BIOLOGICAL AND RECEPTOR-BINDING ACTIVITIES OF HUMAN INTERLEUKIN-2 MUTATED AT RESIDUES 20ASP, 125CYS OR 127SER

We have used site-directed mutagenesis to analyse structure-function r elationships of the human Interleukin-2 molecule, The mutations introd uced targetted residue 20Asp, within the N-terminal A helix, as well a s residues 125Cys and 127Ser in the C-terminal D helix. The results pr esented here demonstrate that destabilizing the C-terminus a helix thr ough introduction of Pro residues in either positions 125 or 127 reduc ed the biological activity of IL-2 by a factor of 10 that was correlat ed with a decreased ability to bind the receptor, A number of substitu tions in position 20 have an even more drastic effect on biological ac tivity and receptor binding, However, specific substitutions such as 2 0Asn and 20Leu displayed a differential effect on human or mouse IL-2 receptors. Furthermore, 2OLeu IL-2 was found to behave as a pal tial a ntagonist of natural IL-2 when tested on murine cells.