Figure 1.

(A) Schematic representation of β1, showing the position numbers where the mutations and the context host-site were introduced with a list of variants used for this study. WT is a variant of β1 with a mutation in position 2 (T2Q) that prevents the cleavage of the N-terminal methionine (23). All of the other variants include the same mutation. The sequence of WT (T2Q) is: NH3+-MTYKLILNGKTLKGETTTEAVDAATAEKVFKQYANDNGVDGEWTYDDATKTFTVTE-COO- where the residues in bold are the positions in which the mutations have been introduced. (B) Refolding recovery of A6A53 and I6T53 at increasing pHs: pH 5.2 (⋄), pH 6.9 (•), pH 8.0 (○), pH 9.0 (▫), and pH 11.0 (▴). The buffer used was 10 mM sodium acetate, 10 mM sodium borate, and 10 mM sodium citrate. (C) Thermal denaturation fraction refolded at pH 5.2 for all variants. WT (x), I6T53 (▾), A6Y53 (•), A6F53 (▪), F6A53 (⋄), A6A53 (○), F6G53 (▴), and G6Y53 (▫). The buffer used was 50 mM sodium acetate. (D) Thermal denaturation refolding at pH 9.0 for all variants. WT (x), I6T53 (▾), A6Y53 (•), A6F53 (▪), F6A53 (⋄), A6A53 (○), F6G53 (▴), and G6Y53 (▫). The buffer used was 10 mM sodium acetate, 10 mM sodium borate, and 10 mM sodium citrate. MRE was used because the fraction folded was impossible to measure because of the lack of unfolded baselines in most of the variants. (E) Electron micrographs showing the fibrils formed during irreversible denaturation for all variants. (F) Thermal denaturation of variant F6G53 at pH 9.0 (•), pH 9.0 in the presence of 1 M Na2SO4 (⋄), refolding at pH 9.0 (▴), and pH 9.0 in the presence of 1 M Na₂SO₄ (○). The buffer used was 10 mM sodium acetate, 10 mM sodium borate, and 10 mM sodium citrate.