Aromatic spectral editing Techniques for magic-Angle-spinning solid-state NMR spectroscopy of uniformly 13C-labeled proteins
Publication date: Available online 14 September 2015
Source:Solid State Nuclear Magnetic Resonance
Author(s): Jonathan K. Williams, Klaus Schmidt-Rohr, Mei Hong
The four aromatic amino acids in proteins, namely histidine, phenylalanine, tyrosine, and tryptophan, give highly overlapped 13C chemical shifts between 100 and 160ppm, and have so far been largely neglected in solid-state NMR determination of protein structures. Yet aromatic residues play important roles in biology through ?-? and cation-? 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 1H-13C dipolar dephasing to selectively detect the C?, C? 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.
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