MAPPING THE BINDING SURFACE OF INTERLEUKIN-8 COMPLEXED WITH AN N-TERMINAL FRAGMENT OF THE TYPE-1 HUMAN INTERLEUKIN-8 RECEPTOR

Interleukin-8 and its receptors are key mediators of immune and inflam matory responses. Heteronuclear NMR spectroscopy has been utilized to map the binding surface on interleukin-8 (IL-8) for an N-terminal frag ment of the human Type-1 IL-8 receptor. A peptide corresponding to res idues 1-40 of the IL-8 type 1 receptor (IL8-rl) was titrated into a sa mple of uniformly N-15-labeled IL-8. IL8-rl binds to IL-8 with a disso ciation constant of 170 +/- 50 mu M assuming the peptide binds with a stoichiometry of one peptide per IL-8 monomer, exchanges rapidly (> 90 0 s(-1)) between free and bound states, and selectively perturbs the c hemical environment of several IL-8 residues. The binding surface on I L-8 suggested by our results is comprised of residues in strand beta 3 of the beta-sheet (Glu(48) to Cys(50)), the turn preceding beta 3 (se r(44)), the C-terminal alpha-helix (Val(61)) and the irregular N-termi nal loop region (Thr(12), Lys(15), Phe(17), His(18), Lys(20) and Phe(2 1)). The IL-8 dimer appears to present two symmetrical binding surface s for the IL8-rl peptide, suggesting two receptor peptides may bind pe r dimer.