Mapping of an epitope of human leukocyte alpha interferon A which is recognized by the murine monoclonal antibody NK2.

An epitope of human leukocyte alpha interferon A (IFN-A), which is recognized by the murine monoclonal antibody NK2, has been mapped by using four successive approaches. Limited proteolysis of the IFN-A chain, followed by electrophoresis, Western blotting, and probing of the proteolytic fragments with NK2 showed that an epitope was located within the sequence residues 110-140. A panel of human IFN subtypes bearing substitutions within the sequence 110-140 was tested for reactivity with NK2 in enzyme-linked immunosorbent assays. The results from these assays suggested that the epitope is within the sequence 112-121. Analysis of a hybrid protein IFN-A(1-92)/F(93-166) revealed that the N-terminal region of IFN-A played no significant role in NK2 binding. Three residues of IFN-F (Asn113, Val114, and Lys121) were substituted for the corresponding residues from IFN-A (Lys113, Glu114, and Arg121) by site-directed mutagenesis of the gene encoding IFN-F. NK2 was able to bind the mutated protein, IFN-F(A 113, 114, 121), as well as unmodified IFN-A. The data show that the epitope recognized by NK2 is located within the C-terminal region of IFN-A (residues 112-121). This epitope consists of the essential residues 114 and 116, and residues 112, 113, 115, 117, and 121 presumably contribute the configuration of the epitope.