Abstract
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.