Figure 2.

Glucagon fibrils contain two distinct β-strand conformations. a, Representative 2D ¹³C-¹³C correlation spectrum with 30 ms ¹³C spin diffusion (SD), showing well resolved chemical shifts of the glucagon fibrils. b, Representative 2D ¹⁵N-¹³Cα correlation spectrum. c, Selected 2D ¹³C-¹³C and ¹⁵N-¹³C spectra reveal peak doubling, indicating the coexistence of two molecular conformations. d, Strips of 3D NCACX (black) and NCOCX (green) correlation spectra, illustrating sequential resonance assignment. e, Absolute chemical shift differences between conformers I and II. Purple bars above the diagram indicate segments for which conformers I and II are unambiguously assigned from the sequential cross peaks, whereas black lines indicate connectivities between residues that are far away in the amino acid sequence, which help to distinguish conformer I and conformer II. f, Backbone (ϕ, ψ) torsion angles obtained from the experimental ¹³C and ¹⁵N chemical shifts. Both conformers correspond to a continuous β-strand.