Assessing the Structural Basis of μ-Conotoxin KIIIA Inhibition of the Voltage-Gated Sodium Channel Nav1.7

Abstract

The voltage-gated sodium channel subtype Nav1.7 has been shown to play a critical role in pain signaling, making it an important drug target. A number of peptide toxins from cone snails (conotoxins) inhibit sodium conduction through Nav1.7 with high affinity, and make potential scaffolds for selective channel inhibitors. However, the atomistic details of protein-protein interactions between conotoxins and Nav channels necessary for rational design of such inhibitors remain unclear. Our study aims to further define the molecular determinants of μ-conotoxin KIIIA action against the human Nav1.7 channel (hNav1.7). We have previously used Rosetta computational modeling software to generate preliminary molecular models of the hNav1.7 pore-forming domain based on the NavAb crystal structure (PDB ID: 3RVY). To capitalize on recent advances, we have updated our hNav1.7 homology model using the recent cryo-EM structure of the electric eel Nav1.4 channel (PDB ID: 5XSY) as a template. To test predicted pairwise contacts between toxin and channel, point mutations of hNav1.7 and conotoxin KIIIA in the putative binding site have been generated. We have identified several residues that alter the kinetics of toxin binding, notably acidic residues on the DII pore-helix. Our experimental and modeling results may be useful for rational design of novel peptides to inhibit hNav1.7 with high affinity and selectivity.