The Val-210-Ile pathogenic Creutzfeldt-Jakob disease mutation increases both the helical and aggregation propensities of a sequence corresponding to helix-3 of PrP(C)

A peptide corresponding to the third helical region within the PrP(C) protein, from residues 198 to 218 (helix-3), was synthesised with and without the familial 210-Val to Ile Creutzfeldt-Jakob disease mutation. The NMR structure of PrP(C) predicts no global variation in stability for this mutation, indicating that local sequence rather than global structural factors are involved in the pathological effects of this mutation. 1H NMR analysis of peptides with and without this mutation indicated that it had no significant effect on local helical structure. Temperature denaturation studies monitored by CD showed that the mutation increased the helical content within this region (helical propensity), but did not stabilise the helix toward denaturation (helical stability). Aggregation data indicated that, in addition to increasing helical propensity, this mutation increased the aggregation propensity of this sequence. CD and NMR data indicate that helical interactions, stabilised by the Val-210-Ile mutation, may precede the formation of beta-sheet aggregates in this peptide sequence. Therefore, this pathological mutation probably does not facilitate PrP(C) to PrP(Sc) conversion by directly destabilising the helical structure of PrP(C), but may preferentially stabilise PrP(Sc) by facilitating beta-sheet formation within this sequence region of PrP. In addition, helical interactions between helix-3 in two or more PrP(C) molecules may promote conversion to PrP(Sc).