Recombinant PrPSc shares structural features with brain-derived PrPSc: 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. [ABSTRACT FROM AUTHOR]