koleratoksiinille

Koleratoksiini, often referred to as cholera toxin (CT), is a protein exotoxin produced by the bacterium Vibrio cholerae, the causative agent of cholera. This toxin plays a crucial role in the pathogenesis of cholera, leading to the severe watery diarrhea characteristic of the disease. It is composed of two subunits: one active subunit (A) and five binding subunits (B). The B subunits are responsible for binding to specific receptors on the surface of intestinal epithelial cells, primarily the GM1 ganglioside. Once bound, the toxin is internalized into the cell. The A subunit then detaches and enters the cytoplasm, where it acts as an enzyme. Specifically, the A1 subunit catalyzes the ADP-ribosylation of a G protein called Gs alpha. This modification permanently activates a key enzyme in the signaling pathway of intestinal cells, adenylyl cyclase. The continuous activation of adenylyl cyclase leads to an excessive production of cyclic AMP (cAMP). Elevated intracellular cAMP levels disrupt the normal ion transport mechanisms in the intestinal epithelium, causing a massive efflux of chloride ions and bicarbonate ions into the intestinal lumen. This ionic imbalance results in the passive movement of water into the lumen, leading to the characteristic profuse, rice-water-like diarrhea. The extensive fluid and electrolyte loss can rapidly lead to dehydration and shock if not treated promptly.