Prion formation by a yeast GLFG nucleoporin

Howard Hughes Medical Institute
Prion (Impact Factor: 2.24). 09/2012; 6(4):391-9. DOI: 10.4161/pri.20199
Source: PubMed


The self-assembly of proteins into higher order structures is both central to normal biology and a dominant force in disease. Certain glutamine/asparagine (Q/N)-rich proteins in the budding yeast Saccharomyces cerevisiae assemble into self-replicating amyloid-like protein polymers, or prions, that act as genetic elements in an entirely protein-based system of inheritance. The nuclear pore complex (NPC) contains multiple Q/N-rich proteins whose self-assembly has also been proposed to underlie structural and functional properties of the NPC. Here we show that an essential sequence feature of these proteins-repeating GLFG motifs-strongly promotes their self-assembly into amyloids with characteristics of prions. Furthermore, we demonstrate that Nup100 can form bona fide prions, thus establishing a previously undiscovered ability of yeast GLFG nucleoporins to adopt this conformational state in vivo.

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Available from: Randal Halfmann
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    • "A number of search algorithms to identify new prion proteins have been developed that take advantage of this fact by testing for compositional similarity to known PFDs [16], [19], [20]. Several prions were discovered using these methods [19], [21], [22]. However, this approach has limitations. "
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    ABSTRACT: Prion formation involves the conversion of proteins from a soluble form into an infectious amyloid form. Most yeast prion proteins contain glutamine/asparagine-rich regions that are responsible for prion aggregation. Prion formation by these domains is driven primarily by amino acid composition, not primary sequence, yet there is a surprising disconnect between the amino acids thought to have the highest aggregation propensity and those that are actually found in yeast prion domains. Specifically, a recent mutagenic screen suggested that both aromatic and non-aromatic hydrophobic residues strongly promote prion formation. However, while aromatic residues are common in yeast prion domains, non-aromatic hydrophobic residues are strongly under-represented. Here, we directly test the effects of hydrophobic and aromatic residues on prion formation. Remarkably, we found that insertion of as few as two hydrophobic residues resulted in a multiple orders-of-magnitude increase in prion formation, and significant acceleration of in vitro amyloid formation. Thus, insertion or deletion of hydrophobic residues provides a simple tool to control the prion activity of a protein. These data, combined with bioinformatics analysis, suggest a limit on the number of strongly prion-promoting residues tolerated in glutamine/asparagine-rich domains. This limit may explain the under-representation of non-aromatic hydrophobic residues in yeast prion domains. Prion activity requires not only that a protein be able to form prion fibers, but also that these fibers be cleaved to generate new independently-segregating aggregates to offset dilution by cell division. Recent studies suggest that aromatic residues, but not non-aromatic hydrophobic residues, support the fiber cleavage step. Therefore, we propose that while both aromatic and non-aromatic hydrophobic residues promote prion formation, aromatic residues are favored in yeast prion domains because they serve a dual function, promoting both prion formation and chaperone-dependent prion propagation.
    Full-text · Article · Feb 2014 · PLoS ONE
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    • "Use of poor nitrogen source Lacroute (1971) and Wickner (1994) Sup35 [PSI + ] Translation termination factor Increased nonsense suppression Cox (1965) and Wickner (1994) Rnq1 [PIN + ]/ [RNQ + ] Unknown Increased de novo formation of other prions Derkatch et al. (1997) (2001) and Sondheimer & Lindquist (2000) Swi1 [SWI + ] Subunit of chromatin remodeling complex Altered carbon source utilization Du et al. (2008) Cyc8 [OCT + ] Transcriptional co-repressor Altered carbon source utilization, flocculation Patel et al. (2009) Mot3 [MOT + ] Transcriptional co-repressor Change in cell wall composition Alberti et al. (2009) Sfp1 [ISP + ] Transcriptional activator Antisuppression Rogoza et al. (2010) Mod5 [MOD + ] tRNA modification enzyme Increased level of ergosterol and resistance to antifungal drugs Suzuki et al. (2012) Nup100 [NUP100 + ] FG-nucleoporin Increase in the rate of nuclear import Halfmann et al. (2012a) "
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    ABSTRACT: Prions are self-perpetuating protein isoforms that cause fatal and incurable neurodegenerative disease in mammals. Recent evidence indicates that a majority of human proteins involved in amyloid and neural inclusion disorders possess at least some prion properties. In lower eukaryotes, such as yeast, prions act as epigenetic elements, which increase phenotypic diversity by altering a range of cellular processes. While some yeast prions are clearly pathogenic, it is also postulated that prion formation could be beneficial in variable environmental conditions. Yeast and mammalian prions have similar molecular properties. Crucial cellular factors and conditions influencing prion formation and propagation were uncovered in the yeast models. Stress-related chaperones, protein quality control deposits, degradation pathways and cytoskeletal networks control prion formation and propagation in yeast. Environmental stresses trigger prion formation and loss, supposedly acting via influencing intracellular concentrations of the prion-inducing proteins, and/or by localizing prionogenic proteins to the prion induction sites via heterologous ancillary helpers. Physiological and environmental modulation of yeast prions points to new opportunities for pharmacological intervention and/or prophylactic measures targeting general cellular systems rather than the properties of individual amyloids and prions. This article is protected by copyright. All rights reserved.
    Full-text · Article · Nov 2013 · FEMS microbiology reviews
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    ABSTRACT: Mammalian and fungal prion proteins form self-perpetuating β-sheet-rich fibrillar aggregates called amyloid. Prion inheritance is based on propagation of the regularly oriented amyloid structures of the prion proteins. All yeast prion proteins identified thus far contain aggregation-prone glutamine/asparagine (Gln/Asn)-rich domains, although the mammalian prion protein and fungal prion protein HET-s do not contain such sequences. In order to fill this gap, we searched for novel yeast prion proteins lacking Gln/Asn-rich domains via a genome-wide screen based on cross-seeding between two heterologous proteins and identified Mod5, a yeast tRNA isopentenyltransferase, as a novel non-Gln/Asn-rich yeast prion protein. Mod5 formed self-propagating amyloid fibers in vitro and the introduction of Mod5 amyloids into non-prion yeast induced dominantly and cytoplasmically heritable prion state [MOD (+) ], which harbors aggregates of endogenous Mod5. [MOD (+) ] yeast showed an increased level of membrane lipid ergosterol and acquired resistance to antifungal agents. Importantly, enhanced de novo formation of [MOD (+) ] was observed when non-prion yeast was grown under selective pressures from antifungal drugs. Our findings expand the family of yeast prions to non-Gln/Asn-rich proteins and reveal the acquisition of a fitness advantage for cell survival through active prion conversion.
    No preview · Article · Nov 2012 · Prion
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