Is the Protein Dynamical Transition useful?

Abstract

Terahertz spectroscopy potentially provides a fast and easy method to measure the protein dynamical transition [1,2].Typically the THz measurements are performed using solutions, avoiding the difficulty in hydration control conditions typically used in for neutron scattering, however there is some question as to whether the freezing of the solution effects protein structure or dynamics. More significantly, does the rapid onset of biomolecular dynamics occurring ∼200 K provide any new insight into specific protein structural dynamics, or is it strictly a reflection of the hydration water? To address these questions we performed terahertz dynamical transition measurements in the 100-270 K range and between 0.15 - 2.00 THz on buffered solutions, dry glycerol solutions and minimally hydrated glycerol solutions. Buffer solution measurements using chicken egg white lysozyme, myoglobin and orange carotenoid protein with concentrations between 2 - 30 mM follow Beer's law concentration dependence below 15 mM from which terahertz molar absorptivity of the hydrated protein can be extracted. For dry glycerol-protein solutions, the dynamical transition is absent. The transition is present for 0.5 g water/g protein. The transition is identical to the buffer solution results, indicating that the freezing of the bulk water does not effect the measurements and it is not necessary to use the hydrated glycerol method. Finally we examine how light induced structural changes of OCP can induce changes in the dynamical transition, and correlate these changes with other structural flexibility measurements to identify the mechanism responsible for the DT's sensitivity to protein structural change. This work is supported by NSF grants DBI 1556359 and MCB 1616529, DOE grant DE-SC0016317 and NIH STTR R41 GM125486.