Molecular Determinants for High-Affinity Block of Human EAG Potassium Channels by Antiarrhythmic Agents

Abstract

Undesired block of human ERG1 potassium channels is the basis for cardiac side effects of many different types of drugs. Therefore, it is important to know exactly why some drugs particularly bind to these channels with high affinity. Upon expression in mammalian cells and Xenopus laevis oocytes, we investigated the inhibition of the closely related hEAG1 and hEAG2 channels by agents that have previously been reported to block hERG1 channels. Clofilium inhibited hEAG1 and hERG1 with the same potency, whereas hEAG2 was about 150-fold less sensitive to this antiarrhythmic agent. The molecular determinants for this difference are residues Ser436 and Val437 in the inner cavity of the pore and Ala453, which is located in S6 (i.e., remote from the inner cavity). A modeling approach that allowed for partial conformational relaxation of hEAG model structures upon ligand docking suggests that highaffinity block of ether à go-go channels is mediated by an anchoring of the clofilium alkane tail between S6 and the pore helices. In qualitative agreement with experiments, the mutations of hEAG1 residues Ser436 and Val437 to the corresponding larger hEAG2 residues (Thr432, Ile433) resulted in reduced sterical fit between the ligand and the binding cavity. The model is further supported by functional assays involving (ϩ)-N-[1Ј-(6-cyano-1,2,3,4-tetrahydro-2(R)-naphthalenyl)-3,4-dihydro-4(R)-hydroxyspiro(2H-1-benzopyran-2,4Ј-piperidin)-6-yl]methanesulfonamide monohydrochloride (MK-499), terfenadine, quinidine, and tetrabutylammonium that are differentially affected by mutations in the pore pocket.

In Vivo Analysis of a Gain-of-Function Mutation in the Drosophila eag-Encoded K+ Channel

“…. This possibility is supported by the observation that mutations in human Eag can alter the binding characteristics of quinidine and other antiarrhythmic agents (Gessner et al 2004). Third, the K 1 channels distinct from I K in which Eag participates (I A , I CS , and I CF ; Ganetzky and Wu 1983;Wu et al 1983;Warmke et al 1991;Zhong and Wu 1991) are not sensitive to quinidine, and it is possible that Eag G297E exerts its effects through one of these channels.…”

Distinct K+conductive pathways are required for Cl−and K+secretion across distal colonic epithelium

“…Clofilium, an aromatic quaternary ammonium, inhibits K ϩ channels with higher affinity than TEA ϩ and has been suggested to have some specificity among the types of K ϩ channels, particularly K V 1.5 (Kcna5), K V 7.1 (K V LQT1, Kcnq1), K V 10.1 (eag, Kcnh1), K V 11.1 (erg, Kcnh2), and K 2P 5.1 (TASK-2, Kcnk5; see Refs. 13,21,22,43,52,53,61). The partial inhibition of flushing secretion by clofilium (Fig.…”

hERG K+Channels: Structure, Function, and Clinical Significance

“…First, not all high-affinity drugs favor binding to the inactivated state. Clofilium, for example, can block Kv10.1 channels with the same affinity as it blocks Kv11.1 channels (206,208). Second, mutations that enhance inactivation can still reduce sensitivity to block (419).…”