Solid State NMR Methods & Measurements

13C-13C distance measurements in hydrophobic core

Magic angle spinning (MAS) NMR spectroscopy enables the determination of both structure and dynamics on an atom-by-atom level, in a variety of biological (and non-biological) “solid” materials. Most importantly, it can do so in amorphous and/or non-crystalline samples, in absence and presence of hydration. Thus, MAS NMR is a crucial tool in studies of amyloid-like fibrils, nanocrystals, nano-materials, biological macro-assemblies as well as membrane-bound proteins. In these challenging contexts, we use ssNMR to provide a wealth of information through a growing toolkit of structural and motional measurements that probe individual atoms and residues:

Structural measurements

  • Distances between atoms (nuclei) can be measured with sub-nm resolution. By combining clever spectroscopic and labeling strategies one can target those sites of particular interest, whether within the protein core (figure to right) of protein-protein interfaces [1,2],
  • Torsion angles define the geometry of the protein backbone and side chains. Various MAS NMR measurements probe this very effectively, based on either the NMR resonance frequencies or direct dipolar correlation measurements.
  • Orientations: in the case of solid-state NMR studies of membrane proteins or peptides, macroscopically aligned lipid bilayer samples allow for complementary data. These include measurements of the orientation (tilt) of proteins or peptides relative to the lipid bilayer membrane. See e.g. our 2H-NMR-based GALA experiments  [3 – 4].

Measuring dynamics & dynamic proteins

  • Dynamics measurements are equally important as structural measurements, both the understand the structure of protein assemblies and to reveal the mechanism of protein function, which relies on dynamics.
  • Variable temperature measurements by MAS NMR can span a very broad temperature range, since the method works equally well on unfrozen hydrated sample at or above room temperature, as on frozen samples far below zero.
  • NMR relaxation measurements work just as well in MAS NMR as in solution NMR, and provide in-depth insights into the motion of individual atoms and amino acids.
  • Order parameter measurements in MAS NMR probe the effect of dynamics on the dipolar couplings or quadrupolar couplings, and thus provide (orientation-dependent!) insight into local dynamics.
  • Solution-NMR-like measurements (using “scalar couplings”) reveal flexible regions of molecules, and allow them to studied in parallel to the more conventional ssNMR studies of the rigid parts of protein aggregates.
  • Solvent exposure measurements by MAS NMR reveal those atoms or residues that are closest to the surface of aggregates, crystals, or membranes. Although not dynamics measurements per se, these usually also are the more dynamic sites.

Tools & techniques

  • Aside from using (and contributing to) the broad palette of MAS NMR structural tools, we also work on more “practical” contributions that make the ssNMR as fast and efficient as possible: e.g. ultracentrifugal packing devices, chemical shift referencing, etc.
  • Dynamic nuclear polarization (DNP) is used to dramatically enhance MAS NMR structural measurements (at low temperature), opening up exciting new frontiers of science [5].

 


Selected References

  1. Van der Wel, P.C.A. et al. (2009) Targeted 13C-13 Distance Measurements in a Microcrystalline Protein via J-Decoupled Rotational Resonance Width Measurements. ChemPhysChem 10 (9-10): 1656-1663 DOI
  2. Li, J. and Van der Wel, P.C.A. (2013) Spinning-rate encoded chemical shift correlations from rotational resonance solid-state NMR experiments. J Magn Reson 230: 117-124
  3. Van der Wel, P. C. A. et al.. (2002) “Geometry and intrinsic tilt of a tryptophan anchored transmembrane alpha-helix determined by 2H NMR.” Biophys. J. 83, 1479-1488 * (Introduces the 2H-NMR based GALA approach)
  4. Van der Wel, P.C.A. et al. (2007) “Orientation and motion of tryptophan interfacial anchors in membrane-spanning peptides.“Biochemistry 46(25):7514-24
  5. Van der Wel, P.C.A. et al. (2006)  “Dynamic nuclear polarization of amyloidogenic peptide nanocrystals: GNNQQNY, a core segment of the yeast prion protein Sup35p.” J. Am. Chem. Soc. 128:10840-10846 *