Kisspeptin-13: natural fragment that triggers the reproductive hormone system
A short piece of kisspeptin, the body's master signal for puberty and fertility; activates the brain's hormone-release cycle. Used mainly 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
Kisspeptin-13 (Kp-13) is a 13-amino-acid fragment of kisspeptin, a naturally occurring signaling peptide that acts as the master switch for the human reproductive hormone system. The body produces several kisspeptin isoforms — all cleaved from the same 54-residue precursor — and Kp-13 is the second-shortest of them, consisting of the C-terminal 13 residues (LPNYNWNSFGLRF). Like the better-studied Kp-10 and Kp-54 isoforms, Kp-13 binds the kisspeptin receptor KISS1R (formerly called GPR54) and can trigger the hormonal cascade that drives reproduction (Kirby and colleagues, Pharmacological Reviews 2010). Kisspeptin itself was first identified as a cancer metastasis-suppressor gene (KISS1) before its central reproductive role was recognized — the nomenclature and early history of these peptides are reviewed in Gottsch and colleagues (Peptides 2009).
History
The KISS1 gene was discovered in 1996 during a screen for metastasis-suppressor factors in melanoma cells — the name "kisspeptin" was coined as a nod to the chocolate brand made in Hershey, Pennsylvania, where the discovery was made. The encoded peptide was initially catalogued as a tumor biology factor. The reproductive endocrinology chapter opened in 2003, when independent research teams showed that loss-of-function mutations in KISS1R (GPR54) caused hypogonadotropic hypogonadism, placing kisspeptin signaling at the top of the hormonal axis governing puberty, fertility, and gonadal function. A historical review of this trajectory from KISS1 to the kisspeptin peptide family and the naming conventions for isoforms is given in Gottsch and colleagues (Peptides 2009). The IUPHAR receptor nomenclature committee formally codified KISS1R distribution and function in Kirby and colleagues (Pharmacological Reviews 2010), providing the pharmacological framework used in subsequent research. Most of the clinical human work has been done with Kp-54 and Kp-10; Kp-13 has been studied primarily in the context of cross-species sequence conservation and receptor pharmacology (Okamura and colleagues, Animal Science Journal 2013; Akazome and colleagues, Journal of Fish Biology 2010).
What it does
Kisspeptin-13 binds KISS1R on neurons in the hypothalamus, prompting them to release gonadotropin-releasing hormone (GnRH) — the hormone that then drives the pituitary to produce LH and FSH, the hormones that in turn signal the gonads to make testosterone and estrogen. This chain of signals is called the hypothalamic–pituitary–gonadal (HPG) axis, and kisspeptin signaling sits at its upstream control point. All kisspeptin isoforms that share the C-terminal GLRF motif — including Kp-13 — are active at KISS1R, with the C-terminal sequence being the primary receptor-engagement pharmacophore (Kirby and colleagues 2010). Beyond reproductive control, the broader kisspeptin system also appears to integrate metabolic signals: circulating kisspeptin levels correlate with measures of glucose handling, and experimental kisspeptin administration affects insulin secretion in human volunteers (Izzi-Engbeaya and colleagues, Seminars in Reproductive Medicine 2019). A behavioral dimension has also been described: kisspeptin neurons are distributed in limbic brain regions beyond the hypothalamus, and kisspeptin signaling appears to modulate emotional and sexual behavioral processing (Mills and colleagues, Seminars in Reproductive Medicine 2019).
Evidence
- Human: Clinical evidence for the broader kisspeptin system in humans is moderate-to-strong. Jayasena and colleagues (Journal of Clinical Endocrinology & Metabolism 2011) demonstrated that kisspeptin-10 acutely stimulates LH and FSH release in both men and women, with sexually dimorphic response patterns — providing the clearest human proof-of-concept for the receptor pharmacology that Kp-13 shares. Jayasena and colleagues (Clinical Pharmacology & Therapeutics 2010) showed that twice-weekly administration of Kp-54 for 8 weeks sustained gonadotropin stimulation in women with hypothalamic amenorrhea, though earlier work from the same group found that chronic subcutaneous Kp-54 causes tachyphylaxis (Jayasena and colleagues, Journal of Clinical Endocrinology & Metabolism 2009). Kp-13 itself has not been the primary intervention in published human trials; the human evidence base belongs predominantly to Kp-10 and Kp-54.
- Animal: Strong. Intrahypothalamic administration of Kp-54 potently increased plasma LH and testosterone in adult male rats (Patterson and colleagues, Journal of Neuroendocrinology 2006), establishing the HPG-axis mechanism in rodents. Evolutionary conservation of the C-terminal kisspeptin sequence — including the Kp-13 region — across vertebrates from fish to mammals is documented in Akazome and colleagues (Journal of Fish Biology 2010) and Pasquier and colleagues (Frontiers in Endocrinology 2012).
- In vitro / mechanistic: KISS1R excitation of GnRH neurons and downstream Ca²⁺ mobilization by kisspeptin are well characterized at the cellular level; the signaling pharmacology of the receptor is reviewed in Rønnekleiv and colleagues (Advances in Experimental Medicine and Biology 2013) and in the IUPHAR nomenclature review (Kirby and colleagues 2010).
Known effects
- GnRH pulse stimulation — Mechanistic; well established across species. The primary and defining action of KISS1R agonism.
- LH and FSH release (acute) — Human, RCT-level evidence for Kp-10 and Kp-54 (Jayasena and colleagues 2011). Shared mechanism with Kp-13 via KISS1R.
- Gonadal steroid production — Downstream consequence of HPG axis activation; documented in animal models (Patterson and colleagues 2006) and inferred from human LH/FSH responses.
- Behavioral and limbic modulation — Preclinical and mechanistic; kisspeptin neurons in limbic regions appear to modulate sexual and emotional processing (Mills and colleagues 2019).
- Glucose homeostasis signaling — Emerging; associations between circulating kisspeptin and insulin secretion reported in human studies (Izzi-Engbeaya and colleagues 2019).
- Reproductive diagnostics (pre-ovulation marker) — Circulating kisspeptin rises at the preovulatory phase; its utility as a biomarker for ovulation prediction has been investigated (Zhai and colleagues, Gynecological Endocrinology 2017).
Safety signals
Safety data for kisspeptin in humans derives almost entirely from studies of Kp-54 and Kp-10, not from Kp-13 specifically. In the clinical trials reviewed across the Jayasena group's work, acute kisspeptin administration was generally well tolerated, with injection-site reactions being the most commonly reported event. The tachyphylaxis signal — receptor desensitization with continuous or high-frequency dosing — is mechanistically important: Jayasena and colleagues (2009) observed that chronic subcutaneous Kp-54 produced diminishing gonadotropin responses, establishing a practical ceiling on repeated-dosing protocols. Loss-of-function mutations in KISS1R cause hypogonadotropic hypogonadism in humans, as reviewed in Bonomi and colleagues (Asian Journal of Andrology 2012), illustrating that this signaling axis is not redundant for reproductive function. The long-term safety of repeated exogenous kisspeptin administration beyond the duration of published trials (typically single doses or courses of weeks) remains uncharacterized.
Regulatory status
- US: Not FDA-approved for any indication. No kisspeptin isoform holds marketing authorization in the United States. Clinical research continues.
- EU/UK: Not EMA- or MHRA-approved. The UK has hosted the majority of published human clinical trials of kisspeptin through Imperial College London, but no marketing authorization has been granted.
- WADA: Not explicitly named, but falls under S2 (peptide hormones and releasing factors) by mechanism — any peptide that acutely stimulates LH and testosterone release is prohibited in competitive sport under catch-all language covering GnRH and its analogs.
- Compounding / research use: Not on FDA's 503A compounding bulk substances list. All human use is in the context of clinical trials or specialist medical settings.
Related peptides
The kisspeptin isoforms share the KISS1R pharmacophore but differ in length and pharmacokinetics. The full-length 54-residue form (Kisspeptin-54), which has the most extensive clinical evidence base covering IVF triggering, hypothalamic amenorrhea, and hypoactive sexual desire disorder, is catalogued separately on this platform. The shorter Kp-10 decapeptide, used in human sexual-dimorphism studies and mechanistic work (Jayasena and colleagues 2011), is likewise a distinct card in this family. For the broader GnRH-axis context, GnRH itself and its clinical analogs (leuprolide, triptorelin) act one step downstream of kisspeptin signaling.
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 middle portion of kisspeptin-13 make the fertility signal last longer inside the cell?
Kisspeptin is a natural hormone that tells the brain to release reproductive hormones. If this hypothesis holds, a specific stretch of kisspeptin-13 could keep the signal switched on longer, which might allow doctors to better tune fertility treatments for conditions like irregular ovulation, potentially improving outcomes without increasing the dose.
Could reshaping kisspeptin-13 into a closed loop stop the body from breaking it down too quickly?
Natural kisspeptin fragments are destroyed in the bloodstream within minutes, which makes them impractical as a drug. If this chemical modification works, it could yield a small, stable version that lasts long enough for patients to inject at home, potentially opening up treatment options for people with hormonal infertility who currently have few convenient choices.
Could kisspeptin-13 stimulate the fertility signal while causing less of the receptor shutdown that makes repeated doses less effective?
A recurring problem with kisspeptin therapy is that the receptor it targets can become desensitized, making the drug less effective with repeated use. If kisspeptin-13 turns out to favor one signaling pathway over the one that triggers desensitization, it could be better suited for ongoing fertility treatment, for example in people with hypothalamic amenorrhea who need repeated stimulation.
Do the two extra building blocks at the start of kisspeptin-13 help it stay attached to the receptor for longer?
Kisspeptin-10 is active but very brief in its action. If the LP addition in kisspeptin-13 slows how quickly the peptide lets go of its receptor, it could provide a longer hormonal pulse without overstimulating the system. That would matter in IVF protocols, where timing and duration of the fertility signal directly affect success rates.
Did the upper portion of kisspeptin-13 evolve specifically to match the human fertility receptor rather than the equivalent receptor in fish?
If the distinctive part of kisspeptin-13 fits the human receptor but not the fish version, researchers could use that difference in two ways: designing peptides that control spawning in farmed fish without affecting other biology, and building sharper drug candidates for human reproductive conditions by understanding exactly which molecular features matter for selectivity.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.9129645824432373 | boltz-2 |
| ranking score | 0.7452750205993652 | 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{pep10619,
sequence = {LPNYNWNSFGLRF},
target = {kiss1r},
author = {peptidemodel},
year = {2026},
status = {synthesized}
}