Cone snail venoms provide a largely untapped source of novel peptide drug leads. To enhance the discovery phase, a detailed comparative proteomic analysis was undertaken on milked venom from the mollusk-hunting cone snail, Conus textile, from three different geographic locations (Hawai’i, American Samoa and Australia's Great Barrier Reef). A novel milked venom conopeptide rich in post-translational modifications was discovered, characterized and named a-conotoxin TxIC. We assign this conopeptide to the 4/7 a-conotoxin family based on the peptide's sequence homology and cDNA pre-propeptide alignment. Pharmacologically, a-conotoxin TxIC demonstrates minimal activity on human acetylcholine receptor models (100 µM, < 5% inhibition), compared to its high paralytic potency in invertebrates, PD50 = 34.2 nMol kg-1. The non-post-translationally modified form, [Pro]2,8[Glu]16a-conotoxin TxIC, demonstrates differential selectivity for the a3ß2 isoform of the nicotinic acetylcholine receptor with maximal inhibition of 96% and an observed IC50 of 5.4 ± 0.5 µM. Interestingly its comparative PD50 (3.6 µMol kg-1) in invertebrates was ~100 fold more than that of the native peptide. Differentiating a-conotoxin TxIC from other a-conotoxins is the high degree of post-translational modification (44% of residues). This includes the incorporation of ?-carboxyglutamic acid, two moieties of 4-trans hydroxyproline, two disulfide bond linkages, and C-terminal amidation. These findings expand upon the known chemical diversity of a-conotoxins and illustrate a potential driver of toxin phyla-selectivity within Conus. |
