Distinct gating mechanisms revealed by the structures of a multi-ligand gated K(+) channel

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 Ca(2+) 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: http://dx.doi.org/10.7554/eLife.00184.001