Colorimetric Detection of Mutant β-Amyloid(1-40) Membrane-Active Aggregation with Biosensing Vesicles

Alzheimer's disease (AD) is a protein misfolding disease commonly characterized by neuritic amyloid plaques and proteinaceous fibrillar aggregate deposits composed of β-amyloid (Aβ) aggregates. The dynamic aggregation of Aβ forms toxic, nanoscale aggregate species which proceed from oligomers to fibrils. Currently, there is need for rapid and direct detection of Aβ peptide aggregation and interaction with lipid membranes, as detecting an interaction with various lipid environments will provide insights to better understand how interactions may modulate membrane function on cellular surfaces, leading to the progression of AD. The goal of this study was to utilize a colorimetric, biomimetic, vesicle-binding assay as a biosensor to detect and investigate the occurrence of neurodegenerative disease-associated protein aggregation and interaction with lipid membranes. Lipid/polydiacetylene (PDA) vesicles were exposed to monomeric preparations of Wild Type Aβ(1-40) or point mutations in Aβ with amino acid substitutions that are commonly associated with familial AD (E22G Arctic, E22Q Dutch, A21G Flemish, D23N Iowa, and E22K Italian). We investigated how these substitutions affect Aβ(1-40) aggregation and interaction with lipid vesicles designed to mimic biological membranes. Time-resolved colorimetric measurements were obtained and reveal that exposure to lipid/PDA vesicle biosensors results in the direct detection of mutant Aβ(1-40) peptide-lipid interaction events. Aβ(1-40) peptide aggregate membrane activity varies among Aβ peptide variants and lipid composition. In addition, we used atomic force microscopy and Thioflavin T fluorescence assays to distinguish the stages of Aβ(1-40) aggregate formation, morphology, and membrane activity. These studies provide a simple means of aggregate detection and insight into the role of cellular surfaces in the mechanism of AD aggregation.