Inhibits Kv2.1/KCNB1 and Kv4.2/KCND2 voltage-gated potassium channels. Acts as a gating modifier by shifting channel openings to more depolarized voltages and acts via the occupancy of multiple binding sites on the channel. The toxin binding sites are situated on the S3-S4 extracellular linker of the channel. At least two hanatoxin molecules can occupy the Kv2.1/KCNB1 channel, and maybe more (three or four). Can also inhibit calcium channels (Cav2.1/CACNA1A). Needs to partition into the membrane in order to bind to the channel. Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Belongs to the neurotoxin 10 (Hwtx-1) family. 09 (HaTx) subfamily.