Thymosin β4 serves as a glutaminyl substrate of transglutaminase. Labeling with fluorescent dansylcadaverine does not abolish interaction with G-actin1

Thymosin β4 possesses actin-sequestering activity and, like transglutaminases, is supposed to be involved in cellular events like angiogenesis, blood coagulation, apoptosis and wound healing. Thymosin β4 serves as a specific glutaminyl substrate for transglutaminase and can be fluorescently labeled with dansylcadaverine. Two (Gln-23 and Gln-36) of the three glutamine residues were mainly involved in the transglutaminase reaction, while the third glutaminyl residue (Gln-39) was derivatized with a low efficiency. Labeled derivatives were able to inhibit polymerization of G-actin and could be cross-linked to G-actin by 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide. Fluorescently labeled thymosin β4 may serve as a useful tool for further investigations in cell biology. Thymosin β4 could provide a specific glutaminyl substrate for transglutaminase in vivo, because of the fast reaction observed in vitro occurring at thymosin β4 concentrations which are found inside cells. Taking these data together, it is tempting to speculate that thymosin β4 may serve as a glutaminyl substrate for transglutaminases in vivo and play an important role in transglutaminase-related processes.