Voltage-gated sodium channel alpha subunit site 3 (Nav Site 3)

The Voltage-gated sodium channel alpha subunit site 3 is a specialized pharmacological receptor site located on the extracellular surface of the domain IV (DIV) voltage-sensing domain, primarily involving the S3-S4 linker (Catterall, 2000, Neuron). This site is critical for the process of fast inactivation, as the outward movement of the DIV-S4 segment is the rate-limiting step that triggers the closure of the inactivation gate (Clairfeuille et al., 2019, Science). Binding of ligands to Site 3, such as alpha-scorpion toxins and sea anemone toxins, slows or prevents this inactivation, leading to a persistent or "late" sodium current and subsequent cellular hyperexcitability (Rogers et al., 1996, J Biol Chem). While primarily characterized through toxin interactions, Site 3 is a significant therapeutic target for modulating channel kinetics in conditions like chronic pain, epilepsy, and cardiac arrhythmias. Mutations in the residues forming Site 3 are associated with various channelopathies, most notably Long QT Syndrome Type 3, where impaired inactivation leads to prolonged cardiac action potentials (Catterall, 2012, J Physiol). Understanding the structural basis of this site is essential for developing selective modulators that can correct gating defects without affecting the primary activation of the channel (Stevens et al., 2011, Channels).

Other names

Neurotoxin receptor site 3Nav DIV-VSD site 3Alpha-toxin binding siteSodium channel site 3Voltage-gated sodium channel domain IV voltage-sensing domain site 3

Ligands bind to the extracellular loops of the domain IV voltage-sensing domain, specifically the S3-S4 linker, trapping the S4 segment in its inward position or impeding its outward movement, which slows or prevents the fast inactivation of the channel.