What is the mechanism of action of diphtheria toxin?

Diphtheria toxin exerts its effects primarily through the ADP ribosylation of elongation factor 2 (EF-2), which is a critical component in the protein synthesis machinery of eukaryotic cells. The toxin is produced by the bacterium Corynebacterium diphtheriae, and upon entering the host cell, it catalyzes the transfer of an ADP-ribose moiety from nicotinamide adenine dinucleotide (NAD) to EF-2.

This modification inhibits EF-2's ability to facilitate the translocation step of the translation process, effectively halting protein synthesis within the affected cells. As a result, the affected cells undergo dysfunction and can lead to local tissue damage, systemic effects, and potentially life-threatening complications, particularly in the respiratory tract.

Understanding this mechanism is crucial, as it underscores the severe impact that bacterial toxins can have on host cell function and provides insight into how such pathogens contribute to disease.