Abstract
A vasoactive intestinal polypeptide (VIP) analog, acylated on the amino-terminal histidine by hexanoic acid (C6-VIP), behaved as a VPAC2 preferring agonist in binding and functional studies on human VIP receptors, and radioiodinated C6-VIP was a suitable ligand for binding studies on wild-type and chimeric receptors. We evaluated the properties of C6-VIP, its analog AcHis1-VIP, and the VPAC2-selective agonist Ro 25-1553 on the wild-type VPAC1 and VPAC2 receptors and on the chimeric receptors exchanging the different domains between both receptors. VIP had a normal affinity and efficacy on the chimeras starting with the amino-terminal VPAC2 receptor sequence. The binding and functional profile of these chimeric receptors suggested that the high affinity of Ro 25-1553 for VPAC2 receptors is supported by the amino-terminal extracellular domain, whereas the ability to prefer C6-VIP over VIP is supported by the VPAC2 fifth transmembrane (TM5)-EC3 receptor domain. These results further support the hypothesis that the central and carboxyl-terminal regions of the peptide (modified in RO 25-1553) recognize the extracellular amino-terminal region domain, whereas the amino-terminal VIP amino acids bind to the TM receptor core. VIP had a reduced affinity and efficacy on the N-VPAC1/VPAC2 and on the N→EC2-VPAC1/VPAC2 chimeric receptors. C6-VIP behaved as a high-affinity agonist on these constructions. The antagonists [AcHis1,d-Phe2,Lys15,Arg16,Leu27]VIP(3-7)/GRF(8-27) and VIP(5-27) had comparable affinities for the wild-type receptors and for the two latter chimeras, supporting the hypothesis that these chimeras were properly folded but unable to reach the high-agonist-affinity, active receptor conformation in response to VIP binding.
Footnotes
- Received June 14, 1999.
- Accepted September 7, 1999.
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Send reprint requests to: Dr. Magali Waelbroeck, Department of Biochemistry and Nutrition, Faculty of Medicine, UniversitéLibre de Bruxelles, Bât. G/E, CP 611, 808 Route de Lennik, 1070 Brussels, Belgium. E-mail: mawadbr{at}ulb.ac.be
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This work was supported by grants from the European Community (PAVE project), the Communauté Française de Belgique (ARC), and an Interuniversity Poles of Attraction, Primer Minister Office, Federal Government, Belgium. M.G.J. was a recipient of a Marie Curie Research Training Grant (European Commission).
- The American Society for Pharmacology and Experimental Therapeutics
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Different Vasoactive Intestinal Polypeptide Receptor Domains Are Involved in the Selective Recognition of Two VPAC2-Selective Ligands
