A Regulator for Eag Family Channels

Abstract

Ether-a-go-go (Eag) family channels, which include hErg1, are voltage-gated K+ channels that are important in cardiac and neural function. From the genetic sequence of this family of channels, we identify two probable ligand-binding sites based on their similarities with well-characterized ligand binding domains. The first putative ligand-binding domain is in the carboxy-terminal region and shares sequence similarity with the cyclic nucleotide-binding domain of cyclic nucleotide-gated (CNG) channels. Yet, this binding domain of Eag family channels lack a critical arginine required for cyclic nucleotide binding, and channel gating was not altered by cAMP or cGMP. The second potential ligand-binding site is a Per-Arnt-Sim (PAS) domain in the amino-terminal region. High conservation of these putative binding domains amongst all Eag family channels indicates their functional importance. We therefore categorize these channels as orphan receptors. We reasoned that a chemical screen of cellular metabolites will lead us to physiologically relevant channel-regulators. Using a novel, high through-put screen of the “Fragments of Life” chemical library of metabolites and metabolite-like compounds (deCODE Biostructures) and inside-out patch-clamp recording, we have identified regulators of Eag family channels. We identified six regulators that cluster into four chemical families. One indole, and one indole-like compound were increased Eag channel opening at hyperpolarizing potentials. Indoles are particularly interesting because of their structural similarity to purines, the core of the cyclic nucleotides that bind to and regulate CNG channels. In contrast to indoles, compounds from the flavonoid family strongly inhibited Eag current. These results indicate that metabolites regulate Eag family channels and may lead us to physiologic channel regulators.