Definition
A family of small proteins first isolated from the thymus, including thymosin alpha-1 and thymosin beta-4.
Thymosins are small polypeptides originally isolated from calf thymus extracts in the 1960s by Allan Goldstein and colleagues. Despite the shared name, the main members are structurally unrelated. Thymosin α1 is a 28-residue acetylated peptide studied for effects on T-cell maturation and immune signalling; as thymalfasin it is approved as a medicine in some countries. Thymosin β4 is a 43-residue protein found in most cells, where it binds and sequesters G-actin, regulating cytoskeletal dynamics; it has been investigated in animal models of tissue repair. TB-500 refers to a synthetic fragment based on the actin-binding region of thymosin β4. Thymosin β4 derivatives appear on the WADA Prohibited List.