Identification and Characterization of PtlC, an Essential Component of the Pertussis Toxin Secretion System

Abstract

ABSTRACT PtlC is a member of a set of proteins necessary for the secretion of pertussis toxin (PT) from Bordetella pertussis . Using polyclonal antibodies specific for PtlC, we identified PtlC as a protein with an apparent molecular weight of 85,000 that localizes to the membrane fraction of bacterial cell extracts. We found that a mutant strain of B. pertussis that contains an in-frame deletion in ptlC is unable to secrete PT and that PT secretion is fully restored by expressing ptlC in trans , indicating that PtlC is essential for transport of PT across the bacterial membrane(s). PT secretion was inhibited in wild-type B. pertussis after introduction of a plasmid expressing a mutant ptlC altered in the putative nucleotide-binding region, suggesting that this region of PtlC is essential for proper function. Moreover, the observed dominant negative phenotype suggests that PtlC either functions as a multimer or interacts with some other component(s) necessary for secretion of PT.