In Situ Observation of Amyloid Nucleation and Fibrillation by FastScan Atomic Force Microscopy.

Amyloidogenic proteins are key components in various amyloid diseases. The aggregation process and the local structural changes of the toxic species from toxic oligomers to protofibrils and subsequently to mature fibrils are crucial for understanding the molecular mechanism of the amyloidgenic process and also for developing a treatment strategy. Exploration on amyloid aggregation dynamics in situ under real liquid condition is feasible for reflection of the whole process with biological correlations. Herein we report the in situ dynamic study and structure exploration of Amylin aggregation by FastScan atomic force microscopy. Amylin nucleation process was observed in which smaller oligomers or monomers were assimilated by the surrounding big oligomers. Amylin protofibril aggregation was positively correlated with monomer concentration, whereas no direct relationship was observed between fibril elongation and monomer concentration. Growing end and passivated end were found during Amylin fibrillation. In the assembly process, the growing end kept its structure, and its stiffness was lower than the aggregate body, whereas the passivated end might experience rearrangements of β-structures, which eventually enabled fibril growth from this end. This work is beneficial to the insights of amyloid fibrillation and may shed light on the development of drugs targeting the specific phase of amyloid aggregation.