Trace amounts of pyroglutaminated Aβ-(3-42) enhance aggregation of Aβ-(1-42) on neuronal membranes at physiological concentrations: FCS analysis of cell surface.

Minor species of amyloid β-peptide (Aβ), such as Aβ-(1-43) and pyroglutaminated Aβ-(3-42) (Aβ-(3pE-42)), have been suggested to be involved in the initiation of the Aβ aggregation process, which is closely associated with the etiology of Alzheimer's disease. They can play important roles in aggregation not only in the aqueous phase but also on neuroral membranes; however, the latter behaviors remain mostly unexplored. Here, initial aggregation processes of Aβ on living cells were monitored at physiological nanomolar concentrations by fluorescence correlation spectroscopy. Membrane-bound Aβ-(1-42) and Aβ-(1-40) formed oligomers composed of ~4 Aβ molecules during 48-h incubation, whereas the peptides remained monomeric in the culture medium, indicating that the membranes facilitated Aβ aggregation. The presence of 5 mol% Aβ-(3pE-42), but not Aβ-(1-43), significantly enhanced the aggregation of Aβ-(1-42) up to ~10-mers. On the other hand, neither trace amounts of Aβ-(1-42) nor Aβ-(3pE-42) enhanced the aggregation of Aβ-(1-40). The observed small Aβ oligomers are expected to act as pathogenic seeds for amyloid fibrils responsible for neurotoxicity. This article is part of a Special Issue entitled: Protein Aggregation and Misfolding at the Cell Membrane Interface edited by Ayyalusamy Ramamoorthy.