Toxin that weakly blocks two voltage-gated potassium channels (IC(50)=1.8-2.5 uM on Kv1.2/KCNA2 and IC(50)=5.6-6.2 uM on Kv1.6/KCNA6). Two similar peptides (OspTx2a-p1 and -p2) are obtained after synthesis and oxidative folding. They may differ by a D-Cys at position 76 (corresponding to OspTx2a-p2). Since C-terminal Cys residues are prone to racemization during solid-phase peptide synthesis, and if the presence of a D-amino acid is correct, it is probable that OspTx2a-p1 (L-Cys-76 form) corresponds to the native peptide. The 49-Phe-Pro-50 bond exists only in the trans-isomerization. Has no effect on rKv1.1/KCNA1, hKv1.3/KCNA3, rKv1.4/KCNA4, rKv1.5/KCNA5, hKv2.1/KCNB1, rKv3.1/KCNC1, rKv4.2/KCND2, hKv10.1/EAG1/KCNH1, Kv11.1/HERG/KCNH2, and Shaker IR (tested at 10 uM). Belongs to the sea anemone type 1 potassium channel toxin family. Type 1b subfamily.