Blocks human voltage-gated potassium channel Kv11.1/KCNH2/ERG1 (IC(50)=16.9 nM). Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Has no effect on voltage-gated potassium channels Kv1.1/KCNA1, Kv1.2/KCNA2, Kv1.3/KCNA3, Kv10.1/KCNH1/EAG1 and Shaker IR (with inactivation domain removed) and on intermediate conductance calcium-activated potassium channel KCa3.1/KCNN4. Belongs to the ergtoxin family. Gamma-KTx 1 subfamily.