Conformational variability of the synthetic peptide 129-141 of the mouse prion protein

The effect of solution conditions on the conformation of the peptide corresponding to residues 129-141 of the mouse prion protein has been examined by experimental and theoretical tools including circular dichroism, secondary structure predictions, and Molecular Dynamics simulations. The conformational properties of the peptide observed by CD confirm the prediction results: the peptide is chiefly random coil in water. The conformational sampling performed by Molecular Dynamics simulations in water also corroborates the flexibility of the peptide, in particular for the N-terminal part. We show, however, that the peptide samples hairpin conformations in one of several approximately 1-ns Molecular Dynamics simulations in water. Interestingly, the analysis of the CD spectra obtained in this study suggests the presence of beta-structure which, given the length of the peptide, can only consist in beta-hairpin. The peptide can also be induced to form a modest percentage of helical structure in the presence of organic cosolvents such as trifluoroethanol, or detergents such as sodium dodecyl sulfate and lysophosphatidylcholine. This result is different from that obtained for a homologous hamster fragment, which differs from the mouse sequence by the single substitution of Ile 139 to Met. Interestingly, this substitution is crucial for the barrier in the transmission of the prion disease between hamsters and mice.