The Residue 129 Polymorphism in Human Prion Protein Does Not Confer Susceptibility to Creutzfeldt-Jakob Disease by Altering the Structure or Global Stability of PrPC

Abstract

There are two common forms of prion protein (PrP) in humans, with either methionine or valine at position 129. This polymorphism is a powerful determinant of the genetic susceptibility of humans toward both sporadic and acquired forms of prion disease and restricts propagation of particular prion strains. Despite its key role, we have no information on the effect of this mutation on the structure, stability, folding, and dynamics of the cellular form of PrP (PrP C ). Here, we show that the mutation has no measurable effect on the folding, dynamics, and stability of PrP C . Our data indicate that the 129M/V polymorphism does not affect prion propagation through its effect on PrP C ; rather, its influence is likely to be downstream in the disease mechanism. We infer that the M/V effect is mediated through the conformation or stability of disease-related PrP (PrP Sc ) or intermediates or on the kinetics of their formation.The prion diseases are a group of fatal neurodegenerative diseases that include scrapie in sheep and goats; bovine spongiform encephalopathy (BSE) 1 in cattle; and Creutzfeldt-Jakob disease (CJD), Gerstmann-Strä ussler-Scheinker disease, fatal familial insomnia (FFI), and kuru in humans. The human diseases may be inherited, arise sporadically, or be acquired through exposure to infectious prions (1, 2). Although rare in humans, intense interest has focused on these diseases both because of their unique biology and because of the occurrence of variant CJD, a new form of human prion disease, and the experimental evidence that it is caused by a BSE-like prion strain (3-5).According to the "protein-only" hypothesis (6), prions are composed principally or entirely of abnormal isoforms of hostencoded prion protein (PrP) (7). The disease-related isoform, PrP Sc , is derived from its normal cellular precursor, PrP C , by a post-translational process that involves conformational change. PrP Sc can be distinguished biochemically from PrP C by its partial protease resistance and detergent insolubility.Although the precise molecular events involved in this conversion remain ill defined, molecular genetic and in vitro studies support the hypothesis that some sort of direct interaction between PrP Sc and either PrP C or some less organized state occurs. This interaction results in the PrP Sc conformation being imposed upon the substrate protein, and the process of conversion is favored by sequence complementarity (8 -13). A key piece of evidence supporting this and the protein-only hypothesis in general is the finding that the large majority of cases of sporadic CJD are homozygous with respect to a common polymorphism at position 129 in the human prion protein, in which either methionine or valine can be encoded (only ϳ49% of the UK population are homozygous with respect to this polymorphism) (9).Elderly survivors of the kuru epidemic (an acquired prion disease largely restricted to the Fore linguistic group of the Papua New Guinea Highlands, which was transmitted during endocannibalistic feasts) who had mult...

Conformational Properties of β-PrP

“…This region of the protein is predominantly unstructured, as indicated by 15 N relaxation rates (6,14). However, previous studies have indicated that this region of the protein may be exchanging between more structured or collapsed states, as it exhibits differential peak intensities (14), and residues 105-126 appear to be capable of forming intra-and/or intermolecular interactions in full-length ␤-PrP oligomers (35).…”

“…Equilibrium Denaturation Data Monitored by CD-The amide CD absorption of 50 M ␤-PrP in 10 mM sodium acetate, 2 mM sodium azide, 2 mM DTT, pH 4.0, was recorded in varying concentrations of urea as previously described (6,13). The mean residue ellipticity signal ([ ]r) at 215 nm was converted to the proportion of molecules in the unfolded state, ␣ U , according to the relationship,…”

“…Expression and purification of 15 N-and 13 C/ 15 N-labeled protein for NMR study was carried out as described previously (6). Samples were stored in 6 M guanidinium hydrochloride, 100 mM EDTA, pH 8.0 at Ϫ20°C, prior to use.…”

“…The disease-associated form of the protein, termed the scrapie form or PrP Sc , differs from the normal cellular form (PrP C ) through a conformational change, resulting in a significant increase in the ␤-sheet content and protease resistance of the protein (3,4). PrP C , in contrast, consists of a predominantly ␣-helical structured domain and an unstructured N-terminal domain, which is capable of binding a number of divalent metals (5)(6)(7)(8)(9)(10)(11)(12). A single disulfide bond links two of the main ␣-helices and forms an integral part of the core of the structured domain (13,14).…”

Specific Features of the Prion Protein Transmembrane Domain Regulate Nascent Chain Orientation

“…The identity of the amino acid at position 129 has a significant impact on infectious, sporadic, and familial prion diseases. Although the importance of the polymorphism has been well documented, studies have only revealed slight effects of the substitution on prion stability and conversion (28,29) and a possible effect on the kinetics of amyloid formation (30).…”