Date Published: February 16, 2017
Publisher: Public Library of Science
Author(s): Henning Leske, Simone Hornemann, Uli Simon Herrmann, Caihong Zhu, Paolo Dametto, Bei Li, Florent Laferriere, Magdalini Polymenidou, Pawel Pelczar, Regina Rose Reimann, Petra Schwarz, Elisabeth Jane Rushing, Kurt Wüthrich, Adriano Aguzzi, Jiyan Ma.
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.
Transmissible spongiform encephalopathies are fatal neurodegenerative diseases associated with the presence of prions . It is well-established that prions contain aggregates of misfolded cellular prion protein (PrPC). Such aggregates have been termed “PrPSc” because they were initially found in scrapie-affected sheep, or alternatively as “PrPres” to denote their extraordinary resistance to proteolytic digestion. Indeed, the carboxy-proximal core of PrPSc can largely withstand proteolysis with 500 μg/ml proteinase-K (PK) [2,3], and the detection of PK-resistant prion protein is commonly regarded as the definitive diagnostic method for prion diseases in humans and other species.
One major goal of prion research is to better understand the relationship between PrPSc structure and pathogenesis. A powerful approach towards this goal relies on developing variants of PrPC with well-defined structural features and molecular dynamics, and analyzing the consequences of their in vivo expression under conditions of health and disease. The design of such in vivo experiments is supported by the availability of atomic-resolution PrPC structures [8–22]. Here we focused on the β2-α2 loop because its conformation affects cross-species transmission of prions and is even associated with the spontaneous generation of prions [35–37].