Mapping the binding surface of interleukin‐8 complexed with an N‐terminal fragment of the Type 1 human interleukin‐8 receptor

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Abstract
Interleukin‐8 and its receptors are key mediators of immune and inflammatory responses. Heteronuclear NMR spectroscopy has been utilized to map the binding surface on interleukin‐8 (IL‐8) for an N‐terminal fragment of the human Type‐1 IL‐8 receptor. A peptide corresponding to residues 1–40 of the IL‐8 type 1 receptor (IL8‐rl) was titrated into a sample of uniformly 15N‐labeled IL‐8. IL8‐rl binds to IL‐8 with a dissociation constant of 170 ± 50 μM assuming the peptide binds with a stoichiometry of one peptide per IL‐8 monomer, exchanges rapidly (> 900 s−1) between free and bound states, and selectively perturbs the chemical environment of several IL‐8 residues. The binding surface on IL‐8 suggested by our results is comprised of residues in strand β3 of the β‐sheet (Glu48 to Cys50), the turn preceding β3 (Ser44), the C‐terminal α‐helix (Val61) and the irregular N‐terminal loop region (Thr123, Lys15, Phe17, His18, Lys20 and Phe21). The IL‐8 dimer appears to present two symmetrical binding surfaces for the IL8‐rl peptide, suggesting two receptor peptides may bind per dimer.