Aims: 

Voltage-dependent potassium channels are tetramers of six transmembrane domain (S1-S6) proteins. Recent crystallographic datademonstrate that the tetrameric pore (S5-S6) is surrounded by four voltage sensor domains (S1-S4). One key question remains: how do the voltage sensors (S4) regulate the pore gating? We tested the hypothesis that the S4-S5 linker is a voltage-dependent ligand binding to the S6 C-terminus and locking the channel in a closed state.

Methods: 

We designed plasmid-encoded peptides corresponding to portions of the S4-S5 linker and the S6 C-terminus of the voltage-gated potassium channel KCNQ1 and evaluated their effects on the activity of the KCNE1-KCNQ1 fusion protein.

Results: 

Two different S4-S5 peptides inhibited the KCNQ1 function, consistent withthe hypothesis. For example, L251-L266 decreased the current density from

22.6 ± 2.9 pA/pF (n = 57) to 10.78 ± 2.6 pA/pF (n = 25) and slowed down the activation kinetics. Two S6 C-ter peptides upregulated KCNQ1, consistent with the S6 C-terminus being the receptor for the endogenous S4-S5. Absence of effect of these peptides on Herg channel suggests the specificity of the interaction. Both kinetic and structural models of the channel were challenged by addition of peptides bound states. The computerized data illustrate well the experimental effects of S4-S5 and S6-C-ter peptides on the channel activity.

Conclusion: 

Our results suggest a mechanistic model in which the channel gate is locked closed by the four S4-S5 linkers in a voltage-dependent manner. We anticipate these results to reflect a general mechanism for voltage-gated channels.