Abstract
Agonist action at receptors is highly specific, affected by the structure of both ligand and receptor. Chimeric constructs of structurally related receptors and/or ligands that have biological differences provide an opportunity to correlate a specific structural domain with function. In this work, we have used a cross-chimeric approach to explore the structural basis for rat secretin and vasoactive intestinal polypeptide action at their closely related secretin and VPAC1 receptors, belonging to class II of the G protein-coupled receptor superfamily. Multiple domains of both ligands and receptors contributed toward their selectivity, with differing combinations of such domains able to support high-potency interactions. The amino-terminal 15 residues of secretin were most critical for potent stimulation of secretin receptors, whereas either the amino- or carboxyl-terminal halves of vasoactive intestinal polypeptide, when complemented by Lys15, provided potent stimulation of the VPAC1 receptor. The amino terminus of the VPAC1 receptor was most critical for potent response to vasoactive intestinal polypeptide, whereas the amino terminus of the secretin receptor was important, but not adequate, requiring the complementation of an extracellular loop domain for potent response to secretin. Differences in the distribution of these determinants within these receptors provided an opportunity to produce a more “universal” receptor that contained the first extracellular loop of the secretin receptor and the remainder of the VPAC1 receptor. This cross-chimeric approach should be applied to other members of this receptor family to test the emerging themes and to expand these insights as broadly as possible.
Footnotes
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Send reprint requests to: Laurence J. Miller, M.D., Mayo Clinic, Gastroenterology Basic Research Unit, Guggenheim 17, Rochester, MN 55905. E-mail: miller{at}mayo.edu
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↵1 This work was supported by grants from the National Institutes of Health (DK46577) and the Fiterman Foundation.
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↵2 These authors contributed equally to this work.
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↵3 Current address: Chosun University, Gastroenterology Division, Department of Internal Medicine, Kwang-Ju, 501-140, Korea.
- Abbreviations:
- VIP
- vasoactive intestinal polypeptide
- CHO
- Chinese hamster ovary
- Sec
- secretin
- VPAC1
- IUPHAR 1998 nomenclature for receptor previously called VIP, VIP1, and VIP/PACAP type II receptor
- Received May 9, 2000.
- Accepted July 10, 2000.
- The American Society for Pharmacology and Experimental Therapeutics