Thermally triggered self-assembly of κ-casein amyloid nanofibrils and their nanomechanical properties

Abstract Understanding the self-assembly process of amyloid nanofibrils is important in protein engineering for their potential uses in material sciences and medical applications. Here, we investigated the nanomechanical properties and structures of κ-casein nanofibrils during thermally induced amyloidogenesis. After treatment with dithiothreitol to reduce disulfide bonds, κ-casein from bovine milk was incubated at various temperatures from 37 to 95 °C. Twisted mature nanofibrils were only obtained at high thermal energies of 95 °C with fast growth kinetics. Nanomechanical studies using atomic force microscopy show the highest Young's moduli (2.6 ± 0.4 GPa) for mature fibrils when compared to those of oligomers and protofibrils (0.6 ± 0.1 and 2.2 ± 0.3 GPa, respectively). These enhanced mechanical properties are mainly attributed to the twisted cores of the mature fibrils containing β-sheet stacks. Amyloidogenesis of κ-casein is highly dependent on the magnitude of thermal energy, determining both the types and shapes of the nanofibrils and their different mechanical properties.