MECHANISM OF HYDROGEN-DEUTERIUM EXCHANGE IN TRP REPRESSOR STUDIED BY H-1-N-15 NMR

Amide proton exchange rates have been measured for fast-exchanging ami des in tup aporepressor, and compared with the rates measured in the h olorepressor. The results indicate that the presence of the ligand sta bilizes all of the amide protons in the molecule against exchange, not just those whose access to solvent it directly hinders. This global h indering of the exchange process by tryptophan implies that there is a non-random element in the transmission mechanism, so that damping of the exchange in one part of the molecule also damps exchange in anothe r region. This damping at a distance is not associated with any measur able changes in the intervening average secondary structure. This sugg ests the existence of a concerted dynamic process in the protein backb one that is modulated by ligand binding and in turn affects the observ ed backbone proton exchange. (C) 1995 Academic Press Limited