Specific Binding of a beta-Cyclodextrin Dimer to the Amyloid beta Peptide Modulates the Peptide Aggregation Process

Summary, in English

Alzheimer's disease involves progressive neuronal loss. Linked to the disease is the amyloid beta (A beta) peptide, a 38-43-amino acid peptide found in extracellular amyloid plaques in the brain. Cyclodextrins are nontoxic, cone-shaped oligosaccharides with a hydrophilic exterior and a hydrophobic cavity making them suitable hosts for aromatic guest molecules in water. beta-Cyclodextrin consists of seven alpha-D-glucopyranoside units and has been shown to reduce the level of fibrillation and neurotoxicity of A beta. We have studied the interaction between A beta and a beta-cyclodextrin dimer, consisting of two beta-cyclodextrin monomers connected by a flexible linker. The beta-cyclodextrin monomer has been found to interact with A beta(1-40) at sites Y10, F19, and/or F20 with a dissociation constant (K-D) of 3.9 +/- 2.0 mM. Here H-1-N-15 and H-1-C-13 heteronuclear single-quantum correlation nuclear magnetic resonance (NMR) spectra show that in addition, the beta-cyclodextrin monomer and dimer bind to the histidines. NMR translational diffusion experiments reveal the increased affinity of the beta-cyclodextrin dimer (apparent K-D of 1.1 +/- .5 mM) for A beta(1-40) compared to that of the beta-cyclodextrin monomer. Kinetic aggregation experiments based on thioflavin T fluorescence indicate that the dimer at 0.05-5 mM decreases the lag time of A beta aggregation, while a concentration of 10 mM increases the lag time. The beta-cyclodextrin monomer at a high concentration decreases the lag time of the aggregation. We conclude that cyclodextrin monomers and dimers have specific, modulating effects on the A beta(1-40) aggregation process. Transmission electron microscopy shows that the regular fibrillar aggregates formed by A beta(1-40) alone are replaced by a major fraction of amorphous aggregates in the presence of the beta-cyclodextrin dimer.