Aggregation Mechanisms and Molecular Structures of Amyloid-β in Alzheimer's Disease

Amyloid plaques are a major pathological hallmark involved in Alzheimer's disease and consist of deposits of the amyloid-beta peptide (A beta). The aggregation process of A beta is highly complex, which leads to polymorphous aggregates with different structures. In addition to aberrant aggregation, A beta oligomers can undergo liquid-liquid phase separation (LLPS) and form dynamic condensates. It has been hypothesized that these amyloid liquid droplets affect and modulate amyloid fibril formation. In this review, we briefly introduce the relationship between stress granules and amyloid protein aggregation that is associated with neurodegenerative diseases. Then we highlight the regulatory role of LLPS in A beta aggregation and discuss the potential relationship between A beta phase transition and aggregation. Furthermore, we summarize the current structures of A beta oligomers and amyloid fibrils, which have been determined using nuclear magnetic resonance (NMR) and cryo-electron microscopy (cryo-EM). The structural variations of A beta aggregates provide an explanation for the different levels of toxicity, shed light on the aggregation mechanism and may pave the way towards structure-based drug design for both clinical diagnosis and treatment.