Structural motifs of pituitary adenylate cyclase-activating polypeptide (PACAP) defining PAC(1)-receptor selectivity

Pituitary adenylate cyclase-activating polypeptide (PACAP) interacts with t hree types of PACAP/VIP-receptors. The PAC(1)-receptor accepts PACAP as a h igh affinity ligand but not vasoactive intestinal peptide (VIP) similarly b inding to VPAC(1)- and VPAC(2)-receptors. To identify those amino acids not present in VIP defining PAC(1)-receptor selectivity of PACAP, radio recept or binding assays on AR4-2J cells were performed. It could be shown that PA CAP(1-27) exhibited a distinct and much higher susceptibility to VIP-amino acid substitutions, compared to PACAP(1-38). Positions 4 and 5 seem to be m ost important fur receptor binding of PACAP(1-27), whereas position 13 was identified to be crucial for maximal affinity of PACAP(1-38). PACAP(29-38) extension analogues of VIP revealed a stabilizing effect of the C-terminus of PACAP(1-38) on the optimal peptide conformation. The substitution analog ues were also checked for their capacity to stimulate IP3 and cAMP formatio n in AR4-2J cells. Compared to PACAP(1-27) and PACAP(1-38), most analogues revealed potencies reduced congruously to their lower binding affinities. H owever, one of the analogues, PACAP(1-27) substituted in position 5, may re present a weak antagonist since this peptide was less potent in inducing se cond messengers than in label displacement. Our findings indicate that PACA P(1-27) and PACAP(1-38) differ in terms of their requirement of the amino a cids in positions 4, 5, 9, 11 and 13 for maximal interaction with the PAC(1 )-receptor. (C) 1999 Elsevier Science B.V All rights reserved.