Labeling strategies for ¹³C-detected aligned-sample solid-state NMR of proteins

¹³C-detected solid-state NMR experiments have substantially higher sensitivity than the corresponding ¹⁵N-detected experiments on stationary, aligned samples of isotopically labeled proteins. Several methods for tailoring the isotopic labeling are described that result in spatially isolated ¹³C sites so that dipole-dipole couplings among the ¹³C are minimized, thus eliminating the need for homonuclear ¹³C-¹³C decoupling in either indirect or direct dimensions of one- or multi-dimensional NMR experiments that employ ¹³C detection. The optimal percentage for random fractional ¹³C labeling is between 25% and 35%. Specifically labeled glycerol and glucose can be used at the carbon sources to tailor the isotopic labeling, and the choice depends on the resonances of interest for a particular study. For investigations of the protein backbone, growth of the bacteria on [2-¹³C]-glucose-containing media was found to be most effective.