Hindered protein dynamics in the presence of a cryoprotecting agent

We present a study of the influence of trehalose, a well-known cryoprotecting disaccharide, on the dynamics of a protein, the C-phycocyanin. The dynamics is investigated in a time range from some picoseconds to several nanoseconds using different neutron-scattering techniques. Data obtained on samples containing hydrated powders of the protein in the presence of trehalose are compared to that of the protein alone, studied by neutron-scattering techniques as well as by molecular dynamics simulations. The analysis of time-of-flight data gives access to the geometry of the observed motions. These motions can be described via a model of a particle diffusing inside a sphere. We observe a slowing down of the movements of the protein due to the presence of trehalose of one to two orders of magnitude, while the geometry of the motions is conserved.