Direct cDNA cloning of novel conotoxins of the T-superfamily from Conus textile.

The T-superfamily is a large and diverse group of peptides, widely distributed in venom ducts of all major feeding types of Conus. These peptides are likely to be functionally diverse. A directed PCR-based approach using primers based on the conserved signal sequence was applied to investigate new conotoxins of the T-superfamily from Conus textile native to Hainan. Using RT-PCR and 3'-RACE, four novel cDNA sequences encoding precursor peptides were identified in C. textile. They share a common T-superfamily cysteine pattern (CC-CC, with two disulfide bridges). The predicted peptides are small (9-12 amino acids). TeAr193 composed of nine amino acid residues is one of the shortest T-superfamily conotoxins ever found. Patterns of sequence divergence and Cys codon usage define the major T-superfamily branches and suggest how these separate branches arose. The sequences of the signal regions exhibited highest conservation, whereas the sequences of the mature peptides were either almost identical or highly divergent; and conservation of the pro-region was intermediate between that observed in signal and toxin regions. The elucidated cDNAs of the four toxins will facilitate a better understanding of the relationship between structure and function.