Abstract
Ion channels respond to changes in transmembrane voltage or ligand concentration by opening or closing an activation gate. In voltage-gated K+ channels, this gate has been localized to an intracellular bundle crossing. Here we examined whether this bundle crossing, or the more internal cytoplasmic pore, acts as a gate for PIP2 activation of inward rectifier K+ (Kir) channels expressed in Xenopus laevis oocytes. We studied the open/closed state-dependence of the accessibility of intracellular cationic modifiers to a position (residue Ile176 in the TM2 helix of Kir2.1) more external to the bundle crossing. Cd2+ blocked I176C mutant channels much more weakly in the closed state than in the open state, but Ag+ and sulfhydryl-specific methanethiosulfonate reagents modified the channels with similar rates in both states. These results suggest that the TM2 helices undergo conformation changes upon PIP2 binding/unbinding, but neither they nor the cytoplasmic pore close fully to form a physical gate for K+ conduction.
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Acknowledgements
We thank J. Cui (Case Western), G. Zhu (Columbia) and members of our laboratory for discussion and reading the manuscript. This work was supported by a grant to J.Y. from the National Institute of Neurological Disorders and Stroke (NS45383). J.Y. is a recipient of the McKnight Scholar Award and the Scholar Research Programme of the EJLB Foundation.
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Xiao, J., Zhen, Xg. & Yang, J. Localization of PIP2 activation gate in inward rectifier K+ channels. Nat Neurosci 6, 811–818 (2003). https://doi.org/10.1038/nn1090
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DOI: https://doi.org/10.1038/nn1090
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