The Conversion of Helix H2 to β-Sheet Is Accelerated in the Monomer and Dimer of the Prion Protein upon T183A Mutation

Abstract

The conversion of the prion protein (PrP) from its cellular form, PrP^C, to its pathogenic scrapie form, PrP^Sc, is a key event in neurodegenerative transmissible spongiform encephalopathies such as Creutzfeldt−Jakob disease (CJD). PrP^C is characterized by three helices (H1−H3) and a small antiparallel β-sheet. One working hypothesis for TSE causation is that oligomeric forms of PrP are the proximate neurotoxic agents. Because these states are transient in character, current experimental studies have failed to provide atomic structures. To gain insights into these intermediates, we have studied PrP125-228 and its CJD-causing T183A variant in their monomer and dimer forms by means of coarse-grained protein molecular dynamics simulations. Our 1.5 microsecond simulations show that the decrease in the thermodynamic stability of PrP monomer upon T183A, consistent with experimental studies, results from a destabilization of the H2H3 subdomain. Comparison of the monomer and dimer properties from wild-type and T183A PrP reveals that helix H1 is robust and the H2H3 subdomain displays a much higher propensity for intra- and inter-β-sheets in T183A than in the wild-type sequence under denaturing conditions. However, both species display negligible β-sheet structure. Implications of our simulations on prion propagation are discussed.