A mechanism for the onset of bioactivity in biomolecules

1
A mechanism for the onset of bioactivity in
biomolecules
S.H. Chen1, L. Liu1, X. Chu1, Y. Zhang1, E.
Fratini2, P. Baglioni2, A. Faraone3,4, E.
Mamontov3,4, and V. García Sakai3,4
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 ltx2gt 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 dltx2gt/dT coincides
with the temperature of the Fragile-to-Strong
dynamic crossover (FSC) phenomenon associated
with ?T, TL222 ? 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).