Prion Protein Fragments Spanning Helix 1 and Both Strands of Beta Sheet (residues 125-170) Show Evidence for Predominantly Helical Propensity by CD and NMR.

Background: Transmissible spongiform encephalopathies are a group of neurodegenerative disorders of man and animals that are believed to be caused by an α-helical to β-sheet conformational change in the prion protein, PrP. Recently determined NMR structures of recombinant PrP (residues 121–231 and 90–231) have identified a short two-stranded anti-parallel β sheet in the normal cellular form of the protein (PrPC). This β sheet has been suggested to be involved in seeding the conformational transition to the disease-associated form (PrPSc) via a partially unfolded intermediate state.Results: We describe CD and NMR studies of three peptides (125–170, 142–170 and 156–170) that span the β-sheet and helix 1 region of PrP, forming a large part of the putative PrPSc–PrPC binding site that has been proposed to be important for self-seeding replication of PrPSc. The data suggest that all three peptides in water have predominantly helical propensities, which are enhanced in aqueous methanol (as judged by deviations from random-coil Hα chemical shifts and 3JHα–NH values). Although the helical propensity is most marked in the region corresponding to helix 1 (144–154), it is also apparent for residues spanning the two β-strand sequences.Conclusions:We have attempted to model the conformational properties of a partially unfolded state of PrP using peptide fragments spanning the region 125–170. We find no evidence in the sequence for any intrinsic conformational preference for the formation of extended β-like structure that might be involved in promoting the PrPC–PrPSc conformational transition.