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Updated: Apr 27, 2026
Deciphering the Molecular Mechanism and Function of Pore-Forming Toxins Using Leishmania major
Published on: October 28, 2022
Clostridial pore-forming toxins: powerful virulence factors
1Institut Pasteur, Unité des Bactéries anaérobies et Toxines, Paris, France.
Abstract:
Pore formation is a common mechanism of action for many bacterial toxins. More than one third of clostridial toxins are pore-forming toxins (PFTs) belonging to the β-PFT class. They are secreted as soluble monomers rich in β-strands, which recognize a specific receptor on target cells and assemble in oligomers. Then, they undergo a conformational change leading to the formation of a β-barrel, which inserts into the lipid bilayer forming functional pore. According to their structure, clostridial β-PFTs are divided into several families. Clostridial cholesterol-dependent cytolysins form large pores, which disrupt the plasma membrane integrity. They are potent virulence factors mainly involved in myonecrosis. Clostridial heptameric β-PFTs (aerolysin family and staphylococcal α-hemolysin family) induce small pores which trigger signaling cascades leading to different cell responses according to the cell types and toxins. They are mainly responsible for intestinal diseases, like necrotic enteritis, or systemic diseases/toxic shock from intestinal origin. Clostridial intracellularly active toxins exploit pore formation through the endosomal membrane to translocate the enzymatic component or domain into the cytosol. Single chain protein toxins, like botulinum and tetanus neurotoxins, use hydrophobic α-helices to form pores, whereas clostridial binary toxins encompass binding components, which are structurally and functionally related to β-PFTs, but which have acquired the specific activity to internalize their corresponding enzymatic components. Structural analysis suggests that β-PFTs and binding components share a common evolutionary origin.
Insights
Clostridial toxins utilize pore formation (PFTs) to cause disease. These toxins, categorized by structure, range from membrane-disrupting cytolysins to those translocating enzymes into cells.
Area of Science:
- Microbiology
- Molecular Biology
- Toxicology
Background:
- Pore formation is a key mechanism for many bacterial toxins, particularly within the Clostridia genus.
- Over one-third of clostridial toxins are beta-pore-forming toxins (β-PFTs), classified by their structural and functional characteristics.
- These toxins are secreted as monomers, recognize cell receptors, oligomerize, and form β-barrels to create pores in cell membranes.
Purpose of the Study:
- To categorize and describe the diverse mechanisms of pore-forming toxins (PFTs) produced by Clostridia.
- To elucidate the structural basis and functional outcomes of different clostridial β-PFT families.
- To explore the evolutionary relationship between β-PFTs and other toxin components.
Main Methods:
- Structural analysis of clostridial toxins.
- Classification of β-PFTs based on pore size and cellular effects.
- Investigation of toxin secretion, receptor binding, oligomerization, and pore formation processes.
Main Results:
- Clostridial β-PFTs are divided into cholesterol-dependent cytolysins (large pores, myonecrosis) and heptameric toxins (small pores, signaling cascades, intestinal/systemic diseases).
- Intracellularly active toxins use pore formation in endosomal membranes for enzyme translocation; some use α-helices, while binary toxins have β-PFT-related binding components.
- Structural similarities suggest a common evolutionary origin for β-PFTs and binding components of binary toxins.
Conclusions:
- Clostridial pore-forming toxins exhibit diverse structures and mechanisms, leading to a range of pathologies from tissue necrosis to toxic shock.
- Understanding the structural and functional diversity of these toxins is crucial for developing targeted interventions.
- The shared evolutionary origin of β-PFTs and related toxin components highlights conserved molecular strategies in bacterial pathogenesis.
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