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Blocker protection in the pore of a voltage-gated K+ channel and its structural implications

Abstract

The structure of the bacterial potassium channel KcsA1 has provided a framework for understanding the related voltage-gated potassium channels (Kv channels) that are used for signalling in neurons. Opening and closing of these Kv channels (gating) occurs at the intracellular entrance to the pore, and this is also the site at which many open channel blockers affect Kv channels2,3,4. To learn more about the sites of blocker binding and about the structure of the open Kv channel, we investigated here the ability of blockers to protect against chemical modification of cysteines introduced at sites in transmembrane segment S6, which contributes to the intracellular entrance. Within the intracellular half of S6 we found an abrupt cessation of protection for both large and small blockers that is inconsistent with the narrow ‘inner pore’ seen in the KcsA structure. These and other results are most readily explained by supposing that the structure of Kv channels differs from that of the non-voltage-gated bacterial channel by the introduction of a sharp bend in the inner (S6) helices. This bend would occur at a Pro-X-Pro sequence that is highly conserved in Kv channels, near the site of activation gating.

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Figure 1: Tetrabutylammonium (TBuA) protects Cys 474 from MTSET modification.
Figure 2: Effects of blocker on MTS reagent modification of cysteines introduced in S6.
Figure 3: Protection results for three blockers overlaid on the lining of the KcsA pore.
Figure 4: The ‘bent S6’ model for Kv channels compared with the inner helices of KcsA.

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Acknowledgements

We thank Ki Soon Shin for performing some preliminary experiments with MTSES; M. MacArthur and J. Thornton for performing a database search; T. Ogren for help with the cells; B. Bean for comments on the manuscript; and members of the Yellen laboratory for helpful discussions. The work was supported by an NIH (NINDS) grant to G.Y., a fellowship from the Muscular Dystrophy Association to M.H. and a fellowship from the Spanish Ministry of Education to D.D.C.

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Correspondence to Gary Yellen.

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del Camino, D., Holmgren, M., Liu, Y. et al. Blocker protection in the pore of a voltage-gated K+ channel and its structural implications. Nature 403, 321–325 (2000). https://doi.org/10.1038/35002099

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