The Physical Relationship between Infectivity and Prion Protein Aggregates Is Strain-Dependent

Abstract

Prions are unconventional infectious agents thought to be primarily composed of PrPSc, a multimeric misfolded conformer of the ubiquitously expressed host-encoded prion protein (PrPC). They cause fatal neurodegenerative diseases in both animals and humans. The disease phenotype is not uniform within species, and stable, self-propagating variations in PrPSc conformation could encode this ‘strain’ diversity. However, much remains to be learned about the physical relationship between the infectious agent and PrPSc aggregation state, and how this varies according to the strain. We applied a sedimentation velocity technique to a panel of natural, biologically cloned strains obtained by propagation of classical and atypical sheep scrapie and BSE infectious sources in transgenic mice expressing ovine PrP. Detergent-solubilized, infected brain homogenates were used as starting material. Solubilization conditions were optimized to separate PrPSc aggregates from PrPC. The distribution of PrPSc and infectivity in the gradient was determined by immunoblotting and mouse bioassay, respectively. As a general feature, a major proteinase K-resistant PrPSc peak was observed in the middle part of the gradient. This population approximately corresponds to multimers of 12–30 PrP molecules, if constituted of PrP only. For two strains, infectivity peaked in a markedly different region of the gradient. This most infectious component sedimented very slowly, suggesting small size oligomers and/or low density PrPSc aggregates. Extending this study to hamster prions passaged in hamster PrP transgenic mice revealed that the highly infectious, slowly sedimenting particles could be a feature of strains able to induce a rapidly lethal disease. Our findings suggest that prion infectious particles are subjected to marked strain-dependent variations, which in turn could influence the strain biological phenotype, in particular the replication dynamics.

Infrared Microspectroscopy Detects Protein Misfolding Cyclic Amplification (PMCA)-induced Conformational Alterations in Hamster Scrapie Progeny Seeds

“…Under these experimental conditions, PrP sedimentation profiles could be expected to reflect the size of PrP assemblies in the analyzed samples. In accordance with previous observations by Tixador et al (29), we found that the purification of PrP27-30 produced faster sedimenting PrP aggregates than observed in non-purified 263K scrapie brain homogenates (not shown). However, irrespective of this purification effect, the PrP sedimentation profiles significantly differed between the mildly and extensively sonicated preparations in that there was a substantially higher proportion of slower sedimenting (i.e.…”

“…Sedimentation Velocity Analysis of PrP from 263K-Brain, 263K-PMCA, and 263K-PMCA-Brain in Iodixanol GradientsIn our ultracentrifugation experiments using iodixanol gradients (29), PrP TSE from 263K-brain and 263K-PMCA-brain exhibited a higher sedimentation velocity (indicating a higher mass or a more compact shape) than PrPres from 263K-PMCA.…”

Prions, proteinase K and infectivity

“…This infectivity was approximately 50-fold higher in the case of the139H strain. 17 Taken together, the above data indicate that the aggregation state or quaternary structure of PrP Sc is relevant for prion infectivity. Furthermore, it is very likely that additional conformational aspects, such as those derived from the tertiary structure, play an important role in determining the differential infectivity of specific prion strains.…”

“…The authors did not interpret the results as an aggregation size difference but as a difference in its tertiary structure. 17 Finally, PK-sensitivity appears to be connected with oligomer stability which in turn is directly proportional to the incubation time. Colby and coworkers demonstrated that stable recombinant OC antibody (which recognizes amyloid fibrils but not monomers or soluble prefibrillar oligomers).…”

Les prions, agents d’encéphalopathies transmissibles chez les mammifères

“…Les analyses par spectrométrie infrarouge indiquent que la PrP Sc est fortement enrichie en feuillets b (~40 % contre 3 % pour la PrP C ). Un certain nombre (Silveira et al, 2005, Tixador et al, 2010. Des études ultra structurales par microscopie électronique à transmission ou par microscopie à force atomique de fractions semi-purifiées de PrP Sc ont également permis la visualisation de structures fibrillaires de taille variable (10 à 100 nm de long, 5 nm de large, (Sim & Caughey, 2009) Sc est dépendante à la fois de leur taille et de la souche considérée (Tixador et al, 2010, Laferriere et al, 2013.…”