New ShK-Like Peptide from the Jellyfish Nemopilema nomurai Has Human Potassium Voltage-Gated Channel-Blocking Activity

We have identified a new human voltage-gated potassium channel (hKv1.3) blocker, NnK-1, in the jellyfish Nemopilema nomurai, based on its genomic information. The gene sequence encoding NnK-1 contains 5,408 base pairs, with five introns and six exons. The coding sequence of the NnK-1 precursor is 894 nucleotides long and encodes 297 amino acids, containing five presumptive ShK-like peptides. An electrophysiological assay demonstrated that the chemically synthesized fifth peptide, NnK-1, is an effective hKv1.3 blocker. A multiple sequence alignment with cnidarian Shk-like peptides, which have Kv1.3-blocking activity, revealed that four residues (3Asp, 25Lys, 33Lys, and 34Thr) of NnK-1, together with six cysteine residues, are conserved. Therefore, we hypothesize that these four residues are crucial for the binding of the toxins to voltage-gated potassium channels.