The peptide pQFYRFamide is encoded on the FMRFamide precursor of the snail Helix aspersa but does not activate the FMRFamide-gated sodium current.

Abstract

The complete sequence of the FMRFamide precursor cDNA from Helix aspersa is reported here. Since the 5' end of this cDNA is identical to that of the precursor that encodes the heptapeptide analogs of FLRFamide, the two transcripts are probably derived by alternative RNA splicing. A novel pentapeptide, Glp-Phe-Tyr-Arg-Phe-NH2 (pQFYRFamide), predicted from the cDNA sequence, was purified from extracts of H. aspersa ganglia and identified by mass spectroscopy. Partial gene sequences for the FMRFamide precursors of two closely related pulmonate species-Cepaea nemoralis and Polydontes acutangula-were also determined and compared with the cDNA sequence of H. aspersa and a partial gene sequence previously determined from H. pomatia. Not only are the FMRFamide-related sequences and proteolytic processing sites conserved, but the linear arrangement of these landmarks is also retained. Synthetic pQFYRFamide has some effects on the isolated heart and on neuronal potassium currents in H. aspersa that are similar to those of FMRFamide, but it does not activate the neuronal FMRFamide-gated sodium channel.