Histidine at position 462 determines the low quinine sensitivity of ether-à-go-go channel superfamily member Kv 12.1.

The ether-à-go-go (Eag) K_v superfamily comprises closely related K_v 10, K_v 11, and K_v 12 subunits. K_v 11.1 (termed hERG in humans) gained much attention, as drug-induced inhibition of these channels is a frequent cause of sudden death in humans. The exclusive drug sensitivity of K_v 11.1 can be explained by central drug-binding pockets that are absent in most other channels. Currently, it is unknown whether K_v 12 channels are equipped with an analogous drug-binding pocket and whether drug-binding properties are conserved in all Eag superfamily members.

We analysed sensitivity of recombinant K_v 12.1 channels to quinine, a substituted quinoline that blocks K_v 10.1 and K_v 11.1 at low micromolar concentrations.

Quinine inhibited K_v 12.1, but its affinity was 10-fold lower than for K_v 11.1. Contrary to K_v 11.1, quinine inhibited K_v 12.1 in a largely voltage-independent manner and induced channel opening at more depolarised potentials. Low sensitivity of K_v 12.1 and characteristics of quinine-dependent inhibition were determined by histidine 462, as site-directed mutagenesis of this residue into the homologous tyrosine of K_v 11.1 conferred K_v 11.1-like quinine block to K_v 12.1(H462Y). Molecular modelling demonstrated that the low affinity of K_v 12.1 was determined by only weak interactions of residues in the central cavity with quinine. In contrast, more favourable interactions can explain the higher quinine sensitivity of K_v 12.1(H462Y) and K_v 11.1 channels.

The quinoline-binding "motif" is not conserved within the Eag superfamily, although the overall architecture of these channels is apparently similar. Our findings highlight functional and pharmacological diversity in this group of evolutionary-conserved channels.