Overlapping Binding Sites of Structurally Different Antiarrhythmics Flecainide and Propafenone in the Subunit Interface of Potassium Channel Kv2.1*

Abstract

Kv2.1 channels, which are expressed in brain, heart, pancreas, and other organs and tissues, are important targets for drug design. Flecainide and propafenone are known to block Kv2.1 channels more potently than other Kv channels. Here, we sought to explore structural determinants of this selectivity. We demonstrated that flecainide reduced the K ؉ currents through Kv2.1 channels expressed in Xenopus laevis oocytes in a voltageand time-dependent manner. By systematically exchanging various segments of Kv2.1 with those from Kv1.2, we determined flecainide-sensing residues in the P-helix and inner helix S6. These residues are not exposed to the inner pore, a conventional binding region of open channel blockers. The flecainide-sensing residues also contribute to propafenone binding, suggesting overlapping receptors for the drugs. Indeed, propafenone and flecainide compete for binding in Kv2.1. We further used Monte Carlo-energy minimizations to map the receptors of the drugs. Flecainide docking in the Kv1.2-based homology model of Kv2.1 predicts the ligand ammonium group in the central cavity and the benzamide moiety in a niche between S6 and the P-helix. Propafenone also binds in the niche. Its carbonyl group accepts an H-bond from the P-helix, the amino group donates an H-bond to the P-loop turn, whereas the propyl group protrudes in the pore and blocks the access to the selectivity filter. Thus, besides the binding region in the central cavity, certain K ؉ channel ligands can expand in the subunit interface whose residues are less conserved between K ؉ channels and hence may be targets for design of highly desirable subtype-specific K ؉ channel drugs.Potassium channels are crucial in physiology. Medically important drugs block the open pore, which is formed by four subunits. Each subunit consists of transmembrane ␣-helical segments S1-S6 and the membrane re-entering extracellular P-loop. The pore-forming domain is composed of four S5-P-S6

Multiple targets for flecainide action: implications for cardiac arrhythmogenesis

“…In K + channels, including the K v 11.1 channels, flecainide may have similar binding sites that also overlap with binding sites for other ligands, such as the structurally related propafenone (Figure B). Binding is again heavily influenced by interactions with a phenylalanine residue in the S6 helix (Madeja et al , ; Melgari et al , ). These effects appeared to be mediated by charged rather than uncharged flecainide accessing the channel from the cell interior.…”

Structural Insights into GIRK Channel Function

“…Local anesthetics have diverse effects on channels and receptors and they have been shown to inhibit voltage-gated K + channels (Gray, Zhorov, & Moczydlowski, 2013;Madeja, Steffen, Mesic, Garic, & Zhorov, 2010;Valenzuela, Delpon, Tamkun, Tamargo, & Snyders, 1995;Valenzuela, Snyders, Bennett, Tamargo, & Hondeghem, 1995). One study demonstrated inhibition of GIRK channels by the local anesthetics bupivacaine, lidocaine, and the permanently charged lidocaine derivative, QX-314 (Zhou, Arrabit, Choe, & Slesinger, 2001).…”

Identification of Novel and Selective KV2 Channel Inhibitors

“…Flecainide and propafenone, two antiarrhythmics with broad ion channel activity, are micromolar K V 2.1 inhibitors with weaker potency on K V 1.2 (Rolf et al, 2000). Flecainide and propafenone are thought to interact with residues at the interface of the P-helix of one subunit and the inner S6 helix of an adjacent subunit and to block ion permeation from within the central cavity (Madeja et al, 2003(Madeja et al, , 2010. Because the residues at the subunit interface are less conserved than those that line the inside of the central cavity, such a binding site may provide a degree of selectivity across families of channels.…”