TY - JOUR T1 - An Allosteric Mechanism for Drug Block of the Human Cardiac Potassium Channel KCNQ1 JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.112.081513 SP - mol.112.081513 AU - Tao Yang AU - Jarrod A Smith AU - Brenda F Leake AU - Charles R Sanders AU - Jens Meiler AU - Dan M Roden Y1 - 2012/11/28 UR - http://molpharm.aspetjournals.org/content/early/2012/11/28/mol.112.081513.abstract N2 - Abstract: The intracellular aspect of the sixth transmembrane segment within the ion permeating pore is a common binding site for many voltage-gated ion channel blockers. However, the exact site(s) at which drugs bind remain controversial. We used extensive site-directed mutagenesis coupled with molecular modeling to examine mechanisms in drug block of the human cardiac potassium channel KCNQ1. A total of 48 amino acid residues in the S6 segment, S4-S5 linker, and the proximal C-terminus of the KCNQ1 channel were mutated individually to alanine; alanines were mutated to cysteines. Residues modulating drug block were identified when mutant channels displayed <50% block on exposure to drug concentrations that inhibited wild-type current by ≥90%. Homology modeling of the KCNQ1 channel based on the Kv1.2 structure unexpectedly predicted that the key residue modulating drug block (F351) faces away from the permeating pore. In the open-state channel model, F351 lines a pocket that also includes residues L251 and V254 in S4-S5 linker. Docking calculations indicated that this pocket is large enough to accommodate quinidine. To test this hypothesis, L251A and V254A mutants were generated that display a reduced sensitivity to blockage with quinidine. Thus, our data support a model in which open state block of this channel occurs not via binding to a site directly in the pore but rather by a novel allosteric mechanism, drug access to a side pocket generated in the open-state channel configuration and lined by S6 and S4-S5 residues. ER -