Expression and purification of recombinant tilapia lake virus segment 4 protein and its in-vitro biological activity for potential use in vaccine development

Tilapia lake virus (TiLV) disease is highly contagious and causes substantial mortality in tilapia. Currently, no effective treatments or commercial vaccines are available to prevent TiLV infection. In this study, TiLV segment 4 (S4) was cloned into the pET28a(+)vector and transformed into Escherichia coli BL21(DE3). Codon optimization was performed to enhance TiLV S4 protein expression, and a range of expression conditions were tested, including various inducers and postinduction temperatures and times for both soluble and insoluble protein expression. The recombinant TiLV S4 protein was purified using affinity chromatography. The optimal conditions for recombinant TiLV S4 expression were achieved via induction using 0.1 mM galactose at 37 °C for 1 h postinduction. The insoluble protein was denatured using 6 M urea and subsequently purified to yield a protein concentration of approximately 250 mg/L. Dot blot immunodetection assays confirmed consistent interactions between the purified TiLV S4 protein and the sera from infected fish and rabbit anti-TiLV antibodies. By identifying the optimal growth conditions and production factors for the recombinant protein, our study offers valuable information for the large-scale production of the TiLV S4 protein, which signals an important step forward in TiLV vaccine development.