Mechanism of Kch activation by Zn²

Escherichia coli has a single K⁺ channel gene, kch, that produces a K⁺ channel with six transmembrane segments and a cytosolic Regulate Conductance of K⁺ channels (RCK) domain. RCK domains are present in both eukaryotic and prokaryotic organisms and known to regulate ion channel activity upon binding of an ion or a nucleotide, however, how Kch is regulated remains unknown. Here, we show that Zn²⁺ or Cu²⁺ activates Kch via the RCK domain. Structural studies reveal that eight RCK domains assemble into a gating ring that can assume three conformations, closed, intermediate, and open, and that Zn²⁺ promotes the open conformation by stabilizing the assembly interface. These results expand our knowledge on Kch and on RCK-mediated regulation of ion channels.