Quasi-elastic neutron scattering studies of protein dynamics. Final report, November 1, 1991--March 31, 1995

Proteins are formed from long polymer chains of amino acids that have been cross linked into a complex three dimensional structure. The structure is not unique, since there are many conformation substates of nearly equal energy, separated by small energy barriers, that are obtained by slight shifts in positions of various segments of the molecule. Transitions among these conformations substates are of a diffusive nature, and they can lead to substantial changes in the shape of the molecule. These changes in shape are important for the biological reactions in the cell. Such diffusive motion is inaccessible to the diffraction methods or to the computer simulations, since it occurs on a long time scale. It is accessible to incoherent quasi-elastic neutron scattering (QNS) studies, which permit a direct determination of the properties of the diffusive motion of the protons in the molecules. The authors have used the IQNS method to study the motions of the side chains in trypsin, a protein of beta-sheet structures and myoglobin, a protein of {alpha}-helical structures, at various D{sub 2}O hydration levels