Gating modifier of Kv2.1/KCNB1 (IC(50)=5.1 nM), Kv2.2/KCNB2 and Kv4.3/KCND3 channels (IC(50)=39 nM). Acts by shifting the channel activation to more depolarized potentials by stabilizing the resting conformation of the voltage sensor. It completely inhibits opening of the Kv2.1/KCNB1 channel at negative membrane voltages and dramatically shifts channel activation to positive voltages. May act by partitioning into lipid membranes and then by binding the voltage sensor paddle of the channel from a place within the membrane. Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Has no significant effects on Kv1.2/KCNA2, Kv1.3/KCNA3, Kv1.5/KCNA5, Kv3.2/KCNC2, Cav1.2/CACNA1C, Cav2.2/CACNA1B, Nav1.5/SCN5A, Nav1.7/SCN9A or Nav1.8/SCN10A channels. Belongs to the neurotoxin 10 (Hwtx-1) family. 44 (Jztx-4) subfamily.