The interplay between the intracellular gate and the selectivity filter modulates ion conduction in potassium ion channels. In this work, we use a combination of semisynthesis, two-dimensional infrared (2D IR) spectroscopy, and molecular dynamics (MD) simulations to probe the ion occupancy at the S1 binding site in the collapsed state of the selectivity filter of KcsA at low pH and low K+, where the gate is open and closed, respectively. The experimental 2D IR spectra reveal two features whose relative intensities are dependent on whether the intracellular gate is open or closed. From the calculated 2D IR spectra of structures predicted in MD simulations, we attribute the two features to states in which the S1 binding site is occupied or unoccupied by K+. Analysis of our experimental and simulated spectra show that the populations of states change with the opening of the intracellular gate. When the gate is closed, &gt;70% of the population of states has a K+ ion bound at the S1 binding site. When the gate opens, however, &lt;15% of the states have an ion in the S1 binding site. We relate the changes in the ion occupancy to structural changes in the selectivity filter that arise from the opening of the intracellular gate. This work shows that the structural motions of the intracellular gate are linked to conformational changes in the selectivity filter.

Opening of the intracellular gate affects the structure and ion occupancy of the selectivity filter of a potassium ion channel

253rd National Meeting (2017)

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