MUTAGENESIS OF THE HUMAN INTERLEUKIN-6 4TH PREDICTED ALPHA-HELIX - INVOLVEMENT OF THE ARG168 IN THE BINDING-SITE

Random substitutions of amino acid 161-184 of human interleukin-6 (hIL -6) have been generated at the cDNA level using oligonucleotide-direct ed mutagenesis. Among the majority of the mutant proteins showing a re duced biological activity on murine hybridoma cells, only those having a substitution of Met161, Arg168, Arg179 or Met184, retained a tertia ry structure similar to the IL-6 folding. These residues are thus prob ably involved in the interaction with the IL-6 receptor. However, the contacts established by Arg168 and Arg179 seem far more important for the biological activity. According to Bazan's model of cytokine foldin g and the receptor binding site on the fourth alpha-helix, based on gr owth hormone similarity, we propose that Arg168 and Arg179 are located on the exposed surface of this presumed helix.