Fig. 6. The S2 and S4 of jShak1 lack favourable electrostatic interactions in the open state that are present in most other K_V1 channels. (A)A structural overlay of S2 transmembrane domains of RatK_V1.2 (gold) and jShak1 (blue) showing the homology of positions of E226 (RatK_V1.2) to N227 (jShak1) and E236 (RatK_V1.2) to E237 (jShak1), respectively. The short non-charged side-chain of N227 prevents favourable electrostatic interactions with S4 residues in the open conformation that can be recovered with mutations to glutamate (N227E). (B)A structural overlay of S4 showing relative locations of the S4 basic residue side chains in RatK_V1.2 (gold) and the shortened S4 of jShak1 (blue). The periodicity and side-chain location of the arginine residues between the channels is preserved at the C-terminal end of the helix. Specifically, positions K306/R309 in RatK_V1.2 overlay K274/R377 in RatK_V1.2. (C)Homology model of the interactions between S2 and S4 residues in the open conformation of the channel illustrating the favourable salt bridge interactions between E226 and R303. The N227 residue in jShak1 (blue) does not form a salt bridge with R291, whereas E226 shows a strong interaction with R303 in RatK_V1.2 (gold).