A mechanism for the onset of bioactivity in biomolecules

1. S.H. Chen1, L. Liu1, X. Chu1, Y. Zhang1, E. Fratini2, P. Baglioni2, A. Faraone3,4, E. Mamontov3,4, and V. García Sakai3,4 A mechanism for the onset of bioactivity in biomolecules 1MIT, 2University of Florence, 3University of Maryland, 4CHRNS DMR-0454672 Below 220 K biomolecules exist in a glassy state with no conformational flexibility and no biological function. Above 220 K this flexibility is restored, as shown by a sudden increase in the rate of change of the mean square displacement with temperature, and hydrated biomolecules become biologically functional. This “dynamical” transition is thought to be triggered by strong coupling between the biomolecules and hydration water, which also shows a transition. Using the backscattering spectrometer we have studied the temperature dependence of (1) the mean square displacement <x2> and (2) the mean translational relaxation time (T) of the hydration water in hydrated samples of lysozyme and DNA. We find that the characteristic temperature triggering biomolecular activity and the “dynamical” transition in d<x2>/dT coincides with the temperature of the Fragile-to-Strong dynamic crossover (FSC) phenomenon associated with T, TL=222  2 K. At this temperature the structure of the hydration water changes from predominantly high-density (more fluid) to low-density (less fluid), reflecting the existence of a second critical point at elevated pressure. Our findings suggest that the change in mobility of the hydration water at the FSC drives the dynamic transition in biomolecular materials. S.-H. Chen, L. Liu, X. Chu, Y. Zhang, E. Fratini, P. Baglioni, A. Faraone, E. Mamontov, submitted to J. Chem. Phys. (2006); S.-H. Chen, L. Liu, E. Fratini, P. Baglioni, A. Faraone, E. Mamontov, Proc. Nat. Acad. Sci. USA 103, 9012 (2006).