Concentration-dependent influence of silver nanoparticles on amyloid fibrillation kinetics of hen egg-white lysozyme

Understanding the influence of nanoparticles on the formation of protein amyloid fibrillation is crucial to extend their application in related biological diagnosis and nanomedicines. In this work, Raman spectroscopy was used to probe the amyloid fibrillation of hen egg-white lysozyme in the presence of silver nanoparticles (Ag-NPs) at different concentrations, combined with atomic force microscopy and thioflavin T (ThT) fluorescence assays. Four representative Raman indicators were utilized to monitor transformation of the protein tertiary and secondary structures at the molecular level: the Trp doublet bands at 1340 and 1360 cm−1, the disulfide stretching vibrational peak at 507 cm−1, the N-Cα-C stretching vibration at 933 cm−1, and the amide I band. All experimental results confirmed the concentration-dependent influence of AgNPs on the hen egg-white lysozyme amyloid fibrillation kinetics. In the presence of AgNPs at low concentration (17 µg/mL), electrostatic interaction of the nanoparticles stabilizes disulfide bonds, and protects the Trp residues from exposure to hydrophilic environment, thus leading to formation of amorphous aggregates rather than fibrils. However, with the action of AgNPs at high concentration (1700 µg/mL), the native disulfide bonds of hen egg-white lysozyme are broken to form Ag-S bonds owing to the competition of electrostatic interaction from a great deal of nanoparticles. As for providing functional surfaces for protein to interact with, AgNPs play a bridge role in direct transformation from α-helices to organized β-sheets. The present investigation sheds light on the controversial effects of AgNPs on the kinetics of hen egg-white lysozyme amyloid fibrillation.