Cholera toxin binds to which receptors in intestine-
**Core Concept**
Cholera toxin is a potent enterotoxin produced by Vibrio cholerae, the causative agent of cholera. It acts by activating adenylate cyclase, leading to an increase in intracellular cyclic AMP (cAMP) levels in intestinal epithelial cells.
**Why the Correct Answer is Right**
Cholera toxin binds to GM1 gangliosides on the surface of intestinal epithelial cells, specifically on the apical membrane of enterocytes. This binding is essential for the toxin's internalization and subsequent activation of adenylate cyclase through its A subunit. The GM1 gangliosides act as receptors for cholera toxin, facilitating its entry into the cell and subsequent activation of the adenylate cyclase pathway.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the correct receptor for cholera toxin is GM1 gangliosides, not G protein-coupled receptors (GPCRs).
* **Option B:** This option is incorrect because cholera toxin does not bind to Toll-like receptors (TLRs), which are involved in the recognition of pathogen-associated molecular patterns (PAMPs) rather than toxins like cholera toxin.
* **Option C:** This option is incorrect because cholera toxin does not bind to nicotinic acetylcholine receptors (nAChRs), which are involved in neurotransmission rather than toxin binding.
**Clinical Pearl / High-Yield Fact**
Cholera toxin's ability to bind to GM1 gangliosides highlights the importance of glycosphingolipid receptors in the pathogenesis of certain bacterial infections. This knowledge can be useful in understanding the mechanisms of other toxins that bind to similar receptors.
**Correct Answer: D. GM1 gangliosides**