Synthetic Analogs of the Snail Toxin 6-Bromo-2-Mercaptotryptamine Dimer (BrMT) Reveal That Lipid Bilayer Perturbation Does Not Underlie Its Modulation of Voltage-Gated Potassium Channels

Abstract

Distinguishing membrane perturbation from more direct protein-ligand interactions is an ongoing challenge in chemical biology. Herein, we present one strategy for doing so, using dimeric 6-bromo-2-mercaptotryptamine (BrMT) and synthetic analogs. BrMT is a chemically unstable marine snail toxin that has unique effects on voltage-gated K+ channel proteins, making it an attractive medicinal chemistry lead. BrMT is amphiphilic and perturbs lipid bilayers, raising the question of whether its action against K+ channels is merely a manifestation of membrane perturbation. To determine whether medicinal chemistry approaches to improve BrMT might be viable, we synthesized BrMT and 11 analogs and determined their activities in parallel assays measuring K+ channel activity and lipid bilayer properties. Our work demonstrates a strategy for determining if drugs act by specific interactions or bilayer-dependent mechanisms, and chemically stable modulators of Kv1 channels are reported.

Fluorescent toxins as ion channel activity sensors

“…To image where the voltage sensors of Kv2 proteins adopt a specific resting conformation in tissue, we exploit the conformation-selective binding of GxTX variants functionalized with optical probes to report Kv2 conformational changes (Fletcher-Taylor et al, 2020;Thapa et al, 2021;Tilley et al, 2014). Given the large number of conformation-specific ion channel toxins (Ahuja et al, 2015;Catterall et al, 2007;Dockendorff et al, 2018;McCormack et al, 2013;McDonough et al, 1997;Peretz et al, 2010;Sack et al, 2004;Schmalhofer et al, 2008;Swartz, 2007;Zhang et al, 2018), this approach may be exploited against numerous channels.…”