Domains determining agonist selectivity in chimaeric VIP2 (VPAC2)/PACAP (PAC1) receptors

1. The VPAC2 and PAC1 receptors are closely related members of the Group II G protein-coupled receptor family. At the VPAC2 receptor, VIP is equipotent to PACAP-38 in stimulating cyclic AMP production, whereas at the PAC1 receptor PACAP-38 is many fold more potent than VIP. In this study, domains which confer this selectivity were investigated by constructing four chimaeric receptors in which segments of the VPAC2 receptor were exchanged with the corresponding segment from the PAC1 receptor.

2. When expressed in COS 7 cells all the chimaeric receptors bound the common ligand [125I]PACAP-27 and produced cyclic AMP in response to agonists.

3. Relative selectivity for agonists was determined primarily by the amino terminal extracellular domain of the PAC1 receptor and the VPAC2 receptor. The interchange of other domains had little effect on the potency of PACAP-38 or PACAP-27.

4. For chimaeric constructs with a PAC1 receptor amino terminal domain, the substitution of increasing portions of the VPAC2 receptor decreased the potency of VIP yet increased that of helodermin.

5. This suggests that the interaction of VIP/helodermin but not PACAP with the PAC1 receptor may be influenced (and differentially so) by additional receptor domains.