Gating modifier of Kv2.1/KCNB1, Kv2.2/KCNB2 and Kv4.3/KCND3 channels. 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. 44 (Jztx-4) subfamily.