Module 3: Figure K+ channel domains
The domain structure of K+ channels.
Like many other ion channels, the α subunits of the K+ channels have a variable number of both the transmembrane (TM) domains (shown in green) and pore-forming loops (P). The latter forms the K+ permeable channel. The two-pore K+ channels (K2P) have two P loops. The voltage sensor in Kv and BK channels is located in TM4. The K+ channels are modulated by a number of auxiliary subunits (shown in yellow) that are either cytoplasmic (KChIP or Kvβ subunits) or integral membrane proteins (DPPX, the MinK/MiRP and the KCaβ subunits). In BK channels, there is a high-affinity Ca2+-binding site called the ‘calcium bowl’ and a low-affinity site called the regulator of conductance for K+ (RCK) located close to TM6. By contrast, the Ca2+-sensitivity of the intermediate-conductance (IK) and small-conductance (SK) channels depends upon a resident calmodulin molecule.