Mg. Juarranz et al., Different vasoactive intestinal polypeptide receptor domains are involved in the selective recognition of two VPAC(2)-selective ligands, MOLEC PHARM, 56(6), 1999, pp. 1280-1287
A vasoactive intestinal polypeptide (VIP) analog, acylated on the amino-ter
minal histidine by hexanoic acid (C-6-VIP), behaved as a VPAC(2) preferring
agonist in binding and functional studies on human VIP receptors, and radi
oiodinated C-6-VIP was a suitable ligand for binding studies on wild-type a
nd chimeric receptors. We evaluated the properties of C-6-VIP, its analog A
cHis(1)-VIP, and the VPAC(2)-selective agonist Ro 25-1553 on the wild-type
VPAC(1) and VPAC(2) receptors and on the chimeric receptors exchanging the
different domains between both receptors. VIP had a normal affinity and eff
icacy on the chimeras starting with the amino-terminal VPAC(2) receptor seq
uence. The binding and functional profile of these chimeric receptors sugge
sted that the high affinity of Ro 25-1553 for VPAC(2) receptors is supporte
d by the amino-terminal extracellular domain, whereas the ability to prefer
C-6-VIP over VIP is supported by the VPAC(2) fifth transmembrane (TM5)-EC3
receptor domain. These results further support the hypothesis that the cen
tral and carboxyl-terminal regions of the peptide (modified in RO 25-1553)
recognize the extracellular aminoterminal region domain, whereas the amino-
terminal VIP amino acids bind to the TM receptor core. VIP had a reduced af
finity and efficacy on the N-VPAC(1)/VPAC(2) and on the N-->EC2-VPAC(1)/VPA
C(2) chimeric receptors. C-6-VIP behaved as a high-affinity agonist on thes
e constructions. The antagonists [AcHis(1),D-Phe(2),Lys(15),Arg(16),Leu(27)
]VIP(3-7)/GRF(8-27) and VIP(5-27) had comparable affinities for the wild-ty
pe receptors and for the two latter chimeras, supporting the hypothesis tha
t these chimeras were properly folded but unable to reach the high-agonist-
affinity, active receptor conformation in response to VIP binding.