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= BcsTx3 Toxin = BcsTx3 is a voltage-gated potassium channel blocker toxin. It is purified from the venom of Bunodosoma caissarum.

This toxin is also named as Kappa-actitoxin-Bcs4a (full name) and Kappa-AITX-Bcs4a (short name).

Source in nature:
This toxin is derived from Sea anemone animal (species: Bunodosoma caissarum) which belongs to the phylum Cnidaria.

Function:
The Toxin Inhibits voltage-gated potassium channels (Kv1/KCNA). The IC50 values are 172.59 nM for Kv1.2/KCNA2, 2245.93 nM for Kv1.6/KCNA6, 1006.48 nM for human Kv1.3/KCNA3, and 94.25 nM for Drosophila Shaker IR channels respectively.

Biochemistry and Structure:
Biochemical analysis of the toxin revealed that it is a small single-chain protein consisting of only 50 base amino acids. However, it selectively binds to voltage-gated potassium channels (Kv1.x) depending on its (BcsTx3) concentration. Neurophysiological analysis showed that the toxin blocks several voltage-gated potassium channels (Kv1.1, Kv1.2, Kv1.3, Kv1.6) out of 12 tested including sodium channels at 3uM of concentration and it blocks shaker IR in Drosophila with higher affinity. However, it showed no effect on sodium channels.

Unlike previously identified subfamilies of the potassium channel inhibitor toxins, BcsTx3 has different cysteine positions, and it is homologous with other new two toxins (nvePTx1 and msePTx1) which makes the three a new subfamily of the toxin family.

Summary:
Kappa-antitoxin-Bcs4a (also named as: BcsTx3) is a voltage-gated potassium channel (Kv1/KCNA) Inhibitor, which is produced by Sea anemone, species Bunodosoma caissarum.

Category: Ion channel toxins