Most known small-molecule inhibitors of voltage-gated ion channels have poor subtype specificity because they interact with a highly conserved binding site in the central cavity. Using alanine-scanning mutagenesis, electrophysiological recordings and molecular modeling, we have identified a new drug-binding site in Kv1.x channels. We report that Psora-4 can discriminate between related Kv channel subtypes because, in addition to binding the central pore cavity, it binds a second, less conserved site located in side pockets formed by the backsides of S5 and S6, the S4–S5 linker, part of the voltage sensor and the pore helix. Simultaneous drug occupation of both binding sites results in an extremely stable nonconducting state that confers high affinity, cooperativity, use-dependence and selectivity to Psora-4 inhibition of Kv1.x channels. This new mechanism of inhibition represents a molecular basis for the development of a new class of allosteric and selective voltage-gated channel inhibitors.

The time course of inactivation of voltage-activated potassium (Kv) channels is an important determinant of the firing rate of neurons. In many Kv channels highly unsaturated lipids as arachidonic acid, docosahexaenoic acid and anandamide can induce fast inactivation. We found that these lipids interact with hydrophobic residues lining the inner cavity of the pore. We analysed the effects of these lipids on Kv1.1 current kinetics and their competition with intracellular tetraethylammonium and Kvb subunits. Our data suggest that inactivation most likely represents occlusion of the permeation pathway, similar to drugs that produce 'open-channel block'. Open-channel block by drugs and lipids was strongly reduced in Kv1.1 channels whose amino acid sequence was altered by RNA editing in the pore cavity, and in Kv1.x heteromeric channels containing edited Kv1.1 subunits. We show that differential editing of Kv1.1 channels in different regions of the brain can profoundly alter the pharmacology of Kv1.x channels. Our findings provide a mechanistic understanding of lipid-induced inactivation and establish RNA editing as a mechanism to induce drug and lipid resistance in Kv channels.

The degree of stereoselective block of Kv1.5 decreases from 9 to 4 when Kvbeta1.3 is present. L510 is determinant for the modulation of bupivacaine block, because it is the only residue of the S6 segment that binds to both bupivacaine and Kvbeta1.3. These findings support an overlapping binding site for drugs and Kvbeta1.3.

A.K.K. performed statistical analyses, generated the figures and contributed to the manuscript writing. N.D., W.G., T.G. and C.V. conceived and designed the experiments. N.D. supervised the whole project and wrote the manuscript.

Background: It is poorly understood how hyperpolarization-activated cyclic nucleotide-gated channels (HCNs) function. Results: We have identified a leucine zipper in the S5 segment of HCNs, regulating hyperpolarization-activated and instantaneous current components. Conclusion:The leucine zipper is essential for HCN channel gating. Significance: The identification and functional characterization of the leucine zipper is an important step toward the understanding of HCN channel function.

Background and Purpose: Local anesthetics block sodium and a variety of potassium channels. Although previous studies identified a residue in the pore signature sequence together with three residues in the S6 segment as a putative binding site, the precise molecular basis of Kv potassium channel inhibition by local anesthetics remained unknown. Kv crystal structures predict that some of these residues point away from the central cavity and face into a drug binding site called 'side pockets . Thus, the question arises whether the binding site of local anesthetics is exclusively located in the central cavity or also involves the 'side pockets . Experimental Approach: A systematic functional alanine mutagenesis approach, scanning 58 mutants, in concert with in silico docking experiments and molecular dynamics simulations were utilized to elucidate the binding site of bupivacaine and ropivacaine. Key Results: Kv1.5 inhibition by local anesthetics requires binding to the central cavity and the 'side pockets , where the latter requires interactions with residues of the S5 and the backside of the S6 segment. Mutations in the 'side pockets remove stereoselectivity of Kv1.5 inhibition by bupivacaine. Strikingly, while we found that binding to the 'side pockets is conserved for the different local anesthetics, the binding mode in the central cavity and the 'side pockets shows considerable variations. Conclusion and Implications: Local anesthetics bind to the central cavity and the 'side pockets which provides a crucial key for the molecular understanding of their Kv channel affinity and stereoselectivity, as well as their spectrum of side effects.