Effect of Silica Nanoparticles on the Amyloid Fibrillation of Lysozyme

Protein fibrils are regarded as undesired products as these are associated with numerous neuro- and non-neurodegenerative disorders. Increasing evidence suggests that the mechanism of fibrillation involves the formation of various oligomeric intermediates, which are known to be more toxic than mature fibrils. Here, we report the impact of synthesized silica nanoparticles (SiNPs) of diameters similar to 52 nm on the aggregation behavior of hen egg white lysozyme (HEWL) under heat and acidic conditions. Congo red as well as ThT binding assays and AFM imaging studies indicate that SiNPs trigger the amyloid formation of HEWL in a dose-dependent manner. ThT kinetic studies and FTIR studies suggest that the fibrillation kinetics does not involve the formation of toxic oligomeric intermediates at higher concentrations of SiNPs. By measuring fluorescence lifetime values of the bound ThT, SiNP-induced fibrillation of HEWL can easily be realized. CD spectroscopic studies indicate that native HEWL becomes unfolded upon incubation under the experimental conditions and is rapidly converted into the beta-sheet-rich fibrillar aggregates in the presence of SiNPs with increasing concentrations. It has been further revealed that fibrillar aggregates formed at higher concentrations of SiNPs preferably adopt an antiparallel beta-sheet configuration. The enhanced fibrillation in the presence of SiNPs is likely because of preferential adsorption of the non-amyloidogenic regions of HEWL, resulting in the exposure of the aggregation-prone regions of HEWL toward the solvent. The study will provide deeper insights into the evolution of oligomer-free fibrillation that can be useful to demonstrate the underlying mechanism of amyloid fibrillation.