Biological characterisation of a recombinant Atlantic salmon type I interferon synthesized in Escherichia coli

Type I (α/β) interferons (IFNs) are a family of cytokines that stimulate the expression of numerous proteins that mediate an antiviral state in uninfected cells. Two Atlantic salmon (Salmo salar) IFN-α (SasaIFN-α1 & 2) genes have previously been cloned and both were found to contain a putative N-linked glycosylation site. Recombinant SasaIFN-α1 (rSasaIFN-α1) produced in eukaryotic systems has repeatedly been shown to confer antiviral properties. However, different IFN-α subtypes may exhibit differential antiviral activities and be subject to glycosylation. To evaluate the potential therapeutic impact of a rSasaIFN-α, the mature form of the SasaIFN-α2 protein was produced in a high-level Escherichia coli expression system. Expression of the rSasaIFN-α2 was detected by SDS-PAGE and Western blot, and its identity was confirmed by mass spectrometry. In the homologous Chinook salmon embryonic (CHSE-214) cell line, the rSasaIFN-α2 incited early expression of the IFN-induced Mx protein and exhibited high antiviral activity of about 2.8 × 10⁶ U mg^-1 against infectious pancreatic necrosis virus (IPNV). Conversely, antiviral protection by rSasaIFN-α2 was not observed in a heterologous Japanese flounder embryo (HINAE) cell line. Hence, a biologically active form of rSasaIFN-α2 was successfully produced using a glycosylation-deficient prokaryotic system and purified to homogeneity, suggesting that glycosylation is not required for its antiviral activity.