A KCNE1 C-Terminus Long QT Mutation Disrupts a Crucial Interaction with the Kv7.1 Coiled-Coil Helix C and Reduces IKS Channel Expression

Kv7.1 α-subunit assembles with the KCNE1 auxiliary subunit to form the cardiac IKS K+ channel. Mutations in these subunit genes produce the long QT syndrome, a life-threatening ventricular arrhythmia. We recently explored the direct interactions between the C-termini of Kv7.1 and KCNE1 using purified recombinant proteins in a series of in-vitro pull-down experiments. We found that the KCNE1 C-terminus physically interacts with the coiled-coil helix-C of the tetramerization domain. Here we show that the missense LQT5 mutation (P127T) located in the KCNE1 distal C-terminus and previously found to produce a dominant Romano-Ward LQT syndrome, disrupted the physical interaction of KCNE1 with the Kv7.1 coiled-coil helix C. When co-expressed in CHO cells with WT Kv7.1, the KCNE1 LQT mutant P127T dramatically reduced IKS current density, without altering channel gating properties. Our results show that deletion of the proximal KCNE1 C-terminus (KCNE1Δ69-77) significantly enhanced the binding of KCNE1 to Kv7.1 C-terminus. In contrast, deletions of the more distal regions of KCNE1 C-terminus (KCNE1Δ78-129 and KCNE1Δ109-129) totally prevented its binding to the Kv7.1 C-terminal region. Our data suggest that the most distal region of the KCNE1 C-terminus (aa.109-129) is crucial for the KCNE1 interaction with the Kv7.1 coiled-coil helix-C and that the missense LQT5 mutation P127T located within this domain affects IKS channel expression by disrupting this coiled-coil interaction and possibly disturbing channel trafficking.