Cartilax vs TB-500

Cartilax

Cartilax corresponds to the tripeptide Ala-Glu-Asp, one of the short peptide bioregulators studied in Russian gerontology research. The published literature names it AED or Kartalax, and PubChem lists Cartalax among the synonyms of Ala-Glu-Asp; the spelling Cartilax appears in no study located. Most of the work is cell culture from one St Petersburg group, covering skin fibroblasts, kidney explants, thymocytes and mesenchymal stem cells. The cartilage reports are three papers from that same group, published in Russian with English abstracts.

TB-500

TB-500 is a synthetic seven-residue peptide, Ac-LKKTETQ, matching residues 17 to 23 of the 43-residue actin-binding protein thymosin β4. The stretch it copies lies in the central actin-binding region of thymosin β4; the N-terminal acetyl cap is a synthetic addition, since that position is internal in the native protein. The name is sometimes applied loosely to full-length thymosin β4, and the two should be kept apart: they differ in length, in mass (about 0.9 kDa against about 5 kDa) and in which parts of the parent protein they contain. Most published research concerns the full-length protein, examined in cell culture and in rodent models of skin, cardiac and corneal injury. Work on the fragment alone is far thinner, and it cannot be assumed to share the properties described for the whole protein.

How Cartilax acts

Short peptides of this class are proposed by their authors to enter the cell and act on gene expression rather than on a receptor. For AED, cell-culture reports describe changes in transcripts and proteins tied to proliferation, apoptosis and matrix turnover, including SOX9, aggrecan, type II collagen and COMP in human mesenchymal stem cells during chondrogenic differentiation. No binding partner or receptor is identified in the papers located, and the epigenetic route remains a proposal of the originating group rather than a demonstrated pathway.

How TB-500 acts

Full-length thymosin β4 binds monomeric G-actin in a one-to-one complex and is a major actin-sequestering protein in many cell types, holding actin in unpolymerised form. Structural studies place the LKKTET motif, shared with the WH2 family of actin-binding domains, at the centre of that contact, flanked by N-terminal and C-terminal segments that also touch actin. A small number of cell studies have reported that the isolated fragment affects endothelial cell migration, but how closely it reproduces the actin binding of the whole protein is not well established. Other activities attributed to thymosin β4 map elsewhere: the N-terminal tetrapeptide Ac-SDKP is released by enzymatic cleavage and has been studied separately.

The records side by side

• Type: Cartilax, Synthetic tripeptide; TB-500, Heptapeptide (thymosin β4 fragment)
• Length: Cartilax, 3 amino acids; TB-500, 7 amino acids
• Molecular weight: Cartilax, 333.29 g/mol; TB-500, 889.0 g/mol
• Molecular formula: Cartilax, C12H19N3O8; TB-500, C38H68N10O14

Reading a comparison

A comparison places two records side by side; it does not merge them. Each description above is drawn from that compound's own record, and the two were not necessarily characterised by the same methods, at the same time, or to the same level of detail. Before comparing any attribute, it is worth establishing that both records describe the substance you think they describe — names are not identifiers, and two entries sharing a name can differ in salt form, stereochemistry or the convention used to state a mass. Where a figure carries no method beside it, the comparison is between two reported numbers rather than between two measurements.