title: The mechanism of toxicity in HET-S/HET-s prion incompatibility.
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.
authors.affiliation: Laboratory of Physical Chemistry, ETH Zürich, Zürich, Switzerland.
authors.forename: Carolin
authors.initials: C
authors.lastname: Seuring
authors.forename: Jason
authors.initials: J
authors.lastname: Greenwald
authors.forename: Christian
authors.initials: C
authors.lastname: Wasmer
authors.forename: Roger
authors.initials: R
authors.lastname: Wepf
authors.forename: Sven J
authors.initials: SJ
authors.lastname: Saupe
authors.forename: Beat H
authors.initials: BH
authors.lastname: Meier
authors.forename: Roland
authors.initials: R
authors.lastname: Riek
mesh_terms: D000595:Amino Acid Sequence; D000682:Amyloid / Q000648:ultrastructure; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004926:Escherichia coli / Q000166:cytology / Q000187:drug effects; D005614:Freeze Fracturing; D005656:Fungal Proteins / Q000737:chemistry / Q000633:toxicity*; D008081:Liposomes / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D008969:Molecular Sequence Data; D009183:Mycotoxins / Q000633:toxicity*; D010641:Phenotype; D010767:Phosphorylcholine / Q000031:analogs & derivatives / Q000494:pharmacology; D048468:Podospora / Q000378:metabolism* / Q000648:ultrastructure; D011328:Prions / Q000633:toxicity* / Q000648:ultrastructure; D055503:Protein Multimerization / Q000187:drug effects; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013816:Thermodynamics
chemical_list: D000682:Amyloid; D005656:Fungal Proteins; C083891:HET-S protein, Podospora anserina; D008081:Liposomes; D009183:Mycotoxins; D011328:Prions; D010767:Phosphorylcholine; C028810:dodecylphosphocholine