Kappa-conotoxins bind and inhibit voltage-gated potassium channels (Kv). This toxin inhibits the drosophila Shaker channel (IC(50)=57-80 nM) (PubMed:12074021, PubMed:10818087, PubMed:27093300). In vivo, when tested in fish, this toxin induces hyperactivity, followed by continuous contraction and extension of major fins, without immobilization or death (PubMed:9417043, PubMed:12074021). Injection of this peptide together with the delta-conotoxin PVIA causes the sudden tetanus of prey (STOP) syndrome, which is a single, lethal 'fin-pop' in envenomed fish (PubMed:9417043, PubMed:12074021). When tested in mice, induces hyperactivity (PubMed:9417043). Expressed by the venom duct. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. The cysteine framework is VI/VII (C-C-CC-C-C). This toxin is not amidated at the C-terminal Val residue. Monoisotopic mass. Was tested under preclinical trial by Cognetix Inc under the name CGX-1051 as a cardioprotective agent. A free N-terminal residue (not acetylated or not cyclizated) is necessary for optimal inhibition of Shaker potassium channel. This toxin has no effect on the rat Kv1.1/KCNA1 channel (PubMed:9417043). Does not inhibit Kv1.3/KCNA3, Kv1.6/KCNA6, Kv2.1/KCNB1, Nav1.4/SCN4A and Nav1.6/SCN8A (PubMed:27093300). Belongs to the conotoxin O1 superfamily. Because analogs resulting of mutagenesis of Hyp-49, Asn-50, Leu-57 and Asp-59 give very low yields upon folding, the results of mutagenesis on these residues should be interpreted with caution.