Blocks in a reversible manner human and rat Kv11.1/KCNH2/ERG1 potassium channels (PubMed:18338253). Also completely and irreversibly blocks rat Kv11.2/KCNH6/ERG2 and human Kv11.3/KCNH7/ERG3 channels (PubMed:18338253). Also weakly inhibits Kir2.1/KCNJ2 and Kv1.2/KCNA2 potassium channels (PubMed:29483648). 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. Does not affect human Kv11.2/KCNH6/ERG2. Belongs to the ergtoxin family. Gamma-KTx 1 subfamily.