A D-enantiomeric peptide interferes with heteroassociation of amyloid- 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 -amyloid (A) into soluble oligomers and insoluble fibrils. Several studies have reported that oligomers rather than fibrils are the most toxic species in AD progression. A oligomers bind with high affinity to membrane-associated prion protein (PrP), leading to toxic signaling across the cell membrane, which makes the A–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 A oligomers to form large complexes above the megadalton size range. Following purification by sucrose density–gradient ultracentrifugation, the A and huPrP contents in these heteroassemblies were quantified by reversed-phase HPLC. The A: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 A to one huPrP in the presence of an excess of huPrP(23–230) or huPrP(23–144) suggested that four A units are required to form one huPrP-binding site. Of note, an A-binding all-D-enantiomeric peptide, RD2D3, competed with huPrP for A oligomers and interfered with A–PrP heteroassem-bly in a concentration-dependent manner. Our results highlight the importance of multivalent epitopes on A oligomers for A–PrP interactions and have yielded an all-D-peptide– based, therapeutically promising agent that competes with PrP for these interactions.