SYNTHETIC MIMICS OF JUXTAPOSED AMINO-TERMINAL AND CARBOXYL-TERMINAL PEPTIDE DOMAINS OF HUMAN GAMMA-INTERFERON BLOCK LIGAND-BINDING TO HUMANGAMMA-INTERFERON RECEPTOR

The epitopes of two neutralizing antibodies (47N3-6 and 47N30A35) rais ed against rhuIFN-gamma each mapped both to amino-terminal regions (22 -29 and 12-19, respectively) and to a carboxyl-terminal region 131-139 , suggesting the juxtaposition of these two domains in the native prot ein. Three novel peptides were designed to mimic a conformation of rhu IFN-gamma that places the two regions in close proximity (discontinuou s peptides 1 (15-21-GGG-132-138), 2 (15-29...111-118...130-138), and 3 (15-21-CGPGC-130-138)), by bridging the amino- and carboxyl-terminal regions of gamma interferon. Each discontinuous peptide inhibits biolo gical or receptor binding activities with an IC50 of 15-50 muM and pro duces a neutralizing antibody when used as an immunogen. Neutralizing rabbit polyclonal antibody (P616) raised against discontinuous peptide 1 was used as immunogen to generate an anti-idiotypic response. This anti-idiotypic antibody inhibits receptor binding and recognizes solub le gamma interferon receptor on direct enzyme-linked immunosorbent ass ay. The anti-idiotypic response suggests that juxtaposed regions at th e amino and carboxyl termini serve as the receptor-ligand binding site of human gamma interferon.