A redox active site containing murrel cytosolic thioredoxin: Analysis of immunological properties

• Cytosolic TRx from murrel characterized bioinformatically.
• Gene expression in gill was up-regulated by fungus, bacteria and H2O2.
• H2O2 assay showed optimum activity at pH 8 and temperature 30 °C.
• Recombinant CsTRx protein enhanced the cell proliferation.
• Antioxidant capacity of recombinant CsTRx was 4.2 U/mg protein.

In this study, we have reported the immunological properties of cDNA encoding thioredoxin which is obtained from the database of Channa striatus (named as CsTRx) cDNA library. The analysis showed that the CsTRx polypeptide contains a thioredoxin domain between Val2 and Asn106. The domain possessed a thioredoxin active family at 24–42 along with a redox active site (also known as catalytic center) at 31WCGPC35. The analysis showed that the catalytic center is responsible for the control of protein function. Phylogenetic study showed that CsTRx clustered together with vertebrate TRx-1. Based on the phylogenetic analysis and other bioinformatics analysis, it is confirmed that the characterized CsTRx belongs to TRx-1 family. In addition, the sub-cellular localization prediction analysis showed that CsTRx is a cytosol thioredoxin. The highest gene expression was observed in gill (P < 0.05). Further, its transcriptional modulation was evaluated under fungal (Aphanomyces invadans), bacterial (Aeromonas hydrophila) and H2O2 challenges. The recombinant CsTRx protein was over-expressed and purified using an Escherichia coli expression vector system. We conducted a H2O2 peroxidase assay using recombinant CsTRx protein under various pH and temperature. Further, we studied the influence of recombinant CsTRx protein on C. striatus spleen leukocyte activation. The recombinant CsTRx protein enhanced the cell proliferation in a concentration dependant manner. The results of antioxidant analysis showed that the antioxidant capacity of recombinant CsTRx protein was determined to be 4.2 U/mg protein. We conducted an insulin disulfides assay to study the enzymatic oxidoreductase activity of CsTRx and we observed no activity in the control group. But the recombinant CsTRx protein addition rapidly increased the enzymatic oxidoreductase activity. Over all, the results showed that the CsTRx may contain potential antioxidant properties, which could regulate the oxidative stress created by various biological pathogens as well as chemical stress in the immune system of C. striatus, thus protecting it.