P21 is a synthetic hexapeptide derived from the active region of ciliary neurotrophic factor and modified with an adamantane group to improve stability and membrane transit. It was identified by epitope mapping of the peptide constituents of Cerebrolysin, and it is used in neuronal culture to study neurotrophic signalling and the cellular events of neurogenesis. NuVion supplies P21 as a laboratory chemical for in vitro research use only.
Key facts
| Type | Synthetic modified hexapeptide |
| Amino acid count | 6 |
| Sequence | Ac-Asp-Gly-Gly-Leu-Ala-Gly-NH2 (Ac-DGGLAG-NH2) |
| Parent protein region | CNTF active region, residues 148 to 151 |
| Modification | Adamantane group, plus N-terminal acetyl and C-terminal amide |
| Origin | Epitope mapping of Cerebrolysin peptide constituents |
| Synonyms | Peptide 021, Ac-DGGLAG-NH2 adamantylated |
| Supplied form | Lyophilised powder in a sealed vial |
Structure and chemistry
P21 is built from a short segment of ciliary neurotrophic factor, a member of the interleukin-6 cytokine family whose active surface was narrowed by epitope mapping to a small linear region. The core hexapeptide is Asp-Gly-Gly-Leu-Ala-Gly. Three of the six residues are glycine, which makes the backbone highly flexible, and the single leucine provides the only substantial hydrophobic side chain in the unmodified sequence.
Three chemical modifications distinguish P21 from the bare hexapeptide. The N-terminus is acetylated and the C-terminus amidated, which removes the charged termini that aminopeptidases and carboxypeptidases recognise and makes the peptide a poorer substrate for exopeptidase attack. The adamantane group, a rigid tricyclic hydrocarbon cage, is attached to increase lipophilicity. Adamantylation is a well established medicinal chemistry approach for improving membrane transit of small polar molecules, and here it converts a peptide that would be effectively membrane-impermeant into one that partitions into lipid.
Those modifications shape handling. The adamantane cage makes P21 considerably less water-soluble than an unmodified hexapeptide of the same length, so a small proportion of organic co-solvent is often required to prepare a concentrated stock, and precipitation on dilution into aqueous medium is the failure mode to watch for. Purity is determined by RP-HPLC, where the adamantylated peptide retains strongly on C18, and identity by mass spectrometry, with the modifications each contributing a defined mass shift that confirms the construct.
Mechanism of action
P21 does not act as a direct agonist at the CNTF receptor complex. The mechanism described in the literature is amplification of endogenous neurotrophic signalling: exposure raises expression and secretion of brain-derived neurotrophic factor and of CNTF itself in cultured neurons and glia, with the increase measured by ELISA on conditioned medium and by qPCR on transcript. The downstream consequence is increased occupancy of the TrkB receptor by the cell’s own BDNF, followed by phosphorylation of TrkB and activation of the PI3K to Akt and the Ras to ERK cascades, measured by Western blot with phospho-specific antibodies.
Two further readouts appear in the cellular literature. Activation of CREB by phosphorylation at serine 133 links the kinase cascades to transcription of plasticity-associated genes, and this is followed by reporter assay or immunoblot. Separately, effects on the cytoskeletal machinery of neurite extension have been described, including changes in the phosphorylation state of microtubule-associated proteins, quantified alongside morphometric measurement of neurite length and branch number. Because the proposed mechanism is indirect, experiments generally include a TrkB blocking control, so that a response driven by secreted endogenous BDNF can be distinguished from any direct action of the peptide.
Research applications
- Neurotrophic factor expression assays: BDNF and CNTF measured in conditioned medium by ELISA and as transcript by qPCR.
- TrkB pathway analysis by Western blot for phosphorylated TrkB, Akt and ERK, with receptor-blocking controls to test indirect action.
- CREB phosphorylation and CRE reporter assays linking kinase activation to transcription.
- Neurite outgrowth morphometry in primary neuronal or neuronal cell line culture.
- Neural progenitor proliferation and differentiation assays using BrdU or EdU incorporation with lineage marker staining.
- Paired comparison with Cerebrolysin, the preparation from which the sequence was originally mapped.
P21 sits in NuVion’s Neuroscience category with the other neuroactive research compounds.
Handling in the laboratory
P21 is supplied lyophilised. Because the adamantane group lowers aqueous solubility, a concentrated stock is usually prepared in a small volume of an organic solvent such as DMSO before dilution into aqueous buffer, and the final solvent concentration in culture is kept low with a matched vehicle control on every plate. Where a fully aqueous stock is wanted, bacteriostatic water is added slowly with gentle swirling and the vial is inspected against light for undissolved material. The reconstitution calculator converts vial content and diluent volume into a stock concentration.
Dilution is the step where material is most often lost. Adding a concentrated organic stock quickly into aqueous medium can precipitate the peptide as a fine haze that is easy to miss, so dilution is done stepwise with mixing between steps, and working solutions are inspected before use. Unopened vials are kept sealed, dry and refrigerated as stated on the product documentation. Reconstituted solution is refrigerated and used within the period given there, or aliquoted and frozen to avoid repeated freeze-thaw cycles.
Testing and supply from NuVion
NuVion’s P21 is manufactured at a GMP-audited facility and independently tested by Janoshik Analytical, with purity determined by RP-HPLC and identity confirmed by mass spectrometry. The Certificate of Analysis for a tested batch is published on the product page and in the COA library. The peptide is supplied lyophilised in sealed vials and dispatched from within Australia.
Related compounds
Cerebrolysin is the preparation from which this sequence was mapped, and other neuroactive peptides used in comparable culture work include Semax and Selank.
Frequently asked questions
What is P21 used for in research?
It is used in neuronal and neural progenitor culture to study neurotrophic factor expression, TrkB pathway activation, CREB phosphorylation and neurite outgrowth. It is also run alongside Cerebrolysin as the defined single peptide derived from that preparation.
Why is P21 modified with adamantane?
The unmodified hexapeptide is small, polar and a poor candidate for crossing membranes. The adamantane cage raises lipophilicity so the peptide partitions into lipid, and the acetyl and amide caps at the termini reduce exopeptidase attack. The trade-off is lower aqueous solubility, which shapes how stocks are prepared.
Is P21 a therapeutic good in Australia?
No. NuVion’s P21 is a laboratory chemical for in vitro research. It is not included in the Australian Register of Therapeutic Goods, has not been assessed by the Therapeutic Goods Administration, and is not for human or veterinary use.
How should P21 be stored?
Lyophilised vials are kept sealed, dry and refrigerated per the product documentation. Stock solution is refrigerated and used within the stated period, or aliquoted and frozen. Working dilutions are inspected for precipitation, since the adamantane group lowers aqueous solubility.
Research use only. This product is a laboratory chemical supplied for in vitro research. It is not included in the Australian Register of Therapeutic Goods and has not been assessed by the Therapeutic Goods Administration for quality, safety or efficacy. It is not for human or veterinary use, and nothing on this page is a representation about therapeutic use.
