Autoproteolytic mechanism of CdiA toxin release reconstituted <i>in vitro</i>

It is challenging to develop new antibiotics capable of killing Gram-negative bacteria because their outer membranes are impermeable to many small molecules. Some Gram-negative bacteria, however, deliver much larger protein toxins through the outer membranes of competing bacteria in their environments using contact-dependent inhibition (CDI) systems. How these toxins traverse the outer membranes of their targets is not well understood. We have therefore developed a method to study the toxin delivery process in a highly simplified system using a fragment of a CDI protein. Our results indicate that the CDI protein assembles into a structure in the target membrane that catalyzes the release of the toxin. This CDI protein fragment enables further studies of the toxin delivery mechanism.