The Human Amyloid-β Precursor Protein₇₇₀ Mutation V717F Generates Peptides Longer Than Amyloid-β-(40-42) and Flocculent Amyloid Aggregates

One of the familial forms of Alzheimer's disease (AD) encodes the amyloid-β precursor protein (AβPP) substitution mutation V717F. This mutation is relevant to AD research, since it has been utilized to generate transgenic mice models to study AD pathology and therapeutic interventions. Amyloid beta (Aβ) peptides were obtained from the cerebral tissue of three familial AD subjects carrying the AβPP V717F mutation. A combination of ultracentrifugation, size-exclusion, and reverse-phase high performance liquid chromatography, tryptic and cyanogen bromide hydrolysis, amino acid analysis, and matrix-assisted laser desorption ionization and surface-enhanced laser desorption ionization mass spectrometry was used to characterize the familial AD mutant Aβ peptides. The AβPP V717F mutation, located 4-6 residues beyond the wild-type AβPP γ-secretase cleavage site, yielded longer Aβ peptides with C termini between residues 43 and 54. In the cerebral cortex these peptides aggregated into thin water- and SDS-insoluble amyloid bundles that condensed into flocculent spherical plaques. In the leptomeningeal arteries the amyloid was deposited in moderate amounts and was primarily composed of the shorter and more soluble Aβ species ending at residues 40, 42, and 44. The single V717F mutation in AβPP results in distinctive and drastic changes in the length and tertiary structure of Aβ peptides, which appear to be responsible for the earlier clinical manifestations of dementia and death of these patients.