Prions

Abstract

The prion hypothesis^1-3 states that the prion and non-prion form of a protein differ only in their 3D conformation and that different strains of a prion differ by their 3D structure.^{4, 5} Recent technical developments have enabled solid-state NMR to address the atomic-resolution structures of full-length prions, and a first comparative study of two of them, HET-s and Ure2p, in fibrillar form, has recently appeared as a pair of companion papers.^{6, 7} Interestingly, the two structures are rather different: HET-s features an exceedingly well-ordered prion domain and a partially disordered globular domain. Ure2p in contrast features a very well ordered globular domain with a conserved fold, and – most probably - a partially ordered prion domain.⁶ For HET-s, the structure of the prion domain is characterized at atomic-resolution. For Ure2p, structure determination is under way, but the highly resolved spectra clearly show that information at atomic resolution should be achievable.

Acknowledgements

Many discussions with present and former members of our groups are acknowledged as well as funding by the Agence Nationale de la Recherche (ANR-JC05_44957, ANR-07-PCVI-0013-03, ANR-06-BLAN-0266, ANR-PCV08_321323 and ANR08-PCVI-0022-02), the ETH Zurich, the ETHIRA grant system and the Swiss National Science Foundation. We acknowledge a Germaine de Staël stipend for the collaboration between the labs involved.

Figures and Tables

Figure 1 Prions identified today and characterized as consisting of a prion domain (blue) and a globular domain (red).

Figure 2 Structure of HET-s (A) five moneomers out of a HET-s(218-289) protofilbril. One monomers forms two turns of a β-solenoid. (B) NMR bundle: superposition on residues N226 to G242, N262 to G278 of the 20 lowest-energy structures of a total of 200 calculated HET-s(218-289) structures. Only the central molecule of the heptamer is shown.24

Figure 3 DARR spectra (100 ms and 20 ms mixing, respectively) of the prion domains of HET-s and Ure2p reveal the considerably higher order encountered in HET-s(218-289) if compared to Ure2p(1-93) which represents itself in a narrow linewidth (see main text) HET-s spectrum adapted from,24,31 Ure2p adapted from.6

Figure 4 (A and B) Extracts of the 100 ms DARR spectra of HET-s(218-289) (blue) and HET-s(black). All peaks of the prion domain are present in the spectrum of the HET-s fibrils. (C and D) Extracts of the 100 ms DARR spectra of HET-s(1-227) (red) and HET-s(black). The structure of the prion domain is the same as in HET-s(218-289) while the globular domain looses its well-defined teritiary structure.7

Figure 5 Structural model of full-length HET-s. A Side view and B top view of 10 HET-s molecules within a HET-s amyloid fibril. The ellipsoids represent the N-terminal domains (residues 1–217) which structure is not precisely known in this context. Each molecule is colored uniquely.7

Figure 6 Extracts from 2D 13C DARR spectra recorded with 20 ms mixing time of Ure2p (black), Ure2p1-93 (blue) and Ure2p70-354 (red) (A and B) indicate that the prion domain is structurally different in its isolated form than in the context of the full-length protein. The globular domain, in contrast, is clearly preserved, as seen in (C and D).