Gonyautoxin II
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Summary
Gonyautoxin II (GTX II) is a naturally occurring paralytic shellfish toxin produced by certain dinoflagellates and accumulated in marine organisms such as crabs. It belongs to the bis‑guanidinium family of toxins that potently block voltage‑gated sodium channels, leading to rapid neurotoxic effects. In research, GTX II is employed as a high‑affinity tool to study sodium channel function and the mechanisms of paralytic shellfish poisoning.
Mechanism of Action
GTX II binds to the extracellular pore region of eukaryotic voltage‑gated Na⁺ channels (e.g., NaV1.4), occluding ion flow and preventing depolarization. The toxin’s guanidinium groups interact electrostatically with the channel, while a sulfated C‑11 moiety contributes to binding affinity without markedly altering potency. This blockade halts action‑potential propagation, producing paralysis at nanomolar concentrations.
What the Research Shows
Structural work in the 1970s identified the stereochemistry of GTX II and related toxins. Recent synthetic chemistry has enabled access to GTX II and analogues, revealing nanomolar IC₅₀ values against rat NaV1.4 comparable to other PSP toxins. Toxicological assays using mouse neuroblastoma cells showed GTX II has roughly half the relative toxicity of saxitoxin (≈48 % of FDA reference). Field studies reported GTX II in crabs from Fiji, often at low (<5 %) levels alongside other paralytic toxins. Electrophysiological recordings on squid giant axons confirmed GTX II blocks Na⁺ channels with a potency of 0.20 relative to saxitoxin, highlighting the importance of hydrogen‑bonding at C‑12 for receptor interaction.
Reported Benefits
GTX II serves as a valuable pharmacological probe for dissecting Na⁺‑channel structure‑function relationships, aiding drug discovery targeting channelopathies. Its high specificity and potency allow precise modulation of neuronal excitability in vitro, facilitating studies of toxin binding sites and channel kinetics.
Limitations of the Evidence
The extreme toxicity of GTX II precludes therapeutic use; its application is limited to controlled laboratory settings. Data are confined to in vitro and animal models, with no clinical trials. Comparative potency varies across channel isoforms, and synthesis remains complex, restricting widespread availability.
Safety Considerations
GTX II is a potent neurotoxin lethal to mice and toxic to cultured neuroblastoma cells at low nanomolar concentrations. Exposure can cause rapid paralysis due to sodium‑channel blockade. Laboratory handling requires strict containment, protective equipment, and disposal procedures to avoid accidental ingestion, inhalation, or skin contact.
How It Is Administered
In research, GTX II is typically prepared as an aqueous solution or diluted in appropriate buffer for in vitro assays. It is not formulated for human administration and is used only under biosafety level‑2 or higher conditions in specialized laboratories.
Routes of Administration
No administration routes recorded yet.
Goals & Uses
No goal associations recorded yet.
Contraindications
No contraindications recorded yet.
Adverse Effects
No adverse effects recorded yet.
Drug Interactions
No drug interactions recorded yet.
Population Constraints
No population constraints recorded yet.
Regulatory Status
No regulatory status recorded yet.
Evidence & Sources
- Journal ArticleLowWalker JR, et al.2019-01-01T00:00:00.000000Z
- Journal ArticleLowShimizu Y, et al.1976-01-01T00:00:00.000000Z
- Journal ArticleLowJellett JF, Stewart JE, Laycock MV1995-01-01T00:00:00.000000Z
- Journal ArticleLowKao CY, et al.1985-01-01T00:00:00.000000Z
- Journal ArticleLowRaj U, et al.1983-01-01T00:00:00.000000Z
Frequently Asked Questions
What natural sources contain gonyautoxin II?
GTX II is produced by marine dinoflagellates such as Gonyaulax tamarensis and accumulates in filter‑feeding organisms, including certain crabs (e.g., Atergatis floridus) and shellfish that cause paralytic shellfish poisoning.
How does gonyautoxin II differ from saxitoxin?
Both share a bis‑guanidinium core, but GTX II possesses a sulfated group at carbon‑11, giving it slightly lower potency (≈0.20‑0.42 relative to saxitoxin) while retaining the same sodium‑channel blocking mechanism.
Can gonyautoxin II be used as a medication?
No. Its high toxicity and lack of clinical data restrict its use to experimental settings as a research tool; it is not approved for any therapeutic indication.
What precautions are needed when working with gonyautoxin II?
Researchers must employ biosafety level‑2 practices, wear gloves and eye protection, work in a fume hood, and follow strict decontamination and waste‑disposal protocols to prevent accidental exposure.
Why is gonyautoxin II useful for studying sodium channels?
Its nanomolar affinity and selective blockade of voltage‑gated Na⁺ channels make GTX II an ideal probe for mapping channel binding sites, assessing channel isoform sensitivity, and testing the effects of mutations on toxin interaction.
What is Gonyautoxin II?
Gonyautoxin II (GTX II) is a naturally occurring paralytic shellfish toxin produced by certain dinoflagellates and accumulated in marine organisms such as crabs. It belongs to the bis‑guanidinium family of toxins that potently block voltage‑gated sodium channels, leading to rapid neurotoxic effects. In research, GTX II is employed as a high‑affinity tool to study sodium channel function and the mechanisms of paralytic shellfish poisoning.