Purification, sequence, and pharmacological properties of sea anemone toxins from Radianthus paumotensis. A new class of sea anemone toxins acting on the sodium channel

Abstract

Four new toxins have been isolated from the sea anemone Radianthus paumotensis: RpI, RpII, RpIII, and RpIV. They are polypeptides comprised of 48 or 49 amino acids; the sequence of RpII has been determined. Toxicities of these toxins in mice and crabs are similar to those of the other known sea anemone toxins, but they fall into a different immunochemically defined class. The sequence of RpII shows close similarities with the N-terminal end (up to residue 20) of the previously sequenced long sea anemone toxins, but most of the remaining part of the molecule is completely different. Like the other sea anemone toxins, Radianthus toxins are active on sodium channels; they slow down the inactivation process. Through their Na+ channel action, Radianthus toxins stimulate Na+ influx into tetrodotoxin-sensitive neuroblastoma cells and tetrodotoxin-resistant rat skeletal myoblasts. The efficiency of the toxins is similar in the two cellular systems. In that respect, Radianthus toxins behave much more like scorpion neurotoxins than sea anemone toxins from Anemonia sulcata or Anthopleura xanthogrammica. In binding experiments to synaptosomal Na+ channels, Radianthus toxins compete with toxin II from the scorpion Androctonus australis but not with toxins II and V from Anemonia sulcata.

Sea anemone venom as a source of insecticidal peptides acting on voltage-gated Na+ channels

“…Presently, some 50 toxins active on Na v channels have been identified. Most of these proteins were first characterized as cardiac stimulants and neurotoxins SanchezRodriguez and Cruz-Vazquez, 2006;Schweitz et al, 1985). In 1991, Norton proposed a classification of sea anemone polypeptides dividing this group into three classes: two made up of molecules containing 46-49 amino acid residues including Type 1 (genera Anthopleura and Anemonia belonging to family Actiniidae) and Type 2 (genera Radianthus and Stichodactyla belonging to family Stichodactylidae) and one comprising shorter polypeptides containing 27-32 residues (Type 3; e.g.…”

“…Due to the fact that the toxin halcurin possesses structural features of both Type 1 and 2 toxins and is present in the primitive Halcurias sp., both Type 1 and 2 toxins are considered to have evolved from the same ancestral gene (Ishida et al, 1997). Nevertheless, they are immunologically distinguishable from each other because there is no antigenic crossreactivity between both types of toxins (Schweitz et al, 1985;Norton, 1991). Recently, three peptide toxins (Am I-III) with acute toxicity in crabs were isolated from the sea anemone Anthopleura maculata (Honma et al, 2005).…”

Bioactive peptides from marine sources: pharmacological properties and isolation procedures

“…A very similar procedure was described for the isolation of toxins from the sea anemone Radianthus paumotensis [131].…”

The amino acid sequence of toxin RpIII from the sea anemone, Radianthus paumotensis

“…Its toxicity toward mice is much greater than that of Rpn [1]; however, only Rpu has been described at the level of primary and secondary structure [2]. Its amino acid sequence is homologous with toxins of two other sea anemones, Anthopleura xanthogramrnica [31 and Anemonia sulcata [4- Pooled peptides V8-1, V8-3, V8-5 and V8-7 were analyzed in detail ( fig.l).…”