title: Biochemical studies on the effect of Clostridium difficile toxin B on actin in vivo and in vitro.
abstract: We describe a simplified procedure for purification of Clostridium difficile toxin B. In this procedure, cytotoxicity is associated with a single protein band with a molecular mass of 230 kilodaltons. We used direct fluorescent staining of actin filaments to study the effect of this toxin on cultured cells. Morphologic changes were preceded by a decrease in the number and length of stress fibers followed by their disappearance with condensation of cellular actin around the nucleus. We then showed that cells treated with either cytochalasin B or toxin B had a significant increase in the monomeric actin pool as quantitated by DNase I inhibition. In contrast to the cytochalasins, toxin B had no direct effect on the rate or extent of actin polymerization or network formation in vitro. Cytoplasmic extracts of toxin B-treated cells had a significantly lower level of modulating activity on actin assembly and interactions in vitro compared with extracts of untreated cells. These results suggest that the action of toxin B on cells is due to direct or indirect effects on cellular proteins involved in controlling the state of actin assembly in the cells.
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects* / Q000648:ultrastructure; D000199:Actins / Q000378:metabolism*; D000818:Animals; D001426:Bacterial Proteins; D001427:Bacterial Toxins / Q000494:pharmacology*; D002474:Cell-Free System; D003599:Cytoskeleton / Q000187:drug effects*; D005347:Fibroblasts; D051379:Mice; D014783:Viscosity
chemical_list: D000199:Actins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; C031815:toxB protein, Clostridium difficile