College Park, Maryland      June 6 - 10 , 2004

M3-B4 (2:30 PM): Dominant effect of solvent on protein dynamics

G. H. Caliskan (The University of Akron, Polymer Science Department), M. T. Cicerone (NIST Polymer Division), M. Gangoda, R. B. Gregory (Kent State University, Department of Chemistry), A. Kisliuk (The University of Akron, Polymer Science Department), I. Peral (University of Maryland, College Park), J. H. Roh, A. P. Sokolov (The University of Akron, Polymer Science Department)

Dynamic transition in proteins and DNA is observed as a sharp increase in mean-squared displacement (MSD) of atoms at the transition temperature (TD). This transition is closely related to the activation of protein’s functions. However, due to MSD being an integrated quantity, the origin of this transition is still not clear. Analysis of energy resolved spectra would shed light on to the origin of the dynamic transition in biological macromolecules.

We measured dynamics of protein lysozyme in various solvents, (water, glycerol, trehalose and dry state) in a broad temperature (150K to 320K) range. High Flux Back-Scattering Spectrometer, in combination with the Time-of-Flight Spectrometer at the National Institute of Standards and Technology Center for Neutron Research have been used for measurements of the spectra in a broad energy range from ~1 µeV up to ~65 meV. Our measurements revealed two different relaxation processes in the accessible energy window. The fast process with the width ~2 meV and is rather independent of temperature, except for the amplitude. The slow process is strongly temperature dependent, and is observed below ~0.5 meV. Our results unambiguously show that the dynamic transition is caused by the slow relaxation process that moves in to µeV energy window. This leads to a sharp increase in the measured MSD. The slow process of the protein is strongly affected by the solvent, and it is possible to shift the TD, by changing the solvent. Moreover, TD observed for lysozyme in water and in glycerol appears to be close to the dynamic crossover temperatures of bulk water and bulk glycerol, respectively. No dynamic transition is observed for protein in trehalose, at least below the glass transition of trehalose. This proves the earlier idea formulated in the field that the solvents control the protein dynamics and activity. It opens a new perspective to control the bioactivity of proteins.

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