13C-Detected Through-Bond Correlation Experiments for Protein Resonance Assignment by Ultra-Fast MAS Solid-State NMR



We present two sequences which combine (1H,15N) and (15N,13C) selective cross-polarization steps with an efficient variant of the J-based homonuclear transfer scheme, in which a spin-state-selective (S3E) block is incorporated to improve both resolution and sensitivity in the direct 13C dimension. We propose these two sequences as a part of a suite of four N–C correlation experiments allowing for the assignment of protein backbone resonances in the solid state. We illustrate these experiments under ultra-fast magic angle spinning conditions on two samples of microcrystalline dimeric human superoxide dismutase (SOD, 153×2 amino acids), in its diamagnetic (“empty”, ZnII) and paramagnetic (CuII, ZnII) states.