Analysis of human IL-2 IL-2 receptor beta chain interactions: Monoclonal antibody H2-8 and new IL-2 mutants define the critical role of alpha helix-A of IL-2

Interleukin 2 (IL-2) interacts with a receptor (IL-2R) composed of three subunits (IL-2R alpha, IL-2R beta and IL-2R gamma), IL-2R beta plays a critical role in signal transduction. An anti-human IL-2 mAb (H2-8) produced after immunization with peptide 1-30 of IL-2 was found to recognize the region occupied by Asp20, at the exposed interface between cr-helices A and C, Muteins at position 17 and 20 are not recognized by mAb H2-8. mAb H2-8 specifically inhibits the IL-2 proliferation of TS1 beta cells which are dependent on the expression of human IL-2R beta chain for IL-2 proliferation, Substitution at internal position Leu17 demonstrates that this position is essential for IL-2 binding and IL-2 bioactivity. New IL-2 mutants at position Asp20 have been analysed, Substitutions Asp --> Asn, Asp --> Lys, Asp --> Leu, show a correlation between diminished affinity for IL-2 receptor and reduced bioactivity measured on TS1 beta cells, Mutein Asp --> Arg lose affinity for IL-2R and bioactivity simultaneously. Furthermore, during the course of the study we have found that mutein Asp20 --> Leu is an IL-2 antagonist, The biological effects of mAb H2-8 and the properties of new mutants at positions 17 and 20 demonstrate that this region of or helix-A is involved in IL-2-IL-2R beta interactions. (C) 1997 Academic Press Limited.