R1 in S4 occupies the gating charge transfer center in the resting state. (A) Cartoon of the resting conformation shows an arginine representing R1 in the gating charge transfer center. (A and B) Ribbons representing the backbone atoms of S2, S3, and S4 are shown in yellow, red, and blue, respectively. Backbone atoms and side chains corresponding to I287, F290, E2, D3, and F324 (mutated in silico from tryptophan) in Shaker were extracted from the Kv1.2/Kv2.1 paddle chimera x-ray structure (2r9r) (Long et al., 2007). (B) Cartoon of the penultimate closed state shows arginines representing R1 in the vicinity of I287 and R2 in the gating charge transfer center. Other side chains and colored ribbons are the same as in A. The figure was made with PyMOL (v1.3).