Comparative characterization of two scorpion toxins, BlTx1 and BlTx2, identifies BlTx2 as a Kv4.1-selective peptide

Voltage-gated potassium channels of the Kv4 subfamily (Kv4.1, Kv4.2, and Kv4.3) mediate transient A-type potassium currents that regulate neuronal excitability, dendritic integration, and cardiac repolarization. Despite their importance, no pharmacological tool has been available to selectively dissect the role of Kv4.1, as existing peptide toxins from the α-KTx15 family display broad activity across Kv4 isoforms. Here, we report the discovery and characterization of two novel scorpion toxins, BlTx1 and BlTx2, isolated from the venom gland transcriptome of Buthacus leptochelys. Both toxins were heterologously expressed in yeast and purified to homogeneity. Electrophysiological recordings from Xenopus laevis oocytes revealed that BlTx1 and BlTx2 potently inhibited Kv4.1 currents, while sparing Kv4.2 and Kv4.3. Among a panel of 20 tested potassium channels, BlTx2 exhibited clear functional selectivity for Kv4.1, with an IC₅₀ of 28 nM, whereas BlTx1 also inhibited Kv1.2. Sequence comparison with related nonselective toxins suggests that a small number of substitutions in the N-terminal half of the peptides underlie BlTx2's unique selectivity profile. This unique isoform selectivity establishes BlTx2 as, to our knowledge, the first toxin showing clear functional selectivity for Kv4.1 within the tested panel, providing a molecular probe for delineating the physiological and pathological contributions of Kv4.1. Such a tool may facilitate clarification of Kv4.1's role in neuronal firing patterns, circadian regulation, and tumor cell proliferation, while avoiding the off-target effects associated with nonselective Kv4 inhibitors. Our findings highlight scorpion venoms as a valuable source of isoform-selective ion channel ligands and open new avenues for basic research and therapeutic development.