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Intracellular gate opening in Shaker K+ channels defined by high-affinity metal bridges

Nature volume 428, pages 864–868 (2004)Cite this article

Abstract

Voltage-gated potassium channels such as Shaker help to control electrical signalling in neurons by regulating the passage of K+ across cell membranes. Ion flow is controlled by a voltage-dependent gate at the intracellular side of the pore, formed by the crossing of four α-helices—the inner-pore helices. The prevailing model of gating is based on a comparison of the crystal structures of two bacterial channels—KcsA in a closed state and MthK in an open state—and proposes a hinge motion at a conserved glycine that splays the inner-pore helices wide open1. We show here that two types of intersubunit metal bridge, involving cysteines placed near the bundle crossing, can occur simultaneously in the open state. These bridges provide constraints on the open Shaker channel structure, and on the degree of movement upon opening. We conclude that, unlike predictions from the structure of MthK, the inner-pore helices of Shaker probably maintain the KcsA-like bundle-crossing motif in the open state, with a bend in this region at the conserved proline motif (Pro-X-Pro) not found in the bacterial channels. A narrower opening of the bundle crossing in Shaker K+ channels may help to explain why Shaker has an approximately tenfold lower conductance than its bacterial relatives.

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Figure 1: The lock-open effect requires metal binding residues at positions 476 and 486.
Figure 2: The blocker affinity and single-channel conductance of the locked-open state are similar to those of the normal open state.
Figure 3: The recovery of ILT V474C channels from Cd2+ blockade suggests that cadmium has little effect on the open/closed equilibrium of bound channels.
Figure 4: Cadmium ions can simultaneously bind V474C and bridge V476C–H486.
Figure 5: A comparison of the models of potassium channel gating.

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Acknowledgements

We thank M. Kanevsky for characterizing the charge movement for ILT 474C and S. Forman for allowing us to use his perfusion setup. We are also grateful to B. Bean and to the members of the Yellen laboratory for helpful discussions, and to T. Abramson for her expert help with transfections. This work was supported by a grant from the NIH/NINDS to G.Y.

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  1. Sarah M. Webster and Donato del Camino: These authors contributed equally to this work

Authors and Affiliations

  1. Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, Massachusetts, 02115, USA

    Sarah M. Webster, Donato del Camino, John P. Dekker & Gary Yellen

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  1. Sarah M. Webster
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Correspondence to Gary Yellen.

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Webster, S., del Camino, D., Dekker, J. et al. Intracellular gate opening in Shaker K+ channels defined by high-affinity metal bridges. Nature 428, 864–868 (2004). https://doi.org/10.1038/nature02468

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