C-terminal domain of the filamentous hemagglutinin FhaB is crucial for interaction of Bordetella pertussis with ciliated epithelial cells

Bordetella pertussis, the causative agent of whooping cough, produces a [~]370 kDa filamentous hemagglutinin FhaB that serves as a major bacterial adhesin in airway infection. FhaB is secreted via a two-partner secretion pathway and under in vitro culture conditions it is proteolytically processed to the shed [~]230 kDa FHA antigen used currently in acellular pertussis vaccines. We show that FhaB remains largely unprocessed during B. pertussis adhesion to ciliated airway epithelial cells and that its C-terminal domain (CT) is essential for the adhesin function of FhaB. CT deletion did not affect FhaB folding, secretion, or surface exposure, but abolished B. pertussis adhesion to primary human nasal ciliated epithelial cells, thus preventing bacterial colonization of the nasal mucosa and shedding and transmission of the pathogen in a murine nasal infection model. In situ cryo-electron tomography revealed a structural reorganization of the FhaB filaments upon contact with the cilia, presumably due to export of the CT from bacterial periplasm and its subsequent delivery across the ciliary membrane. These findings establish the CT of FhaB as a critical determinant of upper airway colonization by B. pertussis and identify the unprocessed FhaB as the biologically relevant adhesin form involved in airway infection. The revised model of FhaB biogenesis underpins its unique mode of action in pertussis pathogenesis and makes the CT domain to a candidate antigen for future pertussis vaccines.