FIGURE 4.

HCCH experiments for measuring side chain angles. (A) Pulse program schematic for a HCCH experiment. (B) Simulated HCCH curves for measurement of the χ₂ angle in glutamine residues (a CβH₂-CγH₂ spin system), for χ₂ = 60 or 180°. (C) Variation of the mid-rotor-period intensity as a function of the χ₂ angle. (D,E) Simulated and experimental data measuring the χ₂ angle of glutamine residues in the core of polyglutamine amyloid. (F) Application to the χ₁ angle in polyglutamine amyloid. (G) Visualized structural model for how the polyglutamine amyloid core is structured, based on the best-fit dihedral angle solutions. (H) Overview of the ambiguity in some, but not all, of the measured χ angles. The colored bars indicate those angles that are consistent with the observed torsion angle curves. The red bars on the left apply to conformer ‘a’, and the blue ones (right) to conformer ‘b’. Figure adapted from ref. (Hoop et al., 2016) with permission.