Figure 4. Atomic model of the water-facing surface of polyQ amyloid.

(A) Atomistic MD snapshot of the D₂Q₁₅K₂ peptide fibril’s polyQ surface in contact with water. Exposed and buried Gln residues are colored green and gray, respectively. Note how the Gln side-chains internal to the (model M1, for M2 see Supplementary Fig. S12) amyloid core are well-ordered, while the water-facing side-chains display more mobility. (B) Side-chain dihedral angle distributions for the buried Gln residues and (C) for the Gln residues on the fibril surface (Amber14SB⁴⁵; for OPLSAA/M⁴⁶ see Supplementary Figs. S13, S14). The surface-facing residues show more disorder, but are nonetheless constrained to just few varyingly prominent specific rotamer states.