ABSTRACT
Voltage-gated sodium (Nav) channels are targets of disease mutations, toxins, and therapeutic drugs. Despite recent advances, the structural basis of voltage sensing, electromechanical coupling, and toxin modulation remains ill-defined. Protoxin-II (ProTx2) from the Peruvian green velvet tarantula is an inhibitor cystine-knot peptide and selective antagonist of the human Nav1.7 channel. Here, we visualize ProTx2 in complex with voltage-sensor domain II (VSD2) from Nav1.7 using X-ray crystallography and cryoelectron microscopy. Membrane partitioning orients ProTx2 for unfettered access to VSD2, where ProTx2 interrogates distinct features of the Nav1.7 receptor site. ProTx2 positions two basic residues into the extracellular vestibule to antagonize S4 gating-charge movement through an electrostatic mechanism. ProTx2 has trapped activated and deactivated states of VSD2, revealing a remarkable â¼10 Å translation of the S4 helix, providing a structural framework for activation gating in voltage-gated ion channels. Finally, our results deliver key templates to design selective Nav channel antagonists.
Subject(s)
NAV1.7 Voltage-Gated Sodium Channel/metabolism , NAV1.7 Voltage-Gated Sodium Channel/ultrastructure , Peptides/metabolism , Spider Venoms/metabolism , Amino Acid Sequence , Animals , Binding Sites , CHO Cells , Cricetulus , Cryoelectron Microscopy/methods , Crystallography, X-Ray/methods , HEK293 Cells , Humans , Ion Channel Gating , Peptides/toxicity , Protein Domains , Spider Venoms/toxicity , Spiders , Voltage-Gated Sodium Channel Blockers , Voltage-Gated Sodium Channels/metabolismABSTRACT
Voltage-gated sodium (Nav) channels respond to changes in the membrane potential of excitable cells through the concerted action of four voltage-sensor domains (VSDs). Subtype Nav1.7 plays an important role in the propagation of signals in pain-sensing neurons and is a target for the clinical development of novel analgesics. Certain inhibitory cystine knot (ICK) peptides produced by venomous animals potently modulate Nav1.7; however, the molecular mechanisms underlying their selective binding and activity remain elusive. This study reports on the design of a library of photoprobes based on the potent spider toxin Huwentoxin-IV and the determination of the toxin binding interface on VSD2 of Nav1.7 through a photocrosslinking and tandem mass spectrometry approach. Our Huwentoxin-IV probes selectively crosslink to extracellular loop S1-S2 and helix S3 of VSD2 in a chimeric channel system. Our results provide a strategy that will enable mapping of sites of interaction of other ICK peptides on Nav channels.