Blocks human and rat Kv11.1/KCNH2/ERG1 and Kv11.3/KCNH7/ERG3, as well as rat (but not human) Kv11.2/KCNH6/ERG2 (PubMed:11755529, PubMed:11864985, PubMed:16497878, PubMed:17369411, PubMed:20600425) by binding to channel outer vestibule (S5P domain) with a 1:1 stoichiometry (PubMed:11755529, PubMed:11864985, PubMed:17369411, PubMed:20600425). Inhibition data are the following: hERG1 (reversible, IC(50)~7 nM) (PubMed:11755529, PubMed:11864985, PubMed:16497878, PubMed:17369411, PubMed:20600425), rERG1 (reversible, Kd=6.8 nM) (PubMed:16497878), rERG2 (irreversible, Kd=2.8 nM) (PubMed:16497878), hERG3 (irreversible, Kd=4.05 nM) (PubMed:16497878) and rERG3 (reversible, Kd=38.1 nM) (PubMed:16497878) potassium channels. The toxin potency is not affected by elevating potassium ion concentration from 2 to 98 mM (PubMed:11864985). This toxin only blocks channels in a closed state (PubMed:12860380). At high toxin concentrations, block of Kv11.1/KCNH2/ERG1 macroscopic current is incomplete (93.5%). This suggests a kinetic mechanism model with two different states of toxin-channel binding (T+C=TC*=TC; in the TC* state, the toxin binds the channel but does not occlude the pore, whereas in the TC state the toxin binds and occludes the pore). In this model, incomplete block is explained by the relatively fast dissociation rate from the blocked channel conformation (TC) relative to the rate of conversion of the toxin-channel encounter complex (TC*) to the blocked channel conformation (TC) (PubMed:17369411). Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Has the CSalpha/beta fold, which comprises one or two short alpha helices connected to anti-parallel beta-sheets stabilized by three or four disulfide bonds. After protein storage at -20 Celsius degrees during a couple of months, the Met-55 of a small number of toxins is naturally oxidized. This oxidized form is about three orders of magnitude less efficient (IC(50)=15 uM) than non-oxidized form. The affinity of the toxin for the channel decreases as temperature increases (Kd=7.3 nM and Kd=64 nM at 22 and 37 degrees Celsius, respectively), likely due to changes in the structure of the channel binding site. Does not affect the function of either mouse EAG/KCNH1 or ELK1 channels at concentration of 200 nM (PubMed:11755529). Does not inhibit hKv1.4/KCNA4, hKv4.3/KCND3, hKv2.1/KCNB1 and rKv7.1/KCNQ1 potassium channels at concentration of 50 nM (PubMed:11864985). Does not inhibit human Kv11.2/KCNH6/ERG2 (PubMed:16497878). Belongs to the ergtoxin family. Gamma-KTx 1 subfamily.