Choleratoksiini

Choleratoksiini is a potent biological toxin produced by the bacterium Vibrio cholerae, the causative agent of cholera. This toxin plays a crucial role in the pathogenesis of cholera by disrupting normal intestinal function, leading to severe diarrhea and dehydration.

Choleratoksiini is classified as an enterotoxin, specifically a cholera toxin (CT), which is a heat-labile exotoxin composed of multiple subunits. It is synthesized and secreted by V. cholerae during infection and adheres to the mucosal lining of the small intestine. The toxin comprises a pentameric B subunit responsible for binding to the host cell surface via ganglioside GM1 receptors, and an A subunit that enters the cell to exert its pathogenic effect.

Once inside the cell, the A subunit catalyzes the ADP-ribosylation of the Gs alpha subunit of heterotrimeric G proteins. This modifies the G protein to remain in an active state, leading to persistent activation of adenylate cyclase. The result is an increased intracellular cyclic AMP (cAMP) concentration, which alters ion transport mechanisms in the intestinal epithelium. Specifically, it causes an excessive secretion of chloride ions and water into the intestinal lumen, culminating in the characteristic profuse diarrhea observed in cholera.

Choleratoksiini's unique mode of action has made it a model for understanding G protein-coupled receptor signaling pathways. Its role in disease and its molecular properties have also been harnessed in research and vaccine development. Despite its pathogenic potential, choleratoksiini is of significant scientific interest for its mechanisms of cellular manipulation and its applications in biotechnology.