Kisspeptin-54 (27-54): reproductive hormone fragment (human)
A lab-made fragment of a natural hormone that triggers the brain's signal chain for sex-hormone production and fertility; experimental, not yet 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
Kisspeptin-54 (27-54) is a 28-residue synthetic fragment spanning positions 27 through 54 of the full-length human kisspeptin-54 peptide — the C-terminal half of the 54-amino-acid form that is the dominant circulating kisspeptin isoform in adult humans. Like all biologically active kisspeptins, it acts on the kisspeptin receptor (KISS1R, formerly called GPR54), a G protein-coupled receptor concentrated on GnRH neurons in the hypothalamus. Because kisspeptin signals sit at the top of the chain that drives sex-hormone production, the kisspeptin family has attracted intense clinical interest for fertility treatment, reproductive hormone disorders, and diagnostic testing of puberty-related conditions. The raw sequence IPAPQGAVLVQREKDLPNYNWNSFGLRF (28 aa) encodes the peptide backbone faithfully, but in the endogenous context the C-terminus carries an amide cap (–NH₂) that is not represented in the stored one-letter sequence.
This fragment is distinct from the two better-characterised clinical forms: full-length kisspeptin-54 (used in IVF and HSDD trials) and kisspeptin-10 (the C-terminal decapeptide, which contains the core binding motif). As a mid-length fragment, its receptor-binding potency is intermediate to weaker: it retains the KISS1R-binding C-terminal motif but lacks portions of the N-terminal extension that contribute to the higher potency of kisspeptin-54.
History
The story of this fragment begins with its parent gene, KISS1, discovered in 1996 as a metastasis-suppressor in melanoma cells at Hershey Medical Center, Pennsylvania — named informally after the town's signature Hershey's Kisses candy. The reproductive role of kisspeptin was established in 2003 when independent groups identified that loss-of-function mutations in KISS1R (GPR54) cause idiopathic hypogonadotropic hypogonadism in humans, positioning the receptor — and its endogenous ligands — as master regulators of reproductive hormone release (Mead and colleagues, 2007).
The KISS1 gene encodes a 145-amino-acid precursor (prepro-kisspeptin-1) that is proteolytically processed to yield kisspeptin-54 as the predominant full-length circulating form, along with shorter isoforms including kisspeptin-14, kisspeptin-13, and kisspeptin-10. The (27-54) fragment catalogued here represents a synthetic sub-fragment of kisspeptin-54 — spanning its C-terminal half — used in research to probe receptor pharmacology and structure–activity relationships within the kisspeptin system.
The kisspeptin receptor (KISS1R/GPR54) was formally named and characterised in the IUPHAR nomenclature framework (Kirby and colleagues, 2010), establishing the framework within which fragments like this one are evaluated.
What it does
All active kisspeptins — including this (27-54) fragment — bind KISS1R on hypothalamic GnRH neurons, triggering GnRH pulse generation. This in turn drives pituitary release of LH and FSH, the gonadotropins that signal the gonads to produce testosterone and estrogen. The kisspeptin system sits at the very top of the reproductive hormone axis (Xie and colleagues, 2022).
The (27-54) fragment contains the conserved C-terminal region that is necessary for KISS1R binding and activation, but its binding potency relative to full-length kisspeptin-54 or the minimal active kisspeptin-10 decapeptide has not been established in published human pharmacology studies available in this dossier. Structure–activity work across the kisspeptin family shows that the C-terminal Arg-Phe (RF) motif is the minimal binding determinant, and that longer C-terminal extensions generally retain activity, while N-terminal extensions of varying length modulate potency and duration of action (Kirby and colleagues, 2010).
Human clinical pharmacology has been most extensively characterised for kisspeptin-54 (full-length) and kisspeptin-10. Dhillo and colleagues (2007) demonstrated that kisspeptin-54 stimulates gonadotropin release in women most potently during the preovulatory phase of the menstrual cycle, establishing phase-dependent sensitivity of the KISS1R axis. George and colleagues (2011) showed that kisspeptin-10 potently stimulates LH and increases LH pulse frequency in men. The (27-54) fragment occupies the pharmacological middle ground between these two well-studied forms but lacks dedicated published human pharmacology studies to date.
Beyond reproduction, kisspeptin signalling has been implicated in metabolic regulation — circulating kisspeptin levels associate with insulin resistance and glucose homeostasis in human observational studies — and emerging evidence from brain-imaging trials suggests effects on sexual and emotional neural processing (Izzi-Engbeaya and colleagues, 2019).
Evidence
- Human: Published clinical pharmacology for this specific (27-54) fragment is not established in the primary literature indexed to this card. Clinical evidence for the broader kisspeptin-54 class includes multiple RCTs on IVF oocyte maturation triggering, hypothalamic amenorrhea, and hypoactive sexual desire disorder, all conducted with full-length kisspeptin-54 or kisspeptin-10 — not with this fragment specifically.
- Animal: The (27-54) sequence is present in species-comparative sequence alignments of kisspeptin across mammals, including goat, sheep, and cattle (Okamura and colleagues, 2013). Cross-species conservation of the C-terminal region confirms the functional importance of this segment, but fragment-specific animal pharmacology is not documented in the dossier refs.
- In vitro: Receptor pharmacology characterised at KISS1R, a class A GPCR, via G protein-coupled signalling assays — the (27-54) fragment retains the C-terminal binding motif described in KISS1R nomenclature reviews (Kirby and colleagues, 2010).
Known effects
- GnRH pulse stimulation — Mechanistic (class-level); the C-terminal KISS1R-binding motif is present in this fragment. Human evidence at the fragment level is not established.
- LH and FSH release — Established for kisspeptin-54 and kisspeptin-10 (Dhillo and colleagues, 2007; George and colleagues, 2011); extrapolated to this fragment by class mechanism, not directly demonstrated.
- Cross-species conservation of reproductive signalling — Preclinical; the kisspeptin system controls the HPG axis in all vertebrates studied (Tsutsui and colleagues, 2010; Akazome and colleagues, 2010).
Safety signals
No published clinical safety data exist specifically for this fragment. Safety characterisation of the kisspeptin-54 class in humans comes from trials using the full 54-residue peptide; the (27-54) fragment has not been studied in registered clinical trials and carries no independent safety record in the accessible literature.
The class-level signals from kisspeptin-54 trials include: injection-site reactions (the most commonly reported adverse event in subcutaneous trials), absence of documented serious adverse events in short-duration trial exposures, and a theoretical concern around tachyphylaxis — receptor desensitisation observed with continuous administration that limits sustained hormonal effects (Mead and colleagues, 2007).
Regulatory status
- US: Not FDA-approved for any indication. No IND-level clinical development appears to be registered for this specific fragment.
- EU/UK: Not authorised by EMA or MHRA. The broader kisspeptin-54 class has been investigated in UK clinical trials (primarily Imperial College London's group) without proceeding to marketing authorisation.
- WADA: Falls under S2 (peptide hormones, growth factors, and related substances) by mechanism — any peptide that stimulates endogenous LH and gonadotropin release is prohibited in competitive sport at all times. Athletes should avoid.
Mechanism
KISS1R (formerly GPR54, also denoted AXOR12 or hOT7T175 in older literature) is a class A GPCR expressed on GnRH neurons in the hypothalamic arcuate nucleus and anteroventral periventricular nucleus (Kirby and colleagues, 2010). Kisspeptin binding activates Gαq/11-coupled phospholipase C signalling, producing IP₃ and DAG, raising intracellular calcium, and triggering GnRH secretion into the pituitary portal circulation. This GnRH pulse activates gonadotroph cells to release LH and FSH, which in turn stimulate gonadal steroidogenesis.
The (27-54) fragment spans the region from position 27 of kisspeptin-54, which lies in the mid-peptide segment connecting the less-conserved N-terminal extension to the conserved C-terminal binding core. The C-terminal Arg-Phe-NH₂ motif — shared with all active kisspeptin isoforms — is the minimal pharmacophore required for KISS1R engagement (Kirby and colleagues, 2010). Rønnekleiv and colleagues (2013) reviewed the electrophysiological mechanisms by which kisspeptin activates GnRH neurons, including membrane depolarisation via closure of GIRK channels and opening of TRPC channels.
Kisspeptin neurons in the arcuate nucleus co-express neurokinin B (NKB) and dynorphin — the so-called KNDy neuron population — which generates the self-sustaining oscillatory drive underlying pulsatile GnRH release (Xie and colleagues, 2022). The (27-54) fragment acts downstream of this oscillatory system as an exogenous KISS1R agonist that can engage the same receptor pathway without reproducing the endogenous NKB-driven pulse architecture.
Idiopathic hypogonadotropic hypogonadism caused by loss-of-function mutations in KISS1R (GPR54) confirms that intact kisspeptin signalling is non-redundant for human reproductive competence (Bonomi and colleagues, 2012; Mead and colleagues, 2007).
Open questions
- Fragment-specific binding affinity and functional potency at KISS1R relative to kisspeptin-54 and kisspeptin-10 have not been published in accessible primary literature.
- Whether the (27-54) fragment offers any pharmacokinetic advantages (altered plasma half-life, modified receptor on-rate/off-rate) compared to the full-length or decapeptide forms remains uncharacterised.
- The biological significance of the N-terminal extension (residues 27-44 of KP-54) beyond serving as a spacer from the binding core is not established.
- Tachyphylaxis kinetics for this specific fragment at KISS1R have not been studied.
- No oral or intranasal formulation data exist for this fragment (intranasal delivery has been validated only for full-length kisspeptin-54 in human trials).
Related peptides
- Kisspeptin-10 — the C-terminal decapeptide (residues 45-54 of kisspeptin-54) containing the minimal KISS1R-binding pharmacophore; the most widely used research form and studied in men for LH pulse stimulation (George and colleagues, 2011).
- Full-length kisspeptin-54 — the parent 54-residue peptide from which this fragment is derived; used in IVF oocyte maturation trigger trials and HSDD clinical research (Dhillo and colleagues, 2007).
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 the proline pair at the start of this fragment prevent the middle section from folding, leaving it as a flexible tail attached to the active tip?
If confirmed, drug designers could strip away the disordered middle and build a shorter, cheaper peptide that works as well as the longer hormone for treating fertility problems.
If the loose, flexible middle of this fragment were replaced with a rigid but neutral connector, would the resulting molecule activate the kisspeptin receptor more strongly?
A more potent kisspeptin fragment could reduce doses needed for fertility treatments like IVF, potentially cutting costs and side effects for patients undergoing hormone stimulation therapy.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.7503631711006165 | boltz-2 |
| ranking score | 0.680412232875824 | 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{pep10605,
sequence = {IPAPQGAVLVQREKDLPNYNWNSFGLRF},
target = {kiss1r},
author = {peptidemodel},
year = {2026},
status = {synthesized}
}