SUBUNIT STRUCTURE

 

The channel is made up of four identical subunits, each having six transmembrane segments, as shown in the figure. The segments are named S1 through S6 from the amino to the carboxy ends of the polipeptide. Segments S5 and S6 and the special P loop structure form the conduction pore. Segments S1, S2, S3 and S4 constitute the voltage sensor, which detects changes in membrane potential and communicates the perturbation to the conduction pore to gate the channel open or closed.

THREE-DIMENSIONAL STRUCTURE

EXTRACELLULAR VIEW
    Each subunit is represented in a different color. The Pore Domain (PD) has a central conduction pore formed by Segments S5 and S6 and the pore loop of all four subunits.
    The Voltage Sensor Domains (VSD) of each subunit, are made up of segments S1, S2, S3 and S4  peripheraly located around the central pore. The voltage sensor moves in response to changes in membrane voltage. (See voltage sensor)
    In many Kv channels, the PD of one subunit is facing the VSD of next subunit (swapped domain channels).
    Segment S4 (the charge bearing segment) is coupled in the intracellular region to the S5 segment by the S4-S5 linker. Each S4-S5 linker controls the position of segment S6 of the pore. The gate of the conduction pore is formed by the all four S6 segments. The gate is open (conducting) only when all four S6 segments are in the open position.(See Channel Operation) MEMBRANE VIEW (only 2 subunits)
 This view shows the pore in the center with the selectivity filter containing the K ions. The voltage sensor are shown on the sides, where the bottom of S4 is communicating via the S4-S5 linker with S6 and touching the S6 segment.

SIMPLIFIED VIEW (only 2 subunits)
The figure below shows the simplified view of the channel used for the stochastic simulations of K channel operation. The S4 segments are in the active position. The S4-S5 linker is the horizontal cylinder touching the bottom of S6 shown in the open gate configuration. In this view the open gate is blocked by the S6 segment, therefore in the simulation the view is from the extracellular side. (There is also an option to see the simulation as a side view but in that case the channel is shown as nonswapped domain case: go to Channel operation).