N-terminal Domain of Amyloid-beta Impacts Fibrillation and Neurotoxicity

Alzheimer's disease is characterized by the presence of distinct amyloid-beta peptide (A beta) assemblies with diverse sizes, shapes, and toxicity. However, the primary determinants of A beta aggregation and neurotoxicity remain unknown. Here, the N-terminal amino acid residues of A beta 42 that distinguished between humans and rats were substituted. The effects of these modifications on the ability of A beta to aggregate and its neurotoxicity were investigated using biochemical, biophysical, and cellular techniques. The A beta-derived diffusible ligand, protofibrils, and fibrils formed by the N-terminal mutational peptides, including A beta 42(R5G), A beta 42(Y10F), and rat A beta 42, 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 A beta 42 and A beta 42(Y10F) generated protofibrils and fibrils with a high proportion of parallel beta-sheet structures. Furthermore, protofibrils formed by other mutant A beta peptides and N-terminally shortened peptides were incapable of inducing neuronal death, with the exception of A beta 42 and A beta 42(Y10F). Our findings indicate that the N-terminus of A beta is important for its fibrillation and neurotoxicity.