Conformational properties of prion strains can be transmitted to recombinant prion protein fibrils in real-time quaking-induced conversion

Abstract

The phenomenon of prion strains with distinct biological characteristics has been hypothesized to be involved in the structural diversity of abnormal prion protein (PrP(Sc)). However, the molecular basis of the transmission of strain properties remains poorly understood. Real-time quaking-induced conversion (RT-QUIC) is a cell-free system that uses Escherichia coli-derived recombinant PrP (rPrP) for the sensitive detection of PrP(Sc). To investigate whether the properties of various prion strains can be transmitted to amyloid fibrils consisting of rPrP (rPrP fibrils) using RT-QUIC, we examined the secondary structure, conformational stability, and infectivity of rPrP fibrils seeded with PrP(Sc) derived from either the Chandler or the 22L strain. In the first round of the reaction, there were differences in the secondary structures, especially in bands attributed to β-sheets, as determined by infrared spectroscopy, and conformational stability between Chandler-seeded (1st-rPrP-fib(Ch)) and 22L-seeded (1st-rPrP-fib(22L)) rPrP fibrils. Of note, specific identifying characteristics of the two rPrP fibril types seen in the β-sheets resembled those of the original PrP(Sc). Furthermore, the conformational stability of 1st-rPrP-fib(Ch) was significantly higher than that of 1st-rPrP-fib(22L), as with Chandler and 22L PrP(Sc). The survival periods of mice inoculated with 1st-rPrP-fib(Ch) or 1st-rPrP-fib(22L) were significantly shorter than those of mice inoculated with mixtures from the mock 1st-round RT-QUIC procedure. In contrast, these biochemical characteristics were no longer evident in subsequent rounds, suggesting that nonspecific uninfected rPrP fibrils became predominant probably because of their high growth rate. Together, these findings show that at least some strain-specific conformational properties can be transmitted to rPrP fibrils and unknown cofactors or environmental conditions may be required for further conservation. Importance: The phenomenon of prion strains with distinct biological characteristics is assumed to result from the conformational variations in the abnormal prion protein (PrP(Sc)). However, important questions remain about the mechanistic relationship between the conformational differences and the strain diversity, including how strain-specific conformations are transmitted. In this study, we investigated whether the properties of diverse prion strains can be transmitted to amyloid fibrils consisting of E. coli-derived recombinant PrP (rPrP) generated by real-time quaking-induced conversion (RT-QUIC), a recently developed in vitro PrP(Sc) formation method. We demonstrate that at least some of the strain-specific conformational properties can be transmitted to rPrP fibrils in the first round of RT-QUIC by examining the secondary structure, conformational stability, and infectivity of rPrP fibrils seeded with PrP(Sc) derived from either the Chandler or the 22L prion strain. We believe that these findings will advance our understanding of the conformational basis underlying prion strain diversity.