The human prion protein α2 helix: A thermodynamic study of its conformational preferences

Abstract

We have synthesized both free and terminally-blocked peptide corresponding to the second helical region of the globular domain of normal human prion protein, which has recently gained the attention of structural biologists because of a possible role in the nucleation process and fibrillization of prion protein. The profile of the circular dichroism spectrum of the free peptide was that typical of alpha-helix, but was converted to that of beta-structure in about 16 h. Instead, below 2.1 x 10(-5) M, the spectrum of the blocked peptide exhibited a single band centered at 200 nm, unequivocally associated to random conformations, which did not evolve even after 24 h. Conformational preferences of this last peptide have been investigated as a function of temperature, using trifluoroethanol or low-concentration sodium dodecyl sulfate as alpha- or beta-structure inducers, respectively. Extrapolation of free energy data to zero concentration of structuring agent highlighted that the peptide prefers alpha-helical to beta-type organization, in spite of results from prediction algorithms. However, the free energy difference between the two forms, as obtained by a thermodynamic cycle, is subtle (roughly 5-8 kJ mol(-1) at any temperature from 280 K to 350 K), suggesting conformational ambivalence. This result supports the view that, in the prion protein, the structural behavior of the peptide is governed by the cellular microenvironment.

Design of anti- and pro-aggregation variants to assess the effects of methionine oxidation in human prion protein

“…This experimental model supports a natural scenario where oxidative conversion of Met residues, especially buried ones, into Met(O) may act as primary event in sporadic prion disease induction, particularly taking into account the pronounced structural ambivalence of PrP C . In fact, model studies on the peptides related to ␣-helix II of PrP C clearly revealed a surprisingly low free energy difference between the ␣-helical and ␤-sheet conformations of only 5-8 kJ⅐mol Ϫ1 , confirming at least for this helix a conformational ambivalence (54,55).…”

Mouse Prion Protein Polymorphism Phe-108/Val-189 Affects the Kinetics of Fibril Formation and the Response to Seeding

“…Both residues have been implicated in prion disease, either by playing a role in the initial stages of PrP C conversion (27)(28)(29) or by influencing the susceptibility to prion infection (13)(14)(15)(16).…”

Molecular Dynamics as an Approach to Study Prion Protein Misfolding and the Effect of Pathogenic Mutations

“…187-194) is significantly less stable than the rest; NMR studies reveal that it can exist in a disordered conformation [39] and hydrogen-exchange protection of the backbone amides is low [39, 76,79]. The many threonine residues in this sequence (HTVTTTTK, conserved in mammalian PrPs) cause this part of HB to have an inherently low helical propensity [80]. Notably, this part of HB appears to be stabilized to some degree by the presence of the flexible Nterminus, likely due to contacts [39].…”