Prion protein self-peptides modulate prion interactions and conversion.

Background: Molecular mechanisms underlying prion agent replication, converting host-encoded cellular prion protein (PrP(C)) into the scrapie associated isoform (PrP(Sc)), are poorly understood. Selective self-interaction between PrP molecules forms a basis underlying the observed differences of the PrP(C) into PrP(Sc) 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 PrP(res) formation) when added before mixing PrP(C) and PrP(Sc), 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 PrP(C)-PrP(Sc) 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 PrP(C)-PrP(Sc) 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 PrP(C) self-interaction during the conversion process and may prove to be prime targets in new therapeutic strategy development, potentially retaining PrP(C) function. These results emphasize the importance of probable PrP(C)-PrP(C) and required PrP(C)-PrP(Sc) interactions during PrP conversion. All interactions are probably part of the complex process in which polymorphisms and species barriers affect TSE transmission and susceptibility.