A soft-paneled research desk — the Ac-LKKTETQ fragment
TB-500 is seven amino acids of thymosin beta-4 — here is what the research carries, and where the human data stop.
A calm reading of the wound, cardiac, and neuro literature, with the central caveat kept in plain sight: most efficacy data are on the full-length protein, not the seven-mer.
TB-500 explained: what is TB-500, and what is it not?
TB-500 is the synthetic, N-acetylated heptapeptide Ac-LKKTETQ — seven amino acids (Leu-Lys-Lys-Thr-Glu-Thr-Gln) corresponding to residues 17 to 23 of thymosin beta-4, the conserved actin-binding region of the parent protein. That sequence is the molecule. Its molecular weight is roughly 889 Da, against the full-length protein's ~4963 Da [1].
The distinction matters more here than for almost any other research peptide. In commerce and in the anti-doping literature, "TB-500" denotes the seven-mer. But the overwhelming majority of published efficacy research — the wound healing, the cardiac repair, the stroke work — was conducted with full-length recombinant or synthetic thymosin beta-4, not the fragment [5]. This site flags that difference at every finding. When a study used the full protein, it says so.
Thymosin beta-4 (gene TMSB4X, UniProt P62328) is a ubiquitous 43-residue peptide present in nearly all human cells and released by platelets and macrophages at sites of injury [5]. It is the body's principal G-actin-sequestering molecule. TB-500 carries that protein's actin-binding core and nothing else — it is a synthetic construct, not an endogenous species. For the full picture of how the two relate, see the TB-500 research findings.
TB-500 peptide: the Ac-LKKTETQ fragment of thymosin beta-4
The TB-500 peptide is defined by one short sequence and one function: it holds the LKKTETQ motif that lets thymosin beta-4 bind monomeric actin. Structural work settled how the parent does this. X-ray crystallography of a gelsolin-domain-1–thymosin beta-4 hybrid bound to actin, resolved to 2 Å, established that the protein forms a 1:1 complex with G-actin and sequesters the monomer by capping both ends, preventing it from polymerizing [1].
That WH2-type actin-interacting motif is the structural basis for thymosin beta-4's actin-buffering role — and it is the part of the protein that TB-500 reproduces. Whether the isolated heptapeptide reproduces the full protein's downstream effects at the doses used in peptide research is a separate question, and it is not one that controlled human trials have answered [5].
TB-500 is supplied as a lyophilized powder for research use, typically reconstituted in bacteriostatic or sterile water and kept refrigerated. As a short acetylated peptide it is more chemically robust than the full-length protein, though still subject to proteolysis and freeze-thaw degradation. You can read the Ac-LKKTETQ actin-binding fragment framing throughout this digest.
TB-500 mechanism: what does TB-500 do in the research literature?
In injury models, thymosin beta-4 and its actin-binding region are associated with accelerated cell migration, angiogenesis, anti-inflammatory and anti-apoptotic signaling, reduced scar formation, and recruitment of progenitor cells [5]. Those are the threads that run through three decades of work on the parent protein.
The mechanism starts with actin. By binding and holding monomeric (globular) actin in a buffered pool, thymosin beta-4 regulates the cytoskeletal dynamics that drive cell motility — and migrating cells are the engine of every repair process the protein has been studied in: keratinocytes resurfacing a wound, endothelial cells building new vessels, myoblasts rebuilding muscle [5].
A consolidating review describes the parent protein binding actin, promoting cell mobilization and stem-cell activity, decreasing myofibroblast number to reduce scarring, limiting apoptosis and inflammation after injury, and promoting angiogenesis — the basis on which dermal, corneal, and cardiac clinical trials of thymosin beta-4 were pursued [5]. The interesting and honest detail is how much of that translated, and how much did not.
Where the human data stop
There are no completed controlled clinical trials of the TB-500 heptapeptide for any indication [5]. That is the single most important sentence on this page, and it is easy to lose under marketing that quotes the parent protein's results.
What human data exist are for full-length thymosin beta-4. A randomized, placebo-controlled Phase 1 study gave synthetic thymosin beta-4 intravenously to 40 healthy volunteers across four dose cohorts — 42, 140, 420, or 1260 mg — and found it well tolerated, with only infrequent mild-to-moderate adverse events and no dose-limiting toxicities [6]. Topical thymosin beta-4 (RGN-259) reached completed dry-eye trials [7], and an injectable acute-myocardial-infarction trial of thymosin beta-4 was registered and completed [8]. An early injectable stroke trial was withdrawn [9].
So the honest shape is this: a real, structured, decades-long research program on a parent protein, and a fragment marketed on its coattails whose own human record is empty. This site reports both, and keeps them separate. The full TB-500 research findings walk through each study, and the TB-500 side effects and safety signals cover the open safety questions.