Nuclear magnetic resonance measurements of slow conformational dynamics in macromolecules

This chapter describes the application of a variety of NMR techniques including line shape analysis, rotating-frame relaxation rate measurements, and saturation transfer methods to slow conformational transitions in macromolecules. In this context, slow refers mainly to processes that occur much slower than overall tumbling rates. All of the NMR parameters—for example, chemical shift, coupling constants, relaxation rates, and line shapes—can be affected by chemical exchange processes. Although molecular dynamics simulations can shed light on the effects of sub-nanosecond motions on NMR observables such as coupling constants and cross-relaxation rate constants, they cannot be used to determine the influence of much slower motions on the NMR parameters. The combined use of rotating-frame relaxation methods, temperature dependent measurements of line shapes and magnetization transfer experiments allows in favorable cases the examination in some detail of exchange processes that occur on the millisecond time scale. Such measurements complement the information obtainable from heteronuclear relaxation methods that probe mainly the fast librational motions in macromolecules and may provide information important for functional studies of biological macromolecules.