1.A.1.14.1
Voltage-activated, Ca²⁺  channel blocker-inhibited, Na⁺ channel, NaChBac (Ren et al., 2001; Zhao et al., 2004; Nurani et al, 2008; Charalambous and Wallace, 2011). Arginine residues in the S4 segment play a role in voltage-sensing (Chahine et al. 2004). Transmembrane and extramembrane regions contribute to thermal stability (Powl et al., 2012). Deprotonation of arginines in S4 is involved in NaChBac gating (Paldi, 2012). Hinge-bending motions in the pore domain of NaChBac have been reported (Barber et al., 2012).  The C-terminal coiled-coli stabilizes subunit interactions (Mio et al. 2010).  Within the 4 TMS voltage sensor, coupling between residues in S1 and S4 determines its resting conformation (Paldi and Gurevitz 2010). The conserved asparagine was changed to aspartate, N225D, and this substitution shifted the voltage-dependence of inactivation by 25 mV to more hyperpolarized potentials. The mutant also displays greater thermostability (O'Reilly et al. 2017).  Possibly, the side-chain amido group of asn₂₂₅ forms one or more hydrogen bonds with different channel elements, and  these interactions are important for normal channel function. The T1-tetramerization domain of Kv1.2 (TC# 1.A.1.2.10) rescues expression and preserves the function of a truncated form of the NaChBac sodium channel (D'Avanzo et al. 2022). The structure of NaChBac embedded in liposomes has been solved by cryo electron tomography (Chang et al. 2023). The small channel has most of its residues embedded in the membrane, and these are flexible, determining the channel dimensions.