ABSTRACT
Alzheimer's disease is characterized by the presence of distinct amyloid-ß peptide (Aß) assemblies with diverse sizes, shapes, and toxicity. However, the primary determinants of Aß aggregation and neurotoxicity remain unknown. Here, the N-terminal amino acid residues of Aß42 that distinguished between humans and rats were substituted. The effects of these modifications on the ability of Aß to aggregate and its neurotoxicity were investigated using biochemical, biophysical, and cellular techniques. The Aß-derived diffusible ligand, protofibrils, and fibrils formed by the N-terminal mutational peptides, including Aß42(R5G), Aß42(Y10F), and rat Aß42, were indistinguishable by conventional techniques such as size-exclusion chromatography, negative-staining transmission electron microscopy and silver staining, whereas the amyloid fibrillation detected by thioflavin T assay was greatly inhibited in vitro. Using circular dichroism spectroscopy, we discovered that both Aß42 and Aß42(Y10F) generated protofibrils and fibrils with a high proportion of parallel ß-sheet structures. Furthermore, protofibrils formed by other mutant Aß peptides and N-terminally shortened peptides were incapable of inducing neuronal death, with the exception of Aß42 and Aß42(Y10F). Our findings indicate that the N-terminus of Aß is important for its fibrillation and neurotoxicity.
