Conformational variations in an infectious protein determine prion strain differences

Abstract

A remarkable feature of prion biology is the strain phenomenon wherein prion particles apparently composed of the same protein lead to phenotypically distinct transmissible states. To reconcile the existence of strains with the 'protein-only' hypothesis of prion transmission, it has been proposed that a single protein can misfold into multiple distinct infectious forms, one for each different strain. Several studies have found correlations between strain phenotypes and conformations of prion particles; however, whether such differences cause or are simply a secondary manifestation of prion strains remains unclear, largely due to the difficulty of creating infectious material from pure protein. Here we report a high-efficiency protocol for infecting yeast with the [PSI+] prion using amyloids composed of a recombinant Sup35 fragment (Sup-NM). Using thermal stability and electron paramagnetic resonance spectroscopy, we demonstrate that Sup-NM amyloids formed at different temperatures adopt distinct, stably propagating conformations. Infection of yeast with these different amyloid conformations leads to different [PSI+] strains. These results establish that Sup-NM adopts an infectious conformation before entering the cell--fulfilling a key prediction of the prion hypothesis--and directly demonstrate that differences in the conformation of the infectious protein determine prion strain variation.

The yeast prion protein Ure2: Structure, function and folding

“…In addition, [Het-s] has been identified as a prion of the filamentous fungus Podospora anserina [16,17]. The relative simplicity and tractability of yeast and other fungal systems has allowed convincing proof of the protein-only hypothesis for Het-s [18], Sup35 [19,20] and Ure2 [21].…”

The self-interaction of native TDP-43 C terminus inhibits its degradation and contributes to early proteinopathies

“…Comparisons among the cellular and misfolded properties of the known Q/N-rich domain are shown in Table 1 [20][21][22][23][24][25][26][27][28][29][30][31] . The cellularfolded Q/N-rich domain shared key properties characteristic of the misfolded proteins, including insolubility and a tendency to form aggregates via intrinsic element-and self-interactions.…”

Disaggregases, molecular chaperones that resolubilize protein aggregates

“…Where present and undisrupted, the [PSI+] phenotype continuously passes from generation to generation. [PSI + ] is mediated via interactions at its N-terminal, which is rich in glutamine and asparagine residues, and middle domains, which are sufficient when in an amyloidogenic form to induce prion conversion (Tanaka et al 2004 The conformational state of the Rnq1 protein, which has a prion domain at the C-terminus, determines the yeast prion [RNQ+] phenotype (Sondheimer and Lindquist 2000). The native function of Rnq1p is not clear, but the prion form interacts and helps other polypeptides, such as sup35 and those with polyQ extensions, to form amyloidlike aggregates in a process called prion crossseeding (Osherovich and Weissman 2001, Meriin et al 2002, Taneja et al 2007).…”