Studies of the low-temperature dynamics of proteins in aqueous solutions are limited by the crystallization of water. In this work, we use a solution of LiCl in D2O as a solvent for a protein to prevent crystallization and study the dynamics of both the protein and its aqueous solvent by quasielastic neutron scattering (QENS) in the temperature range of 210 to 290 K. Our results reveal that, while the dynamics of the aqueous solvent undergoes a crossover at about 220 K, the dynamics of the protein itself shows no transition at this temperature. The prevailing view is that the β-fluctuations of the protein are governed by the α-fluctuations of the solvent; therefore, observation of the apparent decoupling between the dynamics of the protein and its solvent below the crossover temperature is remarkable.
Keywords: LiCl/D2O solution; dynamic transition; protein dynamics; quasielastic neutron scattering; water dynamics.