Opening the shaker K+ channel with hanatoxin.
Voltage-activated ion channels open and close in response to changes in membrane voltage, a property that is fundamental to the roles of these channels in electrical signaling. Protein toxins from venomous organisms commonly target the S1-S4 voltage-sensing domains in these channels and modify their gating properties. Studies on the interaction of hanatoxin with the Kv2.1 channel show that this tarantula toxin interacts with the S1-S4 domain and inhibits opening by stabilizing a closed state. Here we investigated the interaction of hanatoxin with the Shaker Kv channel, a voltage-activated channel that has been extensively studied with biophysical approaches. In contrast to what is observed in the Kv2.1 channel, we find that hanatoxin shifts the conductance-voltage relation to negative voltages, making it easier to open the channel with membrane depolarization. Although these actions of the toxin are subtle in the wild-type channel, strengthening the toxin-channel interaction with mutations in the S3b helix of the S1-S4 domain enhances toxin affinity and causes large shifts in the conductance-voltage relationship. Using a range of previously characterized mutants of the Shaker Kv channel, we find that hanatoxin stabilizes an activated conformation of the voltage sensors, in addition to promoting opening through an effect on the final opening transition. Chimeras in which S3b-S4 paddle motifs are transferred between Kv2.1 and Shaker Kv channels, as well as experiments with the related tarantula toxin GxTx-1E, lead us to conclude that the actions of tarantula toxins are not simply a product of where they bind to the channel, but that fine structural details of the toxin-channel interface determine whether a toxin is an inhibitor or opener.
Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
Mirela
M
Milescu
Hwa C
HC
Lee
Chan Hyung
CH
Bae
Jae Il
JI
Kim
Kenton J
KJ
Swartz
D000818:Animals; D002478:Cells, Cultured; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D010455:Peptides / Q000494:pharmacology*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051637:Shaker Superfamily of Potassium Channels / Q000187:drug effects / Q000502:physiology*; D014982:Xenopus laevis
D010455:Peptides; D026902:Potassium Channel Blockers; D051637:Shaker Superfamily of Potassium Channels; C096469:hanatoxin