Protein self-assemblies play essential roles in many biological processes
ranging from bacterial and viral infections to basic cellular functions. They can be
found in a wide range of supramolecular architectures, in homomeric and heteromeric
forms, and often in symmetric arrangements. The biological function will then be
dictated by the structure of the assembled object rather than by the subunits. Atomicresolution
structural investigations of protein assemblies can be tedious because of their
size, their insolubility, and often their non-crystallinity. Solid-state NMR (ssNMR) is a
powerful technique used to obtain high-resolution structural models of these complex
assemblies and to study their assembly processes and interactions at the atomic level.
Unrestricted by object size or solubility, ssNMR can be applied to study the structures
and interactions of macromolecular assemblies such as proteins in a membrane
environment, protein filaments, pores, fibrils or oligomeric species. This chapter
focusses on the established methods and recent advances in magic angle spinning
(MAS) ssNMR for the detection of structural restraints in macromolecular protein
assemblies and the determination of their atomic-resolution models. We will review
different 13C and 15N isotope labelling approaches necessary to detect and differentiate
intra- and intermolecular distance restraints that define the protein subunit structure and
their relevance in the context of symmetric assemblies. The collection, and
interpretation of, structural restraints in protein assemblies by ssNMR will be
discussed. We will also introduce the recent developments in ultra-fast MAS ssNMR to
study and determine atomic structures of sub-milligram quantities of molecular
assemblies using proton detection. Finally, our aim is to also illustrate the
complementarity of ssNMR to other techniques in structural biology such as solutionstate
NMR, mass-per-length scanning transmission electron microscopy (STEM)
measurements and cryo-electron microscopy.
Keywords: Amyloid fibrils, Bacterial filaments, Macromolecular assemblies, Magic
angle spinning, Nuclear magnetic resonance, Protein assembly, Protein complexes, Selfassemblies,
Solid-state NMR, Structural biology, Structure determination.
