Structure—function analysis of human EL-la: identification of residues required for binding to the human type IIL-1 receptor

2To whom correspondence should be addressed Using oligonucleotide-directed mutagenesis, the binding site on human interleukin-la (IL-la) for the human type I IL-1 receptor (IL-1R) has been analyzed. Substitution of seven amino acids (Argl2, Del4, Asp60, Asp61, De64, Lys96 and TrplO9) resulted in a significant loss of binding to the receptor. Based on crystallographic information, the side chains of these residues are clustered in one region of IL-la and exposed on the surface of the protein. Five of the residues in the IL-la binding site align with the binding residues previously determined in human IL-ljS, demonstrating that the type I IL-1R recognizes homologous regions in both Ugands. Unexpectedly, only three of the aligned residues are identical between IL-la and IL-1/3. These observations suggest that the composition of contact residues in the binding site is unique for each Ugand-receptor complex in the IL-1 system. Key words: site-specific mutagenesis/competitive binding/ sequence alignment/cytokine/receptor antagonis