Recent Developments in Stable-Isotope-Aided Methods for Protein NMR Spectroscopy

The existence of stable isotopes, such as ²H, ¹³C, and ¹⁵N, is a blessing from nature for protein NMR spectroscopy, because protons, carbons, and nitrogens are the major components of proteins. Thus, protein NMR has deeply benefited from these stable isotopes. Since their natural abundance is very low, selective enrichment and/or depletion of these nuclei for incorporation into proteins have/has been desired. These skills are called stable isotope labeling, which is an old technique that is undergoing renewal in protein NMR spectroscopy. Various stable-isotope-labeling methods are illustrated in Figure 1.