Large clostridial cytotoxins: cellular biology of Rho/Ras-glucosylating toxins

Mono-O-glycosylation of eukaryotic target proteins is the molecular mechanism of bacterial protein toxins of the family of large clostridial cytotoxins. This toxin family encompasses several high molecular mass proteins (>250 kDa) of various Clostridia species that are implicated in severe human diseases. Toxin A and toxin B from Clostridium difficile are the causative agents of pseudomembraneous colitis and antibiotic-associated diarrhea. Lethal toxin and hemorrhagic toxin from Clostridium sordellii as well as alpha-toxin from Clostridium novyi are involved in the gas gangrene syndrome. The common mode of action of large clostridial cytotoxins is elicited by specific glycosylation of small GTP-binding proteins in the cytosol of target cells using activated nucleotide sugars as cosubstrates. Specific modification at a single threonine residue in the small GTPases renders these important key players of various signaling pathways inactive. This minireview intends to give an overview on structure-function analysis and mode of action of the large clostridial cytotoxins, as well as on the resulting functional consequences of glycosylation of target proteins. (C) 2004 Elsevier B.V. All rights reserved.