Structural basis of action for a human ether-a-go-go-related gene 1 potassium channel activator

Abstract

Activation of human ether-a-go-go-related gene 1 (hERG1) K ؉ channels mediates cardiac action potential repolarization. Drugs that activate hERG1 channels represent a mechanism-based approach for the treatment of long QT syndrome, a disorder of cardiac repolarization associated with ventricular arrhythmia and sudden death. Here, we characterize the mechanisms of action and the molecular determinants for binding of RPR260243 [(3R,4R)-4-[3-(6-methoxy-quinolin-4-yl)-3-oxo-propyl]-1-[3-(2,3,5-trifluorophenyl)-prop-2-ynyl]-piperidine-3-carboxylic acid] (RPR), a recently discovered hERG1 channel activator. Channels were heterologously expressed in Xenopus laevis oocytes, and currents were measured by using the two-microelectrode voltage-clamp technique. RPR induced a concentration-dependent slowing in the rate of channel deactivation and enhanced current magnitude by shifting the voltage dependence of inactivation to more positive potentials. This mechanism was confirmed by demonstrating that RPR slowed the rate of deactivation, but did not increase current magnitude of inactivation-deficient mutant channels. The effects of RPR on hERG1 kinetics and magnitude could be simulated by reducing three rate constants in a Markov model of channel gating. Point mutations of specific residues located in the S4 -S5 linker or cytoplasmic ends of the S5 and S6 domains greatly attenuated or ablated the effects of 3 M RPR on deactivation (five residues), inactivation (one residue), or both gating mechanisms (four residues). These findings define a putative binding site for RPR and confirm the importance of an interaction between the S4 -S5 linker and the S6 domain in electromechanical coupling of voltage-gated K ؉ channels.voltage clamp ͉ Xenopus ͉ long QT syndrome H uman ether-a-go-go-related gene 1 (hERG1) ␣-subunits coassemble to form channels that conduct I Kr (1-3), the rapid delayed rectifier K ϩ current that contributes to normal repolarization of cardiac action potentials (4). Loss-of-function mutations in hERG1 cause inherited long QT syndrome (LQTS), a disorder characterized by delayed repolarization of ventricular action potentials and prolonged QT interval of the body surface electrocardiogram (5). The acquired form of LQTS is more common and is most often caused by unintended block of hERG1 channels by a plethora of common medications (6). Inherited and acquired LQTS are associated with an increased risk of torsades de pointes, an arrhythmia that can degenerate into ventricular fibrillation and cause sudden death (7).Current treatments for inherited LQTS include the administration of ␤-adrenergic receptor blockers, left cardiac sympathetic denervation, or implantation of cardiac defibrillators for the most severe cases (8). However, pharmacologic treatment is not always effective (9) and surgery or devices are expensive and require invasive procedures. Acute episodes of drug-induced LQTS are treated with magnesium sulfate administration and discontinued use of the suspect medication. Activation of hERG1 could provide an...

PD-118057 contacts the pore helix of hERG1 channels to attenuate inactivation and enhance K + conductance

“…All known hERG1 channel agonists either slow the onset and/or shift the voltage dependence of inactivation to more depolarized potentials (8)(9)(10). The effects on other channel gating properties such as the voltage dependence of activation and rate of channel deactivation are variable and drug specific.…”

“…carboxylic acid] (6), defined here as a ''type 1'' hERG1 agonist, binds to a receptor site located at the intracellular ends of the S5 and S6 segments of a single hERG1 subunit to cause a profound slowing of deactivation rate and a positive shift in the voltage dependence of pore (P)-type inactivation gating (9). P-type inactivation of hERG1 is very rapid, and similar to C-type inactivation of other voltage-gated K ϩ (Kv) channels, is believed to be caused by a subtle structural change in the selectivity filter (SF) of the outer pore domain (11).…”

Activation of human ether-a-go-go related gene (hERG) potassium channels by small molecules

“…However, the exact molecular determinants of hERG activator function remain unresolved, with most of the knowledge about possible binding sites derived from mutagenesis experiments. Sangunetii et al found that two groups of residues have different effects on RPR260243 [24,37] . One group, including L553, F557 (S5), and N658, V659 (S6), affects the inactivation and deactivation effect of RPR260243 on the hERG channel, while mutations in the other group of residues, including V549, L550 (S4-S5 linker), and I662, L666, Y667 (intracellular S6 segment), only hinder the transition to the closed state of the channel.…”

“…However, due to the limitations of existing high throughput screening methods and difficulties in assaying the channel on a large scale, few activators have been reported. Most of the existing activators originated from combinatorial chemistry libraries, including RPR260243 [22][23][24] , PD-118057 [25] , PD-307243 [26] , NS1643 [27] , NS3623 [28] , A-935142 [29] , ICA-105574 [30] , and KB130015 [31] . Addi-www.nature.com/aps Zhou PZ et al Acta Pharmacologica Sinica npg tionally, a natural product, mallotoxin, has also been shown to activate hERG [32] .…”

“…Current treatments for LQTS include beta-adrenergic receptor blockers, left cardiac sympathetic denervation or, in the worst cases, implantation of cardiac defibrillators [24,38] . However, pharmacologic treatment is not always effective, and both surgery and implanted devices are expensive and require invasive procedures [24,39] . Acute episodes of drug-induced LQTS are treated with magnesium sulfate administration and discontinued use of the suspect medication.…”