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, A lthough the three-dimensional structure of CINC/Gro had previously bee n determined to be that of a dimer with 200 mM NaCl, it was shown on b oth ultracentrifugation analysis and H-1-NMR spectral analysis that CI NC/Gro exists mainly as a monomer at a physiological concentration, si milar to other proteins belonging to this family, By reducing the NaCl concentration, the equilibrium could be shifted to the monomer, makin g it possible to observe the monomer and dimer resonances in H-1-NMR s pectra, There were no significant chemical shift changes of alpha prot ons in the beta sheet between the monomer and dimer, suggesting that t he beta sheet structure was retained in the monomer, Instead, the chem ical shift changes of alpha protons were significant at 118 and K21, w hich are located in the long loop region interacting with the alpha he lix, and V59 at the beginning of the alpha helix, indicating structura l changes in the relative positions of the alpha helix and beta sheet.