Cholera Toxin Mechanism for Increased cAMP

Cholera toxin disrupts normal cellular signaling pathways, specifically affecting the regulation of cyclic adenosine monophosphate (cAMP) levels. The toxin achieves this by targeting a key component of the G protein signaling system.

Mechanism of Action

Cholera toxin increases intracellular levels of the second messenger molecule, cAMP. This occurs through the following steps:

• The toxin enters intestinal epithelial cells.
• Inside the cell, it ADP-ribosylates the alpha subunit of the stimulatory G protein, known as $G_s$ protein.
• This modification prevents the intrinsic GTPase activity of the $G_s \alpha$ subunit, effectively locking it in its active, GTP-bound state.
• The constitutively active $G_s \alpha$-GTP complex then continuously stimulates the enzyme adenylate cyclase.
• Sustained activation of adenylate cyclase leads to a massive increase in the production of cAMP.
• High cAMP levels disrupt ion transport in the intestinal cells, causing the characteristic symptoms of cholera (e.g., severe diarrhea).

Therefore, the primary mechanism by which cholera toxin increases cAMP levels is by modifying the $G_s$ protein, leading to its overactivation.