Background
Diphtheria toxin (DT) is one of the most extensively studied bacterial toxins with intracellular action. It is produced by toxigenic strains of Corynebacterium diphtheriae and is responsible for the symptoms of diphtheria. The toxin was isolated in 1888. DT contains three structural domains, each carrying a distinct biological function implicated in the intoxication of the cell: cell-surface binding and internalization into endosomes, crossing of the endosome membrane into the cytosol and blocking of cellular protein synthesis.