Amyloid Prions in Fungi
- Authors: Sven J. Saupe1, Daniel F. Jarosz2, Heather L. True3
- Editors: Joseph Heitman4, Eva Holtgrewe Stukenbrock5
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VIEW AFFILIATIONS HIDE AFFILIATIONSAffiliations: 1: Institut de Biochimie et de Génétique Cellulaire, UMR 5095, CNRS, Université de Bordeaux, Bordeaux, France; 2: Department of Chemical and Systems Biology and Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA; 3: Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO; 4: Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710; 5: Environmental Genomics, Christian-Albrechts University of Kiel, Kiel, Germany, and Max Planck Institute for Evolutionary Biology, Plön, Germany
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Received 20 September 2016 Accepted 04 October 2016 Published 09 December 2016
- Correspondence: Sven J. Saupe, [email protected]

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Abstract:
Prions are infectious protein polymers that have been found to cause fatal diseases in mammals. Prions have also been identified in fungi (yeast and filamentous fungi), where they behave as cytoplasmic non-Mendelian genetic elements. Fungal prions correspond in most cases to fibrillary β-sheet-rich protein aggregates termed amyloids. Fungal prion models and, in particular, yeast prions were instrumental in the description of fundamental aspects of prion structure and propagation. These models established the “protein-only” nature of prions, the physical basis of strain variation, and the role of a variety of chaperones in prion propagation and amyloid aggregate handling. Yeast and fungal prions do not necessarily correspond to harmful entities but can have adaptive roles in these organisms.
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Citation: Saupe S, Jarosz D, True H. 2016. Amyloid Prions in Fungi. Microbiol Spectrum 4(6):FUNK-0029-2016. doi:10.1128/microbiolspec.FUNK-0029-2016.




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Abstract:
Prions are infectious protein polymers that have been found to cause fatal diseases in mammals. Prions have also been identified in fungi (yeast and filamentous fungi), where they behave as cytoplasmic non-Mendelian genetic elements. Fungal prions correspond in most cases to fibrillary β-sheet-rich protein aggregates termed amyloids. Fungal prion models and, in particular, yeast prions were instrumental in the description of fundamental aspects of prion structure and propagation. These models established the “protein-only” nature of prions, the physical basis of strain variation, and the role of a variety of chaperones in prion propagation and amyloid aggregate handling. Yeast and fungal prions do not necessarily correspond to harmful entities but can have adaptive roles in these organisms.

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Figures

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FIGURE 1
Natural situations of prion propagation in fungi. (A) Prion propagation after hyphal anastomosis in a filamentous fungus (for instance, [Het-s] in Podospora anserina). The prion form is transmitted from a donor-infected strain (right) to a recipient strain (left). The prion form then converts the entire mycelium to the prion state due to cytoplasmic continuity throughout the thallus. Prion transmission also occurs in meiotic crosses with maternal inheritance (not depicted here). (B) Prion propagation during mitotic cell divisions in yeast. Prion seeds are transmitted from mother to daughter cells during budding. (C) Prion transmission during sexual crosses. In a cross between a [PRION+] (left) and a [prion –] strain (right), the resulting diploid is [PRION+] and there is non-Mendelian segregation of the [PRION+] character (often, but not always, with 4:0 segregation as in the example depicted here).

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FIGURE 2
Structure of HET-s prion-forming domain. (A) Lateral view of a trimer of HET-s(218-289) in the prion amyloid conformation. Each monomer bears a different color, after pdb 2KJ3. (B) View from the fibril axis of one HET-s(218-289) monomer; the N- and C-terminal ends are marked, after pdb 2KJ3. (C) Structure of the two individual repeats of HET-s(218-289) marked R1 (position 226 to 246) and R2 (position 262 to 282) as well as the C-terminal semihydrophobic loop (position 283 to 289), after pdb 2KJ3. Amino acids are coded by chemical property (G in light gray, polar in green, hydrophobic in yellow, positively charged in red, negatively charged in blue, and aromatic in magenta). The sequence of HET-s(218-289) is given below with the same color coding in R1, R2 (underlined), and the C-terminal loop.
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