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Abstract
A number of protein toxins produced by bacteria interact with the intestinal epithelium of the mammalian host as an essential step for their invasion into the host and for the exertion their pathogenicity. Therefore, elucidation of this step provides us with important information for understanding their pathogenicity. The molecular structures of two bacterial toxins, cholera toxin and botulinum progenitor toxin, and interactions of them with intestinal epithelial cells are focused on in this review. Cholera toxin produced by Vibrio cholerae is composed of a B moiety that binds to a cell-surface receptor and an A moiety that has toxic activity. This toxin is a well-characterized ADP-ribosyltransferase toxin, and the covalent modification of heterotrimeric Gs protein in the cytosol leads to the activation of adenylyl cyclase and a sequence of events culminating in a massive diarrheal disease. The transport pathway followed by this toxin from the plasma membrane to the cytosol was recently revealed. Botulinum neurotoxin causes foodborne botulism only when it is absorbed from the digestive tract and reaches the target neurons. Clostridium botulinum produces the neurotoxin always in the complex form (progenitor toxin), associated with other nontoxic proteins. A part of the nontoxic component was recently found to facilitate binding and internalization of the toxin into the intestinal epithelial cells. Therefore, the nontoxic component possibly has a role in the trans-epithelial transport of the toxin across the intestinal barrier. This review highlights these new insights on the interaction engaged by cholera toxin and botulinum progenitor toxin with intestinal epithelial cells.