Rotational resonance in uniformly ~(13)C-labeled solids: effects on high-resolution magic-angle spinning NMR spectra and applications in structural studies of biomolecular systems

摘要

We describe investigations of the effects of rotational resonance (R_2) on solid state ~(13)C NMR spectra of uniformly 13C-labeled samples obtained under magic-angle spinning (MAS), and of the utility of R_2 measurements as structural probes of peptides and proteins with multiple uniformly labeled residues. We report results for uniformly ~(13)C-labeled -alanine and -valine in polycrystalline form, and for amyloid fibrils formed by the 15-residue peptide Aβ_(11-25) with uniform labeling of a four-residue segment. The MAS NMR spectra reveal a novel J-decoupling effect at R_2 conditions that may be useful in spectral assignments for systems with sharp ~(13)C MAS NMR lines. Pronounced dependences of the apparent isotropic ~(13)C NMR chemical shifts on MAS frequency near R_2 conditions are also observed. We demonstrate the feasibility of quantitative ~(13)C–~(13)C distance determinations in L-valine, and qualitative determinations of inter-residue ~(13)C-~(13)C contacts in Aβ_(11-25) fibrils. Finally, we demonstrate a "relayed" R~2 technique that may be useful in structural measurements on systems with poorly resolved ~(13)C MAS NMR lines.