Antioxidative properties and structural features of atypical 2-Cys peroxiredoxin from Sebastes schlegelii

Prx5 of Cristaria plicata has antioxidant function and is regulated by Nrf2/ARE signaling pathway

Cristaria plicata is one of the more important freshwater pearl bivalves in China, which is susceptible to pathogen infection, and greatly impacts the ability of breeding pearls. Nrf2/ARE signaling pathway and its downstream target gene Prx5 have endogenous antioxidant functions to protect cells from oxidative damage. The full-length cDNA of Prx5 was cloned from C. Plicata, which was 1420 bp, encoding a total of 189 amino acids and had two conserved cysteine residues (Cys78 and Cys179). The amino acid sequence of CpPrx5 was highly similar to Prx5 of other species. Real-time fluorescence quantitative PCR showed that CpPrx5 was distributed in various tissues of mussels, and the highest expression was in hepatopancreas. The expression of CpPrx5 up-regulated in hepatopancreas and gills after LPS, PGN and Poly:I:C stimulation. The recombinant plasmid DE3-PGEX-4T-1-CpPrx5 was expressed in Escherichia coli BL21 and showed antioxidant activity. With the increase of CpPrx5 protein concentration, the superhelical form of DNA was protected. The expression of CpPrx5 was up-regulated after interference CpKeap1 and down-regulated after interference CpNrf2. Gel block assay showed that CpNrf2 and CpMafK proteins blocked CpPrx5 promoter. Subcellular localization showed that CpPrx5 was located in 293T nucleus and cytoplasm and CpMafK was located in 293T nucleus. GST-Pull down verified that CpMafK and CpPrx5 could bind in vitro. These results indicated that Prx5 had antioxidant function and could protects DNA from oxidative damage, and participated in transcriptional regulation by combining with the transcription factor MafK. In addition, MafK could combine with Nrf2 to regulate the downstream target gene Prx5.

Molecular profiling and functional delineation of peroxiredoxin 3 (HaPrx3) from the big-belly seahorses (Hippocampus abdominalis) and understanding their immunological responses

Peroxiredoxins (Prxs) are ubiquitously expressed antioxidant proteins that can protect aerobic organisms from oxidative stress. Here, we characterized the HaPrx3 homolog at the molecular level from big-belly seahorse (Hippocampus abdominalis) and analyzed its functional activities. The coding sequence of HaPrx3 consists of 726 bp, which encodes 241 amino acids. The predicted molecular weight and theoretical isoelectric point (pI) of HaPrx3 was 26.20 kDa and 7.04, respectively. Multiple sequence alignments revealed that the arrangements of domains, catalytic triads, dimers, and decamer interfaces of HaPrx3 were conserved among Prx sequences of other organisms. According to the phylogenetic analysis, HaPrx3 is clustered with the teleost Prx3 subclade. The highest transcript level of HaPrx3 was detected in the ovary tissue among fourteen healthy fish tissues. The mRNA levels of HaPrx3 in blood and liver tissues were significantly (P < 0.05) upregulated in response to lipopolysaccharide (LPS), polyinosinic-polycytidylic (poly I:C), Edwardsiella tarda, and Streptococcus iniae, suggesting its involvement in immune responses. Under functional properties, insulin disulfide reduction assay confirmed the oxidoreductase activity of recombinant HaPrx3. A cell viability assay and Hoechst staining indicated cell survival ability and reduction of apoptotic activity, respectively. Moreover, a peroxidase activity assay verified peroxidase activity, while a metal-catalyzed oxidation (MCO) assay indicated the DNA protection ability of HaPrx3. Collectively, it is concluded that HaPrx3 may play a significant role in oxidative stress and immune responses against pathogenic infections in big-belly seahorses.

Cloning and functional characterization of rockfish peroxiredoxin 4 homolog with its innate immune responses

The fourth member of the typical 2-cysteine peroxiredoxin (Prx4) is a well-known antioxidant enzyme, which reduces different peroxides in their catalytic process. The present study reports the identification of the rockfish Sebastes schlegelii Prx4 (SsPrx4) at a genomic level, as well as the characterization of its structural and functional features. SsPrx4 harbors a complete ORF of 786 bp encoding a polypeptide (29 kDa) of 262 amino acids (aa) with an isoelectric point of 6.2. Thioredoxin 2 domain was prominent in the SsPrx4 sequence, which has a signal peptide (31 bp) at the N-terminus. Hence, the SsPrx4 may be functionally active in the cytoplasm of rockfish cells. Moreover, two VCP motifs and three catalytic triad residues (¹¹²T, ¹¹⁵C, ¹⁹¹R) were identified in the SsPrx4 protein sequence. A peroxidatic cysteine (¹¹⁵C_P) and resolving cysteines (²³⁶C_R) were detected at the VCP motifs. The rockfish Prx4 genome consists of seven exons, which are similar to the architecture of other Prx4 orthologs. The deduced amino acid sequence of SsPrx4 shares a relatively high amino acid sequence identity (91.6%) and close evolutionary relationship with Miichthys miiuy and Stegastes partitus Prx4. The potential for scavenging extracellular H₂O₂ was evidenced by the purified recombinant SsPrx4 protein (rSsPrx4) in vitro system. Moreover, rSsPrx4 may protect the plasmid DNA in a metal-catalyzed oxidation system and catalyze the reduction of an insulin disulfide bond. Quantitative real-time PCR revealed that SsPrx4 mRNA was ubiquitously expressed in fourteen different tissues, with the highest expression observed in the liver followed by the ovary, and kidney tissues. Transcriptional modulations were observed in liver and spleen tissues of rockfish after injecting them with bacterial stimuli, including Streptococcus iniae, LPS, and a viral mimic of poly I:C. Together, the results suggest that SsPrx4 may play an important role in both the antioxidant and innate immune defense of black rockfish. These findings provide structural and functional insights into the SsPrx4 of the teleost.

Peptidylarginine deiminase and deiminated proteins are detected throughout early halibut ontogeny - Complement components C3 and C4 are post-translationally deiminated in halibut (Hippoglossus hippoglossus L.)

Post-translational protein deimination is mediated by peptidylarginine deiminases (PADs), which are calcium dependent enzymes conserved throughout phylogeny with physiological and pathophysiological roles. Protein deimination occurs via the conversion of protein arginine into citrulline, leading to structural and functional changes in target proteins. In a continuous series of early halibut development from 37 to 1050° d, PAD, total deiminated proteins and deiminated histone H3 showed variation in temporal and spatial detection in various organs including yolksac, muscle, skin, liver, brain, eye, spinal cord, chondrocytes, heart, intestines, kidney and pancreas throughout early ontogeny. For the first time in any species, deimination of complement components C3 and C4 is shown in halibut serum, indicating a novel mechanism of complement regulation in immune responses and homeostasis. Proteomic analysis of deiminated target proteins in halibut serum further identified complement components C5, C7, C8 C9 and C1 inhibitor, as well as various other immunogenic, metabolic, cytoskeletal and nuclear proteins. Post-translational deimination may facilitate protein moonlighting, an evolutionary conserved phenomenon, allowing one polypeptide chain to carry out various functions to meet functional requirements for diverse roles in immune defences and tissue remodelling.