We have demonstrated previously that the 20(S) but not the 20(R) form of ginsenoside Rg3 inhibited K+ currents flowing through Kv1.4 (hKv1.4) channels expressed in Xenopus laevis oocytes, pointing to the presence of specific interaction site(s) for Rg3 in the hKv1.4 channel. In the current study, we sought to identify this site(s). To this end, we first assessed how point mutations of various amino acid residues of the hKv1.4 channel affected inhibition by 20(S)-ginsenoside Rg3 (Rg 3). Lys531 residue is known to be a key site for K+ activation and to be part of the extracellular tetraethylammonium (TEA) binding site; the mutation K531Y abolished the Rg3 effect and made the Kv1.4 channel sensitive to TEA applied to the extracellular side of the membrane. Mutations of many other residues, including the pH sensitive-site (H507Q), were without any significant effect. We next examined whether K+ and TEA could alter the effect of Rg3 and vice versa. We found that 1) raising [K+]o reduced the inhibitory effect of Rg 3 on hKv1.4 channel currents, whereas Rg3 shifted the K+ activation curve to the right, and 2) TEA caused a rightward shift of the Rg3 concentration-response curve of wild-type hKv1.4 channel currents, whereas Rg3 caused a rightward shift of the TEA concentration-response curve of K531Y mutant channel currents. The docked modeling revealed that Lys531 plays a key role in forming hydrogen bonds between Rg3 and hKv1.4 channels. These results indicate that Rg3 inhibits the hKv1.4 channel current by interacting with residue Lys531.
ASJC Scopus subject areas
- Molecular Medicine