Trehalose effect on low temperature protein dynamics: Fluctuation and relaxation phenomena

We performed spectral diffusion experiments in trehalose-enriched glycerol/ buffer-glass on horseradish peroxidase where the heme was replaced by metal -free mesoporphyrin IX, and compared them with the respective behavior in a pure glycerol/buffer-glass (Schlichter et al., J. Chem. Phys. 2000, 112:30 45-3050). Trehalose has a significant influence: spectral diffusion broaden ing speeds up compared to the trehalose-free grass. This speeding up is att ributed to a shortening of the correlation time of the frequency fluctuatio ns most probably by preventing water molecules from leaving the protein int erior. Superimposed to the frequency fluctuation dynamics is a relaxation d ynamics that manifests itself as an aging process in the spectral diffusion broadening. Although the trehalose environment speeds up the fluctuations, it does not have any influence on the relaxation. Both relaxation and fluc tuations are governed by power laws in time. The respective exponents do no t seem to change with the protein environment. From the spectral dynamics, the mean square displacement in conformation space can be determined. It is governed by anomalous diffusion. The associated frequency correlation time is incredibly long, demonstrating that proteins at low temperatures are tr uly nonergodic systems.