Large protein complexes with extreme rotational correlation times investigated in solution by magic-angle-spinning NMR spectroscopy

We show that large protein complexes can be investigated in solution using magic-angle-spinning (MAS) NMR spectroscopy without the need for sample crystallization or precipitation. In order to efficiently average anisotropic interactions with MAS, the rotational diffusion of the molecule has to be suppressed. This can be readily achieved by lowering the sample temperature and by adding glycerol to the protein solution. The approach is demonstrated using the human small heat shock protein (sHSP) alphaB-Crystallin, which forms oligomeric assemblies of approximately 600 kDa. We suggest this scheme as an approach for overcoming size limitations imposed by overall tumbling in solution-state NMR investigations of large protein complexes.