Cysteines control the N- and C-linker-dependent gating of KCNH1 potassium channels

KCNH1 (EAG1) is a member of the Kv family of voltage-gated potassium channels. However, KCNH1 channels also show some amino-acid sequence similarity to cyclic-nucleotide-regulated channels: they harbor an N-terminal PAS domain, a C-terminal cyclic nucleotide binding homology domain (cNBHD), and N- and C-terminal binding sites for calmodulin. Another notable feature is the channels' high sensitivity toward oxidative modification. Using human KCNH1 expressed in Xenopus oocytes and HEK 293 cells we investigated how oxidative modification alters channel function. Intracellular application of H2O2 or cysteine-specific modifiers potently inhibited KCNH1 channels in two phases. Our systematic cysteine mutagenesis study showed that the rapid and dominant phase was attributed to a right-shift in the voltage dependence of activation, caused by chemical modification of residues C145 and C214. The slow component depended on the C-terminal residues C532 and C562. The cysteine pairs are situated at structural elements linking the transmembrane S1 segment with the PAS domain (N-linker) and the transmembrane channel gate S6 with the cNBH domain (C-linker), respectively. The functional state of KCNH1 channels is determined by the oxidative status of these linkers that provide an additional dimension of channel regulation.