Koleratoksin

Koleratoksin is a bacterial toxin produced by the bacterium Vibrio cholerae, which is the causative agent of cholera, a severe diarrheal disease. The toxin is responsible for the characteristic symptoms of cholera, including profuse watery diarrhea, which can lead to dehydration and electrolyte imbalance if left untreated. Koleratoksin is an AB toxin, meaning it consists of two distinct subunits: an A subunit, which is the toxic moiety, and a B subunit, which acts as a receptor-binding component.

The A subunit of koleratoksin is an ADP-ribosylating enzyme that targets the Gs alpha subunit of the heterotrimeric G protein, leading to its ADP-ribosylation and subsequent activation. This activation results in increased cyclic AMP (cAMP) production, which disrupts the normal functioning of intestinal epithelial cells and leads to the secretion of large amounts of chloride ions and water into the intestinal lumen, causing the characteristic watery diarrhea.

The B subunit of koleratoksin binds to the ganglioside GM1 on the surface of intestinal epithelial cells, facilitating the entry of the A subunit into the cell. The B subunit also acts as a heat-labile enterotoxin (LT), contributing to the symptoms of cholera by stimulating the secretion of chloride ions and water.

Koleratoksin is a potent toxin, with a median lethal dose (LD50) of approximately 10 ng/kg in mice. The toxin is highly stable and can survive in the environment for extended periods, making it a significant public health concern in areas where cholera is endemic. Vaccines and oral rehydration therapy are the primary means of preventing and treating cholera, respectively.