Cytolethal Distending Toxin: A Unique Variation on the AB Toxin Paradigm

Figure 2

Comparison of the mode of action of the A chain of selected AB toxins. The A chain of ricin and Shiga toxin is a ribosomal inhibiting protein (N-glycoside hydrolase) that carries out a depurination by removing an adenine from the 28S rRNA. The A chain of anthrax toxin is represented by two polypeptides known as the lethal factor (LF), a Zn²⁺-dependent endoprotease, and edema factor (EF), a polypeptide that forms a Ca²⁺- and calmodulin-dependent adenylate cyclase. The A chain of cholera toxin is enzymatically cleaved to create a polypeptide (A1 chain) that ribosylates the guanosine nucleotide-binding protein G_sα. The A chain of botulinum and tetanus toxins degrades specific soluble N-ethylmaleimide-sensitive factor attachment proteins (SNARE) which inhibits vesicle fusion and delivery of neurotransmitters such as acetylcholine. Additional details are provided in the text. MAPKK: mitogen-activated protein kinase kinases; CFTR: cystic fibrosis transmembrane conductance regulator.