IGF-1 growth-factor fragment (residues 24: 41)
A small piece of IGF-1, one of the body's natural growth signals; used in lab research to study how growth signals work. Experimental, not an approved 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
IGF-1 (24–41) is an 18-amino-acid fragment carved out of the middle of human insulin-like growth factor 1 (IGF-1). It corresponds to the tail end of the IGF-1 B-domain together with the full C-domain — the loop that sits between the two cysteine-rich halves of the parent hormone. Because the fragment lies entirely between the disulfide-forming cysteines of native IGF-1, it contains no cysteines itself and folds as a linear peptide rather than as the disulfide-stapled "mini-insulin" shape of the parent. The sequence stored here, YFNKPTGYGSSSRRAPQT, maps verbatim onto residues 24–41 of mature human IGF-1 as published in receptor-binding and isoform studies (Hameed 2004; the same stretch appears inside the full IGF-1 and IGF-1Ec sequences used in those papers).
What it does
In the intact IGF-1 molecule, this stretch forms the C-domain — the loop that contacts the IGF-1 receptor (IGF-1R) and is the principal determinant of why IGF-1 binds IGF-1R more tightly than insulin does, even though the two hormones share their overall fold (Xu 2018; Belfiore 2017). The same region is also the splice junction in the IGF-1Ec isoform, the alternative transcript better known as mechano growth factor (MGF) (Hameed 2004). For the isolated 18-aa fragment specifically, no characterized receptor-binding affinity, downstream signaling readout, or in vivo bioactivity is reported in the references attached to this card — the biology that does exist describes either the parent hormone, the IGF-1R complex, or the separate MGF C-terminal peptide.
Mechanism
IGF-1R is a homodimeric receptor tyrosine kinase whose ectodomain undergoes ligand-induced conformational rearrangement; in the cryo-EM structure of IGF-1 bound to its receptor, the IGF-1 C-domain (the region this fragment corresponds to) inserts into the primary binding site formed at the interface of the L1 and CR domains of one receptor protomer and the FnIII-1 domain of the other (Xu 2018). Downstream, IGF-1R engagement activates IRS/PI3K/AKT and Shc/MAPK cascades to drive proliferation, differentiation, and survival signaling (Józefiak 2021; Girnita 2014). Whether the isolated 18-residue C-domain–containing fragment can engage the receptor on its own — versus only contributing affinity in the context of the intact, disulfide-folded hormone — is not established in the attached literature.
Evidence
- Human: No human trials of this exact 18-aa fragment are reported in the references on this card.
- Animal: No in-vivo studies of this exact fragment are reported in the references on this card. Related IGF-1 fragments (notably the MGF C-terminal peptide, a separate splice-derived peptide from the same gene) have been tested in rodent models of brain ischemia and muscle repair (Dłużniewska 2005; Suetta 2013).
- In vitro: The 24–41 stretch appears as part of the parent IGF-1 sequence in receptor-binding studies (Xu 2018) and as part of the IGF-1Ec sequence in muscle mRNA-expression work (Hameed 2004); no isolated-fragment binding data is included here.
- No registered ClinicalTrials.gov entries for "IGF-1 (24–41)" or the B/C-domain junction peptide as a discrete agent.
Related peptides
This fragment shares a parent gene (IGF1) with other IGF-1–derived peptides on the platform but is structurally distinct from each of them:
- Mechano growth factor (MGF) C-terminal peptide — a 24-residue peptide from the alternatively spliced IGF-1Ec isoform, derived from a different region of the parent transcript (the E-domain C-terminus, not the B/C junction). MGF has its own neuroprotective and muscle-repair literature (Dłużniewska 2005; Hameed 2004; Załocka 2012; Suetta 2013) and is biologically a separate entity from the 24–41 fragment, even though both come from the IGF-1 gene.
- Full-length IGF-1 (IGF-IEa) — the canonical 70-aa hormone within which YFNKPTGYGSSSRRAPQT sits as residues 24–41.
Open questions
- Receptor binding: does the isolated 18-aa fragment retain measurable affinity for IGF-1R, or does C-domain activity depend on presentation in the context of the disulfide-stapled parent fold? Not addressed in the attached references.
- Stability: no serum half-life, proteolytic-stability, or PK data are reported for this fragment.
- Biological readout: no cell-based or in-vivo phenotype has been ascribed to the isolated 24–41 peptide in the literature attached to this card.
- Distinction from MGF: the MGF C-terminal peptide is well-studied; the B/C-domain junction peptide is not. Whether the two share any overlapping receptor-engagement biology is unresolved here.
Regulatory status
- US: Not an approved drug; not an investigational drug in any registered trial visible on ClinicalTrials.gov.
- EU: No EMA listing.
- WADA: The parent IGF-1 and its IGF-1Ec/MGF isoform are addressed under S2 (peptide hormones, growth factors, related substances) of the WADA Prohibited List; mass-spectrometric methods for detecting MGF have been developed in a doping-control context (Thevis 2014). Whether the isolated B/C-domain junction fragment is itself separately characterized for doping control is not stated in the attached refs.
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 fragment, separated from the rest of IGF-1, switch its receptor preference from the IGF-1 receptor to the insulin receptor?
If this fragment binds the wrong receptor when used alone, any therapy or diagnostic based on it could have unintended effects on insulin signaling and metabolism, a safety concern important to understand before clinical development.
Would anchoring this IGF-1 fragment to a supporting protein structure allow it to bind the IGF-1 receptor as effectively as the full hormone?
If scaffolding restores binding, this approach could produce a simpler, more manufacturable replacement for full IGF-1 in conditions like growth hormone insensitivity syndrome or severe muscle wasting, where IGF-1 therapy is used but the full protein is costly and complex to produce.
Can this natural fragment of IGF-1 occupy the IGF-1 receptor without activating it, thereby slowing the growth of rhabdomyosarcoma?
If the fragment can block the IGF-1 receptor in rhabdomyosarcoma cells without the side effects of full IGF-1R inhibitors, it could become part of a combination treatment for this difficult-to-treat pediatric cancer.
Does adding phosphate groups to the three serines in this IGF-1 fragment reduce its ability to activate the IGF-1 receptor?
If IGF-1 can be chemically turned down by its own phosphorylation, this would reveal a new way the body naturally controls growth signaling, which could be exploited in cancers where IGF-1 activity is too high.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.2078525424003601 | boltz-2 |
| ranking score | 0.4423082768917084 | boltz-2 |
▸3-letter notation
▸recipeboltz-2 2.2.1
| parameter | value |
|---|---|
| model | boltz-2 2.2.1 |
| weights | — |
| hardware | vast_v100_32gb |
| mlx version | — |
| python | — |
| random seed | 1 |
| msa strategy | colabfold_local |
| runtime | — |
| predicted by | — |
| predicted at | 2026-05-22 |
▸citationbibtex
@peptide{pep10786,
sequence = {YFNKPTGYGSSSRRAPQT},
target = {igf-1r},
author = {peptidemodel},
year = {2026},
status = {synthesized}
}