Potassium channel. Homotetramer (PubMed:28723891). The six transmembrane regions are tightly packed within each subunit without undergoing domain swapping. Transmembranes TM1-TM3 are positioned on the inner circle of the channel tetramer and participate in inter-subunit interactions that are central to the assembly of the ion conduction pore. The RxxxFSD motif within transmembrane TM1 coordinates a network of specific inter- and intra-subunit interactions with other conserved residues on TM2 and TM3 and plays a key role in the tetrameric assembly of the channel. Transmembrane TM4-TM6 are positioned on the periphery of the channel and do not contribute to contacts with neighboring subunits. Transmembranes TM1 and TM2 are linked by an extended strand-like tail and two short helices (H1 and H2) which protrude outwards from the main body of the transmembrane domain and enclose the external open entrance of the ion conduction pore in the channel tetramer. Transmembrane TM1 forms the pore-lining inner helix at the center of the channel, creating an hourglass-shaped ion permeation pathway in the channel tetramer. Three hydrophobic residues on the C-terminal half of the TM1 helix form a bottleneck along the ion conduction pathway and serve as the selectivity filter of the channel. Ile-16 is probably responsible for channel selectivity. Belongs to the TMEM175 family.