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Evidence for a function‐specific mutation in the neurotoxin, parabutoxin 3

Parabutoxin 3 (PBTx3), a short‐chain α‐K+ neurotoxin from the scorpion, Parabuthus transvaalicus, is a 37‐residue polypeptide cross‐linked by three disulphide bridges. The affinity towards Kv1 channels is very weak (Kd ≈ 79 µm for Kv1.1 channels), or moderate (Kd ≈ 500 nm for Kv1.2 and Kv1.3 channels). In an effort to generate a more potent K+ channel blocker, we recombinantly produced a mutant PBTx3 by the introduction of an aromatic amino acid, fenylalanine in close proximity of the crucial lysine 26 residue, to create a functional diad similar to subfamily three α‐K+ toxins. The mutant was tested for his ability to block Kv1.1, Kv1.2 and Kv1.3 channels in Xenopus laevis oocytes: a hundred‐fold higher affinity towards Kv1.1 channels and a fivefold increase in affinity towards Kv1.3 channels was observed, when compared to the wild‐type toxin. The effect on Kv1.2 channels was similar to the wild‐type toxin, indicating a specific interaction site for the mutated residue onto the different Kv‐type channels.