A functional NaV1.7-NavAb chimera with a reconstituted high affinity ProTx-II binding site

The Na V 1.7 voltage-gated sodium channel is implicated in human pain perception by genetics. Rare gain of function mutations in Na V 1.7 lead to spontaneous pain in humans whereas loss of function mutations results in congenital insensitivity to pain. Hence, agents that specifically modulate the function of Na V 1.7 have the potential to yield novel therapeutics to treat pain. The complexity of the channel and the challenges to generate recombinant cell lines with high Na V 1.7 expression have led to a surrogate target strategy approach employing chimeras with the bacterial channel Na V Ab. In this report we describe the design, synthesis, purification, and characterization of a chimera containing part of the voltage sensor domain 2 (VSD2) of Na V 1.7. Importantly, this chimera, DII S1–S4, forms functional sodium channels and is potently inhibited by the Na V 1.7 VSD2 targeted peptide toxin ProTx-II. Further, we show by [ 125 I]ProTx-II binding and surface plasmon resonance that the purified DII S1–S4 protein retains high affinity ProTx-II binding in detergent. We employed the purified DII S1–S4 protein to create a scintillation proximity assay suitable for high-throughput screening. The creation of a Na V 1.7-Na V Ab chimera with the VSD2 toxin binding site provides an important tool for the identification of novel Na V 1.7 inhibitors and for structural studies to understand the toxin-channel interaction.