Solution structure of an analog of vasoactive intestinal peptide as determined by two-dimensional NMR and circular dichroism spectroscopies and constrained molecular dynamics

158

159

The widespread neuropeptide vasoactive intestinal peptide (VIP) has two receptors VPAC 1 and VPAC 2 . Solid-phase syntheses of VIP analogs in which each amino acid has been changed to alanine (Ala scan) or glycine was achieved and each analog was tested for: (i) threedimensional structure by ab initio molecular modeling; (ii) ability to inhibit 125 ]VIP analog which constitutes the first highly selective (>1,000-fold) human VPAC 1 receptor agonist derived from VIP ever described. The vasoactive intestinal peptide (VIP)1 is a prominent neuropeptide with wide distribution in both peripheral and central nervous systems and a large spectrum of biological actions in mammals (1, 2). VIP-containing nerves and VIP effects have been described in digestive tract, cardiovascular system, airways, reproductive system, immune system, endocrine glands, and brain (1). Besides its short-term actions on exocrine secretions, hormone release, muscle relaxation, and metabolism (1, 2), VIP has been also characterized as a growth regulator for fetuses and tumor cells and during embryonic brain development (3). There are recent evidences for an important role of VIP in the perception of pain (4) and suppression of inflammation (5). Finally, VIP has been involved in diseases such as the watery diarrhea syndrome and clinical applications of VIP have been already suggested in impotence, asthma, lung injury, a variety of tumors and neurodegenerative diseases (1-3).VIP belongs to a large family of structurally related peptides (2, 6, 7) that comprises VIP, pituitary adenylate cyclase-activating peptide PACAP-27, and its C-terminal extended form PACAP-38, secretin, glucagon, and glucagon-like peptides-1 and -2, gastric inhibitory polypeptide, peptide histidine methionine amide, growth hormone-releasing factor (GRF), and peptides isolated from the venom of the Gila Monster. VIP and PACAP are the most closely related peptides in terms of structure and function (2, 6). They share two common receptors, VPAC 1 and VPAC 2 , which display high affinity for both VIP and PACAP (2,8). These receptors together with receptors for VIP-related peptides (see above) clearly constitute an original subfamily within the superfamily of G protein-coupled receptors (2, 9, 10). This subfamily referred to as class II (2) also comprises receptors for parathyroid hormone, calcitonin, corticotropin-releasing factor, and the so called EGF-TM7 receptors (11). Class II family of receptors for peptides display several common properties including large N-terminal extracellular domains containing highly conserved cystein residues, N-terminal leader sequences, and complex gene organization with many introns (2).Although the structure-function relationship of VIP receptors, including VPAC 1 and VPAC 2 , has been recently documented (2,9,(12)(13)(14)(15)(16)(17)(18)(19)(20), the structure-function relationship of VIP itself is still poorly understood. Some old studies carried out before the characterization and cloning of VIP receptor subtypes (21-23) indicated that: (i) th...

Section: Discussionsupporting

confidence: 91%

Identification of Key Residues for Interaction of Vasoactive Intestinal Peptide with Human VPAC1 and VPAC2Receptors and Development of a Highly Selective VPAC1Receptor Agonist

Nicole

Lins

Rouyer‐Fessard

et al. 2000

158

159

“…The dramatic loss of VPAC1 and VPAC2 activation caused by proline replacement at position 19 of R3P65 is consistent with the importance of maintaining the helical structure for its function since proline has been characterized as a "helix breaker" (30). On the other hand, proline did not significantly affect VPAC2 selectivity and potency at positions 27, 29, and 30 presumably because these residues fall outside of the predicted helical region (23)(24)(25)(26). Most of the mutant peptides from saturation mutagenesis at positions 29 and 30 possessed at least 3-fold greater VPAC2 selectivity than R3P49 (V19A/L27K-VIP), which differs from R3P65 in not having the two amino acid extension.…”

Section: Figsupporting

confidence: 63%

“…Both peptides possess a low percentage of stable structure in aqueous solution but an increasing percentage of helicity as the ratio of organic co-solvent is increased (23)(24)(25)(26). At ϳ50% organic solvent, residues 8 -26 generally adopt a helical structure while the N and C termini remain highly flexible with little discernible structure.…”

Section: Discussionmentioning

confidence: 99%

Generation of Highly Selective VPAC2 Receptor Agonists by High Throughput Mutagenesis of Vasoactive Intestinal Peptide and Pituitary Adenylate Cyclase-activating Peptide

Yung¹,

Cruz

Hamren³

et al. 2003

Pituitaryadenylate cyclase-activating peptide (PACAP) has a specific receptor PAC1 and shares two receptors VPAC1 and VPAC2 with vasoactive intestinal peptide (VIP). VPAC2 activation enhances glucose-induced insulin release while VPAC1 activation elevates glucose output. To generate a large pool of VPAC2 selective agonists for the treatment of type 2 diabetes, structure-activity relationship studies were performed on PACAP, VIP, and a VPAC2 selective VIP analog. Chemical modifications on this analog that prevent recombinant expression were sequentially removed to show that a recombinant peptide would retain VPAC2 selectivity. An efficient recombinant expression system was then developed to produce and screen hundreds of mutant peptides. The 11 mutations found on the VIP analog were systematically replaced with VIP or PACAP sequences. Three of these mutations, V19A, L27K, and N28K, were sufficient to provide most of the VPAC2 selectivity. C-terminal extension with the KRY sequence from PACAP38 led to potent VPAC2 agonists with improved selectivity (100 -1000-fold). Saturation mutagenesis at positions 19, 27, 29, and 30 of VIP and chargescanning mutagenesis of PACAP27 generated additional VPAC2 selective agonists. We have generated the first set of recombinant VPAC2 selective agonists described, which exhibit activity profiles that suggest therapeutic utility in the treatment of diabetes.Pituitary adenylate cyclase-activating polypeptide (PACAP), 1 originally isolated from ovine hypothalamus (1) by following pituitary adenylate cyclase activation, belongs to the secretin/glucagon/vasoactive intestinal peptide (VIP) family of peptides (2). These peptides are expressed as part of larger proteins that are processed by proteolysis followed by Cterminal amidation to generate the mature amidated peptides (Fig. 1). PACAP exists as a 38-residue form (PACAP38), and as a shorter form corresponding to the N-terminal 27 amino acids of PACAP38 (PACAP27). Both forms of PACAP bind to and activate the G-protein-coupled receptors PAC1, VPAC1, and VPAC2, whereas the related 28-mer peptide VIP only recognizes VPAC1 and VPAC2 (3). Activation of multiple receptors by PACAP or VIP has broad physiological effects on nervous, endocrine, cardiovascular, reproductive, muscular, and immune systems (4). Thus, clinical applications will require selective activation of a particular receptor to minimize potential side effects mediated by the other receptors. For example, we have previously demonstrated that VPAC2 activation induces glucose-dependent insulin secretion without the undesired side effects mediated by VPAC1 such as watery diarrhea (5). Therefore, to provide a potential therapy for type 2 diabetes, VPAC2 selectivity is an absolute requirement.We sought to identify key determinants of VPAC2 selectivity and generate a peptide with the minimum number of mutations. However, structure-function relationship studies on VIP and PACAP (6 -15) have been restricted by the number of peptides that can be tested due to limitations of peptide synth...

“…The integrity of the helices is important for high affinity binding (33). A similar structural arrangement is also detected in VIP (36). The first 6 amino-terminal residues of PACAP are important for both binding and signal transduction.…”

Section: Discussionsupporting

confidence: 63%

Novel Alternatively Spliced Exon in the Extracellular Ligand-binding Domain of the Pituitary Adenylate Cyclase-activating Polypeptide (PACAP) Type 1 Receptor (PAC1R) Selectively Increases Ligand Affinity and Alters Signal Transduction Coupling during Spermatogenesis

Daniel

Kieffer

Leech

et al. 2001

The expression of the paracrine signaling hormone pituitary adenylate cyclase-activating polypeptide (PACAP) is regulated in a cyclical fashion during the 12-day spermatogenic cycle of the adult rat testis. The precise functions of PACAP in the development of germ cells are uncertain, but cycle-and stage-specific expression may augment cAMP-regulated gene expression in germ cells and associated Sertoli cells. Here we report the existence of a heretofore unrecognized exon in the extracellular domain of the PACAP type 1 receptor (PAC1R) that is alternatively spliced during the spermatogenic cycle in the rat testis. This splice variant encodes a full-length receptor with the insertion of an additional 72 base pairs encoding 24 amino acids (exon 3a) between coding exons 3 and 4. The PAC1R(3a) mRNA is preferentially detected in seminiferous tubules and is expressed at the highest levels in round spermatids and Sertoli cells. Analyses of ligand binding and signaling functions in stably transfected HEK293 cells expressing the two receptor isoforms reveals a 6-fold increase in the affinity of the PAC1R(3a) to bind PACAP-38, and alterations in its coupling to both cAMP and inositol phosphate signaling pathways relative to the wild type PAC1R. These findings suggest that the extracellular region between coding exons 3 and 6 of PAC1R may play an important role in the regulation of the relative ligand affinities and the relative coupling to G s (cAMP) and G q (inositol phosphates) signal transduction pathways during spermatogenesis.