Spider venoms are a rich source of ion channel modulators that are increasingly being used as pharmacological tools and as leads for the development of novel therapeutics. Almost without exception, these toxins are allosteric modulators (“gating modifiers”) that bind to the voltage-sensor domain of the channel in order to alter channel activation or inactivation.Remarkably, despite this ubiquitous mode of action, we know virtually nothing about the molecular basis of the interaction between spider-venom peptides and the voltage-sensor domain of voltage-gated ion channels.
In this study, we used the interaction between the spider-venom peptide VSTx1 and the voltage-sensor domain (VSD) of the archeabacterial voltage-gated potassium channel KvAP as a model system for understanding what drives this type of toxin-channel interaction.
Isotopically labelled VSTx1 and KvAP-VSD were produced recombinantly in Escherichia coli. The structure of VSTx1 was solved using triple resonance heteronuclear NMR experiments. KvAP-VSD was isotopically labelled for NMR studies and purified in detergent micelles. NMR chemical shift mapping with isotopically KvAP-VSD and unlabeled toxin, or vice versa, was then used to probe the molecular details of the VSTx1-VSD interaction as well as the interaction between VSTx1 and lipids. The combined results suggest that the high affinity of VSTx1 is a product of its interaction with its cognate VSD and the membrane, with the latter additionally contributing to increase the peptide concentration near the membrane.