A mutation in the cardiac KV7.1 channel possibly disrupts interaction with Yotiao protein

Here, we characterized the p.Arg583His (R583H) Kv7.1 mutation, identified in two unrelated families suffered from LQT syndrome. This mutation is located in the HС-HD linker of the cytoplasmic portion of the Kv7.1 channel. This linker, together with HD helix are responsible for binding the A-kinase anchoring protein 9 (AKAP9), Yotiao. We studied the electrophysiological characteristics of the mutated channel expressed in CHO-K1 along with KCNE1 subunit and Yotiao protein, using the whole-cell patch-clamp technique. We found that R583H mutation, even at the heterozygous state, impedes IKs activation. Molecular modeling showed that HС and HD helixes of the C-terminal part of Kv7.1 channel are swapped along the C-terminus length of the channel and that R583 position is exposed to the outer surface of HC-HD tandem coiled-coil. Interestingly, the adenylate cyclase activator, forskolin had a smaller effect on the mutant channel comparing with the WT protein, suggesting that R583H mutation may disrupt the interaction of the channel with the adaptor protein Yotiao and, therefore, may impair phosphorylation of the KCNQ1 channel.

Disruption of a Conservative Motif in the C-Terminal Loop of the KCNQ1 Channel Causes LQT Syndrome

We identified a single nucleotide variation (SNV) (c.1264A > G) in the KCNQ1 gene in a 5-year-old boy who presented with a prolonged QT interval. His elder brother and mother, but not sister and father, also had this mutation. This missense mutation leads to a p.Lys422Glu (K422E) substitution in the Kv7.1 protein that has never been mentioned before. We inserted this substitution in an expression plasmid containing Kv7.1 cDNA and studied the electrophysiological characteristics of the mutated channel expressed in CHO-K1, using the whole-cell configuration of the patch-clamp technique. Expression of the mutant Kv7.1 channel in both homo- and heterozygous conditions in the presence of auxiliary subunit KCNE1 results in a significant decrease in tail current densities compared to the expression of wild-type (WT) Kv7.1 and KCNE1. This study also indicates that K422E point mutation causes a dominant negative effect. The mutation was not associated with a trafficking defect; the mutant channel protein was confirmed to localize at the cell membrane. This mutation disrupts the poly-Lys strip in the proximal part of the highly conserved cytoplasmic A−B linker of Kv7.1 that was not shown before to be crucial for channel functioning.