Prion protein self-peptides modulate prion interactions and conversion

Background Molecular mechanisms underlying prion agent replication, converting host-encoded cellular prion protein (PrPC) into the scrapie associated isoform (PrPSc), are poorly understood. Selective self-interaction between PrP molecules forms a basis underlying the observed differences of the PrPC into PrPSc conversion process (agent replication). The importance of previously peptide-scanning mapped ovine PrP self-interaction domains on this conversion was investigated by studying the ability of six of these ovine PrP based peptides to modulate two processes; PrP self-interaction and conversion. Results Three peptides (octarepeat, binding domain 2 -and C-terminal) were capable of inhibiting self-interaction of PrP in a solid-phase PrP peptide array. Three peptides (N-terminal, binding domain 2, and amyloidogenic motif) modulated prion conversion when added before or after initiation of the prion protein misfolding cyclic amplification (PMCA) reaction using brain homogenates. The C-terminal peptides (core region and C-terminal) only affected conversion (increased PrPres formation) when added before mixing PrPC and PrPSc, whereas the octarepeat peptide only affected conversion when added after this mixing. Conclusion This study identified the putative PrP core binding domain that facilitates the PrPC-PrPSc interaction (not conversion), corroborating evidence that the region of PrP containing this domain is important in the species-barrier and/or scrapie susceptibility. The octarepeats can be involved in PrPC-PrPSc stabilization, whereas the N-terminal glycosaminoglycan binding motif and the amyloidogenic motif indirectly affected conversion. Binding domain 2 and the C-terminal domain are directly implicated in PrPC self-interaction during the conversion process and may prove to be prime targets in new therapeutic strategy development, potentially retaining PrPC function. These results emphasize the importance of probable PrPC-PrPC and required PrPC-PrPSc interactions during PrP conversion. All interactions are probably part of the complex process in which polymorphisms and species barriers affect TSE transmission and susceptibility.