier reported the absence of gene coding for the glutathione reductase (GR) enzyme of the GSH system in the facultative air-breathing catfish, Clarias magur. Here, we identified three thioredoxin reductase (TrxR) genes, one of which was later confirmed as a thioredoxin glutathione reductase (TGR). We then characterized the novel recombinant TGR enzyme of C. magur (CmTGR). The tissue-specific expression of the txnrd genes and the tissue-specific activity of the TrxR enzyme were analyzed. The recombinant CmTGR is a dimer of ~133 kDa. The protein showed TrxR activity with 5,5'-diothiobis (2-nitrobenzoic acid) reduction assay with a K_m of 304.40 μM and GR activity with a K_m of 58.91 μM. Phylogenetic analysis showed that the CmTGR was related to the TrxRs of fishes and distantly related to the TGRs of platyhelminth parasites. The structural analysis revealed the conserved glutaredoxin active site and FAD- and NADPH-binding sites. To our knowledge, this is the first report of the presence of a TGR in any fish. This unusual presence of TGR in C. magur is crucial as it helps maintain redox homeostasis under environmental stressors-induced oxidative stress.

Monoclonal antibody against Fasciola gigantica glutathione peroxidase and their immunodiagnosis potential for fasciolosis

Glutathione peroxidases (GPx), major antioxidant enzymes, secreted by Fasciola spp., are important for the parasite evasion and protection against the host's immune responses. In the present study, a monoclonal antibody (MoAb) against recombinant F. gigantica glutathione peroxidase (rFgGPx) was produced by hybridoma technique using spleen cells from BALB/c mice immunized with rFgGPx. This MoAb (named 7B8) is IgG1 with κ light chains, and it reacted specifically with rFgGPx at a molecular weight 19 kDa as shown by immunoblotting, and reacted with the native FgGPx in the extracts of whole body (WB), metacercariae, newly excysted juveniles (NEJs), 4 week-old juveniles and adult F. gigantica as shown by indirect ELISA. It did not cross react with antigens in WB fractions from other adult trematodes, including Fischoederius cobboldi, Paramphistomum cervi, Setaria labiato-papillosa, Eurytrema pancreaticum, Gastrothylax crumenifer and Gigantocotyle explanatum. By immunolocalization, MoAb against rFgGPx reacted with the native protein in the tegument, vitelline cells, and eggs of adult F. gigantica. In addition, the sera from mice experimentally infected with F. gigantica were tested positive by this indirect sandwich ELISA. This result indicated that FgGPx is an abundantly expressed parasite protein that is secreted into the tegumental antigens (TA), therefore, FgGPx and its MoAb may be used for immunodiagnosis of both early and late fasciolosis gigantica in animals and humans.

Structural insights into natural compounds as inhibitors of Fasciola gigantica thioredoxin glutathione reductase

Fascioliasis is caused by the helminth parasites of genus Fasciola. Thioredoxin glutathione reductase (TGR) is an important enzyme in parasitic helminths and plays an indispensable role in its redox biology. In the present study, we conducted a structure-based virtual screening of natural compounds against the Fasciola gigantica TGR (FgTGR). The compounds were docked against FgTGR in four sequential docking modes. The screened ligands were further assessed for Lipinski and ADMET prediction so as to evaluate drug proficiency and likeness property. After refinement, three potential inhibitors were identified that were subjected to 50 ns molecular dynamics simulation and free energy binding analyses to evaluate the dynamics of protein-ligand interaction and the stability of the complexes. Key residues involved in the interaction of the selected ligands were also determined. The results suggested that three top hits had a negative binding energy greater than GSSG (-91.479 KJ · mol^-1 ), having -152.657, -141.219, and -92.931 kJ · mol^-1 for compounds with IDs ZINC85878789, ZINC85879991, and ZINC36369921, respectively. Further analysis showed that the compound ZINC85878789 and ZINC85879991 displayed substantial pharmacological and structural properties to be a drug candidate. Thus, the present study might prove useful for the future design of new derivatives with higher potency and specificity.

Glutathione and thioredoxin systems of the malaria parasite Plasmodium falciparum: Partners in crime?

In P. falciparum, antioxidant proteins of the glutathione and thioredoxin systems are compartmentalized. Some subcellular compartments have only a partial complement of these proteins. This lack of key anti-oxidant proteins in certain sub-cellular compartments might be compensated by functional complementation between these systems. By assessing the cross-talk between these systems, we show for the first time, that the glutathione system can reduce thioredoxins that are poor substrates for thioredoxin reductase (Thioredoxin-like protein 1 and Thioredoxin 2) and thioredoxins that lack access to thioredoxin reductase (Thioredoxin 2). Our data suggests that crosstalk between the glutathione and thioredoxin systems does exist; this could compensate for the absence of certain antioxidant proteins from key subcellular compartments.