Efficient CO-CA transfer in highly deuterated proteins by band-selective homonuclear cross-polarization.

Robust and efficient band-selective magnetization transfer between CO and CA spins can be achieved in highly deuterated solid proteins by dipolar-based homonuclear cross polarization. The approach is designed for moderate magic-angle spinning rates and high external magnetic fields where the isotropic chemical shift difference of CO and CA considerably exceeds the spinning rate. The most efficient recoupling is achieved when the sum of effective radio-frequency fields on CO and CA resonances equals two times the spinning rate. This method can be directly implemented in proton-detected versions of inter-residual correlation experiments as needed for resonance assignment in protein solid-state NMR spectroscopy.