Recombinant PrP(Sc) shares structural features with brain-derived PrP(Sc): Insights from limited proteolysis

Very solid evidence suggests that the core of full length PrP(Sc) is a 4-rung β-solenoid, and that individual PrP(Sc) subunits stack to form amyloid fibers. We recently used limited proteolysis to map the β-strands and connecting loops that make up the PrP(Sc) solenoid. Using high resolution SDS-PAGE followed by epitope analysis, and mass spectrometry, we identified positions ~116/118, 133–134, 141, 152–153, 162, 169 and 179 (murine numbering) as Proteinase K (PK) cleavage sites in PrP(Sc). Such sites likely define loops and/or borders of β-strands, helping us to predict the threading of the β-solenoid. We have now extended this approach to recombinant PrP(Sc) (recPrP(Sc)). The term recPrP(Sc) refers to bona fide recombinant prions prepared by PMCA, exhibiting infectivity with attack rates of ~100%. Limited proteolysis of mouse and bank vole recPrP(Sc) species yielded N-terminally truncated PK-resistant fragments similar to those seen in brain-derived PrP(Sc), albeit with varying relative yields. Along with these fragments, doubly N- and C-terminally truncated fragments, in particular ~89/97-152, were detected in some recPrP(Sc) preparations; similar fragments are characteristic of atypical strains of brain-derived PrP(Sc). Our results suggest a shared architecture of recPrP(Sc) and brain PrP(Sc) prions. The observed differences, in particular the distinct yields of specific PK-resistant fragments, are likely due to differences in threading which result in the specific biochemical characteristics of recPrP(Sc). Furthermore, recombinant PrP(Sc) offers exciting opportunities for structural studies unachievable with brain-derived PrP(Sc).