A Novel cDNA Sequence Encoding the Precursor of the d-Amino Acid-Containing Neuropeptide Fulicin and Multiple α-Amidated Neuropeptides from Achatina fulica

ABSTRACT

Abstract: Fulicin (Phe-d-Asn-Glu-Phe-Val-NH₂) is an endogenous neuropeptide containing a d-amino acid from ganglia of the African giant snail Achatina fulica. We have cloned a novel cDNA (1,995 nucleotides) encoding a fulicin precursor from the snail cerebral and subesophageal ganglia. The fulicin precursor protein (357 amino acids) contains one copy of fulicin and at least nine other putative α-amidated neuropeptides composed of four to six amino acid residues. Seven of the nine neuropeptides were novel, and the other two had the same structures as Mytilus inhibitory peptide-related peptides previously isolated from the ganglia of Helix pomatia. All sequences of 10 peptides are flanked by Lys-Arg(Lys) at the N-terminus and by Gly-Lys-Arg(Lys) at the C-terminus. Nucleotide sequence analysis revealed that d-Asn present in fulicin is encoded by the usual l-Asn codon (AAT). Although fulicin has as yet only been isolated from the central ganglia, RNA blot analysis revealed that single transcripts of ∼2.0 kb in size also exist in the ventricles and atria. These results suggest that fulicin and related peptides are produced in neurons and the heart by the processing of a ribosomally made precursor, although the mechanism of in-chain epimerization remains unclear.