The fungal peptide toxin candidalysin induces distinct membrane repair mechanisms compared to bacterial pore-forming toxins

The common fungal pathogen, Candida albicans , relies on the pore-forming toxin candidalysin to damage host cells. Cells counteract pore-forming toxins by Ca ²⁺ -dependent mechanisms, such as microvesicle shedding and annexin recruitment to resist cholesterol-dependent cytolysins like streptolysin O (SLO), or annexin involvement and patch repair in the case of aerolysin. However, the specific Ca ²⁺ -dependent repair pathways engaged in response to candidalysin remain poorly understood. Here, we determined the involvement of different Ca ²⁺ -dependent repair mechanisms to candidalysin and compared responses to SLO and aerolysin using flow cytometry and high-resolution microscopy. We report that candidalysin triggered Ca ²⁺ -dependent repair, but patch repair and ceramide failed to provide significant protection. MEK-dependent repair and annexins A1, A2 and A6 contributed partially to repairing damage caused by candidalysin. However, annexin translocation after candidalysin challenge was delayed compared to SLO or aerolysin challenge. Surprisingly, extracellular Cl ⁻ improved cell survival after candidalysin challenge, but not after challenge with SLO or aerolysin. Finally, we found that candidalysin is removed via extracellular vesicle shedding. These findings reveal that Ca ²⁺ -dependent microvesicle shedding protects cells from candidalysin and can be engaged by multiple molecular mechanisms during membrane repair. Graphical Abstract.

Candidalysin is resisted by distinct repair mechanisms compared to bacterial PFTs.

After pore formation and membrane damage by each toxin, multiple repair pathways are triggered downstream of Ca²⁺ flux. Candidalysin induces a protective Cl ⁻ influx and activates MEK-dependent repair, which contributes to cell protection. Annexin translocation occurs slowly and provides minor protection, while patch repair is ineffective. In contrast, aerolysin does not benefit from Cl ⁻ influx or MEK protection. Aerolysin triggers moderate annexin translocation and relies primarily on patch repair as the main protective mechanism. Streptolysin O elicits rapid annexin translocation and activates MEK signaling, both of which contribute to robust protection. Patch repair plays only a minor protective role against SLO. The figure was created using BioRender.