Ghrelin-receptor binding peptide (KFLL / CHEMBL2170693)
A tiny four-amino-acid fragment that attaches to the hunger hormone's receptor; used only as a lab research tool, not a drug.
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
KFLL is a four-residue peptide fragment that binds the ghrelin receptor (GHSR / GHS-R1a), the same receptor that the natural "hunger hormone" ghrelin and synthetic growth-hormone secretagogues such as GHRP-6, hexarelin, and ipamorelin act on. The card represents ChEMBL entry CHEMBL2170693, a research compound characterized in a structure-activity study of short ghrelin-receptor ligands rather than a therapeutic or supplement. It is interesting as a tool compound, not as a clinical agent.
What it does
In the binding assay used to characterize it, KFLL engages the ghrelin receptor with a Ki of 31.3 nM (ChEMBL CHEMBL2170693). The peptide is one of several short ligands explored by Els and colleagues (2012) in work mapping how minor structural changes — particularly the introduction of aromatic residues — can flip a short ghrelin-receptor binder between agonist and inverse-agonist behavior at GHSR.
Mechanism
GHSR (GHS-R1a) is a Gq-coupled G-protein-coupled receptor whose endogenous agonist is acyl-ghrelin and whose endogenous inverse agonist is LEAP2. Short peptide ligands such as KFLL occupy the same orthosteric pocket explored by the larger GHRP-class secretagogues. The Els (2012) study from which this ligand is drawn focused on how an aromatic residue placed at a defined position in the short peptide chain acts as a "switch" that toggles the functional response between activation and inverse agonism at GHSR — meaning the same chemotype can either drive or suppress receptor signaling depending on a single side-chain choice. This makes KFLL and its analogs useful as probes for receptor pharmacology rather than as drug candidates in their own right.
Evidence
- Human: No human clinical data. KFLL is a research-grade fragment from a medicinal-chemistry study, not a clinical candidate.
- In vitro: Ki = 31.3 nM at the ghrelin receptor (ChEMBL CHEMBL2170693). Reported in the context of an SAR series exploring the agonism / inverse-agonism switch at GHSR (Els 2012, J. Med. Chem.).
Regulatory status
KFLL is a research compound with no approved indication. It is not on any compounded-peptide formulary and has no recognized therapeutic use. As a ghrelin-receptor ligand, the broader class of GHS-R1a agonists is prohibited under WADA's S2 (peptide hormones, growth factors, related substances and mimetics) class for athletic competition.
▸full evidence table1 metrics
| metric | value | tool |
|---|---|---|
| Ki | 31.3 nM | GPCRDB/ChEMBL |
▸structural qualityopenfold3
| metric | value | note |
|---|---|---|
| gpde | 0.471 | 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{pep10344,
sequence = {KFLL},
target = {ghsr},
author = {peptidemodel},
year = {2026},
status = {bioassayed}
}