A tabbed research binder · TB-500 & thymosin beta-4
TB-500 is the synthetic actin-binding fragment of thymosin beta-4, and most of its evidence is animal.
Each evidence class filed behind its own divider — the seven-residue fragment kept distinct from the full-length protein, the established mechanism kept distinct from the thin human record, every quantitative claim cited.
What TB-500 is, in one divider
TB-500 is the synthetic, N-terminally acetylated heptapeptide Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ), corresponding to residues 17–23 of thymosin beta-4 — the actin-binding core of that 43-amino-acid repair protein [12]. The fragment has a molecular weight near 889 Da; the parent protein is roughly 4,963 Da. That size gap is the single most important entry in this binder.
Here is the distinction the rest of the page keeps separate. "TB-500" in commerce and in the anti-doping literature means the heptapeptide. The overwhelming majority of published efficacy research — wound healing, cardiac repair, stroke, hair, anti-inflammatory signaling — was conducted with full-length thymosin beta-4, not the 7-mer [5]. It is not established that the fragment reproduces the parent protein's effects at the doses used in peptide research, and nearly all human data sit with the full-length protein [6]. Every finding below is labeled fragment or full-length so the two never bleed together.
The binder is organized as dividers: the how TB-500 works section, the parent-protein record under thymosin beta-4, the dose-and-route context with TB-500 half-life, the safety signals and the TB-500 side effects the literature flags, and the access standing — the TB-500 legal status and the FDA 503A status of TB-500. Sources are collected in the study references.
TB-500 the Peptide: Ac-LKKTETQ and Its Actin-Binding Role
The LKKTETQ motif is a WH2-type (Wiskott-Aldrich syndrome protein Homology 2) actin-binding sequence — the same monomer-binding grammar used by the beta-thymosins to manage the cell's cytoskeleton [1]. In the parent protein, this region is what lets thymosin beta-4 grip a single molecule of globular (G-) actin. X-ray crystallography of a gelsolin-domain-1–thymosin beta-4 hybrid bound to actin, resolved to 2 Å, established that thymosin beta-4 forms a 1:1 complex with G-actin and sequesters the monomer by capping both of its ends, preventing it from joining a growing filament [1].
That is the established chemistry. What is not established is the functional question that matters to anyone reading about TB-500: whether the isolated heptapeptide, separated from the rest of the protein, reproduces that actin-buffering behavior — and the downstream migration, angiogenic and anti-inflammatory effects — at research doses in a living human. No completed controlled clinical trial of the TB-500 fragment exists for any indication [6]. The peptide's chemical identity is precise; its standalone biology in humans is unproven.
What Does TB-500 Do? Mechanism in Brief
Full-length thymosin beta-4 is the body's principal G-actin–sequestering peptide, present in nearly all human cells and released by platelets and macrophages at sites of injury [5]. In injury models, it is associated with accelerated cell migration, angiogenesis, anti-inflammatory and anti-apoptotic signaling, reduced myofibroblast number (less scarring), and recruitment of progenitor cells [5]. A consolidating 2012 review framed these properties as the rationale for clinical development in dermal wounds, corneal injury, and heart and CNS repair [5].
The TB-500 heptapeptide carries the actin-binding motif behind that mechanism, but "what does TB-500 do" cannot be answered with the parent protein's data and then quietly relabeled. The how TB-500 works section walks through each pathway and marks, every time, whether the evidence used the fragment or the full-length protein.
The honest gap, stated up front
Three things keep this binder cautious. First, the identity confusion above: marketing for the fragment leans on full-length thymosin beta-4 data [6]. Second, a tumor and angiogenesis safety signal — thymosin beta-4 is overexpressed in several cancers and implicated in metastasis and tumor angiogenesis, so the same pro-migratory, pro-angiogenic properties that aid repair are a theoretical oncologic concern [5]. Third, regulatory standing: TB-500 is not an FDA-approved drug, the FDA placed it in 503A "Category 2," and it is prohibited by the World Anti-Doping Agency [6]. Those entries live behind the TB-500 legal status divider and are stated, not buried.
What this site does not do is sell, supply, dispense, or recommend anything. It is an editorial digest of the published record. Findings are described as "studied at X mg/kg in [species]" — never as a human protocol.