A study of water-protein interactions by high-resolution NMR spectroscopy

The interaction between carbonic anhydrase B in the molten globule state an d water molecules was studied by high-resolution NMR spectroscopy. NMR spin diffusion experiments revealed spin diffusion propagation from the protein to waters. This is a process of complex bioexponential kinetics presented in spin diffusion spectra as a change in water signal intensity dependent o n the protein postexcitation time. Its reverse, spin diffusion propagation from waters to the protein, was also found. These phenomena are protein con centration- and temperature-dependent and shown to be possibly explained wi th the assumption that there exist water-protein complexes provoking format ion of large branched associations. At a temperature above 309 K, a stepwis e increase in the interaction between water and proteins occurs in these co mplexes. The formation of water-protein associations is induced by increasi ng temperature and/or protein concentration. In these associations, at norm al temperature, the protein mobility is close to that of carbonic anhydrase B dimers.