Autocatalytic self-propagation of misfolded prion protein

Prions are thought to replicate in an autocatalytic process that converts cellular prion protein (PrPC) to the disease-associated misfolded PrP isoform (PrPSc). Our study scrutinizes this hypothesis by in vitro protein misfolding cyclic amplification (PMCA). In serial transmission PMCA experiments, PrPSc was inoculated into healthy hamster brain homogenate containing PrPC. Misfolded PrP was amplified by rounds of sonication and incubation and reinoculated into fresh brain homogenate every 10 PMCA rounds. The amplification depended on PrPC substrate and could be inhibited by recombinant hamster PrP. In serial dilution experiments, newly formed misfolded and proteinase K-resistant PrP (PrPres) catalyzed the structural conversion of PrPC as efficiently as PrPSc from brain of scrapie (263K)-infected hamsters, yielding an approximate to300-fold total amplification of PrPres after 100 rounds, which confirms an autocatalytic PrP-misfolding cascade as postulated by the prion hypothesis. PrPres formation was not paralleled by replication of biological infectivity, which appears to require factors additional to PrP-misfolding autocatalysis.