Related Experiment Video
Updated: May 15, 2026
High-throughput Screening for Protein-based Inheritance in S. cerevisiae
Published on: August 8, 2017
The mechanism of toxicity in HET-S/HET-s prion incompatibility
Carolin Seuring1, Jason Greenwald, Christian Wasmer
1Laboratory of Physical Chemistry, ETH Zürich, Zürich, Switzerland.
Abstract:
The HET-s protein from the filamentous fungus Podospora anserina is a prion involved in a cell death reaction termed heterokaryon incompatibility. This reaction is observed at the point of contact between two genetically distinct strains when one harbors a HET-s prion (in the form of amyloid aggregates) and the other expresses a soluble HET-S protein (96% identical to HET-s). How the HET-s prion interaction with HET-S brings about cell death remains unknown; however, it was recently shown that this interaction leads to a relocalization of HET-S from the cytoplasm to the cell periphery and that this change is associated with cell death. Here, we present detailed insights into this mechanism in which a non-toxic HET-s prion converts a soluble HET-S protein into an integral membrane protein that destabilizes membranes. We observed liposomal membrane defects of approximately 10 up to 60 nm in size in transmission electron microscopy images of freeze-fractured proteoliposomes that were formed in mixtures of HET-S and HET-s amyloids. In liposome leakage assays, HET-S has an innate ability to associate with and disrupt lipid membranes and that this activity is greatly enhanced when HET-S is exposed to HET-s amyloids. Solid-state nuclear magnetic resonance (NMR) analyses revealed that HET-s induces the prion-forming domain of HET-S to adopt the β-solenoid fold (previously observed in HET-s) and this change disrupts the globular HeLo domain. These data indicate that upon interaction with a HET-s prion, the HET-S HeLo domain partially unfolds, thereby exposing a previously buried ∼34-residue N-terminal transmembrane segment. The liberation of this segment targets HET-S to the membrane where it further oligomerizes, leading to a loss of membrane integrity. HET-S thus appears to display features that are reminiscent of pore-forming toxins.
Insights
The HET-s prion converts soluble HET-S protein into a membrane-disrupting protein, causing cell death through membrane destabilization. This prion interaction triggers HET-S to embed in membranes, leading to cell death.
Area of Science:
- Mycology
- Molecular Biology
- Biochemistry
Background:
- Podospora anserina HET-s protein forms prions involved in heterokaryon incompatibility.
- This incompatibility involves a cell death reaction when HET-s prions interact with soluble HET-S proteins.
- The mechanism by which HET-s prions induce cell death via HET-S interaction was previously unclear.
Purpose of the Study:
- To elucidate the mechanism by which HET-s prions induce cell death in Podospora anserina.
- To investigate how HET-s prions interact with soluble HET-S proteins and alter their function.
- To understand the structural and functional changes in HET-S upon interaction with HET-s amyloids.
Main Methods:
- Transmission electron microscopy (TEM) of freeze-fractured proteoliposomes.
- Liposome leakage assays.
- Solid-state nuclear magnetic resonance (NMR) analyses.
Main Results:
- HET-s prion interaction causes HET-S to relocalize to the cell periphery, associated with cell death.
- HET-S exhibits innate membrane-disrupting ability, significantly enhanced by HET-s amyloids.
- HET-s prions induce HET-S's prion-forming domain to adopt a β-solenoid fold, disrupting the HeLo domain.
- This unfolding exposes a transmembrane segment, targeting HET-S to membranes and causing destabilization.
Conclusions:
- HET-s prions convert soluble HET-S into an integral membrane protein that destabilizes lipid bilayers.
- The interaction leads to unfolding of the HET-S HeLo domain, exposing a transmembrane segment.
- This process results in membrane integrity loss and cell death, with HET-S acting similarly to pore-forming toxins.
