AFM and STM study of beta-amyloid aggregation on graphite.

Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) have been employed in situ and ex situ to directly study the aggregation of beta-amyloid(1-42) (Abeta42) peptide on hydrophobic graphite. From in situ AFM images, Abeta42 peptides were seen to aggregate into the sheets that preferred to three orientations with characteristic 3-fold symmetry (Proc. Natl. Acad. Sci. USA 96 (1999) 3688). The sheets were formed by parallel narrow lines with a height of 0.8-1.0nm and a width of 12-14nm. The narrow lines looked like beaded chains and have a right-handed axial periodicity. The high-resolution ex situ AFM and STM images showed that some fibrils of beta-amyloid had a characteristic domain texture, indicating they were formed through the association of protofibrils and monomers. The fibril containing lateral associated filaments that exhibited right-handed twist was clearly observed in the STM image. These results provide important clues to study the detailed structure of beta-amyloid aggregates and the mechanism of the Abeta fibrils formation on hydrophobic surface.