AbeTx1 Is a Novel Sea Anemone Toxin with a Dual Mechanism of Action on Shaker-Type K+ Channels Activation

Voltage-gated potassium (K-V) channels regulate diverse physiological processes and are an important target for developing novel therapeutic approaches. Sea anemone (Cnidaria, Anthozoa) venoms comprise a highly complex mixture of peptide toxins with diverse and selective pharmacology on K-V channels. From the nematocysts of the sea anemone Actinia bermudensis, a peptide that we named AbeTx1 was purified and functionally characterized on 12 different subtypes of K-V channels (K(V)1.1-K(V)1.6; K(V)2.1; K(V)3.1; K(V)4.2; K(V)4.3; K(V)11.1; and, Shaker IR), and three voltage-gated sodium channel isoforms (Na(V)1.2, Na(V)1.4, and BgNa(V)). AbeTx1 was selective for Shaker-related K+ channels and is capable of inhibiting K+ currents, not only by blocking the K+ current of K(V)1.2 subtype, but by altering the energetics of activation of K(V)1.1 and K(V)1.6. Moreover, experiments using six synthetic alanine point-mutated analogs further showed that a ring of basic amino acids acts as a multipoint interaction for the binding of the toxin to the channel. The AbeTx1 primary sequence is composed of 17 amino acids with a high proportion of lysines and arginines, including two disulfide bridges (Cys1-Cys4 and Cys2-Cys3), and it is devoid of aromatic or aliphatic amino acids. Secondary structure analysis reveals that AbeTx1 has a highly flexible, random-coil-like conformation, but with a tendency of structuring in the beta sheet. Its overall structure is similar to open-ended cyclic peptides found on the scorpion -KTx toxins family, cone snail venoms, and antimicrobial peptides.