Prion protein insertional mutations increase aggregation propensity but not fiber stability

Background  

Mutations in the PRNPgene account for ~15% of all prion disease cases. Little is understood about the mechanism of how some of these mutations in PRNPcause the protein to aggregate into amyloid fibers or cause disease. We have taken advantage of a chimeric protein system to study the oligopeptide repeat domain (ORD) expansions of the prion protein, PrP, and their effect on protein aggregation and amyloid fiber formation. We replaced the ORD of the yeast prion protein Sup35p with that from wild type and expanded ORDs of PrP and compared their biochemical properties in vitro. We previously determined that these chimeric proteins maintain the [PSI⁺] yeast prion phenotype in vivo. Interestingly, we noted that the repeat expanded chimeric prions seemed to be able to maintain a stronger strain of [PSI ⁺] and convert from [psi ^-] to [PSI ⁺] with a much higher frequency. In this study we have attempted to understand the biochemical properties of these chimeric proteins and to establish a system to study the properties of the ORD of PrP both in vivoand in vitro.