The mechanism of toxicity in HET-S/HET-s prion incompatibility

PLoS Biol. 2012;10(12):e1001451. doi: 10.1371/journal.pbio.1001451. Epub 2012 Dec 27.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amyloid / ultrastructure
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Escherichia coli / cytology
  • Escherichia coli / drug effects
  • Freeze Fracturing
  • Fungal Proteins / chemistry
  • Fungal Proteins / toxicity*
  • Liposomes / metabolism
  • Magnetic Resonance Spectroscopy
  • Models, Biological
  • Molecular Sequence Data
  • Mycotoxins / toxicity*
  • Phenotype
  • Phosphorylcholine / analogs & derivatives
  • Phosphorylcholine / pharmacology
  • Podospora / metabolism*
  • Podospora / ultrastructure
  • Prions / toxicity*
  • Prions / ultrastructure
  • Protein Multimerization / drug effects
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Sequence Alignment
  • Thermodynamics

Substances

  • Amyloid
  • Fungal Proteins
  • HET-S protein, Podospora anserina
  • Liposomes
  • Mycotoxins
  • Prions
  • Phosphorylcholine
  • dodecylphosphocholine

Grant support

This work was supported by grants from the Schweizerische Nationalfonds (SNF) and internal grants by the ETH. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.