Involvement of the Macrobrachium nipponense rhodanese homologue 2, MnRDH2 in innate immunity and antioxidant defense.

In Macrobrachium nipponense, the rhodanese homologue 2 (MnRDH2) gene codes for a single rhodanese domain protein. Considering the lack of information on the biological role of the ubiquitous rhodaneses in invertebrate, we examined the functions of MnRDH2 using both in silico and in vitro approaches. Quantitative PCR analysis of different tissues indicated that expression of MnRDH2 was enriched in hepatopancreas, in which bacterial challenge by Aeromonas hydrophila induced MnRDH2 expression. Knocking down MnRDH2 by RNA interference caused significant accumulations of reactive oxygen species and malondialdehyde (MDA). Using Escherichia coli (DE3), we expressed MnRDH2 and the mutant MnRDH2C78A, in which the predicted catalytic cysteine was mutated to alanine, and found significant rodanese activity of the recombinant MnRDH2 in vitro, but not for the mutant rMnRDH2C78A. We observed that rMnRDH2 was able to significantly increase tolerance of the host bacteria to oxidative stressor phenazine methosulfate. These results suggest that MnRDH2 might have the potential to buffer general levels of oxidants via regulation of redox reactions. In conclusion, our study begins to hint a possible biological functionality of MnRDH2 as a redox switch to activate defensive activities against oxidative damage, which helps host in maintaining the cellular redox balance. These characteristics will facilitate future investigations into the physiological functions for invertebrate rhodanese family genes.