Aromatic spectral editing techniques for magic-angle-spinning solid-state NMR spectroscopy of uniformly 13C-labeled proteins

Author(s)
Jonathan K. Williams , Klaus Schmidt-Rohr and Mei Hong
Publisher
Solid State NMR
Year
2015
Volume
72
Pages
118-126
DOI
10.1016/j.ssnmr.2015.09.006

Abstract

The four aromatic amino acids in proteins, namely histidine, phenylalanine, tyrosine, and tryptophan, give highly overlapped 13C chemical shifts between 100 and 160 ppm, and have so far been largely neglected in solid-state NMR determination of protein structures. Yet aromatic residues play important roles in biology through π−π and cation-π interactions. To better resolve and assign aromatic residues’ 13C signals in magic-angle-spinning (MAS) solid-state NMR spectra, we introduce two spectral editing techniques. The first method uses gated 1H decoupling in a proton-driven spin-diffusion (PDSD) experiment to remove all protonated 13C signals and retain only quaternary 13C signals in the aromatic region of the 13C spectra. The second technique uses chemical shift filters and 1.H-13C dipolar dephasing to selectively detect the Cα, Cβ and CO cross peaks of aromatic residues while suppressing the signals of all aliphatic residues. We demonstrate these two techniques on amino acids, a model peptide, and the microcrystalline protein GB1, and show that they significantly simplify the 2D NMR spectra and both reveal and permit the ready assignment of the aromatic residues’ signals.