Fig. 9. Gating model for KCNQ1, KCNQ1/KCNE1, KCNQ1-F232A/KNCE1, and KCNQ1-F279A/KNCE1 channels.
A simplified six-state model with three closed states and three open states. Horizontal transitions are two-step S4 activation while vertical transition is the channel opening. Upon activation, S4 moves from the resting state to the intermediate state and then to a fully activated state in both KCNQ1 and KCNQ1/KCNE1 channels. The KCNQ1 channel is suggested to open in both states, whereas the KCNQ1/KCNE1 channel only opens from the AO state. IO state is suppressed in KCNQ1/KCNE1 channels. F232A and F279A change the VSD–PD coupling and allow KCNQ1/KCNE1 channels to open from the IO state. RO state is suppressed in wt and mutant KCNQ1/KCNE1 channels at negative voltages. RC: resting closed; IC: intermediate closed; AC: activated closed; RO: resting-open; IO: intermediate-open; AO: activated-open.