Voltage-dependent conformational changes of KVAP S4 segment in bacterial membrane environment

The nature and magnitude of voltage sensor conformational changes during ion channel activation are controversial. We have analyzed the topology of the K(V)AP voltage sensor domain in the absence and presence of a hyperpolarized voltage using native, right-side out membrane vesicles from E. coli. This approach does not disrupt the normal membrane environment of the channel protein and does not involve detergent solubilization. We found that voltage-dependent conformational changes are focused in the N-terminal half of the K(V)AP S4 segment, in excellent agreement with results obtained with Shaker. Homologous residues in the K(V)AP and Shaker S4 segments are transferred from the extracellular to the intracellular compartment upon hyperpolarization. Taken together with X-ray structures indicating that the K(V)AP S4 segment is outwardly displaced at 0 mV compared to S4 in a mammalian Shaker channel, our results are consistent with the idea that S4 moves further during voltage-dependent activation in K(V)AP than in Shaker.