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Conformational dynamics of the KcsA potassium channel governs gating properties

Abstract

K+ channels conduct and regulate K+ flux across the cell membrane. Several crystal structures and biophysical studies of tetrameric ion channels have revealed many of the structural details of ion selectivity and gating. A narrow pore lined with four arrays of carbonyl groups is responsible for ion selectivity, whereas a conformational change of the four inner transmembrane helices (TM2) is involved in gating. We used NMR to examine full-length KcsA, a prototypical K+ channel, in its open, closed and intermediate states. These studies reveal that at least two conformational states exist both in the selectivity filter and near the C-terminal ends of the TM2 helices. In the ion-conducting open state, we observed rapid structural exchange between two conformations of the filter, presumably of low and high K+ affinity, respectively. Such measurements of millisecond-timescale dynamics reveal the basis for simultaneous ion selection and gating.

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Figure 1: Secondary structure of KcsA(tox) in the closed and open conformations.
Figure 2: Correlation between functional and structural data for KcsA.
Figure 3: Conformational difference in the backbone angle φ of Tyr78 between the conducting (pH 4) and nonconducting (pH 7) conformations of KcsA(tox).
Figure 4: pH titration of 15N-Tyr–labeled KcsA(tox) in the presence of K+, and KcsA(E71A) in the absence of K+.
Figure 5: Channel conductance modeled on the basis of different exchange rates of the filter residues and the C terminus of TM2.

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Acknowledgements

This work was supported in part by the US National Institutes of Health (GM74929 and GM56653). R.R. is a Pew Scholar and the Helen McLoraine Development Chair in Neurobiology. K.A.B. would like to thank the American Heart Association for fellowship support.

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Authors and Affiliations

Authors

Contributions

K.A.B. and C.T. prepared KcsA; K.A.B., C.T., W.K. and R.R. collected and analyzed NMR data; K.A.B., C.T., S.C. and R.R. contributed to scientific discussions and prepared the manuscript.

Corresponding authors

Correspondence to Senyon Choe or Roland Riek.

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Supplementary Text and Figures

Supplementary Figures 1–6, Supplementary Table 1–3, Supplementary Methods (PDF 4761 kb)

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Baker, K., Tzitzilonis, C., Kwiatkowski, W. et al. Conformational dynamics of the KcsA potassium channel governs gating properties. Nat Struct Mol Biol 14, 1089–1095 (2007). https://doi.org/10.1038/nsmb1311

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