Thermal motions and function of bacteriorhodopsin in purple membranes: effects of temperature and hydration studied by neutron scattering

摘要: Abstract The internal dynamics of bacteriorhodopsin, the light-driven proton pump in purple membrane Halobacterium halobium, has been studied by inelastic neutron scattering for various conditions temperature and hydration. Light activation can take place when is vibrating harmonically. The ability protein to functionally relax complete photocycle initiated absorption a photon, however, strongly correlated with onset low-frequency, large-amplitude anharmonic atomic motions membrane. For normally hydrated sample, this occurs at about 230 K, where dynamical transition from low-temperature harmonic regime observed. In moderately dry samples, on other hand, which slowed down several orders magnitude, no observed remain approximately up room temperature. These results support hypothesis, made previous diffraction studies, that "softness" modulates function bacteriorhodopsin allowing or not protein.