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Abstract: In the venoms of cone snails, α conotoxins are competitive antagonists of nicotinic acetylcholine receptors. Eleven novel cDNA and eight partial gene sequences (including two pseudogenes) of α conotoxins were identified from five species of cone snail. As expected, every cDNA encodes a precursor of prepropeptide. In all the partial genes of α conotoxins identified, there is a long intron inserted at a fixed position in the pro-region, dividing the encoding region into two exons. The mutation rate in exon I (encoding the signal peptide and a part of pro-region) is much lower than that in exon II (encoding the other part of pro-region, the mature peptide and 3′ untranslational region). Interestingly, the sequences at the 5′ and 3′ end of introns are highly conserved. In addition, in the identified introns exist long dinucleotide (e.g. “GT”, “CA”) or trinucleotide (“CAT”) repeats. In the special case of Pu1.1, there are five almost identical repeats of a 150bp sequence in the long intron. Taking advantage of the conserved 3′ end sequence of intron, 16 α conotoxins, as well as a pseudogene and three κA conotoxins, were identified from their genomic DNAs. Based on the comparison of these cDNA and gene sequences, a hypothesis of the α conotoxin evolution was proposed. [Copyright &y& Elsevier]

Abstract: Remarkable sequence diversity of T-superfamily conotoxins was found in a mollusk-hunting cone snail Conus marmoreus. The sequence of mr5a purified from the snail venom was determined, while six other sequences of Mr5.1a, Mr5.1b, Mr5.2, Mr5.3, Mr5.4a, and Mr5.4b were deduced from their corresponding cDNA cloned by RACE approach. mr5a of 10 amino acid residues is one of the shortest T-superfamily conotoxins ever found. They all share a typical (–CC–CC–) Cys pattern, a conserved signal peptide and a long 3′-untranslated region. A consensus Glu residue is preceded by the second two adjacent cysteines in all these toxins except in mr5a, whereas Mr5.1a, Mr5.1b, Mr5.4a and Mr5.4b are abundant in Trp residues. The identification of these highly divergent T-superfamily conotoxins will facilitate the understanding the relationship of their structure and function. [Copyright &y& Elsevier]