Brain-signaling neuropeptide that activates an orphan receptor (P52 peptide)
A short natural peptide found in humans that switches on a poorly understood brain receptor; studied only in lab experiments, 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.
Snapshot
Class: Endogenous RF-amide neuropeptide
Evidence tier: In vitro / assay evidence
Status: Research peptide; no approved therapeutic status identified
Best-supported effect: Receptor binding and activation of orphan G-protein-coupled receptor SP9155, demonstrated in vitro (Jiang et al., 2003)
Main caveat: Characterization is limited to a single in vitro identification study; no animal or human data are present
What this is
P52 peptide is a 7-residue C-terminally amidated RF-amide peptide found in humans (Homo sapiens). It was identified as a ligand for the orphan G-protein-coupled receptor SP9155 and reported in a 2003 biochemical characterization study. The peptide belongs to the RF-amide family, a class of neuropeptides defined by an Arg-Phe-NH₂ motif at the C-terminus that is conserved across vertebrates.
Evidence map
| Evidence layer | Grade | What it supports |
|---|---|---|
| Human | None | No human trial or observational data are present |
| Animal | None | No animal study data are present |
| In vitro | Weak | Ligand identification and characterization at orphan GPCR SP9155; single study |
| Computational | None | No computational or docking data are present |
| Mechanism | Plausible | RF-amide GPCR binding proposed; downstream pathway not characterized in attached source |
Claim check
| Claim | Verdict | Evidence layer | Confidence |
|---|---|---|---|
| Binds and activates orphan GPCR SP9155 | Supported (in vitro) | In vitro | Medium — single characterization study; independent replication not established in attached source |
| Endogenous neuropeptide in humans | Supported (in vitro) | In vitro | Medium — identified from human source material; functional role in vivo not established |
| Therapeutic or pharmacological effect in any indication | Not established | None | High — no animal or human evidence present |
Assay conditions
This section reports conditions used in assays. It does not establish animal or human exposure.
| Context | System | Assay condition | Timepoint | Endpoint | Limitation |
|---|---|---|---|---|---|
| In vitro receptor characterization | Orphan GPCR SP9155 expressed system | Peptide concentration; exact conditions not individually extracted in source | Not reported in source | Ligand identification and receptor activation | Single study; exact assay conditions not individually extracted from the title-level source description |
Assay limitations
- No animal toxicology or safety data are present.
- In vitro ligand identification does not establish systemic activity, tolerability, or therapeutic potential.
- The available literature provides a single primary reference; independent replication and downstream functional characterization are not represented in the attached source.
- The physiological role and receptor distribution of SP9155 are not described in the available literature identified.
Mechanism
P52 peptide is proposed to act as an agonist at orphan G-protein-coupled receptor SP9155. The RF-amide motif (Arg-Phe-NH₂) at the C-terminus is structurally conserved across vertebrate neuropeptides that activate GPCR family members. Research receptor binding and characterization in vitro; downstream signaling pathways and physiological consequences of SP9155 activation are not individually described in the attached available literature. Target identification is inferred from the in vitro characterization study; in vivo relevance is not established.
Chemistry
| Field | Value |
|---|---|
| Common name | P52 peptide; RFamide ligand for SP9155 |
| Sequence (single-letter) | GGFSFRF |
| Sequence (full notation) | H-Gly-Gly-Phe-Ser-Phe-Arg-Phe-NH₂ |
| Length | 7 amino acids |
| Topology | Linear |
| C-terminal modification | Amide (–NH₂) |
| Molecular weight | Not reported in source |
| Formula | Not reported in source |
| CAS | Not reported in source |
| Sequence confidence | Needs review — single source; sequence from catalog entry cross-referenced to primary paper title only |
Open questions
- In vivo receptor function: The physiological role of SP9155 and its endogenous ligands in human biology has not been characterized. Understanding receptor distribution and downstream signaling would be prerequisite to any translational hypothesis.
- Selectivity and off-target binding: Whether P52 peptide binds other RF-amide receptors (e.g., NPFF1R, NPFF2R, QRFPR) is not addressed in the attached source; RF-amide peptides frequently display cross-reactivity across family members.
- Animal evidence: No animal model data are present. Preclinical characterization would be required before any translational or safety inference.
- Sequence verification: The sequence is sourced from a vendor catalog entry citing one primary paper; direct sequence verification against the primary source has not been performed in this card-writing pass.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.9053924679756165 | boltz-2 |
| ranking score | 0.7905343770980835 | boltz-2 |
▸structural qualityopenfold3
| metric | value | note |
|---|---|---|
| gpde | 0.871 | 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{pep10550,
sequence = {GGFSFRF},
target = {oprm1},
author = {peptidemodel},
year = {2026},
status = {synthesized}
}