A Study of Water-Protein Interactions by High-Resolution NMR Spectroscopy

摘要

The interaction between carbonic anhydrase B in the molten globule state and 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 on the protein postexcitation time. Its reverse, spin diffusion propagation from waters to the protein, was also found. These phenomena are protein concentration-and temperature-dependent and shown to be possibly explained with the assumption that there exist water-protein complexes provoking formation of large branched associations. At a temperature above 309 K, a stepwise increase in the interaction between water and proteins occurs in these complexes. The formation of water-protein associations is induced by increasing temperature and/or protein concentratoin. In these associations, at normal temperature, the protein mobility is close to that of carbonic anhydrase B dimers.