A d-enantiomeric peptide interferes with heteroassociation of amyloid-β oligomers and prion protein

Abstract

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that affects millions of people worldwide. One AD hallmark is the aggregation of β-amyloid (Aβ) into soluble oligomers and insoluble fibrils. Several studies have reported that oligomers rather than fibrils are the most toxic species in AD progression. Aβ oligomers bind with high affinity to membrane-associated prion protein (PrP), leading to toxic signaling across the cell membrane, which makes the Aβ-PrP interaction an attractive therapeutic target. Here, probing this interaction in more detail, we found that both full-length, soluble human (hu) PrP(23-230) and huPrP(23-144), lacking the globular C-terminal domain, bind to Aβ oligomers to form large complexes above the megadalton size range. Following purification by sucrose density-gradient ultracentrifugation, the Aβ and huPrP contents in these heteroassemblies were quantified by reversed-phase HPLC. The Aβ:PrP molar ratio in these assemblies exhibited some limited variation depending on the molar ratio of the initial mixture. Specifically, a molar ratio of about four Aβ to one huPrP in the presence of an excess of huPrP(23-230) or huPrP(23-144) suggested that four Aβ units are required to form one huPrP-binding site. Of note, an Aβ-binding all-d-enantiomeric peptide, RD2D3, competed with huPrP for Aβ oligomers and interfered with Aβ-PrP heteroassembly in a concentration-dependent manner. Our results highlight the importance of multivalent epitopes on Aβ oligomers for Aβ-PrP interactions and have yielded an all-d-peptide-based, therapeutically promising agent that competes with PrP for these interactions.

Aβ receptors specifically recognize molecular features displayed by fibril ends and neurotoxic oligomers

“…Only a few studies have analyzed the interaction of PrP with Aβ fibrils, or its effect on polymerization or assembly processes. Several different effects of PrP on Aβ aggregation have been described, including inhibition of fibril formation 56 , bundling 57 or fragmentation 58,59 of fibrils, and trapping of Aβ in an oligomeric state within PrP-containing complexes [58][59][60] . In a particularly relevant example, it was reported that protofibrils (like those used here) were the most neurotoxic forms of Aβ in an LTP suppression assay, and were the forms that bound most avidly to PrP 21 .…”

Structural details of amyloid beta oligomers in complex with human prion protein as revealed by solid-state MAS NMR spectroscopy

“…These assemblies have a size of a few micrometers as determined by dynamic light scattering and show cloud-like morphologies as seen by atomic force microscopy 33 . The Aβ:huPrP stoichiometry of the hetero-assemblies depends on the PrP concentration added to Aβoligo and reaches a value of 4:1 (monomer ratio) in the presence of an excess of either huPrP or huPrP 33 .…”

“…Several in vitro studies on the Aβ-PrP interaction suggest that Aβoligos bind at two Lys-rich parts (residues 23 to 27 and ≈ 95 to 110) on PrP [28][29][30][31][32][33] , but an additional involvement of the Cterminus of PrP has also been suggested 14 . A structural study of insoluble PrP C -Aβoligo complexes described this as a "hydrogel", in which the A oligomers were rigid, while PrP still has high molecular mobility 34 .…”

“…Additionally, this study reported a conformational change in the N-terminus of PrP C upon complexation with Aβoligo. We recently demonstrated that Aβoligo forms large hetero-assemblies with either full-length (huPrP(23-230)) or C-terminally truncated (huPrP(23-144)) membrane-anchorless monomeric PrP 33 . These assemblies have a size of a few micrometers as determined by dynamic light scattering and show cloud-like morphologies as seen by atomic force microscopy 33 .…”

“…We recently demonstrated that Aβoligo forms large hetero-assemblies with either full-length (huPrP(23-230)) or C-terminally truncated (huPrP(23-144)) membrane-anchorless monomeric PrP 33 . These assemblies have a size of a few micrometers as determined by dynamic light scattering and show cloud-like morphologies as seen by atomic force microscopy 33 . The Aβ:huPrP stoichiometry of the hetero-assemblies depends on the PrP concentration added to Aβoligo and reaches a value of 4:1 (monomer ratio) in the presence of an excess of either huPrP or huPrP 33 .…”