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Abstract
Sea anemones produce proteinaceous toxins for predation and defense, including peptide toxins that act on a large variety of ion channels of pharmacological and biomedical interest. Phymanthus crucifer is commonly found in the Caribbean Sea; however, the chemical structure and biological activity of its toxins remain unknown, with the exception of PhcrTx1, an acid-sensing ion channel (ASIC) inhibitor. Therefore, in the present work, we focused on the isolation and characterization of new P. crucifer toxins by chromatographic fractionation, followed by a toxicity screening on crabs, an evaluation of ion channels, and sequence analysis. Five groups of toxic chromatographic fractions were found, and a new paralyzing toxin was purified and named PhcrTx2. The toxin inhibited glutamate-gated currents in snail neurons (maximum inhibition of 35%, IC50 4.7 µM), and displayed little or no influence on voltage-sensitive sodium/potassium channels in snail and rat dorsal root ganglion (DRG) neurons, nor on a variety of cloned voltage-gated ion channels. The toxin sequence was fully elucidated by Edman degradation. PhcrTx2 is a new β-defensin-fold peptide that shares a sequence similarity to type 3 potassium channels toxins. However, its low activity on the evaluated ion channels suggests that its molecular target remains unknown. PhcrTx2 is the first known paralyzing toxin in the family Phymanthidae.
Highlights
Sea anemones produce a large number of proteinaceous toxins for preying on small crustaceans and fishes, and for defense against predators [1,2]
Due to the large number of crabs needed for determining the ED50 or LD50 of every toxic chromatographic fraction, and the unavailability of such a number, we focused our efforts on characterizing the toxicity of only pure compounds submitted to both chemical and pharmacological characterization
Three crabs were used per sample at the dose of 2000 μg/kg for biological activity screening after every chromatographic step, and only those fractions that paralyzed all of the crabs were selected for further purification/analysis
Summary
Sea anemones produce a large number of proteinaceous toxins for preying on small crustaceans and fishes, and for defense against predators [1,2]. These toxins comprise mainly cytolysins, protease inhibitors, and a large variety of peptides acting on sodium or potassium channels; more recently, acid-sensing ion channel (ASIC) and TRPV1 channels toxins have been discovered [1]. These peptide toxins are valuable pharmacological tools for studying the structure and function of ion channels [2], which are involved in many physiological and pathological processes. Many new peptide toxins or even new families of peptide toxins are expected to be discovered from these organisms
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