β-Sheet core of human prion protein amyloid fibrils as determined by hydrogen/deuterium exchange

Propagation of transmissible spongiform encephalopathies is associated with the conversion of normal prion protein, PrPc, into a misfolded, oligomeric form, PrPSc. Although the high-resolution structure of the PrPc is well characterized, the structural properties of PrPSc remain elusive. Here we used MS analysis of H/D backbone amide exchange to examine the structure of amyloid fibrils formed by the recombinant human PrP corresponding to residues 90-231 (PrP90-231), a misfolded form recently reported to be infectious in transgenic mice overexpressing PrPc. Analysis of H/D exchange data allowed us to map the systematically H-bonded beta-sheet core of PrP amyloid to the C-terminal region (staring at residue approximate to 169) that in the native structure of PrP monomer corresponds to alpha-helix 2, a major part of alpha-helix 3, and the loop between these two helices. No extensive hydrogen bonding (as indicated by the lack of significant protection of amide hydrogens) was detected in the N-terminal part of PrP90-231 fibrils, arguing against the involvement of residues within this region in stable beta-structure. These data provide long-sought experimentally derived constraints for high-resolution structural models of PrP amyloid fibrils.