The Spasmodic Peptide Defines a New Conotoxin Superfamily

We purified and characterized a peptide from the venom of Conus textile that makes normal mice assume the phenotype of a well-known mutant, the spasmodic mouse. This “spasmodic” peptide has 27 amino acids, including two γ-carboxyglutamate (Gla) residues. A cDNA clone encoding the precursor for the peptide was identified; a γ-carboxylation recognition signal sequence (γ-CRS) is present in the −1 → −20 region of the peptide precursor. Both the γ-CRS and the position of the Gla residues in the mature toxin are notably different from other Gla-containing conopeptides. The spasmodic peptide has a novel disulfide framework and distinct signal sequence which together define a new P-superfamily of conopeptides. A cDNA encoding another member of the P-superfamily was identified from a different species, Conus gloriamaris.