Folding and intrinsic stability of deletion variants of PrP(121–231), the folded C-terminal domain of the prion protein Original Research Article

Transmissible spongiform encephalopathies in mammals are believed to be caused by PrPSc, the insoluble, oligomeric isoform of the cellular prion protein PrPC. PrPC and the subunits of PrPSc have identical covalent but different tertiary structure. To address the question of whether parts of the structure of PrPC are sufficiently stable to be retained in PrPSc, we have constructed two deletion variants of the C-terminal PrPC domain, PrP(121–231), which is the only part of recombinant PrP with defined tertiary structure. One of the variants, H2–H3, comprises the last two α-helices of PrP(121–231) that have been proposed to be preserved in models of PrPSc. In the other variant, PrP(121–231)-ΔH1, the first α-helix of PrP(121–231) was deleted and replaced by introduction of the β-turn dipeptide Asn–Gly between the strands of the single β-sheet of PrP(121–231). Although both deletion constructs still show α-helical CD-spectra, they are more disordered and thermodynamically strongly destabilized compared to PrP(121–231), with free energies of folding close to zero. These data demonstrate that the tertiary structure context is critical for the conformation of the segment comprising α-helix 2 and 3 in the solution structure of recombinant PrP.