NMR solution structure and backbone dynamics of the CC chemokine eotaxin-3

Eotaxin-3 is one of three related chemokines that specifically activate che mokine receptor CCR3. We report the 3D structure and backbone dynamics of e otaxin-3 determined by NMR spectroscopy. Eotaxin-3 is monomeric under the c onditions in this study and consists of an unstructured N-terminus before t he first two conserved cysteine residues, an irregularly structured N-loop following the second conserved cysteine, a single turn of 3(10)-helix, a th ree-stranded antiparallel beta -sheet, an alpha -helix, and an unstructured C-terminal tail. As in other chemokines, the alpha -helix packs against on e face of the beta -sheet. The average backbone and heavy atom rmsd values of the 20 structures (residues 9-65) are 0.44 and 1.01 Angstrom, respective ly. A comparison between the structures of eotaxin-3 and related chemokines suggests that the electrostatic potential in the vicinity of a surface gro ove and the structure of the beta2-beta3 turn may be important for maintain ing receptor specificity. The backbone dynamics of eotaxin-3 were determine d from N-15 NMR relaxation data using the extended model free dynamics form alism. Large amplitude motions on the picosecond to nanosecond time scale w ere observed in both termini and in some residues in the N-loop, the beta1- beta2 turn, and the beta (3) strand; the location of these residues suggest s a possible role for dynamics in receptor binding and activation. In contr ast to eotaxin, eotaxin-3 exhibits no substantial mobility on the microseco nd to millisecond time scale.