Structure and dynamics of bio-solids
Instruct has 3 centres offering Solid State NMR across Europe. Navigate the map and click on the pins to discover centres near you.
While solution NMR is already a well-established technique for the structural determination of biomolecules in solution, solid state (SS) NMR has experienced tremendous methodological and technical advancements over the last decade, and is reaching the status of a powerful technique for the mechanistic and structural investigation of biological solids. SS NMR is intrinsically free of the limitations imposed on liquid state NMR by the size of the system under investigation, as long as the number of magnetic nuclei is that of a molecule up to 30 kDa, and can handle molecular systems that are not amenable to X-ray studies, such as insoluble aggregates and fibrils. New exciting possibilities are discovered almost daily and SS NMR is thus expected to open new avenues for modern biology in the near future. SS NMR within Instruct provides an invaluable tool for the determination of the structure and dynamics of systems that are beyond the reach of other structural methods. It has a wide applicability, ranging from membrane proteins to nano-crystalline materials to insoluble aggregates and fibrils. State-of-the-art instruments and experimental protocols enable the determination of a number of biophysical parameters allowing, along with structural determination, the characterization of both the internal and global dynamics of the system at atomic detail. These features make SS NMR a vital technique in structural biology.
Solid State NMR spectroscopy measurements can be performed in virtually any kind of biological solid. 13C-15N labelled samples are required, since the vast majority of the experiments are based on direct heteronuclear detection. Recently, 2H labelled proteins back exchanged in water are becoming popular, since they allow for proton detection. Local order in the solid as well as its hydration state are known to dramatically affect spectral quality; micro- to nanocrystalline proteins are therefore the target of these studies.
Magic angle spinning is used to average the anisotropic interactions, so the sample is packed in zirconia rotors from 1.3 to 4 mm. The amount of sample ranges from about 2 mg in the 1.3 rotor to 50 mg in the 4 mm rotor. Despite the much smaller amount of material, the signal to noise ratio in the 1.3 rotor can be almost as good as in larger rotors, because, among other factors, of the higher efficiency of the smaller coils. Since the RF heating in SSNMR is more severe than in solution, low salt samples are required.
The acquisition of spectra takes from a few minutes (1D spectra) to a few days (3D spectra), depending on the amount of sample and its quality.
Once the sample is placed in the probehead and the desired temperature and spinning rates have been reached, the pulses are calibrated and polarization transfer (from proton to insensitive nuclei) must be set up. Usually it is accomplished by cross-polarization, while in highly mobile systems it may be obtained by INEPT, as in liquids. Several pulse sequences are routinely available for assignment and structural characterization, and local and global dynamics may be easily estimated.
The spectrometer provides time-domain data that are transformed automatically by the software into frequency-domain data.