Acceleration of Amyloid Fibril Formation by Specific Binding of Aβ-(1–40) Peptide to Ganglioside-containing Membrane Vesicles

Abstract

The interaction of Alzheimer's A␤ peptide and its fluorescent analogue with membrane vesicles was studied by spectrofluorometry, Congo Red binding, and electron microscopy. The peptide binds selectively to the membranes containing gangliosides with a binding affinity ranging from 10 ؊6 to 10 ؊7 M depending on the type of ganglioside sugar moiety. This interaction appears to be ganglioside-specific as under our experimental conditions (neutral pH, physiologically relevant ionic strength), no A␤ binding was observed to gangliosidefree membranes containing zwitterionic or acidic phospholipids. Importantly, the addition of ganglioside-containing vesicles to the peptide solution dramatically accelerates the rate of fibril formation as compared with that of the peptide alone. The present results strongly suggest that the membrane-bound form of the peptide may act as a specific "template" (seed) that catalyzes the fibrillogenesis process in vivo.One of the histopathological hallmarks of Alzheimer's disease is the presence of insoluble amyloid deposits within the gray matter regions of the brain and the vascular walls of cerebral blood vessels (1). The principal component of these deposits is the ϳ4-kDa amyloid ␤ peptide (A␤), a product of proteolytic processing of a much larger amyloid precursor protein (2). While biological functions of A␤ are still poorly understood, rapidly accumulating evidence points to a causative (rather than merely consequential) role of the peptide in the pathogenesis of Alzheimer's disease. Such a causative link between A␤ and Alzheimer's disease is indicated by genetic studies which identified specific mutations in amyloid precursor protein (in close proximity to the amino or carboxyl terminus of A␤ or within the A␤ region) that are tightly linked to heritable forms of Alzheimer's disease (3-5). Further support is derived from in vitro studies which show that synthetic A␤ peptide is toxic to neuronal cells in culture (6 -9). However, despite recent important advances, the molecular mechanisms of A␤-induced neuronal cell death remain largely unknown.To understand the neurotoxic action of A␤, it is essential to identify specific cellular components that interact with the peptide and mediate a biological response of the affected cells. A likely primary target of A␤ is the neuronal plasma membrane. Indeed, a rapidly growing number of observations indicate that the peptide may alter important physical and biological properties of the membrane (10 -17). The mechanisms of A␤-membrane interactions remain, however, elusive. Whereas some investigators have proposed the involvement of specific proteinaceous receptors (18,19), other studies postulate models based on the interaction of A␤ with the lipid bilayer matrix of the plasma membrane (14, 15). Our present data show that A␤ binds with high affinity and selectivity to gangliosides. Furthermore, in the presence of ganglioside-containing membrane vesicles, there is a dramatic increase in the rate of fibril formation by the peptide. We postulate that t...

Amyloid precursor protein, although partially detergent-insoluble in mouse cerebral cortex, behaves as an atypical lipid raft protein

“…It is possible that APP in DIGs is rapidly processed such that the steady-state levels of this protein are lower than would otherwise be expected. Another possibility is that, as the Aβ peptide has a high affinity for cholesterol [46] and ganglioside G M" [47][48][49], both of which are enriched in DIGs [8,25], this peptide rapidly translocates to DIGs after it is cleaved from APP. Finally, although depleting cells of cholesterol with methyl-β-cyclodextrin has been shown to decrease the production of Aβ [37], this effect may not be entirely due to disruption of lipid rafts, as such treatment has also been shown to disrupt clathrincoated pits [50] in which APP has been localized [51].…”

Anionic Micelles and Vesicles Induce Tau Fibrillization in Vitro

“…Efficient induction of tau fibrillization above this size may be related to micelle curvature, surface area, or volume. Although not demonstrated for tau protein, other amyloid-forming proteins such as A␤, prion protein, apolipoprotein C-III, and ␣-synuclein can obliquely insert into lipid membranes in a viral peptide fashion (40 -44), and this may contribute to their lipid-dependent aggregation (45)(46)(47)(48)(49)(50)(51). Thus, the size of the hydrophobic micelle core may play a role in favoring polymerization-prone conformations of partially inserted proteins.…”

Application of Surface-Enhanced Raman Spectroscopy for Detection of Beta Amyloid Using Nanoshells

“…Sialic acid is one of many sugars that make up the glycolipids and glycoproteins on a cell surface. Aβ has been shown to have a high affinity for sialic acid containing gangliosides [7,29,[53][54][55][56][57][58] and multivalent sialic acid polymers [18]. Thus, by functionalizing the nanoshell film with sialic acid, we are attempting to mimic the cell surface to create a platform to induce specific binding of Aβ.…”