title: Molecular cloning of the helodermin and exendin-4 cDNAs in the lizard. Relationship to vasoactive intestinal polypeptide/pituitary adenylate cyclase activating polypeptide and glucagon-like peptide 1 and evidence against the existence of mammalian homologues.
abstract: Helodermin and exendin-4, two peptides isolated from the salivary gland of the Gila monster, Heloderma suspectum, are approximately 50% homologous to vasoactive intestinal peptide (VIP) and glucagon-like peptide-1 (GLP-1), respectively, and interact with the mammalian receptors for VIP and GLP-1 with equal or higher affinity and efficacy. Immunohistochemical studies suggested the presence of helodermin-like peptides in mammals. To determine whether helodermin and exendin-4 are present in mammals and their evolutionary relationship to VIP and GLP-1, their cDNAs were first cloned from Gila monster salivary gland. Northern blots and reverse transcription-polymerase chain reaction of multiple Gila monster tissues identified approximately 500-base pair transcripts only from salivary gland. Both helodermin and exendin-4 full-length cDNAs were approximately 500 base pairs long, and they encoded precursor proteins containing the entire amino acid sequence of helodermin and exendin-4, as well as a 44- or 45-amino acid N-terminal extension peptide, respectively, having approximately 60% homology. The size and structural organization of these cDNAs indicated that they were closely related to one another but markedly different from known cDNAs for the VIP/GLP-1 peptide family previously identified in both lower and higher evolved species. Cloning of the Gila monster VIP/peptide histidine isoleucine, pituitary adenylate cyclase activating polypeptide, and glucagon/GLP-1 cDNAs and Southern blotting of Gila monster DNA demonstrate the coexistence of separate genes for these peptides and suggests, along with the restricted salivary gland expression, that helodermin and exendin-4 coevolved to serve a separate specialized function. Probing of a variety of rat and human tissues on Northern blots, human and rat Southern blots, and genomic and cDNA libraries with either helodermin- or exendin-4-specific cDNAs failed to identify evidence for mammalian homologues. These data indicate that helodermin and exendin-4 are not the precursors to VIP and GLP-1 and that they belong to a separate peptide family encoded by separate genes. Furthermore, the existence of as yet undiscovered mammalian homologues to helodermin and exendin-4 seems unlikely.
authors.affiliation: Digestive Diseases Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: M
authors.initials: M
authors.lastname: Pohl
authors.forename: S A
authors.initials: SA
authors.lastname: Wank
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002645:Chickens; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D000077270:Exenatide; D005934:Glucagon; D052216:Glucagon-Like Peptide 1; D004763:Glucagon-Like Peptides; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D008116:Lizards; D008322:Mammals; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000737:chemistry*; D010446:Peptide Fragments / Q000737:chemistry; D010455:Peptides / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D016133:Polymerase Chain Reaction; D011498:Protein Precursors / Q000737:chemistry; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014337:Trout; D014660:Vasoactive Intestinal Peptide / Q000737:chemistry*; D014688:Venoms
chemical_list: C495401:ADCYAP1 protein, human; C495403:Adcyap1 protein, rat; D017931:DNA Primers; D018076:DNA, Complementary; D036341:Intercellular Signaling Peptides and Proteins; D009479:Neuropeptides; D010446:Peptide Fragments; D010455:Peptides; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D011498:Protein Precursors; D011994:Recombinant Proteins; D014688:Venoms; C061970:glucagon-like peptide 1 (7-36); D014660:Vasoactive Intestinal Peptide; D004763:Glucagon-Like Peptides; C040442:heliodermin; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D000077270:Exenatide