The thioredoxin - thioredoxin reductase system is one of key redox homeostatic system which response to environmental stress factors such as ROS, UV light, gamma rays and heat shock. Thioredoxin reductase (TXNRD) restore the oxidized Thioredoxin (TXN) to reduce state, thus keep the sustainability of the redox system. TXNRDs are homodimeric proteins which belong to the flavoprotein family of pyridine nucleotide disulfide oxidoreductases. It contains FAD prosthetic groups, NADPH binding sites and a redox-active disulfide catalytic site. Recently, three isoforms of TXNRDs; cytosolic (TXNRD1), mitochondrial (TXNRD2), Testis specific (TXNRD3) has been identified in mammals. TXNRD1 is the most abundant isozyme found in the cytosol and active site composed of a conserved Cys-(X) 2-Cys motif near the N-terminus of each subunit and a conserved Gly-Cys-Sec-Gly-OH motif at C-terminal of each monomer. With the presence of NADPH, tightly folded TXNRD1 accept electrons to reduce covalent disulfide and selenenyl sulfide bonds into dithiol and seleno thiol groups. Then seleno thiol groups are exposed and act as nucleophile to reduce TXN and other substrates.
Hence, the aim of present study is to characterize molecular structure of TXNRD1 from Hippocampus abdominalis to get better understanding of redox homeostasis. Therefore, we conducted insilico and transcriptional analysis of TXNRD1 ortholog that identified from Big-belly seahorse transcriptome. In this study, various bioinformatics tools were used to identify the sequence characteristics and qPCR was used to investigate the expression profiles of TXNRD in normal and immune stimulated conditions.
The open reading frame (ORF) of TXNRD1 is 1800bp and encoding 600 amino acids. According to In-silico analysis performed, TXNRD1 enzyme has 65.86 kDa molecular weight and theoretical isoelectric point is 5.54. The amino acid sequence contained 2 N-linked glycosylation sites at 6NETG9 and 84NKTH87. TXNRD1 contain Glutaredoxin (GRX) domain at 25 to 106 amino acid residues which are similar to human GRXs. GRX is a glutathione (GSH) dependent reductase and it catalyze the reduction of disulfide in proteins such as ribonucleotide reductase. GRX is involved in many cellular functions including DNA synthesis, signal transduction and the defense against oxidative stress. The qPCR results indicated that highest mRNA expression was observed in blood followed by ovary and gill among fourteen different tissues from healthy seahorses. The different levels of TXNRD1 expression detected in the tissue may reflect distinct levels of metabolic activity. Mainly phagocytic blood cells can produce excessive amounts of ROS in response to the invading pathogens as a first-line host defense mechanism to activate immune signaling pathways. Therefore, TXNRD1 from seahorses can be identified as an immunologically important gene.