Sea anemone polypeptides

Amino acid sequences of eleven homologous sea anemone polypeptides have been elucidated. All possess three disulfide bonds. The six half-cysteine residues always occur in the same positions (7,8). Initial studies concerning the toxin secondary and tertiary structures relied upon circular dichroism, laser Raman, and, to a lesser extent, fluorescence spectral measurements (15—18). The circular dichroism spectra of the four toxins so far examined are essentially superimpos-able and thus indicate a common secondary structure. The only peak observed, a negative ellipticity at 203 nm, largely results from a non-regular ("random")... 

KEM ET AL. Sea Anemone Polypeptide Toxins Affecting Sodium Channels... 

Amino acid sequences of Type 1 sea anemone polypeptides. The residue numbering system is based on the sequences of AP-A and AP-B. Literature references are from Norton [24], except in the case of recently published sequences for Be III [25], Bg II and Bg III... 

Apart from the long sea anemone polypeptides that are the main focus of our interest, there are two other classes of anemone polypeptides that bind at or near... 

Romey, G., J.F. Renaud, M. Fosset, and M. Lazdunski Pharmacological Properties of the Interaction of a Sea Anemone Polypeptide Toxin with Cardiac Cells in Culture. J. Pharmacol. Exp. Ther. 213, 607 (1980). 

Over 40 different types of polypeptide toxins have been found in marine animals (i). Many of these toxins are exquisitely selective in their actions, affecting a single process or receptor at minute concentrations. So far the sea anemone and gastropod Conus) toxins have attracted the most attention as molecular probes of ion channels. In this chapter, we discuss several approaches which are being used to investigate, at the molecular level, the interactions of the sea anemone neurotoxic polypeptides with sodium channels. 

Coelenterates and Echinoderms. Coelenterate and echinoderm toxins range from small molecular weight amines, to sterols, to large complex carbohydrate chains, to proteins of over 100,000 daltons. Molecular size sometimes reflects taxonomy, e.g., sea anemones (Actiniaria) all possess toxic polypeptides varying in size from 3,000 to 10,000 daltons while jellyfish contain toxic proteins (ca. 100,000 daltons). Carotenoids have been isolated from Asterias species (starfish), Echinoidea (sea urchins), and Anthozoans such as Actiniaria (sea anemones) and the corals. These are sometimes complexed with sterols (J5). 

Both sea anemones (order Actinaria) and stony corals (order Scleractinia) belong to the class Zoantharia and sub-phylum Anthozoa and therefore it is not surprising that toxic polypeptides of 12,000 and 30,000 daltons have also been isolate from Goniopora corals. 

Apart from AP-A, the best characterized of these polypeptides with respect to its biological activity is Anemonia sulcata toxin II (ATX II) [19]. This molecule is also cardioactive [28], as would be expected from its similarity to AP-A. Renaud et al. [29] have compared the activities of a number of sea anemone and scorpion toxins on isolated rat atria and found that anthopleurin-B (AP-B, also known as Ax II) had the highest potency and the greatest margin between the concentrations necessary for maximal inotropic activity and for provoking arrhythmias (0.3 versus 10 n . It was also found that sodium channels of rat cardiac cells in culture, which have a low affinity for tetrodotoxin (TTX), have a particularly high affinity for Type 1 anemone toxins [29], whereas Type 2 toxins [30] and scorpion toxins [31] had similar affinities for TTX-sensitive and TTX-insensitive channels in rat neuroblastoma cells and skeletal myotubes, respectively. 

Scriabine A, Van Arman CG, Morgan G, Morris AA, Bennett CD, Bohidar NR. Cardiotonic effects of anthopleurin-A, a polypeptide from a sea anemone. J Cardiovasc Pharmacol 1979 1 571-583. 

Certain species of sea anemones produce basic polypeptide toxins of molecular weights ranging from 2500 to 5000 daltons. They cause persistant activation of sodium channels and lead to paralysis. This is very helpful to the sea anemone is harvesting its prey. 

Bacteria, protozoa, and venomous animals synthesize numerous toxins that are used to kill their prey or to defend themselves. Sea anemones, jellyfish, cone snails, insects, spiders, scorpions, and snakes all make potent and highly specific neurotoxins. Plants form a host of alkaloids and other specialized products, some of which are specifically neurotoxic and able to deter predators. More than 500 species of marine cone snails of the genus Conus synthesize a vast array of polypeptide toxins (conotoxins), 487-489 some with unusual posttranslational modifications.490 491 The slow-moving snails are voracious predators that use their toxins, which they inject with a disposible harpoonlike tooth,492 to paralyze fish, molluscs, or worms.493... 

Produced by the Wax Rose sea anemone (Ammonia sulcata). 47 amino acid basic polypeptide, MW 4770. Prolongs opening of voltage-gated Na+ channels. Reports of human deaths due to exposure in the Mediterranean. 

Schwann cells of squid axons (J. Villegas et al. 1976), ghoma cells (Reiser and Hamprecht 1983), and other preparations. In most of these preparations certain polypeptide toxins (e.g., from sea anemones or scorpions) act synergistically, as in spiking cells, but in contrast are often less sensitive to tetrodotoxin (equilibrium constant of inhibition fTi=l iM in C9 cells Romey et al. 1979). 

A species of sea anemone, Condylactis gigantia, produces a polypeptide toxin of unknown structure and molecular weight of around 13 000 which affects the kinetics of some sodium channels. In the giant axon of the crayfish (but not of the squid) condylactis toxin prolongs the falling phase of the action potential by delaying the inactivation of the transient sodium current, without pronounced effect on the steady-state potassium current [136]. 

The marine flora and animal world are a rich source of biologically active compounds. A large number of sometimes highly toxic metabolites has been isolated inter alia from protozoans, sponges, coelenter-ates, echinoderms, molluscs, nemertines, sea snakes, and fishes (1-4) and the great interest in these chemically varied compounds has resulted in extensive publications (5-13), Among the best known of the toxic substances are tetrodotoxin, saxitoxin, and the polypeptides from sea anemones, but they will not be the main subject of this report. 

Bernheimer and Avigad 285) examined seven kinds of sea anemones for the presence of cytolytic toxins. Tealia lofotensis and Epiactis prolifera yielded especially powerful preparations, whereas the extracts of the other species showed weaker cytolytic activity. Natural-abundance NMR studies have been performed on toxic polypeptides. These studies of APA and ATX II indicated that their overall conformation was very similar 286). 

Mebs, D., and E. Gebauer Isolation of Proteinase Inhibitory, Toxic and Hemolytic Polypeptides from a Sea Anemone, Stoichactis sp. Toxicon 18, 97 (1980). 

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