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Proc Natl Acad Sci U S A. 2014 Nov 4;111(44):E4789-96. doi: 10.1073/pnas.1406876111. Epub 2014 Oct 20.

Chemoselective tarantula toxins report voltage activation of wild-type ion channels in live cells.

Author information

1
Department of Physiology and Membrane Biology, University of California, Davis, CA 95616;
2
Department of Physiology and Membrane Biology, University of California, Davis, CA 95616; Neurobiology Course, Marine Biological Laboratory, Woods Hole, MA 02543;
3
Neurobiology Course, Marine Biological Laboratory, Woods Hole, MA 02543;
4
Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; and.
5
Department of Biochemistry and Molecular Medicine, University of California, Davis, CA 95616.
6
Department of Physiology and Membrane Biology, University of California, Davis, CA 95616; Department of Biochemistry and Molecular Medicine, University of California, Davis, CA 95616.
7
Department of Physiology and Membrane Biology, University of California, Davis, CA 95616; Neurobiology Course, Marine Biological Laboratory, Woods Hole, MA 02543; jsack@ucdavis.edu.

Abstract

Electrically excitable cells, such as neurons, exhibit tremendous diversity in their firing patterns, a consequence of the complex collection of ion channels present in any specific cell. Although numerous methods are capable of measuring cellular electrical signals, understanding which types of ion channels give rise to these signals remains a significant challenge. Here, we describe exogenous probes which use a novel mechanism to report activity of voltage-gated channels. We have synthesized chemoselective derivatives of the tarantula toxin guangxitoxin-1E (GxTX), an inhibitory cystine knot peptide that binds selectively to Kv2-type voltage gated potassium channels. We find that voltage activation of Kv2.1 channels triggers GxTX dissociation, and thus GxTX binding dynamically marks Kv2 activation. We identify GxTX residues that can be replaced by thiol- or alkyne-bearing amino acids, without disrupting toxin folding or activity, and chemoselectively ligate fluorophores or affinity probes to these sites. We find that GxTX-fluorophore conjugates colocalize with Kv2.1 clusters in live cells and are released from channels activated by voltage stimuli. Kv2.1 activation can be detected with concentrations of probe that have a trivial impact on cellular currents. Chemoselective GxTX mutants conjugated to dendrimeric beads likewise bind live cells expressing Kv2.1, and the beads are released by channel activation. These optical sensors of conformational change are prototype probes that can indicate when ion channels contribute to electrical signaling.

KEYWORDS:

allostery; fluorescence; gating modifier; potassium channel; voltage-gated ion channel

PMID:
25331865
PMCID:
PMC4226076
DOI:
10.1073/pnas.1406876111
[Indexed for MEDLINE]
Free PMC Article

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