Analysis of the interdomain interactions between the transmembrane and the cytoplasmic domains. (A) Experimental strategy for changing the linker length and the representative current traces of the mutants recorded at 25°C. Our previous crystal structure analysis for the coiled-coil domain protein (S220-N269) (Fujiwara et al., 2012) showed that an α helix starts from E221 (light green box). (B) Normalized I-V relationship of WT (0 A.A.) and the mutant channels. I-V relationships of the 15 mutants (+10 to −4 A.A.) have an overlap with each other. (C) Accumulated data of activation kinetics of each mutant are plotted against the linker length. A Fourier series fitting to the data (+10 to −4 A.A.) is also indicated (light blue curve). The data were plotted as the mean ± error variance. (D) Power spectrum of the Fourier transform of the data (+10 to −4 A.A.) and the helical wheel diagrams. Vectors (light blue) indicate the activation time constant (Log (1/τ)) of the mutants, and the inverse direction of the sum vector (red) is also indicated. Details of the data analysis are described in Materials and methods.