Neighboring Alpha-Subunit (KCNQ1) Mutations with a Gain-of-Function IKs Phenotype Show Differential Dependence on Presence of Beta-Subunit (KCNE1)

The IKs cardiac potassium channel forms through co-assembly of KCNQ1, a 6 transmembrane-(TM) spanning voltage-gated potassium channel α subunit and KCNE1, a single TM spanning accessory protein. Two mutations in the S1 transmembrane helix of KCNQ1, S140G and V141M, have been shown to cause a hyperpolarizing shift in the voltage dependence of channel activation and to disrupt deactivation, resulting in accumulation of open channels and a gain-of-function phenotype during repetitive activity that is causally related to congenital human atrial fibrillation. Initial reports suggested that the phenotype of these mutants depends on the presence of the accessory protein KCNE1, which has been shown to be close in proximity to KCNQ1 S1, raising the possibility that KCNE1 directly interacts with KCNQ1 position 140 and/or 141. Here, we show that a Cys substituted at KCNQ1 position 141 spontaneously crosslinks with cysteines introduced in two positions in KCNE1, but a Cys substituted at position 140 does not crosslink to any Cys-substituted KCNE1 residues tested. Co-expression of KCNE1 with either S140G or V141M KCNQ1 slows deactivation and causes similar negative shifts in channel activation. However, in whole-cell patch clamp experiments using isotonic potassium to explore channel deactivation across a wide range of hyperpolarized potentials, we find that the V141M channel activity is indistinguishable from WT while the S140G mutation shifts the V1/2 of activation −30mV and drastically slows deactivation (tau ∼1500ms vs. ∼150ms) when compared with wild-type KCNQ1. Taken together, our results support: 1) an orientation in which KCNQ1 residue V141, but not S140, points toward and is in close proximity to KCNE1 and 2) a direct effect of S140G on channel gating but an allosteric effect of V141M on channel gating that requires the presence of KCNE1.