Method Development

Last but not least we continue to develop new solid-state NMR methods. For instance, we described a user-friendly protocol for the chemical shift assignment of the backbone atoms of proteins in the solid state by 1H-detected solid-state NMR. It requires a perdeuterated, uniformly 13C- and 15N-labeled protein sample with subsequent proton back-exchange to the labile sites. The sample needs to be spun at a minimum of 40 kHz in the NMR spectrometer. With a minimal set of five 3D NMR spectra, the protein backbone and some of the side-chain atoms can be completely assigned. These spectra correlate resonances within one amino acid residue and between neighboring residues (see Figure); taken together, these correlations allow for complete chemical shift assignment via a 'backbone walk'. This results in a backbone chemical shift table, which is the basis for further analysis of the protein structure and/or dynamics by solid-state NMR (Fricke et al., Nature Protocols 2017). More recently, we extended our approach to four dimensions (Zinke et al., Angewandte Chemie 2017) and additionally exploited sophisticated methyl labeling schemes for the detection of intra- and intermolecular distance restraints (Zinke et al., ChemPhysChem 2018). Those proton-detected solid-state NMR strategies will be employed to study membrane-integrated proteins.