Importance of Two Arginine Residues in Lapemis Postsynaptic Neurotoxins: Re-examination using Acetylcholine Receptor-neurotoxin Complex Instead of Free Toxin

Abstract

The role of the three arginine residues in Lapemis neurotoxin has been re-examined using an acetylcholine receptor-toxin complex. The receptor-bound neurotoxin was treated with phenylglyoxal to modify available arginine residues. The positions of the modified arginine residues were then identified from the amino acid sequences of proteolytically digested fragments of the detached neurotoxin. The result was compared with the result from modification of the free Lapemis toxin (unbound). Arg-31 and Arg-34 were not modified when Lapemis toxin was bound to receptor although they were modified when the toxin was not bound to receptor. It was concluded that Arg-31 and Arg-34 residues are involved in the toxin-receptor interaction.