β-amyloid fibril formation is promoted by step edges of highly oriented pyrolytic graphite

The aggregation of the amyloid-â-protein (Aâ) is an important step in the pathogenesis of Alzheimer's disease. As Aâ fibrils are not found in all brain regions, endogenous factors may influence Aâ fibril formation. In this study, atomic force microscopy was used to investigate the role of surface phenomena in directing amyloid aggregation. Aâ1-40 was applied to a surface of highly oriented pyrolytic graphite at a concentration of 0.5 ìM. Steps formed by edge-plane surface defects on the graphite were found to act as a template to promote the assembly of Aâ into fibrils. Initially, after being deposited on the graphite surface, Aâ had a uniform beaded morphology. However, after incubating (aging) the Aâ on the surface for several hours, the Aâ assembled along step edges to form linear aggregates. After more prolonged incubation, the linear Aâ aggregates fused to form mature fibrils with a distinctive helical morphology. The results demonstrate that surface interactions can promote the aggregation of Aâ into amyloid fibrils and they suggest that similar interactions could promote amyloid aggregation in vivo.