Solid State NMR Methods & Measurements

13C-13C distance measurements in hydrophobic core

Magic angle spinning (MAS) NMR spectroscopy enables the determination of structure and dynamics on an atom-by-atom level, in both biological and non-biological “solid” or semi-solid materials. Importantly, it can do so in amorphous and/or non-crystalline samples, in absence and presence of hydration, and across a wide range of temperatures. Thus, MAS NMR is a crucial tool in studies of amyloid-like fibrils, nanocrystals, nano-materials, macromolecular assemblies and membrane-bound proteins. In certain cases, we combine the MAS NMR also with DNP enhancement, to allow for studies of otherwise inaccessible. In these challenging contexts, we use ssNMR to provide a wealth of molecular information through a growing toolkit of techniques:

Chemistry by ssNMR

  • The chemical composition of complex (solid) samples can be monitored and analyzed by ssNMR, as the observed signals are determined by the chemical structure.
  • SSNMR can also be used to detect and determine chemical modifications and chemical changes (e.g. degradation).

Structural ssNMR measurements

  • Changes in supramolecular structure and e.g. crystal polymorphs can be detected by ssNMR.
  • Distances between atoms (nuclei) can be measured with sub-nm resolution. By combining spectroscopic and labeling strategies one can target sites of special interest, both within molecules or at intermolecular interfaces [1,2],
  • Torsion angles define the geometry of the protein backbone and side chains. We use MAS NMR experiments to measure these angles, providing unique insights into e.g. the polyQ amyloid core structure [6].
  • Orientations: aligned samples allow for ssNMR measurements of the orientation of molecules or chemical groups (See e.g. our 2H-NMR GALA experiments  [3 – 4]).

Measuring dynamics & dynamic proteins

  • MAS NMR methods enable crucial dynamics measurements, with relevance to elucidating the structure and function of complex nano-assemblies.
  • 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.
  • A toolkit of dynamics-sensitive experiments allow for the detection and measurement of site-specific dynamics:
    • NMR relaxation measurements work provide insight into the motion of individual atoms and amino acids.
    • Order parameter measurements probe the effect of dynamics on the dipolar couplings or quadrupolar couplings, and thus provide (orientation-dependent!) insight into local dynamics.
    • Indirectly related are solvent exposure measurements that reveal those atoms or groups that are closest to the surface of aggregates, crystals, or membranes. Although not dynamics measurements per se, these exposed sites are generally dynamic.
  • Various ssNMR experiments can be used to simplify spectra of complex samples, via “spectral editing”.  Dynamics-based Spectral Editing (DYSE) ssNMR has proved very important to our studies of a wide range of samples (see our review [8])

Dynamic nuclear polarisation (DNP)

DNP is an important modality enhancing and expanding the use of modern solid-state NMR, based on leveraging the higher sensitivity inherent to electron rather than nuclear polarisation. Integrated DNP-ssNMR experiments can be used to dramatically enhance the sensitivity to enable unprecedented new MAS NMR measurements that open up exciting new frontiers of science [5]. In our prior work we showed how DNP can be used to selectively enhance the signal of surfaces of nano materials, and extend this enhancement into the bulk of such materials to allow for multidimensional DNP-enhanced ssNMR [5]. Moreover, we recently used DNP to enable similar multidimensional ssNMR experiments of disease-relevant protein aggregates (from Huntington’s disease) in the absence of isotopic labeling [10].

Other tools & techniques

Aside from using (and contributing to) the broad palette of MAS NMR spectroscopic methods, we also work on more “practical” contributions that make the ssNMR as fast and efficient as possible, such as the ultracentrifugal sample packing devices for which we recently published our blueprints and design principles [9].

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 *
  6. Hoop et al. (2016) Huntingtin exon 1 fibrils feature an interdigitated β-hairpin-based polyglutamine core. PNAS 113(6): 1546-1551 (DOI)
  7. Lin et al. (2017) Fibril polymorphism affects immobilized non-amyloid flanking domains of huntingtin exon1 rather than its polyglutamine core. Nature Commun.  [URL]
  8. Matlahov & Van der Wel (2018) Hidden motions and motion-induced invisibility: dynamics-based spectral editing in solid-state NMR.  Methods in press [URL]
  9. Mandal et al. (2017) On the use of ultracentrifugal devices for routine sample preparation in biomolecular magic-angle-spinning NMR. J Biomol NMR 67:165–178  [online]
  10. Smith et al. (2018) Structural Fingerprinting of Protein Aggregates by Dynamic Nuclear Polarization-Enhanced Solid-State NMR at Natural Isotopic Abundance. JACS 140, 14576−14580 [online]