A 5-year-old child presents with a sore throat and a grayish-white pseudomembrane over the tonsils extending to the uvula. On attempted removal, the membrane bleeds. He has a 'bull neck' appearance. Myocarditis develops on day 8. The toxin responsible for cardiac and neural complications acts by:
- A Inhibition of acetylcholine release at the neuromuscular junction
- B ADP-ribosylation of elongation factor EF-2, inhibiting protein synthesis ✓
- C Cleaving SNARE proteins in synaptic vesicles
- D Activating adenylyl cyclase via ADP-ribosylation of Gs protein
Correct answer: B. ADP-ribosylation of elongation factor EF-2, inhibiting protein synthesis
Explanation
Diphtheria exotoxin (encoded by a bacteriophage) inhibits protein synthesis by ADP-ribosylating elongation factor EF-2 (eEF-2), which is required for translocation of the ribosome during polypeptide elongation. This halts protein synthesis in cardiac myocytes and Schwann cells, causing myocarditis and demyelinating neuropathy. Botulinum toxin inhibits acetylcholine release by cleaving SNARE proteins. Tetanus toxin cleaves synaptobrevin (a SNARE protein) but at inhibitory interneurones. Cholera toxin ADP-ribosylates Gs protein to activate adenylyl cyclase.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.