Dynamic Transition in Proteins and DNA: Role of the Solvent
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Dynamic Transition in Proteins and DNA: Role of the Solvent A.P. Sokolov Department of Polymer Science, The University of Akron, Akron, OH 44325-3909
ABSTRACT Hydrated proteins and DNA demonstrate a dynamic transition at temperatures TD~200230K. Sharp slowing down of protein functions (rate of biochemical reactions) was observed at the same temperature range. These results suggest a direct relationship between the dynamic transition and onset of biochemical activities of proteins. However, the microscopic nature of the dynamic transition in biomolecules remains poorly understood. This contribution presents an overview of neutron scattering and simulations data analyzing dynamics of proteins and DNA. We show that the dynamic transition is related to a “slow” relaxation process that appears in the experimental frequency window at temperatures above TD. Moreover, we show that the dynamic crossover in the solvents controls the activation of the slow process in biological macromolecules. Microscopic details of the slow process and of the dynamic transition are discussed.
INTRODUCTION Understanding protein dynamics is extremely important for understanding their functions. It is obvious that without molecular motions no biochemical reactions is possible and it is crucial to find a relationship between protein dynamics and activity. It has been found that many hydrated proteins shows onset of anharmonic motion at some temperature ~200-230K. It is usually observed as a sharp change in temperature variations of mean-squared atomic displacements, , from nearly harmonic behavior, ∝kT, at low T to much stronger anharmonic behavior at higher T [1-6] (Fig.1). It has been observed in neutron scattering, X-ray and Mossbauer spectroscopic measurements of wet proteins [3-8] and is usually interpreted as a dynamic transition. It has been found that the onset of anharmonicity correlates with onset of measurable biochemical activities [1,3,4,8,9], although exceptions have been reported [10,11]. There is therefore a great deal of interest in understanding the mechanism of the dynamic transition and its relationship to protein activity. Temperature of the dynamic transition, TD, appears to be essentially the same ~200K-230K in different hydrated proteins and DNA [1-8]. The dynamic transition does not appear in dry proteins and DNA even at temperatures as high as T~320K [3,4,6,7,12]. Moreover, the transition can be strongly influenced by solvent, shifting to higher T~270-280K for proteins embedded in glycerol [5,6,13] and being suppressed at least up to T~320K in proteins formulated in solid trehalose [6,14] (Fig.1). Dry proteins do not show measurable biochemical activity [15]. All these results suggest a direct relationship of the molecular motion activated above the dynamic transition to protein activity.
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T [K] Figure1. Mean-squared displacements of hydrogen atoms in lyso
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