What does LKKTETQ stand for?

It is the single-letter sequence: leucine, lysine, lysine, threonine, glutamate, threonine, glutamine.

Where is it in thymosin beta-4?

Residues 17 to 23, an internal stretch of the 43-residue protein.

Why is TB-500 acetylated?

N-terminal acetylation removes a charge not present mid-protein, better approximating the motif's context, and slows aminopeptidase degradation.

The LKKTETQ Actin-Binding Motif

The short answer

LKKTETQ (leucine, lysine, lysine, threonine, glutamate, threonine, glutamine) occupies residues 17 to 23 of thymosin beta-4 and is the motif most directly associated with its actin-binding activity. TB-500 is that motif synthesised alone with an acetylated N-terminus.

Key facts

Sequence: Leu-Lys-Lys-Thr-Glu-Thr-Gln
Position in Tβ4: Residues 17–23
Function: Actin binding
Charge: Two lysines, one glutamate
Cysteine / methionine: Neither present
Free peptide MW: 847.0 Da (CID 10169788)

Why this particular stretch

Deletion and substitution work on thymosin beta-4 localised its actin-binding activity to this internal region. That is how functional motifs are normally identified: by removing parts of a protein and observing which removal abolishes the activity. LKKTETQ emerged as the segment that could not be lost without losing actin binding.

What the residues contribute

Two lysines give the motif a strong positive charge, and actin's surface carries substantial negative charge, so electrostatic complementarity is a plausible part of the interaction. The threonines offer hydroxyls capable of hydrogen bonding, and glutamate provides a counterbalancing negative charge. It is a small, highly polar sequence with no hydrophobic core, which is consistent with a surface-binding rather than a burial interaction.

Research material referenced

TB-500 5mg, third-party HPLC tested

Buy TB-500 · £23.99

A motif is not a domain

The article title uses domain because that is how the material is commonly described, but a seven-residue stretch is properly a motif rather than a domain. A domain folds independently; a motif is a short functional sequence that generally does not. The distinction matters because it predicts that LKKTETQ alone will be flexible and unstructured rather than adopting a defined shape.

Why that flexibility complicates things

Within the protein, this sequence sits in a defined structural context. Isolated, it samples many conformations, only some of which resemble the bound state. That generally costs affinity (the peptide pays an entropic penalty on binding that the structured protein does not), which is one reason a motif's isolated behaviour cannot be assumed to match its behaviour in situ.

The acetylation

TB-500 carries an acetyl group on its N-terminal amine, adding 42.0 Da over the free peptide. N-terminal acetylation is a standard modification in peptide synthesis: it removes a positive charge that would not be present mid-protein, better approximating how the motif sits within the parent sequence, and it slows degradation by aminopeptidases.

Frequently asked questions

What does LKKTETQ stand for?: It is the single-letter sequence: leucine, lysine, lysine, threonine, glutamate, threonine, glutamine.
Where is it in thymosin beta-4?: Residues 17 to 23, an internal stretch of the 43-residue protein.
Why is TB-500 acetylated?: N-terminal acetylation removes a charge not present mid-protein, better approximating the motif's context, and slows aminopeptidase degradation.

Extended research context

The TB-500 (Thymosin β4 fragment) deep dive

Deep dive: TB-500 vs full-length Thymosin Beta-4

'TB-500' is a synthetic peptide corresponding to the active 17-amino-acid actin-binding region of the endogenous 43-residue Thymosin Beta-4 protein. The two are not identical. TB-500 lacks the flanking sequence that gives full-length TB-4 additional binding partners. In the research literature, papers use 'Thymosin β4' when they mean the full protein and 'TB-500' or 'AcSDKP fragment' when they mean the shorter synthetic peptide. Reading a CoA carefully to see which molecule is in the vial matters. Mass spec is the definitive check.

Actin-binding as the core mechanism

The N-terminal region of TB-4 (and TB-500 by inheritance) contains the canonical actin-binding motif. This motif sequesters G-actin monomers, modulating the G:F actin equilibrium in cell cultures. That mechanism is why almost every mechanistic paper on TB-500 traces back to cytoskeletal reorganisation, cell migration, and models of tissue repair.

Handling considerations unique to TB-500

TB-500 is a 17-residue peptide with modest amphipathicity; it reconstitutes cleanly in bacteriostatic water but is sensitive to repeated freeze/thaw. Aliquoting into single-use volumes on first reconstitution preserves potency across a batch. HPLC on the batch CoA should show a single dominant peak; a doublet suggests deamidation.

Research applications

▸In vitro actin-polymerisation assays (G:F actin ratio measurement)
▸Cell-migration and wound-scratch assays in fibroblast lines
▸Angiogenesis models: tube-formation and endothelial migration assays
▸Analytical method development for short peptides on RP-HPLC
▸Reference-material comparisons against endogenous Thymosin β4

Handling checklist

✓Store lyophilised vials at −20 °C long-term
✓Reconstitute with bacteriostatic water (0.9% benzyl alcohol)
✓Aliquot immediately to avoid freeze/thaw cycles
✓Refrigerate reconstituted aliquots at 2–8 °C; use within 28 days
✓Confirm mass (~4,963 Da for TB-500) via CoA before study use

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Assuming TB-500 = full Thymosin β4

Fix: TB-500 is the 17-residue actin-binding fragment; check the CoA sequence.

✗ Repeated freeze/thaw

Fix: Aliquot at first reconstitution; each cycle degrades yield.

✗ Using tap water

Fix: Use bacteriostatic or sterile water only.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

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Written and reviewed by

The UK Peptides Editorial Team · Research library, UK Peptides

The editorial team is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate. Corrections are made in place and the review date updated.

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LKKTETQ: The Actin-Binding Motif