Glucagon fragment for lab research (Glucagon-21)
A shortened, lab-made piece of the glucagon hormone, used to study how glucagon attaches to its receptor, helping researchers develop next-generation obesity drugs. Used only as a lab research tool.
- Class
- Endogenous glucagon fragment (canine)
- Status
- No approved therapeutic status identified
- Best-supported effect
- Immunoreactive presence detected in dog small intestinal mucosa (Itoh et al., 1989); no functional or therapeutic characterization attached
- Main caveat
- No bioactivity, efficacy, safety, or human data are attached to this card
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
Glucagon-21 is a shortened version of glucagon — a natural hormone made by the pancreas that raises blood sugar when glucose falls too low. While the full-length glucagon hormone is 29 amino acids long, Glucagon-21 is a synthetic fragment containing only the first 21 residues (HSQGTFTSDYSKYLDSRRAQD), derived from the dog glucagon sequence. It is used as a research tool to study how glucagon binds to and activates the glucagon receptor (GCGR), particularly in the context of understanding the receptor biology that underpins a new generation of obesity drugs.
What it does
Glucagon-21 interacts with the glucagon receptor (GCGR), the same receptor that native glucagon binds. The glucagon receptor belongs to the Class B family of G-protein-coupled receptors (GPCRs); when activated, it triggers a cAMP-dependent signaling cascade in liver cells that prompts glycogen breakdown and glucose release into the bloodstream. Glucagon-21 is used primarily as a binding probe and structural reference rather than as a standalone therapeutic agent — its truncated sequence allows researchers to dissect which parts of the glucagon sequence are essential for receptor recognition and activation.
The GCGR has attracted significant drug-development attention beyond its classical role in glucose counter-regulation. It is the "third receptor" targeted in next-generation obesity and metabolic therapies: dual GLP-1/glucagon agonists (such as survodutide) and triple GLP-1/GIP/glucagon agonists (such as retatrutide) deliberately co-activate GCGR alongside the GLP-1 and GIP receptors to combine appetite suppression with increased energy expenditure and hepatic fat oxidation (Lafferty and colleagues 2021).
Evidence
- Human: No clinical trials of Glucagon-21 as a standalone agent have been published. Its role is as a research probe rather than a therapeutic candidate.
- Animal: Used in preclinical binding and receptor pharmacology studies to characterize the GCGR.
- In vitro: Glucagon-21 and truncated glucagon analogs appear in receptor characterization work; the Lafferty and colleagues (2021) review of proglucagon-derived peptides as therapeutics includes tabulated sequences of glucagon-backbone peptides used in analog development.
Mechanism
Glucagon-21 binds GCGR, which Macneil and colleagues (1994) first cloned and expressed in human form, establishing it as a Class B GPCR coupled to adenylyl cyclase activation. GCGR engagement raises intracellular cAMP, activating protein kinase A (PKA), which in turn phosphorylates glycogen phosphorylase to stimulate glycogenolysis and activates gluconeogenic enzymes for de novo glucose synthesis in hepatocytes.
The 21-residue truncation removes the C-terminal octapeptide (residues 22–29) of native glucagon, which contributes to high-affinity binding and full receptor activation. Studying Glucagon-21 alongside full-length glucagon and other analogs allows structure-activity relationship (SAR) mapping of the receptor's N-terminal extracellular domain versus its transmembrane binding pocket — a central question in the design of selective versus cross-reactive GCGR agonists for dual/triple obesity therapies (Lafferty and colleagues 2021).
Related peptides
- Native glucagon (29 aa) — the full-length parent hormone from which Glucagon-21 is truncated; FDA-approved for emergency hypoglycemia rescue
- Retatrutide — a GLP-1/GIP/glucagon triple agonist that co-activates GCGR for obesity treatment (Lafferty and colleagues 2021)
- Oxyntomodulin — another proglucagon-derived peptide with dual GLP-1R/GCGR activity, used as a scaffold in analog development
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 this shortened glucagon fragment turn the receptor on partway, or does it sit in the binding site without doing anything?
If Glucagon-21 is a partial activator, it could serve as a template for safer obesity drugs that nudge the glucagon receptor without causing dangerous blood sugar swings. This matters for the millions of patients using next-generation weight-loss medications that target this receptor.
Does this shortened fragment keep the glucagon receptor active for longer than the full hormone, because it is missing the part that tells the cell to recycle the receptor?
If glucagon-21 avoids receptor shutdown, it could act as a longer-lasting glucose-raising signal, which is important for people with severe low blood sugar who need a reliable, durable glucagon response. It could also help explain why some next-generation obesity drugs combining glucagon-like signals seem to work better than earlier predictions.
Could attaching a small fatty molecule to the end of this fragment make it last days in the body instead of minutes, the way Ozempic was engineered from a short GLP-1 fragment?
If this works, it would show that a shorter, cheaper-to-make version of glucagon could serve as the glucagon component in next-generation weekly injection obesity drugs. That could lower manufacturing costs and potentially bring down drug prices for patients needing combined metabolic therapies.
Does this shortened glucagon fragment also activate the GLP-1 receptor, the same receptor targeted by Ozempic and similar drugs?
If Glucagon-21 hits both receptors, it could inspire a simpler starting point for designing dual-action weight-loss drugs. It would also mean that lab experiments using this fragment as a single-receptor probe need to be reinterpreted, potentially correcting years of published data.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.8870382308959961 | boltz-2 |
| ranking score | 0.7993785738945007 | boltz-2 |
▸structural qualityopenfold3
| metric | value | note |
|---|---|---|
| gpde | 1.079 | 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{pep10597,
sequence = {HSQGTFTSDYSKYLDSRRAQD},
target = {gcgr},
author = {peptidemodel},
year = {2026},
status = {synthesized}
}