Solid State Protein NMR
Solid-state NMR may be used to obtain structural and dynamic information on biological molecules which are not easily examined in solution, such as membrane proteins and protein fibrils. Advances in probe and magnet design, pulse sequences, and isotopic labeling strategies have all contributed to the growth of solid state NMR for structural determination of biomolecules.
Although there is no limit to the molecule weight of the compound being studied, limitations to size often correspond to the amount of spectral crowding that can be tolerated. Spectral simplification is achieved with selective amino acid-type labeling and sparse 13C labeling to reduce the number of one-bond 13C-13C dipolar couplings. Significant progress is being made in low-temperature Dynamic Nuclear Polarization (DNP) MAS for studying biomolecules. DNP produces a dramatic enhancement of signal strength over conventional methods which allows for much shorter acquisition times and/or smaller sample amounts. Partial protonation may also be used to enhance 13C resolution and sensitivity at high MAS speeds and for low-temperature DNP methods.