title: Assembly and function of a bacterial genotoxin.
abstract: 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.
authors.affiliation: Laboratory of Structural Microbiology, The Rockefeller University, New York 10021, USA.
authors.forename: Dragana
authors.initials: D
authors.lastname: Nesić
authors.forename: Yun
authors.initials: Y
authors.lastname: Hsu
authors.forename: C Erec
authors.initials: CE
authors.lastname: Stebbins
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D001427:Bacterial Toxins / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity*; D001665:Binding Sites; D002453:Cell Cycle / Q000187:drug effects; D004247:DNA / Q000235:genetics / Q000378:metabolism; D003850:Deoxyribonuclease I / Q000032:analysis / Q000737:chemistry; D006191:Haemophilus ducreyi / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008958:Models, Molecular; D009153:Mutagens / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity*; D009154:Mutation / Q000235:genetics; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D012276:Ricin / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; C468508:CdtA protein, Haemophilus ducreyi; C468509:CdtC protein, Haemophilus ducreyi; D009153:Mutagens; D021122:Protein Subunits; C067044:cytolethal distending toxin; D004247:DNA; D012276:Ricin; D003850:Deoxyribonuclease I