Designed Fluorescent Probes Reveal Interactions between Amyloid-β(1–40) Peptides and GM1 Gangliosides in Micelles and Lipid Vesicles

Abstract

A hallmark of the common Alzheimer's disease (AD) is the pathological conversion of its amphiphatic amyloid-β (Aβ) peptide into neurotoxic aggregates. In AD patients, these aggregates are often found to be tightly associated with neuronal GM1 ganglioside lipids, suggesting an involvement of GM1 not only in aggregate formation but also in neurotoxic events. Significant interactions were found between micelles made of newly synthesized fluorescent GM1 gangliosides labeled in the polar headgroup or the hydrophobic chain and Aβ(1–40) peptide labeled with a BODIPY-FL-C1 fluorophore at positions 12 and 26, respectively. From an analysis of energy transfer between the different fluorescence labels and their location in the molecules, we were able to place the Aβ peptide inside GM1 micelles, close to the hydrophobic-hydrophilic interface. Large unilamellar vesicles composed of a raftlike GM1/bSM/cholesterol lipid composition doped with labeled GM1 at various positions also interact with labeled Aβ peptide tagged to amino acids 2 or 26. A faster energy transfer was observed from the Aβ peptide to bilayers doped with 581/591-BODIPY-C11-GM1 in the nonpolar part of the lipid compared with 581/591-BODIPY-C5-GM1 residing in the polar headgroup. These data are compatible with a clustering process of GM1 molecules, an effect that not only increases the Aβ peptide affinity, but also causes a pronounced Aβ peptide penetration deeper into the lipid membrane; all these factors are potentially involved in Aβ peptide aggregate formation due to an altered ganglioside metabolism found in AD patients.