Module 3: Figure IK/SK channel opening
Intermediate-conductance (IK) and small-conductance (SK) channel opening by chemomechanical coupling induced by Ca2+ binding to calmodulin.
This figure shows two of the four α-subunits, each of which is controlled by a resident calmodulin molecule. In the closed position shown on the left, the α1 helix of each channel subunit is bound by the C lobe of the calmodulin molecules. When Ca2+ binds to the two EF-hand regions of the N lobe of calmodulin, a conformational change occurs that pulls in the α2 helix of a neighbouring subunit to form a dimer with the α2 blue helix that lies antiparallel to the α2 green helix. The formation of this complex then opens the pore by pulling on the transmembrane 6 domains. The structure of this complex is illustrated in Module 3: Figure CaM/SK channel complex.