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

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.

Structural effects of the highly protective V127 polymorphism on human prion protein

“…PrP V127 incorporation would also dope, with a dose-dependent effect, heteromeric polymers composed of both G127 and V127 PrP variants. Their reduced stability could increase cellular clearance, which would also explain the "dominant negative" effect of V127 on prion propagation 58 .…”

“…These conformationally variable elements have been shown to be key determinants of prion transmission and cross-species prion susceptibility, and a number are associated with inherited forms of prion disease, for example G131V, D167N, V210I, E211Q, Q212P and Q217R 26,28,37,[59][60][61][62][63][64] . In particular, the β2-α2 loop (residues 165-172) has been proposed to be a key modulator of prion transmission and disease-associated PrP misfolding [26][27][28]35,36,58 . V127 alters the structural flexibility of the β-sheet and conformational dynamics of the β2-α2 loop by disrupting the electrostatic interaction between R164 of the β-sheet and E168 within the adjacent β2-α2 loop.…”

PrPC knockdown by liposome-siRNA-peptide complexes (LSPCs) prolongs survival and normal behavior of prion-infected mice immunotolerant to treatment

“…LSPC treatment also impaired prion replication in the brains of infected TgA20 mice by up to 90%. A peculiarity of prion disease is that accumulation of PrP Res , as assessed by PK digestion and western blotting, does not always correlate to infectious prion titers, as assessed by mouse bioassay [97–102]. This anomaly could explain why LSPC treated mice replicated less prions and lived longer despite detecting no significant difference in PrP Res .…”

Potential application spectrum of microbial proteases for clean and green industrial production

“…The presence of proteinase-K-resistant prion protein is considered as a definitive diagnostic test for prion diseases in humans and other species (Leske et al 2017). Recently, however, absence of protease resistance in PrP Sc has been observed, and a mechanism for protease-sensitive prion infectivity has been proposed (Leske et al 2017).…”