Protein Conformational Dynamics Measured With Terahertz Time Domain Spectroscopy

摘要

Tertiary structural vibrational modes of proteins are at far infrared or terahertz frequencies. These modes involve collective motion of many atoms and are indicative of the protein structure, hydration and binding with ligands and other proteins[1-3]. Previously we have shown that the absorbance strongly resembles the vibrational mode density of states. Our measurements of conformational change have focused on the hydration, denaturing effects, and photoactive proteins bacteriorhodopsin. In addition we have shown a strong sensitivity of the terahertz response to heme protein oxidation state[4]. We will discuss the impact of these results on biomolecular switching mechanisms as well as applications to biomolecular sensing. In the case of bacteriorhodopsin the conformational state is controlled through photoexcitation and monitored by UV/Vis absorption spectroscopy[3]. In the "active" state, critical to the full photocycling and therefore biological activity, the terahertz absorbance and index are increased relative to the resting state. This increase could be associated with a red shifting of the density of states, consistent with increased structural flexibility in the active state. However in the case of photoactive yellow protein we see a decrease in the index and absorbance consistent with a decrease in tertiary structure suggesting partial unfolding in the active state. We have investigated the effect of unfolding directly by examining denatured samples of hen egg white lysozyme (HEWL). In Figure 1 we show the change in the absorbance and index as HEWL is thermally denatured.