TB-500 Peptide (Thymosin Beta-4): What the Research Shows
TB-500 is the active LKKTETQ fragment of Thymosin Beta-4. What its actin-binding function is, and the in-vitro cell-migration research the fragment appears in.
Thymosin Beta-4 (Tβ4) is a ubiquitous, highly conserved 43-amino-acid protein originally isolated from thymic tissue. It is encoded by the TMSB4X gene and is among the most abundant intracellular peptides identified in mammalian cells, particularly in platelets, macrophages, and neutrophils. The synthetic research peptide TB-500 corresponds to the central actin-binding domain of the full-length protein — specifically the heptapeptide sequence LKKTETQ — and is studied in vitro to isolate the actin-regulatory properties of this fragment.
Primary structure and the LKKTET actin-binding domain
The full 43-residue Tβ4 sequence contains a central WASP-homology 2 (WH2) motif, a conserved structural element shared with a broad family of actin-nucleation proteins. Within this WH2 motif, the hexapeptide core LKKTET (residues 17–22) constitutes the minimal actin-binding sequence. Crystallographic and NMR studies have demonstrated that this region adopts a partially helical conformation upon association with monomeric globular actin (G-actin), positioning the lysine residues at positions 18 and 19 to form electrostatic contacts with acidic residues on the actin surface. This interaction is the molecular basis for Tβ4's G-actin sequestration activity.
G-actin sequestration and cytoskeletal dynamics
The polymerisation of G-actin into filamentous actin (F-actin) is a tightly regulated process central to cell motility, cytokinesis, and endocytosis. Tβ4 functions as a G-actin sequestering protein, maintaining a soluble pool of unpolymerised actin by binding monomers in a 1:1 stoichiometric ratio and inhibiting their spontaneous nucleation. In vitro sedimentation assays and fluorescence pyrene-actin polymerisation studies have quantified the dissociation constant (Kd) of the Tβ4–G-actin interaction at approximately 0.5–0.7 µM, placing it within a physiologically relevant concentration range for cytoskeletal regulation research.
FAK/paxillin signalling and cell migration assays
In cell-migration research models, exogenous Tβ4 has been shown to modulate focal adhesion kinase (FAK) phosphorylation at Tyr397, an autophosphorylation site critical for the assembly and turnover of focal adhesion complexes. FAK activation drives downstream recruitment of the scaffolding protein paxillin to nascent adhesion sites, linking extracellular matrix engagement to cytoskeletal reorganisation. In-vitro scratch-wound assays and Boyden chamber transwell migration experiments have used Tβ4 to investigate how altered G-actin availability influences the FAK–paxillin–vinculin axis and the rate of lamellipodia extension at the leading edge of migrating cells. These assays are conducted in research cell lines for laboratory investigative purposes only.
Angiogenesis research: VEGF and Akt pathway involvement
A parallel body of in-vitro research has investigated Tβ4 in the context of angiogenic signalling. Endothelial cell tube-formation assays and proliferation studies have reported upregulation of vascular endothelial growth factor (VEGF) expression at the transcriptional level following Tβ4 exposure, alongside activation of the PI3K/Akt serine-threonine kinase pathway. Akt phosphorylation at Ser473 is a key node in endothelial survival and migration signalling, and its modulation by Tβ4 in human umbilical vein endothelial cell (HUVEC) models has been a recurring observation in the research literature. ILK (integrin-linked kinase) has also been identified as a potential upstream mediator of this Tβ4–Akt interaction in matrigel-based angiogenesis assays.
Wound-closure research models
Corneal epithelial wound-closure assays: Tβ4 has been studied in rabbit and human corneal epithelial cell lines using standardised scratch assays, with gap closure rates quantified by time-lapse microscopy Dermal fibroblast migration: In-vitro models using primary human dermal fibroblasts have assessed Tβ4's influence on MMP-2 (matrix metalloproteinase-2) secretion and collagen gel contraction Cardiac research models: Neonatal rat ventricular myocyte (NRVM) and H9c2 cardiomyoblast cultures have been used to study Tβ4 in the context of cardiomyocyte survival signalling via the Akt/GSK-3β axis All models described are in-vitro laboratory research systems and do not constitute evidence of effects in living humans Purity requirements for mechanistic research
The mechanistic precision of TB-500 research depends critically on compound identity and purity. Truncated sequences — particularly those missing the C-terminal residues 23–43 — exhibit altered actin-binding kinetics and cannot be assumed to replicate the biological activity of the intact fragment. For this reason, each Vivera batch is independently verified by HPLC purity analysis and mass spectrometry identity confirmation at a US-based third-party laboratory, with batch-specific Certificates of Analysis available on request. TB-500 is supplied by Vivera Labs for in-vitro laboratory research use only.
Frequently Asked Questions What is TB-500? TB-500 is a synthetic research peptide corresponding to the central actin-binding domain of the full-length protein Thymosin Beta-4 — specifically the heptapeptide sequence LKKTETQ. It is studied in vitro to isolate the actin-regulatory properties of this fragment.
What is the difference between TB-500 and Thymosin Beta-4? Thymosin Beta-4 (Tβ4) is a ubiquitous, highly conserved 43-amino-acid protein encoded by the TMSB4X gene and among the most abundant intracellular peptides in mammalian cells. TB-500 corresponds only to the central actin-binding domain of that protein — the heptapeptide LKKTETQ — so it is a short fragment used to study the actin-regulatory part of the larger molecule.
What does TB-500 do to actin in research models? Within the WH2 motif of Tβ4, the hexapeptide core LKKTET is the minimal actin-binding sequence. Tβ4 functions as a G-actin sequestering protein, binding monomers in a 1:1 stoichiometric ratio and inhibiting their spontaneous nucleation, with the dissociation constant of the Tβ4–G-actin interaction quantified in vitro at approximately 0.5–0.7 µM. This is the molecular basis studied in cytoskeletal regulation research.
What laboratory models use TB-500? In-vitro work has used scratch-wound and transwell migration assays to study FAK/paxillin signalling, endothelial tube-formation and HUVEC proliferation studies for angiogenic signalling, and corneal epithelial, dermal fibroblast and cardiomyocyte cultures for wound-closure and cell-survival signalling. All models described are in-vitro laboratory research systems and do not constitute evidence of effects in living humans; TB-500 is supplied by Vivera Labs for in-vitro laboratory research use only.
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For in-vitro laboratory research use only. Not for human or veterinary use, consumption, or therapeutic application. No medical claims are made.
