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 Escherichia coli, was selectively truncated at its C-terminus with chymotrypsin, clostripain or plasmin. The C-terminal amino acid residues of the three truncated IFN-gamma variants were identified as Phe136, Arg129 and Lys128, indicating the removal of 7, 14 and 15 amino acid residues from the full-length molecule. The absence of seven C-terminal residues did not influence the binding of IFN-gamma to its receptor. In contrast, the truncation of 14 residues resulted in a decrease in the Ka value to 1/24, as determined by surface plasmon resonance analysis. The removal of one additional amino acid residue from the C-terminal region of IFN-gamma led to a marked loss of receptor-binding capacity and biological activity. These observations demonstrate that Arg129 is an essential part of a functionally important C-terminal IFN-gamma sequence that is involved in receptor interaction.