Fig. 3.

PrP^Sc diversification during prion replication process by PMCA. a SV-based size distribution of PrP^Sc assemblies at early and late stages of vCJD prion pathogenesis in the brain of human PrP mice. b SV-based PrP^Sc size distribution in PMCA products (127S scrapie strain) analyzed immediately at the end of the PMCA reaction or after further quiescent incubation at 37 °C for the indicated period of time (t). This allows identifying two populations of PrP^Sc assemblies termed A_i and B_j (with i < j). A_i is mostly generated during the active phase of the PMCA reaction. During the quiescent phase, A_i decreases over time in favor of B_j according to a bimodal process (without appearance of assemblies of intermediate size). The inset graph shows the variations of the percentage of A_i and B_j as a function of the quiescent phase (t). The sigmoidal form of the curves is indicative of an autocatalytic reaction process. c Kinetic scheme describing the transformation process of A_i into B_j. A_i and B_j are in equilibrium with their respective suPrP (Igel-Egalon et al. 2017; steps I and II). The best model to account for the cooperative, PrP^C-dependent transformation of A_i into B_j implicates the formation of a complex between suPrP^A and suPrP^B (step III). This complex is at the origin of the secondary templating pathway whereby the transformation of suPrP^A to suPrP^B is assisted by suPrP^B, making the process autocatalytic (data from Igel-Egalon et al. 2019b)