What is the mechanism of action of the virulence factor in diphtheria.
Q141 marks
Answer
Mechanism of action of the diphtheria virulence factor (diphtheria toxin): diphtheria toxin, produced by toxigenic (lysogenized, tox gene-bearing) strains of Corynebacterium diphtheriae, acts by ADP-ribosylating elongation factor-2 (EF-2), using the toxin’s enzymatically active A subunit (after receptor-mediated endocytosis via the B subunit binding to the host cell heparin-binding EGF-like growth factor receptor). ADP-ribosylation inactivates EF-2, which is essential for translocation during protein synthesis on ribosomes — this blocks host cell protein synthesis, ultimately causing cell death and the characteristic tissue necrosis (e.g., the pseudomembrane formation in the pharynx, and myocardial/neural toxicity when absorbed systemically).
