Vasoactive intestinal polypeptide VPAC(1) and VPAC(2) receptor chimeras identify domains responsible for the specificity of ligand binding and activation

In order to identify the receptor domains responsible for the VPAC(1) selec tivity of the VIP1 agonist, [Lys15, Arg16, Leu27] VIP (1-7)/GRF (8-27) and VIP1 antagonist, Ac His1 [D-Phe2, Lys15, Arg16, Leu27] VIP (3-7)/GRF (8-27) , we evaluated their binding and functional properties on chimeric VPAC(1)/ VPAC(2) receptors. Our results suggest that the N-terminal extracellular do main is responsible for the selectivity of the VIP1 antagonist. Selective r ecognition of the VIP1 agonist was supported by a larger receptor area: in addition to the N-terminal domain, the first extracellular loop, as well as additional determinants in the distal part of the VPAC(1) receptor were in volved. Furthermore, these additional domains were critical for an efficien t receptor activation, as replacement of EC1 in VPAC(1) by its counter part in the VPAC(2) receptor markedly reduced the maximal response.