Figure 8: Schematic drawings of the gating in a dimeric Hv channel.

(a) Schematic drawings of the regulation of temperature-dependent gating by the cooperation of coiled-coil region (red arrow) and the dimerization of Hv protomers by coiled-coil (blue arrow) in the WT (or the AAA mutant) channel. Rigid structure of the linker region and the stable coiled-coil mediate the thermostability of channel activation based on the cooperative gating within the dimer . (b) Model of the 4R mutant channel. The channel dimerization is disrupted due to the instability of the coiled-coil assembly (broken blue arrow) that results in instability, the lower threshold, of the temperature-dependent activation (red broken arrow). (c) Model of the GGG mutant channel. Although the channel is dimerized (blue arrow), the thermostability of channel activation is not mediated by the coiled-coil domain (red broken arrow) due to the loose connection by the GGG linker.