ABSTRACT
Diphtheria toxin (DT) has served in recent years as a paradigm for the investigation of toxic bacterial proteins, particularly those that act intracellularly and more specifically those that catalyze ADP-ribosylation reactions. DT was the first toxin shown to act intracellularly and the first identified as catalyzing ADP-ribosylation of its cytoplasmic target protein. The toxin was crystallized in 1982 by two groups (McKeever and Sarma, 1982; Collier et al., 1982), and a 2.5 A structure was reported in 1992 by Choe et al. (1992). The crystallographic model has provided a basis for interpreting known structurefunction relationships and will undoubtedly foster additional advances in our understanding of how this toxin binds to its receptor, penetrates membranes, and catalyzes the covalent modification of its target protein.
