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What Is TB-500?

TB-500 (Thymosin Beta-4, CAS 77591-33-4, MW 4963.4 g/mol) is a synthetic 43-amino acid peptide corresponding to the full sequence of human thymosin beta-4 (Tβ4), a ubiquitous member of the beta-thymosin family of actin-sequestering proteins. It carries the molecular formula C₂₁₅H₃₅₅N₅₆O₇₈S and is encoded by the TMSB4X gene (chromosome Xq21.3–q22). The N-terminus of thymosin beta-4 is acetylated (Ac-Ser), a post-translational modification conserved across vertebrate species. The central LKKTETQ motif (residues 17–23) constitutes the primary G-actin binding sequence responsible for beta-thymosin’s role as a cellular actin monomer buffer. Published research characterizes TB-500/Tβ4 in wound healing, angiogenesis, anti-inflammatory signalling, hair follicle biology, and cardiac tissue research.

Chemical Properties

Property	Value
Common name	TB-500; Thymosin Beta-4; Tβ4
Gene	TMSB4X (X chromosome)
CAS Number	77591-33-4
Molecular Weight	4963.4 g/mol
Molecular Formula	C₂₁₅H₃₅₅N₅₆O₇₈S
Amino Acid Count	43 residues
N-terminus	N-acetyl serine (Ac-Ser); acetylation conserved in vertebrates
Actin-binding motif	LKKTETQ (residues 17–23); WH2 domain; primary G-actin sequestration site
Family	Beta-thymosin family; small actin-monomer sequestering proteins (~5 kDa)
Distribution	Ubiquitously expressed; highest in platelets, macrophages, neutrophils, brain, cardiac tissue

Historical Development and Discovery

The thymosins were initially isolated by Allan Goldstein and colleagues in the 1960s–1970s as thymic peptide fractions with immunological activity. Thymosin beta-4 was first purified from thymus tissue and subsequently characterized as the predominant intracellular actin-sequestering peptide in eukaryotic cells. It is present at high concentrations (up to 0.5 mM) in platelets and white blood cells, where it maintains a pool of unpolymerized actin monomers (G-actin) available for rapid cytoskeletal remodelling. Unlike many peptide signalling molecules, thymosin beta-4 lacks a signal sequence for conventional secretion, yet substantial evidence from wound healing and repair research documents extracellular and paracrine activities, suggesting non-classical secretion pathways.

Research into thymosin beta-4’s tissue repair activities accelerated through the 1990s and 2000s with studies by Kleinman, Malinda, Sosne, and colleagues demonstrating wound healing, angiogenic, and anti-inflammatory effects in multiple preclinical models. A landmark 2004 paper by Bock-Marquette et al. in Nature Medicine characterized thymosin beta-4 as activating integrin-linked kinase (ILK) and promoting cardiomyocyte survival after ischemia, opening a line of investigation into cardiac tissue biology. Thymosin beta-4 has subsequently been examined in corneal wound healing, hair follicle stem cell activation, CNS neuroprotection, and inflammatory modulation.

Chemical Architecture and Structural Features

Structural Feature	Detail
Peptide class	Beta-thymosin family; actin-monomer sequestering protein
Structure	Largely disordered in solution; adopts helical conformation upon G-actin binding
N-terminus	Ac-Ser (N-acetyl serine); conserved modification across vertebrate orthologs
Actin-binding domain	LKKTETQ (WH2-like motif); residues 17–23; primary contact region with G-actin
Disulfide bonds	None
Active N-terminal tetrapeptide	Ac-SDKP (N-acetyl-seryl-aspartyl-lysyl-proline; residues 1–4); substrate for angiotensin-converting enzyme (ACE)
Key structural homologue	Thymosin beta-10 and thymosin beta-15; other beta-thymosin family members

Research Mechanisms

Published research has characterized the following molecular and physiological mechanisms of TB-500 (thymosin beta-4):

• G-actin sequestration and cytoskeletal regulation: Thymosin beta-4’s primary defined intracellular function is sequestration of actin monomers (G-actin) through its LKKTETQ WH2-like domain. By maintaining a large pool of monomeric actin, Tβ4 regulates the availability of G-actin for polymerization at barbed ends of actin filaments, controlling cell migration, shape change, and cytoskeletal dynamics. Intracellular Tβ4 concentrations of 200–500 µM in platelets and leukocytes establish it as the predominant cellular G-actin buffer.
• Cell migration promotion: Extracellular thymosin beta-4 promotes migration of keratinocytes, endothelial cells, macrophages, and fibroblasts in wound closure assay research models. The mechanism involves cell surface receptor interactions and downstream activation of signalling pathways regulating lamellipodia formation and directed cell movement. Actin dynamics within migrating cells are also influenced by both extracellular Tβ4 signalling and intracellular pools.
• Angiogenesis: Research characterizes thymosin beta-4 as promoting endothelial cell migration, tube formation, and neovascularization. In vivo models demonstrate accelerated capillary formation in wound beds following Tβ4 treatment. Proposed mechanisms include upregulation of VEGF, HIF-1α, and MMP production by endothelial cells in response to thymosin beta-4.
• Integrin-linked kinase (ILK) activation: The landmark 2004 study by Bock-Marquette et al. identified ILK as a downstream mediator of thymosin beta-4’s cardiac effects. ILK activation promotes cardiomyocyte survival through Akt phosphorylation, anti-apoptotic signalling, and integrin-matrix interaction enhancement, positioning this pathway as central to Tβ4’s cardiac tissue research profile.
• Anti-inflammatory signalling: Thymosin beta-4 modulates inflammatory responses through multiple mechanisms including reduction of NF-κB activity, downregulation of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α), and promotion of macrophage polarization toward anti-inflammatory phenotypes. The N-terminal Ac-SDKP tetrapeptide is also an ACE substrate and has independent anti-fibrotic and anti-inflammatory activities.
• Hair follicle stem cell activation: Research by Bhagavati and others has characterized thymosin beta-4 as activating hair follicle stem cells, promoting the transition from telogen to anagen phase. Tβ4 upregulates proangiogenic factors and matrix metalloproteinases that facilitate follicle activation, making hair follicle biology an active area of thymosin beta-4 research.

Research Areas

Wound Healing and Tissue Repair Research

The most extensively published research application of thymosin beta-4 involves wound healing and tissue repair biology. Multiple preclinical models — including cutaneous wound healing, corneal wound healing, and intestinal repair — have characterized accelerated re-epithelialization, enhanced angiogenesis, and modulated inflammatory markers in thymosin beta-4-administered animals compared to controls. Malinda et al. and Sosne et al. contributed seminal papers establishing Tβ4’s ability to promote keratinocyte and endothelial cell migration in wound contexts, providing mechanistic framing for subsequent research in this area.

Cardiac Biology and Ischemia Research

Thymosin beta-4 has been investigated in cardiac ischemia and repair contexts following the identification of ILK as a downstream mediator of its cardioprotective effects. Research using Tβ4 in rodent myocardial infarction models has characterized outcomes including reduced cardiomyocyte apoptosis, improved cardiac function metrics, and promotion of cardiac progenitor cell differentiation and epicardial activation. Smart et al. (2007, 2011) contributed to characterizing the role of thymosin beta-4 in priming epicardium-derived progenitor cells for cardiac repair, an area with implications for myocardial regeneration research.

Corneal and Ocular Wound Healing Research

A substantial body of research by Sosne, Bhargava, and colleagues has characterized thymosin beta-4 in corneal wound healing models. Research demonstrates promotion of corneal epithelial cell migration, anti-inflammatory effects on the corneal stroma, and reduction of scarring following injury. Thymosin beta-4 eye drops (RGN-259) were advanced into clinical trials for dry eye disease and neurotrophic keratopathy, providing human pharmacological data in the context of ocular surface biology.

Neurological and CNS Research

TMSB4X expression in brain tissue and the presence of thymosin beta-4 in CSF have motivated research into its roles in CNS biology. Research has characterized neuroprotective effects in models of traumatic brain injury, stroke, and spinal cord injury, with proposed mechanisms including promotion of oligodendrocyte precursor cell differentiation, reduction of neuroinflammation, and support of neural progenitor cell function. These findings position thymosin beta-4 as a research tool for investigating endogenous repair mechanisms in neurological injury contexts.

Frequently Asked Questions

What is the CAS number for TB-500?

The CAS registry number for TB-500 (Thymosin Beta-4) is 77591-33-4. It is a synthetic 43-amino acid peptide with molecular formula C₂₁₅H₃₅₅N₅₆O₇₈S and molecular weight of 4963.4 g/mol, encoded by the human TMSB4X gene.

What is the relationship between TB-500 and thymosin beta-4?

TB-500 is a synthetic research peptide corresponding to the full 43-amino acid sequence of human thymosin beta-4 (Tβ4). The name “TB-500” is used in the research compound market to refer to synthetic thymosin beta-4 manufactured for laboratory research. The underlying compound is chemically identical to endogenous thymosin beta-4 in primary sequence, though the research-grade synthetic version is produced by solid-phase peptide synthesis rather than purified from biological sources.

What is the LKKTETQ motif in thymosin beta-4?

LKKTETQ (Leu-Lys-Lys-Thr-Glu-Thr-Gln) is the central actin-binding sequence of thymosin beta-4, located at residues 17–23 of the 43-amino acid peptide. This sequence constitutes a WH2 (Wiskott-Aldrich homology 2)-like domain that binds to the barbed-face of G-actin monomers, sequestering them from polymerization. The LKKTETQ motif is conserved across beta-thymosin family members and is considered the primary pharmacophore responsible for thymosin beta-4’s G-actin buffering function and many of its downstream biological activities in research models.

How does thymosin beta-4 promote wound healing?

Research characterizes multiple mechanisms by which thymosin beta-4 influences wound healing: (1) promotion of keratinocyte migration and re-epithelialization through actin cytoskeletal remodelling; (2) stimulation of endothelial cell migration and angiogenesis through upregulation of VEGF and MMP production; (3) anti-inflammatory effects reducing pro-inflammatory cytokine levels in the wound environment; and (4) activation of fibroblast migration for extracellular matrix remodelling. The relative contributions of these mechanisms in different wound types and tissue compartments remain an active research focus.

What is the molecular weight of TB-500?

TB-500 (thymosin beta-4) has a molecular weight of 4963.4 g/mol with molecular formula C₂₁₅H₃₅₅N₅₆O₇₈S. It is a 43-amino acid peptide with an N-terminal acetyl group (Ac-Ser). Its molecular weight places it in the medium-range among research peptides — larger than BPC-157 (1419.55 g/mol) but smaller than tesamorelin (5135.92 g/mol).

What is the Ac-SDKP tetrapeptide derived from thymosin beta-4?

Ac-SDKP (N-acetyl-seryl-aspartyl-lysyl-proline) is a tetrapeptide corresponding to residues 1–4 of thymosin beta-4 that is released by enzymatic cleavage of Tβ4. Ac-SDKP is a substrate for angiotensin-converting enzyme (ACE) and is degraded by ACE — explaining elevated Ac-SDKP levels observed with ACE inhibitor treatment. Independent research has characterized Ac-SDKP with anti-fibrotic properties in renal and cardiac models, representing a distinct signalling peptide derived from thymosin beta-4 with its own research literature separate from the full-length Tβ4 molecule.

Does thymosin beta-4 have intracellular functions?

Yes. Thymosin beta-4’s primary defined intracellular function is as a G-actin sequestering protein, maintaining a large pool of unpolymerized actin monomers (G-actin) available for rapid cytoskeletal remodelling. Intracellular Tβ4 concentrations range from 200–500 µM in platelets and leukocytes, making it the predominant cellular G-actin buffer. This intracellular function is distinct from the extracellular/paracrine activities observed in wound healing and tissue repair research, and the mechanisms by which thymosin beta-4 is secreted or released from cells — given its lack of a signal peptide — remains an active area of investigation.

What gene encodes thymosin beta-4?

Thymosin beta-4 is encoded by the TMSB4X gene located on the X chromosome (Xq21.3–q22). TMSB4X is ubiquitously expressed across human tissues, with highest mRNA levels in hematopoietic cells (platelets, neutrophils, macrophages), heart, and brain. The protein product is highly conserved across vertebrates, with >90% sequence identity between human and rodent orthologs, facilitating translation of research findings across model systems.

Published Research

The following peer-reviewed studies are representative of the published research literature on TB-500 (thymosin beta-4):

• Malinda KM, et al. (1997). Thymosin beta4 stimulates directional migration of human umbilical vein endothelial cells. FASEB Journal. PMID: 9194452
• Sosne G, et al. (2004). Thymosin beta 4 promotes corneal wound healing and decreases inflammation in vivo following alkali injury. Experimental Eye Research. PMID: 14981262
• Bock-Marquette I, et al. (2004). Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. PMID: 15520225
• Smart N, et al. (2007). Thymosin beta4 induces adult epicardial progenitor mobilization and neovascularization. Nature. PMID: 17548834
• Goldstein AL, et al. (2012). Thymosin beta4: a multi-functional regenerative peptide. Basic properties and clinical applications. Expert Opinion on Biological Therapy. PMID: 22413937
• Huff T, et al. (2001). Beta-thymosins, small acidic peptides with multiple functions. International Journal of Biochemistry & Cell Biology. PMID: 11399366

Research Use Only Disclaimer

TB-500 (Thymosin Beta-4) as supplied by ITide Laboratories is intended for laboratory research purposes by qualified professionals only. Not for human, animal, diagnostic, or therapeutic use. This compound has not been evaluated by the FDA for clinical application, is not manufactured to pharmaceutical standards, and all applicable local, state, and federal regulations governing research compounds apply.