Importance of holotoxin assembly in Ptl-mediated secretion of pertussis toxin from Bordetella pertussis.

We examined the structural components of pertussis toxin that are required for efficient export from Bordetella pertussis via the Ptl system, a member of the type IV family of macromolecular transporters. First, we constructed a strain of B. pertussis that contains a functional Ptl system but does not produce pertussis toxin. Plasmids which express either the S1 subunit or the B oligomer were then introduced into this strain. We found that the B oligomer of the toxin is not secreted in the absence of the S1 subunit. Conversely, the S1 subunit is also not secreted by a Ptl-mediated mechanism in the absence of the B oligomer. Thus, an assembled holotoxin is required for Ptl-mediated export of pertussis toxin from B. pertussis.