Cholera toxin is a powerful protein complex secreted by the bacterium Vibrio cholerae. As an enterotoxin, it specifically targets the cells lining the small intestine, triggering the massive fluid loss that characterizes the disease. The toxin's structure is highly specialized, consisting of an AB5 multimeric arrangement that is essential for its function.
The toxin features one enzymatically active A subunit and five receptor-binding B subunits. The B subunits act as a delivery mechanism, binding to the surface of host cells to allow the A subunit to enter. Once inside, the A subunit disrupts cellular signaling pathways, leading to the uncontrolled secretion of water and electrolytes into the intestinal lumen.