Structural Basis of Nav1.7 Inhibition by the Tarantula Toxin Protoxin-II

Abstract

Voltage-gated sodium (Nav) channels are targets of disease mutations, toxins, and therapeutic drugs. Neurotoxins have provided important insights into Nav channels, but the structural basis for toxin modulation of channel gating is not well-defined. Protoxin-II (ProTx2) is an inhibitor cystine-knot peptide and a selective antagonist of the human Nav1.7 channel. Here, using X-ray crystallography and cryo-electron microscopy, we have captured ProTx2 in complex with voltage-sensor domain II (VSD2) from Nav1.7. Membrane partitioning orients ProTx2 for unfettered access to VSD2, where ProTx2 interrogates distinct structural features of the Nav1.7 receptor site. ProTx2 positions two basic residues into the extracellular vestibule of VSD2 to antagonize S4 gating charge movement through an electrostatic mechanism. ProTx2 engages a small interaction surface and few direct contacts on VSD2, allowing the S4 helix to be visualized in both activated and deactivated states. Our results illuminate pharmacological concepts employed by membrane-partitioning peptide toxins, clarify the structural basis of electromechanical coupling in voltage-gated ion channels, and provide new templates to design selective Nav channel antagonists.