Scorpion toxin peptide BMK86-P1 achieves mutation-reversible inhibition of KCNA2 at the cost of reduced efficacy in heteromers and murine neurons

The discovery of distinctive function-phenotype relationships in monogenetic channelopathies has turned out to be critical for the development of precision medicine approaches. However, the best prediction of clinical phenotypes depends on neuronal function, where existing models lack tools to isolate currents of individual voltage-gated potassium channel subunits and differentiate variant effects in complex systems. Ideally, one should be able to overexpress subunit variants with an additional mutation that confers resistance against the tool to isolate the variant effect. Therefore, we solid-phase synthesized the KV1.2 specific scorpion toxin peptide BMK86-P1 and oxidized it with modest efficacy. In mammalian cells this BMK86-P1 selectively inhibited KV1.2 homomers, but not heteromers with KV1.1. Critically, the KCNA2 p.Val381Tyr mutation, which reverses BMK86-P1's selective inhibition of KV1.2, also altered the activation of KV1.2 homomers to resemble those of KV1.1. In addition, BMK86-P1 in murine neurons did not alter passive membrane properties, single action potential properties, or action potential firing. Surprisingly, it induced only minimal changes in spontaneous excitatory postsynaptic currents. In summary, this KV1.2 subunit selective toxin peptide asserts its effects primarily on homomeric channels, while only weakly inhibiting KV1.2-heteromeric channels and consequently preventing any meaningful impact on neuronal function. This highlights the limits of peptide synthesis together with the need for testing specific compounds on complex systems.