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Updated: Jun 19, 2026
Identification of Host Pathways Targeted by Bacterial Effector Proteins using Yeast Toxicity and Suppressor Screens
Published on: October 25, 2019
A yeast killer toxin screen provides insights into a/b toxin entry, trafficking, and killing mechanisms
Susheela Y Carroll1, Peter C Stirling, Helen E M Stimpson
1Department of Molecular and Cell Biology, University of California, Berkeley, 16 Barker Hall, Berkeley, CA 94720, USA.
Abstract:
Like Ricin, Shiga, and Cholera toxins, yeast K28 is an A/B toxin that depends on endocytosis and retrograde trafficking for toxicity. Knowledge of the specific proteins, lipids, and mechanisms required for trafficking and killing by these toxins remains incomplete. Since K28 is a model for clinically relevant toxins, we screened over 5000 yeast mutants, identifying 365 that affect K28 sensitivity. Hypersensitive mutants revealed cytoprotective pathways, including stress-activated signaling and protein degradation. Resistant mutants clustered to endocytic, lipid organization, and cell wall biogenesis pathways. Furthermore, GPI anchors and transcriptional regulation are important for K28-cell binding. Strikingly, the AP2 complex, which in metazoans links endocytic cargo to the clathrin coat, but had no assigned function in yeast, was critical for K28 toxicity. Yeast AP2 localizes to endocytic sites and has a cargo-specific function in K28 uptake. This comprehensive genetic analysis identified conserved processes important for A/B toxin trafficking and killing.
Insights
Yeast K28 toxin uses endocytosis and retrograde trafficking. A large genetic screen identified key pathways and the AP2 complex, crucial for A/B toxin uptake and toxicity.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- A/B toxins like Ricin, Shiga, and Cholera rely on endocytosis and retrograde trafficking for cellular toxicity.
- The precise molecular mechanisms governing the trafficking and cytotoxic effects of these toxins are not fully understood.
- Yeast K28 toxin serves as a valuable model system for studying clinically relevant A/B toxins.
Purpose of the Study:
- To comprehensively identify genetic factors influencing yeast K28 toxin sensitivity and trafficking.
- To elucidate conserved cellular pathways involved in A/B toxin uptake and toxicity.
- To investigate the role of the AP2 complex in yeast toxin endocytosis.
Main Methods:
- Conducted a large-scale genetic screen of over 5000 yeast mutants to identify those affecting K28 toxin sensitivity.
- Analyzed hypersensitive mutants to uncover cytoprotective pathways and resistant mutants to identify trafficking-related pathways.
- Utilized genetic analysis to determine the function of the AP2 complex in K28 toxin uptake.
Main Results:
- Identified 365 yeast mutants affecting K28 toxin sensitivity, revealing roles for stress signaling, protein degradation, endocytosis, lipid organization, and cell wall biogenesis.
- Discovered that glycosylphosphatidylinositol (GPI) anchors and transcriptional regulation are important for K28 toxin binding.
- Demonstrated that the AP2 complex, previously uncharacterized in yeast, is essential for K28 toxin uptake and toxicity, localizing to endocytic sites.
Conclusions:
- This study provides a comprehensive genetic framework for understanding conserved mechanisms of A/B toxin trafficking and toxicity.
- The findings highlight the critical, cargo-specific role of the yeast AP2 complex in mediating toxin endocytosis.
- The identified pathways offer potential targets for therapeutic interventions against A/B toxin-mediated diseases.
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