Stress-hormone blocker used in brain research (α-helical CRF 9-41)
A lab-made peptide that blocks the brain's main stress-signaling hormone, used in animal studies to explore anxiety and stress-driven appetite loss, a research tool, 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
α-helical CRF (9-41) is a synthetic research peptide that blocks the body's main stress hormone signal. It binds to the receptors that normally respond to corticotropin-releasing factor (CRF) — the brain peptide that kicks off the cortisol stress response — and prevents CRF from activating them. The compound is a research tool, not a drug; it is used in laboratory animals to ask what happens when CRF signaling is silenced. It was designed in 1984 at the Salk Institute by Jean Rivier, Catherine Rivier and Wylie Vale, who built it by truncating the first eight residues from a parent analog of CRF that they had previously engineered to maximize α-helical content (Rivier, Rivier & Vale, Science 1984).
History
Predictive and physicochemical analysis indicated that CRF and several of its homologs adopt an internal α-helical conformation roughly 25 residues long, and that helical content correlated with receptor potency. Rivier, Rivier and Vale (Science 1984) synthesized a 41-residue analog with substitutions chosen to maximize α-helix-forming propensity at non-conserved positions ("α-helical CRF"), then removed the N-terminal residues 1–8 to abolish receptor activation while retaining binding. The resulting 33-residue fragment, α-helical CRF (9-41), became the first widely used peptidic CRF receptor antagonist and the standard pharmacological tool for in vivo CRF blockade for more than a decade (reviewed in Rivier & Rivier, Front Neuroendocrinol 2014). It was eventually superseded for many bench applications by structurally constrained successors such as astressin and antisauvagine-30, which are more potent and longer-acting (Rivier & Rivier 2014).
What it does
When injected into the brain or cerebrospinal fluid of laboratory rodents, α-helical CRF (9-41) blunts the behavioral and physiological consequences of CRF release. Swerdlow, Britton and Koob (Neuropsychopharmacology 1989) showed that intracerebroventricular α-helical CRF (9-41) reversed both the increase in acoustic startle produced by CRF infusion and the potentiation of startle produced by conditioned fear, providing some of the earliest direct evidence that endogenous CRF participates in fear states. In feeding studies, pretreatment with α-helical CRF (9-41) into the fourth ventricle blocks the food-intake suppression normally produced by central CRF and, in the same paradigm, amplifies the hypophagic response to cocaine- and amphetamine-regulated transcript (CART) peptide — implying that brainstem CRF and CART act through overlapping but distinguishable circuits (Smedh and colleagues, BMC Neuroscience 2019).
Mechanism
α-helical CRF (9-41) is a non-selective competitive antagonist at the mammalian CRF receptors CRF₁ (gene CRHR1) and CRF₂ (gene CRHR2), both class B G-protein-coupled receptors. The peptide's design follows the standard agonist-truncation strategy for class-B GPCRs: the C-terminal portion of the agonist (here residues 9–41) retains the binding determinants that engage the receptor's extracellular domain, while removal of the N-terminal residues that contact the transmembrane bundle abolishes the conformational change required for receptor activation. In rat ACTH-release bioassays the parent α-helical CRF behaves as a potent agonist; the 9-41 truncation acts as a competitive antagonist that blocks CRF-induced ACTH secretion in vivo (Rivier, Rivier & Vale, Science 1984).
The antagonist's potency in vivo varies markedly with the bioassay used. Fisher, Rivier, Rivier and Brown (Endocrinology 1991) showed in conscious rats that an antagonist:agonist ratio of roughly 6:1 was sufficient to abolish CRF-induced hypotension and tachycardia, but blocking CRF-induced ACTH and β-endorphin release required ratios of approximately 3000:1 — an early piece of pharmacological evidence that more than one CRF receptor subtype exists. Later head-to-head work established that constrained peptides such as astressin and the CRF₂-selective antisauvagine-30 are more potent and more receptor-subtype-selective, but α-helical CRF (9-41) remained the reference tool antagonist of the field for many years (Rivier & Rivier 2014). As a peptide it does not meaningfully cross the blood–brain barrier, so its central effects are demonstrated by intracerebroventricular, intraparenchymal or intracisternal delivery in animals.
Evidence
- Human: No human trials. α-helical CRF (9-41) has been used exclusively as a preclinical research probe; it has not entered clinical development as a therapeutic.
- Animal: Multiple rodent studies establish in vivo CRF receptor blockade. Intracerebroventricular α-helical CRF (9-41) reverses CRF- and fear-potentiated acoustic startle in rats (Swerdlow, Britton & Koob, Neuropsychopharmacology 1989). Skórzewska and colleagues (Neuropharmacology 2009) reported that the antagonist modulates rat fear responses and the release of glutamate, aspartate and GABA in the central nucleus of the amygdala during anxiety-like behavior. Fourth-ventricular α-helical CRF (9-41) blocks central CRF-induced hypophagia and reshapes the feeding response to CART peptide (Smedh and colleagues, BMC Neuroscience 2019).
- In vitro: The parent α-helical CRF analog from which the 9-41 fragment is derived was characterized in pituitary cell ACTH-release assays as more potent than native CRF, and the 9-41 truncation was shown to competitively inhibit CRF-stimulated ACTH release (Rivier, Rivier & Vale, Science 1984).
Known effects
- CRF receptor blockade in vivo — Established, preclinical (Rivier, Rivier & Vale 1984; reviewed in Rivier & Rivier 2014).
- Reduction of CRF- and fear-potentiated startle — Preclinical, rodent (Swerdlow, Britton & Koob 1989).
- Modulation of amygdala neurotransmitter release during fear — Preclinical, rodent (Skórzewska and colleagues 2009).
- Block of central CRF-induced feeding suppression — Preclinical, rodent (Smedh and colleagues 2019).
Regulatory status
- US: Not an approved drug. Supplied as a research-grade peptide by chemical vendors for laboratory use only.
- EU: Not an approved drug.
- WADA: Not listed by name on the Prohibited List.
Related peptides
- Native CRF / CRH — the 41-residue endogenous agonist that α-helical CRF (9-41) was designed to mimic in binding and oppose in signaling.
- Astressin and antisauvagine-30 — later-generation peptidic CRF receptor antagonists with higher potency and, for antisauvagine-30, CRF₂-selectivity (Rivier & Rivier, Front Neuroendocrinol 2014).
- Urocortins 1/2/3 — endogenous CRF-family agonists whose receptor activation is also blocked by α-helical CRF (9-41), particularly at CRF₂.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.746777355670929 | openfold3-mlx |
| ranking score | 0.8155010938644409 | openfold3-mlx |
▸structural qualityopenfold3
| metric | value | note |
|---|---|---|
| gpde | 0.742 | global PDE — lower = better |
| disorder | 0.160 | fraction disordered |
| chain pair ipTM (A, B) | 0.747 | interface quality |
▸3-letter notation
▸recipeopenfold3-mlx 0.3.1
| parameter | value |
|---|---|
| model | openfold3-mlx 0.3.1 |
| weights | aedd8f3eb814e392… |
| hardware | apple_m4_base_16gb |
| mlx version | 0.31.1 |
| python | 3.14.3 |
| random seed | 42 |
| msa strategy | colabfold |
| diffusion samples | 1 |
| runtime | 335s |
| predicted by | mlx@peptide |
| predicted at | 2026-04-23 |
python3 openfold3/run_openfold.py predict --query_json {query.json} --runner_yaml examples/example_runner_yamls/mlx_runner.yml --output_dir {output_dir} --num_diffusion_samples 1 ▸citationbibtex
@peptide{pep10526,
sequence = {DLTFHLLREMLEMAKAEQEAEQAALNRLLLEEA},
target = {crhr2},
author = {peptidemodel},
year = {2026},
status = {synthesized}
}