Inactivation of a serotonin-gated ion channel by a polypeptide toxin from marine snails.

The venom of predatory marine snails is a rich source of natural products that act on specific receptors and ion channels within the mammalian nervous system. A 41-amino acid peptide, final sigma-conotoxin GVIIIA, was purified on the basis of its ability to inactivate the 5-HT3 receptor, an excitatory serotonin-gated ion channel. final sigma-Conotoxin contains a brominated tryptophan residue, which may be important for peptide activity because the endogenous ligand for the 5-HT3 receptor is a hydroxylated derivative of tryptophan. final sigma-Conotoxin inactivates the 5-HT3 receptor through competitive antagonism and is a highly selective inhibitor of this receptor. Serotonin receptors can now be included among the molecular targets of natural polypeptide neurotoxins.