Corynebacterium diphtheriae produces a toxin encoded by a bacteriophage. The specific biochemical target of diphtheria toxin that halts protein synthesis is:
- A Elongation Factor 2 (EF-2), ADP-ribosylated at a modified histidine residue called diphthamide ✓
- B Ribosomal 28S rRNA, depurinated at position A4324
- C Aminoacyl-tRNA synthetase, competitively inhibited
- D Peptidyl transferase center of 23S rRNA, blocked by toxin binding
Correct answer: A. Elongation Factor 2 (EF-2), ADP-ribosylated at a modified histidine residue called diphthamide
Explanation
Diphtheria toxin (encoded by beta-phage) fragment A ADP-ribosylates EF-2 (eukaryotic elongation factor 2) at a unique modified histidine called diphthamide; this irreversibly inactivates EF-2, blocking translocation during protein synthesis and causing cell death (one toxin molecule can kill a cell). Ribosomal 28S rRNA depurination at A4324 is the mechanism of Shiga toxin/ricin. Aminoacyl-tRNA synthetase inhibition is not a bacterial toxin mechanism. Peptidyl transferase center blockade is the mechanism of chloramphenicol.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.