LAUSR

ABSTRACT Atypical 2‐Cys peroxiredoxin (Prx5) is an antioxidant protein that exerts its antioxidant function by detoxifying different reactive oxygen species (ROS). Here, we identified mitochondrial Prx5 from rockfish (SsPrx5) and described its specific structural and functional characteristics. The open reading frame (ORF) of SsPrx5 (570 bp) was translated into a 190‐amino acid polypeptide that contained a mitochondrial targeting sequence (MTS), thioredoxin 2 domain, two Prx‐specific signature motifs, and three conserved cysteine residues. Sequence comparison indicated that the SsPrx5 protein sequence shared greatest identity with teleost orthologs, where the phylogenetic results showed an evolutionary position within the fish Prx5. The coding sequence of SsPrx5 was scattered in six exons as found in other vertebrates. Additionally, the potent antioxidant functions of recombinantly expressed SsPrx5 protein was demonstrated by insulin reduction and extracellular H2O2 scavenging both in vitro and in vivo. Quantitative real time PCR (qPCR) detected ubiquitous mRNA expression of SsPrx5 in healthy rockfish tissues, with remarkable expression observed in gill, liver, and reproductive tissues. Prompt transcription of SsPrx5 was shown in the immune‐stimulated gill and liver tissues against Streptococcus iniae and lipopolysaccharide injection. Taken together, present results suggest the indispensable role of SsPrx5 in the rockfish antioxidant defense system against oxidative stresses and its role in maintaining redox balance upon pathogen invasion. HighlightsAtypical 2‐Cys peroxiredoxin homolog was identified from Sebastes schlegelii (SsPrx5).SsPrx5 genomic structure was consisted with six exons and five introns.Extracellular H2O2 scavenge of rSsPrx5 was observed in in vitro and in vivo assays.SsPrx5 transcripts were ubiquitously detected in fourteen different tissues.Time course bacterial challenge showed the transcriptional modulation of SsPrx5.