College Park, Maryland      June 6 - 10 , 2004

MP3: Influence of hydration on protein dynamics

J.H. Roh (University of Akron, Department of Polymer Science), G. Caliskan (Johns Hopkins University, Department of Biophysics), R. Gregory (Kent State University, Department of Chemistry), I. Peral, Z. Chowdhuri (NIST Center for Neutron Research), A.P. Sokolov (University of Akron, Department of Polymer Science)

It is obvious that protein dynamics affects significantly their biological activity. Direct relationship between the protein dynamics and the enzymatic activity, however, remains unclear. One way to observe simultaneous changes in protein motions and their functions is to analyze dependence of these parameters on hydration level of a protein. We present analysis of internal motion of proteins at different hydration levels in nano- and picosecond time window. Quasielastic incoherent neutron scattering spectra have been measured in a broad energy range (from ~1 μeV up to ~10 meV) by combining data from backscattering and time of flight spectrometers. The data show nonlinear increase of quasielastic contribution with increase of hydration level. Three different regions are identified: (i) slight change with hydration up to 0.20 g D2O / 1 g protein; (ii) strong change with hydration between 0.20 and 0.55 g D2O / 1 g protein; (iii) asymptotic behavior with hydration above 0.55 g D2O / 1 g protein. The dynamic transition observed in the temperature dependence of mean square displacements (MSDs) around 200 K appears only at hydration levels higher than 0.20 g D2O / 1 g protein. We ascribe the observed variations to a change in the slow relaxation process. It is shown that the intensity of the slow process correlates to the enzyme activity. The results suggest that slow relaxation process might be the essential internal motion to trigger the onset of enzymatic activity in proteins.

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