Protein dynamics in viscous solvents

The mechanism of protein stabilization by glassy solvents is not entirely clear, and the stabilizer effective for a given protein is often discovered empirically. We use low frequency Raman spectroscopy as an effective tool to directly evaluate the ability of different solvents to suppress the conformational fluctuations that can lead to both protein activity and denaturation. We demonstrate that while trehalose provides superior suppression at high temperatures, glycerol is more effective at suppressing protein dynamics at low temperatures. These results suggest that viscosity of the solvent is not the only parameter important for biopreservation. It is also shown that glycerol and water enhance the high temperature conformational fluctuations relative to dry lysozyme, which explains the lower melting temperatures $T_m$ in the hydrated protein and protein formulated in glycerol.