Functional Studies of Interaction Between Huwentoxin-IV and Voltage-Gated Sodium Channel Nav1.7

Voltage-gated sodium channel 1.7 (Nav1.7) plays a role in the conduction of action potentials and is involved in the sensation of pain. Spider toxins such as Huwentoxin IV (HwTx-IV) are potent inhibitors of Nav1.7, functioning as a gating modifier trapping the voltage sensor in an inward closed conformation. HwTx-IV interacts with specific residues in the voltage sensor S3-S4 region of domain II. The purpose of the present study was to understand the residues important for interaction between HwTx-IV and Nav1.7. Computationally, molecular dynamics was used to study wild type HwTx-IV along with various alanine and cystine mutations to determine residues important for the stability of toxin and to obtain a model of the interacting surface. A homology model of Nav1.7 was built and the toxin docked to determine key interactions. Experimentally, alanine mutants of HwTx-IV were tested for functional activity using FLIPR, QPatch, and manual patch. Computational and experimental results suggest key residues critical for binding of the toxin to Nav1.7, particularly S25, W30 and K32. These studies provide a more clear idea of the nature of interaction between HwTx-IV and Nav1.7 and may therefore be a useful guide in designing novel peptides with improved selectivity for sodium channel subtypes.