Adenylate cyclase toxin (ACT) is an important virulence factor secreted by Bordetella pertussis. When a lung infection is underway, ACT interacts with tracheal epithelial cells, inserting itself into cytoplasmic membranes, aiding the adhesion of bacteria to the airway lining. Host phagocytes responding to the site of infection are disabled by cAMP generated by ACT. Encoded by the Bordetella pertussis cyaA gene, adenylate cyclase toxin is single 1706aa polypeptide, with an apparent molecular weight of 220kD. The N-terminal of this protein contains an adenylate cyclase domain which binds to host cell calmodulin and catalyzes unregulated conversion of cellular ATP to cAMP. The C-terminal, receptor binding domain, contains numerous repeat in toxin (RTX) motifs and is responsible for binding to the cellular receptor on the surface of immune cells, translocation to the cell cytosol and creating cation-selective pores in the host cell membrane.