[The effect of chemical modification on the immunochemical activity of Rm-III neurotoxin from the anemone Radiantus macrodactylus]. / Vliianie khimicheskoi modifikatsii na immunokhimicheskuiu aktivnost' neirotoksina Rm-III iz aktinii Radiantus macrodactylus.

A chemical modification was used for studying the organization of antigenic determinants of neurotoxin Rm-III from the sea anemone Radianthus macrodactylus. Immunochemical experiments were performed using competitive enzyme-linked immunosorbent assay (ELISA) with polyclonal antibodies to Rm-III. The modification affected N-terminal amino group of Gly1, Lys4, Arg13, Trp30 residues, a residue in the Lys46-Lys47-Lys48 sequence, two different residues in the Asp6-Asp7-Glu8 sequence in two samples of the toxin, and two disulphide bonds. Only the modification of the disulphide bonds led to a considerable change in the toxin's affinity to antibodies. The modification of Trp30 resulted in two-fold decrease of the toxin concentration necessary for 50% inhibition of the test-system, whereas upon modification of any other amino acid residue this concentration increased but not more than by 2.2 times. It is suggested that Rm-III sequence lacks individual residues which are of great importance for the toxin's antigenic activity, its conformation being of vital importance for the formation of the toxin's antigenic determinants.

[Modification of the neurotoxin RTX-III from the sea anemone Radianthus macrodactylus]. / Modifikatsiia neirotoksina RTX-III iz morskoi aktinii Radianthus macrodactylus.

The influence of chemical modification on neurotoxin RTX-III toxicity in mice has been studied. The toxicity was not affected by modification of Trp30 residue with 2-hydroxy-5-nitrobenzyl bromide but was diminished by a factor of 100 after reduction of the toxin's two disulfide bonds with 2-mercaptoethanol followed by derivatization with iodoacetamide. Blocking carboxyl groups with [3H]glycine methyl ester in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide led to only a two-fold drop in toxicity in the case of monocarboxylate-modified derivatives and a six-fold decrease for dimodified derivatives. A conception of multipoint attachment of the toxin to sodium channel is discussed.

[A modification of neurotoxin RTX-III from Radianthus macrodactylus actinin with acetic anhydride]. / Modifikatsiia neurotoksina RTX-III iz aktinin Radianthus macrodactylus ukusnym angidridom.

Upon modification of neurotoxin RTX-III at amino groups with [3H]acetic anhydride, four monoacetyl and four diacetyl derivatives have been obtained. Acetylation of the N-terminal amino group led to 12-fold decrease of toxicity in mice. Monoderivatives of the toxin with either Lys or two out of three C-terminal Lys residues modified showed a 2-fold drop in toxicity as compared with the native RTX-III. Diacetylation caused a 30 to 35-fold decrease in toxicity, the N-terminal amino group being modified in all the derivatives. As assessed by circular dichroism method, the modification of amino groups, except for N-terminal one, affected secondary structure of the toxin. The data suggest the N-terminal amino group to be essential for toxicity of RTX-III.