Calcitonin receptor blocker: research tool (Calcitonin (8-32) salmon fragment)
A lab-made fragment of salmon calcitonin that blocks the calcitonin receptor without switching it on, used by scientists to study bone and blood-sugar signaling. 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
Calcitonin (8-32) (salmon I) is a synthetic 25-residue fragment derived from the C-terminal region of salmon calcitonin — the same peptide hormone used clinically for bone-metabolism disorders. Whereas full-length salmon calcitonin (32 residues) is a potent receptor agonist that suppresses bone resorption, this truncated fragment lacks the N-terminal domain responsible for receptor activation and instead binds the calcitonin receptor (CTR) without activating it, making it an antagonist. Researchers use it as a pharmacological tool to block calcitonin and amylin signaling at the CTR and at AMY receptors (CTR/RAMP heterodimers), allowing them to map out what those receptor systems do in isolation (Lee and colleagues, JBC 2016; Pozvek and colleagues, Mol Pharmacol 1997). The stored sequence VLGKLSQELHKLQTYPRTNTGSGTP represents the fragment backbone; the active synthesized form carries a C-terminal amide (−NH₂) that is not encoded in that raw string (Lee and colleagues, Biochemistry 2017).
History
Salmon calcitonin itself was characterized as a 32-amino acid peptide following Harold Copp's 1962 discovery of a calcium-lowering hormone produced by thyroid parafollicular C-cells. The structure–function relationship of calcitonin and its fragments was investigated systematically in the 1990s. Pozvek and colleagues (Mol Pharmacol 1997) described the properties of truncated calcitonin analogues — including the (8-32) fragment — as agonists, antagonists, or inverse agonists depending on the expression system and receptor context, establishing the fragment as a useful pharmacological tool for dissecting class B GPCR signaling. Subsequent work on the calcitonin/amylin receptor system — including the discovery that amylin receptors are CTR/RAMP heterodimers — further motivated use of sCT(8-32) as a selective probe to distinguish CTR from AMY receptor pharmacology (Hay and colleagues, Br J Pharmacol 2018).
What it does
Within a research context, sCT(8-32) competes with calcitonin and amylin at the calcitonin receptor and at AMY receptor subtypes (which are formed by CTR pairing with receptor activity-modifying proteins, RAMP1, RAMP2, or RAMP3). Because the fragment binds but does not activate these receptors, it can reverse the inhibitory effect that amylin exerts on glucose-induced insulin release — an effect documented in the card's target indication and consistent with AMY receptor blockade at pancreatic sites. The peptide's primary value is as a selectivity probe: by blocking CTR-based signaling, researchers can attribute observed biological responses to that receptor system and distinguish them from CLR-based pathways (CGRP receptor, adrenomedullin receptors) that share the same peptide family but use CLR rather than CTR as the GPCR core (Hay and colleagues, Br J Pharmacol 2018).
Evidence
- Human: No clinical trial evidence. sCT(8-32) is a pharmacological research tool, not an approved or investigational therapeutic.
- Animal: Used in animal pharmacology to characterize calcitonin/amylin receptor biology. Evidence for AMY receptor antagonism and reversal of amylin-mediated insulin suppression derives from preclinical receptor pharmacology work.
- In vitro: Used as a reference antagonist in binding and functional assays at the human calcitonin receptor, including studies of glycosylation effects on receptor affinity (Lee and colleagues, Biochemistry 2017) and mechanistic studies of peptide–receptor interaction at the CTR (Lee and colleagues, JBC 2016; dal Maso and colleagues, ACS Pharmacol Transl Sci 2019).
Mechanism
sCT(8-32) binds the calcitonin receptor — a secretin-family class B GPCR — at the same site as full-length salmon calcitonin and amylin, but lacks the N-terminal "trigger" residues (positions 1-7, including the Cys1–Cys7 disulfide bridge of native sCT) required to activate the receptor's transmembrane signaling domain. The result is competitive antagonism: the fragment occupies the receptor's extracellular binding cleft without inducing the conformational change that drives cAMP/PKA and intracellular calcium signaling (Pozvek and colleagues, Mol Pharmacol 1997; dal Maso and colleagues, ACS Pharmacol Transl Sci 2019). AMY receptors are heterodimers of CTR with one of three receptor activity-modifying proteins (RAMP1, RAMP2, or RAMP3), giving AMY₁, AMY₂, and AMY₃ subtypes; sCT(8-32) antagonizes these as well by virtue of acting through the CTR component (Hay and colleagues, Br J Pharmacol 2018). N-glycosylation of Asn130 in the CTR extracellular domain substantially increases peptide hormone affinity, a finding established using sCT(8-32) alongside other fragments as competition ligands in binding assays (Lee and colleagues, Biochemistry 2017).
Known effects
- CTR antagonism — Preclinical / mechanistic: competes with agonists (full-length calcitonin, amylin) at the calcitonin receptor without activating downstream cAMP signaling (Pozvek and colleagues, Mol Pharmacol 1997)
- AMY receptor antagonism — Preclinical / mechanistic: blocks amylin signaling at CTR/RAMP heterodimers, reversing amylin-mediated inhibition of glucose-induced insulin secretion per card indication (consistent with Hay and colleagues, Br J Pharmacol 2018)
- Pharmacological selectivity probe — Research tool: used to distinguish CTR-driven from CLR-driven biology in the calcitonin peptide family; no therapeutic use
Regulatory status
- US (FDA): Not approved. Research reagent only.
- EU (EMA): Not approved. Research reagent only.
- WADA: Not listed; no performance-enhancing use established.
Related peptides
The calcitonin/CGRP peptide family shares a common receptor architecture built around CTR and CLR paired with RAMPs. Related cards on this platform include full-length salmon calcitonin and members of the amylin and CGRP branches of the family. For the structural and pharmacological context of the CTR/RAMP system, see also CGRP receptor ligands discussed in Conner and colleagues (Biochem Soc Trans 2007) and the IUPHAR family review (Hay and colleagues, Br J Pharmacol 2018).
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.
If two parts of this calcitonin fragment are chemically clipped together to hold its shape, would it survive in the bloodstream long enough to be useful as a drug or research tool?
Current calcitonin fragments break down too fast to be useful in animals or patients. A stapled version that lasts longer could make it practical to test calcitonin receptor-blocking drugs for osteoporosis, pain, and addiction, opening entirely new lines of research.
Does this commonly used research tool block all three amylin receptor subtypes equally, or does it preferentially block some while leaving others active?
If this tool peptide is biased toward blocking certain receptor subtypes, decades of experiments using it to study bone loss and blood sugar regulation may need to be reinterpreted. Knowing the true selectivity profile would make future research more reliable and could guide better drug design.
Does the proline at the very end of this calcitonin fragment prevent it from forming the shape needed to activate the receptor, and would changing it turn the blocker into an activator?
Understanding exactly why this fragment blocks rather than activates the calcitonin receptor would give drug designers precise control over whether a new peptide drug turns the receptor on or off, which is critical for developing treatments for both osteoporosis and rare hypercalcemia disorders.
At calcitonin receptors that are stuck in the 'on' position by a genetic mutation, does this fragment do more than just block, actually pushing the receptor back toward 'off'?
Some people carry rare mutations that keep the calcitonin receptor permanently active, causing calcium imbalance. A drug that actively suppresses this stuck receptor could treat these rare conditions more effectively than one that merely blocks it.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.7850109934806824 | openfold3-mlx |
| ranking score | 0.8860973715782166 | openfold3-mlx |
▸structural qualityopenfold3
| metric | value | note |
|---|---|---|
| gpde | 0.854 | global PDE — lower = better |
| disorder | 0.236 | fraction disordered |
| chain pair ipTM (A, B) | 0.785 | 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 | 438s |
| predicted by | mlx@peptide |
| predicted at | 2026-04-24 |
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{pep10678,
sequence = {VLGKLSQELHKLQTYPRTNTGSGTP},
target = {calcr},
author = {peptidemodel},
year = {2026},
status = {synthesized}
}