Venomous animals produce small protein toxins that inhibit ion channels with high affinity. In several well-studied cases the inhibitory proteins are water-soluble and bind at a channel's aqueous-exposed extracellular surface1,2,3,4. Here we show that a voltage-sensor toxin (VSTX1) from the Chilean Rose Tarantula (Grammostola spatulata) reaches its target by partitioning into the lipid membrane. Lipid membrane partitioning serves two purposes: to localize the toxin in the membrane where the voltage sensor resides and to exploit the free energy of partitioning to achieve apparent high-affinity inhibition. VSTX1, small hydrophobic poisons and anaesthetic molecules reveal a common theme of voltage sensor inhibition through lipid membrane access. The apparent requirement for such access is consistent with the recent proposal that the sensor in voltage-dependent K+ channels is located at the membrane–protein interface5,6.
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We thank D. King for toxin synthesis for initial experiments, F. Valiyaveetil for help with fluorescence experiments, V. Ruta for help with toxin purification and electrophysiology and S. Long for providing AgTx2. This work was supported by a National Institutes of Health grant to R.M. R.M. is an investigator in the Howard Hughes Medical Institute.
The authors declare that they have no competing financial interests.
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Lee, SY., MacKinnon, R. A membrane-access mechanism of ion channel inhibition by voltage sensor toxins from spider venom. Nature 430, 232–235 (2004). https://doi.org/10.1038/nature02632
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