Quantitative Mapping of Interactions in the Voltage-Sensor Pore Interface of the Shaker Potassium Channel

Abstract

Changes in the membrane potential of an excitable cell induce movement of voltage-sensing units within voltage-gated ion channels (VGICs). The energy associated with this movement is transmitted to the channel gate, ultimately promoting its opening. Numerous proposals have been made as to how this signal is relayed from the voltage-sensors to the channel gate, such as side chain interactions and backbone movement; however, it has been difficult to ascertain the precise molecular mechanisms underlying energy transduction. Recently, it was shown that median voltage estimates from the charge-voltage relationship of VGICs can be used to derive the net free energy change (ΔGnet) associated with their voltage-dependent activation. By combining this approach with mutant cycle analysis, it is possible to identify residues that are energetically coupled and contribute to the activation process. Here, we have undertaken a systematic analysis of contact pairs at the interface between the voltage-sensor and pore domains of Shaker potassium channel in order to gain insight into how an initial signal can propagate from one region of the channel to another and trigger the opening of the channel gate. Our results will be discussed in the context of overall molecular mechanism of electromechanical coupling in voltage-gated ion channels.