Question:
Which of the following bacterial toxins acts by inhibiting elongation factor 2 (EF-2)?
Which of the following bacterial toxins acts by inhibiting elongation factor 2 (EF-2)?
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The classic EF-2 ADP-ribosylating A-B exotoxin is from Corynebacterium.
Updated On: Jun 25, 2026
- Diphtheria toxin
- Cholera toxin
- Tetanospasmin
- Heat-labile toxin of E. coli
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The Correct Option is A
Solution and Explanation
Step 1: Identify the molecular target.
Elongation factor 2 (EF-2) is required for the translocation step of protein synthesis on the ribosome. Inhibiting EF-2 halts host-cell protein synthesis and kills the cell.
Step 2: Recall the toxin mechanism.
Diphtheria toxin (from Corynebacterium diphtheriae) is an A-B exotoxin. Its A subunit catalyses ADP-ribosylation of the unique amino acid diphthamide on EF-2, inactivating it. Pseudomonas aeruginosa exotoxin A works by the identical mechanism, but diphtheria toxin is the classic answer.
Step 3: Eliminate the distractors.
Cholera toxin and the heat-labile toxin of E. coli ADP-ribosylate the Gs alpha subunit, locking adenylate cyclase ON and raising cAMP (watery diarrhoea) - they do not touch EF-2. Tetanospasmin is a protease that cleaves synaptobrevin, blocking inhibitory neurotransmitter release - again not EF-2.
Key fact: Diphtheria toxin inhibits EF-2 by ADP-ribosylating diphthamide, arresting host protein synthesis.
Elongation factor 2 (EF-2) is required for the translocation step of protein synthesis on the ribosome. Inhibiting EF-2 halts host-cell protein synthesis and kills the cell.
Step 2: Recall the toxin mechanism.
Diphtheria toxin (from Corynebacterium diphtheriae) is an A-B exotoxin. Its A subunit catalyses ADP-ribosylation of the unique amino acid diphthamide on EF-2, inactivating it. Pseudomonas aeruginosa exotoxin A works by the identical mechanism, but diphtheria toxin is the classic answer.
Step 3: Eliminate the distractors.
Cholera toxin and the heat-labile toxin of E. coli ADP-ribosylate the Gs alpha subunit, locking adenylate cyclase ON and raising cAMP (watery diarrhoea) - they do not touch EF-2. Tetanospasmin is a protease that cleaves synaptobrevin, blocking inhibitory neurotransmitter release - again not EF-2.
Key fact: Diphtheria toxin inhibits EF-2 by ADP-ribosylating diphthamide, arresting host protein synthesis.
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