Structural Mechanism of Barriers for Interspecies Seeding Transmissibility of Full‐length Prion Protein Amyloid

: A puzzling feature of prion diseases is the cross-species barriers. The detailed molecular mechanisms underlying these interspecies barriers remain poorly understood because of a lack of high-resolution structural information on the scrapie isoform of the prion protein (PrPSc ). In this study we identified the critical role of the residues 165/167 in the barrier to seeding mouse PrP (mPrP) fibril seeds to human cellular prion protein (PrPC ). Solid-state NMR revealed a C-terminal β-sheet core spanning residues 165-230 and the packing arrangement of mPrP fibrils. Residues 165/167 are located on one end of the fibril core. Molecular dynamics simulations demonstrated that the stabilities of the seeding-induced β-strand structures are significantly impacted by hydrogen bonds involving the side chain of residue 167 and steric resistance involving residue 165. These findings suggest that the α2-β2 loop containing residues 165/167 could be the initial site of seed-template conformational conversion.