FoldX has been shown to accurately predict the effect of point mutations on the stability of folded proteins as well as transition state structures , and was recently used to study fibril structural stability but without comparison to thermodynamic data from experiments . We used the cryo-EM structure (PDB 6r4r) as input to FoldX to calculate the change in fibril stability, ∆∆G calc A-U for each mutation in Table (excluding I82A which is not present in the structure). We calculated ∆∆G calc A-U as the per-monomer effect of introducing the substitution in all four monomer units. There is good agreement between ∆∆G exp A-U and ∆∆G calc A-U , with a Pearson linear correlation coefficient of 0.86 (Figure ), comparable with the performance of FoldX for thermodynamic calculations of folded proteins .