NMR Study of the Interaction of Cardiotoxic Drugs with the Extracellular Segment Ile583 - Tyr597 from the hERG Channel

Abstract

Long QT syndrome (LQTS) is a cardiac muscle abnormality caused either by congenital or drug-induced malfunctioning of potassium channels localized in the myocardium cell membranes. LQTS can lead to ventricular arrhythmia and sudden cardiac death. A number of prescription medications inducing long QT have been withdrawn from the market over the past decades, and virtually all cases of drug-induced LQTS are due to the blockade of the heart human ether-a-go-go-related-gene (hERG) potassium channel. Evidences show that most of the hERG-channel blockers would exert their activity by binding one or several sites located in the pore region composed of the last two TM helices (S5 and S6) or on the extracellular region connecting S5 and S6 together. In this work, we studied the binding of 4 cardiotoxic drugs (bepridil, cetirizine, diphenhydramine, pentamidine) with a portion of the extracellular segment (Ile583 - Tyr597) of the hERG channel and a model membrane. Drug-peptide interactions were studied using 1H liquid-state NMR with pulsed field gradient self-diffusion measurements. According to our CD and 1H NMR results, the peptide appears to be unstructured both in water and membrane mimetic isotropic bicelles. Diffusion measurements suggest that there is no or only weak drug binding to the peptide. However, a strong interaction with the model membrane was evidenced for the bepridil molecule, thus suggesting a potential role of the membrane in the cardiotoxicity of LQTS-active drugs. Our current work, which focuses on drug-membrane interactions and hERG peptide-membrane interactions by 31P and 2H solid-state NMR will also be presented.