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8.B.14 The Sea Anemone Peptide Toxin, Class 1 (BgK) Family

Peptide cnidarian toxin families, including peptide neurotoxins (voltage-gated Na+ and K+ channel-targeting toxins: NaTxs and KTxs, respectively, pore-forming toxins (actinoporins, aerolysin-related toxins, and jellyfish toxins), and the newly discovered small cysteine-rich peptides (SCRiPs). These have been isolated from several species of sea anemones and shown to block currents through various potassium ion channels, particularly in excitable cells. The toxins can be grouped into four structural classes: type 1 with 35-37 amino acid residues and three disulphide bridges; type 2 with 58-59 residues and three disulphide bridges; type 3 with 41-42 residues and three disulphide bridges; and type 4 with 28 residues and two disulphide bridges (Castañeda & Harvey, 2009). Examples from the first class are BgK from Bunodosoma granulifera, ShK from Stichodactyla helianthus and AsKS (or kaliseptine) from Anemonia sulcata (now A. viridis). These interfere with binding of radiolabelled dendrotoxin to synaptosomal membranes and block currents through channels with various Kv1 subunits and also intermediate conductance K(Ca) channels. Toxins in the second class are homologous to Kunitz-type inhibitors of serine proteases; these toxins include kalicludines (AsKC 1-3) from A. sulcata and SHTXIII from S. haddoni; they block Kv1.2 channels. The third structural group (8.B.11) includes proteins from A. sulcata and Anthropleura elegantissima. Their pharmacological specificities differs: BDS-I and -II toxins block currents involving Kv3 subunits while APETx1 blocks ERG channels. The fourth group comprises the SHTX I and II toxins from S. haddoni. Their channel blocking specificity is not yet known, but they displace dendrotoxin binding from synaptosomal membranes (Castañeda & Harvey, 2009).

References associated with 8.B.14 family:

Braud, S., P. Belin, J. Dassa, L. Pardo, G. Mourier, A. Caruana, B.T. Priest, P. Dulski, M.L. Garcia, A. Ménez, J.C. Boulain, and S. Gasparini. (2004). BgK, a disulfide-containing sea anemone toxin blocking K+ channels, can be produced in Escherichia coli cytoplasm as a functional tagged protein. Protein Expr Purif 38: 69-78. 15477084
Jouiaei, M., K. Sunagar, A. Federman Gross, H. Scheib, P.F. Alewood, Y. Moran, and B.G. Fry. (2015). Evolution of an ancient venom: recognition of a novel family of cnidarian toxins and the common evolutionary origin of sodium and potassium neurotoxins in sea anemone. Mol Biol Evol 32: 1598-1610. 25757852
Minagawa, S., M. Ishida, Y. Nagashima, and K. Shiomi. (1998). Primary structure of a potassium channel toxin from the sea anemone Actinia equina. FEBS Lett. 427: 149-151. 9613617
Rangaraju, S., K.K. Khoo, Z.P. Feng, G. Crossley, D. Nugent, I. Khaytin, V. Chi, C. Pham, P. Calabresi, M.W. Pennington, R.S. Norton, and K.G. Chandy. (2010). Potassium channel modulation by a toxin domain in matrix metalloprotease 23. J. Biol. Chem. 285: 9124-9136. 19965868