Correlation of structural elements and infectivity of the HET-s prion

Abstract

Alzheimer's, prion diseases and other neurodegenerative disorders are associated with insoluble protein fibres called amyloid fibrils. Gathering structural information about these has proved difficult, but three groups now report success with contrasting approaches to the problem. The cover shows the atomic structure of the ‘spine’ of an amyloid-like fibril formed by the yeast prion protein Sup35. To obtain this structure, Nelson et al. performed X-ray crystallography on amyloid microcrystals. Krishnan and Lindquist used a raft of techniques to study folding of the amyloid core. And Ritter et al. determined the infectious conformation of HET-s prion of a filamentous fungus. Christopher Dobson ponders on what this flood of structural data says about prion and amyloid formation in sickness and in health. Prions are believed to be infectious, self-propagating polymers of otherwise soluble, host-encoded proteins1,2. This concept is now strongly supported by the recent findings that amyloid fibrils of recombinant prion proteins from yeast3,4,5, Podospora anserina6 and mammals7 can induce prion phenotypes in the corresponding hosts. However, the structural basis of prion infectivity remains largely elusive because acquisition of atomic resolution structural properties of amyloid fibrils represents a largely unsolved technical challenge. HET-s, the prion protein of P. anserina, contains a carboxy-terminal prion domain comprising residues 218–289. Amyloid fibrils of HET-s(218–289) are necessary and sufficient for the induction and propagation of prion infectivity6. Here, we have used fluorescence studies, quenched hydrogen exchange NMR and solid-state NMR to determine the sequence-specific positions of amyloid fibril secondary structure elements of HET-s(218–289). This approach revealed four β-strands constituted by two pseudo-repeat sequences, each forming a β-strand-turn-β-strand motif. By using a structure-based mutagenesis approach, we show that this conformation is the functional and infectious entity of the HET-s prion. These results correlate distinct structural elements with prion infectivity.