Crocein Orange G mediated detection and modulation of amyloid fibrillation revealed by surface-enhanced Raman spectroscopy

Protein fibrous aggregation is associated with many neurodegenerative diseases including Alzheimer's and Parkinson's diseases. To modulate the process, a number of fibrillation inhibitors have been reported, although their working mechanism remains vague, calling for new means to decipher their interaction. Herein, we identified and characterized a novel inhibitor called Crocein Orange G (COG), which inhibited the nucleation and impeded the protofibril formation, revealed by various experimental approaches as well as molecular docking. In particular, the surface-enhanced Raman spectroscopy (SERS) helps to identify the binding sites and illustrate the interaction mechanism and fibrillation process by using Ag IMNPs as SERS substrate for a label-free detection. Combining with molecular docking, the SERS-based approach provides structural information concerning protein-ligand interaction and protein fibrillation. This study suggests that SERS can be a powerful new means to study the interaction between inhibitors and amyloid proteins and can potentially be a common tool for amyloid research. Strikingly, the SERS signal of COG corresponds very well with the state of protein fibrillation, hinting its function as an amyloid SERS signal amplifier. Therefore, this study provides a new means to monitor and interfere amyloid fibrillation.