Cone snail analogs of the pituitary hormones oxytocin/vasopressin and their carrier protein neurophysin. Proteomic and transcriptomic identification of conopressins and conophysins.

Transcriptomic analysis of cone snail venom duct tissue has permitted the identification of diverse conopressin/conophysin precursor sequences from seven distinct Conus species. Multiple precursor isoforms are present in C.monile, C.lividus and C.loroisii. Aqueous extracts of the venom duct tissue from C.monile yield a band, at ~ 15-20 kDa on SDS-PAGE. In-gel trypsin digestion, followed by mass spectrometry establishes the presence of two distinct conopressin/conophysin isoforms that differ at position 8 in the predicted conopressin nonapeptide sequence. Mass spectrometric analysis of aqueous extracts revealed the presence of four conopressin related peptides, whose sequences could be deduced from MS/MS fragmentation patterns. The four sequences determined in this study are CFIRNCPKG*, CFIRNCPEG*, CFIRNCPK* and CFIRNCPE* (∗ indicates amide), which were further confirmed by comparison with chemically synthesized peptides. A conophysin with a mass of 9419.7 Da was also detected, corresponding to one of the isoforms revealed by the transcriptome data. Complete conservation of fourteen Cys residues and the key residues involved in peptide hormone binding is established by comparison of conophysin sequences, with the crystallographically characterized sequence of bovine neurophysin, in complex with vasopressin. A survey of available sequences for oxytocin/vasopressin peptides in both vertebrates and invertebrates establishes the conopressins as a distinct group in this family. C-terminal amidated, truncated conopressin analogs may arise by alternate post-translational processing.