Interaction of Peptide Aptamers with Prion Protein Central Domain Promotes α-Cleavage of PrP

Prion diseases are infectious and fatal neurodegenerative diseases affecting humans and animals. Transmission is possible within and between species with zoonotic potential. Currently, no prophylaxis or treatment exists. Prions are composed of the misfolded isoform PrP of the cellular prion protein PrP. Expression of PrP is a prerequisite for prion infection, and conformational conversion of PrP is induced upon its direct interaction with PrP. Inhibition of this interaction can abrogate prion propagation, and we have previously established peptide aptamers (PAs) binding to PrP as new anti-prion compounds. Here, we mapped the interaction site of PA8 in PrP and modeled the complex in silico to design targeted mutations in PA8 which presumably enhance binding properties. Using these PA8 variants, we could improve PA-mediated inhibition of PrP replication and de novo infection of neuronal cells. Furthermore, we demonstrate that binding of PA8 and its variants increases PrP α-cleavage and interferes with its internalization. This gives rise to high levels of the membrane-anchored PrP-C1 fragment, a transdominant negative inhibitor of prion replication. PA8 and its variants interact with PrP at its central and most highly conserved domain, a region which is crucial for prion conversion and facilitates toxic signaling of Aβ oligomers characteristic for Alzheimer's disease. Our strategy allows for the first time to induce α-cleavage, which occurs within this central domain, independent of targeting the responsible protease. Therefore, interaction of PAs with PrP and enhancement of α-cleavage represent mechanisms that can be beneficial for the treatment of prion and other neurodegenerative diseases.