Examining Clostridium difficile
Researchers using the LS-CAT 21-ID-D beamline at the APS are exploring the crystal structure of Clostridium difficile toxin A to develop better vaccines and novel therapeutics.
Clostridium difficile is the leading cause of health-care-associated infection in the USA, with clinical outcomes that range from mild diarrhoea to pseudomembranous colitis, toxic megacolon and death.
Clostridium difficile infection is the leading cause of hospital-acquired diarrhoea and pseudomembranous colitis. Disease is mediated by the actions of two toxins, TcdA and TcdB, which cause the diarrhoea, as well as inflammation and necrosis within the colon. The toxins are large (308 and 270 kDa, respectively), homologous (47% amino acid identity) glucosyltransferases that target small GTPases within the host. The multidomain toxins enter cells by receptor-mediated endocytosis and, upon exposure to the low pH of the endosome, insert into and deliver two enzymatic domains across the membrane.
Eukaryotic inositol-hexakisphosphate (InsP6) binds an autoprocessing domain to activate a proteolysis event that releases the N-terminal glucosyltransferase domain into the cytosol. Here, we report the crystal structure of a 1,832-amino-acid fragment of TcdA (TcdA1832), which reveals a requirement for zinc in the mechanism of toxin autoprocessing and an extended delivery domain that serves as a scaffold for the hydrophobic α-helices involved in pH-dependent pore formation. A surface loop of the delivery domain whose sequence is strictly conserved among all large clostridial toxins is shown to be functionally important, and is highlighted for future efforts in the development of vaccines and novel therapeutics.
Nicole M. Chumbler, Stacey A. Rutherford, Zhifen Zhang, Melissa A. Farrow, John P. Lisher, Erik Farquhar, David P. Giedroc, Benjamin W. Spiller, Roman A. Melnyk and D. Borden Lacy, “Crystal Structure of Clostridium difficile Toxin A,” Nature Microbiology 1, Article number: 15002 (2016), DOI:10.1038/nmicrobiol.2015.2, Published Online January 11, 2016.