Structural and biochemical analysis of the unique interactions of the Campylobacter jejuni CorA channel protein with...

CorA is a Mg²⁺ channel that plays a key role in the homeostasis of intracellular Mg²⁺ in bacteria and archaea. CorA consists of a cytoplasmic domain and a transmembrane domain and generates a Mg²⁺ pathway by forming a pentamer in the cell membrane. CorA gating is regulated via negative feedback by Mg²⁺, which is accommodated by the pentamerization interface of the CorA cytoplasmic domain (CorA_CD). The Mg²⁺-binding sites of CorA_CD differ depending on the species, suggesting that the Mg²⁺-binding modes and Mg²⁺-mediated gating mechanisms of CorA vary across prokaryotes. To define the Mg²⁺-binding mechanism of CorA in the Campylobacter jejuni pathogen, we structurally and biochemically characterized C. jejuni CorA_CD (cjCorA_CD). cjCorA_CD adopts a three-layered α/β/α structure as observed in other CorA orthologs. Interestingly, cjCorA_CD exhibited enhanced thermostability in the presence of Ca²⁺, Ni²⁺, Zn²⁺, or Mn²⁺ in addition to Mg²⁺, indicating that cjCorA_CD interacts with diverse divalent cations. This cjCorA_CD stabilization is mediated by divalent cation accommodation by negatively charged residues located at the bottom of the cjCorA_CD structure away from the pentamerization interface. Consistently, cjCorA_CD exists as a monomer irrespective of the presence of divalent cations. We concluded that cjCorA_CD binds divalent cations in a unique pentamerization-independent manner.