Thymosins and Fragments

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Introduction

The thymosin proteins are all short, highly charged, intrinsically unstructured proteins under natural conditions. However, by providing charge neutralization at low pH or adding Zn²⁺ ions, organic reagents (such as trifluoroethanol, hexafluoropropanol or n-dodecyltrimethylammonium bromide) or their natural binding partners protein interactions, thymidine proteins can induce many structures. Although the thymosin proteins were originally discovered from fractionations of calf thymus tissue, and thus so named, they are genetically unrelated while being distributed widely throughout most tissues and play important, yet very different, roles in cells. They are highly charged proteins with no or few aromatic amino acids and thus lack stable tertiary structure unless induced by interactions with partnering proteins or unnatural solvent conditions. The active peptides are typically short. The β-thymosins are each about 43 amino acids long, while thymosin α1 (Tα1) is only 28 amino acids long, although its precursor, prothymosin, is nearly 100 bases long. β-Thymosins are a family of heat-stable multifunctional polypeptides that are expressed as small proteins of about 5 kDa (45 amino acids) almost exclusively in multicellular animals.

Mechanism of action

Thymosin polypeptides have a role in regulating immune and neuroendocrine circuits. Thymosins have been reported to regulate the biological activity of different subpopulations of T lymphocytes. β-Thymosins are systemically or truncated polypeptides that appear to stimulate a wide range of signaling pathways for extracellular activity, including tissue repair and regeneration, inflammation, cell migration, and immune defense. The thymus is now considered to be the major lymphoid organ of the immune system and is involved in the maturation of immune T lymphocytes (T stands for the thymus). Full-length or truncated variants of βT are therefore found in some human extracellular fluids including serum and plasma and are shown to have hormonal or paracrine activity regulating immune responses and cascading tissue healing and regeneration after injury.

Application of Thymosins

Tα1 and prothymosin α have been used to treat a variety of viral infections, including HIV, chronic hepatitis B, chronic hepatitis C, cytomegalovirus, and invasive aspergillosis, due to their immunological effects. The thymosin beta proteins are major sequestering agents of monomeric actin protein, thus allowing cells to have a high concentration of G-actin at the ready for quick use. As such, these proteins are clinically important.

References

1. Hoch, K., & Volk, D.E. (2016). Structures of Thymosin Proteins, Vitamins and Hormones, 102, pp. 1–24.
2. Mosoian, A., Teixeira, A., Burns, C. S., Sander, L. E., Gusella, G. L., He, C., et al. (2010). Prothymosin-a inhibits HIV-1 via toll-like receptor 4-mediated type I interferon induction. Proceedings of the National Academy of Sciences of the United States of America, 107, 10178–10183.
3. Mosoian, A., Teixeira, A., High, A. A., Christian, R. E., Hunt, D. F., Shabanowitz, J., et al. (2006). Novel function of prothymosin alpha as a potent inhibitor of human immunodeficiency virus type 1 gene expression in primary macrophages. Journal of Virology, 80, 9200–9206.