Highly conserved amino acids in the S2 and S4 segments. Sequence alignment of the S2 region (left) and the S4 voltage sensor (right) of Shaker and hERG channels. Conserved residues forming the putative gating charge transfer center in S2 are highlighted in green. The positive S4 residues investigated in this study are highlighted in blue. The remaining S4 charges are shown in bold font. The conserved negative residues in S2 suggested to contribute to the gating charge transfer center in Shaker channels (i.e., E293) are shown in red.