Adenylate cyclase toxin of bacteria Bordetella pertussis: mechanism of potassium efflux from macrophages

The adenylate cyclase toxin-hemolysin (ACT or CyaA) is a key virulence factor of Bordetella pertussis, the agent of the human respiratory disease whooping cough. CyaA penetrates phagocytes expressing the CD11b/CD18 integrin and exhibits two different activities. One toxin conformer oligomerizes in cell membrane and permeabilizes it by forming small cation-selective pores. Another toxin conformer appears to act as monomer. It forms a calcium influx path in the membrane, concomitantly with translocating into cells the adenylate cyclase enzyme domain that binds calmodulin and catalyzes unregulated conversion of cytosolic ATP into cAMP. We show here that CyaA causes efflux of K+ from CD11b+ cells by a mechanism that requires binding of CyaA to integrin CD11b/CD18 and permeabilization of the cellular membrane by pore-forming conformer of CyaA. Intact CyaA and the enzymatically inactive CyaA-AC- toxoid unable to generate cAMP produced the same kinetics of K+ efflux showing that elevation or signaling of cAMP had no role in this activity. The truncated CyaA variant (CyaA-AC) devoid of its invasive AC domain failed to promote K+ efflux despite a normal pore forming activity on erythrocyte and artificial membranes. However, binding of the MAb 3D1, which recognizes the distal segment of the AC domain..