Final answer:
Cholera toxin activates guanylate cyclase leading to increased fluid secretion in the intestines, causing severe diarrhea.
Step-by-step explanation:
Pathological activation of guanylate cyclase is the mechanism of action (MOA) of cholera toxin. Cholera toxin is produced by the bacterium Vibrio cholerae and consists of one A subunit and five B subunits.
When the B subunits of the toxin bind to receptors on intestinal epithelial cells, the A subunit activates an intracellular G protein, leading to the activation of guanylate cyclase.
This results in increased cyclic GMP (cGMP) levels and disruption of normal intestinal cell physiology, causing excessive fluid and electrolyte secretion into the intestinal lumen, leading to severe diarrhea.