Biomolecular Flexibility Characterization Using Solution Phase THz Protein Dynamical Transition

The dynamical transition (DT) corresponds to the rapid onset of atomic motions at ca. 200K seen for minimally hydrated biomolecules. The DT is present in solution phase terahertz protein absorption measurements suggesting a benchtop DT technique. To move towards this application, several outstanding questions must be addressed: 1) does the THz absorption of protein solution reflect the protein structural dynamics, or the biological water dynamics; and 2) are THz solution phase DT measurements consistent with direct root mean square displacement measurements of hydrated powders. We show that for T<273 K protein absorption dominates terahertz transmission at 1 THz for protein solutions. Further we find that solution phase measurements reproduce the hydration dependence of the dynamical transition measured using neutron inelastic scattering. These results enable the use of THz DT for providing a fast measurement of biomacromolecule picosecond flexibility.