Structural organization of the functional domains of Clostridium difficile toxins
Structural organization of the functional domains of Clostridium difficile toxins A and B
Rory N. Pruitta,
Melissa G. Chambersb,
Kenneth K.-S. Ngc,
Melanie D. Ohib,1, and
D. Borden Lacya,d,1
+ Author Affiliations
Departments of aMicrobiology and Immunology,
bCell and Developmental Biology, and
dBiochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232; and
cDepartment of Biological Sciences and the Alberta Ingenuity Centre for Carbohydrate Science, University of Calgary, Calgary, AB, Canada T2N IN4
Edited by Stephen C. Harrison, Harvard Medical School, Boston, MA, and approved May 18, 2010 (received for review February 24, 2010)
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.