Biological Activity of Optimized Codon Bovine Type III Interferon Expressed in Pichia pastoris

Type III interferons (IFN–λs) exhibit potent antiviral activity and immunomodulatory effects in specific cells. Nucleotide fragments of the bovine ifn–λ (boifn–λ) gene were synthetized after codon optimization. The boifn–λ gene was then amplified by splicing using overlap extension PCR (SOE PCR), resulting in the serendipitous acquisition of the mutated boIFN–λ3(V18M). The recombinant plasmid pPICZαA–boIFN–λ3/λ3(V18M) was constructed, and the corresponding proteins were expressed in Pichia pastoris with a high–level extracellular soluble form. Dominant expression strains of boIFN–λ3/λ3(V18M) were selected by Western blot and ELISA and cultured on a large scale, and the recombinant proteins purified by ammonium sulfate precipitation and ion exchange chromatography yielded 1.5g/L and 0.3 g/L, with 85% and 92% purity, respectively. The antiviral activity of boIFN–λ3/λ3(V18M) exceeded 10(6) U/mg, and they were neutralized with IFN–λ3 polyclonal antibodies, were susceptible to trypsin, and retained stability within defined pH and temperature ranges. Furthermore, boIFN–λ3/λ3(V18M) exerted antiproliferative effects on MDBK cells without cytotoxicity at 10(4) U/mL. Overall, boIFN–λ3 and boIFN–λ3(V18M) did not differ substantially in biological activity, except for reduced glycosylation of the latter. The development of boIFN–λ3 and comparative evaluation with the mutant provide theoretical insights into the antiviral mechanisms of boIFN–λs and provide material for therapeutic development.