# Cangitoxin

**Cangitoxin** (CGTX, also abbreviated CGX) is a neurotoxic peptide of 48 amino acid residues and 4958 Da produced by the sea anemone *Bunodosoma cangicum*, a common anemone found along the Brazilian seashores.<sup>[1](https://www.sciencedirect.com/science/article/pii/S0041010104004404)</sup> It belongs to the type 1 family of sea anemone toxins that act on voltage-gated sodium (Na\(_{\mathrm{V}}\)) channels, and it is notable as one of the few anemone toxins for which strong in vivo epileptogenic effects in mammals have been demonstrated.<sup>[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC3663410/)</sup>

| Key fact | Detail |
|---|---|
| Source organism | *Bunodosoma cangicum*, family Actiniidae, Brazilian coast<sup>[1](https://www.sciencedirect.com/science/article/pii/S0041010104004404)</sup> |
| Size | 48 amino acid residues, 4958 Da; sequence GVACRCDSDGPTVRGNSLSGTLWLTGGCPSGWHNCRGSGPFIGYCCKK<sup>[1](https://www.sciencedirect.com/science/article/pii/S0041010104004404)</sup> |
| Structural class | Type 1 sea anemone Na\(_{\mathrm{V}}\) channel toxin; contains all 11 conserved and 5 conservatively substituted residues of the type 1 and 2 toxin sequences<sup>[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC3663410/)</sup><sup> • </sup><sup>[1](https://www.sciencedirect.com/science/article/pii/S0041010104004404)</sup> |
| Mechanism | Binds neurotoxin receptor site 3 on Na\(_{\mathrm{V}}\) channels and delays channel inactivation<sup>[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC3663410/)</sup> |
| In vivo effect | Intrahippocampal injection in rats produced status epilepticus lasting 8 to 12 hours, resembling the acute pilocarpine model of epilepsy<sup>[1](https://www.sciencedirect.com/science/article/pii/S0041010104004404)</sup> |
| Isoforms | CGTX-II (Asn16 to Asp substitution) and CGTX-III (Arg14 to His minor isoform), purified from venom in 2008<sup>[3](https://pubmed.ncbi.nlm.nih.gov/18342901/)</sup> |
| Subtype selectivity | CGTX-II preferentially targets Na\(_{\mathrm{V}}\)1.5, then Na\(_{\mathrm{V}}\)1.6 and Na\(_{\mathrm{V}}\)1.1<sup>[4](https://www.sciencedirect.com/science/article/pii/S019697811100283X)</sup> |
| Database entries | CGX P82803; CGTX-II P0C7P9; CGTX-III P0C7Q0<sup>[5](https://www.researchgate.net/publication/10918506_An_epidermal_growth_factor-like_toxin_and_two_sodium_channel_toxins_from_the_sea_anemone_Stichodactyla_gigantea)</sup> |

## Structural family

[Sea anemone](https://www.edgepedia.org/sea-anemone) sodium channel toxins are polypeptides of about 5 kDa, and more than 50 had been isolated or cloned from a variety of species by the mid-2000s.<sup>[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC3663410/)</sup> Norton's classification divides them by amino acid sequence: type 1 and type 2 toxins are polypeptides of 46 to 49 amino acids, while the shorter type 3 peptides contain 27 to 32 residues.<sup>[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC3663410/)</sup> Toxins from the Actiniidae family, which includes *Bunodosoma*, are type 1.<sup>[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC3663410/)</sup>

Cangitoxin fits this family closely. Its sequence includes every one of the 11 invariant residues, as well as the 5 replaced conservatively, among the type 1 and type 2 sea anemone peptide sequences that specifically target voltage-sensitive sodium channels.<sup>[1](https://www.sciencedirect.com/science/article/pii/S0041010104004404)</sup> It also shares 6 identities (Asp9, Arg14, Asn16, Leu18, Trp33, and Lys48) and 1 homology (Arg36) with the 8 residues of the pharmacophore of Anthopleurin B (ApB) from *Anthopleura xanthogrammica* that are essential for interaction with mammalian sodium channels.<sup>[1](https://www.sciencedirect.com/science/article/pii/S0041010104004404)</sup> Molecular modeling of CGX reproduced the main structural features of known anemone toxins, three disulfide bridges and antiparallel beta-sheet strands.<sup>[6](https://www.researchgate.net/publication/229325403_The_structure_of_a_new_sea_anemone_toxin_A_molecular_modeling_study_of_cangitoxin)</sup>

## Mechanism of action

Anemone Na\(_{\mathrm{V}}\) channel toxins were initially characterized as cardiac stimulants and neurotoxins, and were subsequently shown to interact with neurotoxin receptor site 3 of Na\(_{\mathrm{V}}\) channels, delaying channel inactivation so that the open state is prolonged during depolarization.<sup>[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC3663410/)</sup> Receptor site 3 includes the extracellular loop between transmembrane segments S3 and S4 in domain IV of the channel, and is also a receptor for alpha-scorpion toxins, which share no sequence homology with the anemone toxins.<sup>[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC3663410/)</sup> [Sodium channel](https://www.edgepedia.org/sodium-channel) toxins of this kind are used as tools for dissecting the biophysical properties of inactivation in voltage-gated sodium channels.<sup>[3](https://pubmed.ncbi.nlm.nih.gov/18342901/)</sup>

## Epileptogenic activity

**In vivo effects.** Most studies of type 1 anemone toxins had been in vitro; cangitoxin is among the few demonstrated to produce convulsant effects in mammals.<sup>[1](https://www.sciencedirect.com/science/article/pii/S0041010104004404)</sup> When CGX was injected into the hippocampus of freely moving rats, it produced a series of behavioral changes unfolding in order, bouts of akinesia that alternated with facial automatisms and head tremor, plus salivation, rearing, jumping, barrel-rolling, wet dog shakes, and clonic movements of the forelimbs, after which seizure periods set in and progressed into status epilepticus lasting 8 to 12 hours, resembling the acute phase of the pilocarpine model of epilepsy.<sup>[1](https://www.sciencedirect.com/science/article/pii/S0041010104004404)</sup> The authors proposed CGX as a tool for developing a new experimental model of status epilepticus for studying epilepsy and testing antiepileptic drugs.<sup>[1](https://www.sciencedirect.com/science/article/pii/S0041010104004404)</sup> Reviews of cnidarian toxins cite cangitoxin as evidence for in vivo epileptogenic effects of sea anemone toxins.<sup>[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC3663410/)</sup>

## Isoforms and channel selectivity

The original isolation procedures for cangitoxin from *B. cangicum* secretions were controversial and could lead to incorrect information, so Zaharenko and colleagues developed a simple two-step chromatographic procedure to obtain a CGTX analog directly from the venom.<sup>[3](https://pubmed.ncbi.nlm.nih.gov/18342901/)</sup> The main peptide carried an N16D substitution and an inseparable minor isoform carried an R14H substitution; these were named CGTX-II and CGTX-III, and their effects on Na\(_{\mathrm{V}}\)1.1 channels were demonstrated in patch clamp experiments.<sup>[3](https://pubmed.ncbi.nlm.nih.gov/18342901/)</sup>

Screening of CGTX-II and the related toxin delta-AITX-Bcg1a, also from *B. cangicum*, across mammalian Na\(_{\mathrm{V}}\)1.1 to 1.7 isoforms expressed in cell lines showed preferential targets of Na\(_{\mathrm{V}}\)1.5, then 1.6, then 1.1, with the two toxins producing different shifts in activation and inactivation Boltzmann curves on Na\(_{\mathrm{V}}\)1.1 and 1.6.<sup>[4](https://www.sciencedirect.com/science/article/pii/S019697811100283X)</sup> Cangitoxin-II is reported as most potent at Na\(_{\mathrm{V}}\)1.5 and Na\(_{\mathrm{V}}\)1.6, with little activity at Na\(_{\mathrm{V}}\)1.1, 1.2, 1.3, 1.4, and 1.7 at 50 nM.<sup>[7](https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/sea-anemone-toxin)</sup>

## Context in the toxin repertoire

Cangitoxins are listed among the type 1 sodium channel toxins that define the most common structural group of [sea anemone neurotoxins](https://www.edgepedia.org/sea-anemone-neurotoxin), alongside ATX toxins from *Anemonia sulcata*, the anthopleurins from *Anthopleura xanthogrammica*, BcIII from *Bunodosoma caissarum*, and BgII and BgIII from *Bunodosoma granulifera*.<sup>[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC9863223/)</sup> The venom of *B. cangicum* itself contains additional bioactive components, including a cytolytic fraction that hemolyses mouse erythrocytes and a neuroactive fraction that prolongs compound action potentials in crab nerves, and the whole venom selectively blocks calcium-dependent potassium currents in crayfish muscle.<sup>[9](https://pubmed.ncbi.nlm.nih.gov/11449308/)</sup><sup> • </sup><sup>[10](https://pubmed.ncbi.nlm.nih.gov/8568940/)</sup>

## References

1. [Cunha, R.B. et al. (2005). Primary structure, behavioral and electroencephalographic effects of an epileptogenic peptide from the sea anemone *Bunodosoma cangicum*. Toxicon 45(2): 207-217.](https://www.sciencedirect.com/science/article/pii/S0041010104004404)
2. [Messerli, S.M. & Greenberg, R.M. (2006). Cnidarian Toxins Acting on Voltage-Gated Ion Channels. Marine Drugs 4(3): 70-81.](https://pmc.ncbi.nlm.nih.gov/articles/PMC3663410/)
3. [Zaharenko, A.J. et al. (2008). Revisiting cangitoxin, a sea anemone peptide: purification and characterization of cangitoxins II and III from the venom of *Bunodosoma cangicum*. Toxicon 51(7): 1303-1307.](https://pubmed.ncbi.nlm.nih.gov/18342901/)
4. [Characterization of selectivity and pharmacophores of type 1 sea anemone toxins by screening seven Nav sodium channel isoforms. Peptides (2011).](https://www.sciencedirect.com/science/article/pii/S019697811100283X)
5. [An epidermal growth factor-like toxin and two sodium channel toxins from the sea anemone *Stichodactyla gigantea* (accession listing for CGTX, CGTX-II, CGTX-III).](https://www.researchgate.net/publication/10918506_An_epidermal_growth_factor-like_toxin_and_two_sodium_channel_toxins_from_the_sea_anemone_Stichodactyla_gigantea)
6. [Treptow, W. et al. (2003). The structure of a new sea anemone toxin: A molecular modeling study of cangitoxin. Journal of Molecular Structure: THEOCHEM 624: 87-95.](https://www.researchgate.net/publication/229325403_The_structure_of_a_new_sea_anemone_toxin_A_molecular_modeling_study_of_cangitoxin)
7. [Sea Anemone Toxin, ScienceDirect Topics overview.](https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/sea-anemone-toxin)
8. [The Sea Anemone Neurotoxins Modulating Sodium Channels: An Insight at Structure and Functional Activity after Four Decades of Investigation. Marine Drugs (2023).](https://pmc.ncbi.nlm.nih.gov/articles/PMC9863223/)
9. [Identification of hemolytic and neuroactive fractions in the venom of the sea anemone *Bunodosoma cangicum*. Brazilian Journal of Medical and Biological Research (2001).](https://pubmed.ncbi.nlm.nih.gov/11449308/)
10. [Selective block of Ca(2+)-dependent K+ current in crayfish neuromuscular system and chromaffin cells by sea anemone *Bunodosoma cangicum* venom (1995).](https://pubmed.ncbi.nlm.nih.gov/8568940/)

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*Topic: Encyclopedia › Life and health › Animals › Invertebrates › Other invertebrate lineages › Cnidarians and ctenophores › Anthozoans › Hexacorallia › Sea anemones (Actiniaria) › Anemone toxins and venoms*

*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*

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