Effects of Familial Alzheimer's Disease Mutations on the Assembly of a beta-Hairpin Peptide Derived from A beta(16-36)

Familial Alzheimer's disease (FAD) is associated with mutations in the beta-amyloid peptide (A beta) or the amyloid precursor protein (APP). FAD mutations of A beta were incorporated into a macrocyclic peptide that mimics a beta-hairpin to study FAD point mutations K16N, A21G, E22 Delta, E22G, E22Q, E22K, and L34V and their effect on assembly, membrane destabilization, and cytotoxicity. The X-ray crystallographic structures of the four E22 mutant peptides reveal that the peptides assemble to form the same compact hexamer. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) experiments reveal that the mutant FAD peptides assemble as trimers or hexamers, with peptides that have greater positive charge assembling as more stable hexamers. Mutations that increase the positive charge also increase the cytotoxicity of the peptides and their propensity to destabilize lipid membranes.