The T-superfamily of Conotoxins

We report the discovery and initial characterization of the T-superfamily of conotoxins. Eight different T-superfamily peptides from five Conusspecies were identified; they share a consensus signal sequence, and a conserved arrangement of cysteine residues (- -CC- -CC-). T-superfamily peptides were found expressed in venom ducts of all major feeding types of Conus; the results suggest that the T-superfamily will be a large and diverse group of peptides, widely distributed in the 500 different Conusspecies. These peptides are likely to be functionally diverse; although the peptides are small (11–17 amino acids), their sequences are strikingly divergent, with different peptides of the superfamily exhibiting varying extents of post-translational modification. Of the three peptides tested for in vivo biological activity, only one was active on mice but all three had effects on fish. The peptides that have been extensively characterized are as follows: p5a, GCCPKQMRCCTL*; tx5a, γCCγDGW+CCT§AAO; and au5a, FCCPFIRYCCW (where γ = γ-carboxyglutamate, W+ = bromotryptophan, O = hydroxyproline, T§ = glycosylated threonine, and * = COOH-terminal amidation). We also demonstrate that the precursor of tx5a contains a functional γ-carboxylation recognition signal in the −1 to −20 propeptide region, consistent with the presence of γ-carboxyglutamate residues in this peptide.