INTERNAL DYNAMICS OF GLOBULAR-PROTEINS - COMPARISON OF NEUTRON-SCATTERING MEASUREMENTS AND THEORETICAL-MODELS

The picosecond internal dynamics of globular proteins are explored by measuring inelastic neutron scattering and comparing the results with theoretical models. For frequencies below 200 cm-1, the spectra from different proteins are similar under the same experimental conditions. At low temperatures or hydration the dynamics are approximately harmonic, whereas at high temperatures or hydration there is considerable quasielastic scattering. The quasielastic scattering can be explained by a shift of the density of states to lower frequences with increased friction, but picosecond timescale transitions between slightly different conformations might also contribute. Spectra calculated from molecular dynamics simulations of myoglobin at 80 K and 300 K approximately reproduce the observed changes with temperature. The simulations show evidence for restriction of the conformational space sampled at 80 K, relative to 300 K.