Rapid assignment of protein side chain resonances using projection-reconstruction of (4,3)D HC(CCO)NH and intra-HC(C)NH experiments.

The reconstruction of higher-dimensional NMR spectra from projections can provide significant savings in instrument time. Here, we demonstrate its application to the (4,3)D HC(CCO)NH and intra-HC(C)NH experiments. The latter experiment contains a novel intra-residue filter element, which selectively correlates the side chain resonances with the corresponding intra-residue amide resonances. Compared to the conventional HC(C)NH experiment, the intra-HC(C)NH experiment reduces the spectral complexity and thus the minimum number of projections required for artifact-free reconstruction by half. The use of the projection-reconstruction technique allows rapid data collection and unambiguous assignment of aliphatic side chain nuclei at high resolution.