Skin-pigmentation research peptide (MSH-B)
A hormone fragment first found in sea lamprey, tested in the lab for effects on skin pigment cells and appetite signals; used only as a research tool, not a medicine.
- Class
- Melanotropin peptide (melanocyte-stimulating hormone variant)
- Status
- Research peptide; no approved therapeutic status identified
- Best-supported effect
- Greater potency than alpha-MSH and MSH-A in a frog skin melanotropin bioassay (in vitro / ex vivo assay evidence only)
- Main caveat
- Evidence is limited to a single 1995 bioassay; no animal or human data are attached to this card
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.
Named peptide fragment — synthesized for research; ClinicalTrials.gov trials registered for parent compound or class
Fork this card to add platform evidence →
Endogenous peptide fragment — receptor binding/activity established in published literature; CT.gov evidence
Fork this card to add platform evidence →
Snapshot
Class: Melanotropin peptide (melanocyte-stimulating hormone variant)
Evidence tier: In vitro / assay evidence
Status: Research peptide; no approved therapeutic status identified
Best-supported effect: Greater potency than alpha-MSH and MSH-A in a frog skin melanotropin bioassay (in vitro / ex vivo assay evidence only)
Main caveat: Evidence is limited to a single 1995 bioassay; no animal or human data are identified
What this is
MSH-B peptide is a 20-amino-acid (eicosapeptide) melanotropin isolated from the sea lamprey (Petromyzon marinus). It contains the canonical melanotropin-core sequence shared with alpha-MSH and related melanocyte-stimulating hormones. In the single published assay identifieds source, MSH-B demonstrated approximately 10-fold greater potency than alpha-MSH and approximately 100-fold greater potency than MSH-A in a frog skin bioassay, an established model for melanotropin receptor activity.
Evidence map
| Evidence layer | Grade | What it supports |
|---|---|---|
| Human | None identified | No human trial or clinical data are identified |
| Animal | None identified | No dedicated animal study data are identified |
| In vitro / bioassay | Weak | Single frog skin assay demonstrating melanotropin receptor activity and relative potency versus alpha-MSH and MSH-A |
| Computational | None identified | No structure prediction or docking data are identified |
| Mechanism | Plausible | Melanotropin-core sequence implies melanocortin receptor engagement; receptor subtype specificity not established in attached source |
The evidence base is restricted to one 1995 comparative bioassay. No independent replication data are identified.
Claim check
| Claim | Verdict | Evidence layer | Confidence |
|---|---|---|---|
| Melanotropin receptor activity in bioassay | Supported (in vitro / ex vivo frog skin assay) | In vitro | Low — single assay, 1995; no independent replication in attached source |
| Greater potency than alpha-MSH in frog skin assay (~10-fold) | Supported (in vitro / ex vivo) | In vitro | Low — single published assay; assay system is not a mammalian model |
| Greater potency than MSH-A in frog skin assay (~100-fold) | Supported (in vitro / ex vivo) | In vitro | Low — single published assay; no replication in attached source |
| Melanotropin activity in mammalian or human systems | Not established | None | Low — no mammalian cell, animal, or human data are identified |
Assay conditions
This section reports conditions used in the assay described in the attached source. It does not establish animal or human exposure.
| Context | System | Assay condition | Timepoint | Endpoint | Limitation |
|---|---|---|---|---|---|
| Frog skin melanotropin bioassay | Frog skin preparation (classical melanotropin bioassay) | Peptide concentration not individually extracted in source | Not individually extracted | Melanotropin potency (skin darkening response); relative to alpha-MSH and MSH-A | Ex vivo bioassay system; does not establish mammalian receptor binding, selectivity, or in vivo activity; single 1995 publication; no mammalian or human translation established |
Mechanism
MSH-B contains the melanotropin-core amino acid sequence present in melanocyte-stimulating hormones, which engage melanocortin receptors (MC1R through MC5R in mammals). The frog skin bioassay measures skin-darkening responses mediated through melanophore pigment dispersion, a classical functional readout for melanotropin receptor engagement. The specific melanocortin receptor subtype(s) engaged by MSH-B, and whether its enhanced potency relative to alpha-MSH reflects altered receptor binding affinity, selectivity, or downstream signaling, are not established in the attached source. Target confidence is inferred from peptide class and assay context; no direct binding data are identified.
Chemistry
| Field | Value |
|---|---|
| Sequence (one-letter) | VQESADGYRMQHFRWGQPLP |
| Full notation | H-Val-Gln-Glu-Ser-Ala-Asp-Gly-Tyr-Arg-Met-Gln-His-Phe-Arg-Trp-Gly-Gln-Pro-Leu-Pro-NH2 |
| Length | 20 amino acids (eicosapeptide) |
| Topology | Linear |
| C-terminal modification | Amidation (C-terminal -NH2) |
| Origin | Isolated from sea lamprey (Petromyzon marinus) |
| Molecular weight | Not reported in attached source |
| CAS | Not reported in attached source |
| Sequence confidence | Needs review — sequence is sourced from a single vendor/catalog entry; no cross-source verification is identified |
Open questions
- Mammalian receptor binding: Which melanocortin receptor subtype(s) does MSH-B engage, and does its higher potency relative to alpha-MSH reflect subtype selectivity or general affinity enhancement? The frog skin assay does not resolve this.
- In vivo activity: No animal model data are identified. Whether the frog skin potency advantage translates to mammalian or human physiological systems is unknown.
- Mechanism of potency enhancement: The structural basis for MSH-B's approximately 10-fold and 100-fold potency advantage over alpha-MSH and MSH-A respectively is not explained in the attached source.
- Independent replication: The single 1995 Takahashi et al. bioassay result has not been independently replicated in attached source material.
- Sequence verification: The sequence is derived from a single catalog source; confirmation against the original Takahashi et al. primary publication is warranted.
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.
Could the lab test that first measured this peptide have pointed scientists at the wrong target in the body?
If the peptide turns out to bind the skin receptor (MC1R) more tightly than the appetite receptor it was labeled with, it could become a starting point for new treatments for pigmentation conditions or sun-damage-linked inflammation, for people who need alternatives to existing therapies. The finding would also be a caution: a single frog-skin assay shaped years of assumptions about where this molecule acts.
What if a molecule could make your gut release the 'I'm full' hormones more strongly than anything we have now?
If this holds, the peptide could stimulate cells in the colon to release natural satiety hormones (GLP-1 and PYY) at higher levels than the body normally produces after a meal, potentially helping people with obesity feel full sooner. Because the action would happen in the gut rather than the brain, it might avoid some of the mood or mental-health side effects linked to centrally acting appetite drugs.
If you clip both ends of a chain-shaped molecule together so it holds a fixed shape, does it work better?
Ring-shaped (cyclic) versions of related peptides have historically been around 100 times more potent than the straight-chain versions. If this lamprey peptide, which is already about 10 times more active than the natural human equivalent, could be cyclised, the combined gain might produce a molecule active at extremely low doses. That matters for anyone developing treatments for obesity or skin-pigmentation disorders, where minimizing the dose reduces the risk of side effects.
Could a molecule known for controlling skin pigmentation also quiet down the immune response in inflamed tissue?
Related peptides from the same family are known to dial back immune overactivation in conditions like inflammatory bowel disease. If this lamprey peptide shares that anti-inflammatory ability through the MC3R receptor, it could be useful for people with chronic inflammatory conditions, and its unusual non-mammalian structure gives chemists a fresh scaffold to build more selective drugs from.
Could one specific building block in a 19-piece molecule be responsible for most of its extra strength?
Pinpointing which piece of a peptide drives its potency lets chemists build shorter, simpler drug-like molecules that keep the benefit and drop the rest. If tyrosine at position 8 turns out to be the key contact point, it could guide the design of compact, stable analogs useful as obesity or pigmentation-disorder treatments, potentially with better manufacturing economics than larger peptides.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.9444080591201782 | boltz-2 |
| ranking score | 0.8346496820449829 | boltz-2 |
▸structural qualityopenfold3
| metric | value | note |
|---|---|---|
| gpde | 0.569 | global PDE — lower = better |
| disorder | NaN | fraction disordered |
▸3-letter notation
▸recipeboltz-2 1.0
| parameter | value |
|---|---|
| model | boltz-2 1.0 |
| weights | — |
| hardware | nvidia_nim_api |
| mlx version | — |
| python | — |
| random seed | — |
| msa strategy | none |
| diffusion samples | 1 |
| runtime | — |
| predicted by | mlx@peptide |
| predicted at | 2026-04-24 |
▸citationbibtex
@peptide{pep10681,
sequence = {VQESADGYRMQHFRWGQPLP},
target = {mc4r},
author = {peptidemodel},
year = {2026},
status = {bioassayed}
}