Abstract
Voltage-sensor domains (VSDs) are modular transmembrane domains of voltage-gated ion channels that respond to changes in membrane potential by undergoing conformational changes that are coupled to gating of the ion-conducting pore. Most spider-venom peptides function as gating modifiers by binding to the VSDs of voltage-gated channels and trapping them in a closed or open state. To understand the molecular basis underlying this mode of action, we used nuclear magnetic resonance to delineate the atomic details of the interaction between the VSD of the voltage-gated potassium channel KvAP and the spider-venom peptide VSTx1. Our data reveal that the toxin interacts with residues in an aqueous cleft formed between the extracellular S1-S2 and S3-S4 loops of the VSD whilst maintaining lipid interactions in the gaps formed between the S1-S4 and S2-S3 helices. The resulting network of interactions increases the energetic barrier to the conformational changes required for channel gating, and we propose that this is the mechanism by which gating modifier toxins inhibit voltage-gated ion channels.
Highlights
Several structural models have recently been proposed to explain how venom peptides interact with VSDs and modulate ion channel function: (i) a docking model, supported primarily by mutagenesis data, suggests that these peptide bind to a cavity formed between the four VSD helices[19]; (ii) a docking model where the peptide binds in a cleft between helix S1 and S4 supported by ambiguous NMR restraints[13]; and (iii) a docking model supported by fluorescence data indicating that the peptide binds residues on the S3 helix[21]
NMR data and complementary mutagenesis studies reveal that VSTx1 interacts with residues within the aqueous cavity formed on the extracellular surface of the channel between the S1-S2 and S3-S4 loops
Recombinant VSTx1 was produced as an maltose-binding protein (MBP) fusion protein using an E. coli periplasmic expression system designed for production of disulfide-rich peptides[29]
Summary
Several structural models have recently been proposed to explain how venom peptides interact with VSDs and modulate ion channel function: (i) a docking model, supported primarily by mutagenesis data, suggests that these peptide bind to a cavity formed between the four VSD helices[19]; (ii) a docking model where the peptide binds in a cleft between helix S1 and S4 supported by ambiguous NMR restraints[13]; and (iii) a docking model supported by fluorescence data indicating that the peptide binds residues on the S3 helix[21] In parallel to these peptide-binding studies it was recently demonstrated, using X-ray crystallography that a small-molecule antagonist of NaV1.7 binds into a cleft formed between the four helices of the domain IV VSD, accessing the cavity from a gap formed between the S2 and S3 helices.
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