Gastrin-releasing peptide: natural gut-brain messenger (GRP, human)
A natural signaling molecule made in the gut and lungs that tells the stomach to release acid and helps coordinate digestion; used only as a lab research tool.
A researcher, an agent, or an algorithm wrote down the sequence and picked a target to hit.
An AI model like OpenFold3 or AlphaFold built a 3D structure and scored how well it fits the binding site.
A second contributor repeated the computation on their own hardware and the scores matched.
A chemistry service or a researcher ordered the sequence, it was manufactured, and mass spectrometry confirmed the right molecule was produced.
A binding or activity measurement confirmed that it actually does what the computer predicted — or didn't.
What this is
Gastrin-releasing peptide (GRP) is a 27-amino acid neuropeptide produced naturally in the body — primarily by nerve cells lining the gut and lungs — that acts as a chemical messenger linking the nervous system to the digestive system. Its most prominent job in the gut is to prompt G cells in the stomach lining to release gastrin, the hormone that drives acid secretion and digestion; this signaling occurs via the vagus nerve, where GRP serves as the key neurotransmitter relaying the "food has arrived" signal (Spindel and colleagues, PNAS 1984). GRP is the mammalian counterpart of bombesin, a peptide originally found in amphibian skin, and the two share a nearly identical C-terminal sequence that accounts for their shared biological activities; the mature processed peptide carries a C-terminal amide (−NH₂) that is absent from the stored raw sequence shown here. Beyond the stomach, GRP is widely expressed in the brain, spinal cord, and lung, where it participates in appetite regulation, fear memory, and neuroendocrine signaling.
History
GRP was first purified from porcine stomach tissue and characterized in 1979 as the mammalian equivalent of the frog skin peptide bombesin. The molecular identity of the human form was established in 1984, when Spindel and colleagues cloned the cDNA encoding human GRP from a pulmonary carcinoid tumor — a neuroendocrine lung tumor that overproduces the peptide — and showed that the gene encodes a 148-amino acid precursor (prepro-GRP) from which the mature 27- or 28-amino acid peptide is processed (Spindel and colleagues, PNAS 1984). Cloning revealed that human GRP is closely related in structure to amphibian bombesin, with the shared C-terminal heptapeptide sequence (−WAVGHLM) being the principal pharmacophore for receptor activation. The gene was subsequently mapped to human chromosome 18q21. Interest in the GRP/gastrin–CCK receptor axis intensified after GRP-like peptides were found to be overproduced in several neuroendocrine cancers, motivating the development of radiolabeled GRP analogs as imaging and therapeutic agents (Roosenburg and colleagues, Amino Acids 2011; Berna and colleagues, Current Opinion in Pharmacology 2007).
What it does
In the gastrointestinal tract, GRP acts as a neurotransmitter released from vagal nerve endings onto antral G cells, triggering gastrin secretion and thereby stimulating gastric acid production and promoting digestion (Zeng and colleagues, Frontiers in Endocrinology 2020). GRP also stimulates the contraction of smooth muscle along the gut, promotes pancreatic enzyme secretion, and contributes to gallbladder emptying through pathways that overlap with the cholecystokinin A receptor (CCKAR) system expressed in the gallbladder and small intestine (Wang and colleagues, Genes 2020). In the brain, GRP acts as a neuromodulator involved in appetite suppression, circadian rhythm synchronization, and the formation of fear-related memories. In the lung, GRP has mitogenic effects on bronchial epithelial cells and serves as an autocrine growth signal in certain lung cancers, particularly small cell lung cancer, where its precursor (pro-GRP) is produced abundantly enough to be used as a diagnostic serum biomarker.
Evidence
- Human: Pro-GRP, the stable circulating precursor of GRP, is an established serum biomarker for small cell lung cancer (SCLC), with superior specificity compared with neuron-specific enolase for distinguishing SCLC from non–small cell lung cancer (Roosenburg and colleagues, Amino Acids 2011). Radiolabeled bombesin/GRP analogs targeting GRP-preferring receptors have entered clinical imaging trials for receptor-overexpressing tumors including prostate cancer; antagonist analogs have shown favourable pharmacokinetics compared with agonists in early-phase studies.
- Animal: Systemic administration of GRP reduces food intake in animal models; this effect is absent in mice lacking GRP-preferring receptors, confirming a central satiety role. GRP knockout or receptor-blocking studies in rodents have mapped roles in fear memory consolidation and male sexual behavior.
- In vitro: GRP and its receptor system have been characterized in binding assays across the bombesin receptor family. The CCK and gastrin receptor system, which GRP engages indirectly through gastrin release, has been extensively characterized pharmacologically; Miller and colleagues (Pharmacology & Therapeutics 2008) reviewed the structural basis of CCK receptor binding and regulation, and Berna and colleagues (Current Opinion in Pharmacology 2007) surveyed CCK/gastrin receptor ligands with therapeutic potential.
Mechanism
GRP binds the GRP-preferring receptor (also classified as the BB2 bombesin receptor subtype), a class A G protein-coupled receptor that couples to Gq, raising intracellular calcium and activating the phospholipase C and MAPK/ERK pathways. This signaling is distinct from — though functionally linked to — the cholecystokinin receptor family. When GRP-expressing vagal neurons fire, released GRP acts on antral G cells to increase gastrin output; gastrin then travels via the bloodstream to act on CCK2 (gastrin/CCKB) receptors on parietal cells, driving acid secretion. The cholecystokinin A receptor (CCKAR), expressed predominantly in the gallbladder and small intestine (Wang and colleagues, Genes 2020), responds primarily to cholecystokinin to regulate gallbladder contraction and intestinal cholesterol absorption; GRP's influence on this axis is indirect, mediated through the gastrin it releases rather than through direct CCKAR binding. The structural basis of CCK receptor binding — including the determinants of peptide selectivity and receptor regulation — has been reviewed by Miller and colleagues (Pharmacology & Therapeutics 2008). In neuroendocrine tumors, GRP and bombesin-like peptides act as autocrine mitogens through constitutive or overexpressed receptor activation, making the GRP receptor a target for diagnostic imaging and peptide receptor radionuclide therapy using radiolabeled GRP/bombesin analogs (Roosenburg and colleagues, Amino Acids 2011).
Known effects
- Gastric acid stimulation — Physiological: GRP triggers gastrin release from antral G cells via vagal neurotransmission, driving parietal cell acid secretion (Spindel and colleagues, PNAS 1984; Zeng and colleagues, Frontiers in Endocrinology 2020)
- Gastrointestinal motility and secretion — Physiological: promotes smooth muscle contraction, pancreatic enzyme secretion, and interacts with the CCK/CCKAR axis governing gallbladder emptying (Wang and colleagues, Genes 2020; Zeng and colleagues, Frontiers in Endocrinology 2020)
- Appetite suppression — Preclinical: central GRP signaling reduces food intake in animal models; mechanism involves hypothalamic circuits
- Cancer growth signal — Preclinical / translational: autocrine mitogen in small cell lung cancer and other neuroendocrine tumors; GRP receptor overexpression in prostate, breast, and lung cancers makes it a theranostic target (Roosenburg and colleagues, Amino Acids 2011)
- Pro-GRP as SCLC biomarker — Translational: serum pro-GRP levels are elevated in small cell lung cancer, enabling differential diagnosis from other lung malignancies
Safety signals
GRP is an endogenous neuropeptide present throughout the body and gut; no adverse safety profile is associated with its physiological presence. Exogenous administration of GRP and bombesin-like peptides has been studied in human subjects as part of investigational imaging agent trials, where they have been reported to be generally well tolerated intravenously in early-phase studies. No approved therapeutic application currently exists. Radiolabeled GRP analogs for theranostic use are under clinical investigation; their safety profiles in this context are being evaluated in ongoing trials.
Regulatory status
- US (FDA): Not approved as a therapeutic. Pro-GRP measurement is a laboratory diagnostic tool, not an FDA-approved drug product. Radiolabeled GRP/bombesin analogs for imaging are under clinical investigation.
- EU (EMA): Not approved as a therapeutic. Investigational imaging and radionuclide therapy applications are in development.
- WADA: Not listed on the prohibited list.
Related peptides
GRP belongs to the bombesin-like peptide family, whose members share the C-terminal pharmacophore responsible for receptor activation. Closely related mammalian peptides include neuromedin C (the 10-residue C-terminal fragment of GRP, also called GRP-10) and neuromedin B, a distinct 10-residue bombesin-family peptide that preferentially binds the NMB receptor (BB1 subtype). Gastrin and cholecystokinin (CCK) occupy the downstream arm of this signaling axis: gastrin acts on CCK2/CCKB receptors on parietal cells to drive acid secretion, while CCK acts on CCKAR in the gallbladder and intestine to regulate motility and cholesterol absorption (Wang and colleagues, Genes 2020; Miller and colleagues, Pharmacology & Therapeutics 2008; Berna and colleagues, Current Opinion in Pharmacology 2007). For the broader CCK/gastrin receptor pharmacology see also the gastrin and cholecystokinin cards on this platform.
Research directions for this peptide, selected from the current sources — hypotheses you can explore and model. None of it is proven yet; tap any one to see the full thinking.
Does GRP primarily act on the bombesin receptor rather than the cholecystokinin receptor it was assigned to in this dataset?
Clarifying GRP's true primary target matters for cancer research: the bombesin receptor it likely favors is overexpressed in prostate and breast cancers and is being studied as a drug target. Correcting the annotation could redirect productive research.
If the flexible middle section of GRP is made more rigid or resistant to breakdown, would GRP-based cancer tracers and drugs stay active longer in the bloodstream?
GRP-based imaging agents are already being tested to find prostate and breast cancer tumors. If the peptide's floppy middle section is stabilized, these tracers might last long enough to light up tumors more reliably, improving cancer detection for patients.
Does the shape that tryptophan adopts in GRP's active tip decide whether it binds the GRP receptor or the closely related NMB receptor?
If a single residue controls receptor choice, drug designers could lock this switch in one position to build highly selective peptide drugs that activate only one receptor, reducing off-target effects in cancer therapy or appetite control.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.7453140020370483 | boltz-2 |
| ranking score | 0.7247037887573242 | boltz-2 |
▸structural qualityopenfold3
| metric | value | note |
|---|---|---|
| gpde | 1.420 | global PDE — lower = better |
| disorder | NaN | fraction disordered |
▸3-letter notation
▸recipeboltz-2 1.0
| parameter | value |
|---|---|
| model | boltz-2 1.0 |
| weights | — |
| hardware | nvidia_nim_api |
| mlx version | — |
| python | — |
| random seed | — |
| msa strategy | none |
| diffusion samples | 1 |
| runtime | — |
| predicted by | mlx@peptide |
| predicted at | 2026-04-24 |
▸citationbibtex
@peptide{pep10679,
sequence = {VPLPAGGGTVLTKMYPRGNHWAVGHLM},
target = {cckar},
author = {peptidemodel},
year = {2026},
status = {synthesized}
}