Translocation domain mutations affecting cellular toxicity identify the Clostridium difficile toxin B pore

Significance Clostridium difficile is the leading cause of antibiotic-associated infection in hospitals worldwide. Disease symptoms are caused by toxins A and B, which form membrane-spanning pores that deliver associated cytotoxic enzyme domains into target cells leading to cellular death and tissue damage. Despite a wealth of information for the enzymatic domains that act once inside the cell, very little is known about the translocation pore and its role in disease pathogenesis. Here we describe the structural features of the pore and identify mutants that prevent pore formation and show that they are no longer toxic to host cells. These findings offer a glimpse into the elusive translocation pore and further provide the basis for a unique strategy to target toxins therapeutically.