A single amino acid change in IFN-β₁ abolishes its antiviral activity

Abstract

The cloning and expression of human fibroblast Interferon (IFN-β₁) cDNA sequences in Escherichia coli have been reported by several groups^1–3; this will allow extensive study of its biological and physical properties. Aside from the cloning and expression of interesting and useful cDNA sequences, recombinant DNA techniques make possible the in vitro construction of gene sequences encoding novel polypeptides which do not occur naturally^4,5, which is difficult to achieve by direct chemical modification of proteins. We describe here the isolation of an IFN-β₁ cDNA sequence encoding the 117 C-terminal amino acids of a variant IFN-β₁ (Cys→Tyr at amino acid position 141) and in vitro recombination with sequences coding for the N-terminal amino acids of IFN-β₁ to form a DNA sequence encoding a mature variant IFN-β₁ polypeptide, and its expression in E. coli. We show that the replacement of Cys at position 141 with Tyr inactivates antiviral activity in a cytopathic effect (CPE) inhibition assay and that the variant protein does not compete with normal fibroblast Interferon for reaction with heterospecific antibodies to IFN-β₁. These effects are attributed to an alteration in protein structure of IFN-β₁^Cys→Tyr which result from its inability to form an essential disulphide bond.