Variation Of Two S3b Residues In K(V)4.1-4.3 Channels Underlies Their Different Modulations By Spider Toxin Kappa-Lhtx-1

The naturally occurred peptide toxins from animal venoms are valuable pharmacological tools in exploring the structure-function relationships of ion channels. Herein we have identified the peptide toxin kappa-LhTx-1 from the venom of spider Pandercetes sp (the Lichen huntsman spider) as a novel selective antagonist of the K(V)4 family potassium channels. kappa-LhTx-1 is a gating-modifier toxin impeded K(V)4 channels' voltage sensor activation, and mutation analysis has confirmed its binding site on channels' S3b region. Interestingly, kappa-LhTx-1 differently modulated the gating of K(V)4 channels, as revealed by toxin inhibiting K(V)4.2/4.3 with much more stronger voltage-dependence than that for K(V)4.1. We proposed that kappa-LhTx-1 trapped the voltage sensor of K(V)4.1 in a much more stable resting state than that for K(V)4.2/4.3 and further explored the underlying mechanism. Swapping the non-conserved S3b segments between K(V)4.1(280FVPK283) and K(V)4.3(275VMTN278) fully reversed their voltage-dependence phenotypes in inhibition by kappa-LhTx-1, and intensive mutation analysis has identified P282 in K(V)4.1, D281 in K(V)4.2 and N278 in K(V)4.3 being the key residues. Furthermore, the last two residues in this segment of each K(V)4 channel (P282/K283 in K(V)4.1, T280/D281 in K(V)4.2 and T277/N278 in K(V)4.3) likely worked synergistically as revealed by our combinatorial mutations analysis. The present study has clarified the molecular basis in K(V)4 channels for their different modulations by kappa-LhTx-1, which have advanced our understanding on K(V)4 channels' structure features. Moreover, kappa-LhTx-1 might be useful in developing anti-arrhythmic drugs given its high affinity, high selectivity and unique action mode in interacting with the K(V)4.2/4.3 channels.