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Department of Physiology, MS 7756, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229

Correspondence to Mark S. Shapiro: shapirom{at}uthscsa.edu

The regulation of M-type (KCNQ [Kv7]) K⁺ channels by phosphatidylinositol 4,5-bisphosphate (PIP₂) has perhaps the best correspondence to physiological signaling, but the site of action and structural motif of PIP₂ on these channels have not been established. Using single-channel recordings of chimeras of Kv7.3 and 7.4 channels with highly differential PIP₂ sensitivities, we localized a carboxy-terminal inter-helix linker as the primary site of PIP₂ action. Point mutants within this linker in Kv7.2 and Kv7.3 identified a conserved cluster of basic residues that interact with the lipid using electrostatic and hydrogen bonds. Homology modeling of this putative PIP₂-binding linker in Kv7.2 and Kv7.3 using the solved structure of Kir2.1 and Kir3.1 channels as templates predicts a structure of Kv7.2 and 7.3 very similar to the Kir channels, and to the seven-β-sheet barrel motif common to other PIP₂-binding domains. Phosphoinositide-docking simulations predict affinities and interaction energies in accord with the experimental data, and furthermore indicate that the precise identity of residues in the interacting pocket alter channel–PIP₂ interactions not only by altering electrostatic energies, but also by allosterically shifting the structure of the lipid-binding surface. The results are likely to shed light on the general structural mechanisms of phosphoinositide regulation of ion channels.

Abbreviations used in this paper: CaM, calmodulin; CRMS, carbon root mean squared; CHO, Chinese hamster ovary; diC8-PIP₂, dioctanoyl-PIP₂; GPMI-P2, L--glycerophospho-D-myo-inositol 4,5-bisphosphate; Kv7, KCNQ; PIP₂, phosphatidylinositol 4,5-bisphosphate; P_o, open probabilities; RMSD, root mean square distance; wt, wild-type.

© 2008 Hernandez et al. This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.jgp.org/misc/terms.shtml). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

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This article has been cited by other articles:

				C. C. Hernandez, B. Falkenburger, and M. S. Shapiro Affinity for phosphatidylinositol 4,5-bisphosphate determines muscarinic agonist sensitivity of Kv7 K+ channels J. Gen. Physiol., October 26, 2009; 134(5): 437 - 448. [Abstract] [Full Text] [PDF]

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