Characterization of insulin and atypically processed proglucagon-derived peptides from the surinam toad Pipa pipa (Anura:Pipidae).
Electrospray mass spectrometry was used to identify insulin, glucagon and two peptides related to glucagon-like peptide-1 (GLP-1) in an extract of the pancreas of the Surinam toad, Pipa pipa, a species belonging to the same family as the African clawed frog, Xenopus laevis. Purification and characterization of the peptides established the primary structure of Pipa insulin as A-chain: GIVEQCCHSS(10)CTLLQLETYC(20) N and B-Chain: FSNQR LCGSH(10) LVEALHLVCG(20) DRGFFYYPKA(30). This amino acid sequence contains several substitutions (B5 His --> Arg, B16 Tyr --> His, A12 Ser --> Thr, A14 Tyr--> Leu, A18Asn --> Thr) of residues that have otherwise been quite strongly conserved during vertebrate evolution. Pipa glucagon comprises 37 amino acid residues (HSQGTFTSDY(10) SKYLDSRRAQ(20) DFVQWLMNTK(30)QSGGLSS) and the 29 amino-acid-residue peptide was not identified in the extract. In Xenopus and mammalian preproglucagons, the glucagon-29 sequence is followed by Lys-Arg which functions as a recognition site for a prohormone convertase. We propose that a point mutation in the gene encoding Pipa preproglucagon has transformed the Lys(30)-Arg(31) processing site into Lys-Gln with the result that the site in no longer recognized by the processing enzyme. In contrast, Pipa GLP-32 and GLP-37 are of the same molecular size as the corresponding peptides from Xenopus.
Matutte
B
B
Regulatory Peptide Center, Department of Biomedical Sciences, Creighton University Medical School, Omaha, NE 68178-0405, USA.
Conlon
J M
JM
D000595:Amino Acid Sequence; D000818:Animals; D019143:Evolution, Molecular; D005934:Glucagon / Q000737:chemistry*; D007328:Insulin / Q000737:chemistry*; D008969:Molecular Sequence Data; D010179:Pancreas / Q000737:chemistry*; D010446:Peptide Fragments / Q000737:chemistry; D010884:Pipidae; D052336:Proglucagon; D011498:Protein Precursors / Q000737:chemistry*; D011499:Protein Processing, Post-Translational; D017386:Sequence Homology, Amino Acid
D007328:Insulin; D010446:Peptide Fragments; D011498:Protein Precursors; D052336:Proglucagon; D005934:Glucagon