Backbone dynamics of the human CC-chemokine eotaxin

Eotaxin is a CC chemokine with potent chemoattractant activity towards eosinophils. ¹⁵N NMR relaxation data have been used to characterize the backbone dynamics of recombinant human eotaxin. ¹⁵N longitudinal (R₁) and transverse (R₂) auto relaxation rates, heteronuclear ¹H-¹⁵N steady-state NOEs, and transverse cross-relaxation rates (_xy) were obtained at 30 °C for all resolved backbone secondary amide groups using ¹ H-detected two-dimensional NMR experiments. Ratios of transverse auto and cross relaxation rates were used to identify NH groups influenced by slow conformational rearrangement. Relaxation data were fit to the extended model free dynamics formalism, yielding parameters describing axially symmetric molecular rotational diffusion and the internal dynamics of each NH group. The molecular rotational correlation time (_m) is 5.09±0.02 ns, indicating that eotaxin exists predominantly as a monomer under the conditions of the NMR study. The ratio of diffusion rates about unique and perpendicular axes (D/D) is 0.81±0.02. Residues with large amplitudes of subnanosecond motion are clustered in the N-terminal region (residues 1–19), the C-terminus (residues 68–73) and the loop connecting the first two -strands (residues 30–37). N-terminal flexibility appears to be conserved throughout the chemokine family and may have implications for the mechanism of chemokine receptor activation. Residues exhibiting significant dynamics on the microsecond–millisecond time scale are located close to the two conserved disulfide bonds, suggesting that these motions may be coupled to disulfide bond isomerization.