Yeast prions form infectious amyloid inclusion bodies in bacteria

Alba Espargaró,Anna Villar-Piqué,Salvador Ventura,Raimon Sabaté

doi:10.1186/1475-2859-11-89

Abstract

BackgroundPrions were first identified as infectious proteins associated with fatal brain diseases in mammals. However, fungal prions behave as epigenetic regulators that can alter a range of cellular processes. These proteins propagate as self-perpetuating amyloid aggregates being an example of structural inheritance. The best-characterized examples are the Sup35 and Ure2 yeast proteins, corresponding to [PSI+] and [URE3] phenotypes, respectively.ResultsHere we show that both the prion domain of Sup35 (Sup35-NM) and the Ure2 protein (Ure2p) form inclusion bodies (IBs) displaying amyloid-like properties when expressed in bacteria. These intracellular aggregates template the conformational change and promote the aggregation of homologous, but not heterologous, soluble prionogenic molecules. Moreover, in the case of Sup35-NM, purified IBs are able to induce different [PSI+] phenotypes in yeast, indicating that at least a fraction of the protein embedded in these deposits adopts an infectious prion fold.ConclusionsAn important feature of prion inheritance is the existence of strains, which are phenotypic variants encoded by different conformations of the same polypeptide. We show here that the proportion of infected yeast cells displaying strong and weak [PSI+] phenotypes depends on the conditions under which the prionogenic aggregates are formed in E. coli, suggesting that bacterial systems might become useful tools to generate prion strain diversity.

Highlights

Prions were first identified as infectious proteins associated with fatal brain diseases in mammals
Ure2 protein (Ure2p) and Sup35-NM form β-sheet enriched inclusion bodies (IBs) We analyzed the cellular distribution of Ure2p and Sup35-NM proteins when expressed recombinantly in bacteria at 37°C
Western blotting and densitometry of the soluble and insoluble fractions indicate that about 50% of Ure2p and 40% of Sup35-NM recombinant proteins reside in the insoluble cellular fraction in these conditions (Figure 1A and C)

Summary

Introduction

Prions were first identified as infectious proteins associated with fatal brain diseases in mammals. The best-characterized yeast prionogenic proteins are Sup and Ure, which, in their aggregated state, form two cytosolic inheritable elements named [PSI+] and [URE3], respectively Whether this property is detrimental and prion formation constitutes a pathological yeast trait or it is, in contrast, associated to beneficial phenotypes is controversial [2]. The fact that in wild-type yeast, the [PSI+] or [URE3] prions were initially not found was interpreted in favour of the first possibility [3,4], but a recent study by the Lindquist’s group demonstrates that various yeast prions can be found in several isolates of wild type yeast [5], favouring the second possibility Regardless of their cellular effects, both mammalian and fungal prion proteins are characterized by a high propensity to assemble into amyloid-like aggregates under physiological conditions both in vitro and in the cell [6]. It is suggested that this phenomenon results from a single protein being able to adopt multiple misfolded conformations, each one corresponding to a specific strain

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