A Functional Na1.7-NaAb Chimera with a Reconstituted High-Affinity ProTx-II Binding Site.

The Na1.7 voltage-gated sodium channel is implicated in human pain perception by genetics. Rare gain of function mutations in Na1.7 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 Na1.7 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 Na1.7 expression have led to a surrogate target strategy approach employing chimeras with the bacterial channel NaAb. In this report we describe the design, synthesis, purification, and characterization of a chimera containing part of the voltage sensor domain 2 (VSD2) of Na1.7. Importantly, this chimera, DII S1-S4, forms functional sodium channels and is potently inhibited by the Na1.7 VSD2 targeted peptide toxin ProTx-II. Further, we show by [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 Na1.7-NaAb chimera with the VSD2 toxin binding site provides an important tool for the identification of novel Na1.7 inhibitors and for structural studies to understand the toxin-channel interaction.