Highly Promiscuous Nature of Prion Polymerization

Abstract

The primary structure of the prion protein (PrP) is believed to be the key factor in regulating the species barrier of prion transmission. Because the strength of the species barrier was found to be affected by the prion strain, the extent to which the barrier can indeed be attributed to differences in the PrP primary structures of either donor and acceptor species remains unclear. In this study, we exploited the intrinsic property of PrP to polymerize spontaneously into disease-related amyloid conformations in the absence of a strain-specified template and analyzed polymerization of mouse and hamster full-length recombinant PrPs. Unexpectedly, we found no evidence of species specificity in cross-seeding polymerization assays. Even when both recombinant PrP variants were present in mixtures, preformed mouse or hamster fibrils displayed no selectivity in elongation reactions and consumed equally well both homologous and heterologous substrates. Analysis of individual fibrils revealed that fibrils can elongate in a bidirectional or unidirectional manner. Our work revealed that, in the absence of a cellular environment, post-translational modifications, or strain-specified conformational constraints, PrP fibrils are intrinsically promiscuous and capable of utilizing heterologous PrP variants as a substrate in a highly efficient manner. This study suggests that amyloid structures are capable of accommodating local perturbations arising because of a mismatch in amino acid sequences and highlights the promiscuous nature of the self-propagating activity of amyloid fibrils.

Prion detection by an amyloid seeding assay

“…At the time this work was undertaken, others reported the presence of species barriers in seeding amyloids by using recombinant amyloid fibers with sequences from humans and mice (13). More recently, promiscuous cross-seeding between mouse and hamster amyloids was reported (28). In a separate study (J. Stöhr, N. Weinmann, H. Wille, T. Kaimann, L. Nagel-Steger, E. Birkmann, G. Panza, S.B.P., M. Eigen, and D.R., unpublished data), it was shown that, under fibrillization conditions, the substrate PrP assumes a partially denatured structure and is in a monomer-dimer equilibrium with well defined contact sites between the molecules.…”

Prion agent diversity and species barrier

“…Of note, similar polymerisation experiments using full-length recombinant mouse and hamster PrP failed to reproduce these data. There was no specificity in cross-seeding fibrilization of mouse and hamster and the fibrils formed were a hybrid of both polymers [128]. Further studies may thus be needed to learn to which extent such mechanisms do control the transmissibility of prions across species.…”

Mouse Prion Protein Polymorphism Phe-108/Val-189 Affects the Kinetics of Fibril Formation and the Response to Seeding

“…For seeding experiments, the reaction was carried out in the presence of sonicated preformed fibrils (1 min in a cup sonicator). Estimation of lag phase was done as reported previously (33). In brief, the data were fitted to the limiting forms of the hyperbolic cosine solution of the equation developed by Bishop and Ferrone (34).…”