Protein reference
Thymosin β-4 (Tβ4): structure and relation to TB-500
Thymosin β-4 (Tβ4) is a 43-amino-acid, N-terminally acetylated protein of about 4.9 kDa, encoded by the gene TMSB4X. It is the parent protein of the research fragment commonly supplied as TB-500. This page is a chemistry reference: sequence, mass, public identifier, and the actin-binding motif that the TB-500 fragment is drawn from.
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Definition
Thymosin β-4 is a member of the β-thymosin family of small, intracellular, actin-sequestering proteins. It is one of the most abundant proteins in many cell types. The canonical reference entry is UniProt P62328; the gene is TMSB4X on the X chromosome (gene page NCBI Gene 7114). The reported length is 43 amino acids and the computed average mass is approximately 4.9 kDa.
Primary sequence and N-terminal acetylation
The 43-residue sequence is given below (UniProt P62328). The protein is N-terminally acetylated; the N-terminal methionine is removed and the resulting serine is acetylated, so the mature sequence begins Ac-SDKPDMAEI….
| Length | 43 amino acids |
|---|---|
| Mature sequence | Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES |
| N-terminal modification | Acetylation on Ser1 (initiator methionine removed) |
| Approximate mass | ≈ 4.9 kDa (computed from the canonical sequence) |
| Gene / locus | TMSB4X, Xq22.2 |
| UniProt | P62328 |
| Family | β-thymosin (actin-sequestering proteins) |
Actin-binding motif (LKKTETQ)
Within the thymosin β-4 sequence, the seven-residue motif LKKTETQ (residues 17–23) is the commonly described actin-binding region. This motif is the basis of the synthetic research fragment that most vendors label TB-500, typically supplied as Ac-LKKTETQ with an N-terminal acetyl group. Different suppliers may define the fragment slightly differently; the molecular mass on the vial should match the fragment definition on the COA.
Thymosin β-4 vs TB-500
Thymosin β-4 is the full parent protein. TB-500 is a shorter synthetic fragment drawn from the actin-binding region of that protein. The two differ chemically and are prepared differently (recombinant or synthetic for the full protein; solid-phase peptide synthesis for the short fragment).
| Field | Thymosin β-4 (Tβ4) | TB-500 (synthetic fragment) |
|---|---|---|
| Length | 43 residues | Vendor-dependent (commonly 7 residues for Ac-LKKTETQ) |
| Mass | ≈ 4.9 kDa | ≈ 889 g/mol for Ac-LKKTETQ (verify on COA) |
| Origin | Naturally occurring intracellular protein | Synthetic fragment drawn from the Tβ4 actin-binding region |
| How it is supplied | Recombinant or purified full-length protein | Lyophilized research peptide, solid-phase synthesis |
| Reference page | This page | TB-500 reference |
Other described β-thymosin fragments (named, not endorsed)
Beyond LKKTETQ, the published β-thymosin literature names other short fragments. The N-terminal tetrapeptide Ac-SDKP (acetyl-seryl-aspartyl-lysyl-proline), derived from the extreme N-terminus of thymosin β-4, is one example that appears in the literature. These names are listed here for reference only and do not imply they are supplied, studied or recommended by this site.
Analytical identification
Full-length thymosin β-4 and its synthetic fragments are identified by mass spectrometry (observed molecular mass vs. the computed mass of the stated sequence, with the N-terminal acetyl group accounted for) and quantified or purity-reported by HPLC. The purity testing methods explainer walks through each technique.
Frequently asked questions
What is thymosin beta-4?
Thymosin β-4 (Tβ4) is a naturally occurring 43-amino-acid, N-terminally acetylated protein of about 4.9 kDa. It is encoded by the gene TMSB4X on the X chromosome and belongs to the β-thymosin family of actin-sequestering proteins. The reference database entry is UniProt P62328.
Is TB-500 the same as thymosin beta-4?
No. Thymosin β-4 is the full 43-residue parent protein. TB-500 is a synthetic peptide fragment based on the actin-binding region of thymosin β-4 (commonly supplied as Ac-LKKTETQ, residues 17–23). The two differ in length, mass and how they are synthesized.
How many amino acids are in thymosin beta-4?
43 amino acids. The sequence is N-terminally acetylated. See the sequence table below and the UniProt entry P62328 for the canonical sequence.
What is the molecular weight of thymosin beta-4?
Approximately 4.9 kDa for the full 43-residue, N-acetylated protein (see UniProt P62328 for the computed mass). The common TB-500 fragment Ac-LKKTETQ is much smaller, around 889 g/mol; verify the exact mass against the supplier COA for whichever fragment is on the vial.
What is the actin-binding region of thymosin beta-4?
The commonly cited actin-binding motif is the seven-residue sequence LKKTETQ, corresponding to residues 17–23 of thymosin β-4. This motif is the basis of the synthetic TB-500 fragment used in research.