Thymulin is a nine-residue peptide hormone produced by thymic epithelial cells. It was first described as a serum factor with T cell differentiating activity, and it is unusual among short peptides in that its activity in bioassays depends on a bound zinc ion. In research it is used as a tool compound in T cell lineage marker assays, in NF-κB and cytokine signalling work in cultured cells, and as a small model system for metal-dependent peptide folding. Thymulin from NuVion is supplied as a laboratory chemical for in vitro research use only.
Key facts
| Type | Synthetic peptide, thymic nonapeptide hormone |
| Amino acid count | 9 |
| Sequence | pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn |
| Molecular formula | C33H54N12O15 (metal-free peptide) |
| Molecular weight | 858.9 g/mol (metal-free peptide) |
| CAS number | 63958-90-7 |
| Synonyms | Facteur thymique sérique (FTS), serum thymic factor, nonathymulin |
| Supplied form | Lyophilised powder in a sealed vial |
Structure and chemistry
The sequence is pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn. The N-terminal residue is pyroglutamic acid, formed when the side chain of an N-terminal glutamine or glutamate cyclises onto the backbone amine. The pyroglutamate ring removes the N-terminal positive charge and blocks aminopeptidase access, which is part of the reason the native peptide survives in serum long enough to have been isolated from it. The rest of the chain is small and polar: one lysine, two serines, a glutamine, an asparagine and two glycines. There are no aromatic residues, so the peptide has no useful absorbance at 280 nm and is quantified by absorbance at 210 to 220 nm or by amino acid analysis. There is no cysteine or methionine, so oxidation and disulfide scrambling are not concerns during handling.
Zinc is the defining feature. The metal-free peptide is largely unstructured in solution and is inactive in the classical bioassays. Adding equimolar Zn2+ gives a folded, more compact conformation, and NMR work has placed the coordinating groups in the C-terminal Ser-Asn region together with backbone carbonyl oxygens. Because the sequence contains none of the cysteine or histidine ligands that give zinc-finger motifs their affinity, the thymulin-zinc complex is comparatively labile, and the free zinc concentration of an assay buffer governs how much of the peptide is in the active form. Chelators such as EDTA strip the metal and abolish activity, which provides a convenient negative control.
Thymulin was isolated from serum by Bach and Dardenne in the 1970s and named facteur thymique sérique, later shortened to FTS. The sequence is identical in each mammalian species in which it has been characterised. Synthetic thymulin is prepared by solid-phase synthesis and is normally supplied as the metal-free peptide, with the active complex formed in the laboratory by adding a zinc salt at the point of use.
Mechanism of action
No thymulin receptor has been cloned. Saturable, high-affinity binding sites have been described on T lymphoblastoid cell lines, and binding depends on the zinc-bound form, but the protein responsible has not been identified. Mechanism is therefore described from cellular readouts.
The historical readout is T cell lineage marker induction. In the original bioassays, the zinc-thymulin complex induced expression of T cell surface markers on lymphoid precursor cells in culture and shifted the azathioprine sensitivity of spontaneous rosette-forming cells. This azathioprine rosette assay remained the standard measure of thymulin activity for two decades. The molecular events between binding and marker expression have still not been mapped.
The second body of work concerns NF-κB. In alveolar epithelial cells exposed to bacterial lipopolysaccharide, thymulin in the presence of zinc reduced degradation of the inhibitor IκB-α, lowered nuclear translocation and DNA binding of NF-κB, and reduced release of IL-1β, IL-6 and TNF-α into the medium. Zinc alone reproduced part of this effect and the zinc-free peptide did not, so the complex is regarded as the active species. Phosphorylation of p38 MAPK and transcription of IL-10 are the other readouts measured alongside NF-κB activity in these cell models.
Thymulin has also been described as a hypophysiotropic peptide. In dispersed pituitary cell cultures it has been reported to modulate release of growth hormone and prolactin, and its own production by thymic epithelial cells is regulated by pituitary and thyroid hormones. That two-way relationship is the basis for interest in it as a link between endocrine and lymphoid signalling. All of these observations sit at the level of cultured cells and isolated pathways.
Research applications
- NF-κB reporter assays, IκB-α western blotting and cytokine ELISA in epithelial or macrophage-like cell lines stimulated with lipopolysaccharide, run with and without added zinc
- T cell lineage marker induction on precursor cells in culture, with the azathioprine rosette bioassay as the functional reference
- Metal binding and conformational studies by NMR, circular dichroism and isothermal titration calorimetry, using thymulin as a nine-residue model of zinc-dependent folding
- Ligand binding studies on lymphoid cell lines aimed at identifying the thymulin binding protein
- Secretion assays in dispersed pituitary cell cultures
- RP-HPLC and LC-MS method development for pyroglutamate-containing peptides
Thymulin sits in the Immune Signalling category alongside the other thymus-derived peptides and the cathelicidin fragment LL-37.
Handling in the laboratory
The lyophilised powder is reconstituted with bacteriostatic water. Run the water slowly down the inside of the vial and let the powder dissolve without shaking; the peptide is hydrophilic and goes into solution readily. The reconstitution calculator gives the concentration that a chosen water volume produces from the vial content. If an assay needs the active complex, zinc chloride or zinc sulfate is added at a 1:1 molar ratio to the peptide in the assay buffer, and buffers containing EDTA or other chelators are avoided for that step.
Keep the sealed vial dry, away from light and refrigerated as described in the product documentation. Once reconstituted, keep the solution refrigerated and use it within the period stated on the documentation, and avoid repeated freeze-thaw cycles by aliquoting on the day of reconstitution. The compound is characterised by RP-HPLC for purity and by mass spectrometry for identity. The pyroglutamate N-terminus means the observed mass is 17 Da below that of the linear glutamine-initiated sequence, which is a useful check when reading the spectrum.
Testing and supply from NuVion
NuVion has thymulin independently tested by Janoshik Analytical. Most batches are tested, and the Certificate of Analysis for a tested batch is published on the product page, reporting purity by RP-HPLC and identity by mass spectrometry. Manufacture is GMP-audited, the peptide is supplied lyophilised in sealed vials, and orders are dispatched from within Australia. Certificates for other compounds are collected in the Certificate of Analysis library.
Related compounds
Two other thymus-derived peptides sit in the same category: Thymogen, the Glu-Trp dipeptide, and Thymosin Alpha-1, a 28-residue acetylated peptide used in Toll-like receptor signalling work. LL-37, the cathelicidin fragment, is the category’s antimicrobial peptide.
Frequently asked questions
What is thymulin used for in research?
Thymulin is used as a tool compound in three areas: T cell lineage marker assays in cultured precursor cells, NF-κB and cytokine signalling studies in epithelial and macrophage-like cell lines, and metal-binding studies where a nine-residue zinc-dependent peptide is a tractable model. It also serves as a reference standard in RP-HPLC and mass spectrometry method development.
Why does thymulin need zinc?
The metal-free peptide is unstructured and inactive in bioassays. Binding one Zn2+ ion folds the peptide into the conformation that cell assays recognise. Synthetic thymulin is normally supplied metal-free, so the active complex is formed by adding an equimolar zinc salt in the assay buffer, with chelators kept out of that step.
How is thymulin supplied and stored?
NuVion supplies thymulin as a lyophilised powder in a sealed vial. Store the sealed vial dry, away from light and refrigerated per the product documentation. After reconstitution with bacteriostatic water, keep the solution refrigerated and use it within the period given on the documentation.
Is thymulin a therapeutic good in Australia?
No. Thymulin from NuVion is a laboratory chemical for in vitro research. It is not included in the Australian Register of Therapeutic Goods and has not been assessed by the TGA. It is not for human or veterinary use.
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.
