Inhibition of interleukin-2/p55 receptor subunit interaction by complementary peptides

Complementary peptides to interleukin-2 (IL-2) sequences important for receptor binding were tested for their ability to mimic natural receptors and act as inhibitors of the IL-2/p55 receptor subunit interaction. Peptides hydropathically complementary to IL-2 sequences 15-27 and 40-54 were synthesized in a linear and in a multimeric form and then characterized first by solid-phase binding assays for their ability to interact with IL-2. Binding between the multimeric complementary peptides and biotinylated IL-2 was specific, saturable, and inhibited by linear as well as multimeric complementary peptides. Saturable interactions, characterized by dissociation constants in the micromolar range, occurred also between IL-2 immobilized on microtiter plates and biotinylated linear and multimeric complementary peptides. Peptides corresponding to the IL-2 target sequences were able to interfere with this interaction, as well as full-length IL-2. Peptide recognition was sequence dependent, since scrambling of complementary peptide sequences or IL-2 target peptide sequences abolished binding. Multimeric complementary peptides after immobilization on solid supports proved useful also for affinity purifications of recombinant IL-2 or IL-2 fragments corresponding to the target sites, directly from crude mixtures, in high yield and with high recovery. Complementary peptides to IL-2 sequence 15-27, but not to IL-2 sequence 40-54, in the linear or in the multimeric form, even if with different potency, interfered with the IL-2/p55 receptor subunit interaction in vitro, thus suggesting a possible role of this IL-2 site in receptor recognition.