High-resolution proton-detected NMR of proteins at very fast MAS
Résumé
When combined with high-frequency (currently 60 kHz) magic-angle spinning (MAS), proton detection boosts sensitivity and increases coherence lifetimes, resulting in narrow H-1 lines. Herein, we review methods for efficient proton detected techniques and applications in highly deuterated proteins, with an emphasis on 100% selected H-1 site concentration for the purpose of sensitivity. We discuss the factors affecting resolution and sensitivity that have resulted in higher and higher frequency MAS. Next we describe the various methods that have been used for backbone and side-chain assignment with proton detection, highlighting the efficient use of scalar-based C-13-C-13 transfers. Additionally, we show new spectra making use of these schemes for side-chain assignment of methyl C-13-H-1 resonances. The rapid acquisition of resolved 2D spectra with proton detection allows efficient measurement of relaxation parameters used as a measure of dynamic processes. Under rapid MAS, relaxation times can be measured in a site-specific manner in medium-sized proteins, enabling the investigation of molecular motions at high resolution. Additionally, we discuss methods for measurement of structural parameters, including measurement of internuclear H-1-H-1 contacts and the use of paramagnetic effects in the determination of global structure.