Backbone assignment of perdeuterated proteins by solid-state NMR using proton detection and ultrafast magic-angle spinning

Solid-state NMR is useful for getting structural information for insoluble proteins. In this protocol, chemical shifts for backbone atoms are assigned using proton detection and ultrafast magic-angle spinning of perdeuterated proteins. Solid-state NMR (ssNMR) is a technique that allows the study of protein structure and dynamics at atomic detail. In contrast to X-ray crystallography and cryo-electron microscopy, proteins can be studied under physiological conditions—for example, in a lipid bilayer and at room temperature (0–35 °C). However, ssNMR requires considerable amounts (milligram quantities) of isotopically labeled samples. In recent years, 1 H-detection of perdeuterated protein samples has been proposed as a method of alleviating the sensitivity issue. Such methods are, however, substantially more demanding to the spectroscopist, as compared with traditional 13 C-detected approaches. As a guide, this protocol describes a procedure for the chemical shift assignment of the backbone atoms of proteins in the solid state by 1 H-detected ssNMR. It requires a perdeuterated, uniformly 13 C- and 15 N-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; 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 ssNMR. Depending on the spectral quality and complexity of the protein, data acquisition and analysis are possible within 2 months.