title: Isolation of a Defective Prion Mutant from Natural Scrapie.
abstract: It is widely known that prion strains can mutate in response to modification of the replication environment and we have recently reported that prion mutations can occur in vitro during amplification of vole-adapted prions by Protein Misfolding Cyclic Amplification on bank vole substrate (bvPMCA). Here we exploited the high efficiency of prion replication by bvPMCA to study the in vitro propagation of natural scrapie isolates. Although in vitro vole-adapted PrPSc conformers were usually similar to the sheep counterpart, we repeatedly isolated a PrPSc mutant exclusively when starting from extremely diluted seeds of a single sheep isolate. The mutant and faithful PrPSc conformers showed to be efficiently autocatalytic in vitro and were characterized by different PrP protease resistant cores, spanning aa ∼155-231 and ∼80-231 respectively, and by different conformational stabilities. The two conformers could thus be seen as different bona fide PrPSc types, putatively accounting for prion populations with different biological properties. Indeed, once inoculated in bank vole the faithful conformer was competent for in vivo replication while the mutant was unable to infect voles, de facto behaving like a defective prion mutant. Overall, our findings confirm that prions can adapt and evolve in the new replication environments and that the starting population size can affect their evolutionary landscape, at least in vitro. Furthermore, we report the first example of "authentic" defective prion mutant, composed of brain-derived PrPC and originating from a natural scrapie isolate. Our results clearly indicate that the defective mutant lacks of some structural characteristics, that presumably involve the central region ∼90-155, critical for infectivity but not for in vitro replication. Finally, we propose a molecular mechanism able to account for the discordant in vitro and in vivo behavior, suggesting possible new paths for investigating the molecular bases of prion infectivity.
authors.affiliation: Department of Veterinary Public Health and Food Safety, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Ilaria
authors.identifier: http://orcid.org/0000-0003-2617-4263
authors.initials: I
authors.lastname: Vanni
authors.affiliation: Istituto Zooprofilattico Sperimentale of Sicily "A. Mirri", Palermo, Italy.
authors.forename: Sergio
authors.initials: S
authors.lastname: Migliore
authors.affiliation: Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise "G. Caporale", Teramo, Italy.
authors.forename: Gian Mario
authors.initials: GM
authors.lastname: Cosseddu
authors.affiliation: Department of Veterinary Public Health and Food Safety, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Michele Angelo
authors.identifier: http://orcid.org/0000-0003-0943-6823
authors.initials: MA
authors.lastname: Di Bari
authors.affiliation: Department of Veterinary Public Health and Food Safety, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Pirisinu
authors.affiliation: Department of Veterinary Public Health and Food Safety, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Claudia
authors.identifier: http://orcid.org/0000-0002-0696-1641
authors.initials: C
authors.lastname: D'Agostino
authors.affiliation: Department of Veterinary Public Health and Food Safety, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Geraldina
authors.initials: G
authors.lastname: Riccardi
authors.affiliation: Department of Veterinary Public Health and Food Safety, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Umberto
authors.identifier: http://orcid.org/0000-0001-7828-0186
authors.initials: U
authors.lastname: Agrimi
authors.affiliation: Department of Veterinary Public Health and Food Safety, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Romolo
authors.initials: R
authors.lastname: Nonno
mesh_terms: D000818:Animals; D003411:Arvicolinae; D015153:Blotting, Western; D009154:Mutation; D018620:PrPSc Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D011487:Protein Conformation; D012608:Scrapie / Q000378:metabolism*; D012756:Sheep
chemical_list: D018620:PrPSc Proteins