Voltage Sensor Conformations

Side View: The closed conformation is shown from within the plane of the membrane. The horizontal lines mark the approximate boundaries of the membrane. This membrane thickness is about 40 Å.
Six K⁺ ions are shown; K1-K4 are in the selectivity filter. Residues 196-199 comprise the selectivity filter and are shown as Backbone, colored white. The mainchain C=O's of these residues coordinate the K⁺ ions.

Toggle, Open / Closed: The switch between the open and closed states of the channel can be "toggled" by successive clicks on this button. The closed state corresponds to the resting potential of the cell (~-100 mV). The open state occurs upon membrane depolarization. In this model, S2 is assumed to be unaltered in the switch; S3a and S3b undergo substantial rearrangement; and the connection between S4-S5 is also hypothesized to be remodeled (not shown).

Voltage Sensor Close-Ups

One Subunit, Closed: Helices S2-S4 are shown as thick Backbone. The arginines that confer voltage sensitivty to the sensor are shown as Sticks, colored CPK. The K⁺ ions are Spacefill. The selectivity filter backbone is Sticks, colored CPK.

Toggle, Open / Closed: The switch between the open (red) and closed (blue) states of the channel can be "toggled" by successive clicks on this button. In addition to the movement of the "voltage-sensor paddle", note the formation of a salt bridge between Asp 80 and Arg 133 in the open state.

Residue Accessibility
Toggle, External / Internal: In the open conformation, the red highlighted residues are either close to (10 Å) or extend into the external space. In the closed conformation, the magenta highlighted residues are exposed to the internal space. See Jiang et al. (B), Figs. 3 & 5.

[Note: The conformational changes shown here are based on superposing helix S2 in the 1ORQ and 1ORS coordinate files (Jiang, et al., A below). They are most likely smaller than the switch in the intact channel. Jiang, et al., B conclude that the voltage-sensor paddles nearly move through the full thickness of the membrane as evidenced by the residue accessibilities shown above.]

The structure of the KvAP potassium channel is described in:
A. Jiang Y, Lee A, Chen J, Ruta V, Cadene M, Chait BT, & MacKinnon, R. (2003) "X-Ray Structure of a Voltage-Dependent K⁺ Channel". Nature 423: 33     PubMed [1ORQ.pdb & 1ORS.pdb]
The voltage paddle motions are described in:
B. Jiang Y, Ruta V, Chen J, Lee A, & MacKinnon, R. (2003) "The principle of gating charge movement in a voltage-dependent K⁺ Channel". Nature 423: 42     PubMed References to Figs. above are to those of Jiang et al.)