Regarding Aβ 25-35 , we are unaware of any detailed fibril structures being reported in the literature. In the case of the full-length (1 -40 or 1 -42) wildtype Aβ peptide, residues 25 -29 adopt a bend structure that brings the two β-sheets of the fibril protofilaments together. In contrast, Aβ 25-35 is too small to adopt bend or turn structures. Its cross-β core structure resembles that of amylin 20-29 polymorph 2. Interestingly, Aβ 25-35 fibrils appear to be more structurally heterogeneous than amylin 20-29 polymorph 2 fibrils, as evidenced by the former's broader ψ-angle distribution (c.f. Figure and). This may be due to the difference in side chain composition of the two peptides. Amylin 20-29 polymorph 2 adopts parallel βsheets that allows Phe, Ala, and Leu side chains to be aligned in-register between neighboring β-strands, thereby allowing hydrophobic and π-stacking interactions that make the fibril structures more rigid. The MD simulations suggest that this does not occur for Aβ 25-35 fibrils since the side chains hydrophobic residues in the interior between the two β-sheets are more disordered (Figure ). This side chain disordering could give rise to the greater conformational heterogeneity observed in the Raman spectra for Aβ 25-35 fibrils compared to amylin 20-29 polymorph 2.