Homonuclear carbon 3D spectroscopy with ultrafast magic-angle spinning

Three-dimensional (3D) spectra are essential for resonance assignment of complex biomolecules. Here we present a CCC spectrum that correlates the three backbone carbon resonances of protein residues and is applicable for the fast magic-angle spinning regime, here 55 kHz. The corresponding pulse sequence is constructed from dipolar recoupling elements that transfer both x- and y-elements of magnetization (preservation of equivalent pathways). The sequence is proposed as a well-resolved option for assignment of CB resonances, which are particularly useful for determination of residue type. The sensitivity of this CCC spectrum is found to be surprisingly high, considering that it is a carbon detected sequence, at about 50-100 percent of the sensitivity measured in a comparable CB(CA)NH spectrum. The sequence affords high resolution intra-residue correlations for all standard amino acids, including for proline residues.