The inverse relationship between protein dynamics and thermal stability

Protein powders that are dehydrated or mixed with a glassy compound are kno wn to have improved thermal stability. We present elastic and quasielastic neutron scattering measurements of the global dynamics of lysozyme and ribo nuclease A powders. In the absence of solvation water, both protein powders exhibit largely harmonic motions on the timescale of the measurements. Upo n partial hydration, quasielastic scattering indicative of relaxational pro cesses appears at sufficiently high temperature. When the scattering spectr um are analyzed with the Kohlrausch-Williams-Watts formalism, the exponent beta decreases with increasing temperature, suggesting that multiple relaxa tion modes are emerging. When lysozyme was mixed with glycerol, its beta va lues were higher than the hydrated sample at comparable temperatures, refle cting the viscosity and stabilizing effects of glycerol.