Electrostatic interactions of S4 voltage sensor in shaker K⁺ channel

The S4 segment comprises part of the voltage sensor in Shaker K⁺ channels. We have used a strategy similar to intragenic suppression, but without a genetic selection, to identify electrostatic interactions of the S4 segment that may be important in the mechanism of voltage-dependent activation. The S4 neutralization mutations K374Q and R3770 block maturation of the protein, suggesting that they prevent proper folding. K374Q is specifically and efficiently rescued by the second site mutations E2930 and D316N, located in putative transmembrane segments S2 and S3, respectively. These results suggest that K374, E293, and D316 form a network of strong, local, electrostatic interactions that stabilize the structure of the channel. Some other double mutant combinations result in inefficient suppression, identifying weak, presumably longrange electrostatic interactions. A simple structural hypothesis is proposed to account forthe effects of the rescued double mutant combinations on the relative stabilities of open and closed channel conformations. © 1995.