Fig. 2.
K+ channel auxiliary subunits. (A) Voltage-gated K+ channels (VGKCs). The conducting subunit, Kvα forms tetramers within the membrane that are accompanied and functionally modulated by four Kvβs (for Kv1), four KChIPs (for Kv4) or two KCNEs (Kv7.1) [[119], [120], [121], [122]]. The function of Kvβ is modulated by pyridine nucleotides [143]. KChIPs are involved in regulating gene expression [173]. (B) Large conductance Ca2+-activated K+ (BK) channels. BK channels consist of a K+-conducting, seven-pass (S0-S6) membrane protein subunit (BKα/Slo) accompanied and modulated by dual-pass BKβ and BKγ [182,187]. S0 of BKα is required for interaction with BKβ, S4 is involved in voltage-sensing, the pore region is formed by the linker of S5-6 and an enlarged C-terminus containing two RCK (regulator of conductance of K+) domains sense intracellular Ca2+ [330]. (C) Inwardly rectifying K+ (Kir) channels. Tetrameric Kir6 subunits, containing the K+-conducting pore, are functionally regulated at the membrane by 17-pass SUR subunits (1:1 stoichiometry), which confer ATP-sensitivity onto Kir6 via NBDs (nucleotide binding domains) [196]. Kir1-4 can be bound and modulated by various C-terminal binding proteins [331].