Resolution Enhancement in Multidimensional Solid-State NMR Spectroscopy of Proteins Using Spin-State Selection

We show that the resolution of homonuclear multidimensional solid-state NMR correlation experiments can be significantly improved using transition selection and spin-state-selective polarization transfer techniques. The selection and transfer of single states allow the removal of the J-coupling contribution from the line width in both the direct and indirect spectral dimensions. This is demonstrated with a new spin-state-selective CO−Cα correlation experiment, applied to a microcrystalline 85-residue protein. With this new sequence, all four components of the CO−Cα cross-peaks are separated into different spectra, obtained by linear combination of four recorded data sets. Line narrowing of up to 44% was obtained on the protein sample for the spin-state-selective CO−Cα spectrum compared to a standard spin-diffusion experiment. The new technique also allows an easy distinction between “direct” and “relayed” transfer cross-peaks.