The gating ring-forming RCK domain regulates channel gating in response to various cellular chemical stimuli in eukaryotic Slo channel families and the majority of ligand-gated prokaryotic K+ channels and transporters. Here we present structural and functional studies of a dual RCK-containing, multi-ligand gated K+ channel from Geobacter sulfurreducens, named GsuK. We demonstrate that ADP and NAD+ activate the GsuK channel, whereas Ca2+ serves as an allosteric inhibitor. Multiple crystal structures elucidate the structural basis of multi-ligand gating in GsuK, and also reveal a unique ion conduction pore with segmented inner helices. Structural comparison leads us to propose a novel pore opening mechanics that is distinct from other K+ channels. >DOI:
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