Distilling a crowded spectrum: the overlap of terahertz protein collective vibrations with functional motions

We use massive averaging over the thermally populated energy landscape to calculate a realistic terahertz vibrational density of states (VDOS), isotropic absorption and anisotropic absorption for the protein chicken egg white lysozyme (CEWL). We find that the VDOS shows little variation with starting structure, however both the isotropic and anisotropic absorption vary considerably with starting structure. Averaging over the population leads to a smooth featureless average isotropic spectrum, in agreement with THz absorption measurements however resonant bands emerge for the anisotropic averaging. Further we find the vibrational ensemble in fact has frequency dependent features associated with large overlap with functional displacements.