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Tethered blockers as molecular ‘tape measures’ for a voltage-gated K+ channel

Abstract

The propagation of electrical signals in excitable cells is orchestrated by a molecular family of voltage-dependent ion channel proteins. These K+, Na+, and Ca++ channels are all composed of four identical or similar units, each containing six transmembrane segments (S1–S6) in a roughly four-fold symmetric structure. The S5–S6 sequences fold into a central pore unit, which is surrounded by a voltage-gating module composed of S1–S4. The recent structure of KcsA, a two-transmembrane bacterial K+ channel, illuminates the physical character of the pore unit, but little is known about the arrangement of the surrounding S1–S4 sequences. To locate regions of this gating module in space, we synthesized a series of compounds of varying length that function as molecular ‘tape measures’: quaternary ammonium (QA) pore blockers that can be tethered to specific test residues. We show that in a Shaker K+ channel, the extracellular ends of S1 and S3 are 30 Å from the tetraethylammonium (TEA) blocking site at the external opening of the pore. A portion of the S3-S4 loop is, at 17–18 Å, considerably closer.

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Figure 1: Maleimido-QA compounds as tethered blockers.
Figure 2: Effect of 21 Å tethered QAs on Shaker K+ channels.
Figure 3: Effects of maleimido-QAs on S1–S4.
Figure 4: Single-channel block by a 32 Å maleimido-QA.

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Acknowledgements

We are grateful to B. Snider for advice on organic synthesis, T. Muir, J. Camarero and G. Cotton for advice on peptide synthesis, A. Cha and P. Bezanilla for sharing results prior to publication, Rick Aldrich for suggesting the A463I mutation for single-channel work, and B. Kobertz, M. Maduke, J. Mindell for comments on the manuscript. This work was supported in part by grants from the NIH.

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Correspondence to Christopher Miller.

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Blaustein, R., Cole, P., Williams, C. et al. Tethered blockers as molecular ‘tape measures’ for a voltage-gated K+ channel. Nat Struct Mol Biol 7, 309–311 (2000). https://doi.org/10.1038/74076

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