PT  - JOURNAL ARTICLE
AU  - Vivek Garg
AU  - Anna Stary-Weinzinger
AU  - Frank Sachse
AU  - Michael Sanguinetti
TI  - Molecular determinants for activation of human ERG1 potassium channels by 3-nitro-N-(4-phenoxyphenyl) benzamide
AID  - 10.1124/mol.111.073809
DP  - 2011 Jul 08
TA  - Molecular Pharmacology
PG  - mol.111.073809
4099  - http://molpharm.aspetjournals.org/content/early/2011/07/08/mol.111.073809.short
4100  - http://molpharm.aspetjournals.org/content/early/2011/07/08/mol.111.073809.full
AB  - Human ether-a-go-go-related gene 1 (hERG1) channels mediate repolarization of cardiac action potentials. Inherited long QT syndrome (LQTS) caused by loss-of-function mutations, or unintended blockade of hERG1 channels by many drugs, can lead to severe arrhythmia and sudden death. Drugs that activate hERG1 are a novel pharmacological approach to treat LQTS. Recently, ICA-105574 (3-nitro-N-(4-phenoxyphenyl) benzamide, ICA) was discovered to activate hERG1 by strong attenuation of P-type inactivation. Here we utilized scanning mutagenesis of hERG1 to identify the molecular determinants of ICA action. Three mutations abolished the activator effects of 30 μM ICA, including L622C in the pore helix, F557L in the S5 segment and Y652A in the S6 segment. One mutation in S6 (A653M) switched the activity of ICA from an activator to an inhibitor, revealing its partial agonist activity. This was confirmed by showing that the non-inactivating mutant hERG1 channel (G628C/S631C) was inhibited by ICA and that addition of the F557L mutation rendered the channel drug-insensitive. Simulated molecular docking of ICA to homology models of hERG1 corroborated the scanning mutagenesis findings. Together our findings indicate that ICA is a mixed agonist of hERG1 channels. Activation or inhibition of currents is mediated by the same or overlapping binding site located in the pore module between two adjacent subunits of the homotetrameric channel.