**Core Concept**
Cholera toxin is a potent enterotoxin secreted by Vibrio cholerae, causing severe diarrhea by activating adenylate cyclase in intestinal epithelial cells. The toxin binds to specific receptors on the surface of these cells to initiate its pathogenic effects.

**Why the Correct Answer is Right**
Cholera toxin binds to GM1 gangliosides on the surface of intestinal epithelial cells, specifically to the GM1 receptors. This binding activates the toxin's enzymatic activity, which leads to the ADP-ribosylation of the alpha-subunit of the Gs protein (Gsα). This modification increases the activity of adenylate cyclase, resulting in a significant increase in intracellular cyclic AMP (cAMP) levels. The elevated cAMP levels in turn stimulate the secretion of chloride ions into the intestinal lumen, causing a massive efflux of water and electrolytes.

**Why Each Wrong Option is Incorrect**
* **Option A:** Cholera toxin does not bind to G protein-coupled receptors.
* **Option B:** GM2 gangliosides are not the primary receptors for cholera toxin.
* **Option C:** Cholera toxin does not bind to the enterocyte-specific receptor for vitamin B12.

**Clinical Pearl / High-Yield Fact**
Cholera toxin's mechanism of action is a classic example of a "signal transduction" pathway, where the binding of a ligand to a receptor triggers a cascade of intracellular signaling events that ultimately lead to a specific physiological response.

**Correct Answer: D. GM1 gangliosides**