Protein Fibrillation Mechanism By Infrared Spectroscopy

Hen egg white lysozyme (HEWL) is widely used as a model protein foramyloid research. In this study, we aim to use Fourier transform infrared (FTIR)spectroscopy to gain new structural insights into amyloid formation of HEWLunder heat and acidic condition. We reveal that the fibril-forming solution ofHEWL has the capability to form fibril and oligomer with distinct β-sheetconfigurations under different temperatures. Amyloid fibril with parallelβ-sheetconfiguration is formed at elevated temperature, while oligomer withantiparallel β-sheet configuration is formed at room temperature. The interplaybetween fibrillation and oligomerization suggests that the two β-sheetaggregates consume the same amyloidogenic materials such as peptidefragments and nicked HEWL due to lysozyme hydrolysis under heat and acidiccondition. Temperature-dependent FTIR reveals that the oligomer is unstable atelevated temperature, demonstrating its off-pathway nature. Thetemperature-dependent formation of parallel and antiparallel β-sheetconfigurations discovered in lysozyme system is compared with that ofamyloid-β and α-synuclein systems and the implication is discussed.