Response to crowded conditions reveals compact nucleus for amyloid formation of folded protein

Abstract Although the consequences of crowded cell environments may affect protein folding, function and misfolding reactions, these processes are often studied in dilute solutions vitro. We here used biophysical experiments to investigate amyloid fibril formation process fish apo-β-parvalbumin solvent conditions that mimic steric solvation aspects vivo milieu. Apo-β-parvalbumin is a folded readily adopts an state via nucleation–elongation mechanism. Aggregation presence macromolecular crowding agents (probing excluded volume, entropic effects) as well small molecule osmolytes solvation, enthalpic revealed both types accelerate overall formation, but elongation step was faster with slower osmolytes. The observations can be explained by effects volume favoring assembled states nucleation does not involve monomer unfolding. In contrast, due osmolyte promote elongation. Therefore, amyloid-competent nuclei must compact less from surface than either monomers or fibers. conclude that, contrast other amyloidogenic proteins, accelerated cell-like large-scale