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Toxin-induced conformational changes in a potassium channel revealed by solid-state NMR


The active site of potassium (K+) channels catalyses the transport of K+ ions across the plasma membrane1—similar to the catalytic function of the active site of an enzyme—and is inhibited by toxins from scorpion venom. On the basis of the conserved structures of K+ pore regions2 and scorpion toxins3,4, detailed structures for the K+ channel–scorpion toxin binding interface have been proposed. In these models and in previous solution-state nuclear magnetic resonance (NMR) studies using detergent-solubilized membrane proteins5,6, scorpion toxins were docked to the extracellular entrance of the K+ channel pore assuming rigid, preformed binding sites7,8,9,10,11,12,13. Using high-resolution solid-state NMR spectroscopy, here we show that high-affinity binding of the scorpion toxin kaliotoxin to a chimaeric K+ channel (KcsA-Kv1.3)14,15 is associated with significant structural rearrangements in both molecules. Our approach involves a combined analysis of chemical shifts and proton–proton distances and demonstrates that solid-state NMR is a sensitive method for analysing the structure of a membrane protein–inhibitor complex. We propose that structural flexibility of the K+ channel and the toxin represents an important determinant for the high specificity of toxin–K+ channel interactions.

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Figure 1: Comparison of ssNMR data of KTX and KcsA-Kv1.3 in free and complex form.
Figure 2: Analysis of ssNMR data for KTX–KcsA-Kv1.3.
Figure 3: Competition binding assays of KTX mutants and structural model of the KTX–KcsA-Kv1.3 complex.
Figure 4: Comparison of the selectivity filter in the KTX–KcsA-Kv1.3 complex derived from ssNMR data to KcsA X-ray structures.


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We are grateful to H. Kratzin and K. Overkamp for peptide analysis. Technical assistance by B. Angerstein is gratefully acknowledged. We thank C. Griesinger for continuous support of this project. This work was funded in part by the DFG and by a PhD. fellowship to A.L. from the Stiftung Stipendien-Fonds of the Verband der Chemischen Industrie. Author Contributions O.P., S.B. and M.B. are co-senior authors.

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Correspondence to Marc Baldus.

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This file contains Supplementary Methods, Supplementary Figures 1-3 and legends, Supplementary Tables 1–7 and Supplementary References. (PDF 2560 kb)

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Lange, A., Giller, K., Hornig, S. et al. Toxin-induced conformational changes in a potassium channel revealed by solid-state NMR. Nature 440, 959–962 (2006).

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