AB toxin

PDB 1giq EBI

AB toxin refers to a class of bacterial toxins consisting of two components: the 'A' part, which is the active or enzymatic component, and the 'B' part, which is the binding component. These toxins are secreted by certain pathogenic bacteria and play a significant role in the disease processes of various bacterial infections. The 'A' component is typically responsible for the toxic effects, acting inside the host cells to inhibit specific cellular functions or to modify key cellular processes. The 'B' component, on the other hand, binds to specific receptors on the surface of the target cell, facilitating the entry of the 'A' component into the cell.

Mechanism of Action

The mechanism of action of AB toxins involves several steps. Initially, the 'B' component binds to a receptor on the cell surface of the host. This binding is highly specific, with different AB toxins targeting specific cell types based on the receptors present. Following binding, the toxin-receptor complex is internalized by the cell through endocytosis. Once inside the cell, the AB toxin is transported to various cellular compartments, where the 'A' and 'B' components are separated. The 'A' component is then translocated into the cytoplasm, where it exerts its toxic effect. The exact mechanism by which the 'A' component causes disease varies among different AB toxins but often involves the modification of key cellular enzymes or the disruption of normal cellular signaling pathways.

Examples of AB Toxins

Several well-known AB toxins play significant roles in human diseases:

• Diphtheria toxin produced by Corynebacterium diphtheriae inhibits protein synthesis in host cells, leading to diphtheria.
• Cholera toxin produced by Vibrio cholerae activates adenylate cyclase in intestinal epithelial cells, causing cholera.
• Pertussis toxin produced by Bordetella pertussis interferes with immune cell signaling, contributing to whooping cough.
• Shiga toxin produced by Shigella dysenteriae and certain strains of Escherichia coli (e.g., E. coli O157:H7) inhibits protein synthesis, leading to dysentery or hemolytic uremic syndrome.

Clinical Significance

Understanding the structure and function of AB toxins is crucial for the development of effective treatments and preventive measures against bacterial diseases. Vaccines targeting the 'B' component of certain AB toxins have been developed to prevent diseases by blocking the binding of toxins to host cells. Additionally, research into inhibitors that can block the action of the 'A' component offers potential therapeutic avenues for treating diseases caused by AB toxins.

See Also

• Bacterial pathogenesis
• Toxin-antitoxin system
• Vaccine
• Infectious disease