Ergtoxin (also known as CnErg1, CnErgTx1, ErgTx, ErgTx1, γ‑KTx1.1) is a peptide toxin isolated from the venom of the Mexican scorpion Centruroides noxius. It belongs to the γ‑KTx subfamily of short‑chain scorpion toxins that block voltage‑gated potassium (K⁺) channels, with a particular affinity for the human ether‑à‑go‑go‑related gene (hERG) potassium channel (Kv11.1).
Chemical structure
Ergtoxin is a 42‑amino‑acid polypeptide with the primary sequence
DRDSCVDKSRCAKYGYYQECQDCCKNAGHNGGTCMFFKCKCA.
The molecule contains four disulfide bridges (Cys⁵‑Cys²³, Cys¹¹‑Cys³⁴, Cys²⁰‑Cys³⁹, Cys²⁴‑Cys⁴¹) that stabilize a compact fold consisting of a triple‑stranded β‑sheet and one to two α‑helices. Its molecular mass is approximately 4 730 Da. The three‑dimensional structure, determined by NMR spectroscopy, resembles that of the scorpion toxin OSK1 despite limited sequence identity.
Target and pharmacology
Ergtoxin selectively inhibits hERG channels, reducing their potassium conductance by ~50 % at concentrations as low as 10 nM. Binding involves hydrophobic interactions with residues in the channel pore (notably Tyr¹⁴, Phe³⁶, and Phe³⁷). Oxidation of Met³⁵ markedly diminishes affinity, indicating the importance of this residue for proper folding or channel interaction.
Mode of action
The toxin blocks hERG channels by two complementary mechanisms:
- Pore occlusion – the toxin binds to the outer vestibule or the extracellular S5‑S6 pore region, physically obstructing ion flow.
- Gating interference – interaction with the voltage‑sensing domain (S1‑S4) perturbs channel opening and closing kinetics.
Both actions result in reduced repolarizing K⁺ currents in excitable cells.
Toxicity
By inhibiting hERG channels in nerve, endocrine, and cardiac tissues, Ergtoxin can disrupt normal electrical activity. It is more potent than some related scorpion toxins (e.g., CsEKerg1) and has been shown to be toxic in various animal models, although detailed LD₅₀ values are not widely reported.
Potential therapeutic applications
Research has explored Ergtoxin as a pharmacological tool for studying hERG channel physiology and drug‑induced cardiotoxicity. Preliminary investigations suggest that selective hERG blockade may affect proliferation of certain cancer cell lines (e.g., ovarian cancer SK‑OV‑3 cells), raising the possibility of therapeutic exploitation. However, the clinical relevance of these findings remains unconfirmed, and further studies are required to assess safety and efficacy.
References
Information summarized from peer‑reviewed literature and public biochemical databases (e.g., Wikipedia, PubChem, UniProt) describing the isolation, structure, and pharmacology of Ergtoxin.
