What is TB-500?
TB-500 is a synthetic peptide studied in research as a structural analog of a defined region within Thymosin Beta-4 (Tβ4), the endogenous 43-amino-acid protein associated with actin sequestration and cytoskeletal regulation. It is catalogued under CAS number 885340-08-9 with a molecular formula of C₃₉H₆₇N₉O₁₃ and an approximate molecular weight of 889 Da (877.99 g/mol), corresponding to the acetylated seven-residue fragment Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln drawn from the Tβ4 17–23 region. The compound is produced through solid-phase peptide synthesis, supplied as a lyophilized powder, and is intended solely for laboratory research purposes, not for human use.
Within the peptide research landscape, TB-500 holds a well-established position. The Thymosin Beta-4 literature stretches back several decades, making it one of the more extensively characterized small proteins in cell biology and cytoskeletal research. TB-500 — the synthetic fragment corresponding to Tβ4's actin-binding domain — is studied as a tractable, research-grade proxy for investigating the biological activities associated with that domain. Understanding the compound requires understanding both the full Thymosin Beta-4 protein it is derived from and what the fragment retains from the parent molecule's structural and biological profile.
Amino Line catalogues TB-500 as a heritage compound: one of the classic research peptides with a long and substantive publication history predating the modern wave of synthetic peptide research tools. It is not a novel probe compound — it is a well-characterized research chemical with a defined structural identity and an established place in the actin and tissue biology literature.
What is Thymosin Beta-4, and how does TB-500 relate to it?
Thymosin Beta-4 is a naturally occurring, ubiquitously expressed small protein of 43 amino acids. It was originally isolated from thymic tissue but is now recognized as a widely distributed intracellular protein, expressed in most cell types and found at particularly high concentrations in platelets and certain immune-adjacent tissues in studied model systems. The most extensively characterized function of Tβ4 is its role as an actin-sequestering protein.
Actin exists in two interconverting forms in cells: globular actin (G-actin), the monomeric pool, and filamentous actin (F-actin), the polymerized structural form. The ratio of G-actin to F-actin in a cell is tightly regulated and governs cytoskeletal dynamics, cell shape, motility, and division. Tβ4 binds G-actin monomers with high affinity, sequestering them in a non-polymerizable complex. By modulating the available pool of free G-actin, Tβ4 participates in the regulation of actin filament assembly and disassembly dynamics. This central role in cytoskeletal regulation is the structural and biochemical foundation on which the broader Tβ4 research literature is built.
TB-500 corresponds to the region of Tβ4 that encodes this actin-binding activity. The LKKTET motif — a short sequence within the central domain of Tβ4 — is the structural element identified in the literature as critical for G-actin binding. TB-500, as a synthetic peptide built around this domain, retains actin-binding capacity in research assays. This is why TB-500 is studied as a research probe for Tβ4-associated biology rather than as a structurally unrelated synthetic compound: it is a fragment-based representation of a well-characterized endogenous protein's functional domain.
What is the molecular structure of TB-500?
TB-500 is a synthetic seven-amino-acid peptide — the acetylated Ac-LKKTETQ heptapeptide — with an approximate molecular weight of 889 Da. The peptide sequence corresponds to the actin-sequestering domain of Thymosin Beta-4, centered on the LKKTET hexapeptide motif that structural research has identified as the minimal actin-binding element within the full Tβ4 sequence. The compound is substantially smaller than the full 43-amino-acid Thymosin Beta-4 protein, reflecting its design as a focused fragment rather than a full-length synthetic reproduction.
The peptide is produced through solid-phase peptide synthesis followed by high-performance liquid chromatography purification. Research-grade TB-500 is characterized by HPLC purity analysis and mass spectrometry identity confirmation at the point of manufacture. The compound is supplied in lyophilized form as a white to off-white powder, which is the standard presentation for peptides intended for research storage and handling.
An important distinction for researchers entering the TB-500 literature: the compound is categorized differently across publications. Some earlier literature describes Thymosin Beta-4 itself (the full 43-aa protein) under compound numbering schemes that were in use before the synthetic fragment research era; more recent literature isolates the actin-binding fragment as the research-relevant entity. TB-500 as catalogued and studied in the contemporary peptide research context refers specifically to the synthetic fragment — not the full-length Tβ4 protein — even though the research literature on both overlaps considerably.
What is the LKKTET motif, and why is it central to TB-500 research?
The LKKTET sequence is the hexapeptide within Thymosin Beta-4 that structural and functional research has identified as the core actin-binding element. Studies using deletion mutants and synthetic fragment competition assays have mapped G-actin binding activity to this region, establishing that peptides containing the LKKTET motif retain the actin-sequestering property of the full-length protein in in vitro assays, while fragments that omit it lose this capacity.
The biological relevance of this motif extends beyond simple structural characterization. G-actin binding by the LKKTET-containing region of Tβ4 positions the protein as a direct participant in the regulation of the G-actin/F-actin equilibrium. Research examining cytoskeletal dynamics in cell motility, wound contraction, and related processes has used LKKTET-containing peptides — including TB-500 — to probe the contribution of actin sequestration to those cellular events.
Published structural analyses using nuclear magnetic resonance and crystallographic methods have characterized the geometry of the LKKTET-actin interaction, providing atomic-resolution detail of the binding interface. This structural depth makes TB-500 a well-grounded research probe: researchers working with it are not inferring mechanism from phenomenological observations but operating within a framework of characterized binding geometry and structural biology. This level of structural characterization is one of the hallmarks of the classic compounds Amino Line catalogues — the mechanistic foundation is established, not speculative.
How does TB-500 compare to full-length Thymosin Beta-4 in research applications?
The difference between studying full Tβ4 and TB-500 is the difference between characterizing a multifunctional protein and isolating its actin-binding domain. Full-length Tβ4 has been studied in contexts beyond actin sequestration: signal transduction, nuclear function, and cell migration in ways not reducible to the LKKTET domain's actin-binding activity. Studies have suggested Tβ4 interacts with additional intracellular partners beyond G-actin, and some of these interactions may map to regions outside the actin-binding fragment.
TB-500, as the seven-amino-acid synthetic fragment, is studied specifically for the actin-binding domain's contribution. This makes it a more focused but narrower probe than full-length Tβ4. When experimental design calls for isolating the actin-sequestration axis from other Tβ4 activities, TB-500 is the appropriate research compound. When the full-length protein's broader activity profile is of interest, researchers work with recombinant Tβ4 or related tools rather than the synthetic fragment.
From a practical research standpoint, TB-500's smaller molecular weight relative to recombinant full-length Tβ4 also affects compound behavior in experimental settings: diffusion rates, membrane penetration in certain model systems, and stability in aqueous conditions can differ between a 43-aa protein and a 7-aa synthetic fragment. These physical-chemical differences are relevant to experimental design and are separate from the biological questions the compound is used to address.
What cellular processes has TB-500 been studied in relation to?
The Thymosin Beta-4 and TB-500 literature encompasses several cellular processes, all connected through the central role of actin dynamics in cell biology. The most directly studied cellular contexts include:
Cell migration. Actin cytoskeletal remodeling is a primary driver of directed cell motility. G-actin availability modulated by actin-sequestering proteins directly affects the rate and character of lamellipodia extension. Research using TB-500 in cell migration assays characterizes the contribution of the actin-sequestering domain to migration-associated cytoskeletal activity.
Wound contraction and tissue remodeling models. The Tβ4 literature has a substantial section dedicated to wound-related in vitro models, particularly scratch assays used to study collective cell migration and wound closure dynamics in cell culture. TB-500 appears in this literature as the synthetic fragment used to study actin-binding-domain-specific contributions to these processes.
Cardiac and vascular cell research. A distinct branch of the Tβ4 literature has examined the protein's presence and activity in cardiac tissue contexts, particularly in studies using cardiomyocyte models. The actin dynamics relevant to cardiomyocyte biology — where cytoskeletal organization is tied to contractile function — make the LKKTET domain a research subject in this specialized area.
Angiogenesis-adjacent models. In vitro angiogenesis models using endothelial cell tube formation assays have been used in conjunction with Tβ4 and TB-500 research. Endothelial migration and cytoskeletal remodeling are central to these assays, connecting them to the actin-binding research context.
Amino Line does not make therapeutic or outcome claims regarding TB-500 in any of these contexts. The compound is studied at the level of actin-binding activity and cellular behavior in laboratory model systems. All of the above represents characterized research contexts, not claims about the compound's physiological effects in any organism.
How should TB-500 be stored and handled for research?
TB-500 is supplied as a lyophilized powder and is stored at −20°C to preserve structural integrity. As a synthetic peptide, it is sensitive to the same degradation pathways that affect related compounds: oxidation of susceptible residues, moisture-induced hydrolysis of the peptide backbone, and thermal denaturation. Repeated freeze-thaw cycles increase the cumulative exposure to these degradation pathways and are avoided in best-practice research handling.
The lyophilized state is significantly more stable than solution-state peptide, which is why research-grade TB-500 is supplied in lyophilized form. Long-term cold storage should maintain the sealed lyophilized material at −20°C with desiccant to guard against humidity intrusion.
Cold-chain shipping protects the same integrity during transit. A compound characterized at research-grade purity at manufacture can lose specification through thermal excursion in shipment. Amino Line ships all peptide compounds with cold-chain packaging as standard. This article does not provide handling or preparation protocols; those are the researcher's responsibility and are determined by experimental requirements and applicable regulations.
How does Amino Line source and catalog TB-500?
Amino Line supplies TB-500 as a research-grade compound characterized by HPLC purity analysis and mass spectrometry identity confirmation, with batch-specific Certificates of Analysis available for every order. All shipments are cold-chain packaged as standard, and operations are US-based.
TB-500 sits within Amino Line's heritage compound catalog — compounds with long publication histories, established mechanistic frameworks, and well-characterized research applications. Related research compounds in the tissue and cytoskeletal biology category are available at all compounds. All material is for laboratory research use only and is not for human use.
This compound is a research chemical intended for laboratory and scientific research purposes only. It is not a drug, supplement, or food, and is not intended to diagnose, treat, cure, or prevent any disease. Amino Line does not sell products intended for human use. Researchers are responsible for compliance with all applicable local, state, and federal regulations.