Helix H1 of the prion protein is rather stable against environmental perturbations: molecular dynamics of mutation and deletion variants of PrP(90-231)

We need to understand the underlying factors that promote or reverse the amyloid-type structure of the prion protein (PrP). In an earlier study, we showed that mutations within the first beta strand can extend the short beta sheet in the normal protein into a larger sheet at neutral pH. To determine the impact of the point mutation P102L and the deletion of either the first or the second beta strand on PrP, we performed further long molecular explicit water dynamics simulations. The trajectories show that all mutations do not exert a uniform effect on the dynamics of the N-terminal tail. The results of the deletion of the two beta strands confirm the idea that partially unfolded conformations are involved in the structural transition. In the deletion variants, the alpha helices H2 and H3 are disordered, while helix H1 is either fully stable or partially disordered. This finding, consistent with recent spectroscopic analyses on peptides spanning helix H1 and flanking sequences, demonstrates that unfolding of the full domain containing helix H1 is not an early step in PrP interconversion. This result also raises questions regarding a current view of PrPSc structure that transforms helix H1 into a beta sheet conformation.