Analysis of the interdomain interaction between two transmembrane VSDs. (A) Experimental strategy for the cross-linking Western blots by disulfide bonds (left), and the box plot for the cross-linking of each transmembrane segment (right). Bars indicate maximum/minimum, and boxes denote interquartile ranges for the individual transmembrane segments. Averaged data are plotted as color dots. (B) A representative image of the Western blot analysis for the S4 segment. Channels that are cross-linked by an interdomain disulfide bond show twice the molecular weight of monomer on the gel (×2 vs. ×1). (C) Accumulated data of the cross-linking analysis and a Fourier series fitting to the data (light red curve). The data were plotted as the mean ± SEM (n = 3). A blue dashed line indicates background signal of the negative control in this analysis. (D) Power spectrum of the Fourier transform of the data (197–212) and the helical wheel diagrams. Vectors (light red) indicate |rRcys| for each Cys position introduced, and the sum vector (deep red) is indicated.
