Up-regulation of voltage-gated sodium channels by peptides mimicking S4-S5 linkers reveals a variation of the ligand-receptor mechanism.

Prokaryotic Na(V) channels are tetramers and eukaryotic Na(V) channels consist of a single subunit containing four domains. Each monomer/domain contains six transmembrane segments (S1-S6), S1-S4 being the voltage-sensor domain and S5-S6 the pore domain. A crystal structure of Na(V)Ms, a prokaryotic Na(V) channel, suggests that the S4-S5 linker (S4-S5(L)) interacts with the C-terminus of S6 (S6(T)) to stabilize the gate in the open state. However, in several voltage-gated potassium channels, using specific S4-S5(L)-mimicking peptides, we previously demonstrated that S4-S5(L)/S6(T) interaction stabilizes the gate in the closed state. Here, we used the same strategy on another prokaryotic Na(V) channel, Na(V)Sp1, to test whether equivalent peptides stabilize the channel in the open or closed state. A Na(V)Sp1-specific S4-S5(L) peptide, containing the residues supposed to interact with S6(T) according to the Na(V)Ms structure, induced both an increase in Na(V)Sp1 current density and a negative shift in the activation curve, consistent with S4-S5(L) stabilizing the open state. Using this approach on a human Na(V) channel, hNa(V)1.4, and testing 12 hNa(V)1.4 S4-S5(L) peptides, we identified four activating S4-S5(L) peptides. These results suggest that, in eukaryotic Na(V) channels, the S4-S5(L) of DI, DII and DIII domains allosterically modulate the activation gate and stabilize its open state.