Bordetella pertussis BctCBA Mediates Citrate-Dependent Zn 2+ and Ni 2+ binding
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Bordetella pertussis , the causative agent of whooping cough, is a reemerging public health threat. While the Tripartite Tricarboxylate Transporter (TTT) system BctCBA was previously implicated solely in citrate uptake, we demonstrate that the solute-binding protein BctC specifically binds citrate chelated with Zn²⁺ and Ni²⁺. To elucidate the molecular mechanism of this interaction, we determined the crystal structures of BctC in three states: apo, open, and closed (citrate–zinc-bound), defining the structural determinants for metal-citrate recognition. Comparative analyses suggest that citrate-mediated divalent cation binding is a widespread feature among bacterial TTT homologs. Finally, in silico modeling of the full BctCBA complex predicts an elevator-type transport mechanism. Together, these findings redefine the functional scope of BctCBA, revealing a sophisticated strategy by which B. pertussis exploits organic chelators to acquire essential trace metals during infection.
