• Comparative Biology of Bacterial Enterotoxins:
• Heat-Labile Toxin (LT) Family: The heat-labile toxin (LT-I, LT-II) of E. coli is an $AB_5$ holotoxin that is structurally and functionally homologous to Cholera toxin of Vibrio cholerae, as well as the enterotoxins of Campylobacter jejuni and Salmonella Typhimurium. All act by catalyzing the ADP-ribosylation of the $\alpha$-subunit of heterotrimeric stimulatory G protein ($G_{s\alpha}$), constitutively activating host adenylate cyclase and elevating intracellular cAMP.
• Contrasting Shiga Toxin (Stx): Shiga toxin of Shigella dysenteriae type 1 (and Shiga toxins Stx1/Stx2 of EHEC) is an $AB_5$ toxin with a completely different enzymology: the catalytic $A$ subunit is an RNA $N$-glycosidase that cleaves a specific adenine base ($A_{4324}$) from the 28S rRNA of the eukaryotic 60S ribosomal subunit, irreversibly halting host protein synthesis.

Correct option: (2) Shiga toxin of Shigella dysenteriae type 1