Magic angle spinning (MAS) NMR methods have the demonstrated ability to measure distances between atoms (nuclei) as well as a variety of angular constraints (e.g. peptide bond and side chain torsion angles). These methods were initially developed and demonstrated in test samples, such as small peptide crystals and model proteins, but are increasingly applied to a wide range of proteins. The measurement of 13C-13C distances via R2 width methods [1,2] is but one example of an increasingly versatile array of distance and torsion angle measurements. Macroscopically aligned lipid bilayer samples allow other approaches, in particular measurements that allow determination of the orientation (and motion) of proteins or peptides relative to the membrane, such as transmembrane helix tilt and tryptophan interfacial anchors [3 - 5].
The weak point of most NMR methods is the relatively low sensitivity of the method, compared to other biophysical techniques. The results in the requirements for relatively large sample sizes and long acquisition times. Ongoing develpments on the hardware and methodology aim at substantial sensitivity improvements, for example through the application of dynamic nuclear polarization (DNP) methods . See also this page.