Abstract
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.
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