NMR residual dipolar couplings as probes of biomolecular dynamics

Residual dipolar couplings (RDCs) offer a view of dynamic processes that is very complementary to other nuclear magnetic resonance (NMR) spectroscopic approaches. This review discusses three topics: the relationship of RDCs to molecular structure and dynamics; molecular alignment; and biomolecular dynamics from residual dipolar couplings. For the first topic, focus is on anisotropic averaging of the dipolar interaction, rigid molecules, and flexible molecules. As for molecular alignment, emphasis is on methods for inducing molecular alignment, experimental determination of the alignment tensor, and assessment of the independence of RDC data acquired in multiple alignment media. Finally under biomolecular dynamics, discussion is on domain motions, local segmental motions, generalized order parameters from residual dipolar couplings, peptide plane dynamics, ensemble simulated annealing, and side-chain dynamics.