Discrimination of Formation Processes of Amyloid β Fibrils with Distinct Morphologies Using Rheo-NMR Spectroscopy

The accumulation of abnormal protein fibrillar aggregates is a hallmark of various neurodegenerative diseases. Notably, a single type of protein species can form fibrils with distinct morphologies, and recent studies have linked fibril polymorphism to variations in disease symptoms. However, the mechanisms underlying the formation and structural distinction of these morphologies remain elusive. Here, we monitored the real-time formation of amyloid-β peptide (Aβ_1-40) fibrils with two distinct morphologies at atomic resolution using Rheo-NMR spectroscopy, a method which enables the observation of protein NMR signals under shear flow. Under quiescent conditions, Aβ_1-40 formed relatively thick fibrils, accompanied by structural rigidification in the region spanning from residues E22 to A30. In contrast, fibrils formed under shear were thinner, with Aβ_1-40 adopting more elongated conformations. Molecular dynamics simulations corroborated the NMR results, indicating that shear flow impedes essential structural transitions required for one specific fibril morphology, and instead promoted formation of a different morphology. Intriguingly, a fluorinated amyloid-binding dye, FSB, distinguished these two types of Aβ_1-40 fibrils and their formation processes based on its ¹⁹F NMR signals. These findings not only provide atomic-level insights into the formation of different fibril morphologies but also propose a new framework for distinguishing pathological fibril types relevant to neurodegenerative disease.