Adenylate cyclase toxin domain (CyaA-ACD) is a calmodulin (CaM)-dependent adenylate cyclase involved in Bordetella pertussis pathogenesis. Calcium (Ca2+) and magnesium (Mg2+) concentrations impact CaM-dependent CyaA-ACD activation, but the structural mechanisms remain unclear. In this study, NMR, dynamic light scattering, and native PAGE were used to probe Mg2+-induced transitions in CaM's conformation in the presence of CyaA-ACD. Mg2+ binding was localized to sites I and II, while sites III and IV remained Ca2+ loaded when CaM was bound to CyaA-ACD. 2Mg2+/2Ca2+-loaded CaM/CyaA-ACD was elongated, whereas mutation of site I altered global complex conformation. These data suggest that CyaA-ACD interaction moderates CaM's Ca2+- and Mg2+-binding capabilities, which may contribute to pathobiology.
Keywords: adenylate cyclase; calcium; calmodulin; magnesium; nuclear magnetic resonance.