X. Hou et al., STRUCTURAL REQUIREMENTS FOR THE OCCUPANCY OF RAT-BRAIN PACAP RECEPTORS AND ADENYLATE-CYCLASE ACTIVATION, Neuropharmacology, 33(10), 1994, pp. 1189-1195
N-terminally shortened analogues of PACAP(1-27) and PACAP(1-38), and a
nalogues modified in position 1, 2 or 3 were compared for their abilit
y to interact with PACAP receptors and to activate or inhibit adenylat
e cyclase in rat brain hippocampus membranes. In the PACAP(1-27) serie
s, deletion of the first two amino acids decreased the potency 3000-fo
ld. PACAP fragments (3-27) to (9-27) were inactive on the enzyme. N-te
rminally shortened PACAP(1-38) analogues showed a similar profile but
were 70 to 300-fold more potent than their PACAP(1-27) equivalents. PA
CAP(6-27) and PACAP(6-38) were competitive inhibitors of the PACAP(1-2
7) stimulated enzyme. The K-d values of PACAP(6-27) and PACAP(6-38) we
re of 1000 and 2 nM respectively. Surprisingly, the K-d values of PACA
P(6-31) and (6-35), that were also unable to stimulate adenylate cycla
se activity, were of 3 and 300 nM respectively. Replacement of His 1 b
y Phe1 in PACAP(1-27) reduced the potency 600-fold. Replacement of Ser
2 by Ala2 in PACAP(1-27) and PACAP(1-38) was of little consequence. Su
bstitution of Ser2 by Phe2, DPheZ, Arg2 or DArg2 reduced 60 to 1000-fo
ld the PACAP(1-27) potency but only 7 to 30-fold the PACAP(1-38) poten
cy. Phe2 derivatives were inactive on the enzyme. Replacement of Asp3
by Asn reduced 4000-fold the PACAP(1-27) potency. These results sugges
t that three domains of PACAP(1-38) were involved in binding to rat br
ain receptors: the N-terminal triplet His-Ser-Asp, the (11-27) area an
d the C-terminal (27-38) extension; the integrity of two out of three
domains sufficed for high affinity interaction at the binding level wh
ile His1 and Ser2 and part of the 11-27 area were key elements in rece
ptor-effector coupling.