Lipid/Polydiacetylene Vesicle Composition Alters Mutant Beta-Amyloid Peptide Interaction

Abstract

Alzheimer's disease (AD) is commonly identified by the formation of proteinaceous fibrillar aggregate deposits known as amyloids, and the presence of neuritic amyloid plaques containing aggregated β-amyloid (Aβ). Point mutations grouped in the hydrophobic core of Aβ (positions 21–23) are linked to familial forms of AD. Understanding Aβ peptide interactions with lipid surfaces will provide detailed information into how surface interactions can drive protein aggregation. We hypothesized changes in the lipid composition of a vesicle will result in varied mutant Aβ peptide aggregation morphology and kinetics, further modulating peptide-lipid interactions. To test our hypothesis we utilized a colorimetric, lipid vesicle-binding assay exposed to specific Aβ peptides. The assay integrates a lipid within a polydiacetylene (PDA) matrix forming a blue vesicle when polymerized by UV irradiation. Lipid/PDA vesicles are able to detect peptide-lipid interaction by quantitatively measuring a blue-to-red conversion as a percent colorimetric response (%CR). We investigated the interaction of Wild Type (Aβ1-40) and five mutant Aβ peptides (E22G Arctic, E22Q Dutch, A21G Flemish, D23N Iowa, and E22K Italian) with lipid/PDA vesicle systems comprised of total brain lipid extract (TBLE), dimyristoylphosphatideylcholine (DMPC), and dimyristoylphosphatidylglycerol (DMPG). Time-resolved absorbance measurements of the “blue” (630 nm) and “red” (490 nm) wavelengths were obtained. Statistical analysis (ANOVA and t-tests) was performed to test for significant differences between peptides among the lipid/PDA compositions, as well as compare each mutant Aβ peptide to Wild Type within the context of each lipid. The most peptide-lipid interaction was observed on the negatively charged DMPG/PDA vesicle system, and the least on the neutral DMPC/PDA system. Dutch and Flemish induced the smallest, while Arctic induced the largest %CR on all lipid/PDA vesicles, respectively. These studies illustrate the role of lipid composition and Aβ interactions in the onset of familial AD.