Fig. 5.

Schematic diagrams for the phase transitions producing distinct aggregates. (A) NaCl-dependent conformational transition of a folded protein (e.g. hen egg lysozyme at pH 4.7). As a representative parameter, specific volume is plotted against NaCl concentration. (B) Phase diagrams of β2m at pH 2.5 depending on the NaCl and β2m concentrations. Agitation causes a downward shift of the metastability curve, which is indicated by an arrow. Filled circles indicate the experimental conditions employed in this study, illustrating the agitation-triggered fibrillation at 100 mM NaCl. In panels A and B, Regions 1, 2, 3, and 4 represent thermodynamically stable region with soluble monomers, metastable region without spontaneous nucleation, labile region with spontaneous nucleation, and glass region produced with too many nuclei, respectively. (C) General phase diagram of the conformational states of peptides and proteins dependent on conformational uniqueness and concentration. The representative conformational states are monomers, crystals, amyloid fibrils, and amorphous aggregates. In this phase diagram, amorphous aggregates of unfolded proteins and those of folded proteins are not distinguished. As for crystallization and amyloid fibrillation, supersaturation critically determines the phase transition as shown in panels A and B.