Voltage-sensor activation with a tarantula toxin as cargo

L. Revell Phillips, Mirela Milescu, Yingying Li-Smerin, Joseph A. Mindell, Jae Il Kim and Kenton J. Swartz ()
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L. Revell Phillips: Molecular Physiology and Biophysics Section
Mirela Milescu: Molecular Physiology and Biophysics Section
Yingying Li-Smerin: Molecular Physiology and Biophysics Section
Joseph A. Mindell: National Institute of Neurological Disorders and Stroke, National Institutes of Health
Jae Il Kim: Gwangju Institute of Science and Technology
Kenton J. Swartz: Molecular Physiology and Biophysics Section

Nature, 2005, vol. 436, issue 7052, 857-860

Abstract: Abstract The opening and closing of voltage-activated Na+, Ca2+ and K+ (Kv) channels underlies electrical and chemical signalling throughout biology, yet the structural basis of voltage sensing is unknown. Hanatoxin is a tarantula toxin that inhibits Kv channels by binding to voltage-sensor paddles1,2,3,4,5, crucial helix-turn-helix motifs within the voltage-sensing domains that are composed of S3b and S4 helices6. The active surface of the toxin is amphipathic7,8, and related toxins have been shown to partition into membranes9,10,11,12, raising the possibility that the toxin is concentrated in the membrane and interacts only weakly and transiently with the voltage sensors. Here we examine the kinetics and state dependence of the toxin–channel interaction and the physical location of the toxin in the membrane. We find that hanatoxin forms a strong and stable complex with the voltage sensors, far outlasting fluctuations of the voltage sensors between resting (closed) conformations at negative voltages and activated (open) conformations at positive voltages. Toxin affinity is reduced by voltage-sensor activation, explaining why the toxin stabilizes the resting conformation. We also find that when hanatoxin partitions into membranes it is localized to an interfacial region, with Trp 30 positioned about 8.5 Å from the centre of the bilayer. These results demonstrate that voltage-sensor paddles activate with a toxin as cargo, and suggest that the paddles traverse no more than the outer half of the bilayer during activation.

Date: 2005
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DOI: 10.1038/nature03873

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