The S4-S5 linker of KCNQ1 channels forms a structural scaffold with the S6 segment controlling gate closure
Faculty of Pharmaceutical, Biomedical and Veterinary Sciences . Biomedical Sciences
Journal of biological chemistry. - Baltimore, Md
, p. 717-725
University of Antwerp
In vivo, KCNQ1 α-subunits associate with the β-subunit KCNE1 to generate the slowly activating cardiac potassium current (IKs). Structurally, they share their topology with other Kv channels and consist out of six transmembrane helices (S1S6) with the S1S4 segments forming the voltage-sensing domain (VSD). The opening or closure of the intracellular channel gate, which localizes at the bottom of the S6 segment, is directly controlled by the movement of the VSD via an electromechanical coupling. In other Kv channels, this electromechanical coupling is realized by an interaction between the S4-S5 linker (S4S5L) and the C-terminal end of S6 (S6T). Previously we reported that substitutions for Leu353 in S6T resulted in channels that failed to close completely. Closure could be incomplete because Leu353 itself is the pore-occluding residue of the channel gate or because of a distorted electromechanical coupling. To resolve this and to address the role of S4S5L in KCNQ1 channel gating, we performed an alanine/tryptophan substitution scan of S4S5L. The residues with a high impact on channel gating (when mutated) clustered on one side of the S4S5L α-helix. Hence, this side of S4S5L most likely contributes to the electromechanical coupling and finds its residue counterparts in S6T. Accordingly, substitutions for Val254 resulted in channels that were partially constitutively open and the ability to close completely was rescued by combination with substitutions for Leu353 in S6T. Double mutant cycle analysis supported this cross-talk indicating that both residues come in close contact and stabilize the closed state of the channel.