Assembly and function of a bacterial genotoxin

Nature. 2004 May 27;429(6990):429-33. doi: 10.1038/nature02532.


The tripartite cytolethal distending toxin (CDT) induces cell cycle arrest and apoptosis in eukaryotic cells. The subunits CdtA and CdtC associate with the nuclease CdtB to form a holotoxin that translocates CdtB into the host cell, where it acts as a genotoxin by creating DNA lesions. Here we show that the crystal structure of the holotoxin from Haemophilus ducreyi reveals that CDT consists of an enzyme of the DNase-I family, bound to two ricin-like lectin domains. CdtA, CdtB and CdtC form a ternary complex with three interdependent molecular interfaces, characterized by globular, as well as extensive non-globular, interactions. The lectin subunits form a deeply grooved, highly aromatic surface that we show to be critical for toxicity. The holotoxin possesses a steric block of the CdtB active site by means of a non-globular extension of the CdtC subunit, and we identify putative DNA binding residues in CdtB that are essential for toxin activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry
  • Bacterial Proteins / metabolism
  • Bacterial Proteins / toxicity
  • Bacterial Toxins / chemistry*
  • Bacterial Toxins / metabolism
  • Bacterial Toxins / toxicity*
  • Binding Sites
  • Cell Cycle / drug effects
  • DNA / genetics
  • DNA / metabolism
  • Deoxyribonuclease I / analysis
  • Deoxyribonuclease I / chemistry
  • Haemophilus ducreyi / chemistry*
  • Haemophilus ducreyi / enzymology
  • Haemophilus ducreyi / genetics
  • HeLa Cells
  • Humans
  • Models, Molecular
  • Mutagens / chemistry*
  • Mutagens / metabolism
  • Mutagens / toxicity*
  • Mutation / genetics
  • Protein Structure, Quaternary
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism
  • Protein Subunits / toxicity
  • Ricin / chemistry


  • Bacterial Proteins
  • Bacterial Toxins
  • CdtA protein, Haemophilus ducreyi
  • CdtC protein, Haemophilus ducreyi
  • Mutagens
  • Protein Subunits
  • cytolethal distending toxin
  • DNA
  • Ricin
  • Deoxyribonuclease I

Associated data

  • PDB/1SR4