The α-Helical C-Terminal Domain of Full-Length Recombinant PrP Converts to an In-Register Parallel β-Sheet Structure in PrP Fibrils: Evidence from Solid State Nuclear Magnetic Resonance

Abstract

We report the results of solid state nuclear magnetic resonance (NMR) measurements on amyloid fibrils formed by the full-length prion protein PrP (residues 23−231, Syrian hamster sequence). Measurements of intermolecular ¹³C−¹³C dipole−dipole couplings in selectively carbonyl-labeled samples indicate that β-sheets in these fibrils have an in-register parallel structure, as previously observed in amyloid fibrils associated with Alzheimer’s disease and type 2 diabetes and in yeast prion fibrils. Two-dimensional ¹³C−¹³C and ¹⁵N−¹³C solid state NMR spectra of a uniformly ¹⁵N- and ¹³C-labeled sample indicate that a relatively small fraction of the full sequence, localized to the C-terminal end, forms the structurally ordered, immobilized core. Although unique site-specific assignments of the solid state NMR signals cannot be obtained from these spectra, analysis with a Monte Carlo/simulated annealing algorithm suggests that the core is comprised primarily of residues in the 173−224 range. These results are consistent with earlier electron paramagnetic resonance studies of fibrils formed by residues 90−231 of the human PrP sequence, formed under somewhat different conditions [Cobb, N. J., Sonnichsen, F. D., McHaourab, H., and Surewicz, W. K. (2007) Proc. Natl. Acad. Sci. U.S.A.104, 18946−18951], suggesting that an in-register parallel β-sheet structure formed by the C-terminal end may be a general feature of PrP fibrils prepared in vitro.