Identification and molecular diversity of T-superfamily conotoxins from Conus lividus and Conus litteratus

The T-superfamily conotoxins comprise a large and diverse group of biologically active peptides and are widely distributed in venom ducts of all major feeding types of Conus. Six novel T-superfamily peptides from the two worm-hunting cone snail species of Conus lividus andConus. litteratus native to Hainan were identified and determined to share a common signal sequence as well as a conserved arrangement of cysteine residues (CC-CC). The predicted mature peptides consist of 11-15 amino acids only. Phylogenetic analyses of new conotoxins from C. lividus andC. litteratus in present study and published homologue T-superfamily sequences from the other Conus species was systematically performed. Phylogenetic trees, residue substitutions to view evolutionary relationships of the precursors' signal, propeptide, and mature toxin regions were explored, as well as residue frequency component and cystine codon usage. Percent divergence of the amino acid sequences of the signal-region exhibited high conservation, whereas the sequences of the mature peptides ranged from high similarity to high divergence between inter- and intro-species. Notably, diversity of pro-peptide region was also high with intermediate percent divergence between that observed in signal and toxin-regions. Consensus hydrophobic residues Leu, Val, Ala, Ile and Pro of signal regions were abundant, whereas among propeptides, basic residues Arg and Lys and acidic residue Asp, addition of hydrophilic residues Thr and Ser were abundant. Residue frequency components were hypervariable in mature toxin region except for highly conservative cystine frame residues. The T-superfamily conotoxins have been previously found mainly in piscivorous and molluscivorous cone snails. The newly identified six T-superfamily peptides described in this investigation exemplify the first to be found from vermivorousC. lividus andC. litteratus. The elucidated cDNAs of the six toxins will facilitate a better understanding of the relationship between structure and function as well as provide a framework for their further research and development.