title: Ferric ions are essential for the biological activity of the hormone glycine-extended gastrin.
abstract: Amidated and nonamidated gastrins elicit different biological effects via distinct receptors in different tissues. Amidated gastrin 17 stimulates gastric acid secretion and the development of gastric carcinoids, whereas glycine-extended gastrin 17 stimulates proliferation of the colonic mucosa and the development of colorectal cancers. Because glycine-extended gastrin 17 binds two ferric ions with high affinity (Baldwin, G. S., Curtain, C. C., and Sawyer, W. H. (2001) Biochemistry 40, 10741-10746), we have investigated the identity of the iron ligands and the role of ferric ions in biological activity. Here we report the solution structure of glycine-extended gastrin 17, determined by NMR spectroscopy. The spectral changes observed upon the addition of ferric ions revealed that Glu(7) acted as a ligand at the first ferric binding site, and that Glu(8) and Glu(9) acted as ligands at the second ferric ion binding site. Fluorescence quenching experiments confirmed that a GglyE7A mutant bound only one ferric ion. The inability of this mutant to stimulate proliferation or migration in the IMGE-5 cell line and the observation that the iron chelator desferrioxamine selectively blocked the effects of glycine-extended gastrin 17 indicated that binding of a ferric ion to Glu(7) was essential for biological activity. This is the first report of an essential role for a metal ion in the action of a hormone.
authors.affiliation: University of Melbourne Department of Surgery, Austin Campus, ARMC, Heidelberg, Victoria 3084, Australia.
authors.forename: Julie
authors.initials: J
authors.lastname: Pannequin
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Barnham
authors.forename: Frederic
authors.initials: F
authors.lastname: Hollande
authors.forename: Arthur
authors.initials: A
authors.lastname: Shulkes
authors.forename: Raymond S
authors.initials: RS
authors.lastname: Norton
authors.forename: Graham S
authors.initials: GS
authors.lastname: Baldwin
mesh_terms: D000595:Amino Acid Sequence; D002460:Cell Line; D005290:Ferric Compounds / Q000737:chemistry*; D005755:Gastrins / Q000737:chemistry / Q000502:physiology*; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence
chemical_list: D005290:Ferric Compounds; D005755:Gastrins; D008024:Ligands; C086854:glycine-extended gastrin 17