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

Figure 3

Organization of the CdtA, CdtB, and CdtC subunits in the AaCdt holotoxin. The computer model was generated with UCSF Chimera 1.8.1 using the PDB file 2F2F. CdtA and CdtC are shown as surface mesh models. Surface-exposed heterocyclic amino acid residues in the aromatic patch are shown in magenta. A putative receptor binding groove is formed between CdtA and CdtC. Cysteines in CdtA and CdtC are in red and form two putative internal disulfide bridges in CdtA and CdtC. CdtB is depicted as a ribbon structure. The two histidine residues (H160 and H274) in the active site are required for nuclease and phosphatidylinositol-3,4,5-triphosphate 3-phosphatase activities and are shown in cyan. All three subunits are held together by noncovalent forces.