Backbone dynamics of the human CC-chemokine eotaxin

Eotaxin is a CC chemokine with potent chemoattractant activity towards eosi nophils. N-15 NMR relaxation data have been used to characterize the backbo ne dynamics of recombinant human eotaxin. N-15 longitudinal (R-1) and trans verse (R-2) auto relaxation rates, heteronuclear H-1-N-15 steady-state NOEs , and transverse cross-relaxation rates (eta(xy)) were obtained at 30 degre es C for all resolved backbone secondary amide groups using H-1-detected tw o-dimensional NMR experiments. Ratios of transverse auto and cross relaxati on 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 rota tional diffusion and the internal dynamics of each NH group. The molecular rotational correlation time (tau(m)) is 5.09 +/- 0.02 ns, indicating that e otaxin exists predominantly as a monomer under the conditions of the NMR st udy. The ratio of diffusion rates about unique and perpendicular axes (D pa rallel to/perpendicular to) is 0.81 +/- 0.02. Residues with large amplitude s 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 tw o beta-strands (residues 30-37). N-terminal flexibility appears to be conse rved throughout the chemokine family and may have implications for the mech anism of chemokine receptor activation. Residues exhibiting significant dyn amics on the microsecond-millisecond time scale are located close to the tw o conserved disulfide bonds, suggesting that these motions may be coupled t o disulfide bond isomerization.