Investigation of the Aggregation Process of Amyloid-β-(16-22) Peptides and the Dissolution of Intermediate Aggregates

The aggregation processes of amyloid-beta-(16-22) peptides (A beta(16-22)) are investigated by atomic force microscopy (AFM). It is found that A beta(16-22) peptides quickly aggregate from monomers to oligomers and flakelike structures and finally to fibrils. In particular, unusual morphology change is observed in an early stage of aggregation; that is, the originally formed flakelike structures would disappear in the following aggregation processes. To determine the evolution of the flakelike structures, in situ AFM imaging is carried out in liquid to reveal the real-time morphology change of A beta(16-22). The results provide clear evidence that the flakelike structures are in an unstable intermediate state, which would be dissolved into oligomers or short protofibrils for reorganization. Further fluorescence and attenuated total reflectance Fourier transform infrared (ATR-FTIR) experiments on thioflavin T(ThT) suggest that those flakelike structures contain beta-sheet components.