Understanding modes of AB toxin virulence and host defence mechanisms

About the Project

Lead supervisor:Dr Chris MacDonald

Co-supervisors:Dr Martin FascioneandDr C Spicer

The student will be registered with the Department of Biology

Background

AB toxins are virulence factors that hijack host-cell pathways to cause disease and show promise for therapeutic functionalization. Progress in both combating AB toxin–related disease and developing therapeutic applications is limited by poor understanding of host responses.

Using budding yeast, which secretes the AB toxin K28 upon viral infection, we established hyper-secretor strains and different physiological assays to measure toxin sensitivity (2025, JCS). A genetic screen identified many host mutants with distinct toxin sensitivity phenotypes (unpublished). We also discovered a novel defence factor, Killer Toxin Defence Factor 1 (Ktd1), which we propose performs a conserved function to oligomerize and sequester internalized toxin for lysosomal degradation (2023, PNAS).

Objectives

1. Purify and fluorescently label the yeast AB toxin K28.
2. Dissect spatiotemporal dynamics of internalised K28 toxin during induced death and defence, in sensitive and resistant cells, respectively.
3. Define the interplay between toxin and the novel defence factor Ktd1.

Novelty

This project combines novel discoveries and new techniques and assays developed to study AB toxins in a model organism (Supervisor 1), with customised methods for toxin purification and successful bioconjugation (Supervisors 2/3).

Specific aims

1. Using our engineered hyper secretor cells, CRISPR and induced plasmid expression will be employed to secrete a range of genetically modified versions of the AB toxin K28. Toxins will be purified , then a range of site-selective chemistries (e.g. N-terminal targeting, cysteine-ligation) will be trialled for optimal conjugation of fluorescent dyes.
2. Validated active toxins will be imaged using 3D super resolution time-lapse imaging coupled to customised microfluidics (2022, JCB), to perfuse media containing labelled toxins during live-cell imaging of both sensitive and resistant cells. Toxin and labelled cellular markers will be imaged using our unpublished 4-colour simultaneous imaging platform.
3. Purified toxin will be used to define how it engages with and is neutralised by the novel defence factor Ktd1, using 1) the above-described cell biology approaches combined with fluorescently tagged-Ktd1 and genetic perturbations that affect defence and 2) in vitro biochemical approaches using recombinant fragments of Ktd1.

The University of York is committed to recruiting future scientists regardless of age, ethnicity, gender, gender identity, disability, sexual orientation or career pathway to date. We understand that commitment and excellence can be shown in many ways and we have built our recruitment process to reflect this. We welcome applicants from all backgrounds, particularly those underrepresented in science, who have curiosity, creativity and a drive to learn new skills.

The Department of Biology holds an Athena SWAN Gold Award. We are committed to supporting equality and diversity and strive to provide a positive working environment for all staff and students.

Entry Requirements: Students with, or expecting to gain, at least an upper second class honours degree, or equivalent, are invited to apply. The interdisciplinary nature of this programme means that we welcome applications from students with any biological, chemical, and/or physical science backgrounds, or students with mathematical background who are interested in using their skills in addressing biological questions.

Programme: PhD in Biomedical Science (3 year)

Start Date: 21 September 2026