N-terminal Domain of Amyloid-β Impacts Fibrillation and Neurotoxicity.

Alzheimer's disease is characterized by the presence of distinct amyloid-β peptide (Aβ) assemblies with diverse sizes, shapes, and toxicity. However, the primary determinants of Aβ aggregation and neurotoxicity remain unknown. Here, the N-terminal amino acid residues of Aβ42 that distinguished between humans and rats were substituted. The effects of these modifications on the ability of Aβ to aggregate and its neurotoxicity were investigated using biochemical, biophysical, and cellular techniques. The Aβ-derived diffusible ligand, protofibrils, and fibrils formed by the N-terminal mutational peptides, including Aβ42(R5G), Aβ42(Y10F), and rat Aβ42, 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 Aβ42 and Aβ42(Y10F) generated protofibrils and fibrils with a high proportion of parallel β-sheet structures. Furthermore, protofibrils formed by other mutant Aβ peptides and N-terminally shortened peptides were incapable of inducing neuronal death, with the exception of Aβ42 and Aβ42(Y10F). Our findings indicate that the N-terminus of Aβ is important for its fibrillation and neurotoxicity.