“Prion-proof” for [PIN+]: Infection with In Vitro-made Amyloid Aggregates of Rnq1p-(132–405) Induces [PIN+]

Prions are self-propagating, infectious protein conformations. The mammalian prion, PrPSc, responsible for neurodegenerative diseases like bovine spongiform encephalopathy (BSE; “mad cow” disease) and Creutzfeldt-Jakobʹs disease, appears to be a β-sheet-rich amyloid conformation of PrPc that converts PrPc into PrPSc. However, an unequivocal demonstration of ”protein-only” infection by PrPSc is still lacking. So far, protein only infection has been proven for three prions, [PSI+], [URE3] and [Het-s], all of fungal origin. Considerable evidence supports the hypothesis that another protein, the yeast Rnq1p, can form a prion, [PIN+]. While Rnq1p does not lose any known function upon prionization, [PIN+] has interesting positive phenotypes: facilitating the appearance and destabilization of other prions as well as the aggregation of polyglutamine extensions of the Huntingtin protein. Here, we polymerize a Gln/Asn-rich recombinant fragment of Rnq1p into β-sheet-rich amyloid-like aggregates. While the method used for [PSI+] and [URE3] infectivity assays did not yield protein-only infection for the Rnq1p aggregates, we did successfully obtain protein-only infection by modifying the protocol. This work proves that [PIN+] is a prion mediated by amyloid-like aggregates of Rnq1p, and supports the hypothesis that heterologous prions affect each otherʹs appearance and propagation through interaction of their amyloid-like regions.