Events during the cell membrane lysis by toxins

– Arnab Chatterjee and Somnath Dutta

Cryo-EM structure of different heptameric conformations of alpha-hemolysin toxin during pore formation process in the presence of cells

Staphylococcus aureus infections have become a global threat to human health due to the rapid emergence of multidrug-resistant strains. The limited availability of antibiotics and the absence of approved vaccines make it extremely challenging to combat S. aureus. To address this issue, it is crucial to study the pathophysiology of S. aureus.

Alpha-hemolysin (α-HL), a pore-forming toxin (PFT), is the most important virulence factor responsible for S. aureus pathogenesis. IISc researchers, led by Somnath Dutta in the Molecular Biophysics Unit, were keen to understand the impact and mode of action of α-HL on the target cell membrane.

Most pre-existing structures of these PFTs have been elucidated using detergent or lipid components. The team’s previous study revealed the structure of α-HL in an artificial composite lipid membrane. There have, however, been no detailed studies on the interactions and behaviours of small pore-forming toxins in the cellular environment.

In the current study, the team employed fluorescence microscopy, negative-staining TEM, mutation studies, cryo-EM, and single-particle-based structural studies to capture toxin-induced cell membrane remodelling and oligomerisation in the presence of a host cell membrane, particularly erythrocytes (red blood cells). Structural studies revealed the presence of an arc-like intermediate oligomeric species, octameric species, and various heptameric pre-pore states, further indicating a step-by-step assembly formation.

Moreover, the team captured changes in cell membrane shape during toxin-mediated pore formation using different imaging techniques. Taken together, this study reveals the structure-function analysis of the arc-shaped intermediate assembly during the pre-pore to pore transition of wild-type α-HL toxin, as it cross-talks with the cell membrane. These insights offer a valuable framework for the rational design of novel inhibitors and vaccine strategies targeting α-HL–mediated cytotoxicity.

REFERENCE:

Chatterjee A, Roy A, Das PP, Chakraborty D, Ghoshal B, Jhunjhunwala S, Dutta S, Stepwise assembly of α-hemolysin from intermediates to the mature pore in native erythrocytes, Journal of Cell Biology (2026).

https://rupress.org/jcb/article/225/3/e202506129/281409/Stepwise-assembly-of-hemolysin-from-intermediates

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