Lipid interaction converts prion protein to a PrPSc-like proteinase K-resistant conformation under physiological conditions.

The conversion of prion protein (PrP) to the pathogenic PrPSc conformation is central to prion disease. Previous studies revealed that PrP interacts with lipids and the interaction induces PrP conformational changes, yet it remains unclear whether in the absence of any denaturing treatment, PrP-lipid interaction is sufficient to convert PrP to the classic proteinase K-resistant conformation. Using recombinant mouse PrP, we analyzed PrP-lipid interaction under physiological conditions and followed lipid-induced PrP conformational change with proteinase K (PK) digestion. We found that the PrP-lipid interaction was initiated by electrostatic contact and followed by hydrophobic interaction. The PrP-lipid interaction converted full-length alpha-helix-rich recombinant PrP to different forms. A significant portion of PrP gained a conformation reminiscent of PrPSc, with a PrPSc-like PK-resistant core and increased beta-sheet content. The efficiency for lipid-induced PrP conversion depended on lipid headgroup structure and/or the arrangement of lipids on the surface of vesicles. When lipid vesicles were disrupted by Triton X-100, PrP aggregation was necessary to maintain the lipid-induced PrPSc-like conformation. However, the PK resistance of lipid-induced PrPSc-like conformation does not depend on amyloid fiber formation. Our results clearly revealed that the lipid interaction can overcome the energy barrier and convert full-length alpha-helix-rich PrP to a PrPSc-like conformation under physiological conditions, supporting the relevance of lipid-induced PrP conformational change to in vivo PrP conversion.