Shigatoxin

Shigatoxin is a potent enterotoxin produced by the bacterium Shigella dysenteriae, a leading cause of bacterial dysentery and diarrhea. It is a member of the AB5 toxin family, which includes cholera toxin and heat-labile enterotoxin. Shigatoxin is composed of two subunits: A and B. The B subunit binds to the glycolipid globotriaosylceramide (Gb3) on the surface of intestinal epithelial cells, facilitating the entry of the A subunit into the cell. The A subunit then ADP-ribosylates the Gs alpha protein, leading to the activation of adenylate cyclase and an increase in intracellular cAMP levels. This results in the secretion of chloride ions and water into the intestinal lumen, causing diarrhea. Shigatoxin is highly toxic, with an LD50 (lethal dose for 50% of the population) of approximately 10 ng/kg in mice. It is also heat-stable, which allows it to survive the cooking process and cause illness even when ingested from contaminated food. Shigatoxin is the primary virulence factor of Shigella dysenteriae, contributing to its ability to cause severe diarrhea and dysentery. The toxin is also used as a research tool to study the molecular mechanisms of enterotoxin action and the development of vaccines against Shigella dysenteriae.