Polymorphism at Residue 129 Modulates the Conformational Conversion of the D178N Variant of Human Prion Protein 90−231

Abstract

One of the arguments in favor of the protein-only hypothesis of transmissible spongiform encephalopathies is the link between inherited prion diseases and specific mutations in the PRNP gene. One such mutation (Asp178 → Asn) is associated with two distinct disorders: fatal familial insomnia or familial Creutzfeldt−Jakob disease, depending upon the presence of Met or Val at position 129, respectively. In this study, we have characterized the biophysical properties of recombinant human prion proteins (huPrP90−231) corresponding to the polymorphic variants D178N/M129 and D178N/V129. In comparison to the wild-type protein, both polymorphic forms of D178N huPrP show a greatly increased propensity for a conversion to β-sheet-rich oligomers (at acidic pH) and thioflavine T-positive amyloid fibrils (at neutral pH). Importantly, the conversion propensity for the D178N variant is strongly dependent upon the M/V polymorphism at position 129, whereas under identical experimental conditions, no such dependence is observed for the wild-type protein. Amyloid fibrils formed by wild-type huPrP90−231 and the D178N variant are characterized by different secondary structures, and these structures are further modulated by residue 129 polymorphism. Although on the basis of only in vitro data, this study strongly suggests that polymorphism-dependent phenotypic variability of familial prion diseases may be linked to differences in biophysical properties of prion protein variants.

β-Sheet core of human prion protein amyloid fibrils as determined by hydrogen/deuterium exchange

“…As shown previously (25), incubation of huPrP90-231 under the conditions described in Materials and Methods resulted in time-dependent conversion of the protein to amyloid fibrils that bind thioflavine T dye. Although variable in length, morphologically these fibrils appeared quite homogenous (Fig.…”

“…Such long-term protection is typical of a cross ␤-structure, a motif common to many amyloids (27, 31-33, 35, 36). Infrared spectroscopic data indicate that the conversion of PrP23-231 and PrP90-231 to amyloid fibrils is indeed accompanied by a major increase in ␤-structure (24,25). This newly formed ␤-structure is highly unlikely to arise from segments N-terminal to residue Ϸ169, because all peptic fragments derived from this part of PrP90-231 fibrils show very rapid deuterium incorporation.…”

“…Recently it has been shown that the recombinant PrP (PrP23-231), or a biologically relevant fragment, PrP90-231, can be converted into a variety of oligomeric forms that are rich in ␤-sheet structure and have increased resistance to PK digestion (22)(23)(24)(25). These aggregates include amyloid fibrils, a form of PrP recently reported to be infectious in a transgenic mice model overproducing PrP C (8).…”

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

“…Urea-induced unfolding studies indicated that the thermodynamic stability of PrP decreases by ~22 kJ mol -1 upon introduction of the mutation [136]. It was further found that the structure of D178N PrP Sc is different from WT PrP Sc obtained under the same conditions [137,138].…”

Instability of familial spongiform encephalopathy-related prion mutants

“…Recently, MD simulation has shown that the mutation of Asp to Asn at position 178 plays an important role in the conformational conversion to -sheet-rich PrP [18]. Linkages between familial prion diseases and mutations in the gene encoding human prion protein were reported and over 20 such mutations have been shown to date to segregate familial CJD, GSS and FFI [1,19,20].…”