Abstract:
The thioredoxin (Trx) system plays a significant role in cellular antioxidative defense by dismutating the
surpluses of reactive oxygen species. Thus, the role of thioredoxin reductase (TrxR) cannot be ignored, owing
to its participation in initiating the Trx enzyme cascade. Here, we report the identification and molecular characterization of a teleostean TrxR (RbTrxR-3) ortholog that showed high similarity with the TrxR-3 isoforms of other
vertebrates. The complete RbTrxR-3 coding sequence comprised 1800 nucleotides, encoding a 600-amino acid
protein with a predicted molecular mass of ~66 kDa. RbTrxR-3 consisted of 16 exons separated by 15 introns
and had a total length of 12,658 bp. In silico analysis of the RbTrxR-3 protein sequence revealed that it possesses
typical TrxR domain architecture. Moreover, using multiple sequence alignment and pairwise sequence
alignment strategies, we showed that RbTrxR-3 has high overall sequence similarity to other teleostean TrxR-3
proteins, including highly conserved active site residues. Phylogenetic reconstruction of RbTrxR-3 affirmed its
close evolutionary relationship with fish TrxR-3 orthologs, as indicated by its clustering pattern. RbTrxR-3 transcriptional analysis, performed using quantitative polymerase chain reaction (qPCR), showed that RbTrxR-3
was ubiquitously distributed, with the highest level of mRNA expression in the blood, followed by the gill, and
liver. Live bacterial and viral stimuli triggered the modulation of RbTrxR-3 basal transcription in liver tissues
that correlated temporally with that of its putative substrate, rock bream thioredoxin1 under the same conditions
of pathogenic stress. Finally, resembling the typical function of TrxR protein, purified recombinant RbTrxR-3
showed detectable dose-dependent thiol reductase activity against 5,5′-dithiobis (2-nitrobenzoic) acid. Taken
together, these results suggest that RbTrxR-3 plays a role in the host Trx system under conditions of oxidative
and pathogenic stress.
