C-terminal peptides modelling constitutive PrPC processing demonstrate ameliorated toxicity predisposition consequent to α-cleavage

Misfolding of PrPC (cellular prion protein) to beta-strand-rich conformations constitutes a key event in. prion disease pathogenesis. PrPC can undergo either of two constitutive endoproteolytic events known as alpha- and beta-cleavage, yielding C-terminal fragments known as C1 and C2 respectively. It is unclear whether C-terminal fragments generated through alpha- and beta-cleavage, especially C2, influence pathogenesis directly. Consequently, we compared the biophysical properties and neurotoxicity of recombinant human PrP fragments recapitulating alpha- and beta-cleavage, namely huPrP-(112-231) (equating to Cl) and huPrP-(90-231) (equating to C2). Under conditions we employed, huPrP-(112-231) could not be induced to fold into a beta-stranded isoform and neurotoxicity was not a feature for monomeric or multimeric assemblies. In contrast, huPrP-(90-231) easily adopted a beta-strand conformation, demonstrated considerable thermostability and was toxic to neurons. Synthetic PrP peptides modelled on alpha- and beta-cleavage of the unique Y145STOP (Tyr(145)-> stop) mutant prion protein corroborated the differential toxicity observed for recombinant huPrP-(112-231) and huPrP-(90-231) and suggested that the persistence of soluble oligomeric beta-strand-rich conformers was required for significant neurotoxicity. Our results additionally indicate that alpha- and beta-cleavage of PrPC generate biophysically and biologically non-equivalent C-terminal fragments and that C1 generated through alpha-cleavage appears to be pathogenesis-averse.