Observation of protein domain motions by neutron spectroscopy.

High-resolution inelastic neutron scattering, which is available with neutron spin-echo spectroscopy (NSE) is introduced as a tool for the analysis of biomolecule flexibility. Coherent scattering in a range where it is sensitive to length scales of nanometers and covering a time range from picoseconds to several 100 ns makes the motion of larger subdomains within proteins visible. We show that and how the internal domain motion within a protein in solution can be measured. Comparison with displacement patterns from normal mode analysis provides further insight into the nature of the geometry of the motions that lead to the observed dynamic signature. The NSE experiment on alcohol dehydrogenase (ADH) is used as example to illustrate the general principles of the method.