Prion protein NMR structures of elk and of mouse/elk hybrids

Abstract

The NMR structure of the recombinant elk prion protein (ePrP), which represents the cellular isoform (ePrP C ) in the healthy organism, is described here. As anticipated from the highly conserved amino acid sequence, ePrP C has the same global fold as other mammalian prion proteins (PrPs), with a flexibly disordered ''tail'' of residues 23-124 and a globular domain 125-226 with three ␣-helices and a short antiparallel ␤-sheet. However, ePrP C shows a striking local structure variation when compared with most other mammalian PrPs, in particular human, bovine, and mouse PrP C . A loop of residues 166 -175, which links the ␤-sheet with the ␣2-helix and is part of a hypothetical ''protein X'' epitope, is outstandingly well defined, whereas this loop is disordered in the other species. Based on NMR structure determinations of two mouse PrP variants, mPrP[N174T] and mPrP[S170N,N174T], this study shows that the structured loop in ePrP C relates to these two local amino acid exchanges, so that mPrP[S170N,N174T] exactly mimics ePrP C . These results are evaluated in the context of recent reports on chronic wasting disease (CWD) in captive and free-ranging deer and elk in the U.S. and Canada, and an animal model is proposed for support of future research on CWD.transmissible spongiform encephalopathy ͉ chronic wasting disease C hronic wasting disease (CWD) is a neurological disorder in cervids that has been shown to be a transmissible spongiform encephalopathy (TSE) or ''prion disease''; other prion diseases include scrapie in sheep, bovine spongiform encephalopathy (BSE), and Creutzfeldt-Jakob disease in humans (1-3). CWD was diagnosed in 1978 as a TSE in a captive mule deer (Odocoileus hemionus) (4, 5) and was diagnosed in 1981 in a free-ranging elk (Cervus elaphus nelsoni) (6). Today, CWD is known to affect captive and free-ranging elk, mule deer, and white-tailed deer (O. virginianus), and the disease seems to be endemic in areas of the western United States and Canada.CWD is unique among TSEs by the fact that is has been studied in free-ranging species (7). The natural route of exposure appears to be oral, possibly through direct interaction between animals or through environmental contamination (8, 9). Although there is evidence for transmission to different mammalian species by intracerebral inoculation (7, 10, 11), domestic animals such as cattle, sheep, and goats are not known to be naturally susceptible to CWD (12). Compared with bovine spongiform encephalopathy (BSE), CWD transmission to cattle, goats, and laboratory animals has been reported to be inefficient, suggesting that there is a rather stringent species barrier (13-15). Cell-free conversion experiments (15) led to the prediction that TSE transmission efficiency from cervids to humans might be similar to that from cattle to humans, which is clearly of serious concern. Overall, the potential threat to livestock and the human population from the recent spread of CWD in free-ranging cervids in the U.S. and Canada is still difficult to assess, and further r...

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

“…For PrP, the first [8] and most abundant structural information has been obtained by nuclear magnetic resonance techniques (NMR), which has resulted in experimentally derived models of PrP of a wide variety of species [64][65][66][67][68][69][70]. For human and sheep PrP, structures determined by X-ray crystallography have also been reported, both with and without antibodies bound [71][72][73][74][75].…”

A prion disease of cervids: Chronic wasting disease

“…The PrP C structure has been solved by nuclear magnetic resonance (NMR) analysis from recombinant prion protein from a library of vertebrate species [13,21,31,[45][46][47]63]. The global architecture of the various mammalian PrP structures are nearly identical.…”

“…The global architecture of the various mammalian PrP structures are nearly identical. Intriguingly, elk PrP possesses an extremely well-defined loop connecting the second alpha helix and beta sheet (amino acids 166-175), whereas the homologous region is flexibly disordered in human and bovine PrP C [21]. In the laboratory of Kurt Wüthrich, this loop region has been studied in detail, and the loop is thought to provide structural insights into species barriers for prion disease [12].…”

“…In the laboratory of Kurt Wüthrich, this loop region has been studied in detail, and the loop is thought to provide structural insights into species barriers for prion disease [12]. Further structural studies in two mutant mouse PrP variants derived from the elk PrP primary structure, mPrP[N174T] and mPrP[S170N, N174T], have confirmed that the defined loop in the elk is due to two amino acid exchanges, as the mPrP[S170N, N174T] has the conformationally identical rigid loop of the elk [21]. It is of great interest to determine whether the loop region of the elk influences TSE susceptibility and CWD transmission to other species.…”

Misfolding of the prion protein: linking biophysical and biological approaches

“…The conformation of the S2-H2 loop seems to play an important role in PrP C /PrP Sc conversion. (i) Protein X was putatively proposed to target the S2-H2 loop and to promote the opening of the molecule like a lever [54]; (ii) in sheep, mutation Q171R located in the S2-H2 loop confers a resistance phenotype to sheep scrapie [49]; (iii) the conformation of this loop was proposed as the basis of TSE susceptibility differences in domestic animals [41]. Since the separation of H1-S2 from the rest of the protein is a prerequisite unfolding event for oligomerization, all mutations affecting the H1-S2 expansion from the H2-H3 bundle may be involved in the PrP C /PrP Sc conversion as for the human Q217R mutation.…”