Protease resistance of infectious prions is suppressed by removal of a single atom in the cellular prion protein

PLoS One. 2017 Feb 16;12(2):e0170503. doi: 10.1371/journal.pone.0170503. eCollection 2017.

Abstract

Resistance to proteolytic digestion has long been considered a defining trait of prions in tissues of organisms suffering from transmissible spongiform encephalopathies. Detection of proteinase K-resistant prion protein (PrPSc) still represents the diagnostic gold standard for prion diseases in humans, sheep and cattle. However, it has become increasingly apparent that the accumulation of PrPSc does not always accompany prion infections: high titers of prion infectivity can be reached also in the absence of protease resistant PrPSc. Here, we describe a structural basis for the phenomenon of protease-sensitive prion infectivity. We studied the effect on proteinase K (PK) resistance of the amino acid substitution Y169F, which removes a single oxygen atom from the β2-α2 loop of the cellular prion protein (PrPC). When infected with RML or the 263K strain of prions, transgenic mice lacking wild-type (wt) PrPC but expressing MoPrP169F generated prion infectivity at levels comparable to wt mice. The newly generated MoPrP169F prions were biologically indistinguishable from those recovered from prion-infected wt mice, and elicited similar pathologies in vivo. Surprisingly, MoPrP169F prions showed greatly reduced PK resistance and density gradient analyses showed a significant reduction in high-density aggregates. Passage of MoPrP169F prions into mice expressing wt MoPrP led to full recovery of protease resistance, indicating that no strain shift had taken place. We conclude that a subtle structural variation in the β2-α2 loop of PrPC affects the sensitivity of PrPSc to protease but does not impact prion replication and infectivity. With these findings a specific structural feature of PrPC can be linked to a physicochemical property of the corresponding PrPSc.

MeSH terms

  • Amino Acid Substitution
  • Animals
  • Brain / metabolism*
  • Brain / pathology
  • Endopeptidase K / metabolism*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Mutagenesis, Site-Directed
  • Mutation / genetics
  • PrPSc Proteins / chemistry
  • PrPSc Proteins / genetics
  • PrPSc Proteins / metabolism*
  • Prion Diseases / pathology
  • Prion Diseases / transmission*
  • Prions / pathogenicity*
  • Protein Conformation
  • Proteolysis

Substances

  • PrPSc Proteins
  • Prions
  • Endopeptidase K

Grant support

AA is a recipient of an Advanced Grant of the European Research Council (ERC: 670958 http://erc.europa.eu/advanced-grants) and the Swiss National Foundation (SNF: 160329 and 147660), the Clinical Research Priority Programs "Small RNAs" and "Human Hemato-Lymphatic Diseases", SystemsX.ch (2014/260 and 2015/320), the Novartis Research Foundation, and the JPND Neurodegenerative Disease Research "Reframe" and "CureALS". KW is the Cecil H. and Ida M. Green Professor of Structural Biology at The Scripps Research Institute. SH is the recipient of SystemsX.ch (2015/320) and the commission innovations of the University Hospital of Zurich. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.