MAS solid state NMR of proteins: simultaneous 15N-13CA and 15N-13CO dipolar recoupling via low-power symmetry-based RF pulse schemes

The generation of efficient RN (n) (nu)s,(nu)k symmetry-based low-power RF pulse schemes for simultaneous N-15-(13)CA and N-15-(CO)-C-13 dipolar recoupling is demonstrated. The method involves mixing schemes employing phase and amplitude-modulated dual band-selective 180A degrees pulses as basic R element and tailoring of the RF field-modulation profile of the 180A degrees pulses so as to obtain efficient magnetisation transfer characteristics over the resonance offset range of the nuclei involved. Mixing schemes leading to simultaneous N-15-(13)CA and N-15-(CO)-C-13 dipolar recoupling would permit the one-shot acquisition of different chemical shift correlation spectra that are typically utilized for protein backbone resonance assignments and thereby save data acquisition time. At representative MAS frequencies the efficacies of the mixing schemes presented here have been experimentally demonstrated via the simultaneous acquisition of {3D CONH and 3D CANH}, {3D CONH and 3D CO(CA)NH} and {3D CONH, 3D CANH, 3D CO(CA)NH and 3D CA(CO)NH} spectra generated via the magnetisation transfer pathways H-1 -> (CO)-C-13 -> N-15 -> H-1 (CONH), H-1 -> (13)CA -> N-15 -> H-1 (CANH) and H-1 -> (CO)-C-13 -> (13)CA -> N-15 -> H-1 (CO(CA)NH) and H-1 -> (13)CA -> (CO)-C-13 -> N-15 -> H-1 (CA(CO)NH).