Solid-state NMR

  • Solid-state NMR is a powerful method to investigate biomolecules under physiologically relevant conditions. Similarly to X-ray crystallography and solution NMR, solid-state NMR produces high resolution information but it offers unique advantages. For example, it does not require fast tumbling of molecules as solution NMR does. As a result, large complexes such as proteins inserted in lipid membranes can be investigated. In fact, excellent sensitivity and homogeneity can be obtained from last molecular systems. Another important advantage of solid-state NMR is that it does not require crystals as X-ray crystallography does. Therefore, heterogeneous samples, including proteins in complex with lipids an aggregates, can be effectively analyzed using solid-state NMR. The combination of these assets uniquely positions solid-state NMR to the studies of biomolecular systems not amenable to other techniques. In recent years, solid-state NMR has also been used to study phenomena in living cells, a new methodology which is extracting high resolution information about in vivo phenomena.
  • Modern biological solid-state NMR is typically performed on isotopically labeled biomolecules. For instance, proteins can be uniformly or site-specifically labeled with 13C, 15N, and 2H. High resolution multidimensional experiments that characterize various nuclear spin interactions, such as chemical shifts, dipolar interactions and quadrupolar interactions, are carried out on these samples to assign the individual signals. Subsequently, computational methods are used to calculate and refine structures based on the NMR restraints (e.g. distances, torsion angles). Not only structures but also dynamics can be obtained from solid-state NMR experiments since relaxation rates can be measured. This is very important because motions play important roles in the function of biomolecules, including molecular recognition between receptors and ligands and allosteric communication within binding sites of proteins.