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. Author manuscript; available in PMC: 2018 Oct 3.
Published in final edited form as: Nat Struct Mol Biol. 2018 Mar 26;25(4):320–326. doi: 10.1038/s41594-018-0047-3

Figure 6. Schematic showing the two modes of electromechanical coupling in a prototypical potassium channel.

Figure 6

(A) In the canonical mode, S4 (blue) acts a lever arm moving the S4–S5 linker (green) directly and thereby causing the lower half of the S6 helix (cyan) to readjust. In the resting state, the S4 helix is down which through the S4–S5 linker keeps the lower half of S6 in the closed state (left panel). When the S4 helix is up, the S4–S5 linker rotates upwards and allows the lower S6 helices to splay open (right panel). (B) Gear like movement of S4 helices directly shifts the position of the neighboring S5 helix. In this rack and pinion type of coupling, when S4 is in the resting state (left), it holds the S5 helix in a down position which forces the S6 gates to remain closed. The upward movement of the S4 helix (right panel), drives the S5 helix up and causes the S6 helices to open.