Reproductive-hormone fragment (LHRH 1-6)
A partial piece of the brain's main reproductive-control hormone; it's missing the part needed to switch on the reproductive-hormone receptor, so it is 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
LHRH (1-6) is the N-terminal hexapeptide fragment of gonadotropin-releasing hormone (GnRH), the master hypothalamic hormone that controls the reproductive axis. The full GnRH decapeptide (sequence pyroGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH₂, as described in Tukun and colleagues (2017)) is responsible for triggering the pituitary release of LH and FSH, which in turn drive testosterone and estrogen production. LHRH (1-6) retains only the first six residues of that decapeptide — Gln-His-Trp-Ser-Tyr-Gly — and lacks the C-terminal half (positions 7-10) that is required for canonical GnRH receptor activation. As a result, this fragment has been studied not as a GnRH mimetic but as a biologically distinct signaling entity in its own right. The stored sequence begins with Q (glutamine), but in native GnRH the N-terminal glutamine cyclizes to pyroglutamate (pGlu); whether this cyclization occurs in isolated fragment preparations is not established by the available sources.
History
GnRH itself was isolated and sequenced in the early 1970s by Andrew Schally's and Roger Guillemin's laboratories — work recognized with the 1977 Nobel Prize in Physiology or Medicine, as noted in the peptidelist entry for gonadorelin. Interest in the N-terminal fragments of GnRH arose from the observation that the full decapeptide undergoes rapid proteolytic processing in vivo, generating fragments including GnRH-(1-5) and GnRH-(1-6). These fragments were initially regarded as inactive degradation products, but later work identified independent biological activity for the N-terminal pentapeptide GnRH-(1-5). Cho-Clark and colleagues (2014) demonstrated that GnRH-(1-5) transactivates the epidermal growth factor receptor (EGFR) in Ishikawa human endometrial cells through an orphan G protein-coupled receptor distinct from the canonical GnRHR — establishing that the N-terminal fragment lineage has signaling activity that does not require the C-terminal receptor-binding residues of the parent decapeptide. LHRH (1-6) sits one residue beyond that pentapeptide, encompassing the same first five positions plus Gly-6.
What it does
Unlike the full GnRH decapeptide, LHRH (1-6) does not robustly stimulate LH and FSH release from pituitary gonadotrophs through the canonical GnRH receptor pathway, because the receptor-activating C-terminal residues (positions 7-10) are absent. The fragment's documented activity centers on the N-terminal pharmacophore: Cho-Clark and colleagues (2014) showed that the closely related GnRH-(1-5) pentapeptide acts via an orphan GPCR to transactivate EGFR in endometrial cells, engaging intracellular signaling cascades independent of the classical GnRHR/Gq axis that governs pituitary LH/FSH secretion. The GnRHR, as reviewed by Sperduti and colleagues (2019), signals through multiple pathways (including IP3/DAG downstream of Gq/11 as well as ERK and other MAPK branches); fragment activity at non-canonical receptors may tap into overlapping or distinct components of this network.
Evidence
- Human: No published clinical trials specifically evaluating LHRH (1-6) as an isolated fragment were identified in the available sources.
- Animal: No animal-model studies specifically examining LHRH (1-6) biology were identified in the available sources.
- In vitro: Cho-Clark and colleagues (2014) demonstrated EGFR transactivation via an orphan GPCR for the related GnRH-(1-5) pentapeptide in Ishikawa human endometrial cells; direct in vitro data for the hexapeptide LHRH (1-6) are not present in the dossier.
Known effects
- GnRH receptor binding — Weak or absent; the C-terminal residues required for canonical GnRHR agonism are not present in this fragment (Tukun et al. 2017; Sperduti et al. 2019)
- N-terminal fragment signaling — The related pentapeptide GnRH-(1-5) transactivates EGFR via an orphan GPCR in endometrial cells (Cho-Clark et al. 2014; extrapolated to the hexapeptide context, not directly demonstrated for LHRH (1-6))
Mechanism
The full GnRH decapeptide binds GnRHR on anterior pituitary gonadotrophs and activates Gq/11-mediated phospholipase C signaling, generating IP3 and DAG, driving LH and FSH secretion — a pathway documented across multiple GnRH antagonist comparator studies (Sperduti et al. 2019). Receptor transcription and activity in gonadotrophs are reviewed by Janjic and colleagues (2017). LHRH (1-6) lacks residues 7-10 (Leu-Arg-Pro-Gly-NH₂) which form the canonical receptor-binding pharmacophore; this C-terminal deficiency underlies the fragment's weak classical receptor activity. Cho-Clark and colleagues (2014) identified that GnRH-(1-5) — the pentapeptide one residue shorter than LHRH (1-6) — can still transduce signal in endometrial tissue via an orphan GPCR that transactivates EGFR, pointing to a distinct receptor-engagement mode for N-terminal GnRH fragments that is independent of the pituitary GnRHR axis. Whether GnRH-2, a second mammalian GnRH form with its own receptor (GnRHR2), has any cross-reactivity with LHRH (1-6) is unresolved; Desaulniers and colleagues (2017) reviewed GnRH-2 receptor expression and function in mammals, but specific fragment interaction data are absent.
Open questions
- Whether LHRH (1-6) itself (as distinct from the pentapeptide GnRH-(1-5)) engages the orphan GPCR identified by Cho-Clark and colleagues (2014) has not been directly demonstrated
- The N-terminal pyroglutamate cyclization status of isolated fragment preparations, and its impact on bioactivity, is not established in published literature
- No binding affinity or functional potency data (Ki, EC50) for LHRH (1-6) at any receptor are present in the dossier
- Physiological relevance of endogenous LHRH (1-6) generation as a GnRH metabolite in reproductive tissues remains uncharacterized
Related peptides
- Full-length GnRH (gonadorelin) — the parent decapeptide from which this fragment is derived; see also leuprolide, a synthetic GnRH agonist analog with high GnRHR affinity
- GnRH-(1-5) — the pentapeptide N-terminal fragment one residue shorter than LHRH (1-6); the Cho-Clark (2014) EGFR transactivation data apply to this form
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 activate a poorly understood receptor that normally helps cells move, which could be relevant to how endometriosis spreads or cancers invade?
Endometriosis and gynecological cancers involve tissue that invades where it should not. A naturally occurring hormone fragment that drives this invasion through a specific receptor could be a key missing piece in understanding these diseases and could point to new drug targets to stop the spread.
Does this fragment only bind its target receptor after its first building block spontaneously converts into a slightly different chemical form that fits the receptor properly?
If the fragment converts itself into the active form inside the body, it behaves like a prodrug, possibly with a built-in delay that could be tuned for timed-release therapy. Understanding this would guide how chemists should make and store the compound for clinical use.
Could this natural hormone fragment reduce the pain and tissue growth of endometriosis by both suppressing estrogen levels and stopping invasive cell movement?
Endometriosis causes severe pain for millions of women and current treatments are either hormonal, with major side effects, or surgical. A therapy derived from a natural human hormone that addresses both the hormonal and invasive aspects of the disease simultaneously could be less harmful and more effective than current options.
Could this fragment lock into the receptor that controls sex hormone production and prevent the natural hormone from binding, without itself causing any hormone release?
A drug that silently blocks the GnRH receptor without first triggering a hormone surge could be used to treat hormone-sensitive conditions, like endometriosis or prostate cancer, more safely than current treatments, which cause a harmful initial hormone spike.
Does this fragment only produce its full effect in tissues that have both of its target receptors at once, naturally limiting where in the body it acts?
Hormonal treatments for endometriosis and uterine fibroids often affect the whole body, causing hot flashes and bone loss. A drug that is only active in the uterus, because both its target receptors happen to be present there, could treat these conditions locally without the systemic side effects that make current hormonal therapies so difficult for women to tolerate.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.9569584727287292 | boltz-2 |
| ranking score | 0.838503360748291 | 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{pep10732,
sequence = {QHWSYG},
target = {gnrhr},
author = {peptidemodel},
year = {2026},
status = {computed}
}