Small molecule ago-allosteric modulators of the human glucagon-like peptide-1 (hGLP-1) receptor

Following our previous publication describing the biological profiles, we herein describe the structure-activity relationships of a core set of quinoxalines as the hGLP-1 receptor agonists. The most potent and efficacious compounds are 6,7-dichloroquinoxalines bearing an alkyl sulfonyl group at the C-2 position and a secondary alkyl amino group at the C-3 position. These findings serve as a valuable starting point for the discovery of more drug-like small molecule agonists for the hGLP-1 receptor.     

Influence of glucagon-like peptide 2 on energy homeostasis

Glucagon like peptide-2 (GLP-2) is a gastrointestinal hormone released from enteroendocrine L-type cells together with glucagon like peptide-1 in response to dietary nutrients. GLP-2 acts through a specific receptor, the GLP-2 receptor, mainly located in the gut and in the brain. Classically, GLP-2 is considered a trophic hormone involved in the maintenance of intestinal epithelial morphology and function. This role has been targeted for therapies promoting repair and adaptive growth of the intestinal mucosa. Recently, GLP-2 has been shown to exert beneficial effects on glucose metabolism specially in conditions related to increased uptake of energy, such as obesity. Several actions of GLP-2 are related to a positive energy balance: GLP-2 increases not only the absorptive surface, but also expression and activity of epithelial brush-border nutrient transporters and digestive enzymes, intestinal blood flow, postprandial chylomicron secretion and it inhibits gastrointestinal motility, providing the opportunity to increase absorption of nutrients. Other actions, including anorexigenic effects, appear in opposition to the energy intake. In this review, we discuss the GLP-2 functions related to energy homeostasis. GLP-2 could be considered an hormone causing positive energy balance, which, however has the role to mitigate the metabolic dysfunctions associated with hyper-adiposity.     

A unique hormonal recognition feature of the human glucagon-like peptide-2 receptor

Glucagon-like peptides (GLP-1 and GLP-2) are two proglucagon-derived intestinal hormones that mediate distinct physiological functions through two related receptors (GLP-1R and GLP-2R) which are important drug targets for metabolic disorders and Crohn’s disease, respectively. Despite great progress in GLP-1R structure determination, our understanding on the differences of peptide binding and signal transduction between these two receptors remains elusive. Here we report the electron microscopy structure of the human GLP-2R in complex with GLP-2 and a G_s heterotrimer. To accommodate GLP-2 rather than GLP-1, GLP-2R fine-tunes the conformations of the extracellular parts of transmembrane helices (TMs) 1, 5, 7 and extracellular loop 1 (ECL1). In contrast to GLP-1, the N-terminal histidine of GLP-2 penetrates into the receptor core with a unique orientation. The middle region of GLP-2 engages with TM1 and TM7 more extensively than with ECL2, and the GLP-2 C-terminus closely attaches to ECL1, which is the most protruded among 9 class B G protein-coupled receptors (GPCRs). Functional studies revealed that the above three segments of GLP-2 are essential for GLP-2 recognition and receptor activation, especially the middle region. These results provide new insights into the molecular basis of ligand specificity in class B GPCRs and may facilitate the development of more specific therapeutics.Subject terms: Cryoelectron microscopy, Hormone receptors     

胰高血糖素样肽-2研究的新进展

胰高血糖素样肽-2(glucagon-like peptide-2,GLP-2)是胰高血糖素原基因转录、翻译后处理加工的33氨基酸的多肽,GLP-2经二酰肽酶Ⅳ水解后,则失去生物学活性。GLP-2作为一种肠上皮特异性生长因子,能促进正常肠黏膜的生长及损伤肠上皮的修复。GLP-2通过作用于GLP-2受体(GLP-2R)来发挥生物学作用。GLP-2R在肠道的广泛分布(肠上皮细胞、肠内在神经元、肠内分泌细胞、肠黏膜下的肌纤维母细胞),提示GLP-2可能通过直接、间接等多条途径发挥生物学作用。本文概括介绍GLP-2的特性、生理作用及机制等方面的研究进展。     

Allosteric modulators of human A2B adenosine receptor

Background

Among adenosine receptors (ARs) the A_2B subtype exhibits low affinity for the endogenous agonist compared with the A₁, A_2A, and A₃ subtypes and is therefore activated when concentrations of adenosine increase to a large extent following tissue damages (e.g. ischemia, inflammation). For this reason, A_2B AR represents an important pharmacological target.

Methods

We evaluated seven 1-benzyl-3-ketoindole derivatives (7–9) for their ability to act as positive or negative allosteric modulators of human A_2B AR through binding and functional assays using CHO cells expressing human A₁, A_2A, A_2B, and A₃ ARs.

Results

The investigated compounds behaved as specific positive or negative allosteric modulators of human A_2B AR depending on small differences in their structures. The positive allosteric modulators 7a,b and 8a increased agonist efficacy without any effect on agonist potency. The negative allosteric modulators 8b,c and 9a,b reduced agonist potency and efficacy.

Conclusions

A number of 1-benzyl-3-ketoindole derivatives were pharmacologically characterized as selective positive (7a,b) or negative (8c, 9a,b) allosteric modulators of human A_2B AR.

General significance

The 1-benzyl-3-ketoindole derivatives 7–9 acting as positive or negative allosteric modulators of human A_2B AR represent new pharmacological tools useful for the development of therapeutic agents to treat pathological conditions related to an altered functionality of A_2B AR.     

Interleukin-10-independent anti-inflammatory actions of glucagon-like peptide 2

Glucagon-like peptide 2 (GLP-2) is an important intestinal growth factor with anti-inflammatory activity. We hypothesized that GLP-2 decreases mucosal inflammation and the associated increased epithelial proliferation by downregulation of Th1 cytokines attributable to reprogramming of lamina propria immune regulatory cells via an interleukin-10 (IL-10)-independent pathway. The effects of GLP-2 treatment were studied using the IL-10-deficient (IL-10(-/-)) mouse model of colitis. Wild-type and IL-10(-/-) mice received saline or GLP-2 (50 microg/kg sc) treatment for 5 days. GLP-2 treatment resulted in significant amelioration of animal weight loss and reduced intestinal inflammation as assessed by histopathology and myeloperoxidase levels compared with saline-treated animals. In colitis animals, GLP-2 treatment also reduced crypt cell proliferation and crypt cell apoptosis. Proinflammatory (IL-1beta, TNF-alpha, IFN-gamma,) cytokine protein levels were significantly reduced after GLP-2 treatment, whereas IL-4 was significantly increased and IL-6 production was unchanged. Fluorescence-activated cell sorting analysis of lamina propria cells demonstrated a decrease in the CD4(+) T cell population following GLP-2 treatment in colitic mice and an increase in CD11b(+)/F4/80(+) macrophages but no change in CD25(+)FoxP3 T cells or CD11c(+) dendritic cells. In colitis animals, intracellular cytokine analysis demonstrated that GLP-2 decreased lamina propria macrophage TNF-alpha production but increased IGF-1 production, whereas transforming growth factor-beta was unchanged. GLP-2-mediated reduction of crypt cell proliferation was associated with an increase in intestinal epithelial cell suppressor of cytokine signaling (SOCS)-3 expression and reduced STAT-3 signaling. This study shows that the anti-inflammatory effects of GLP-2 are IL-10 independent and that GLP-2 alters the mucosal response of inflamed intestinal epithelial cells and macrophages. In addition, the suggested mechanism of the reduction in inflammation-induced proliferation is attributable to GLP-2 activation of the SOCS-3 pathway, which antagonizes the IL-6-mediated increase in STAT-3 signaling.     

A free-energy landscape for the glucagon-like peptide 1 receptor GLP1R

G-protein-coupled receptors (GPCRs) are among the most important receptors in human physiology and pathology. They serve as master regulators of numerous key processes and are involved in as well as cause debilitating diseases. Consequently, GPCRs are among the most attractive targets for drug design and pharmaceutical interventions (>30% of drugs on the market). The glucagon-like peptide 1 (GLP-1) hormone receptor GLP1R is closely involved in insulin secretion by pancreatic β-cells and constitutes a major druggable target for the development of anti-diabetes and obesity agents. GLP1R structure was recently solved, with ligands, allosteric modulators and as part of a complex with its cognate G protein. However, the translation of this structural data into structure/function understanding remains limited. The current study functionally characterizes GLP1R with special emphasis on ligand and cellular partner binding interactions and presents a free-energy landscape as well as a functional model of the activation cycle of GLP1R. Our results should facilitate a deeper understanding of the molecular mechanism underlying GLP1R activation, forming a basis for improved development of targeted therapeutics for diabetes and related disorders.     

Novel signal transduction and peptide specificity of glucagon-like peptide receptor in 3T3-L1 adipocytes

Glucagon-like peptide-1 (7–36) amide (GLP-1), in addition to its well known effect of enhancing glucose-mediated insulin release, has been shown to have insulinomimetic effects and to enhance insulin-mediated glucose uptake and lipid synthesis in 3T3-L1 adipocytes. To elucidate the mechanisms of GLP-1 action in these cells, we studied the signal transduction and peptide specificity of the GLP-1 response. In 3T3-L1 adipocytes, GLP-1 caused a decrease in intracellular cAMP levels which is the opposite to the response observed in pancreatic beta cells in response to the same peptide. In 3T3-L1 adipocytes, free intracellular calcium was not modified by GLP-1. Peptide specificity was examined to help determine if a different GLP receptor isoform was expressed in 3T3-L1 adipocytes vs. beta cells. Peptides with partial homology to GLP-1 such as GLP-2, GLP-1 (1–36), and glucagon all lowered cAMP levels in 3T3-L1 adipocytes. In addition, an antagonist of pancreatic GLP-1 receptor, exendin-4 (9–39), acted as an agonist to decrease cAMP levels in 3T3-L1 adipocytes as did exendin-4 (1–39), a known agonist for the pancreatic GLP-1 receptor. Binding studies using ¹²⁵I-GLP-1 also suggest that pancreatic GLP-1 receptor isoform is not responsible for the effect of GLP-1 and related peptides in 3T3-L1 adipocytes. Based on these results, we propose that the major form of the GLP receptor in 3T3-L1 adipocytes is functionally different from the pancreatic GLP-1 receptor. J. Cell. Physiol. 172:275–283, 1997. Published 1997 Wiley-Liss, Inc.

1 This article was prepared by a group of United States government employees and non-United States government employees, and as such is subject to 17 U.S.C. Sec. 105.

     

The glucagon-like peptide 2 receptor is expressed in enteric neurons and not in the epithelium of the intestine

Glucagon-like peptide 2 (GLP-2) is a potent intestinotrophic growth factor with therapeutic potential in the treatment of intestinal deficiencies. It has recently been approved for the treatment of short bowel syndrome. The effects of GLP-2 are mediated by specific binding of the hormone to the GLP-2 receptor (GLP-2R) which was cloned in 1999. However, consensus about the exact receptor localization in the intestine has never been established.By physical, chemical and enzymatic tissue fragmentation, we were able to divide rat jejunum into different compartments consisting of: (1) epithelium alone, (2) mucosa with lamina propria and epithelium, (3) the external muscle coat including myenteric plexus, (4) a compartment enriched for the myenteric plexus and (5) intestine without epithelium. Expression of Glp2r; chromogranin A; tubulin, beta 3; actin, gamma 2, smooth muscle, enteric and glial fibrillary acidic protein in these isolated tissue fractions was quantified with qRT-PCR. Expression of the Glp2r was confined to compartments containing enteric neurons and receptor expression was absent in the epithelium.Our findings provide evidence for the expression of the GLP-2R in intestinal compartments rich in enteric neurons and, importantly they exclude significant expression in the epithelium of rat jejunal mucosa.     

The discovery of glucagon-like peptide 1

The discovery of glucagon-like peptide 1 (GLP-1) began more than two decades ago with the observations that anglerfish islet proglucagon messenger RNAs (mRNAs) contained coding sequences for two glucagon-related peptides arranged in tandem. Subsequent analyses revealed that mammalian proglucagon mRNAs encoded a precursor containing the sequence of pancreatic glucagon, intestinal glicentin and two glucagon-related peptides termed GLP-1 and GLP-2. Multidisciplinary approaches were then required to define the structure of biologically active GLP-1 7-36 amide and its role as an incretin, satiety hormone and, most recently, a neuroprotective peptide. This historial perspective outlines the use of traditional recombinant DNA approaches to derive the GLP-1 sequence and highlights the challenges and combination of clinical and basic science approaches required to define the physiology and pathophysiology of bioactive peptides discovered through genomics.     

Structures of peptide agonists for human protease activated receptor 2

Protease activated receptor 2 (PAR2) is an unusual G-protein coupled receptor in being self-activated, after pruning of the N-terminus by serine proteases like trypsin and tryptase. Short synthetic peptides corresponding to the newly exposed N-terminal hexapeptide sequence also activate PAR2 on immunoinflammatory, cancer and many normal cell types. (1)H nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopy were used here to search for structural clues to activating mechanisms of the hexapeptide agonists SLIGRL (rat), SLIGKV (human) and the peptidomimetic analogue, 2-furoyl-LIGRLO. Either with a free or acetyl capped N-terminus, these agonist peptides display significant propensity in aprotic (DMSO) or lipidic (water-SDS) solvents for turn-like conformations, which are predicted to be receptor-binding conformations in the transmembrane or loops region of PAR2. These motifs may be valuable for the design of small molecule PAR2 agonists and antagonists as prospective new drugs for regulating inflammatory and proliferative diseases.     

Immunohistochemical localization of glucagon-like peptide 1

Summary We report the use of poly-and monoclonal antibodies to study the immunohistochemical distribution of glucagon-like peptide-1 immunoreactivity (GLP-1-IR) in various tissues. The polyclonal antibodies against GLP-1 reacted with pancreatic A cells, enteroglucagon (L) cells in the gut, and some neurons in the central nervous system of all species tested. In pancreas and gut the monoclonal antibodies against GLP-1 exhibited a similar, but species specific distribution, relative to the polyclonal antibodies. The colocalization of GLP-1 and glucagon immunoreactivity in pancreatic, intestinal, and nervous tissues is in agreement with previously reported findings that both peptides are part of a single precursor molecule (preproglucagon).Supported by the DFG, SFB 90     

The contribution of serotonin 5-HT2C and melanocortin-4 receptors to the satiety signaling of glucagon-like peptide 1 and liragultide, a glucagon-like peptide 1 receptor agonist, in mice

Glucagon-like peptide 1 (GLP-1), an insulinotropic gastrointestinal peptide produced mainly from intestinal endocrine L-cells, and liraglutide, a GLP-1 receptor (GLP-1R) agonist, induce satiety. The serotonin 5-HT2C receptor (5-HT2CR) and melanoroctin-4 receptor (MC4R) are involved in the regulation of food intake. Here we show that systemic administration of GLP-1 (50 and 200 μg/kg)-induced anorexia was blunted in mice with a 5HT2CR null mutation, and was attenuated in mice with a heterozygous MC4R mutation. On the other hand, systemic administration of liraglutide (50 and 100 μg/kg) suppressed food intake in mice lacking 5-HT2CR, mice with a heterozygous mutation of MC4R and wild-type mice matched for age. Moreover, once-daily consecutive intraperitoneal administration of liraglutide (100 μg/kg) over 3 days significantly suppressed daily food intake and body weight in mice with a heterozygous mutation of MC4R as well as wild-type mice. These findings suggest that GLP-1 and liraglutide induce anorexia via different central pathways.     

The putative signal peptide of glucagon-like peptide-1 receptor is not required for receptor synthesis but promotes receptor expression

GLP-1R (glucagon-like peptide-1 receptor) mediates the ‘incretin effect’ and many other anti-diabetic actions of its cognate ligand, GLP-1 (glucagon-like peptide-1). It belongs to the class B family of GPCRs (G protein-coupled receptors) and possesses an N-terminal putative SP (signal peptide). It has been reported that this sequence is required for the synthesis of GLP-1R and is cleaved after receptor synthesis. In the present study, we conducted an in-depth exploration towards the role of the putative SP in GLP-1R synthesis. A mutant GLP-1R without this sequence was expressed in HEK293 cells (human embryonic kidney 293 cells) and displayed normal functionality with respect to ligand binding and activation of adenylate cyclase. Thus the putative SP does not seem to be required for receptor synthesis. Immunoblotting analysis shows that the amount of GLP-1R synthesized in HEK293 cells is low when the putative SP is absent. This indicates that the role of the sequence is to promote the expression of GLP-1R. Furthermore, epitopes tagged at the N-terminal of GLP-1R are detectable by immunofluorescence and immunoblotting in our experiments. In conclusion, the present study points to different roles of SP in GLP-1R expression which broadens our understanding of the functionality of this putative SP of GLP-1R and possibly other Class B GPCRs.     

The contribution of serotonin 5-HT2C and melanocortin-4 receptors to the satiety signaling of glucagon-like peptide 1 and liraglutide, a glucagon-like peptide 1 receptor agonist, in mice

Glucagon-like peptide 1 (GLP-1), an insulinotropic gastrointestinal peptide produced mainly from intestinal endocrine L-cells, and liraglutide, a GLP-1 receptor (GLP-1R) agonist, induce satiety. The serotonin 5-HT2C receptor (5-HT2CR) and melanoroctin-4 receptor (MC4R) are involved in the regulation of food intake. Here we show that systemic administration of GLP-1 (50 and 200μg/kg)-induced anorexia was blunted in mice with a 5HT2CR null mutation, and was attenuated in mice with a heterozygous MC4R mutation. On the other hand, systemic administration of liraglutide (50 and 100μg/kg) suppressed food intake in mice lacking 5-HT2CR, mice with a heterozygous mutation of MC4R and wild-type mice matched for age. Moreover, once-daily consecutive intraperitoneal administration of liraglutide (100μg/kg) over 3days significantly suppressed daily food intake and body weight in mice with a heterozygous mutation of MC4R as well as wild-type mice. These findings suggest that GLP-1 and liraglutide induce anorexia via different central pathways.     

Enteric neural pathways mediate the anti-inflammatory actions of glucagon-like peptide 2

Glucagon-like peptide-2 (GLP-2) is an important regulator of nutritional absorptive capacity with anti-inflammatory actions. We hypothesized that GLP-2 reduces intestinal mucosal inflammation by activation of vasoactive intestinal polypeptide (VIP) neurons of the submucosal plexus. Ileitis or colitis was induced in rats by injection of trinitrobenzene sulfonic acid (TNBS), or colitis was induced by administration of dextran sodium sulfate (DSS) in drinking water. Subsets of animals received (1-33)-GLP-2 (50 mug/kg sc bid) either immediately or 2 days after the establishment of inflammation and were followed for 3-5 days. The involvement of VIP neurons was assessed by concomitant administration of GLP-2 and the VIP antagonist [Lys(1)-Pro(2,5)-Arg(3,4)-Tyr(6)]VIP and by immunohistochemical labeling of GLP-2-activated neurons. In all models, GLP-2 treatment, whether given immediately or delayed until inflammation was established, resulted in significant improvements in animal weights, mucosal inflammation indices (myeloperoxidase levels, histological mucosal scores), and reduced levels of inflammatory cytokines (IFN-gamma, TNF-alpha, IL-1beta) and inducible nitric oxide synthase, with increased levels of IL-10 in TNBS ileitis and DSS colitis. Reduced rates of crypt cell proliferation and of apoptosis within crypts in inflamed tissues were also noted with GLP-2 treatment. These effects were abolished with coadministration of GLP-2 and the VIP antagonist. GLP-2 was shown to activate neurons and to increase the number of cells expressing VIP in the submucosal plexus of the ileum. These findings suggest that GLP-2 acts as an anti-inflammatory agent through activation of enteric VIP neurons, independent of proliferative effects. They support further studies to examine the role of neural signaling in the regulation of intestinal inflammation.     

Renal catabolism of human glucagon-like peptides 1 and 2

The renal catabolism of [125I]glucagon-like peptide 1 (GLP-1) and [125I]glucagon-like peptide 2 (GLP-2) has been studied both in vivo, by the disappearance of these peptides from the plasma of bilaterally nephrectomized (BNX), ureteral-ligated (BUL) or normal rats, and in vitro, analyzing their catabolism by the isolated, perfused rat kidney. Results from in vivo studies demonstrated that half-disappearance time for both peptides was lower in controls than in BUL rats, and this value in BUL rats was not significantly different from that in BNX rats. In addition, metabolic clearance rate of GLP-1 was higher in control rats than in the other two groups of animals. Urinary clearance rate of both peptides was negligible. In isolated kidney experiments, values for organ clearance of both [125I]GLP-1 and [125I]GLP-2 were similar to those of inulin clearance, which represents the glomerular filtration rate. Urinary clearance of trichloroacetic acid precipitable radioactivity represented less than 1% of total clearance. In conclusion, these results demonstrate a significant role for the kidney in the plasma removal of [125I]GLP-1 and [125I]GLP-2 by a mechanism that involves glomerular filtration and tubular catabolism.     

Second extracellular loop of human glucagon-like peptide-1 receptor (GLP-1R) has a critical role in GLP-1 peptide binding and receptor activation

The glucagon-like peptide-1 receptor (GLP-1R) is a therapeutically important family B G protein-coupled receptor (GPCR) that is pleiotropically coupled to multiple signaling effectors and, with actions including regulation of insulin biosynthesis and secretion, is one of the key targets in the management of type II diabetes mellitus. However, there is limited understanding of the role of the receptor core in orthosteric ligand binding and biological activity. To assess involvement of the extracellular loop (ECL) 2 in ligand-receptor interactions and receptor activation, we performed alanine scanning mutagenesis of loop residues and assessed the impact on receptor expression and GLP-1(1-36)-NH(2) or GLP-1(7-36)-NH(2) binding and activation of three physiologically relevant signaling pathways as follows: cAMP formation, intracellular Ca(2+) (Ca(2+)(i)) mobilization, and phosphorylation of extracellular signal-regulated kinases 1 and 2 (pERK1/2). Although antagonist peptide binding was unaltered, almost all mutations affected GLP-1 peptide agonist binding and/or coupling efficacy, indicating an important role in receptor activation. However, mutation of several residues displayed distinct pathway responses with respect to wild type receptor, including Arg-299 and Tyr-305, where mutation significantly enhanced both GLP-1(1-36)-NH(2)- and GLP-1(7-36)-NH(2)-mediated signaling bias for pERK1/2. In addition, mutation of Cys-296, Trp-297, Asn-300, Asn-302, and Leu-307 significantly increased GLP-1(7-36)-NH(2)-mediated signaling bias toward pERK1/2. Of all mutants studied, only mutation of Trp-306 to alanine abolished all biological activity. These data suggest a critical role of ECL2 of the GLP-1R in the activation transition(s) of the receptor and the importance of this region in the determination of both GLP-1 peptide- and pathway-specific effects.     

Characterization of glucagon-like peptide-1 receptor beta-arrestin 2 interaction: a high-affinity receptor phenotype

To dissect the interaction between beta-arrestin ((beta)arr) and family B G protein-coupled receptors, we constructed fusion proteins between the glucagon-like peptide 1 receptor and (beta)arr2. The fusion constructs had an increase in apparent affinity selectively for glucagon, suggesting that (beta)arr2 interaction locks the receptor in a high-affinity conformation, which can be explored by some, but not all, ligands. The fusion constructs adopted a signaling phenotype governed by the tethered (beta)arr2 with an attenuated G protein-mediated cAMP signal and a higher maximal internalization compared with wild-type receptors. This distinct phenotype of the fusion proteins can not be mimicked by coexpressing wild-type receptor with (beta)arr2. However, when the wild-type receptor was coexpressed with both (beta)arr2 and G protein-coupled receptor kinase 5, a phenotype similar to that observed for the fusion constructs was observed. We conclude that the glucagon-like peptide 1 fusion construct mimics the natural interaction of the receptor with (beta)arr2 with respect to binding peptide ligands, G protein-mediated signaling and internalization, and that this distinct molecular phenotype is reminiscent of that which has previously been characterized for family A G protein-coupled receptors, suggesting similarities in the effect of (beta)arr interaction between family A and B receptors also at the molecular level.     

Activation of human monocytes by a formyl peptide receptor 2-derived pepducin

We synthesized and investigated the effect of formyl peptide receptor 2 (FPR2)-derived pepducins in human monocytes. The FPR2-based cell-penetrating lipopeptide, “pepducin” (F2pal-16), stimulated intracellular calcium increase in human monocytes via pertussis toxin (PTX)-sensitive G-protein and phospholipase C (PLC) activity. From a functional aspect, we showed that F2pal-16 stimulated monocyte chemotaxis. F2pal-16 also stimulated the generation of superoxide anion in human monocytes. Moreover, F2pal-16 dramatically increased the production of several kinds of pro-inflammatory cytokines (CXCL8, CCL2, IL-1β and TNF-α) in human monocytes via NF-κB activation. Since FPR2 plays an important role in immune responses, F2pal-16 can serve as a useful reagent for the study of FPR2-mediated immune modulation.