Amyloid-like fibrils formed from intrinsically disordered caseins: physicochemical and nanomechanical properties

• Published in: Soft matter 2015-08, Vol.11 (29), p.5898-5904
• Main Authors: Pan, Kang, Zhong, Qixin
• Format: Article
• Language: English
• Subjects: Acids - chemistry; Amyloid - chemistry; Amyloid - metabolism; Atomic structure; Caseins - chemistry; Caseins - metabolism; Dispersions; Elastic Modulus; Fibrillation; Heating; Hydrogen-Ion Concentration; Hydrolysis; Kinetics; Lactoglobulins - chemistry; Microscopy, Atomic Force; Modulus of elasticity; Nanostructure; Nanostructures - chemistry; Protein Structure, Secondary; Proteins; Rheology; Spectroscopy, Fourier Transform Infrared
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/c5sm01037c

Amyloid-like fibrils are studied because of their significance in understanding pathogenesis and creating functional materials. Amyloid-like fibrils have been studied by heating globular proteins at acidic conditions. In the present study, intrinsically disordered α-, β-, and κ-caseins were studied to form amyloid-like fibrils at pH 2.0 and 90 °C. No fibrils were observed for α-caseins, and acid hydrolysis was found to be the rate-limiting step of fibrillation of β- and κ-caseins. An increase of β-sheet structure was observed after fibrillation. Nanomechanic analysis of long amyloid-like fibrils using peak-force quantitative nanomechanical atomic force microscopy showed the lowest and highest Young's modulus for β-casein (2.35 ± 0.29 GPa) and κ-casein (4.14 ± 0.66 GPa), respectively. The dispersion with β-casein fibrils had a viscosity more than 10 and 5 times higher than those of κ-casein and β-lactoglobulin, respectively, at 0.1 s(-1) at comparable concentrations. The current findings may assist not only the understanding of amyloid fibril formation but also the development of novel functional materials from disordered proteins.