title: Molecular determinants of voltage-dependent human ether-a-go-go related gene (HERG) K+ channel block.
abstract: The structural determinants for the voltage-dependent block of ion channels are poorly understood. Here we investigate the voltage-dependent block of wild-type and mutant human ether-a-go-go related gene (HERG) K(+) channels by the antimalarial compound chloroquine. The block of wild-type HERG channels expressed in Xenopus oocytes was enhanced as the membrane potential was progressively depolarized. The IC(50) was 8.4 +/- 0.9 microm when assessed during 4-s voltage clamp pulses to 0 mV. Chloroquine also slowed the apparent rate of HERG deactivation, reflecting the inability of drug-bound channels to close. Mutation to alanine of aromatic residues (Tyr-652 or Phe-656) located in the S6 domain of HERG greatly reduced the potency of channel block by chloroquine (IC(50) > 1 mm at 0 mV). However, mutation of Tyr-652 also altered the voltage dependence of the block. In contrast to wild-type HERG, block of Y652A HERG channels was diminished by progressive membrane depolarization, and complete relief from block was observed at +40 mV. HERG channel block was voltage-independent when the hydroxyl group of Tyr-652 was removed by mutating the residue to Phe. Together these findings indicate a critical role for Tyr-652 in voltage-dependent block of HERG channels. Molecular modeling was used to define energy-minimized dockings of chloroquine to the central cavity of HERG. Our experimental findings and modeling suggest that chloroquine preferentially blocks open HERG channels by cation-pi and pi-stacking interactions with Tyr-652 and Phe-656 of multiple subunits.
authors.affiliation: Unidad de Investigación Carlos Méndez del Centro Universitario de Investigaciones Biomédicas de la Universidad de Colima, 23000 Colima, México.
authors.forename: Jose A
authors.initials: JA
authors.lastname: Sánchez-Chapula
authors.forename: Ricardo A
authors.initials: RA
authors.lastname: Navarro-Polanco
authors.forename: Chris
authors.initials: C
authors.lastname: Culberson
authors.forename: Jun
authors.initials: J
authors.lastname: Chen
authors.forename: Michael C
authors.initials: MC
authors.lastname: Sanguinetti
mesh_terms: D001578:Benzopyrans / Q000494:pharmacology; D001665:Binding Sites; D027682:Cation Transport Proteins; D002738:Chloroquine / Q000494:pharmacology; D004268:DNA-Binding Proteins; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; D006801:Humans; D008564:Membrane Potentials; D010880:Piperidines / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000737:chemistry / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated; D013329:Structure-Activity Relationship; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG
chemical_list: D001578:Benzopyrans; D027682:Cation Transport Proteins; D004268:DNA-Binding Proteins; C072312:ERG protein, human; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; C092509:KCNH6 protein, human; D010880:Piperidines; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; C087257:L 706000; D002738:Chloroquine