A 7-year-old unvaccinated child develops a greyish-white adherent pseudomembrane in the throat that bleeds on attempted removal. The organism produces a toxin encoded by a bacteriophage that acts by:
- A Inhibiting release of acetylcholine at neuromuscular junctions
- B ADP-ribosylation of elongation factor-2 (EF-2) blocking protein synthesis ✓
- C Activating adenylate cyclase by ADP-ribosylating Gs-alpha protein
- D Cleaving SNARE proteins preventing vesicle fusion
Explanation
Diphtheria toxin, produced by Corynebacterium diphtheriae lysogenized with beta-bacteriophage (corynephage), inhibits eukaryotic protein synthesis by ADP-ribosylating EF-2 (elongation factor-2, also called translocase). This blocks the translocation step of ribosomal translation, and since a single toxin molecule can inactivate all EF-2 in a cell, it is extremely potent. Fragment A carries the enzymatic activity while Fragment B is responsible for receptor binding and entry. Option C describes cholera toxin mechanism; option D describes tetanus/botulinum toxin.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.