title: Structural organization of the functional domains of Clostridium difficile toxins A and B.
abstract: Clostridium difficile toxins A and B are members of an important class of virulence factors known as large clostridial toxins (LCTs). Toxin action involves four major steps: receptor-mediated endocytosis, translocation of a catalytic glucosyltransferase domain across the membrane, release of the enzymatic moiety by autoproteolytic processing, and a glucosyltransferase-dependent inactivation of Rho family proteins. We have imaged toxin A (TcdA) and toxin B (TcdB) holotoxins by negative stain electron microscopy to show that these molecules are similar in structure. We then determined a 3D structure for TcdA and mapped the organization of its functional domains. The molecule has a "pincher-like" head corresponding to the delivery domain and two tails, long and short, corresponding to the receptor-binding and glucosyltransferase domains, respectively. A second structure, obtained at the acidic pH of an endosome, reveals a significant structural change in the delivery and glucosyltransferase domains, and thus provides a framework for understanding the molecular mechanism of LCT cellular intoxication.
authors.affiliation: Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
authors.forename: Rory N
authors.initials: RN
authors.lastname: Pruitt
authors.forename: Melissa G
authors.initials: MG
authors.lastname: Chambers
authors.forename: Kenneth K-S
authors.initials: KK
authors.lastname: Ng
authors.forename: Melanie D
authors.initials: MD
authors.lastname: Ohi
authors.forename: D Borden
authors.initials: DB
authors.lastname: Lacy
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry* / Q000648:ultrastructure; D001427:Bacterial Toxins / Q000737:chemistry*; D001665:Binding Sites; D016466:CHO Cells; D016360:Clostridioides difficile / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D004591:Electrophoresis, Polyacrylamide Gel; D004768:Enterotoxins / Q000737:chemistry*; D005964:Glucosyltransferases / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008807:Mice, Inbred BALB C; D008854:Microscopy, Electron; D008958:Models, Molecular; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004768:Enterotoxins; C041348:tcdA protein, Clostridium difficile; C031815:toxB protein, Clostridium difficile; D005964:Glucosyltransferases