The thioredoxin domain containing protein 5 (TXNDC5), also known as resident endoplasmic reticulum 46 (Erp46); has categorized as a member of the family PDI. As a common feature of PDI family, all the members comprise one or more thioredoxin- like domain which contain CXXC signature sequence. TXNDC5 was first identified in 2003 with six splicing variants, where two of them (TXNDC5-001, TXNDC5-003) can be translated in to proteins. The full-length version of TXNDC5 bears three TXN-like domains while lacking peptide binding domain . TXNDC5 mainly expressed in liver and endothelial cells and regarding its cellular location the highest expression was observed int endoplasmic reticulum (ER).
The deduced amino acid sequence of shTXNDC5 was identified and it consisted with an open reading frame (ORF) of 1286 bp which codes a protein with 433 amino acids. The molecular weight of shTXNDC5 was predicted as 49.3 kDa with a 5.01 theoretical isoelectric point (pI). Following the in-silico predictions, shTXNDC5 consisted with three thioredoxin – like domains at the positions of 35-141, 165-270, 324-428 aa and endoplasmic reticulum (ER) retention signal at the C- terminus (D430EL433).
The spatial and temporal expression profiles of shTXNDC5 showed its highest expression in sea horse ovary while exhibiting potential protective roles against bacterial and viral invasions, respectively. The significant changes in their expression allow us to propose possible functions of shTXNDC5 in the innate immune system of big belly sea horse. Moreover, its thiol-disulfide, protein disulfide isomerase and mixed disulfide isomerase ability were determined by the HED, insulin disulfide reductase and the MTT assays. Altogether the outcomes of this study afford the first comprehensive report of TXNDC5 in teleost by providing sufficient evidences for the involvement of TXNDC5 in sea horse immunity.