Blocks human and/or rat Kv11.1/KCNH2/ERG1, Kv11.2/KCNH6/ERG2 and Kv11.3/KCNH7/ERG3 by binding to channel outer vestibule (S5P domain) with a 1:1 stoichiometry. Inhibition data are the following: hERG1 (reversible, Kd=7.7 nM (PubMed:16497878), IC(50)=3.3 nM (PubMed:11136720), IC(50)=11.9 nM (PubMed:21205913)), rERG1 (reversible, Kd=19 nM) (PubMed:16497878), hERG2 (reversible, Kd=77 nM) (PubMed:16497878), rERG2 (irreversible, Kd=4.2 nM) (PubMed:16497878), hERG3 (reversible, Kd=11.5 nM) (PubMed:16497878) and rERG3 (reversible, Kd=747 nM) (PubMed:16497878) potassium channels. Has also a minimal effect on rat ELK1/KCNH4 potassium channels (9% inhibition at 100 nM (PubMed:15137031)). Both this toxin and CnErgTx1 (AC Q86QT3) share mechanism of action and have overlapping binding sites on ERG1 (PubMed:12719233). The potency of these two toxins is not affected by elevating potassium ion concentration from 2 to 98 mM (PubMed:12719233). In addition, at high toxin concentrations, block of ERG1 macroscopic currents by these two toxins is incomplete (88%) (PubMed:12719233). The blockade by this toxin is preferentially closed channel state-dependent, with a component of open, but not inactive state-dependent blockade (PubMed:12860380). This toxin produces a concentration-dependent prolongation of QTc in the isolated rabbit heart (16.3% at 100 nM) (PubMed:21205913). Expressed by the venom gland. 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. The inhibition potency of the toxin for ERG1 decreases as temperature increases (IC(50)=7.6 nM and IC(50)=15.3 nM at room temperature and 37 degrees Celsius, respectively), likely due to changes in the structure of the channel binding site. The toxin (at 100 nM) does not inhibit hEAG1/KCNH1, hBK/KCa1.1/KCNMA1, hSK1/KCa2.1/KCNN1, rSK2/KCa2.2/KCNN2, hIK/KCa3.1/KCNN4, KCNQ1+KCNE1, KCNQ2+KCNQ3 and KCNQ4 channels (PubMed:11136720). The toxin (at 50 nM) does not inhibit Kv1.2/KCNA2, Kv1.4/KCNA4, Kv2.1/KCNB1, Kv4.3/KCND3, Kir1.1/KCNJ1 (PubMed:15137031). Belongs to the short scorpion toxin superfamily. Potassium channel inhibitor family. Gamma-KTx 2 subfamily. Has been classified as a gamma-KTx toxin due to its molecular target (Kv11/ERG), but may be classified as an alpha-KTx since it shares a high level of homology in both primary and 3D structures with other alpha-KTx scorpion toxins. However, it is noteworthy that surface by which BeKm-1 interacts with ERG1 is formed by residues located in the alpha-helix and the following loop, while the traditional functional site of other alpha-KTxs is formed by residues on the beta-sheet.