What Can be Learned About the Structure and Dynamics of Biomolecules from NMR

NMR can provide structural and dynamic information on proteins. The three-dimensional structure of a protein determined from NMR data consists of an ensemble (bundle) of different conformers that equally satisfy the experimental restraints. The precision of the bundle is described quantitatively by the root mean square deviation (RMSD) of the atomic coordinates. The RMSD can be computed by including all of the atoms of the protein or only a selection of them; the RMSD of the backbone atoms of ordered residues is the most commonly reported parameter. Protein dynamics can affect RMSD values. At the per-residue level, the motions of the proteins can reduce the local density of experimental restraints, leading to elevated (with respect to the rest of the protein) backbone RMSD values. However, the reverse is not true - locally high RMSD values do not necessarily indicate the presence of enhanced dynamics, but can simply be a consequence of restraint inconsistency. Protein dynamics takes place on a variety of different timescales, which can be sampled by different types of NMR measurements. The measurement of nuclear relaxation rates is a particularly relevant and common approach to sampling some of these timescales. NMR has provided ample evidence of the importance of protein dynamics for processes such as catalysis and molecular recognition. Finally, NMR experiments provide an easy, fast, and very convenient means of investigating intermolecular interactions. Chemical shift mapping is the most widely used approach for this kind of applications.