Protein crystal dynamics studied by time-resolved analysis of X-ray diffuse scattering

IT has been known for many years that information about the dynamics of molecules in crystals can be obtained from diffusely scattered radiation1–3. Intermolecular motions coupled on a large scale generate diffuse spots centred on the Bragg peaks, whereas locally coupled intramolecular motions produce a diffuse background. Although information about protein dynamics has recently been derived from diffusely scattered radiation4–6, molecular motions could not be distinguished from static disorder in these experiments, because of a lack of time resolution. Provided the energy of the radiation is well defined, however, time resolution can be obtained from an energy analysis of the scattered radiation. We report here the use of Mössbauer radiation, the energy of which is characteristically well defined, to probe the molecular dynamics of a myoglobin crystal. Information about molecular motions is extracted from the ratio of elastically to inelastically scattered photons, which by using Mössbauer radiation can be precisely determined7. At room temperature we obtain a rpot-mean-squared amplitude for intermolecular motions of 0.13 Å.