Voltage-gated ion channels are responsible for generating electrical impulses in nerves and other excitable cells. The fourth transmembrane helix (S4) in voltage-gated channels is the primary voltage-sensing unit that mediates the response to a changing membrane electric field1,2. The molecular mechanism of voltage sensing, particularly with respect to the magnitude of the transmembrane movement of S4, remains controversial3,4,5. To determine the extent of this transmembrane movement, we use fluorescent resonance energy transfer between the S4 domain and a reference point in the lipid bilayer. The lipophilic ion dipicrylamine distributes on either side of the lipid bilayer depending on the membrane potential, and is used here as a resonance-energy-transfer acceptor from donor molecules attached to several positions in the Shaker K+ channel. A voltage-driven transmembrane movement of the donor should produce a transient fluorescence change because the acceptor also translocates as a function of voltage. In Shaker K+ channels no such transient fluorescence is observed, indicating that the S4 segment does not translocate across the lipid bilayer. Based on these observations, we propose a molecular model of voltage gating that can account for the observed 13e gating charge with limited transmembrane S4 movement.
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We thank M. J. Hahn for technical assistance, M. Holmgren for the cysteine-less Shaker clone, W. Hubell for the gift of dipicrylamine and the members of Bezanilla and Correa laboratories for their comments. This work was supported by funds from an AHA postdoctoral fellowship to B.C., NRSA funding to O.K.A, DFG funding to R.B. and an NIH grant to F.B.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
The kinetics and profile of different FRET signals are explained and discussed in detail. Theoretical background and case studies are provided. This file also contains Supplementary Figure Legends. (DOC 48 kb)
This file contains Supplementary Figures S1–S6. Text to accompany these figures is found in the Supplementary Discussion. (PPT 780 kb)
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Chanda, B., Kwame Asamoah, O., Blunck, R. et al. Gating charge displacement in voltage-gated ion channels involves limited transmembrane movement. Nature 436, 852–856 (2005). https://doi.org/10.1038/nature03888
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