Ginsenoside Rg3 activates human KCNQ1 K+ channel currents through interacting with the K318 and V319 residues: A role of KCNE1 subunit

The slowly activating delayed rectifier K+ channels (IKs) are one of the main pharmacological targets for development of drugs against cardiovascular diseases. Cardiac IKs consists of KCNQ1 plus KCNE1 subunits. Ginsenoside, one of the active ingredient of Panax ginseng, enhances cardiac IKs currents. However, little is known about the molecular mechanisms of how ginsenoside interacts with channel proteins to enhance cardiac IKs. In the present study, we investigated ginsenoside Rg3 (Rg3) effects on human IKs by co-expressing human KCNQ1 plus KCNE1 subunits in Xenopus oocytes. Rg3 enhanced IKs currents in concentration- and voltage-dependent manners. The EC50 was 15.2 ± 8.7 µM. However, in oocytes expressing KCNQ1 alone, Rg3 inhibited the currents with concentration- and voltage-dependent manners. The IC50 was 4.8 ± 0.6 µM. Since Rg3 acts opposite ways in oocytes expressing KCNQ1 alone or KCNQ1 plus KCNE1 subunits, we examined Rg3 effects after co-expression of different ratios of KCNE1 and KCNQ1. The increase of KCNE1/KCNQ1 ratio converted IKs inhibition to IKs activations. One to ten ratio of KCNE1 and KCNQ1 subunit is required for Rg3 activation of IKs. Mutations of K318 and V319 into K318Y and V319Y of KCNQ1 channel abolished Rg3 effects on KCNQ1 or KCNQ1 plus KCNE1 channel currents. The docked modeling revealed that K318 residue plays a key role in stabilization between Rg3 and KCNQ1 plus KCNE1 or KCNQ1 subunit. These results indicate that Rg3-induced activation of IKs requires co-assembly of KCNQ1 and KCNE1 subunits and achieves this through interaction with residues K318 and V319 of KCNQ1 subunit.