A practical guide for solid-state NMR distance measurements in proteins

Rotational resonance (R²) and rotational echo double resonance (REDOR) are powerful solid-state NMR techniques that can be applied in a site-directed fashion for precise distance measurements in proteins. These tools are well suited for systems in which a few precise distance measurements are needed to understand a mechanism or map a binding site, particularly if this information is unavailable from x-ray crystallography or solution NMR, as is often the case for membrane proteins. Strategies and challenges in the design and implementation of such experiments are described and illustrated with experiments probing mechanisms of transmembrane signaling in bacterial chemotaxis receptors.