RESEARCH DIGEST / ACTIN-BINDING PEPTIDE
TB-500 is the actin-binding heptapeptide fragment of thymosin beta-4, read panel by panel through the research.
The synthetic Ac-LKKTETQ 7-mer, the parent protein where most of the data actually live, and the repair, neuro, and regulatory record — every quantitative claim stamped to its source.
TB-500, in one panel
TB-500 is the synthetic, N-acetylated heptapeptide Ac-LKKTETQ — leucine, two lysines, threonine, glutamate, threonine, glutamine, capped at the N-terminus. Molecular weight 889.02 Da; formula C38H68N10O14. Those seven residues are positions 17 through 23 of thymosin beta-4 (Tβ4), a 43-amino-acid protein the body uses as its principal actin-sequestering peptide [1]. That short stretch is the conserved actin-binding motif of the beta-thymosins.
Here is the distinction this whole site is built around. In commerce and in the anti-doping literature, "TB-500" means the 889 Da fragment. But the overwhelming majority of efficacy research — the wound-healing numbers, the cardiac signaling, the stroke and brain-injury work — was done with full-length recombinant or synthetic Tβ4 (~4963 Da), not the 7-mer. Whether the isolated fragment reproduces the parent protein's effects at the doses used in peptide research has not been established in controlled human trials.
We keep the two apart on every page. Where a finding is on the full-length protein, we say so. Where it is on the fragment, we say so. The fragment-versus-parent line is the first thing to get right, and most marketing gets it wrong.
TB-500 is not an FDA-approved drug, it has no approved therapeutic indication, and it is prohibited in sport by the World Anti-Doping Agency. This is an editorial digest of the published record — read the actin-sequestration mechanism, the TB-500 neuroprotection research, and the TB-500 legal status, or jump straight to the references.
TB-500 peptide: what the research describes
The TB-500 peptide is studied for one core piece of biology: actin binding. The LKKTETQ motif is a WH2-type actin-interacting sequence, and in the parent protein it lets thymosin beta-4 grab a single monomer of globular (G-)actin and hold it 1:1, capping both ends of the monomer to keep it out of growing filaments [1]. That actin-buffering job is the spine from which every downstream story — cell migration, angiogenesis, anti-scarring — hangs.
In the literature on full-length Tβ4, that actin biology is associated with accelerated re-epithelialization, endothelial migration, reduced myofibroblast number, and survival signaling in injured tissue [3][5][2]. The 7-mer carries the binding motif but lacks the rest of the protein, including the N-terminal segment that generates the separate anti-fibrotic peptide Ac-SDKP — so the fragment is not a small copy of the whole.
Most "TB-500" sold for research is supplied as a lyophilized powder, reconstituted in bacteriostatic or sterile water and kept refrigerated. As a short acetylated peptide it is more chemically robust than the full protein, but identity and purity in unregulated supply are a recurring concern — peptide sequence and full-length-versus-fragment confusion are documented quality problems [11].
Thymosin beta-4: the parent protein behind TB-500
Thymosin beta-4 is a ubiquitous 43-residue peptide present in nearly every human cell and released by platelets and macrophages at sites of injury [5]. Gene TMSB4X; UniProt P62328; approximate mass 4963 Da. It is the body's main G-actin-sequestering molecule, and it does far more than the thymosin beta-4 parent protein name suggests — a 2012 review consolidates the picture: actin binding, cell mobilization and migration, decreased scar-forming myofibroblasts, limited apoptosis and inflammation after injury, and promotion of angiogenesis, all of which provided the rationale for clinical trials in dermal wounds, corneal injury, and heart and CNS repair [5]. A 2021 progress review brings that mechanism-and-application picture up to date [14].
That is the protein. TB-500 is one motif clipped out of it. The reason the distinction matters so much is evidentiary: when a vendor cites "clinical-grade" or "trial" data for TB-500, the underlying study is almost always full-length Tβ4 — for example the topical ophthalmic formulation RGN-259, or the intravenous Phase 1 safety study that dosed synthetic Tβ4, not the heptapeptide [6].
A fragment-versus-parent comparison: the fragment is seven residues at ~889 Da and carries the actin-binding motif; the parent is forty-three residues at ~4963 Da and carries the full functional repertoire. The data overwhelmingly describe the parent. The honest reading of the TB-500 record is the reading that keeps that column visible.