Interaction with adenylate cyclase toxin from Bordetella pertussis affects the metal binding properties of calmodulin

Adenylate cyclase toxin domain (CyaA‐ACD) is a calmodulin (CaM)‐dependent adenylate cyclase involved in Bordetella pertussis pathogenesis. Calcium (Ca(2+)) and magnesium (Mg(2+)) 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 Mg(2+)‐induced transitions in CaM's conformation in the presence of CyaA‐ACD. Mg(2+) binding was localized to sites I and II, while sites III and IV remained Ca(2+) loaded when CaM was bound to CyaA‐ACD. 2Mg(2+)/2Ca(2+)‐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 Ca(2+)‐ and Mg(2+)‐binding capabilities, which may contribute to pathobiology.