1.A.1.13.1
6TMS K⁺ channel (Munsey et al. 2002; Kuo et al., 2003).  The kch gene, the only known potassium channel gene in E. coli, has the property to express both full-length Kch and its cytosolic domain (RCK) due to a methionine at position 240. The RCK domains form an octameric ring structure and regulate the gating of the potassium channels after having bound certain ligands. Several different gating ring structures have been reported for the soluble RCK domains.  The octameric structure of Kch may be composed of two tetrameric full-length proteins through RCK interaction (Kuang et al. 2013).  The RCK domains face the solution, and an RCK octameric gating ring arrangement does not form under certain conditions (Kuang et al. 2015).