A designer saxitoxin-engineered sodium channel pair as a general tool for subtype-selective inhibition

We have used small molecule chemical design and protein engineering to fashion an orthogonal ligand-channel pair that enables acute and selective inhibition of a genetically encoded voltage-gated sodium channel (Na_V). A modified ligand based on the nerve toxin, saxitoxin (STX), binds potently and reversibly to a Na_V bearing two unique amino acid mutations in the outer mouth of the channel (Site 1). The same ligand is ineffective at blocking wild-type Na_Vs and does not disrupt action potential signals in neuronal cells or brain tissue at working concentrations. The versatility of this tool derives from the highly conserved outer pore, as the same two amino acid replacements can be introduced in Na_V1.1-1.4, 1.6, or 1.7, thus sensitizing each channel to inhibition by the designer STX ligand. This technology will empower studies of Na_V-isoform physiology to better understand the role of Na_Vs in health and disease.