Thymosin alpha-1 is a 28-residue, N-terminally acetylated peptide first isolated from calf thymus in 1977. In the body it is the N-terminal fragment of a larger protein, prothymosin alpha. A synthetic version, thymalfasin, is sold as Zadaxin and is approved in more than 30 countries, mainly in Asia, the Middle East and Latin America; it is not approved by the FDA in the United States.
This profile covers the peptide's sequence and identifiers, where it comes from, what it has been studied in at the molecular and cellular level, its regulatory status and how to handle it in the lab.
Thymosin alpha-1 at a glance
| Property | Value |
|---|---|
| Sequence | Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn |
| One-letter code | Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN |
| Length | 28 residues |
| N-terminal modification | Acetylated serine |
| Molecular formula | C129H215N33O55 |
| Molecular weight | 3108.3 g/mol |
| CAS number | 62304-98-7 |
| PubChem CID | 16130571 |
| Precursor | Prothymosin alpha (UniProt P06454), residues 2 to 29 |
| INN and brand | Thymalfasin; Zadaxin |
| Disulfide bonds | None (no cysteine) |
| US status | Not FDA approved |
Formula, weight and CAS values are from the PubChem record for thymalfasin; the sequence and precursor positions are from the UniProt entry for human prothymosin alpha. Catalog material is described on the Thymosin Alpha-1 page.
Where thymosin alpha-1 comes from
Isolation from thymosin fraction 5
In the 1960s, Allan Goldstein and colleagues prepared extracts of calf thymus to study factors involved in lymphocyte development. A partially purified extract, called thymosin fraction 5, turned out to be a family of polypeptides with molecular weights from about 1,000 to 15,000.
In 1977 the same group reported the isolation and amino acid sequence of one component, which they named thymosin alpha-1. They described it as heat stable, highly acidic and composed of 28 amino acid residues. A 1979 follow-up paper reported that it was 10 to 1,000 times as active as fraction 5 in the in-vitro and animal bioassays the group used to measure T-cell differentiation. The 1977 paper also proposed a naming system for the family of polypeptides in fraction 5, which is where the alpha and beta labels come from.
A fragment of prothymosin alpha
Thymosin alpha-1 was later found to be the N-terminal portion of a larger protein. UniProt lists human prothymosin alpha (gene PTMA) as a 111-residue protein whose initiator methionine is removed; residues 2 to 29 form the thymosin alpha-1 peptide, and serine 2 is acetylated. UniProt lists prothymosin alpha as a nuclear protein, and it is studied in its own right, separately from the 28-residue fragment.
Not the same family as thymosin beta-4
The shared name is historical: both were named under the thymosin nomenclature that came out of the fraction 5 work. They are unrelated in sequence, size and function. Thymosin beta-4 binds and sequesters actin monomers (UniProt P62328), and TB-500 is a fragment of it. See what TB-500 is for that family.
| Thymosin alpha-1 | Thymosin beta-4 | |
|---|---|---|
| Length | 28 residues | 43 residues after removal of the initiator methionine |
| Precursor | Prothymosin alpha | Its own gene (TMSB4X) |
| Main research focus | Immune signaling | Actin binding |
| Approved product | Thymalfasin (Zadaxin), outside the US | None |
Structure and chemistry
The sequence has nine acidic residues (six glutamates and three aspartates) against four lysines, and the acetylated N terminus removes the usual positive charge at that end. The peptide therefore carries a strong net negative charge at neutral pH, which is why Goldstein's group described it as highly acidic.
There is no cysteine, so no disulfide bonds, no methionine and no tryptophan. That removes the most common oxidation routes. There are no glycosylation sites in the synthetic product. The C-terminal asparagine and the internal Asp-Leu and Asp-Ala bonds are the places to watch for slow chemical change in solution, through deamidation and aspartate-related reactions.
At 28 residues, thymosin alpha-1 sits near the boundary between a peptide and a small protein. Our note on peptides versus proteins discusses where that line falls.
How it is made
A 2023 review by Tao and colleagues lists three ways to produce thymosin alpha-1: extraction from tissue, chemical solid-phase synthesis, and expression in engineered organisms. The review states that solid-phase synthesis is the only method approved for producing the medicine. Recombinant routes must also reproduce the N-terminal acetylation, which bacterial expression does not reliably provide, and non-acetylated thymosin alpha-1 is a different molecule.
Synthesis of a 28-residue acidic peptide is routine but not trivial: deletion sequences and incomplete deprotection are the typical impurities. How peptides are made covers the chemistry.
What thymosin alpha-1 has been studied in
The published literature places thymosin alpha-1 in immune signaling research. At the molecular level, the 2023 review summarizes reports that it interacts with Toll-like receptors, including TLR2, TLR3, TLR4, TLR7 and TLR9, and activates downstream pathways including NF-kB, IRF3 and p38 MAPK. At the cellular level, work has focused on dendritic cells (both myeloid and plasmacytoid subsets) and T lymphocytes.
Typical research systems include:
- Cell culture of dendritic cells, T cells and other immune cells, measuring signaling and cytokine expression.
- Receptor studies examining Toll-like receptor involvement.
- Animal models of infection and immune function.
Human studies of thymalfasin have centered on the areas of its approvals, chiefly viral hepatitis, vaccine adjuvant use and oncology settings. This profile does not report their findings. For a different immune-related peptide, see the profile of the human cathelicidin LL-37.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United States | Not approved by the FDA |
| Internationally | Thymalfasin (Zadaxin) approved in more than 30 countries, primarily in Asia, the Middle East and Latin America, per the 2004 annual report of its developer |
| China | The developer's largest market by sales, per the same report |
| Approved uses | Principally chronic hepatitis B, with additional approvals in some countries for hepatitis C, as a vaccine adjuvant or as a chemotherapy adjuvant |
A 2023 review gives the figure as more than 35 countries. National approvals change, so a country's own medicines register is the reference for current status. The US developer, SciClone, also reported holding an orphan drug designation for thymosin alpha-1 in hepatocellular carcinoma in the United States and Europe; an orphan designation is not an approval.
Research material is a separate matter. Anhydrolabs supplies thymosin alpha-1 for in-vitro laboratory research only, as set out on the research use page.
Laboratory handling
Anhydrolabs supplies thymosin alpha-1 as a lyophilized powder in vacuum-sealed vials, and also as 10-vial kits. Each vial is labeled by net content (for example, 5 mg).
Dissolving. Because the peptide is so acidic, it dissolves readily in water and in neutral or mildly basic buffers. Avoid dissolving it in acid: near its isoelectric point, well below pH 7, solubility drops. Stock solutions are described by concentration, for example 1 mg/mL, and can be converted to molarity with the molecular weight of 3108.3 g/mol, allowing for any counter-ion and water content stated on the certificate.
Storage. Keep lyophilized vials at -20 °C, dry and away from light. Once dissolved, split the stock into single-use aliquots and freeze them; repeated freeze-thaw encourages aggregation and adsorption losses. How to store peptides covers the general rules.
Adsorption. At low concentrations, peptides can be lost to plastic and glass surfaces. Low-binding tubes and a carrier protein in dilute working solutions reduce this.
Identity and purity. Mass spectrometry should show a mass matching 3108.3 g/mol for the acetylated peptide; a species 42 Da lighter would indicate missing N-terminal acetylation. Purity by HPLC is reported as the area of the principal peak relative to all integrated signals.
Variants and impurities to recognize
A certificate or a mass spectrum for thymosin alpha-1 is easier to read if you know which related species can appear.
| Species | Mass shift from 3108.3 | What it indicates |
|---|---|---|
| Non-acetylated peptide | About -42 Da | N-terminal acetylation missing or lost |
| Deamidated peptide | About +1 Da | Asn28 converted to Asp in solution or storage |
| Deletion sequences | Minus one residue mass | A coupling step missed during synthesis |
| Sodium or potassium adducts | +22 or +38 Da | An ionization artifact, not an impurity |
Salt form matters too. Synthetic peptides are usually isolated as acetate or trifluoroacetate salts, and the certificate should state which. The counter-ion and residual water add to the weight of the powder, so the net peptide content of a vial is lower than the gross weight of solid. When exact molar concentrations matter, work from the net peptide content rather than the label mass alone.
Finally, check names carefully when searching suppliers' documents or the literature. "Thymosin alpha-1", "thymalfasin", "Tα1" and "TA1" refer to the same 28-residue acetylated peptide. "Prothymosin alpha" is the full 111-residue precursor, and "thymosin beta-4" and "TB-500" belong to the unrelated beta family.
