Koleratoksiini

Koleratoksiini, also known as cholera toxin (CT), is a protein complex produced by the bacterium Vibrio cholerae, the causative agent of cholera. This toxin plays a crucial role in the pathogenesis of the disease, leading to the characteristic severe diarrhea. The toxin is an AB-type toxin, meaning it consists of two functionally distinct subunits: subunit A and multiple copies of subunit B.

Subunit B is responsible for binding the toxin to specific receptors on the surface of host intestinal cells, primarily GM1 gangliosides. Once bound, the toxin is internalized into the cell. Subunit A then dissociates and enters the cytoplasm, where it exerts its enzymatic activity. Specifically, subunit A is an ADP-ribosyltransferase that activates adenylyl cyclase, an enzyme involved in cyclic AMP (cAMP) production.

The elevated levels of cAMP within the intestinal cells disrupt ion transport. This disruption leads to a massive efflux of water and electrolytes (such as sodium and chloride ions) from the intestinal cells into the lumen. The excessive loss of fluid and salts causes the severe, watery diarrhea that defines cholera, which can rapidly lead to dehydration and electrolyte imbalance if left untreated. Understanding koleratoksiini's mechanism of action is vital for developing treatments and vaccines against cholera.