ETEC (Enterotoxigenic E. coli) causes watery diarrhea via heat-labile toxin (LT). LT is structurally homologous to cholera toxin. The specific G-protein that LT ADP-ribosylates to cause persistent adenylate cyclase activation is:

• A Giα (inhibitory G-protein alpha subunit)
• B Gq (phospholipase C-activating G-protein)
• C Transducin (retinal G-protein)
• D Gsα (stimulatory G-protein alpha subunit) ✓

Explanation

LT fragment A ADP-ribosylates Gsα, specifically the arginine-201 residue; this modification locks Gsα in the GTP-bound active state, preventing its intrinsic GTPase from hydrolyzing GTP to GDP; constitutively active Gsα perpetually stimulates adenylate cyclase, elevating cAMP which activates PKA, phosphorylating CFTR causing Cl- efflux and net secretion. Giα ADP-ribosylation (at cysteine) is the mechanism of pertussis toxin, which inhibits adenylate cyclase. Gq activates PLC-IP3 pathway. Transducin is specific to retinal phototransduction.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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