Diphtheria toxin causes its lethal effect by inactivating which cellular enzyme/factor?
- A Adenylate cyclase (increasing cAMP)
- B Elongation factor 2 (EF-2) by ADP-ribosylation, halting protein synthesis ✓
- C GTP-binding protein Gs (activating adenylate cyclase)
- D Rho GTPase (disrupting actin polymerisation)
Correct answer: B. Elongation factor 2 (EF-2) by ADP-ribosylation, halting protein synthesis
Explanation
Diphtheria toxin (produced by Corynebacterium diphtheriae lysogenised by beta-phage) ADP-ribosylates and inactivates elongation factor 2 (EF-2/translocase), irreversibly halting eukaryotic protein synthesis and causing cell death. A single toxin molecule can inactivate all EF-2 molecules in a cell, explaining its potency. Adenylate cyclase activation is the mechanism of cholera toxin and pertussis toxin (via different pathways). Rho GTPase disruption characterises C. difficile toxin B.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.