The authors have successfully converted a small α/β protein, acylphosphatase, from its soluble and native form into insoluble amyloid fibrils, a process observed in various pathological conditions. This transformation was achieved by allowing slow growth in a solution containing moderate concentrations of trifluoroethanol (TFE). Electron microscopy revealed that the protein aggregate after long incubation times consisted of extended, unbranched filaments with a width of 30–50 Å, which subsequently assembled into higher-order structures. These fibrils exhibited extensive β-sheet structure, as confirmed by far-UV CD and IR spectroscopy, and showed typical amyloid characteristics such as Congo red birefringence, increased fluorescence with thioflavine T, and a redshift of the Congo red absorption spectrum. The results suggest that amyloid formation occurs when the native fold of a protein is destabilized under conditions where noncovalent interactions, particularly hydrogen bonding, remain favorable. The authors propose that amyloid formation is not limited to a small number of protein sequences but is a common property of many, if not all, natural polypeptide chains under appropriate conditions. This study provides insights into the conditions necessary for amyloid fibril formation and highlights the potential for designing conditions to observe fibrillation in a broader range of proteins.The authors have successfully converted a small α/β protein, acylphosphatase, from its soluble and native form into insoluble amyloid fibrils, a process observed in various pathological conditions. This transformation was achieved by allowing slow growth in a solution containing moderate concentrations of trifluoroethanol (TFE). Electron microscopy revealed that the protein aggregate after long incubation times consisted of extended, unbranched filaments with a width of 30–50 Å, which subsequently assembled into higher-order structures. These fibrils exhibited extensive β-sheet structure, as confirmed by far-UV CD and IR spectroscopy, and showed typical amyloid characteristics such as Congo red birefringence, increased fluorescence with thioflavine T, and a redshift of the Congo red absorption spectrum. The results suggest that amyloid formation occurs when the native fold of a protein is destabilized under conditions where noncovalent interactions, particularly hydrogen bonding, remain favorable. The authors propose that amyloid formation is not limited to a small number of protein sequences but is a common property of many, if not all, natural polypeptide chains under appropriate conditions. This study provides insights into the conditions necessary for amyloid fibril formation and highlights the potential for designing conditions to observe fibrillation in a broader range of proteins.