In depth analysis of the N-terminal bioactive domain of gastric inhibitory polypeptide.
Gastric inhibitory polypeptide/glucose-dependent insulinotropic polypeptide (GIP) is an important gastrointestinal regulator of insulin release and glucose homeostasis following a meal. Strategies have been undertaken to delineate the bioactive domains of GIP with the intention of developing small molecular weight GIP mimetics. The molecular cloning of receptors for GIP and the related hormone GLP-1 (glucagon-like peptide-1) has allowed examination of the characteristics of incretin analogs in transfected cell models. The current report examines the N-terminal bioactive domain of GIP residing in residues 1-14 by alanine scanning mutagenesis and N-terminal substitution/modification. Further studies examined peptide chimeras of GIP and GLP-1 designed to localize bioactive determinants of the two hormones. The alanine scan of the GIP(1-14) sequence established that the peptide was extremely sensitive to structural perturbations. Only replacement of amino acids 2 and 13 with those found in glucagon failed to dramatically reduce receptor binding and activation. Of four GIP(1-14) peptides modified by the introduction of DP IV-resistant groups, a peptide with a reduced bond between Ala2 and Glu3 demonstrated improved receptor potency compared to native GIP(1-14). The peptide chimera studies supported recent results on the importance of a mid-region helix for bioactivity of GIP, and confirmed existence of two separable regions with independent intrinsic receptor binding and activation properties. Furthermore, peptide chimeras showed that binding of GLP-1 also involves both N- and C-terminal domains, but that it apparently contains only a single bioactive domain in its N-terminus. Together, these results should facilitate development of incretin based therapies using rational drug design for potential treatment of diabetes.
Department of Physiology, Faculty of Medicine, University of British Columbia, 2146 Health Sciences Mall, Vancouver, British Columbia, V6T 1Z3, Canada.
Simon A
SA
Hinke
Susanne
S
Manhart
Madeleine
M
Speck
Raymond A
RA
Pederson
Hans-Ulrich
HU
Demuth
Christopher H S
CH
McIntosh
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D016466:CHO Cells; D006224:Cricetinae; D000242:Cyclic AMP / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D005260:Female; D005749:Gastric Inhibitory Polypeptide / Q000737:chemistry / Q000494:pharmacology*; D005934:Glucagon / Q000494:pharmacology; D052216:Glucagon-Like Peptide 1; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology*; D010957:Plasmids / Q000235:genetics; D011498:Protein Precursors / Q000494:pharmacology; D011869:Radioligand Assay; D011964:Receptors, Gastrointestinal Hormone / Q000187:drug effects; D013268:Stimulation, Chemical
D007202:Indicators and Reagents; D010446:Peptide Fragments; D011498:Protein Precursors; D011964:Receptors, Gastrointestinal Hormone; C489884:gastric inhibitory polypeptide (1-14); D005749:Gastric Inhibitory Polypeptide; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; C041086:gastric inhibitory polypeptide receptor; D000242:Cyclic AMP