Thymosin beta(4) serves as a glutaminyl substrate of transglutaminase. Labeling with fluorescent dansylcadaverine does not abolish interaction with G-actin

Thymosin beta(4) possesses actin-sequestering activity and, like transgluta minases, is supposed to be involved in cellular events like angiogenesis, b lood coagulation, apoptosis and wound healing. Thymosin beta(4) serves as a specific glutaminyl substrate for transglutaminase and can be fluorescentl y labeled with dansylcadaverine. Two (Gln-23 and Gln-36) of the three gluta mine 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 co uld be cross-linked to G-actin by 1-ethyl-3-[3-(dimethylamino)propyl]carbod iimide. Fluorescently labeled thymosin PI may serve as a useful tool for fu rther investigations in cell biology. Thymosin beta(4) could provide a spec ific glutaminyl substrate for transglutaminase in vice, because of the fast reaction observed in vitro occurring at thymosin beta(4) concentrations wh ich are found inside cells. Taking these data together, it is tempting to s peculate that thymosin beta(4) may serve as a glutaminyl substrate for tran sglutaminases in vivo and play an important role in transglutaminase-relate d processes. (C) 1999 Federation of European Biochemical Societies.