The extracellular domain of the GLP-I receptor is essential for ligand binding and shows intrinsic binding activity

Abstracts from the 1l th International Symposium on Regulatory Peptides

The Extraceilular Domain of the GLP-I Receptor is Essential for Ligand Binding and Shows Intrinsic Binding Activity

ANDREAS WILMEN, BRIGITTE VAN EYLL, RUDIGER GOKE, BURKHARD GOKE*, Marburg, Germany Together with the receptors for VIP, secretin, PACAP, parathormone, glucagon, gastric inhibitory peptide, calcitonin, and growth hormone releasing hormone the GLP-I receptor forms a subclass of seven transmembrane, G-protein coupled receptors. The receptors of this family share many common motifs including a relatively large N-terminal extracellular domain. In order to investigate the role of the Nterminal domain in receptor-ligand interaction we designed two different experimental setups. At first, we constructed a chimera consisting of the N-terminal part of the glucagon receptor (an 1-89) and the GLP-I receptor core sequence (an 89-463). Neither GLP-I nor glucagon bound to the receptor chimera demonstrating the importance of the N-terminal domain for receptor-ligand interaction. Furthermore, we purified the N-terminal domain of the GLP-I receptor using E. coli as expression system. In ligand binding assays using CHL cells expressing the cloned GLP-I receptor, addition of the solubilized the N-terminal pan of the receptor protein competed for GLP-I. Moreover, in crosslinking experiments radioactively labeled GLP-I was covalently attached to the N-terminus showing direct physical interaction of both components. In Western blot analysis employing specific bands (MW 22 kD and 28 kD) were detectable representing N-terminal receptor protein in the presence or absence of bound ligand. Our results show that the N-terminal domain of the GLP-I receptor is essential for receptor-ligand interaction and shows intrinsic binding activity.

DEFICIENT GASTRIC LIPASE SECRETION IN PANCREATIC INSUFFICIENCY. O.Olsen, S.Larsen, B.Sternby, JF.gehr'eld. Depts. of Surgery & Clinical Biochemistry, Rigshospitalet. Depts.of Surgery & Medicine, Glostrup Hospital, University of Copenhagen, Denmark. Dept. of Medicine, University Hospital of Lurid, Sweden. Background: Gastrin is an important stimulator of gastric lipase secretion in man. In

advanced pancreatic insufficiency gastric lipases might compensate for the lack of pancreatic fipases, but the role of gastrin by such compensation remains to be evaluated. Aims: The aim of this study was to examine the effect of g~trin on the gastric iipase secretion

in patients suffering from pancreatic inmfficiency. Patients: Eight patients with pancreatic insufficiency secondary to alcohol abuse were studied and 6 healthy subjects volunteered as controls for the study. Methods: All volunteers received identical doses of intravenous gastrin-17 ( 10,30 and 60

pmol/kg/h.). Using a n~og~tric tube for aspiration, the g~tric content was me~ured and the amount as well as the activity of gastric lipaso output were determined. Plasma concentrations of gastrin, secretin and cholecystokinin (CCK) were measured by radioimmunoassays. Results: The increased plasma levels of 8astrin were accompanied by a dose-dependent increase in amount and activity of gastric iipase in controls, but in the patients the response was almost abolished. Conclusions: Gastrin in postprandial concentrations does not influence the secretion of gastric

lipase in patients with pancreatic insufficiency due to chronic pancreatitis.

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