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

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