NMR Solution Structure and Receptor Peptide Binding of the CC Chemokine Eotaxin-2

The human CC chemokine eotaxin-2 is a specific agonist for the chemokine receptor CCR3 and may play a role in the recruitment of eosinophils in allergic diseases and parasitic infections. We report the solution structure of eotaxin-2 determined using heteronuclear and triple resonance NMR methods. A family of 20 structures was calculated by hybrid distance geometry-simulated annealing from 854 NOE distance restraints, 48 dihedral angle restraints, and 12 hydrogen bond restraints. The structure of eotaxin-2 (73 amino acid residues) consists of a helical turn (residues 17−20) followed by a 3-stranded antiparallel β-sheet (residues 22−26, 37−41, and 44−49) and an α-helix (residues 54−66). The N-loop (residues 9−16) is packed against both the sheet and the helix with the two conserved disulfide bonds tethering the N-terminal/N-loop region to the β-sheet. The average backbone and heavy atom rmsd values of the 20 structures (residues 7−66) are 0.52 and 1.13 Å, respectively. A linear peptide corresponding to the N-terminal region of CCR3 binds to eotaxin-2, inducing concentration-dependent chemical shift changes or line broadening of many residues. The distribution of these residues suggests that the peptide binds into an extended groove located at the interface between the N-loop and the β2−β3 hairpin. The receptor peptide may also interact with the N-terminus of the chemokine and part of the α-helix. Comparison of the eotaxin-2 structure with those of related chemokines indicates several structural features that may contribute to receptor specificity.