Characterization of a 1-cysteine peroxiredoxin from big-belly seahorse (Hippocampus abdominalis); insights into host antioxidant defense, molecular profiling and its expressional response to septic conditions

Molecular characterization, cytoprotective, DNA protective, and immunological assessment of peroxiredoxin-1 (Prdx1) from yellowtail clownfish (Amphiprion clarkii)

Peroxiredoxin-1 (Prdx1) is a thiol-specific antioxidant enzyme that detoxifies reactive oxygen species (ROS) and regulates the redox status of cells. In this study, the Prdx1 cDNA sequence was isolated from the pre-established Amphiprion clarkii (A. clarkii) (AcPrdx1) transcriptome database and characterized structurally and functionally. The AcPrdx1 coding sequence comprises 597 bp and encodes 198 amino acids with a molecular weight of 22.1 kDa and a predicted theoretical isoelectric point of 6.3. AcPrdx1 is localized and functionally available in the cytoplasm and nucleus of cells. The TXN domain of AcPrdx1 comprises two peroxiredoxin signature VCP motifs, which contain catalytic peroxidatic (Cp-C52) and resolving cysteine (CR-C173) residues. The constructed phylogenetic tree and sequence alignment revealed that AcPrdx1 is evolutionarily conserved, and its most closely related counterpart is Amphiprion ocellaris. Under normal physiological conditions, AcPrdx1 was ubiquitously detected in all tissues examined, with the most robust expression in the spleen. Furthermore, AcPrdx1 transcripts were significantly upregulated in the spleen, head kidney, and blood after immune stimulation by polyinosinic:polycytidylic acid (poly (I:C)), lipopolysaccharide (LPS), and Vibrio harveyi injection. Recombinant AcPrdx1 (rAcPrdx1) demonstrated antioxidant and DNA protective properties in a concentration-dependent manner, as evidenced by insulin disulfide reduction, peroxidase activity, and metal-catalyzed oxidation (MCO) assays, whereas cells transfected with pcDNA3.1(+)/AcPrdx1 showed significant cytoprotective function under oxidative and nitrosative stress. Overexpression of AcPrdx1 in fathead minnow (FHM) cells led to a lower viral copy number following viral hemorrhagic septicemia virus (VHSV) infection, along with upregulation of several antiviral genes. Collectively, this study provides insights into the function of AcPrdx1 in defense against oxidative stressors and its role in the immune response against pathogenic infections in A. clarkii.

Cloning, Expression, Characterization, and Antioxidant Protection of Glutaredoxin3 From Psychrophilic Bacterium Psychrobacter sp. ANT206

Glutaredoxins (Grxs) are proteins that catalyze the glutathione (GSH)-dependent reduction of protein disulfides. In this study, a Grx-related gene (264 bp), encoding a Ps-Grx3, was cloned from Psychrobacter sp. ANT206. Sequence analysis indicated the presence of the active site motif CPYC in this protein. Homology modeling showed that Ps-Grx3 had fewer hydrogen bonds and salt bridges, as well as a lower Arg/(Arg + Lys) ratio than its mesophilic homologs, indicative of an improved catalytic ability at low temperatures. Site-directed mutagenesis demonstrated that the Cys13, Pro14, and Cys16 sites were essential for the catalytic activity of Ps-Grx3, while circular dichroism (CD) spectroscopy confirmed that point mutations in these amino acid residues led to the loss or reduction of enzyme activity. Furthermore, analysis of the biochemical properties of Ps-Grx3 showed that the optimum temperature of this enzyme was 25 °C. Importantly, Ps-Grx3 was more sensitive to tBHP and CHP than to H₂O₂, and retained approximately 40% activity even when the H₂O₂ concentration was increased to 1 mm Regarding substrate specificity, Ps-Grx3 had a higher affinity for HED, L-cystine, and DHA than for S-sulfocysteine and BSA. We also investigated the DNA-protective ability of Ps-Grx3 using the pUC19 plasmid, and found that Ps-Grx3 could protect supercoiled DNA from oxidation-induced damage at 15°C for 1.5 h. This study provides new insights into the structure and catalytic activity of a cold-adapted Grx3.

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.

Identification and molecular characterization of peroxiredoxin 6 from noble scallop Chlamys nobilis revealing its potent immune response and antioxidant property

The 1-cyseine peroxiredoxin (Prx6) is an importantly antioxidant enzyme that protects cells from oxidative damage caused by excessive production of reactive oxygen species (ROS). In this study, we described the molecular characteristics of the noble scallop Chlamys nobilis peroxiredoxin 6 (designed as CnPrx6), immune responses and DNA protection activity of the recombinant protein. The complete ORF (696 bp) of CnPrx6 encoded a polypeptide (25.5 kDa) of 231 amino acids, harboring a conserved peroxidase catalytic center (⁴¹PVCTTE⁴⁶) and the catalytic triads putatively involved in peroxidase and phospholipase A2 activities. The deduced amino acid sequence of CnPrx6 shared a relatively high amino acid sequence similarity (more than 50%). The qRT-PCR revealed that the CnPrx6 mRNA was constitutively expressed in all examined tissues, with the highest expression observed in adductor. Upon immunological challenge with Vibrio parahaemolyticus, lipopolysaccharides (LPS) and polyinosinic-polycytidylic acid (Poly I:C), the expression level of CnPrx6 mRNA was significantly up-regulated (P < 0.05). Furthermore, there was a significant difference (P < 0.05) in the expression level of CnPrx6 between golden and brown scallops. The purified recombinant CnPrx6 protein protected the supercoiled plasmid DNA from metal-catalyzed ROS damage. Taken together, these results indicated that the CnPrx6 may play an important role in modulating immune responses and minimizing DNA damage in noble scallop Chlamys nobilis.

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.

Two metalloenzymes from rockfish (Sebastes schligellii): Deciphering their potential involvement in redox homeostasis against oxidative stress

Disturbance in the balance between pro-oxidants and anti-oxidants result oxidative stress in aerobic organisms. However, oxidative stress can be inhibited by enzymatic and non-enzymatic defense mechanisms. Superoxide dismutases (SODs) are well-known scavengers of superoxide radicals, and they protect cells by detoxifying hazardous reactive oxygen species. Here, we have identified and characterized two different SODs, CuZnSOD and MnSOD, from black rockfish (RfCuZnSOD and RfMnSOD, respectively). In silico analysis revealed the well-conserved molecular structures comprising all essential properties of CuZnSOD and MnSOD. Phylogenetic analysis revealed that both RfCuZnSOD and RfMnSOD cladded with their fish counterparts. The recombinant RfSOD proteins demonstrated their potential superoxide scavenging abilities through a xanthine oxidase assay. The optimum temperature and pH conditions for both rRfSODs were 25 °C and pH 8, respectively. Moreover, the potential peroxidation function of rRfCuZnSOD was observed in the presence of HCO₃^-. The highest peroxidation activity was observed at 100 μg/mL of rRfCuZnSOD using the MTT cell viability assay and flow cytometry. The analogous tissue-specific expression profile indicated ubiquitous expression of both RfCuZnSOD and RfMnSOD in selected tissues of healthy juvenile rockfish. An immune challenge experiment illustrated the altered expression profiles of both RfCuZnSOD and RfMnSOD against lipopolysaccharide, Streptococcus iniae, and polyinosinic-polycytidylic acid (poly I:C). Collectively, these results strengthen the general understanding of the structural and functional characteristics of SODs within the host defense system.