8.B.19. The Sea Anemone K+ Channel Blocker Toxin, BcsTx3 (BcsTx3) Family
Sea anemone venoms are a rich source of peptide toxins which provide tools for studying the structures and functions of ion channels. BcsTx3, a toxin found in the venom of a Bunodosoma caissarum (from Brazil) has been purified and biochemically and pharmacologically characterized (Orts et al. 2013). The pharmacological effects were studied on 12 different subtypes of voltage-gated potassium 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; hERG and Shaker IR) and three cloned voltage-gated sodium channel isoforms (Na(V)1.2, Na(V)1.4 and BgNa(V)1.1), all expressed in Xenopus laevis oocytes. BcsTx3 showed a high affinity for Drosophila Shaker IR channels over rKv1.2, hKv1.3 and rKv1.6, and was not active on NaV channels. Biochemical characterization revealed that BcsTx3 is a 50 amino acid peptide crosslinked by four disulfide bridges, and sequence comparison allowed BcsTx3 to be classified as a novel type of sea anemone toxin acting on KV channels. Putative toxins homologous to BcsTx3 from two additional actiniarian species were identified (Orts et al. 2013).
These sea anemone toxins (subfamily 1) are clearly related to spider toxins (subfamily 2), and families 8.B.6 and 8.B.19 seem to be related to each other as well as possibly to 1.C.52, 8.B.3 and 8.B.5. These tentative possibilities need to be confirmed. However 8.B.3 and 8.B.5 are for sure related.