Purification and molecular cloning of SE-cephalotoxin, a novel proteinaceous toxin from the posterior salivary gland of cuttlefish Sepia esculenta

Cephalopods contain toxins in their salivary glands, presumably to paralyze prey animals such as crabs and bivalves. Proteinaceous toxins (called cephalotoxins) with crab lethality have previously been purified from three species of octopodiform cephalopods (octopuses) but their detailed properties and primary structures have remained unknown. In this study, salivary glands of six species of decapodiform cephalopods were newly found to be toxic; three species of cuttlefish were lethal only to crabs and three species of squid to both mice and crabs. A proteinaceous toxin (named SE-cephalotoxin) in the salivary gland of cuttlefish Sepia esculenta was soluble only in high-salt solvents. This unique solubility enabled us to purify SE-cephalotoxin by gel filtration HPLC and hydroxyapatite HPLC. SE-cephalotoxin was shown to be a 100 kDa monomeric glycoprotein with an LD50 (against crabs) of 2 μg/kg. Based on the determined partial amino acid sequence, a full-length cDNA (3402 bp) coding for SE-cephalotoxin was cloned by RT-PCR and RACE. The SE-cephalotoxin precursor protein (1052 amino acid residues) is composed of a signal peptide (region 1–21), propeptide (region 22–29) and mature protein (region 30–1052). A database search failed to find any proteins sharing homology with SE-cephalotoxin.