Bookshelf

Topologic diagram of Na_v1.1, the alpha subunit of the neuronal voltage-gated sodium channel encoded by SCN1A. Na_v1.1 is 2,000 amino acids in size and has four homologous domains (D1-D4) that fold around a central pore and are connected by cytoplasmic loops. Each domain has six transmembrane segments, S1-S6. The cytoplasmic loop between the third and fourth domain forms the inactivation gate, while the S4 segments make up the voltage sensor. The pore is formed by parts of S5, S6, and the P loop between them. Voltage-gated sodium channels have one or more modulatory beta subunits (230 amino acids each, not pictured) that consist of a single transmembrane segment, an extracellular IgG loop, and a short intracellular C terminus. All voltage-gated sodium channels (Na_v1.1 - 1.9) have structural homology [Catterall 2000].