Binding characteristics of a sea anemone toxin from Parasicyonis actinostoloides with crayfish leg nerves
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Abstract:
A sea anemone toxin from Parasicyonis actinostoloides which inhibits the inactivation process of the sodium channel was acylated by using cold or tritium labeled propionyl N-hydroxysuccinimide ester. Acylation changed the isoelectric point of the peptide but did not change the toxicity to the crayfish nerve. Propionyl-toxin bound to leg nerves with Kd of 310 nM and Bmax of 104 pmol/g of wet nerve. The binding affinity and physiological activity of the toxin to crayfish nerves were suppressed with a common dependence on membrane depolarizations induced by elevated external K+ concentrations.
Insights
Sea anemone toxin acylation did not alter its toxicity to crayfish nerves. Modified toxin binding affinity and activity depended on membrane depolarization, indicating specific interactions with sodium channels.
Area of Science:
- Neuroscience
- Biochemistry
- Marine Biology
Background:
- Sea anemone toxins are crucial tools for studying ion channel function.
- Parasicyonis actinostoloides toxin inhibits sodium channel inactivation, impacting nerve impulse transmission.
Purpose of the Study:
- To investigate the effects of acylation on the properties of a sea anemone toxin.
- To determine how acylation influences the toxin's binding affinity and physiological activity on crayfish nerves.
Main Methods:
- Acylation of sea anemone toxin using propionyl N-hydroxysuccinimide ester (cold or tritium labeled).
- Isoelectric point determination of the acylated toxin.
- Toxicity assays on crayfish nerve preparations.
- Radioligand binding studies to quantify toxin-nerve interactions (Kd and Bmax).
- Assessment of toxin activity under varying external potassium concentrations to induce membrane depolarization.
Main Results:
- Acylation altered the toxin's isoelectric point but preserved its toxicity to crayfish nerves.
- Propionyl-toxin exhibited a binding affinity (Kd) of 310 nM and a maximum binding capacity (Bmax) of 104 pmol/g wet nerve.
- Both binding affinity and physiological activity of the toxin were diminished by membrane depolarization.
Conclusions:
- Acylation is a viable method for modifying sea anemone toxins without compromising their core neurotoxic activity.
- The toxin's interaction with crayfish nerves is sensitive to membrane potential, suggesting a voltage-dependent binding mechanism.
- These findings enhance our understanding of sodium channel modulation by marine toxins.