Early stage prion assembly involves two subpopulations with different quaternary structures and a secondary templating pathway

Abstract

The dynamics of aggregation and structural diversification of misfolded, host-encoded proteins in neurodegenerative diseases are poorly understood. In many of these disorders, including Alzheimer’s, Parkinson’s and prion diseases, the misfolded proteins are self-organized into conformationally distinct assemblies or strains. The existence of intrastrain structural heterogeneity is increasingly recognized. However, the underlying processes of emergence and coevolution of structurally distinct assemblies are not mechanistically understood. Here, we show that early prion replication generates two subsets of structurally different assemblies by two sequential processes of formation, regardless of the strain considered. The first process corresponds to a quaternary structural convergence, by reducing the parental strain polydispersity to generate small oligomers. The second process transforms these oligomers into larger ones, by a secondary autocatalytic templating pathway requiring the prion protein. This pathway provides mechanistic insights into prion structural diversification, a key determinant for prion adaptation and toxicity.

Complementation between pathological prion protein subassemblies to cross existing species barriers

“…This approach has been unsuccessfully attempted in the case of LA21K fast . This fail could be due to the weakness of the suPrP A :suPrP B complex, as previously observed [20]. Indeed, size exclusion chromatography analysis of the 127S suPrP A :suPrP B complex revealed that this last is highly labile and can be observed only in conditions where the concentration of suPrPA and suPrPB were high.…”

“…It implicates interactions between structurally distinct PrP Sc subsets in order to create a new structural information absent in each individual PrP Sc population and leading to heterologous PrP C integration. During the early stage of prion replication, we showed that two sets of structurally distinct PrP Sc assemblies are generated, in fractions 1-5 and 10-18 [20]. These sets are defined by their elementary subunit [13] as suPrP A and suPrP B , respectively [27].…”

“…( a ) In the homotypic PrP transmission context, prion replication involves two templating pathways: a primary templating pathway where structurally distinct PrP Sc subsets, taken individually (A j and B i ), are able to perpetuate the strain information and a PrP C -dependent autocatalytic secondary templating pathway contributing to structural diversification, which requires the formation of a heterocomplex between the elementary subunits of two structurally distinct sets of PrP Sc assemblies (suPrP A and suPrP B ) [20]. …”

“…The sedimentation velocity procedure has been previously and comprehensively described [15,18,20,13]. Briefly, detergent-solubilized brain homogenates were loaded atop a continuous 10–25% iodixanol gradient (Optiprep, Axys-shield).…”

“…A broad panel of experimental observations, including by size fractionation supports the existence of structurally different PrP Sc subsets within a given prion strain [11–19]. This intra-strain structural heterogeneity results from the intrinsic and deterministic properties of the prion replication process to generate structurally diverse PrP Sc subsets [20]. Structural diversity can be observed at different levels.…”