Subunit association and monomer structure of CINC/Gro revealed by H-1-NMR

Rat CINC/Gro is a 72 residue chemotactic factor of neutrophils, and a member of the CXC chemokine family, that includes IL-8 and MGSA/GRO, Although the three-dimensional structure of CINC/Gro had previously been determined to be that of a dimer with 200 mM NaCl, it was shown on both ultracentrifugation analysis and H-1-NMR spectral analysis that CINC/Gro exists mainly as a monomer at a physiological concentration, similar to other proteins belonging to this family, By reducing the NaCl concentration, the equilibrium could be shifted to the monomer, making it possible to observe the monomer and dimer resonances in H-1-NMR spectra, There were no significant chemical shift changes of alpha protons in the beta sheet between the monomer and dimer, suggesting that the beta sheet structure was retained in the monomer, Instead, the chemical shift changes of alpha protons were significant at 118 and K21, which are located in the long loop region interacting with the alpha helix, and V59 at the beginning of the alpha helix, indicating structural changes in the relative positions of the alpha helix and beta sheet.