INTERACTION OF TRUNCATED HUMAN INTERFERON-GAMMA VARIANTS WITH THE INTERFERON-GAMMA RECEPTOR - CRUCIAL IMPORTANCE OF ARG-129

Recombinant human interferon gamma (IFN-gamma), produced in Escherichi a coli, was selectively truncated at its C-terminus with chymotrypsin, clostripain or plasmin. The C-terminal amino acid residues of the thr ee truncated IFN-gamma variants were identified as phe(136), Arg(129) and Lys(128), indicating the removal of 7, 14 and amino acid residues from the full-length molecule. The absence of seven C-terminal residue s did not influence the binding of IFN-gamma to its receptor. In contr ast, the truncation of 14 residues resulted in a decrease in the K-a v alue to 1/24, as determined by surface plasmon resonance analysis. The removal of one additional amino acid residue from the C-terminal regi on of IFN-gamma led to a marked loss of receptor-binding capacity and biological activity. These observations demonstrate that Arg(129) is a n essential part of a functionally important C-terminal IFN-gamma sequ ence that is involved in receptor interaction.