The KCNH voltage dependent potassium channels are key regulators of cellular excitability,
involved in cardiac long QT syndrome type 2 (LQTS2), epilepsy, schizophrenia and cancer. The
intracellular domains of KCNH channels are structurally distinct from other voltage-gated
channels, and include an amino-terminal eag domain, composed from a Per-Arnt-Sim (PAS)
module and a PAS-cap region, and a carboxy-terminal cyclic nucleotide-binding homology
domain (CNBHD), connected to the pore domain through a C-linker domain. These specialized
intracellular domains are the site of many disease-causing mutations and bestow unique gating
and regulation on KCNH channels. Using fluorescence, x-ray crystallography and
electrophysiological approaches, we determined and validated the structure of the intracellular
complex of mEAG1 channel. Harboring many LQTS2 and cancer-associated mutations, the eag
domain-CNBHD interface involves three important regions: (i) the “intrinsic ligand” motif, a
unique structural feature of the CNBHD; (ii) the post-CNBHD region, known to mediate EAG
channels regulation by a variety of cellular signaling events; and finally, (iii) the PAS-cap region,
which constitutes the first 25 amino acids of the eag domain, and forms a highly conserved
amphipathic helix (αCAP). Together, this work provides a detailed physiological and
pathophysiological description of the intracellular domain of the KCNH family.
