Cortisol-signaling research fragment (Acetyl-ACTH 1-17)
A lab-made piece of ACTH, the pituitary hormone that tells the adrenal glands to release cortisol; used to study how that stress-hormone signal is triggered. 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
Acetyl-ACTH(1-17) is the N-terminally acetylated 17-amino-acid fragment from the front end of adrenocorticotropic hormone (ACTH) — the pituitary hormone that tells the adrenal glands to release cortisol. The stored sequence (SYSMEHFRWGKPVGKKR) is the bare backbone; the active synthetic form carries an N-terminal acetyl cap that protects the α-amine from aminopeptidase cleavage and is not represented in the 17-letter string. The 1-17 fragment matters because it contains every residue required to bind and activate the melanocortin-2 receptor (MC2R), the adrenal-cortex-specific receptor that recognizes only ACTH (Fridmanis, Frontiers in Endocrinology 2017). It is generated naturally in the body as well — in skin and the intermediate pituitary, prohormone convertase PC2 cleaves full-length ACTH into ACTH(1-17) plus a corticotropin-like intermediate peptide (CLIP, ACTH 18-39), and ACTH(1-17) is then trimmed further to become α-MSH (Wakamatsu and colleagues, Pigment Cell Research 1997). Synthetic Acetyl-ACTH(1-17) is used in research as a minimal, fully MC2R-competent probe of ACTH biology.
History
ACTH itself was isolated from anterior pituitary extracts and chemically characterized in the early 1950s, most notably by Choh Hao Li at UC Berkeley; the full 39-residue sequence was determined in 1953. Once the active N-terminus was localized, shorter synthetic fragments became central tools: the 1-24 fragment (cosyntropin / tetracosactide) was developed in the 1960s and remains the standard diagnostic stimulator for assessing adrenal reserve. The 1-17 fragment emerged from two parallel lines of work — biochemical mapping of how short an ACTH N-terminal peptide could be and still bind MC2R, and the discovery that PC2-mediated cleavage of ACTH inside pituitary intermediate-lobe and skin cells actually produces ACTH(1-17) endogenously en route to α-MSH (Wakamatsu, Pigment Cell Research 1997). MC2R itself was cloned and shown to be uniquely ACTH-selective in the early 1990s; later work established that it cannot function in heterologous cells without its accessory protein MRAP1, which is required for receptor trafficking and ligand recognition (Fridmanis 2017).
What it does
Acetyl-ACTH(1-17) acts at the same receptors that full-length ACTH acts on: principally MC2R on adrenal-cortex cells, where it drives synthesis and release of cortisol with smaller contributions to aldosterone and adrenal androgens (Fridmanis 2017). The N-terminal melanocortin pharmacophore (the conserved His-Phe-Arg-Trp core at residues 6-9) also lets it bind the other melanocortin receptors that recognize MSH peptides — MC1R on melanocytes (driving pigment production), MC3R, MC4R, and MC5R — though it is most studied as an MC2R-activating probe and as a melanocyte stimulator. In side-by-side comparisons on cultured human melanocytes, ACTH(1-17) was the most potent activator of MC1R-mediated melanogenesis tested, with potency order ACTH(1-17) > α-MSH > ACTH(1-39) > desacetyl-α-MSH > acetylated ACTH(1-10) > ACTH(1-10) (Wakamatsu 1997).
Mechanism
MC2R is a Gαs-coupled GPCR that is unique among the five melanocortin receptors in two ways: it binds only ACTH (not α-, β-, or γ-MSH despite their shared HFRW core), and it cannot reach the cell surface or bind ligand without its accessory protein MRAP1 — the functional unit is a hetero-hexameric complex of two MC2R molecules and four MRAP1 molecules, and without MRAP1 the receptor is inert (Fridmanis 2017). Two regions of ACTH together drive MC2R-specific activation: the conserved melanocortin "message" core (HFRW, residues 6-9) shared with all MSH peptides, and an "address" element in the 15-18 region (KKRR) that distinguishes ACTH from MSH peptides and is required for high-affinity MC2R binding (Fridmanis 2017). The minimum ACTH N-terminal fragment that retains MC2R binding and signaling activity was mapped by Chen and colleagues (Biochemistry 2007) to ACTH(1-16); ACTH(1-14) lost binding entirely, while ACTH(1-17) retains full activity and includes the complete distinguishing address motif. Downstream of MC2R activation, Gαs raises intracellular cAMP, activates PKA, and phosphorylates StAR (steroidogenic acute regulatory protein), which shuttles cholesterol from the outer to the inner mitochondrial membrane — the rate-limiting step in steroidogenesis — followed by CYP11A1-mediated conversion to pregnenolone and the zonally expressed downstream CYP enzymes that produce cortisol, aldosterone, and DHEA (Yeo and colleagues, Molecular Metabolism 2021; Ericson and colleagues, BBA Molecular Basis of Disease 2017). At MC1R on melanocytes, the same N-terminal melanocortin core drives Gαs-cAMP signaling, MITF activation, and eumelanin synthesis, which is why ACTH(1-17) is also a potent melanogenesis stimulator (Suzuki and colleagues, Endocrinology 1996; Wakamatsu 1997).
Evidence
- Human: No clinical trials of Acetyl-ACTH(1-17) as a therapeutic. The closely related cosyntropin (ACTH 1-24) is the FDA-approved diagnostic and has extensive validation for adrenal-reserve testing, and repository corticotropin injection (Acthar Gel, full-length ACTH 1-39 in gelatin) is approved for infantile spasms, MS exacerbations, and several inflammatory/nephrotic indications — providing the human clinical anchor for the ACTH–MC2R axis that the 1-17 fragment activates (Ericson 2017; Yeo 2021). The 1-17 fragment itself is a research peptide, not a drug.
- Animal: ACTH and short N-terminal fragments restore adrenal function in adrenalectomized rodents; MC2R-null mice have adrenal hypoplasia and fail to respond to ACTH stimulation, confirming MC2R as the obligate receptor for adrenocorticotropic activity (Fridmanis 2017; Yeo 2021).
- In vitro: ACTH(1-17) binds and activates MC2R only in cells co-expressing MRAP1; binding/signaling assays in heterologous systems (mouse adrenocortical Y6/OS3 cells, HEK293 reconstituted with MC2R + MRAP1) confirm cAMP and PKA-mediated signaling, with truncation below 16 residues abolishing activity (Chen, Biochemistry 2007; Fridmanis 2017). On human melanocyte cultures, ACTH(1-17) is the most potent peptide tested for MC1R-mediated dendricity and melanin content (Wakamatsu 1997).
Known effects
- Adrenal cortisol, aldosterone, and DHEA secretion via MC2R (mechanistic and in-vitro evidence; clinical evidence is from cosyntropin and Acthar Gel, not Acetyl-ACTH(1-17) specifically)
- Melanocyte stimulation and melanogenesis via MC1R — directly characterized for ACTH(1-17) in cultured human melanocytes (Wakamatsu 1997)
- Broader melanocortin-system signaling at MC3R/MC4R/MC5R (energy homeostasis, immune modulation, exocrine signaling) by virtue of containing the conserved HFRW pharmacophore (Cai and colleagues, Current Protein & Peptide Science 2016; Xu and colleagues, Cellular and Molecular Life Sciences 2020)
Safety signals
There are no clinical safety data for Acetyl-ACTH(1-17) as a discrete product. The safety profile of ACTH-mediated adrenal stimulation in general — when sustained — is the safety profile of glucocorticoid excess: hypertension, hyperglycemia, fluid retention, osteoporosis, immunosuppression, Cushingoid features, and psychiatric effects, established from chronic Acthar Gel and exogenous-corticosteroid exposure. Hypersensitivity, including anaphylaxis, has been reported with animal-derived repository ACTH formulations. None of these have been characterized for short synthetic 1-17 fragments at experimental exposures.
Regulatory status
- US: Acetyl-ACTH(1-17) is not an FDA-approved drug. Cosyntropin (ACTH 1-24, Cortrosyn) and repository corticotropin (Acthar Gel, ACTH 1-39 in gelatin) are FDA-approved prescription products; the 1-17 fragment is not.
- EU: No approved ACTH(1-17) product; tetracosactide (Synacthen) and depot formulations are the approved corticotropin agents.
- WADA: Corticotropins are explicitly prohibited under the WADA peptide-hormone class when used to stimulate endogenous glucocorticoid production; tetracosactide is named in WADA technical documents. MC2R-active ACTH N-terminal fragments fall within the same regulatory category.
- Wellness / compounded-peptide market: Acetyl-ACTH(1-17) is not part of the compounded-peptide ecosystem and is not a self-administered peptide. It appears in research contexts as a minimal MC2R/MC1R probe.
Myths
"Short ACTH fragments don't really act like full ACTH." At MC2R, the relevant determinants are concentrated in the N-terminal ~16-17 residues. Fragments at or above ACTH(1-16) retain MC2R binding and full agonism, while shorter fragments such as ACTH(1-14) do not bind (Chen, Biochemistry 2007). The C-terminal residues 17-39 contribute to clearance and immunogenicity rather than to receptor activation (Fridmanis 2017), which is why cosyntropin (1-24) is functionally equivalent to ACTH(1-39) in adrenal stimulation tests.
"MC2R is the same as the other melanocortin receptors." MC2R is the exception. It recognizes only ACTH (not α-, β-, or γ-MSH) and it requires MRAP1 to traffic to the membrane and to bind ligand at all. The other four melanocortin receptors (MC1R, MC3R, MC4R, MC5R) function without MRAPs and accept multiple MSH-family peptides (Fridmanis 2017).
Related peptides
- ACTH (1-39) — full-length adrenocorticotropic hormone; the parent molecule from which the 1-17 fragment is derived by PC2 cleavage
- Cosyntropin (ACTH 1-24, tetracosactide) — the FDA-approved synthetic ACTH analog used for adrenal-reserve testing
- α-MSH (Ac-SYSMEHFRWGKPV-NH₂; ACTH 1-13 with N-acetyl and C-amide) — the next downstream POMC product, derived from ACTH(1-17) by further processing; MC1R/MC3R/MC4R/MC5R agonist
- CLIP (ACTH 18-39) — the C-terminal counterpart released alongside ACTH(1-17) during PC2 cleavage; minimal known receptor activity
- CRH (corticotropin-releasing hormone) — the hypothalamic driver of pituitary ACTH release upstream of this signaling axis
- POMC — the shared precursor protein that gives rise to ACTH, α-/β-/γ-MSH, β-endorphin, and CLIP
Open questions
- Whether Acetyl-ACTH(1-17) offers any pharmacological advantage over cosyntropin (1-24) as a diagnostic or research stimulator — head-to-head MC2R potency, MRAP1-dependence, and clearance comparisons are sparse
- Whether selective N-terminal ACTH fragments can be designed to discriminate cleanly between MC2R (adrenal/steroidogenic) and MC1R (melanocyte/anti-inflammatory) signaling, which would let the broader melanocortin anti-inflammatory pathway be targeted without cortisol elevation (Hruby and colleagues, Expert Opinion on Drug Discovery 2011)
- Whether the locally generated ACTH(1-17) in skin contributes meaningfully to UV-induced pigmentation in vivo, beyond its established MC1R potency in melanocyte cultures (Wakamatsu 1997)
- Whether MC1R/MC3R-mediated immune effects of ACTH-derived peptides — independent of MC2R-driven cortisol — can be exploited therapeutically, an active question for the broader melanocortin field (Cai 2016; Xu 2020)
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 chemical oxidation of the methionine in ACTH(1-17) reduce its ability to stimulate the adrenal gland to make cortisol?
If oxidized ACTH is less potent, this could explain why some sepsis and ICU patients appear to have adequate ACTH levels but still suffer adrenal insufficiency, a life-threatening condition. Identifying oxidized ACTH as the culprit could lead to better diagnostic tests and treatments for critical illness-related adrenal failure.
Can Acetyl-ACTH(1-17) activate the skin tanning receptor on its own, before cells finish converting it into alpha-MSH?
If this fragment activates tanning independently, it would explain why people with Addison disease, who have high ACTH levels, develop unusually dark skin even without sun exposure. It could also inspire new approaches to conditions of abnormal pigmentation, including treatments to restore color in vitiligo patches.
Do the four basic amino acids at the end of ACTH(1-17) make it specific to the adrenal MC2 receptor while sparing the brain's MC4 appetite receptor?
If this four-residue tail controls receptor selectivity, it could be attached to other compounds to direct them precisely to the adrenal gland. This could help design adrenal stimulating drugs that do not suppress appetite or affect sexual function, reducing side effects for patients receiving long-term ACTH-based therapy.
Is the acetyl group at the tip of this hormone fragment the main reason it grips the MC2 receptor so tightly compared to longer or uncapped versions?
If the acetyl cap is responsible for superior binding, chemists could add similar caps to other short hormone fragments to improve their potency without changing the biological activity, leading to better, more efficient diagnostic tools for adrenal gland testing.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.898748517036438 | boltz-2 |
| ranking score | 0.8478389978408813 | 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{pep10667,
sequence = {SYSMEHFRWGKPVGKKR},
target = {mc2r},
author = {peptidemodel},
year = {2026},
status = {synthesized}
}