Hydration and temperature dependent dynamics of lysozyme in glucose-water matrices. A neutron scattering study

Through a neutron scattering experiment, we studied the dynamics of lysozyme embedded in glucose-water matrices. Two distinct quasielastic contributions, corresponding to motions in the sub- and picosecond timescales, are revealed after the subtraction of the inelastic intensity, as estimated at low temperature. Their characteristic times are hydration and temperature independent, and quite similar to those revealed when the environment around the biomolecule surface is pure water or glycerol. The momentum transfer dependence of each quasielastic signal has been interpreted in terms of the rotational diffusion model. The faster component corresponds to a more localized rotational motion on a radius of 1 Å, while the slower contribution is associated to a larger radius of 1.9 Å. The behavior of the fraction of moving protein hydrogen atoms as a function of temperature and hydration suggests that the protein undergoes a dynamical transition just at conditions corresponding to the dynamical onset of the enclosing matrix.