Thymosin beta-4 is a protein that in humans is encoded by the TMSB4X gene. Recommended INN (International Nonproprietary Name) for thymosin beta-4 is ‘timbetasin’, as published by the World Health Organization (WHO). 
The protein consists (in humans) of 43 amino acids (sequence: SDKPDMAEI EKFDKSKLKK TETQEKNPLP SKETIEQEKQ AGES) and has a molecular weight of 4921 g/mol.
Thymosin-β4 is a major cellular constituent in many tissues. Its intracellular concentration may reach as high as 0.5 mM. Following Thymosin α1, β4 was the second of the biologically active peptides from Thymosin Fraction 5 to be completely sequenced and synthesized.
Work with cell cultures and experiments with animals have shown that administration of thymosin β4 can promote migration of cells, formation of blood vessels, maturation of stem cells, survival of various cell types and lowering of the production of pro-inflammatory cytokines. These multiple properties have provided the impetus for a worldwide series of on-going clinical trials of potential effectiveness of thymosin β4 in promoting repair of wounds in skin, cornea and heart.
Such tissue-regenerating properties of thymosin β4 may ultimately contribute to repair of human heart muscle damaged by heart disease and heart attack. In mice, administration of thymosin β4 has been shown to stimulate formation of new heart muscle cells from otherwise inactive precursor cells present in the outer lining of adult hearts, to induce migration of these cells into heart muscle and recruit new blood vessels within the muscle.
Anti-inflammatory role for sulfoxide
In 1999 researchers in Glasgow University found that an oxidised derivative of thymosin β4 (the sulfoxide, in which an oxygen atom is added to the methionine near the N-terminus) exerted several potentially anti-inflammatory effects on neutrophil leucocytes. It promoted their dispersion from a focus, inhibited their response to a small peptide (F-Met-Leu-Phe) which attracts them to sites of bacterial infection and lowered their adhesion to endothelial cells. (Adhesion to endothelial cells of blood vessel walls is pre-requisite for these cells to leave the bloodstream and invade infected tissue). A possible anti-inflammatory role for the β4 sulfoxide was supported by the group’s finding that it counteracted artificially-induced inflammation in mice.
The group had first identified the thymosin sulfoxide as an active factor in culture fluid of cells responding to treatment with a steroid hormone, suggesting that its formation might form part of the mechanism by which steroids exert anti-inflammatory effects. Extracellular thymosin β4 would be readily oxidised to the sulfoxide in vivo at sites of inflammation, by the respiratory burst.
GRCh38: Ensembl release 89: ENSG00000205542 – Ensembl, May 2017
“Human PubMed Reference:”. National Center for Biotechnology Information, U.S. National Library of Medicine.
Gómez-Márquez J, Dosil M, Segade F, Bustelo XR, Pichel JG, Dominguez F, Freire M (Oct 1989). “Thymosin-beta 4 gene. Preliminary characterization and expression in tissues, thymic cells, and lymphocytes”. Journal of Immunology. 143 (8): 2740–4. PMID 2677145.
Lahn BT, Page DC (Oct 1997). “Functional coherence of the human Y chromosome”. Science. 278(5338): 675–80. Bibcode:1997Sci…278..675L. doi:10.1126/science.278.5338.675. PMID 9381176.
“Entrez Gene: TMSB4X thymosin, beta 4, X-linked”.
“Lists of Recommended and Proposed INNs: List 80”. 2018.
“protein NP_066932”. NCBI.
Hannappel E (September 2007). “beta-Thymosins”. Annals of the New York Academy of Sciences. 1112 (1): 21–37. Bibcode:2007NYASA1112…21H. doi:10.1196/annals.1415.018. PMID 17468232.
Low TL, Hu SK, Goldstein AL (February 1981). “Complete amino acid sequence of bovine thymosin beta 4: a thymic hormone that induces terminal deoxynucleotidyl transferase activity in thymocyte populations”. Proceedings of the National Academy of Sciences of the United States of America. 78 (2): 1162–6. Bibcode:1981PNAS…78.1162L. doi:10.1073/pnas.78.2.1162. PMC 319967. PMID 6940133.