Reversibly inhibits potassium currents in oocytes expressing Kv2.1/KCNB1 channels (Kd=2.7 uM) (PubMed:15051809). Acts by shifting activation of the channel to more depolarized voltages. The toxin may bind to the S3b-S4 helices of the voltage sensor paddle. One, two, three or four toxin molecules may bind the Kv2.1/KCNB1 channel. It shows low to moderate affinity for lipid bilayers (PubMed:29703751). It partitions into the bilayer membrane, where it stabilizes at the water/membrane interface (PubMed:17071657, PubMed:20643084). Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Shows no or very low activity on Nav1.2/SCN2A, Nav1.4/SCN4A, Nav1.5/SCN5A, Nav1.6/SCN8A, and Nav1.7/SCN9A (IC(50)>3 uM). Belongs to the neurotoxin 10 (Hwtx-1) family. 09 (HaTx) subfamily.